全文获取类型
收费全文 | 13668篇 |
免费 | 134篇 |
国内免费 | 271篇 |
专业分类
安全科学 | 286篇 |
废物处理 | 639篇 |
环保管理 | 1428篇 |
综合类 | 2215篇 |
基础理论 | 3184篇 |
环境理论 | 3篇 |
污染及防治 | 3441篇 |
评价与监测 | 1077篇 |
社会与环境 | 1725篇 |
灾害及防治 | 75篇 |
出版年
2023年 | 82篇 |
2022年 | 184篇 |
2021年 | 177篇 |
2020年 | 103篇 |
2019年 | 143篇 |
2018年 | 235篇 |
2017年 | 264篇 |
2016年 | 356篇 |
2015年 | 255篇 |
2014年 | 443篇 |
2013年 | 1161篇 |
2012年 | 486篇 |
2011年 | 622篇 |
2010年 | 504篇 |
2009年 | 563篇 |
2008年 | 663篇 |
2007年 | 695篇 |
2006年 | 546篇 |
2005年 | 503篇 |
2004年 | 500篇 |
2003年 | 464篇 |
2002年 | 438篇 |
2001年 | 535篇 |
2000年 | 376篇 |
1999年 | 194篇 |
1998年 | 141篇 |
1997年 | 153篇 |
1996年 | 156篇 |
1995年 | 196篇 |
1994年 | 152篇 |
1993年 | 134篇 |
1992年 | 134篇 |
1991年 | 142篇 |
1990年 | 143篇 |
1989年 | 121篇 |
1988年 | 105篇 |
1987年 | 105篇 |
1986年 | 96篇 |
1985年 | 106篇 |
1984年 | 113篇 |
1983年 | 92篇 |
1982年 | 102篇 |
1981年 | 94篇 |
1980年 | 86篇 |
1979年 | 88篇 |
1977年 | 62篇 |
1976年 | 60篇 |
1974年 | 63篇 |
1973年 | 67篇 |
1972年 | 84篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
831.
The rate of growth of any population is a quantity of interest in conservation and management and is constrained by biological
factors. In this study, recent data on life-history parameters influencing rates of population growth in humpback whales,
including survival, age at first parturition and calving rate are reviewed. Monte Carlo simulations are used to compute a
distribution of rates of increase (ROIs) taking into account uncertainty in biological parameter estimates. Two approaches
for computing juvenile survival are proposed, which taken into account along with other life-history data, resulted in the
following estimates of the rate of population growth: Approach A: mean of 7.3%/year (95% CI = 3.5–10.5%/year) and Approach
B: mean of 8.6%/year (95% CI = 5.0–11.4%/year). It is proposed that the upper 99% quantile of the resulting distribution of
the ROI for Approach B (11.8%/year) be established as the maximum plausible ROI for humpback whales and be used in population
assessment of the species. Possible sources of positive and negative biases in the present estimates are presented and include
measurement error in estimation of life-history parameters, changes in the environment within the period these quantities
are measured, density dependence or other natural factors. However, it is difficult to evaluate potential biases without additional
data. The methods presented in this study can be applied to other species for which life-history parameters are available
and are useful in assessing plausibility in the estimation of population growth rates from time series of abundance estimates. 相似文献
832.
The burrowing and movement ability of the New Zealand cockle Austrovenus stutchburyi is reduced when infected by echinostome trematodes. Previous experimental evidence from a single site suggests that this
parasite-induced behavioural change of a key bivalve can affect the structure of the surrounding benthic community. By using
multiple regression analyses on data collected from 17 intertidal flats, we here show that cockle parasitism is associated
with macrozoobenthic community structure on a larger spatial scale. Regressions were performed for animal abundance, biomass,
species diversity and species richness separately, entering cockle parasitism (infection intensity), presence/absence of ghost
shrimps (Callianassa filholi), cockle density, primary producer abundance and organic content, particle size, sorting coefficient and gravel content of
the substrate as predictors. Next to ghost shrimps, cockle parasitism was the best predictor of animal abundance by affecting
(mainly positively) 8 of the 49 most widespread species significantly. Cockle parasitism was also associated with the biomass
of anthozoans (positively), nemerteans (negatively) and bivalves (positively), whereas overall animal biomass was positively
related to the sorting coefficient of the substrate. Species diversity was positively associated with cockle parasitism and
gravel content of the substrate. Species richness was significantly associated with cockle parasitism (positively), ghost
shrimps (negatively) and abundance of primary producers (positively) in combination. The impact of cockle parasitism on benthic
community structure is believed governed directly or indirectly by (1) reduced sediment disturbance, (2) increased surface
structural complexity and (3) availability of larval trematodes as an additional food source. 相似文献
833.
V.V. Mazalov 《Ecological modelling》2010,221(12):1545-1553
In this paper, a discrete-time game model related to a bioresource management problem (fish catching) is considered. We divide a fishery into regions, which are exploited by single players. The center (referee) shares a reservoir between the competitors. The players (countries), which harvest the fish stock are the participants of this game.We assume that there are migratory exchanges between the regions of the reservoir. Therefore, the stock in one region depends not only on the previous stock and catch in the region, but also on the stock and catch in neighboring regions. We derive the Nash and cooperative equilibria for an infinite planning horizon.We consider two ways to maintain the cooperation: incentive equilibrium and time-consistent imputation distribution procedure. We investigate the cooperative incentive equilibrium in the case when the center punishes players for a deviation.Also we consider the case when the center is a player and find the Shapley value and time-consistent imputation distribution procedure. We introduce a new condition which offers an incentive to players to keep cooperating. 相似文献
834.
Extrapolating simulations of bioenergy crop agro-ecosystems beyond data-rich sites requires biophysically accurate ecosystem models and careful estimation of model parameters not available in the literature. To increase biophysical accuracy we added C4 perennial grass functionality and agricultural practices to the Biome-BGC (BioGeochemical Cycles) ecosystem model. This new model, Agro-BGC, includes enzyme-driven C4 photosynthesis, individual live and dead leaf, stem, and root carbon and nitrogen pools, separate senescence and litter fall processes, fruit growth, optional annual seeding, flood irrigation, a growing degree day phenology with a killing frost option, and a disturbance handler that simulates nitrogen fertilization, harvest, fire, and incremental irrigation. To obtain spatially generalizable vegetation parameters we used a numerical method to optimize five unavailable parameters for Panicum virgatum (switchgrass) using biomass yield data from three sites: Mead, Nebraska, Rockspring, Pennsylvania, and Mandan, North Dakota. We then verified simulated switchgrass yields at three independent sites in Illinois (IL). Agro-BGC is more accurate than Biome-BGC in representing the physiology and dynamics of C4 grass and management practices associated with agro-ecosystems. The simulated two-year average mature yields with single-site Rockspring optimization have Root Mean Square Errors (RMSE) of 70, 152, and 162 and biases of 43, −87, 156 g carbon m−2 for Shabbona, Urbana, and Simpson IL, respectively. The simulated annual yields in June, August, October, December, and February have RMSEs of 114, 390, and 185 and biases of −19, −258, and 147 g carbon m−2 for Shabbona, Urbana, and Simpson IL, respectively. These RMSE and bias values are all within the largest 90% confidence interval around respective IL site measurements. Twenty-four of twenty-six simulated annual yields with Rockspring optimization are within 95% confidence intervals of Illinois site measurements during the mature fourth and fifth years of growth. Ten of eleven simulated two-year average mature yields with Rockspring optimization are within 65% confidence intervals of Illinois site measurements and the eleventh is within the 95% confidence interval. Rockspring optimized Agro-BGC achieves accuracies comparable to those of two previously published models: Agricultural Land Management Alternatives with Numerical Assessment Criteria (ALMANAC) and Integrated Farm System Model (IFSM). Agro-BGC suffers from static vegetation parameters that can change seasonally and as plants age. Using mature plant data for optimization mitigates this deficiency. Our results suggest that a multi-site optimization scheme using mature plant data from more sites would be adequate for generating spatially generalizable vegetation parameters for simulating mature bioenergy crop agro-ecosystems with Agro-BGC. 相似文献
835.
This article describes a new forest management module (FMM) that explicitly simulates forest stand growth and management within a process-based global vegetation model (GVM) called ORCHIDEE. The net primary productivity simulated by ORCHIDEE is used as an input to the FMM. The FMM then calculates stand and management characteristics such as stand density, tree size distribution, tree growth, the timing and intensity of thinnings and clear-cuts, wood extraction and litter generated after thinning. Some of these variables are then fed back to ORCHIDEE. These computations are made possible with a distribution-based modelling of individual tree size. The model derives natural mortality from the relative density index (rdi), a competition index based on tree size and stand density. Based on the common forestry management principle of avoiding natural mortality, a set of rules is defined to calculate the recurrent intensity and frequency of forestry operations during the stand lifetime. The new-coupled model is called ORCHIDEE-FM (forest management).The general behaviour of ORCHIDEE-FM is analysed for a broadleaf forest in north-eastern France. Flux simulation throughout a forest rotation compare well with the literature values, both in absolute values and dynamics.Results from ORCHIDEE-FM highlight the impact of forest management on ecosystem C-cycling, both in terms of carbon fluxes and stocks. In particular, the average net ecosystem productivity (NEP) of 225 gC m−2 year−1 is close to the biome average of 311 gC m−2 year−1. The NEP of the “unmanaged” case is 40% lower, leading us to conclude that management explains 40% of the cumulated carbon sink over 150 years. A sensitivity analysis reveals 4 major avenues for improvement: a better determination of initial conditions, an improved allocation scheme to explain age-related decline in productivity, and an increased specificity of both the self-thinning curve and the biomass-diameter allometry. 相似文献
836.
Caio F. Gromboni George L. Donati Wladiana O. Matos Eduardo F. A. Neves Ana Rita A. Nogueira Joaquim A. Nóbrega 《Environmental Chemistry Letters》2010,8(1):73-77
Efficiency of metabisulfite and a commercial steel wool as reducing agents in the removal of Cr(VI) from wastewaters was evaluated.
Chromium(VI) was converted to Cr(III), precipitated with NaOH, and removed by filtration. A reduction of more than 1.0 × 105 and 4.0 × 105 fold in total Cr and the Cr(VI) concentrations, respectively, was observed by employing steel wool masses as low as 0.4420 g
to 30-mL solutions of wastewater. Chromium(III) hydroxide obtained after the treatment was recycled and used as marker in
cattle nutrition studies. The liquid residue obtained after the treatment was reused as precipitation agent replacing NaOH. 相似文献
837.
Biodegradation of phenol by native microorganisms isolated from coke processing wastewater 总被引:2,自引:0,他引:2
Chakraborty S Bhattacharya T Patel TN Tiwari KK 《Journal of environmental biology / Academy of Environmental Biology, India》2010,31(3):293-296
The present investigation was undertaken to assess the biodegradation of phenol by native bacteria strains isolated from coke oven processing wastewater. The strains were designated ESDSPB1, ESDSPB2 and ESDSPB3 and examined for colony morphology Gram stain characters and biochemical tests. Phenol degrading performance of all the strains was evaluated initially. One of the strains namely ESDSPB2 was found to be highly effective for the removal of phenol, which was used as sole carbon and energy source. From an initial concentration of 200 mg I(-1) it degraded to 79.84 +/- 1.23 mg l(-1). In turn the effect of temperature (20 to 45 degrees C), pH (5-10) and glucose concentration (0, 0.25 and 0.5%) on the rate of phenol degradation by that particular strain was investigated. Observations revealed that the rate of phenol biodegradation was significantly affected by pH, temperature of incubation and glucose concentration. The optimal conditions for phenol removal were found to be pH of 7 (84.63% removal), temperature, 30 degrees C (76.69% removal) and 0.25% supplemented glucose level (97.88% removal). The main significance of the study is the utilization of native bacterial strains from the waste water itself having potential of bioremediation. 相似文献
838.
The polar bear (Ursus maritimus) depends on sea ice for feeding, breeding, and movement. Significant reductions in Arctic sea ice are forecast to continue because of climate warming. We evaluated the impacts of climate change on polar bears in the southern Beaufort Sea by means of a demographic analysis, combining deterministic, stochastic, environment-dependent matrix population models with forecasts of future sea ice conditions from IPCC general circulation models (GCMs). The matrix population models classified individuals by age and breeding status; mothers and dependent cubs were treated as units. Parameter estimates were obtained from a capture-recapture study conducted from 2001 to 2006. Candidate statistical models allowed vital rates to vary with time and as functions of a sea ice covariate. Model averaging was used to produce the vital rate estimates, and a parametric bootstrap procedure was used to quantify model selection and parameter estimation uncertainty. Deterministic models projected population growth in years with more extensive ice coverage (2001-2003) and population decline in years with less ice coverage (2004-2005). LTRE (life table response experiment) analysis showed that the reduction in lambda in years with low sea ice was due primarily to reduced adult female survival, and secondarily to reduced breeding. A stochastic model with two environmental states, good and poor sea ice conditions, projected a declining stochastic growth rate, log lambdas, as the frequency of poor ice years increased. The observed frequency of poor ice years since 1979 would imply log lambdas approximately - 0.01, which agrees with available (albeit crude) observations of population size. The stochastic model was linked to a set of 10 GCMs compiled by the IPCC; the models were chosen for their ability to reproduce historical observations of sea ice and were forced with "business as usual" (A1B) greenhouse gas emissions. The resulting stochastic population projections showed drastic declines in the polar bear population by the end of the 21st century. These projections were instrumental in the decision to list the polar bear as a threatened species under the U.S. Endangered Species Act. 相似文献
839.
Flying vertebrates, such as bats, face exceptionally high energy costs during active flapping flight. Once airborne, energy turnover may exceed basal metabolic rate by a factor of up to 15. Here, we asked whether fuel that powers flight originates from exogenous (dietary nutrients), endogenous sources (mostly body lipids or glycogen), or a combination of both. Since most insectivorous bats fly continuously over relatively long time periods during foraging, we assumed that slowly mobilized glycogen, although suitable for supporting brief sallying flights, is inadequate to power aerial insect-hunting of bats. We hypothesized that the insect-feeding Noctilio albiventris rapidly mobilizes and combusts nutrients from insects it has just eaten instead of utilizing endogenous lipids. We used the stable carbon isotope ratio in the bats' exhaled breath (delta13C(brth)) to assess the origin of metabolized substrates of resting and flying N. albiventris in two nutritional conditions: fasted and recently fed. The breath of fasted resting bats was depleted in 13C in relation to their insect diet (delta13C(diet)), indicating the combustion of 13C depleted body lipids. In contrast to this, delta13C(brth) of bats that had recently fed closely matched delta13C(diet) in both resting and flying bats, suggesting a quick mobilization of ingested nutrients for metabolism. In contrast to most non-volant mammals, bats have evolved the ability to fuel their high energy expenditure rates through the rapid combustion of exogenous nutrients, enabling them to conquer the nocturnal niche of aerial insectivory. 相似文献
840.
The background noise generated in large social aggregations of calling individuals is a potent source of auditory masking for animals that communicate acoustically. Despite similarities with the so-called "cocktail-party problem" in humans, few studies have explicitly investigated how non-human animals solve the perceptual task of separating biologically relevant acoustic signals from ambient background noise. Under certain conditions, humans experience a release from auditory masking when speech is presented in speech-like masking noise that fluctuates in amplitude. We tested the hypothesis that females of Cope's gray treefrog (Hyla chrysoscelis) experience masking release in artificial chorus noise that fluctuates in level at modulations rates characteristic of those present in ambient chorus noise. We estimated thresholds for recognizing conspecific advertisement calls (pulse rate=40-50 pulses/s) in the presence of unmodulated and sinusoidally amplitude modulated (SAM) chorus-shaped masking noise. We tested two rates of modulation (5 Hz and 45 Hz) because the sounds of frog choruses are modulated at low rates (e.g., less than 5-10 Hz), and because those of species with pulsatile signals are additionally modulated at higher rates typical of the pulse rate of calls (e.g., between 15-50 Hz). Recognition thresholds were similar in the unmodulated and 5-Hz SAM conditions, and 12 dB higher in the 45-Hz SAM condition. These results did not support the hypothesis that female gray treefrogs experience masking release in temporally fluctuating chorus-shaped noise. We discuss our results in terms of modulation masking, and hypothesize that natural amplitude fluctuations in ambient chorus noise may impair mating call perception. 相似文献