全文获取类型
收费全文 | 13296篇 |
免费 | 148篇 |
国内免费 | 112篇 |
专业分类
安全科学 | 369篇 |
废物处理 | 379篇 |
环保管理 | 2014篇 |
综合类 | 3286篇 |
基础理论 | 3122篇 |
环境理论 | 6篇 |
污染及防治 | 3352篇 |
评价与监测 | 596篇 |
社会与环境 | 366篇 |
灾害及防治 | 66篇 |
出版年
2018年 | 126篇 |
2017年 | 137篇 |
2016年 | 190篇 |
2015年 | 156篇 |
2014年 | 202篇 |
2013年 | 974篇 |
2012年 | 311篇 |
2011年 | 443篇 |
2010年 | 311篇 |
2009年 | 411篇 |
2008年 | 453篇 |
2007年 | 487篇 |
2006年 | 441篇 |
2005年 | 332篇 |
2004年 | 358篇 |
2003年 | 387篇 |
2002年 | 329篇 |
2001年 | 472篇 |
2000年 | 325篇 |
1999年 | 219篇 |
1998年 | 159篇 |
1997年 | 151篇 |
1996年 | 186篇 |
1995年 | 182篇 |
1994年 | 209篇 |
1993年 | 190篇 |
1992年 | 188篇 |
1991年 | 190篇 |
1990年 | 210篇 |
1989年 | 196篇 |
1988年 | 167篇 |
1987年 | 167篇 |
1986年 | 150篇 |
1985年 | 165篇 |
1984年 | 149篇 |
1983年 | 159篇 |
1982年 | 160篇 |
1981年 | 165篇 |
1980年 | 149篇 |
1979年 | 145篇 |
1978年 | 142篇 |
1977年 | 130篇 |
1976年 | 137篇 |
1975年 | 114篇 |
1974年 | 142篇 |
1973年 | 125篇 |
1972年 | 125篇 |
1971年 | 106篇 |
1970年 | 106篇 |
1967年 | 116篇 |
排序方式: 共有10000条查询结果,搜索用时 968 毫秒
881.
The predation impact of the two chaetognaths Eukrohnia hamata and Sagitta gazellae on mesozooplankton standing stock were investigated in three depth layers during two 24 h stations occupied in the vicinity
of Marion Island in late austral summer (April/May) 1986. The zooplankton community at both stations was dominated by small
copepods (Oithona spp., Microcalanus spp.), which accounted for >95% of total zooplankton abundance. Chaetognaths comprised <2% of total zooplankton abundance.
E. hamata constituted >95% of the total chaetognath stock. The general trend in both species was decreasing abundance with increasing
depth, which appeared to be correlated to the distribution of copepods (r
2 = 0.45; P <0.05). Gut-content analysis showed that copepods (mainly Oithona spp., Calanus spp. and Rhincalanus gigas) and ostracods were the main prey of both species, accounting for 87 and 61% of the total number of prey in E. hamata and S.␣gazellae stomachs, respectively. In the guts of S.␣gazellae, pteropods (Limacina spp.) and chaetognaths were also well represented. The mean number of prey items (NPC) for E. hamata ranged from 0.02 to 0.06 prey individual−1 which corresponds to an individual feeding rate (Fr) of between 0.05 and 0.12 prey d−1. For S.␣gazellae, the NPC values were higher, varying between 0.04␣and 0.20 prey individual−1, or between 0.15 and 0.76 prey d−1. The daily predation impact of the two chaetognaths was estimated at between 0.3 and 1.2% of the copepod standing stock or
between 7 and 16% of the daily copepod production. Predation by S. gazellae on chaetognaths accounted for up to 1.6% of the chaetognath standing stock per day.
Received: 26 November 1996 / Accepted: 31 October 1997 相似文献
882.
Common shrimp, Crangon crangon (L.), were exposed to inorganic arsenic (arsenate), trimethylarsine oxide, or arsenobetaine in sea water (100 μg As l−1) or in food (1 mg As g−1 wet wt) for up to 24 d, followed by 16 d depuration in clean sea water with undosed food, in order to determine the efficiency
of uptake and retention of the compounds. Accumulation of arsenic in the tail muscle, gills, midgut gland, exoskeleton, and
remaining tissues was found to depend on the chemical form of the arsenic and the route of exposure. No arsenic was accumulated
by C. crangon exposed to arsenate or trimethylarsine oxide in sea water. Shrimps exposed to waterborne arsenobetaine initially accumulated
a small amount of arsenic in their tail muscle and gills. After 16 d, C. crangon fed arsenate, trimethylarsine oxide, or arsenobetaine had accumulated arsenic in their tail muscle to levels ∼2-, 2-, or
40-times, respectively, that of the control group. A roughly linear rate of accumulation was shown by shrimps fed trimethylarsine
oxide or arsenobetaine, but C. crangon fed arsenate accumulated arsenic for 16 d, then lost arsenic such that their concentration on Day 24 was not significantly
different from that of the control group. Patterns of arsenic accumulation in the gills of shrimps fed the compounds were
similar to those seen in the tail muscle. On a whole animal basis, C. crangon retained ∼1.2% of the arsenate, 1.6% of the trimethylarsine oxide, and 42% of the arsenobetaine consumed over the first 16 d
of exposure, with roughly half present in the tail muscle in each case. Data obtained support the view that the direct uptake
of arsenobetaine from sea water does not make a significant contribution to the relatively high concentrations of this compound
in marine crustaceans, and that food is the primary source. Naturally occurring arsenic compounds in C. crangon and possible transformations of the administered arsenic compounds were examined by high performance liquid chromatography
using an inductively coupled plasma mass spectrometer as the arsenic-specific detector. Control C. crangon contained arsenobetaine as the major arsenic compound (>95% of total arsenic); tetramethylarsonium ion (0.7%) and an unknown
arsenic compound (1.7%) were also present as minor constituents. Shrimp ingesting arsenobetaine accumulated it unchanged.
Shrimp ingesting arsenate did not form methylated arsenic compounds; they appeared to contain their accumulated arsenic as
unchanged arsenate only, although the possibility that some of the arsenic was reduced to arsenite could not be excluded.
C. crangon ingesting trimethylarsine oxide biotransformed the compound predominantly to dimethylarsinate.
Received: 9 October 1997 / Accepted: 11 February 1998 相似文献
883.
Larval development in Amphiglena mediterranea is direct in the parental tube, and larvae crawl away as young juveniles with a radiolar crown capable of feeding. The non-feeding
larvae of A. nathae are initially brooded in the parental tube, and then have a swimming phase before settling and developing a radiolar crown.
Developmental data and reproductive features such as sperm structure are combined with other morphological data for an assessment
of the cladistic relationships of the species in the genus Amphiglena. Two species of Laonome are included as part of the ingroup. Six genera, representing a sister group to the Laonome/Amphiglena clade, are used as an outgroup. Two most-parsimonious cladograms were found, and the evolution of reproductive features are
discussed. The monophyly of Amphiglena is indicated by features previously identified, as well as two features based on sperm morphology. At present a plesiomorphic
larval form cannot be identified for the genus Amphiglena.
Received: 16 June 1997 / Accepted: 29 January 1998 相似文献
884.
J. Jaron Hill Matthew M. Chumchal Ray W. Drenner John E. Pinder III S. Matthew Drenner 《Environmental monitoring and assessment》2010,161(1-4):509-516
We examined the effects of a commonly used preservation technique on mercury concentration in fish tissue. After fixing fish muscle tissue in formalin followed by preservation in isopropanol, we found that mercury concentration in fish muscle tissue increased by 18%, reaching an asymptote after 40 days. We used formalin–isopropanol-preserved longear sunfish (Lepomis megalotis) from the Sam Noble Oklahoma Museum of Natural History to examine historical changes and predict current mercury concentrations in fish from two rivers in southeastern Oklahoma. Glover River was free-flowing, while Mountain Fork River was impounded in 1970 and a coldwater trout fishery was established upstream from the collection site in 1989. Mercury concentrations in longear sunfish from Glover River showed no historical changes from 1963 to 2001. Mercury concentrations in longear sunfish from Mountain Fork River showed no change from 1925 to 1993 but declined significantly from 1993 to 2003. We also compared mercury concentrations of the most recently collected longear sunfish in the museum to mercury concentrations of unpreserved fish collected from the rivers in 2006. Concentrations of mercury in museum fish were not significantly different from mercury concentrations in unpreserved fish we collected from the rivers. Our study indicates that preserved museum fish specimens can be used to evaluate historical changes and predict current levels of mercury contamination in fish. 相似文献
885.
Tzu-Yi Pai C. L. Chen H. Chung H. H. Ho T. W. Shiu 《Environmental monitoring and assessment》2010,171(1-4):551-560
In this study, the variation of sewage quality was investigated and the active fraction of different microbial functional groups in biofilm was quantified in a 5.6-km trunk sewer line. The sewage quality including suspended solids, biochemical oxygen demand, total chemical oxygen demand (COD), total nitrogen, total Kjeldahl nitrogen, ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen were measured and compared with the values in literatures. The results indicated that since the wastewater treatment plant was not operated at its full capacity, the concentrations of different compounds were lower compared with the values in literatures. The values of heterotrophic growth rate constant lay between 5.6 and 8.6 day???1. Its average value was 7.7 day???1. The values of heterotrophic lysis rate constant lay between 0.2 and 0.4 day???1. The active heterotrophic biomass in biofilm varied from 240 to 800 mg COD m???2 and average value was 497 mg COD m???2. The biofilm mass varied from 880 to 1,080 mg m???2. The percentage of heterotroph to biofilm mass fall within the range of 24.0–90.9% and average value was 52.9%. In the oxygen uptake rate batch tests, the biomass, growth rate constant, and lysis rate constant of autotroph could not be determined because the fraction of autotroph in biofilm was relatively few. It revealed that the degradation of organic matters, nitrification, and denitrification occurred in the trunk sewer line. But the results indicate that the condition seem favorable for nitrification. 相似文献
886.
Jill D. Frankforter Holly S. Weyers Jerad D. Bales Patrick W. Moran Daniel L. Calhoun 《Environmental monitoring and assessment》2010,168(1-4):461-479
Stream metabolism was measured in 33 streams across a gradient of nutrient concentrations in four agricultural areas of the USA to determine the relative influence of nutrient concentrations and habitat on primary production (GPP) and respiration (CR-24). In conjunction with the stream metabolism estimates, water quality and algal biomass samples were collected, as was an assessment of habitat in the sampling reach. When data for all study areas were combined, there were no statistically significant relations between gross primary production or community respiration and any of the independent variables. However, significant regression models were developed for three study areas for GPP (r 2 = 0.79–0.91) and CR-24 (r 2 = 0.76–0.77). Various forms of nutrients (total phosphorus and area-weighted total nitrogen loading) were significant for predicting GPP in two study areas, with habitat variables important in seven significant models. Important physical variables included light availability, precipitation, basin area, and in-stream habitat cover. Both benthic and seston chlorophyll were not found to be important explanatory variables in any of the models; however, benthic ash-free dry weight was important in two models for GPP. 相似文献
887.
888.
Alexander Lorenz Matthias G. W. Schmidt Elmar Kriegler Hermann Held 《Environmental Modeling and Assessment》2012,17(1-2):163-175
Several integrated assessment studies have concluded that future learning about the uncertainties involved in climate change has a considerable effect on welfare but only a small effect on optimal short-term emissions. In other words, learning is important but anticipation of learning is not. We confirm this result in the integrated assessment model “model of investment and technological development” for learning about climate sensitivity and climate damages. If learning about an irreversible threshold is included, though, we show that anticipation can become crucial both in terms of necessary adjustments of pre-learning emissions and resulting welfare gains. We specify conditions on the time of learning and the threshold characteristic, for which this is the case. They can be summarized as a narrow “anticipation window.” 相似文献
889.
The aggregation of 12 nm citrate-stabilized gold nanoparticles (cit-AuNPs) in the presence of four different natural organic matter (NOM) isolates and a monovalent electrolyte (KCl) was evaluated using time-resolved dynamic light scattering. All four NOM isolates stabilized the cit-AuNPs with respect to aggregation. However, specific effects varied among the different NOM isolates. At pH = 6 in 80 mM KCl, low concentrations (<0.25 mg C per L) of large molecular weight Suwannee River Humic Acid (SRHA) was required to stabilize cit-AuNPs, while larger concentrations (>2 mg C per L) of smaller Suwannee River Fulvic Acid (SRFA) were necessary at the same ionic strength. Suwannee River NOM (SRNOM) which contains both SRHA and SRFA behaved in a manner intermediate between the two. Pony Lake Fulvic Acid (PLFA), an autochthonous NOM isolate, provided substantial stability at low concentrations, yet aggregation was induced at NOM concentrations > 2 mg C per L, a trend that is hypothesized to be the result of favourable hydrophobic interactions between coated particles induced at increased surface coverage. For all NOM isolates, it appears that NOM adsorption or conformational changes at the AuNP surfaces result in significant increases in the hydrodynamic diameter that aren't attributable to NP-NP aggregation. 相似文献
890.
MW Nonnenmann G Coronado B Thompson WC Griffith JD Hanson S Vesper EM Faustman 《Journal of environmental monitoring : JEM》2012,14(8):2038-2043
Molecular techniques are an alternative to culturing and counting methods in quantifying indoor fungal contamination. Pyrosequencing offers the possibility of identifying unexpected indoor fungi. In this study, 50 house dust samples were collected from homes in the Yakima Valley, WA. Each sample was analyzed by quantitative PCR (QPCR) for 36 common fungi and by fungal tag-encoded flexible (FLX) amplicon pyrosequencing (fTEFAP) for these and additional fungi. Only 24 of the samples yielded amplified results using fTEFAP but QPCR successfully amplified all 50 samples. Over 450 fungal species were detected by fTEFAP but most were rare. Twenty-two fungi were found by fTEFAP to occur with at least an average of ≥0.5% relative occurrence. Many of these fungi seem to be associated with plants, soil or human skin. Combining fTEFAP and QPCR can enhance studies of fungal contamination in homes. 相似文献