全文获取类型
收费全文 | 10699篇 |
免费 | 27篇 |
国内免费 | 25篇 |
专业分类
安全科学 | 131篇 |
废物处理 | 575篇 |
环保管理 | 1172篇 |
综合类 | 1333篇 |
基础理论 | 3285篇 |
环境理论 | 1篇 |
污染及防治 | 1962篇 |
评价与监测 | 804篇 |
社会与环境 | 1461篇 |
灾害及防治 | 27篇 |
出版年
2023年 | 42篇 |
2022年 | 76篇 |
2021年 | 59篇 |
2020年 | 29篇 |
2019年 | 42篇 |
2018年 | 636篇 |
2017年 | 616篇 |
2016年 | 558篇 |
2015年 | 123篇 |
2014年 | 152篇 |
2013年 | 416篇 |
2012年 | 374篇 |
2011年 | 978篇 |
2010年 | 619篇 |
2009年 | 677篇 |
2008年 | 853篇 |
2007年 | 1080篇 |
2006年 | 240篇 |
2005年 | 274篇 |
2004年 | 217篇 |
2003年 | 310篇 |
2002年 | 307篇 |
2001年 | 269篇 |
2000年 | 172篇 |
1999年 | 105篇 |
1998年 | 64篇 |
1997年 | 58篇 |
1996年 | 53篇 |
1995年 | 60篇 |
1994年 | 64篇 |
1993年 | 59篇 |
1992年 | 58篇 |
1991年 | 61篇 |
1990年 | 66篇 |
1989年 | 52篇 |
1988年 | 56篇 |
1987年 | 54篇 |
1986年 | 55篇 |
1985年 | 41篇 |
1984年 | 58篇 |
1983年 | 50篇 |
1982年 | 48篇 |
1980年 | 30篇 |
1979年 | 32篇 |
1978年 | 29篇 |
1977年 | 28篇 |
1976年 | 29篇 |
1974年 | 31篇 |
1973年 | 30篇 |
1972年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 222 毫秒
971.
We describe the development and parameterization of a grid-based model of African savanna vegetation processes. The model
was developed with the objective of exploring elephant effects on the diversity of savanna species and structure, and in this
formulation concentrates on the relative cover of grass and woody plants, the vertical structure of the woody plant community,
and the distribution of these over space. Grid cells are linked by seed dispersal and fire, and environmental variability
is included in the form of stochastic rainfall and fire events. The model was parameterized from an extensive review of the
African savanna literature; when available, parameter values varied widely. The most plausible set of parameters produced
long-term coexistence between woody plants and grass, with the tree–grass balance being more sensitive to changes in parameters
influencing demographic processes and drought incidence and response, while less sensitive to fire regime. There was considerable
diversity in the woody structure of savanna systems within the range of uncertainty in tree growth rate parameters. Thus,
given the paucity of height growth data regarding woody plant species in southern African savannas, managers of natural areas
should be cognizant of different tree species growth and damage response attributes when considering whether to act on perceived
elephant threats to vegetation. 相似文献
972.
Temperature inversion characteristics in relation to synoptic circulation above Athens,Greece 总被引:1,自引:0,他引:1
P. A. Kassomenos A. K. Paschalidou S. Lykoudis I. Koletsis 《Environmental monitoring and assessment》2014,186(6):3495-3502
In this paper, the characteristic properties of inversions formed inside the lower boundary layer over Athens, Greece, were studied using 35-year radiosonde measurements of temperature, humidity, and atmospheric pressure. The analysis revealed that the inversion parameters demonstrate considerable seasonal variation. Specifically, inversions associated with weak anticyclonic conditions are more frequent during the winter and summer months, while during spring, weak lows are more probable to produce inversions. Some theoretically expected associations between synoptic circulation patterns and certain inversion parameters were also identified. 相似文献
973.
974.
The feasibility of adding crude glycerol from the biodiesel industry to the anaerobic digesters treating sewage sludge in wastewater treatment plants was studied in both batch and continuous experiments at 35 °C. Glycerol addition can boost biogas yields, if it does not exceed a limiting 1% (v/v) concentration in the feed. Any further increase of glycerol causes a high imbalance in the anaerobic digestion process. The reactor treating the sewage sludge produced 1106 ± 36 ml CH4/d before the addition of glycerol and 2353 ± 94 ml CH4/d after the addition of glycerol (1% v/v in the feed). The extra glycerol-COD added to the feed did not have a negative effect on reactor performance, but seemed to increase the active biomass (volatile solids) concentration in the system. Batch kinetic experiments showed that the maximum specific utilization rate (μmax) and the saturation constant (KS) of glycerol were 0.149 ± 0.015 h?1 and 0.276 ± 0.095 g/l, respectively. Comparing the estimated values with the kinetics constants for propionate reported in the literature, it can be concluded that glycerol uptake is not the rate-limiting step during the process. 相似文献
975.
I. M. Rutskina N. A. Litvinov I. M. Roshchevskaya M. P. Roshchevskii 《Russian Journal of Ecology》2009,40(5):314-319
Changes in the heart rate (HR) in more and less thermophilic reptiles (Natrix natrix L., Vipera berus L., and V. renardi Christoph) exposed to heating from 0 to 40°C under anesthesia have been found to depend on the previous adaptation of the
animals to the temperature parameters characteristic of the natural habitats of their populations. 相似文献
976.
R. Y. M. Kangalawe 《Environment, Development and Sustainability》2010,12(4):449-461
This article examines the changes in land-use/cover types in the Irangi Hills, central Tanzania during the last 45 years and
how such changes have influenced environmental and agricultural sustainability in the area. The spatial and temporal changes
of land-use/cover were analysed through aerial photographs interpretation. Local perceptions and experiences of changes were
addressed through household interviews and field observations. Results from this study show that during the last 45 years
open and wooded grasslands, and other tree-cover types covered about 40% of the land area, ranging from 29% in 1960 to 43–45%
between 1977 and 1992. Also, during the same period both the total area and spatial distribution of cultivated fields varied
greatly. The cultivated area increased from 31% in 1977 to 35% in 1992, mainly due to agricultural expansion into areas formerly
used for grazing and in sandy watercourses that shrunk by 55% between 1977 and 1992. The spatial distribution of the different
land-use/cover types is influenced by variations in the scale of soil erosion and soil-conservation initiatives implemented
in the Irangi Hills since the early 1970s. However, with increasing pressure on the land, and the declining capacity of the
soil conservation authority, sustaining agricultural production in the area remains a major challenge. 相似文献
977.
Tushar Yadav Alka A. Mungray Arvind K. Mungray 《Environmental science and pollution research international》2016,23(5):4063-4072
The continuous rise in production and applications of carbon nanotubes (CNTs) has grown a concern about their fate and toxicity in the environment. After use, these nanomaterials pass through sewage and accumulate in wastewater treatment plants. Since, such plants rely on biological degradation of wastes; their activity may decrease due to the presence of CNTs. This study investigated the effect of multiwalled carbon nanotubes (MWCNTs) on upflow anaerobic sludge blanket (UASB) microbial activity. The toxic effect on microbial viability, extracellular polymeric substances (EPS), volatile fatty acids (VFA), and biogas generation was determined. The reduction in a colony-forming unit (CFU) was 29 and 58 % in 1 and 100 mg/L test samples, respectively, as compared to control. The volatile fatty acids and biogas production was also found reduced. The scanning electron microscopy (SEM) and fluorescent microscopy images confirmed that the MWCNT mediated microbial cell damage. This damage caused the increase in EPS carbohydrate, protein, and DNA concentration. Fourier transform infrared (FTIR) spectroscopy results supported the alterations in sludge EPS due to MWCNT. Our observations offer a new insight to understand the nanotoxic effect of MWCNTs on UASB microflora in a complex environment system. 相似文献
978.
979.
Kapheim KM Bernal SP Smith AR Nonacs P Wcislo WT 《Behavioral ecology and sociobiology》2011,65(6):1179-1190
Developmental maternal effects are a potentially important source of phenotypic variation, but they can be difficult to distinguish
from other environmental factors. This is an important distinction within the context of social evolution, because if variation
in offspring helping behavior is due to maternal manipulation, social selection may act on maternal phenotypes, as well as
those of offspring. Factors correlated with social castes have been linked to variation in developmental nutrition, which
might provide opportunity for females to manipulate the social behavior of their offspring. Megalopta genalis is a mass-provisioning facultatively eusocial sweat bee for which production of males and females in social and solitary
nests is concurrent and asynchronous. Female offspring may become either gynes (reproductive dispersers) or workers (non-reproductive
helpers). We predicted that if maternal manipulation plays a role in M. genalis caste determination, investment in daughters should vary more than for sons. The mass and protein content of pollen stores
provided to female offspring varied significantly more than those of males, but volume and sugar content did not. Sugar content
varied more among female eggs in social nests than in solitary nests. Provisions were larger, with higher nutrient content,
for female eggs and in social nests. Adult females and males show different patterns of allometry, and their investment ratio
ranged from 1.23 to 1.69. Adult body weight varied more for females than males, possibly reflecting increased variation in
maternal investment in female offspring. These differences are consistent with a role for maternal manipulation in the social
plasticity observed in M. genalis. 相似文献
980.
Pasan Samarasin Brian J. Shuter Stephen I. Wright F. Helen Rodd 《Conservation biology》2017,31(1):126-135
Accurate understanding of population connectivity is important to conservation because dispersal can play an important role in population dynamics, microevolution, and assessments of extirpation risk and population rescue. Genetic methods are increasingly used to infer population connectivity because advances in technology have made them more advantageous (e.g., cost effective) relative to ecological methods. Given the reductions in wildlife population connectivity since the Industrial Revolution and more recent drastic reductions from habitat loss, it is important to know the accuracy of and biases in genetic connectivity estimators when connectivity has declined recently. Using simulated data, we investigated the accuracy and bias of 2 common estimators of migration (movement of individuals among populations) rate. We focused on the timing of the connectivity change and the magnitude of that change on the estimates of migration by using a coalescent‐based method (Migrate‐n) and a disequilibrium‐based method (BayesAss). Contrary to expectations, when historically high connectivity had declined recently: (i) both methods over‐estimated recent migration rates; (ii) the coalescent‐based method (Migrate‐n) provided better estimates of recent migration rate than the disequilibrium‐based method (BayesAss); (iii) the coalescent‐based method did not accurately reflect long‐term genetic connectivity. Overall, our results highlight the problems with comparing coalescent and disequilibrium estimates to make inferences about the effects of recent landscape change on genetic connectivity among populations. We found that contrasting these 2 estimates to make inferences about genetic‐connectivity changes over time could lead to inaccurate conclusions. 相似文献