全文获取类型
收费全文 | 53735篇 |
免费 | 474篇 |
国内免费 | 258篇 |
专业分类
安全科学 | 1489篇 |
废物处理 | 2034篇 |
环保管理 | 7334篇 |
综合类 | 10573篇 |
基础理论 | 13980篇 |
环境理论 | 26篇 |
污染及防治 | 13480篇 |
评价与监测 | 3060篇 |
社会与环境 | 2157篇 |
灾害及防治 | 334篇 |
出版年
2022年 | 367篇 |
2021年 | 407篇 |
2020年 | 333篇 |
2019年 | 472篇 |
2018年 | 687篇 |
2017年 | 675篇 |
2016年 | 1036篇 |
2015年 | 863篇 |
2014年 | 1234篇 |
2013年 | 4023篇 |
2012年 | 1503篇 |
2011年 | 2122篇 |
2010年 | 1757篇 |
2009年 | 1862篇 |
2008年 | 2178篇 |
2007年 | 2276篇 |
2006年 | 2020篇 |
2005年 | 1705篇 |
2004年 | 1709篇 |
2003年 | 1640篇 |
2002年 | 1596篇 |
2001年 | 1994篇 |
2000年 | 1431篇 |
1999年 | 917篇 |
1998年 | 727篇 |
1997年 | 698篇 |
1996年 | 741篇 |
1995年 | 813篇 |
1994年 | 758篇 |
1993年 | 691篇 |
1992年 | 672篇 |
1991年 | 643篇 |
1990年 | 689篇 |
1989年 | 666篇 |
1988年 | 573篇 |
1987年 | 534篇 |
1986年 | 486篇 |
1985年 | 515篇 |
1984年 | 527篇 |
1983年 | 552篇 |
1982年 | 557篇 |
1981年 | 538篇 |
1980年 | 448篇 |
1979年 | 480篇 |
1978年 | 394篇 |
1977年 | 338篇 |
1976年 | 347篇 |
1975年 | 330篇 |
1973年 | 336篇 |
1972年 | 359篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
681.
Spring wheat (Triticum aestivum L. cv. Turbo) was exposed to different levels of ozone and water supply in open-top chambers in 1991. Air was charcoal filtered (CF), non-filtered (NF) and CF plus proportional addition of ambient or twice ambient ozone (CF1, CF2). Seasonal means of O(3), taken over 24 h, were 2.3, 20.6, 17.3, and 34.5 nl litre(-1) for CF, NF, CF1 and CF2 treatments, respectively. A split-plot design was used to obtain two levels of water supply: one-half of the pots was irrigated sufficiently not to show any symptoms of drought stress; the others were exposed to low water supply and received 50% of these amounts. Using a steady-state porometer approximately 800 measurements of stomatal conductance (g(s)) were made on flag leaves from 68 to 106 days after sowing. The measurements yielded only small differences of maximum conductance between the two levels of water supply. Therefore, low water supply did not protect wheat plants against ozone injury via reduced stomatal uptake in this experiment. To describe the effects of environmental variables on the stomatal behaviour, boundary-line analysis and non-linear regression analysis were used. Besides microclimatic parameters, the ozone dose of flag leaves was introduced as an independent variable affecting stomatal aperture. A well-defined boundary line for ozone dose was found, suggesting that increasing ozone dose caused stomatal closure in wheat flag leaves. But at high ozone doses, co-acting senescence seems also responsible for the decrease in stomatal conductance. A multiplicative boundary-line model was used to predict stomatal conductance from combinations of environmental variables. In the test carried out with the measurements of stomatal conductance, the model accounted only for 40% of the variation of g(s). Generalized stomatal response patterns of the herbaceous growth form, the dependence of the variables' age and ozone dose and the lack of an important factor influencing stomatal response (water status of the plant) in the model, are suggested as explanations of the poor results of the test. 相似文献
682.
Climatic hazards warning process in Bangladesh: Experience of,and lessons from,the 1991 April cyclone 总被引:6,自引:0,他引:6
C. Emdad Haque 《Environmental management》1995,19(5):719-734
Science and technology cannot control entirely the causes of natural hazards. However, by using multifaceted programs to modify
the physical and human use systems, the potential losses from disasters can effectively be minized. Predicting, identifying,
monitoring, and forecasting extreme meteorological events are the preliminary actions towards mitigating the cyclone-loss
potential of coastal inhabitants, but without the successful dissemination of forecasts and relevant information, and without
appropriate responses by the potential victims, the loss potential would probably remain the same. This study examines the
process through which warning of the impending disastrous cyclone of April 1991 was received by the local communities and
disseminated throughout the coastal regions of Bangladesh. It is found that identification of the threatening condition due
to atmospheric disturbance, monitoring of the hazard event, and dissemination of the cyclone warning were each very successful.
However, due to a number of socioeconomic and cognitive factors, the reactions and responses of coastal inhabitants to the
warning were in general passive, resulting in a colossal loss, both at the individual and national level. The study recommends
that the hazard mitigation policies should be integrated with national economic development plans and programs. Specifically,
it is suggested that, in order to attain its goals, the cyclone warning system should regard the aspects of human response
to warnings as a constituent part and accommodate human dimensions in its operational design. 相似文献
683.
We tested the effect of mono-ortho and di-ortho PCB congeners on northern leopard frog (Rana pipiens) hatching success, survival and sexual development. Embryos and tadpoles were exposed to two levels (0.5 and 50 microg/l) of two PCBs. PCBs 101 and 70 were selected because they were present in amphibians collected in the Fox River-Green Bay ecosystem and they have the theoretical structural requirements to be able to bind to the estrogen receptor and mediate estrogenic responses. The exposure of leopard frog embryos and tadpoles to PCB 70 and 101 did not significantly affect hatchability, survival, deformities or growth. There were significant departures from the expected 50:50 sex ratio in tadpoles/froglets exposed to PCB 101 and PCB 70. In all the cases of significant departure, the bias was towards higher number of females. Decrease in the proportion of male gonads and increase in the proportion of intersex gonads were observed with increasing PCB tissue concentrations. The effects of PCB congeners on sexual differentiation occur at concentrations higher than observed in frogs in the Fox River/Green Bay ecosystem. 相似文献
684.
Jones JM 《Environmental pollution (Barking, Essex : 1987)》1987,48(2):131-144
Measurement of operationally defined chemical fractions in ombrotrophic peat samples provides information not obtained by total metal extractions. Examination of such sequential data permits interpretation of process dynamics. Results for copper, lead and zinc chemical fractionation of peat profiles from Ringinglow Bog, near Sheffield, Great Britain, are reported and discussed. Lead and zinc share similar patterns of partitioning. A considerable proportion of these records is in a form predisposed to transformation and mobilisation. In contrast, much of the copper is comparatively immobile, it being associated with the more chemically intractable fractions. The results suggest that peat copper deposition records may be used for reconstruction of pollution history. The use of lead and zinc records for these purposes is problematic. 相似文献
685.
The fine roots and myocorrhizae of beech, spruce and fir trees exposed to ozone, sulphur dioxide and simulated acid precipitation in open-top chambers (OTC) were examined both in situ by rhizoscopy and in the laboratory using root samples from soil cores. Prior to measurements the trees were treated for about one year. During the second year of treatment the fine root production of all three tree species was determined rhizoscopically. The OTC experiments were concluded after an additional three years at which time fine root and small root dry matter as well as the absolute and relative frequencies of mycorrhizae of spruce and fir were determined from soil cores. The vitality of spruce mycorrhizae was examined by fluorescein diacetate staining. In addition total contents of essential cations of spruce mycorrhizae were measured. Long-term exposure to SO(2), SO(2) + O(3), and simulated acid precipitation led to an increased mycorrhizal production by fir. On spruce, a decreased number of mycorrhizae was found in the chambers polluted with SO(2), but a high proportion of dead fine roots indicated an increased root production with an intensified turnover or a delayed decomposition of spruce mycorrhizae. The cation analyses showed an accumulation of Ca(2+) and Zn(2+) in the mycorrhizae of spruce exposed to ozone. 相似文献
686.
Sorption of imidazolium-based ionic liquids to aquatic sediments 总被引:1,自引:0,他引:1
Ionic liquids (ILs) have received much attention as "green" alternatives to traditional solvents because they do not evaporate, eliminating concerns over fugitive emissions. However, if ionic liquids are used in industrial applications, they may enter aquatic systems via effluent, and their fate and transport may be influenced by sorption to sediments. In this study, we conducted batch mixing experiments with four alkylmethylimidizolium-based ILs and four types of aquatic sediments to asses the capacity for natural aquatic sediments to remove these chemicals from the water column. The concentration isotherms were non linear with point estimates of the distribution coefficient (K(d)) decreasing with increasing concentration. Apparent distribution coefficients ranged from 7.9 to 95.7l kg(-1) at an initial concentration of 0.5mM and were positively related to sediment organic matter (SOM) content. These K(d) values indicate that the ILs did not sorb strongly to the tested sediments. Increased alkyl chain length did not lead to increased sorption suggesting that hydrophobic interactions were not the most important sorption mechanism. We conclude that aquatic sediments have a limited capacity to sorb alkylmethylimidazolium ILs and that the transport of these contaminants in aquatic systems will not be strongly attenuated by sediments. 相似文献
687.
Fourteen single-family detached houses in Spokane, Washington, and Coeur D'Alene, Idaho, were monitored for two years after high concentrations of indoor radon had been mitigated. Each house was monitored quarterly using mailed alpha-track radon detectors deployed in each zone of the structure. To assess performance of mitigation systems during the second heating season after mitigation, radon concentrations in seven houses were monitored continuously for several weeks, mitigation systems in all houses were inspected, and selected other measurements were taken. In addition, occupants were also interviewed regarding their maintenance, operation, and subjective evaluation of the radon mitigation systems. Quarterly alpha-track measurements showed that radon levels had increased in most of the homes during many follow-up measurement periods when compared with concentrations measured immediately after mitigation. Mitigation-system performance was adversely affected by (1) accumulated outdoor debris blocking the outlets of subsurface pressurization pipes; (2) fans being turned off (e.g., because of excessive noise or vibration); (3) air-to-air heat exchanger, basement pressurization, and subsurface ventilation fans being turned off and fan speeds reduced; and (4) crawl-space vents being closed or sealed. 相似文献
688.
689.
690.