首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1718篇
  免费   16篇
  国内免费   45篇
安全科学   24篇
废物处理   113篇
环保管理   159篇
综合类   159篇
基础理论   309篇
环境理论   2篇
污染及防治   583篇
评价与监测   318篇
社会与环境   108篇
灾害及防治   4篇
  2023年   65篇
  2022年   180篇
  2021年   118篇
  2020年   25篇
  2019年   47篇
  2018年   83篇
  2017年   92篇
  2016年   112篇
  2015年   48篇
  2014年   82篇
  2013年   185篇
  2012年   78篇
  2011年   91篇
  2010年   77篇
  2009年   63篇
  2008年   80篇
  2007年   59篇
  2006年   68篇
  2005年   35篇
  2004年   29篇
  2003年   24篇
  2002年   34篇
  2001年   8篇
  2000年   8篇
  1999年   5篇
  1998年   3篇
  1997年   2篇
  1996年   6篇
  1995年   3篇
  1994年   4篇
  1993年   3篇
  1992年   3篇
  1989年   3篇
  1988年   3篇
  1985年   2篇
  1984年   3篇
  1983年   6篇
  1982年   5篇
  1980年   2篇
  1979年   2篇
  1965年   2篇
  1964年   3篇
  1962年   2篇
  1961年   4篇
  1958年   3篇
  1957年   4篇
  1956年   2篇
  1955年   4篇
  1954年   1篇
  1953年   1篇
排序方式: 共有1779条查询结果,搜索用时 31 毫秒
131.
132.
Controlled release (CR) formulations of azadirachtin-A, a bioactive constituent derived from the seed of Azadirachta indica A. Juss (Meliaceae), have been prepared using commercially available polyvinyl chloride, polyethylene glycol (PEG) and laboratory synthesized poly ethylene glycol–based amphiphilic copolymers. Copolymers of polyethylene glycol and various dimethyl esters, which self assemble into nano micellar aggregates in aqueous media, have been synthesized. The kinetics of azadirachtin-A, release in water from the different formulations was studied. Release from the commercial polyethylene glycol (PEG) formulation was faster than the other CR formulations. The rate of release of encapsulated azadirachtin-A from nano micellar aggregates is reduced by increasing the molecular weight of PEG. The diffusion exponent (n value) of azadirachtin-A, in water ranged from 0.47 to 1.18 in the tested formulations. The release was diffusion controlled with a half release time (t1/2) of 3.05 to 42.80 days in water from different matrices. The results suggest that depending upon the polymer matrix used, the application rate of azadirachtin-A can be optimized to achieve insect control at the desired level and period.  相似文献   
133.
Stabilizing global greenhouse gas concentrations at levels to avoid significant climate risks will require massive "decarbonization" of all the major economies over the next few decades, in addition to the reduced emissions from other GHGs and carbon sequestration. Achieving the necessary scale of emissions reductions will require a multifaceted policy effort to support a broad array of technological and behavioral changes. Change on this scale will require sound, well-thought-out strategies. In this article, we outline some core principles, drawn from recent social science research, for guiding the design of clean technology policies, with a focus on energy. The market should be encouraged to make good choices: pricing carbon emissions and other environmental damage, removing distorting subsidies and barriers to competition, and supporting RD&D broadly. More specific policies are required to address particular market failures and barriers. For those technologies identified as being particularly desirable, some narrower RD&D policies are available.  相似文献   
134.
Brassinosteroids (BRs) are involved in the amelioration of various biotic and abiotic stresses. With an aim to explore the role of BRs under heavy metal stress, plants of Brassica juncea L. were grown in pots. The plants were subjected to various concentrations of Nickel metal (0.0, 0.2, 0.4 and 0.6 mM) and harvested on 60th day in order to observe the expression of these hormones. The isolated BRs from the leaves of Brassica plants characterized by GC-MS include 24-Epibrassinolide (24-EBL), Castasterone, Dolicholide and Typhasterole. The effect of isolated 24-EBL was studied on Ni metal uptake and antioxidative defense system in 60 d old plants of Brassica. It was observed that 24-EBL significantly increased the activities of stress ameliorating enzymes and lowered the metal uptake in plants. This is the first report in B. juncea L. plants showing the expression of BRs under metal treatments and effect of the isolated 24-EBL on metal uptake and in oxidative stress management.  相似文献   
135.
The interaction of the phototoxic alkaloid coralyne with bovine and human serum albumins (BSA, HSA) was investigated. Absorbance and fluorescence quenching experiments revealed the formation of strong complexes. Based on the binding parameters calculated from Stern-Volmer quenching method, coralyne has higher affinity to BSA (∼105 M−1) compared to HSA (∼104 M−1). Forster resonance energy transfer studies showed that the specific binding distances between Trp (donor) of the proteins and coralyne (acceptor) were 2.95 and 3.10 nm, respectively. The bindings were favored by negative enthalpy and a stronger favorable entropy contribution. The heat capacity values for binding to BSA and HSA were similar, indicating the involvement of similar molecular forces in the complexation. Competitive binding experiments using site markers demonstrated that coralyne binds to site I (subdomain IIA) of both proteins. The secondary structure of the proteins was altered, suggesting a small but definitive partial unfolding on complexation.  相似文献   
136.
Verma V  Yu QJ  Connell DW 《Chemosphere》2012,89(9):1026-1033
Traditionally in toxicological studies time is not studied as quantifiable variable but as a fixed endpoint. The Reduced Life Expectancy (RLE) model which relates exposure time and exposure concentration with lethal toxic effects was tested previously using fish data. In this current paper the effects of exposure time on aquatic toxicity with zooplanktons and various toxicants were evaluated using the RLE model based on ambient exposure concentration. The model was evaluated by plotting ln LT50 against LC50 using toxicity data with zooplanktons from the literature for metal, metalloid and organic compounds. Most of the experimental data sets can be satisfactorily correlated by use of the RLE model, but deviations occurred for some data sets. Those data sets were satisfactorily fitted by a two stage RLE model. This model was based on two phases: one in the peripheral system and other in the central system. Both the single and two stage RLE model support the hypothesis that toxicity is time dependent and decreases in a systematic way with increasing exposure time. A calculated normal life expectancy (NLT) can be obtained from the single stage model and is in accord with reported NLT but those obtained from the two stage RLE model are in excellent agreement.  相似文献   
137.
Diclofenac, a non-steroidal anti-inflammatory drug (NSAID), has caused catastrophic vulture declines across the Indian sub-continent. Here, an indirect ELISA is used to detect and quantify diclofenac in 1251 liver samples from livestock carcasses collected across India between August 2007 and June 2008, one to two years after a ban on diclofenac manufacture and distribution for veterinary use was implemented. The ELISAs applicability was authenticated with independent data obtained using LC-ESI/MS. Of 1251 samples, 1150 (91.9%) were negative for diclofenac using both methods, and 60 (4.8%) were positive at 10-4348 and 10-4441 μg kg(-1) when analysed by ELISA and LC-ESI/MS, respectively. The residue level relationship in the 60 positive samples was highly significant (p < 0.001, r(2) = 0.644). Data suggest that this immunological assay could be used not only for cost effective sample screening, but also for residue level semi-quantification.  相似文献   
138.
In the present investigation, the bioefficacy of developed carbofuran formulations, with PEG-600 (7a, CP1) & PEG-900 (7b, CP2) @ 5, 10 and 20 ppm, along with commercial formulation of carbofuran 3G (CP0) were evaluated against the root-knot nematode, Meloidogyne incognita infecting tomato (cv. Pusa Ruby) in pot and field conditions. The bioefficacy data indicated that the formulations developed by utilizing polymers having PEG - 900 (7b) as hydrophilic segment were effective even at 14 days post inoculation (dpi) as evident from shoot and root length. Also, the reduction in penetration was found to be maximum with CP2 (3.6 - 4.6 J2s) at all concentrations compared to CP1 (6.6-16.4 J2s) and CP0 (29.3-32.6 J2s). Overall, CP2 was more effective in reducing the number of nematodes up to 14 days, compared to CP1 and CP0. Both the CR formulations (CP1 and CP2) in general significantly reduced the number of galls, when compared to CP0. However, under field conditions, lower concentrations (5, and 10 ppm) of CP2, were less effective in controlling the gall formation whereas, CP2 at 20 ppm, was most effective than other treatments. The study revealed that the developed CR formulations of carbofuran have the potential for effective management of M. incognita in tomato under field conditions.  相似文献   
139.

Introduction  

In the nuclear industry 1,4-dioxane is used as a solvent in liquid scintillation technique for measuring low-energy beta-emitters such as 3H or C14 in aqueous media. Improper disposal of 1,4-dioxane can contaminate the ground and surface waters. Conventional wastewater treatment processes like chemical treatment, air stripping, carbon adsorption, and biological treatment are ineffective for the degradation of 1,4-dioxane.  相似文献   
140.
In this study, Talinum triangulare Jacq. (Willd.) treated with different lead (Pb) concentrations for 7 days has been investigated to understand the mechanisms of ascorbate–glutathione metabolisms in response to Pb-induced oxidative stress. Proteomic study was performed for control and 1.25 mM Pb-treated plants to examine the root protein dynamics in the presence of Pb. Results of our analysis showed that Pb treatment caused a decrease in non-protein thiols, reduced glutathione (GSH), total ascorbate, total glutathione, GSH/oxidized glutathione (GSSG) ratio, and activities of glutathione reductase and γ-glutamylcysteine synthetase. Conversely, cysteine and GSSG contents and glutathione-S-transferase activity was increased after Pb treatment. Fourier transform infrared spectroscopy confirmed our metabolic and proteomic studies and showed that amino, phenolic, and carboxylic acids as well as alcoholic, amide, and ester-containing biomolecules had key roles in detoxification of Pb/Pb-induced toxic metabolites. Proteomic analysis revealed an increase in relative abundance of 20 major proteins and 3 new proteins (appeared only in 1.25 mM Pb). Abundant proteins during 1.25 mM Pb stress conditions have given a very clear indication about their involvement in root architecture, energy metabolism, reactive oxygen species (ROS) detoxification, cell signaling, primary and secondary metabolisms, and molecular transport systems. Relative accumulation patterns of both common and newly identified proteins are highly correlated with our other morphological, physiological, and biochemical parameters.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号