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   1500篇
  免费   6篇
  国内免费   42篇
安全科学   48篇
废物处理   86篇
环保管理   149篇
综合类   288篇
基础理论   342篇
环境理论   1篇
污染及防治   404篇
评价与监测   101篇
社会与环境   121篇
灾害及防治   8篇
  2023年   13篇
  2022年   46篇
  2021年   10篇
  2020年   6篇
  2019年   15篇
  2018年   54篇
  2017年   22篇
  2016年   28篇
  2015年   52篇
  2014年   36篇
  2013年   121篇
  2012年   36篇
  2011年   69篇
  2010年   61篇
  2009年   73篇
  2008年   71篇
  2007年   60篇
  2006年   47篇
  2005年   45篇
  2004年   80篇
  2003年   66篇
  2002年   43篇
  2001年   104篇
  2000年   43篇
  1999年   24篇
  1998年   16篇
  1997年   12篇
  1996年   9篇
  1995年   20篇
  1994年   8篇
  1993年   9篇
  1992年   16篇
  1991年   10篇
  1990年   12篇
  1989年   10篇
  1988年   7篇
  1987年   7篇
  1985年   8篇
  1984年   10篇
  1983年   7篇
  1981年   6篇
  1980年   6篇
  1975年   8篇
  1974年   10篇
  1973年   7篇
  1972年   13篇
  1965年   5篇
  1959年   5篇
  1957年   6篇
  1925年   6篇
排序方式: 共有1548条查询结果,搜索用时 546 毫秒
391.
392.
393.
394.
Although evidence-based approaches have become commonplace for determining the success of conservation measures for the management of threatened taxa, there are no standard metrics for assessing progress in research or management. We developed 5 metrics to meet this need for threatened taxa and to quantify the need for further action and effective alleviation of threats. These metrics (research need, research achievement, management need, management achievement, and percent threat reduction) can be aggregated to examine trends for an individual taxon or for threats across multiple taxa. We tested the utility of these metrics by applying them to Australian threatened birds, which appears to be the first time that progress in research and management of threats has been assessed for all threatened taxa in a faunal group at a continental scale. Some research has been conducted on nearly three-quarters of known threats to taxa, and there is a clear understanding of how to alleviate nearly half of the threats with the highest impact. Some management has been attempted on nearly half the threats. Management outcomes ranged from successful trials to complete mitigation of the threat, including for one-third of high-impact threats. Progress in both research and management tended to be greater for taxa that were monitored or occurred on oceanic islands. Predation by cats had the highest potential threat score. However, there has been some success reducing the impact of cat predation, so climate change (particularly drought), now poses the greatest threat to Australian threatened birds. Our results demonstrate the potential for the proposed metrics to encapsulate the major trends in research and management of both threats and threatened taxa and provide a basis for international comparisons of evidence-based conservation science.  相似文献   
395.
Environmental and Ecological Statistics - Species distribution modelling (SDM) is a family of statistical methods where species occurrence/density/richness are combined with environmental...  相似文献   
396.
In this research a gas–liquid fluidized bed reactor was developed for removing chlorine (Cl) from polyvinyl chloride (PVC) to favor its pyrolysis treatment. In order to efficiently remove Cl within a limited time before extensive generation of hydrocarbon products, the gas–liquid fluidized bed reactor was running at 280–320 °C, where hot N2 was used as fluidizing gas to fluidize the molten polymer, letting the molten polymer contact well with N2 to release Cl in form of HCl. Experimental results showed that dechlorination efficiency is mainly temperature dependent and 300 °C is a proper reaction temperature for efficient dechlorination within a limited time duration and for prevention of extensive pyrolysis; under this temperature 99.5% of Cl removal efficiency can be obtained within reaction time around 1 min after melting is completed as the flow rate of N2 gas was set around 0.47–0.85 Nm3 kg?1 for the molten PVC. Larger N2 flow rate and additives in PVC would enhance HCl release but did not change the final dechlorination efficiency; and excessive N2 flow rate should be avoided for prevention of polymer entrainment. HCl is emitted from PVC granules or scraps at the mean time they started to melt and the melting stage should be taken into consideration when design the gas–liquid fluidized bed reactor for dechlorination.  相似文献   
397.
398.
Pesticide leaching models are being used to assist in the regulation and management of pesticides by indicating their potential for leaching to groundwater. Uncertainty in model input data is not, regrettably, included in most pesticide leaching assessments. In the work described here, we use logarithmic transformations of the attenuation factor (AF), a simple process-based index model, to represent uncertainty in a pesticide leaching assessment. Characterization of a wide range of pesticides as `leachers' or `non-leachers' for a specific Hawaii hydrogeological setting is facilitated by comparing the log-transformed AF, designated AFR, for each chemical with two reference chemicals for which leaching behavior in Hawaii is known. Defining a mean and uncertainty interval for the AFR index of each chemical being ranked provides a practical method of incorporating data uncertainty into a regulatory protocol.  相似文献   
399.
In the present study, a new sensitive and simple kinetic-spectrophotometric method for the determination of the insecticide diflubenzuron [1-(4-chlorophenyl)-3-(2,6-diflubenzoil)urea] is proposed. The method is based on the inhibited effect of diflubenzuron on the oxidation of sulphanilic acid (SA) by hydrogen peroxide in phosphate buffer in presence Cu(II) ion. Diflubenzuron was determined with linear calibration graph in the interval from 0.31 to 3.1 μg mL?1 and from 3.1 to 31.0 μg mL?1. The optimized conditions yielded a theoretical detection limit of 0.18 μg mL?1corresponding to 0.036 mg Kg?1mushroom sample based on the 3Sb criterion. The RSD is 5.03–1.83 % and 2.81–0.71 % for the concentration interval of diflubenzuron 0.31–3.1 μg mL?1and 3.1–31.0 μg mL?1, respectively. The reaction was followed spectrophotometrically at 370 nm. The kinetic parameters of the reaction are reported, and the rate equations are suggested. The developed procedure was successfully applied to the rapid determination of diflubenzuron in spiked mushroom samples of different mushroom species. The HPLC method was used like a comparative method to verify results.  相似文献   
400.
The cationic polymerization of soybean oils was initiated by boron trifluoride diethyl etherate in supercritical carbon dioxide medium. The resulting polymers had molecular weight ranging from 21,842 to 118,300 g/mol. Nuclear magnetic resonance spectroscopy and gel permeation chromatography analysis confirmed the polymerization had occurred. Parameters affecting the polymerization were studied, which included initiator amount and reaction time. Results show that the longer reaction time, up to 3 h, favored the higher molecular weight of polymers at conditions of 140 °C and initiator BF3·OEt2 (2.5 g, 0.018 mol). When reaction time was increased further, the molecular weight of polymers stayed the same or slightly decreased. Increased concentration of initiator gave the higher molecular weight of polymers. The high molecular weight polymers were possibly formed through two path ways: polymerization and intermolecular Diels-Alder reaction.  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