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   26947篇
  免费   680篇
  国内免费   2294篇
安全科学   971篇
废物处理   1193篇
环保管理   2826篇
综合类   8062篇
基础理论   5966篇
环境理论   7篇
污染及防治   6651篇
评价与监测   1933篇
社会与环境   2002篇
灾害及防治   310篇
  2023年   241篇
  2022年   610篇
  2021年   551篇
  2020年   489篇
  2019年   467篇
  2018年   597篇
  2017年   672篇
  2016年   801篇
  2015年   741篇
  2014年   1065篇
  2013年   2146篇
  2012年   1167篇
  2011年   1383篇
  2010年   1114篇
  2009年   1177篇
  2008年   1313篇
  2007年   1195篇
  2006年   1106篇
  2005年   925篇
  2004年   863篇
  2003年   875篇
  2002年   835篇
  2001年   1015篇
  2000年   714篇
  1999年   455篇
  1998年   323篇
  1997年   311篇
  1996年   334篇
  1995年   344篇
  1994年   307篇
  1993年   254篇
  1992年   266篇
  1991年   264篇
  1990年   250篇
  1989年   219篇
  1988年   229篇
  1987年   162篇
  1986年   182篇
  1985年   188篇
  1984年   185篇
  1983年   168篇
  1982年   179篇
  1981年   181篇
  1980年   126篇
  1979年   137篇
  1978年   134篇
  1976年   123篇
  1974年   135篇
  1972年   138篇
  1967年   126篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Living veligers of the Cassoidea have been observed to use a mantle appendage to form and resorb periostracum. Anatomical and histological examinations of a ranellid (Cymatium sp.) larva collected from the Red Sea in 1987 revealed the structure and location of the pallial appendage. The mantle edges of juvenile or adult species of the Cassoidea do not show a comparable specialization. It is demonstrated that cassoid larval conch characters are sufficient to prove the existence of a pallial appendage without anatomical confirmation. A mantle appendage is not known from teleplanic (long-living planktic) veligers of other gastropod superfamilies. In cases where the larval strategies of the latter are known they are totally different. Therefore it is suggested that the adaptation of cassoid larvae to pelagic life is unique among gastropods representing an autapomorphic character of the superfamily.  相似文献   
72.
This paper examines the relationship between survivor reactions to a downsizing and retention subsequent to a downsizing. We hypothesize that survivors who experience the downsizing as distributively, procedurally, and interactionally just and who see top management as trustworthy will feel more attached to the organization because each reduces the threat inherent in downsizing. In addition, we hypothesize that survivors who feel empowered will also feel more attached to the organization because they feel better able to cope with the downsizing. We further hypothesize that those survivors who feel more attached to the organization following the downsizing will be more likely to remain with the organization in the coming year. The theoretical model is tested on a sample of aerospace employees who survived an organizational downsizing. The trustworthiness of management, distributive justice, procedural justice, and three dimensions of empowerment are found to facilitate more organizational attachment. Higher levels of attachment are found, in turn, to facilitate less voluntary turnover in the year following the downsizing. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   
73.
74.
75.
Stormwater runoff is now a major contributor to the pollution of coastal waters in the United States. Public agencies are responding by requiring stormwater monitoring to satisfy the National Pollutant Discharge Elimination System stormwater permit. However, studies to understand the utility of the current programs or to improve their usefulness have not yet been performed. In this paper, we evaluate the land-use-based program, the industrial stormwater permit program, and beach water-quality monitoring in the County of Los Angeles, California, to determine if the results will be helpful to planners and regulators in abating stormwater pollution. The utility of the program has been assessed based on the programs' ability to accurately estimate the emissions for different classes of land use. The land-use program appears successful, while the industrial monitoring program does not. Beach water-quality monitoring suffers from a lack of real-time monitoring techniques. We also provide suggested improvements, such as sampling method and time, and parameter selection.  相似文献   
76.
77.
78.
79.
Guzman N  Paz MX  Paz MI  Moreno NR  Nino F 《Disasters》1989,13(2):153-164
In the past 20 years a variety of indices have been suggested for measuring the severity of trauma, however none of them meets the requirement of being a simple and objective instrument that can be utilized efficiently by lay persons and providers of health services without previous experience in triaging. A new system has been proposed which meets this requirement and which has been validated with 197 injured persons at the emergency ward of the Valle University Hospital in Call, Colombia. The instrument showed a high level of concordance with the conventional triaging method and classifies victims into four categories: critical with recovery unlikely, critical but recoverable, moderately serious, and ambulatory. There is discussion on the reliability of this instrument and it is recommended that it be validated with victims from larger disasters. Regardless, it has the advantage of being specific and free of the subjectivity that characterizes other indices.  相似文献   
80.
Winer N 《Disasters》1989,13(1):1-8
Food security in Ethiopia is discussed in the context of the repeated famines and the international responses both to them and to the socialist agricultural policies being pursued by Ethiopia. Increasing concern has been expressed by the international donor community regarding the ability of Ethiopia to absorb development funds without a major shift in emphasis in agricultural policy-making. The background to Ethiopia's present vulnerability is shown both in terms of the size of the vulnerable population and in terms of the poor performance of the agricultural sector in the last decade. The author looks at the present agricultural and marketing policy reforms and questions whether they are sufficient to generate the sort of international response needed to create the level of food security that would be required to avert future famines.  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