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   20908篇
  免费   242篇
  国内免费   1454篇
安全科学   611篇
废物处理   858篇
环保管理   2180篇
综合类   7169篇
基础理论   4233篇
环境理论   3篇
污染及防治   5579篇
评价与监测   1010篇
社会与环境   739篇
灾害及防治   222篇
  2022年   298篇
  2021年   211篇
  2020年   169篇
  2019年   183篇
  2018年   340篇
  2017年   348篇
  2016年   445篇
  2015年   423篇
  2014年   611篇
  2013年   1509篇
  2012年   692篇
  2011年   807篇
  2010年   719篇
  2009年   810篇
  2008年   833篇
  2007年   809篇
  2006年   728篇
  2005年   610篇
  2004年   607篇
  2003年   591篇
  2002年   561篇
  2001年   709篇
  2000年   524篇
  1999年   407篇
  1998年   344篇
  1997年   279篇
  1996年   269篇
  1995年   304篇
  1994年   301篇
  1993年   261篇
  1992年   271篇
  1991年   246篇
  1990年   271篇
  1989年   240篇
  1988年   193篇
  1987年   185篇
  1986年   186篇
  1985年   182篇
  1984年   201篇
  1983年   189篇
  1982年   197篇
  1981年   214篇
  1980年   169篇
  1979年   181篇
  1974年   148篇
  1968年   156篇
  1967年   184篇
  1966年   154篇
  1965年   148篇
  1964年   151篇
排序方式: 共有10000条查询结果,搜索用时 23 毫秒
181.
The female silkmoth Bombyx mori L. emits a second pheromone component bombykal (E-10, Z-12-hexade-cadien-1-al) in addition to the well-known sexual attractant bombykol (E-10, Z-12-hexadecadien-1-ol). Bombykal stimulates its own specialized and highly sensitive olfactory cells of the male moth. Surprisingly, the aldehyde inhibits the release of the male's wing-fluttering response to bombykol.  相似文献   
182.
183.
184.
As screening for Down syndrome becomes increasingly sophisticated, it is important to evaluate the newer technologies in terms of their cost-effectiveness. One recent addition to Down syndrome screening programmes is maternal serum unconjugated oestriol (uE3), especially when used in conjunction with maternal serum α-fetoprotein and human chorionic gonadotropin. Using assumptions used in a California proposal to justify an expanded screening programme for Down syndrome, we calculated both the average and the incremental cost-effectiveness of adding uE3. Using the base case assumptions, including an $8 fee for the uE3, the incremental cost-effectiveness of adding uE3 to the proposed California programme is $119 100 per case detected, a value that compares favourably with other Down syndrome screening programmes. The sensitivity analysis supports this conclusion over a wide range of assumptions. However, because of the uncertainty with some key data, it is still too early to fully support the inclusion of uE3 in Down syndrome screening programmes.  相似文献   
185.
东海海域春季降水的化学特征   总被引:5,自引:2,他引:5  
根据1994年4月17日-27日东海海域的降水雨样化学组份分析,并将春与我国上海及日本西海岸的降水化学组分进行了地比。认为东海海域的降水经与陆地源污染的输送有关,在东南风系作用下,降水肥东南海上气闭影响,从上海以东到日本以西的广阔的海域中,降水呈弱酸或中性,其化学组份表现为海洋化学的特征;在东北风系作用下,东海海域的降水主要受朝鲜半岛和日本方面污染源的影响,降水中SO4^2-非海盐浓度比东南风系时  相似文献   
186.
In recent years, an increasing number of inherited diseases in man have been recognized in which there is an impairment in the peroxisomal β-oxidation of very-long-chain fatty acids. In general, these disorders are associated with severe neurological and physical abnormalities and death within the first years of life. In this paper we describe our experience with regard to the prenatal diagnosis of a number of different inborn errors of peroxisomal β-oxidation. Eleven pregnancies at risk were monitored by measuring very-long-chain fatty acid levels as well as very-long-chain fatty acid β-oxidation in cultured chorionic villous fibroblasts and/or amniotic fluid cells. Five affected fetuses were identified. It is concluded that prenatal diagnosis in this group of diseases can be done reliably using cultured chorionic villous fibroblasts or amniotic fluid cells.  相似文献   
187.
Chorionic villus sampling (CVS) with either transcervical catheters or transabdominal needles is a widely-accepted method for prenatal diagnosis. However, there exists a small subset of patients in whom sampling is difficult or impossible with either route because of individual anatomic variations. A new method of chorionic villus biopsy has been developed to circumvent these problems, utilizing transvaginal chorionic needle aspiration guided by an intravaginal ultrasound probe. This technique was performed successfully in 15 patients in whom villi could not be obtained by either of the conventional methods. This method now makes CVS possible in essentially all women regardless of their uterine anatomy or placental placement; it may also prove useful for very early chorionic sampling.  相似文献   
188.
189.
190.
Plasticity of honeybee castes   总被引:1,自引:0,他引:1  
  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