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   21459篇
  免费   208篇
  国内免费   219篇
安全科学   584篇
废物处理   1047篇
环保管理   2527篇
综合类   2922篇
基础理论   5478篇
环境理论   5篇
污染及防治   5886篇
评价与监测   1767篇
社会与环境   1528篇
灾害及防治   142篇
  2023年   99篇
  2022年   227篇
  2021年   245篇
  2020年   154篇
  2019年   193篇
  2018年   359篇
  2017年   362篇
  2016年   562篇
  2015年   390篇
  2014年   629篇
  2013年   1826篇
  2012年   714篇
  2011年   927篇
  2010年   850篇
  2009年   843篇
  2008年   951篇
  2007年   1036篇
  2006年   916篇
  2005年   759篇
  2004年   772篇
  2003年   764篇
  2002年   714篇
  2001年   959篇
  2000年   656篇
  1999年   412篇
  1998年   283篇
  1997年   257篇
  1996年   296篇
  1995年   282篇
  1994年   259篇
  1993年   245篇
  1992年   250篇
  1991年   211篇
  1990年   217篇
  1989年   225篇
  1988年   203篇
  1987年   160篇
  1986年   131篇
  1985年   146篇
  1984年   173篇
  1983年   160篇
  1982年   199篇
  1981年   137篇
  1980年   120篇
  1979年   152篇
  1978年   118篇
  1977年   107篇
  1976年   102篇
  1975年   83篇
  1974年   89篇
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
271.
We describe the prenatal diagnosis of isolated bilateral fetal microphthalmia in a woman at increased risk of having a fetus with microphthalmia. Ultrasound examinations at 161 and 19-5 weeks' gestation demonstrated bilateral fetal microphthalmia with no other associated structural defects. The patient elected to terminate her pregnancy at 19.5 weeks. Pathological evaluation of the products of conception obtained by dilation and evacuation confirmed the prenatal diagnosis of isolated bilateral fetal microphthalmia.  相似文献   
272.
炼油污水气浮絮凝处理中试   总被引:2,自引:1,他引:2  
气浮絮凝是炼油污水处理工艺中重要的一步 ,它是确保炼油污水生化处理顺利运行的关键 ,而开发和筛选优良的絮凝剂则又是提高气浮处理效果的保证。采用无机—有机复合絮凝剂进行炼油污水的中试试验 ,通过一系列条件试验 ,确定了复合絮凝剂投药剂量、投药间隔时间和投药方式 ,取得了令人满意的试验效果 ,CODCr的去除率 5 5 % ,石油类去除率 >75 % ,为后续的生化处理提供了合格的水质  相似文献   
273.
While true mosaicism occurs in only 0–25 per cent of genetic amniocenteses, nearly 2–5 per cent of amniotic fluid cell cultures contain a second cell line. In the common practice of prenatal diagnosis, an aberrant cell line confined to a single colony is usually disregarded. We present a case of mosaic trisomy 14 which was not detected on initial chromosome analysis. At birth, multiple malformations were apparent. Newborn cytogenetic studies revealed mosaicism [46,XX/46,XX,-14,+i(14q)] with an isochromosome 14 in 37 per cent of lymphocytes. Additional cells from the initial amniotic fluid culture were analysed post-delivery and the isochromosome 14 identified in only one of 12 total colonies. This case illustrates two important lessons in prenatal diagnosis. First, amniotic fluid cell cultures may not accurately reflect the relative distribution of the normal and abnormal cell lines within a mosaic fetus. Second, while it is generally reasonable to disregard mosaicism confined to a single colony, this policy will, on rare occasion, result in diagnostic error. This should be taken into consideration, particularly when dealing with autosomal trisomies potentially compatible with livebirth.  相似文献   
274.
The Henze precipitate, a peculiar blue-green microparticulate obtained by lysis of the blood cells of the ascidian Phallusia mammillata (Protochordata), was investigated with atomic force microscopy (AFM), scanning electron microscopy (SEM) and X-ray microanalysis. The precipitate was collected from the Henze solution, an unstable red-brown product obtained by treating blood with distilled water, whose degradation yields a characteristic blue-green product. The microparticulates measured 50–100 µm in diameter and appeared irregular in shape. SEM examination showed smooth, roughly round boundaries. The microparticulate surface examined with AFM appeared as an irregular matrix formed by 70–320-nm-wide mammillate composites, including and embedding small (500–800 nm wide) crystal-like multilayered formations. X- ray analysis showed that the elements present in these same precipitates were mainly C, Si, Al and O. The microparticulate composition appeared close to those of natural waxes or lacquers, embedding amorphous silicates and/or other Si–Al components. The unusual occurrence of Si in ascidian blood and its role are discussed.  相似文献   
275.
276.
277.
278.
Polyacetylene is presented as the prototype of a metallic conducting polymer. The concepts of one-dimensional metal physics are illustrated and special attention is drawn to a structural defect called “soliton”. Electrical, magnetic, and optical experiments connected with solitons are discussed. The authors' opinion is expressed that present experimental results do not yet furnish strong evidence for the existence of solitons in polyacetylene, but that the soliton idea is a fruitful stimulus for further investigations and novel applications.  相似文献   
279.
280.
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