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   16961篇
  免费   191篇
  国内免费   333篇
安全科学   426篇
废物处理   798篇
环保管理   2075篇
综合类   2438篇
基础理论   4411篇
环境理论   2篇
污染及防治   4495篇
评价与监测   1242篇
社会与环境   1504篇
灾害及防治   94篇
  2023年   94篇
  2022年   218篇
  2021年   172篇
  2020年   120篇
  2019年   160篇
  2018年   267篇
  2017年   277篇
  2016年   413篇
  2015年   305篇
  2014年   465篇
  2013年   1389篇
  2012年   544篇
  2011年   771篇
  2010年   640篇
  2009年   696篇
  2008年   808篇
  2007年   818篇
  2006年   693篇
  2005年   614篇
  2004年   580篇
  2003年   630篇
  2002年   557篇
  2001年   785篇
  2000年   511篇
  1999年   301篇
  1998年   208篇
  1997年   207篇
  1996年   232篇
  1995年   272篇
  1994年   208篇
  1993年   176篇
  1992年   197篇
  1991年   195篇
  1990年   206篇
  1989年   194篇
  1988年   152篇
  1987年   158篇
  1986年   110篇
  1985年   148篇
  1984年   150篇
  1983年   138篇
  1982年   132篇
  1981年   132篇
  1980年   107篇
  1979年   113篇
  1977年   86篇
  1975年   81篇
  1974年   80篇
  1973年   95篇
  1972年   88篇
排序方式: 共有10000条查询结果,搜索用时 546 毫秒
331.
This study was undertaken to evaluate the relationship between maternal serum alpha-fetoprotein (MSAFP) levels and oesophageal atresia (OA). OA occurred in 16 fetuses of mothers who had an MSAFP test in the study interval. The multiple of the median (MOM) value for MSAFP averaged 1·54 ± 0·65 (range 0·5–2·9 MOM), which was significantly higher than the value seen in controls. The median MOM was 1·35. Using a cut-off of 2·5 MOM, the sensitivity of MSAFP for detecting OA was 19 per cent. Although OA should be considered in the differential diagnosis of an elevated MSAFP level, MSAFP cannot be considered an appropriate screening test for OA given the low sensitivity.  相似文献   
332.
The histochemical measurement of urea-resistant alkaline phosphatase from maternal blood neutrophils is known to have a high detection rate for the prenatal detection of Down's syndrome pregnancies. However, because the histochemical method is laborious and subjective to use, it has not gained widespread acceptance in prenatal screening programmes. We present a simple and objective method for the measurement of urea-resistant alkaline phosphatase by flow cytometry. The method should allow the design of larger studies aimed at evaluating the role of neutrophil urea-resistant alkaline phosphatase in the prenatal screening for Down's syndrome.  相似文献   
333.
Information on maternal age and maternal serum alpha-fetoprotein, unconjugated oestriol (uE3), and human chorionic gonadotrophin (hCG) levels was used to investigate retrospectively the effect of estimating Edward's syndrome risk in women having multi-marker screening for Down's syndrome. The screened population comprised 15 pregnancies affected by Edward's syndrome, 15 with Down's syndrome and 5472 unaffected pregnancies. The use of all three markers to estimate Edward's syndrome risk would have led to the detection of 10–12 (67–80 per cent) cases with a false-positive rate of 0.3–0.6 per cent depending on the risk cut-off. A further case would have been detected as a result of screening for Down's syndrome alone. Similar results were obtained when the Edward's syndrome risk was based on uE3 and hCG only. These data suggest that extending Down's syndrome screening to include Edward's syndrome risk will yield a high detection rate with only a small increase in the false-positive rate.  相似文献   
334.
各种环境因素的协同作用已经导致保护运动在解释保护运动的基本信念时尤其缺乏信心。“反对派”行动主义者以为他们的论据是得到证实的,而“制度派”战术主义者倾向于采取他们并不赞同的功利主义的或经济的观点。根据现有的证据,在几百年以后,这个星球上主要的自然区域将基本消失,人类的生活质量将会受到极大的威胁。一种更可靠的观点认为:自然界是人类体验自由(这也是一种精神环境)的能力中不可或缺的一部分。这一观点将改变我们对待自然环境的方式,也关乎今后生物多样性长期生存的前景。  相似文献   
335.
In a case of fetal heart failure caused by endocardial fibroelastosis, prenatal echocardiography clearly demonstrated; a thickened endocardium. We therefore suggest that an abnormal endocardium may be detected in utero by ultrasound, thus representing an important clue in the differential diagnosis of fetal nonimmune hydrops and in the evaluation of pregnancies at risk for endocardial fibroelastosis.  相似文献   
336.
The polymerase chain reaction has been used to detect an abundant class of short repeat DNA families of the form (dC-dA)n.(dG-dT)n, known as microsatellites. These units are found throughout the human genome and have been characterized for several loci including APOC2 on chromosome 19ql2-ql3.2. The locus APOC2 is linked to the gene for dystrophia myotonica and a microsatellite within this locus was used to derive polymorphisms in a family to predict the inheritance of the disease. Chorionic villus sampling (CVS) was performed at 151/2 weeks' gestation. Following DNA extraction from the CVS material and parental blood samples, microsatellite analysis was carried out by the polymerase chain reaction.  相似文献   
337.
338.
339.
340.
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