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   29224篇
  免费   280篇
  国内免费   243篇
安全科学   667篇
废物处理   1171篇
环保管理   3454篇
综合类   5986篇
基础理论   7316篇
环境理论   10篇
污染及防治   7306篇
评价与监测   1905篇
社会与环境   1796篇
灾害及防治   136篇
  2022年   218篇
  2021年   208篇
  2019年   202篇
  2018年   373篇
  2017年   399篇
  2016年   596篇
  2015年   472篇
  2014年   722篇
  2013年   2145篇
  2012年   837篇
  2011年   1188篇
  2010年   998篇
  2009年   1035篇
  2008年   1199篇
  2007年   1267篇
  2006年   1099篇
  2005年   926篇
  2004年   939篇
  2003年   935篇
  2002年   885篇
  2001年   1132篇
  2000年   772篇
  1999年   511篇
  1998年   331篇
  1997年   375篇
  1996年   387篇
  1995年   417篇
  1994年   419篇
  1993年   362篇
  1992年   371篇
  1991年   361篇
  1990年   363篇
  1989年   340篇
  1988年   294篇
  1987年   287篇
  1986年   279篇
  1985年   281篇
  1984年   296篇
  1983年   288篇
  1982年   279篇
  1981年   248篇
  1980年   232篇
  1979年   235篇
  1978年   211篇
  1977年   212篇
  1976年   169篇
  1975年   177篇
  1974年   194篇
  1973年   179篇
  1972年   168篇
排序方式: 共有10000条查询结果,搜索用时 578 毫秒
721.
It has been shown that the potential for environmental, and financial improvements through the increased substitution of in-person meetings by virtual communication is considerable. However, it has also been shown that this potential is not automatically realized by investing in the technology that can enable virtual meetings. This paper describes two case studies that explored the factors that influenced communication and meeting behavior. A number of drivers and barriers for virtual meetings are identified, and, in addition, measures are proposed to improve the utilization of virtual tools for business communication.  相似文献   
722.
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   
723.
In this study, we describe a simple strategy to detect β-thalassaemia mutations in prospective parents and to make prenatal diagnosis in pregnancies at risk in the Mediterranean population. Screening of prospective parents is carried out by dot blot analysis on enzymatically amplified DNA with a set of oligonucleotide probes complementary to the most common mutations in this population. Prenatal diagnosis is accomplished by the same procedure on enzymatically amplified amniocyte or trophoblast DNA. The main advantages of this procedure are the simplicity, sensitivity (0.05 μg of DNA), and rapidity (12–24 h). Further simplification is obtained by amplification of the DNA from crude amniotic cell lysate. The very low amount of fetal material necessary for this analysis eliminates the need to culture amniotic fluid cells and may decrease the fetal loss rate associated with trophoblast sampling. The number of specific DNA sequences obtained by the amplification procedure allowed us to use non-radioactive labelled oligonucleotide probes, which have several advantages compared to radioactive probes.  相似文献   
724.
Prenatal diagnosis in a pregnancy at risk for a juvenile B1 variant of GM2-gangliosidosis was carried out. The biochemical study of the cultured amniocytes and the affected fetal brain is reported. The results obtained show that the sulphated artificial substrate can be used in the diagnosis of B1 variant, but not the neutral one. The accumulation of GM2-ganglioside in the fetal brain of the B1 juvenile form and an infantile form of GM2-gangliosidosis (0 variant) was compared.  相似文献   
725.
Foci of calcification were observed at autopsy in the liver of a fetus with complete trisomy 9 on which two cordocenteses had been performed. It is suggested that liver calcifications are a possible complication of the procedure. As several other cases of calcifications in the liver and other organs of fetuses with autosomal trisomies have been described without a history of cordocentesis, further studies should be carried out to determine whether fetuses with chromosomal anomalies are more prone to thrombus formation and embolization.  相似文献   
726.
Prenatal diagnosis on chorionic villous tissue was performed for a woman with the karyotype 46,XX,t(2;18)(q32;q12)—a subtle ‘difficult’ translocation. The case illustrates the necessity of good quality cytogenetics for accurate prenatal diagnosis. For chorionic villi this can be obtained only with long-term culture.  相似文献   
727.
728.
729.
730.
Serum PAPP-A measurements taken from 254 women in the first trimester are reported. Eleven chromosomal abnormalities were detected. The mean serum PAPP-A levels in cases of Down syndrome were 0.44 MOM at 9 weeks gestation, 0.15 MOM at 10 weeks, and 0.29 MOM at 11 weeks. The PAPP-A level at 10 weeks was below those of pregnancies which aborted spontaneously. At 11 weeks, the pregnancies with Down syndrome recorded the lowest PAPP-A levels at that gestation. On this small sample, offering chorionic villus sampling to women with singleton pregnancies and a PAPP-A level below 0.3 MOM (approximately 6.5 per cent of this at-risk group) would have detected all the Down syndrome fetuses at 10 weeks and 50 per cent at 11 weeks without selecting those cases destined to abort. This suggests that serum PAPP-A should continue to be investigated as a potential first-trimester screening test for Down syndrome.  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