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   43791篇
  免费   489篇
  国内免费   313篇
安全科学   1241篇
废物处理   1706篇
环保管理   5973篇
综合类   7187篇
基础理论   12506篇
环境理论   30篇
污染及防治   11151篇
评价与监测   2664篇
社会与环境   1828篇
灾害及防治   307篇
  2022年   272篇
  2021年   292篇
  2019年   310篇
  2018年   562篇
  2017年   568篇
  2016年   867篇
  2015年   699篇
  2014年   998篇
  2013年   3288篇
  2012年   1253篇
  2011年   1824篇
  2010年   1487篇
  2009年   1501篇
  2008年   1818篇
  2007年   1911篇
  2006年   1686篇
  2005年   1448篇
  2004年   1395篇
  2003年   1371篇
  2002年   1339篇
  2001年   1704篇
  2000年   1225篇
  1999年   772篇
  1998年   587篇
  1997年   615篇
  1996年   625篇
  1995年   690篇
  1994年   642篇
  1993年   584篇
  1992年   592篇
  1991年   556篇
  1990年   573篇
  1989年   596篇
  1988年   508篇
  1987年   461篇
  1986年   428篇
  1985年   441篇
  1984年   479篇
  1983年   480篇
  1982年   516篇
  1981年   441篇
  1980年   377篇
  1979年   416篇
  1978年   360篇
  1977年   303篇
  1976年   296篇
  1975年   285篇
  1974年   283篇
  1973年   291篇
  1972年   298篇
排序方式: 共有10000条查询结果,搜索用时 387 毫秒
671.
A prenatally detected case of a rare mosaic tetrasomy 12p/trisomy 12p is reported, presenting as the well-known accessory isochromosome 12p and a supernumerary single 12p marker in 17/24 and 6/24 clones of cultured amniotic fluid cells, respectively. The chromosomal nature of both marker chromosomes was investigated in cultured amniotic fluid cells by fluorescent in situ hybridization with various probes: the 12-centromeric probes pa12H8 and D12Z3, a whole chromosome 12 paint, and the chromosome 12p-specific paint M28. DNA analysis revealed a maternal origin of the extra 12p material. After counselling, the parents requested termination of pregnancy. Inspection and autopsy of the fetus revealed many of the dysmorphisms and internal structural abnormalities of the Pallister–Killian syndrome.  相似文献   
672.
In a case of hydrops fetalis, serological examination showed a recent maternal human parvovirus B19 infection. Amniocentesis revealed a unique unbalanced translocation between chromosomes 3 and 11 of the fetus. The mother proved to have a balanced reciprocal translocation between chromosomes 3 and 11. A grossly macerated hydropic male fetus was delivered with a flat nose and low implanted deformed ears. Histopathological examination revealed nuclear inclusion bodies in fetal erythroid cells, confirming human parvovirus B19 infection. Parvovirus B19 DNA was demonstrated by in situ hybridization in the nuclei of heart muscle cells. Our finding of two different disorders in one case illustrates the importance of a complete evaluation of every case of hydrops fetalis, especially concerning counselling on the outcome of future pregnancies. The human parvovirus B19 infection will not recur due to the acquired immunity of the mother, whereas the balanced reciprocal translocation will endanger future pregnancies.  相似文献   
673.
A 17-year-old woman was referred for amniocentesis due to a low maternal serum alpha-fetoprotein (AFP) concentration in a voluntary screening test. The fetal karyotype was 48,XXYY, and the pregnancy was terminated. Autopsy of the fetus disclosed agenesis of the corpus callosum and unusual facial features.  相似文献   
674.
A simplified method is described for processing both direct preparations and long-term cultures from the same fragment of chorionic villi. Enzyme separation of the outer trophoblast layers (used for direct preparations) from the inner mesenchymal core (used to initiate long-term cultures) facilitates the utilization of the same fragments for the two procedures, without jeopardizing the success of either method. This has proved useful in cases where the sample was so small that only one method of chromosome preparation may have been possible using other techniques.  相似文献   
675.
676.
We describe a patient with a significantly elevated serum alphafetoprotein (AFP) concentration at 17 weeks of gestation, who showed only a marginally increased amniotic fluid AFP and lacked the second rapidly migrating band of acetylcholinesterase electrophoresis. Ultrasound examination revealed an encephalocele and ventriculomegaly. Autopsy showed that the encephalocele was not covered by skin.  相似文献   
677.
678.
Reverse phase HPLC of radioactive globin chains has been compared to classical carboxy methyl cellulose chromatography for the prenatal diagnosis of β thalassaemia. The two methods correlated highly (r = 0.97 p < 0.0005) and provided an identical diagnosis for 40 fetal blood samples of fetuses homozygous or heterozygous for β thalassaemia. The HPLC procedure was much faster and required fewer biochemical steps (no globin preparation). It was at least as accurate and more sensitive than the classical chromatography. A single column can be used for 150 analyses and is always ready to be used. Last but not least it is much less expensive than CMC chromatography.  相似文献   
679.
Mitigation and Adaptation Strategies for Global Change - In Mexico an estimated 4.5 × 106ha are available for farm forestry, while up to 6.1 × 106 ha could be saved from deforestation by...  相似文献   
680.
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