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   45464篇
  免费   466篇
  国内免费   570篇
安全科学   1284篇
废物处理   1986篇
环保管理   5223篇
综合类   10342篇
基础理论   10971篇
环境理论   25篇
污染及防治   11343篇
评价与监测   2832篇
社会与环境   2248篇
灾害及防治   246篇
  2022年   444篇
  2021年   401篇
  2020年   306篇
  2019年   374篇
  2018年   671篇
  2017年   655篇
  2016年   985篇
  2015年   753篇
  2014年   1157篇
  2013年   3383篇
  2012年   1386篇
  2011年   1863篇
  2010年   1572篇
  2009年   1654篇
  2008年   1915篇
  2007年   1964篇
  2006年   1680篇
  2005年   1463篇
  2004年   1392篇
  2003年   1441篇
  2002年   1318篇
  2001年   1677篇
  2000年   1181篇
  1999年   758篇
  1998年   527篇
  1997年   538篇
  1996年   511篇
  1995年   626篇
  1994年   633篇
  1993年   519篇
  1992年   538篇
  1991年   530篇
  1990年   580篇
  1989年   525篇
  1988年   436篇
  1987年   408篇
  1986年   369篇
  1985年   405篇
  1984年   425篇
  1983年   414篇
  1982年   405篇
  1981年   396篇
  1980年   319篇
  1979年   348篇
  1978年   305篇
  1977年   248篇
  1972年   258篇
  1971年   250篇
  1967年   282篇
  1965年   246篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
861.
862.
863.
864.
865.
Although malignant transformation of fetal cervical teratoma is extremely rare, perinatal morbidity is high and usually related to the size of the tumour, which may compromise fetal swallowing and subsequently lead to upper airway obstruction. We present a case in which mid-trimester serial sonography demonstrated markedly rapid early growth of a lesion of this type between 17 and 19 weeks' gestation indicating the aggressive nature of this tumour, assisting parental decision to terminate the pregnancy. Histopathology confirmed grade 3 immaturity of the lesion.  相似文献   
866.
The coastal seawater of Mediterranean of Alexandria receives large amount of discharged waters containing industrial wastes, sewage, and agricultural and domestic drainage. Fluoride and some parameters were(chemical and physical) determined. The data gave indication that the content and the amount of the discharged water largely affect the chemical composition of the coastal water. Stepwise regression analysis was highly significant and the model was very fruitful, where the observed and calculated values were mostly concordant. This may indicated that there was a relation between fluoride content in coastal seawater and its content in the discharged water.  相似文献   
867.
亚洲和非洲山区自然资源的可持续管理   总被引:1,自引:0,他引:1  
Hurni.  H 《Ambio-人类环境杂志》1999,28(5):382-389
  相似文献   
868.
The diagnosis of Freeman–Sheldon syndrome was made by ultrasonographic evaluation of a 20-week fetus with a positive family history. The ultrasonographic features were abnormalities of the extremities and mouth.  相似文献   
869.
This study explores if assay of cancer antigen 125 (CA 125) in maternal serum might aid the detection of Down's syndrome in the second trimester of pregnancy. CA 125 levels were determined retrospectively in stored maternal serum samples from ten Down's syndrome pregnancies and 78 controls matched for gestational and maternal age. In addition, second-trimester amniotic fluid samples from nine Down's syndrome and 109 unaffected pregnancies were analysed for CA 125. Maternal serum CA 125 values for Down's syndrome pregnancies were lower, with the median being 0.72 multiples of the unaffected population median. The medians for affected and unaffected pregnancies did not differ significantly and there was a considerable overlap in the range of values of cases and controls. The distribution of amniotic fluid CA 125 levels for Down's syndrome pregnancies resembled that for controls. From our present results, we could not find an association between Down's syndrome and second-trimester maternal serum or amniotic fluid CA 125 levels.  相似文献   
870.
Ten-ml samples of amniotic fluid were taken from pregnancies being terminated at 8–14 weeks' gestation. DNA was extracted from the amniotic cells by sequential centrifugation and analysed using the polymerase chain reaction (PCR). Fifteen samples were analysed for evidence of maternal contamination using Mfd5 oligo-nucleotide primers for repeat polymorphisms. Ten amniotic fluid samples were tested for the Delta-F508 deletion characteristic of cystic fibrosis to demonstrate a diagnostic application for the technique. In each case, DNA extracted from fetal tissue from the same pregnancy was included in the controls. In 14 of the 15 cases tested with the Mfd5 primers, both the amniotic fluid DNA and the fetal DNA showed no evidence of contaminating DNA. In one case, neither the amniotic fluid cells nor the fetal cells yielded results. In nine of the ten cases tested with the Delta-F508 primers, the amniotic fluid cell DNA provided accurate information about the genetic status of the fetus; in the tenth, the fetal DNA failed to amplify. The results indicate that adequate DNA can be extracted from amniotic fluid from 8 weeks' gestation onward and these samples are suitable for prenatal diagnosis using PCR.  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