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   47742篇
  免费   448篇
  国内免费   392篇
安全科学   1252篇
废物处理   1990篇
环保管理   6277篇
综合类   6967篇
基础理论   13519篇
环境理论   25篇
污染及防治   11991篇
评价与监测   3278篇
社会与环境   2984篇
灾害及防治   299篇
  2022年   346篇
  2021年   370篇
  2020年   262篇
  2019年   342篇
  2018年   1031篇
  2017年   976篇
  2016年   1247篇
  2015年   797篇
  2014年   1106篇
  2013年   3496篇
  2012年   1478篇
  2011年   2392篇
  2010年   1892篇
  2009年   1932篇
  2008年   2308篇
  2007年   2588篇
  2006年   1807篇
  2005年   1580篇
  2004年   1520篇
  2003年   1494篇
  2002年   1476篇
  2001年   1846篇
  2000年   1292篇
  1999年   807篇
  1998年   635篇
  1997年   604篇
  1996年   653篇
  1995年   655篇
  1994年   609篇
  1993年   563篇
  1992年   565篇
  1991年   516篇
  1990年   524篇
  1989年   549篇
  1988年   483篇
  1987年   402篇
  1986年   364篇
  1985年   403篇
  1984年   416篇
  1983年   433篇
  1982年   449篇
  1981年   366篇
  1980年   328篇
  1979年   383篇
  1978年   311篇
  1977年   271篇
  1976年   272篇
  1975年   253篇
  1974年   237篇
  1972年   248篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
681.
682.
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   
683.
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   
684.
685.
686.
The polymerase chain reaction (PCR) was used on material from a blighted ovum to confirm indirectly the carrier status of a woman with a family history of Becker muscular dystrophy. Conventional testing including creatine kinase levels, muscle biopsy, and EMG had been inconclusive, and on the basis of one elevated creatine kinase level, the woman had been designated a possible carrier. Ultrasound examination at 10 weeks of pregnancy indicated a blighted ovum, from which DNA was subsequently extracted and subjected to PCR testing for determination of sex and genotypic status with respect to the known familial deletion of the dystrophin gene. The blighted ovum was found to have a Y chromosome and also to be deleted for at least exon 6 of the dystrophin gene, indirectly indicating that the mother most likely carried the family mutation for Becker muscular dystrophy.  相似文献   
687.
688.
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   
689.
IntroductionFertilizationisessentialforagriculturalproduction ,butunreasonablyapplyingfertilizerscouldresultinseriesofproblemssuchascropqualitydecline,fertilizeruseefficiencydecrease,residualfertilizerspollution groundwaterandriversandnitrogencontented …  相似文献   
690.
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   
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