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   33881篇
  免费   360篇
  国内免费   474篇
安全科学   1043篇
废物处理   1623篇
环保管理   3985篇
综合类   5601篇
基础理论   8829篇
环境理论   19篇
污染及防治   8865篇
评价与监测   2305篇
社会与环境   2243篇
灾害及防治   202篇
  2023年   159篇
  2022年   368篇
  2021年   355篇
  2020年   251篇
  2019年   303篇
  2018年   522篇
  2017年   532篇
  2016年   810篇
  2015年   610篇
  2014年   967篇
  2013年   2693篇
  2012年   1167篇
  2011年   1588篇
  2010年   1298篇
  2009年   1327篇
  2008年   1593篇
  2007年   1624篇
  2006年   1414篇
  2005年   1212篇
  2004年   1101篇
  2003年   1210篇
  2002年   1056篇
  2001年   1395篇
  2000年   959篇
  1999年   582篇
  1998年   371篇
  1997年   399篇
  1996年   385篇
  1995年   463篇
  1994年   485篇
  1993年   395篇
  1992年   404篇
  1991年   395篇
  1990年   438篇
  1989年   375篇
  1988年   333篇
  1987年   312篇
  1986年   270篇
  1985年   284篇
  1984年   296篇
  1983年   290篇
  1982年   281篇
  1981年   241篇
  1980年   197篇
  1979年   215篇
  1978年   198篇
  1975年   155篇
  1974年   143篇
  1972年   151篇
  1971年   142篇
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
581.
582.
The nature of the cosmic redshift is one of the most fundamental questions in modern science. Hubble's discovery of the apparent Expansion of the Universe is derived from observations on a small number of galaxies at very low redshifts. Today, quasar redshifts have a range more than 1000 times greater than those in Hubble's sample, and represent more than 100 times as many objects. A recent comprehensive compilation of published measurements provides the basis for a study indicating that quasar observations are not in good agreement with the original predictions of the Expanding Universe theory, but are well fit by the predictions of an alternative theory having fewer adjustable parameters.  相似文献   
583.
584.
585.
We describe our experience of prenatal diagnosis of non-ketotic hyperglycinaemia in four at-risk pregnancies using the glycine/serine ratio in amniotic fluid obtained between 18 and 20 weeks of gestation. All glycine levels were in the normal range. Serine levels were normal in two patients and borderline in the others. Glycine/serine ratios were normal in two patients, moderately increased in one patient ( + 3 SD), and highly increased in one patient ( + 8 SD). All the children were perfectly normal at birth. Because of this false-positive prediction and the false-negative prediction recently reported, we suggest that this unreliable method should not be used.  相似文献   
586.
The index patient is a female fetus in which prenatal diagnosis of 8p trisomy was established after amniocentesis at 16 weeks of gestation. This fetus was the unbalanced product of a maternal translocation of 5q/8p (karyotype: 46,XX,t(5;8)(q35;pl 1). Internal malformations include an anomalous lobature of the right lung, a little and high atrio-ventricular communication, and an anomaly in the number and shape of the aortic semilunar valves. The possible relationship between the phenotype and the chromosomal abnormality is briefly discussed.  相似文献   
587.
This research was supported by a grant from the National Council for Research and Development, Israel, and the KFK, Karlsruhe, Germany.  相似文献   
588.
A technique is described for measuring pressure within the amniotic cavity and within fetal vessels and/or body compartments. Two saline-filled catheters were connected at one end to needles inserted during indicated invasive procedures and at the other to silicon strain gauge transducers. In 36 pregnancies with normal liquor volume, stable intra-amniotic pressure (IAP, range 1–14 mmHg) increased with gestation (r=0·48, p<0·01). In pregnancies complicated by severe oligohydramnios, IAP was ≤ 1 mm Hg and rose to normal levels with saline amnioinfusion. Raised IAP (range 17–26 mm Hg), found in pregnancies with gross polyhydramnios, fell with drainage of amniotic fluid. Subtraction manometry was used to determine supra-amniotic pressure within the intervillus space, umbilical vein, umbilical artery, abdominal and thoracic cavities, and the urinary tract in normal and/or pathological fetuses. Low intravesical and intrapelvicalyceal pressures (median 6·5, range 2–10 mmHg) were noted in fetuses with obstructive uropathies. Intrauterine subtraction manometry appears to be a useful tool in the understanding of fetal pathophysiology and may be of clinical benefit in the therapeutic drainage and infusion of amniotic fluid and in the assessment of certain fetal disease states.  相似文献   
589.
Dr. Mertin haben wir für seine Hilfe bei der Interpretation der elektronenmikroskopischen Aufnahmen, der Deutschen Forschungsgemeinschaft und dem Fonds der Chemischen Industrie für ihre finanzielle Unterstützung zu danken.  相似文献   
590.
Dedicated to Professor H. J. Berthold, Hannover, on the occasion of his 65th birthday.  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