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   18948篇
  免费   415篇
  国内免费   903篇
安全科学   741篇
废物处理   754篇
环保管理   2500篇
综合类   4115篇
基础理论   4844篇
环境理论   4篇
污染及防治   4931篇
评价与监测   1141篇
社会与环境   982篇
灾害及防治   254篇
  2023年   113篇
  2022年   266篇
  2021年   291篇
  2020年   284篇
  2019年   253篇
  2018年   338篇
  2017年   353篇
  2016年   483篇
  2015年   421篇
  2014年   538篇
  2013年   1549篇
  2012年   693篇
  2011年   896篇
  2010年   741篇
  2009年   674篇
  2008年   866篇
  2007年   841篇
  2006年   780篇
  2005年   621篇
  2004年   664篇
  2003年   591篇
  2002年   539篇
  2001年   740篇
  2000年   517篇
  1999年   324篇
  1998年   283篇
  1997年   242篇
  1996年   239篇
  1995年   273篇
  1994年   289篇
  1993年   233篇
  1992年   258篇
  1991年   229篇
  1990年   256篇
  1989年   242篇
  1988年   195篇
  1987年   175篇
  1986年   159篇
  1985年   168篇
  1984年   192篇
  1983年   181篇
  1982年   185篇
  1981年   179篇
  1980年   137篇
  1979年   153篇
  1978年   131篇
  1977年   117篇
  1975年   119篇
  1974年   115篇
  1972年   133篇
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
321.
Dedicated to Prof. H. Autrum on the occasion of his 85th birthday.  相似文献   
322.
323.
This paper, based on the autonomy concept, continues to investigate hierarchical forms and spatial structure of ecosystems. The former can lead to limits for the selection of the component parts of an ecosystem and a distinction between its endogenous and exogenous variables; and the latter can be lead to a hypothesis of the space of an ecosystem: the space of an ecosystem = its habitat area + supporting area + impact area, and two characteristics of ecosystems, space-overlapping and the area of ecosystem space, have been further studied referring to human activities.  相似文献   
324.
325.
The sinusoidal fetal heart rate pattern has been described in association with severe fetal anaemia, with fetal hypoxaemia, and with the administration of parenteral narcotics. Here, we report a case of decreased fetal movement in which a sinusoidal tracing was recorded. The sonographic diagnosis of a massive fetal intracranial haemorrhage was made. A non-interventive approach was taken and the fetus died soon after in utero. We review 28 previous cases in which the prenatal sonographic diagnosis of fetal intracranial haemorrhage was made, including the underlying maternal and fetal factors and neonatal outcomes. We propose that the sinusoidal tracing in this case was due to the intracranial bleed and suggest that fetal intracranial haemorrhage be considered in the sonographic evaluation of the fetus with a sinusoidal pattern.  相似文献   
326.
We report two cases of apparently balanced complex de novo chromosomal rearrangements (BCCR) detected prenatally at 17 weeks and 10 weeks of gestation, respectively. Chromosomes were studied using GTG-banding and fluorescent in situ hybridization (FISH). In one case four chromosomes and in the other case three chromosomes were involved in the rearrangements. One of the pregnancies was terminated and no external or internal abnormalities were detected at autopsy. The other pregnancy continued to term. Level III ultrasound examination showed no abnormalities. The child is now 3 years old and has neither congenital anomalies nor evidence of delayed psychomotor development.  相似文献   
327.
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   
328.
329.
330.
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   
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