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   90244篇
  免费   1249篇
  国内免费   1287篇
安全科学   3722篇
废物处理   3328篇
环保管理   13823篇
综合类   21264篇
基础理论   26212篇
环境理论   72篇
污染及防治   14525篇
评价与监测   5428篇
社会与环境   3865篇
灾害及防治   541篇
  2022年   820篇
  2021年   823篇
  2020年   663篇
  2019年   876篇
  2018年   1169篇
  2017年   1200篇
  2016年   2182篇
  2015年   1858篇
  2014年   2587篇
  2013年   9256篇
  2012年   2186篇
  2011年   2419篇
  2010年   3271篇
  2009年   3423篇
  2008年   1990篇
  2007年   1869篇
  2006年   2214篇
  2005年   2269篇
  2004年   2544篇
  2003年   2415篇
  2002年   1919篇
  2001年   2268篇
  2000年   1974篇
  1999年   1503篇
  1998年   1359篇
  1997年   1356篇
  1996年   1484篇
  1995年   1569篇
  1994年   1460篇
  1993年   1318篇
  1992年   1311篇
  1991年   1284篇
  1990年   1235篇
  1989年   1198篇
  1988年   1033篇
  1987年   979篇
  1986年   988篇
  1985年   1059篇
  1984年   1160篇
  1983年   1164篇
  1982年   1174篇
  1981年   1095篇
  1980年   943篇
  1979年   915篇
  1978年   819篇
  1977年   720篇
  1976年   646篇
  1975年   605篇
  1973年   631篇
  1972年   635篇
排序方式: 共有10000条查询结果,搜索用时 703 毫秒
301.
Two cases with a large cystic mass within the placenta are reported. By ultrasonography, it was found that both women had a subchorionic hypoechoic lesion (11.0 × 4.8 × 4.0 cm and 6.6 × 3.7 × 2.2 cm, respectively) at 24 and 35 weeks of gestation, respectively. In both cases, turbulent blood flow generated by a pulsatile jet flow (pulse rate; 40 to 60 beats per minute) into the cystic lesion seen on real-time imaging and lesions being low intensity on T1-weighted and isointensity on T2-weighted magnetic resonance image suggested that they contained fresh maternal blood. In both cases, the sonolucency of the lesions did not change until cesarean deliveries of females, both of whom were small-for-gestational-age infants (1940 g at 37 weeks and 2195 g at 37 weeks, respectively). Biochemical analysis of the fluid in the cystic lesion sampled during the cesarean section in the latter case confirmed that the fluid had originated from the maternal blood. These lesions histologically corresponded to large avillous areas surrounded by normal villi. Thus, a huge placental lake was diagnosed in both cases. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   
302.
303.
The towed undulating vehicle (TUV), named SARAGO, was used for two fine-scale surveys between the Italian and the Sardinian coasts during the Astraea 2 cruise (6-7 and 26-27 September 1995), studying the deep chlorophyll maximum distribution. SARAGO sections identify a sub-surface doming with higher chlorophyll a and primary production concentrations in the upwelling area of a cyclonic gyre region, detected by sea-surface temperature images. In the first section, the cyclone presents a double doming, in density and salinity, with shallower and concentrated patches of chlorophyll a for about 2 miles. Twenty days later, the second section shows that the gyre changes shape and extension, showing a single doming with higher primary production and chlorophyll a concentrations, distributed over a large area of about 40 nautical miles. SARAGO allows analysis of this high-variability phenomenon (cyclonic gyre) and allows concentrated patches (2 nm) to be identified, thus proving the importance of TUVs in the study of mesoscale processes.  相似文献   
304.
305.
306.
Spilt notochord syndrome is an extremely rare form of spinal dysraphism characterized by a complete cleft of the spine and a persistent communication between endoderm and ectoderm. A variant of split notochord syndrome was diagnosed in a 25-week-old fetus showing a prolapsed congenital colostomy and a spinal cystic lesion. The final diagnosis included protruding colon segment, imperforate anus with a rectourethral fistula and lipomyelomeningocele. The ultrasound features of the condition and the post-natal management are discussed. The neonate was successfully treated with a posterior sagittal anorectoplasty, while the lipomyelomeningocele was resected at a later stage. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   
307.
308.
309.
310.
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