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   91753篇
  免费   1226篇
  国内免费   1122篇
安全科学   3725篇
废物处理   3356篇
环保管理   14015篇
综合类   21151篇
基础理论   26490篇
环境理论   74篇
污染及防治   15280篇
评价与监测   5539篇
社会与环境   3915篇
灾害及防治   556篇
  2022年   808篇
  2021年   824篇
  2020年   657篇
  2019年   868篇
  2018年   1193篇
  2017年   1214篇
  2016年   2221篇
  2015年   1847篇
  2014年   2587篇
  2013年   9263篇
  2012年   2235篇
  2011年   2526篇
  2010年   3324篇
  2009年   3418篇
  2008年   2066篇
  2007年   1965篇
  2006年   2349篇
  2005年   2315篇
  2004年   2626篇
  2003年   2470篇
  2002年   2042篇
  2001年   2415篇
  2000年   2069篇
  1999年   1541篇
  1998年   1385篇
  1997年   1364篇
  1996年   1497篇
  1995年   1582篇
  1994年   1484篇
  1993年   1336篇
  1992年   1335篇
  1991年   1298篇
  1990年   1248篇
  1989年   1219篇
  1988年   1057篇
  1987年   992篇
  1986年   995篇
  1985年   1060篇
  1984年   1159篇
  1983年   1169篇
  1982年   1177篇
  1981年   1096篇
  1980年   944篇
  1979年   928篇
  1978年   823篇
  1977年   720篇
  1976年   639篇
  1974年   605篇
  1973年   634篇
  1972年   632篇
排序方式: 共有10000条查询结果,搜索用时 875 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