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   88532篇
  免费   1228篇
  国内免费   1080篇
安全科学   3759篇
废物处理   3159篇
环保管理   13725篇
综合类   21099篇
基础理论   26040篇
环境理论   73篇
污染及防治   13631篇
评价与监测   5304篇
社会与环境   3519篇
灾害及防治   531篇
  2022年   782篇
  2021年   789篇
  2020年   652篇
  2019年   868篇
  2018年   1114篇
  2017年   1147篇
  2016年   2130篇
  2015年   1841篇
  2014年   2594篇
  2013年   9260篇
  2012年   2109篇
  2011年   2302篇
  2010年   3243篇
  2009年   3364篇
  2008年   1845篇
  2007年   1646篇
  2006年   2113篇
  2005年   2153篇
  2004年   2434篇
  2003年   2274篇
  2002年   1851篇
  2001年   2101篇
  2000年   1902篇
  1999年   1449篇
  1998年   1363篇
  1997年   1339篇
  1996年   1465篇
  1995年   1563篇
  1994年   1462篇
  1993年   1320篇
  1992年   1301篇
  1991年   1276篇
  1990年   1232篇
  1989年   1189篇
  1988年   1016篇
  1987年   971篇
  1986年   989篇
  1985年   1060篇
  1984年   1148篇
  1983年   1162篇
  1982年   1168篇
  1981年   1095篇
  1980年   936篇
  1979年   914篇
  1978年   817篇
  1977年   710篇
  1976年   635篇
  1975年   608篇
  1973年   628篇
  1972年   626篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
301.
302.
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   
303.
304.
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   
305.
306.
Juberg–Hayward syndrome is a rare autosomal recessive syndrome characterised by the association of growth retardation, microcephaly, cleft lip and palate, and thumb and radial ray abnormalities. To date, no prenatal cases have been reported. Here, we report on the first prenatal case of Juberg–Hayward syndrome. The diagnosis was established following fetopathological study. Besides the cardinal features of the syndrome, this prenatal case was remarkable for the severity of the short arm malformation and by the finding of big toe agenesis and cerebral abnormalities including hydrocephalus, agenesis of corpus callosum, and cerebellar hypoplasia. We conclude that the diagnosis of Juberg–Hayward syndrome can be discussed prenatally following ultrasound diagnosis of the association of intrauterine growth restriction, microcephaly, thumb/radial anomalies, and cleft lip/palate. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   
307.
308.
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   
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