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   33577篇
  免费   363篇
  国内免费   274篇
安全科学   1038篇
废物处理   1603篇
环保管理   4077篇
综合类   6209篇
基础理论   8451篇
环境理论   15篇
污染及防治   8109篇
评价与监测   2338篇
社会与环境   2179篇
灾害及防治   195篇
  2023年   159篇
  2022年   313篇
  2021年   358篇
  2020年   220篇
  2019年   274篇
  2018年   502篇
  2017年   508篇
  2016年   788篇
  2015年   598篇
  2014年   941篇
  2013年   2638篇
  2012年   1128篇
  2011年   1440篇
  2010年   1208篇
  2009年   1255篇
  2008年   1532篇
  2007年   1479篇
  2006年   1312篇
  2005年   1169篇
  2004年   1118篇
  2003年   1089篇
  2002年   1011篇
  2001年   1164篇
  2000年   836篇
  1999年   554篇
  1998年   419篇
  1997年   431篇
  1996年   425篇
  1995年   511篇
  1994年   442篇
  1993年   371篇
  1992年   402篇
  1991年   385篇
  1990年   364篇
  1989年   351篇
  1988年   319篇
  1987年   258篇
  1986年   269篇
  1985年   281篇
  1984年   285篇
  1983年   270篇
  1982年   293篇
  1981年   238篇
  1980年   188篇
  1979年   215篇
  1978年   190篇
  1977年   162篇
  1973年   194篇
  1972年   163篇
  1967年   164篇
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
781.
Routine ultrasound examination at 30 weeks gestation revealed an intrapulmonary cystic mass in an otherwise normal fetus. Following delivery at term, the diagnosis of congenital cystic adenomatoid malformation of the right lung was confirmed, and an elective right middle lobectomy successfully performed at nine days of age.  相似文献   
782.
783.
784.
785.
阐述了高浓度Cl-水样,以铬酸钾做指示剂,加入适量的硝酸银,形成AgCl沉淀,消除了Cl-的干扰,再用离心沉淀机充分沉淀,取上清液,用COD快速测定仪测定CODcr,有很高的准确度,符合测定要求.  相似文献   
786.
There has been growing concern over the build-up of greenhouse gase(GHGs) in the atmosphere, particularly carbon dioxide (CO2), as acause of global warming. The IPCC Third Assessment Report (2001) suggests two ways in which the choice of materials could berelevant. First, some materials, particularly wood, have the advantage thatthey continue to hold carbon (C)in their cells even after being convertedto products. The implications of this feature are well researched. Second,an area that is not well researched relates to the different energyrequirements for producing similar products made with different materials. Using the findings of recent research, this paper compares the energyrequirements and C emissions of manufacturing a product using wood withthat of other materials. The case study of utility poles demonstrates thepositive C and global warming consequences of the lower energyrequirements of wood in the U.S., compared to other materials such assteel or concrete. It demonstrates that GHG emissions associated withutility poles are a small but significant percent of total US annual emissions. Wood utility poles are associated with GHG emission reductions of 163Terragrams (Tg) of CO2 when compared with steel poles. This isabout 2.8 percent of US annual GHG emissions, which are estimated atabout 5.28 Petragrams (Pg) of CO2 annually. Thus, the use ofwooden utility poles rather than steel results in a small but significantreduction in total US emissions.  相似文献   
787.
Fluid from pleural effusion (n=2) and cystic hygroma (n=7) was obtained from eight fetuses, between 13 and 32 weeks of pregnancy at the time when a conventional prenatal diagnosis procedure was carried out. As these fluids contain lymphocytes, they were processed like peripheral blood. A karyotype was obtained in 4 days in both cases of pleural effusion and in four out of seven samples of cystic hygroma. An abnormal karyotype was detected in three of the four samples of cystic hygroma: two trisomies 21 and a monosomy X. Different parameters were evaluated in order to predict the feasibility of obtaining a cytogenetic diagnosis. Our data showed that if the amount of fluid obtained was ⩾4 ml and the initial lymphocyte count (ILC) was >0.2 × 106 cells/ml, a cytogenetic diagnosis was possible from an initial concentration of cultured lymphocytes )ICCL) of >0.06 × 106 cells/ml.  相似文献   
788.
We describe molecular prenatal diagnosis and carrier detection of tyrosinase-negative oculocutaneous albinism (OCA1A) in two families. In one family, we carried out DNA-based prenatal diagnosis of OCA1A. In the other family, mutation analysis and carrier detection obviated the need for prenatal diagnosis. Molecular analysis is safer and probably more accurate than fetoscopy and fetal scalp biopsy, and should become the method of first choice for prenatal diagnosis of OCA1.  相似文献   
789.
In this paper we describe the use of five-colour fluorescence in situ hybridization for prenatal diagnosis of aneuploidy using uncultured amniotic fluid cells. The analysis is based on ratio mixing of dual-labelled probes and digital imaging for the detection and visualization of five different probes specific for the five target chromosomes, 13, 18, 21, X, and Y. A retrospective blind analysis of 30 coded uncultured amniotic fluid samples correctly detected fetal sex and five trisomy 21 cases. Multicolour fluorescence in situ hybridization used in this way allows rapid and simultaneous detection of the most frequent aneuploidies.  相似文献   
790.
This study was undertaken to evaluate the relationship between maternal serum alpha-fetoprotein (MSAFP) levels and oesophageal atresia (OA). OA occurred in 16 fetuses of mothers who had an MSAFP test in the study interval. The multiple of the median (MOM) value for MSAFP averaged 1·54 ± 0·65 (range 0·5–2·9 MOM), which was significantly higher than the value seen in controls. The median MOM was 1·35. Using a cut-off of 2·5 MOM, the sensitivity of MSAFP for detecting OA was 19 per cent. Although OA should be considered in the differential diagnosis of an elevated MSAFP level, MSAFP cannot be considered an appropriate screening test for OA given the low sensitivity.  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