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   8416篇
  免费   104篇
  国内免费   247篇
安全科学   172篇
废物处理   398篇
环保管理   990篇
综合类   1412篇
基础理论   2064篇
污染及防治   2079篇
评价与监测   637篇
社会与环境   965篇
灾害及防治   50篇
  2023年   66篇
  2022年   137篇
  2021年   108篇
  2020年   72篇
  2019年   102篇
  2018年   149篇
  2017年   162篇
  2016年   230篇
  2015年   169篇
  2014年   263篇
  2013年   725篇
  2012年   292篇
  2011年   396篇
  2010年   325篇
  2009年   356篇
  2008年   411篇
  2007年   428篇
  2006年   331篇
  2005年   297篇
  2004年   303篇
  2003年   293篇
  2002年   277篇
  2001年   343篇
  2000年   222篇
  1999年   119篇
  1998年   91篇
  1997年   90篇
  1996年   108篇
  1995年   129篇
  1994年   98篇
  1993年   88篇
  1992年   93篇
  1991年   97篇
  1990年   85篇
  1989年   74篇
  1988年   70篇
  1987年   78篇
  1986年   55篇
  1985年   63篇
  1984年   67篇
  1983年   60篇
  1982年   60篇
  1981年   66篇
  1980年   51篇
  1979年   53篇
  1978年   38篇
  1977年   40篇
  1976年   37篇
  1973年   43篇
  1972年   51篇
排序方式: 共有8767条查询结果,搜索用时 312 毫秒
961.
962.
963.
A wide spectrum of genetic causes may lead to nonimmune hydrops fetalis (NIHF), and a thorough phenotypic and genetic evaluation are essential to determine the underlying etiology, optimally manage these pregnancies, and inform discussions about anticipated prognosis. In this review, we outline the known genetic etiologies of NIHF by fetal organ system affected, and provide a systematic approach to the evaluation of NIHF. Some of the underlying genetic disorders are associated with characteristic phenotypic features that may be seen on prenatal ultrasound, such as hepatomegaly with lysosomal storage disorders, hyperechoic kidneys with congenital nephrosis, or pulmonary valve stenosis with RASopathies. However, this is not always the case, and the approach to evaluation must include prenatal ultrasound findings as well as genetic testing and many other factors. Genetic testing that has been utilized for NIHF ranges from standard chromosomal microarray or karyotype to gene panels and broad approaches such as whole exome sequencing. Family and obstetric history, as well as pathology examination, can yield additional clues that are helpful in establishing a diagnosis. A systematic approach to evaluation can guide a more targeted approach to genetic evaluation, diagnosis, and management of NIHF.  相似文献   
964.
965.
966.
967.
Abstract: The use of voluntary approaches to achieve conservation goals is becoming increasingly popular. Nevertheless, few researchers have quantitatively evaluated their efficacy. In 1998 industry, government agencies, and nongovernmental organizations established a voluntary conservation program for whale watching in the northeast region of the United States, with the intent to avoid collisions with and harassment of endangered whales by commercial and recreational whale‐watching vessels. One important aspect of the program was the establishment of 3 speed zones within specific distances of whales. We wanted to determine the level of compliance with this aspect of the program to gauge its efficacy and gain insights into the effectiveness of voluntary measures as a conservation tool. Inconspicuous observers accompanied 46 commercial whale‐watching trips from 12 companies in 2003 (n= 35) and 2004 (n= 11). During each trip, vessel position and speed were collected at 5‐second intervals with a GPS receiver. Binoculars with internal laser rangefinders and digital compasses were used to record range and bearing to sighted whales. We mapped whale locations with ArcGIS. We created speed‐zone buffers around sighted whales and overlaid them with vessel‐track and speed data to evaluate compliance. Speeds in excess of those recommended by the program were considered noncompliant. We judged the magnitude of noncompliance by comparing a vessel's maximum speed within a zone to its maximum recorded trip speed. The level of noncompliance was high (mean 0.78; company range 0.74–0.88), some companies were more compliant than others (p= 0.02), noncompliance was significantly higher in zones farther from whales (p < 0.001), and operators approached the maximum speed capabilities of their vessel in all zones. The voluntary conservation program did not achieve the goal of substantially limiting vessel speed near whales. Our results support the need for conservation programs to have quantifiable metrics and frequent evaluation to ensure efficacy.  相似文献   
968.
969.
Residues of cypermethrin and deltamethrin in wheat herbage and grain and deltamethrin in sweetclover herbage were determined. Cypermethrin was applied at 28 g/ha to wheat and the residues on the herbage declined exponentially from 3.74 ppm immediately after spraying to 0.20 ppm 27 days after spraying. No cypermethrin residues were detected in the grain. Deltamethrin was applied at 6 g/ha to wheat and the residues on the herbage declined exponentially from 0.70 ppm immediately after spraying to 0.05 ppm 27 days after spraying. No deltamethrin residues were detected in the grain. Deltamethrin was applied to sweetclover at 3, 4, 5, 10, and 16 g/ha. Residues on the herbage declined exponentially from 0.10, 0.16, 0.22, 0.40 and 0.70 ppm immediately after spraying to 0.02, 0.03, 0.04, 0.15 and 0.18 ppm 5 days after spraying, respectively.  相似文献   
970.
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