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   7297篇
  免费   55篇
  国内免费   44篇
安全科学   185篇
废物处理   366篇
环保管理   727篇
综合类   1146篇
基础理论   1793篇
环境理论   5篇
污染及防治   1816篇
评价与监测   530篇
社会与环境   794篇
灾害及防治   34篇
  2023年   61篇
  2022年   85篇
  2021年   82篇
  2020年   53篇
  2019年   66篇
  2018年   115篇
  2017年   137篇
  2016年   156篇
  2015年   116篇
  2014年   196篇
  2013年   542篇
  2012年   245篇
  2011年   352篇
  2010年   292篇
  2009年   311篇
  2008年   350篇
  2007年   369篇
  2006年   332篇
  2005年   282篇
  2004年   259篇
  2003年   283篇
  2002年   252篇
  2001年   289篇
  2000年   188篇
  1999年   120篇
  1998年   61篇
  1997年   81篇
  1996年   72篇
  1995年   83篇
  1994年   89篇
  1993年   72篇
  1992年   75篇
  1991年   77篇
  1990年   78篇
  1989年   64篇
  1988年   71篇
  1987年   66篇
  1986年   70篇
  1985年   46篇
  1984年   56篇
  1983年   57篇
  1982年   58篇
  1981年   35篇
  1980年   36篇
  1979年   42篇
  1978年   36篇
  1977年   33篇
  1976年   34篇
  1974年   37篇
  1973年   32篇
排序方式: 共有7396条查询结果,搜索用时 640 毫秒
81.
从环境监测数据管理的意义和重要性出发,介绍了环境监测网络数据管理系统,并给出了空气质量监测数据在系统中流程和计算处理的方法,实现了环境监测数据网络管理的功能,保证了空气质量数据传输的准确性和实时性。  相似文献   
82.
Five cases of mosaicism for an isochromosome of 20q have been detected from a total of 50 000 cases analysed for prenatal diagnosis by amniocentesis. Karyotypes were designated mos 46,X_/46,X_,i(20q). In all cases, the abnormal cell line was detected in more than one primary culture, thus fulfilling the criterion for true (level III) mosaicism. Indications for prenatal diagnosis were parental anxiety (two cases), low maternal serum alpha-fetoprotein (AFP) (two cases), and high maternal serum AFP (one case). Level II ultrasounds on all five fetuses were normal, and the abnormal cell line was never detected in fetal blood and/or cord blood. All five pregnancies were continued and had normal outcomes, with birth weights ranging from 2.4 to 3.8 kg. The development of all five children has been normal, with the oldest child in the study now 4 years of age. We suggest that the abnormal cell line in each case was of extrafetal origin, and that this may be one of the more common examples of this phenomenon, occurring in approximately 1/10000 prenatal diagnoses. Mosaicism i(20q) may have been missed in the past because of the higher resolution necessary to detect this subtle change.  相似文献   
83.
84.
With growing awareness of the problems associated with prenatal cytogenetic diagnoses after CVS, attempts have been made to provide early amniocentesis as an alternative to CVS. Since 1990, at our clinic the gestational age limit for routine diagnostic amniocentesis has been successively lowered, first to 14 and then to 13 weeks of gestation. Thus, 811 prenatal diagnoses were performed after early amniocentesis at 13 weeks (n = 217) and at 14 weeks of gestation (n = 594). No problems were encountered. Culture failure was never observed in the early samples. Using the criteria ‘number of colonies’ and ‘culture duration until harvest’, early samples taken at 14 weeks did not differ significantly from the controls after standard amniocentesis performed at 15 and 16 weeks, respectively, whereas a minority of samples taken at 13 weeks experienced some delay in culturing. However, in each group at least 85 per cent of samples led to a diagnosis fulfilling our standard criteria of a safe diagnosis (at least 20 metaphases of at least five colonies from at least one primary culture after trypsinization) within 15 days. Some differences between the different groups can be recognized: culture duration of less than 11 days tends to be increasing after standard amniocentesis, whereas long culture duration (more than 20 days) is more often associated with early amniocentesis. However, this trend is only minimal and did not result in an increased risk of missing a diagnosis.  相似文献   
85.
86.
87.
Upper limb reduction was diagnosed by ultrasound scan at 17 weeks after chorion villus sampling at 9 weeks' gestation. Pregnancy was terminated and necropsy confirmed limb reduction in an otherwise normal fetus. The relationship of limb reduction to amniotic band syndrome is discussed.  相似文献   
88.
IntroductionSiberiaandtheFarEastaretheoldestandtherichestgold miningareasofRussia .Intensivegold miningherestartedinthebeginningofthe 19thcentury(Vyazelshchikov ,1963) .Forthemostpartgold bearingoresandsandswereprocessedwiththeuseofamalgamationmethodforgolde…  相似文献   
89.
90.
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