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   20996篇
  免费   353篇
  国内免费   474篇
安全科学   722篇
废物处理   937篇
环保管理   2889篇
综合类   3563篇
基础理论   5241篇
环境理论   10篇
污染及防治   5723篇
评价与监测   1323篇
社会与环境   1260篇
灾害及防治   155篇
  2023年   122篇
  2022年   296篇
  2021年   262篇
  2020年   259篇
  2019年   233篇
  2018年   405篇
  2017年   380篇
  2016年   582篇
  2015年   439篇
  2014年   636篇
  2013年   1722篇
  2012年   821篇
  2011年   1172篇
  2010年   824篇
  2009年   932篇
  2008年   1022篇
  2007年   1071篇
  2006年   867篇
  2005年   748篇
  2004年   716篇
  2003年   647篇
  2002年   625篇
  2001年   722篇
  2000年   572篇
  1999年   338篇
  1998年   228篇
  1997年   244篇
  1996年   232篇
  1995年   293篇
  1994年   232篇
  1993年   222篇
  1992年   191篇
  1991年   193篇
  1990年   193篇
  1989年   190篇
  1988年   165篇
  1987年   136篇
  1986年   159篇
  1985年   147篇
  1984年   191篇
  1983年   153篇
  1982年   173篇
  1981年   159篇
  1980年   132篇
  1979年   152篇
  1978年   97篇
  1977年   98篇
  1975年   91篇
  1974年   95篇
  1972年   97篇
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
221.
222.
Egyptian Blue, a multicomponent synthetic blue pigment has been recorded in ancient Egypt since the Fourth Dynasty of the Old Kingdom (2600–2480 B.C.). The pigment consisting of cuprorivaite (CaCuSi4O10) with variable amounts of wollastonite (CaSiO3), Cu-rich glass and cuprite (Cu3O) or tenorite (CuO) was prepared by melting the copper-rich ingredient with lime and desert sand. Low melting temperatures (below 742 °C) were achieved by addition of flux-like plant ashes. The high quality of the pigments collected from monuments of the Fifth Dynasty (2480–2320 B.C.) may indicate that the first manufacture was in early dynastic or perhaps predynastic eras. During the reign of Thutmosis III (18th Dynasty, 1490–1436 B.C.) probably bronze filings were first applied as starting material, thus indicating a technological innovation. This new method was employed till the Roman times.  相似文献   
223.
The perception of pitch   总被引:1,自引:0,他引:1  
  相似文献   
224.
225.
226.
227.
We present a technique to aspirate amniotic fluid from both sacs in biamniotic twin pregnancies using a single abdominal insertion with a spinal needle. It was successful in 48 out of 55 cases of biamniotic twin pregnancies referred to our perinatal unit between 1985 and 1994. The single insertion technique was used when the inter-amniotic membrane was clearly evident and two separate free amniotic fluid pools could be reached by the operator with a single puncture. An adequate amount of amniotic fluid was sampled from both sacs to make a cytogenetic diagnosis in all cases. There were four fetuses with trisomy 21 in three twin pregnancies. In two cases, only one twin was affected whilst the co-twin was normal, so that a selective feticide was performed. No miscarriages due to genetic amniocentesis were reported. After 1990, all genetic amniocenteses in biamniotic twin pregnancies (except for one case due to late booking) were performed between 14 and 15 weeks of gestation and with all cases except one, it was possible to sample both twins by a single puncture. We suggest that early amniocentesis (14–15 weeks) by a single abdominal puncture could be a reliable and safe alternative to first-trimester chorionic villus sampling in twin pregnancies.  相似文献   
228.
The observation that thyroid disease is frequent in mothers of children with Down syndrome (DS) has suggested that maternal thyroid antibodies could be a factor predisposing to trisomy 21 in their offspring. In this study, the incidences of thyroglobulin (Tg) and thyroid peroxidase (TPO) antibodies were analysed with a sensitive solid-phase immunosorbent radioassay in sera from 29 mothers giving birth to children with trisomy 21 and 87 control mothers. The serum samples were collected at delivery. There was no statistical difference regarding the proportion of thyroid antibodies (against Tg and/or TPO) in the two groups. Thyroid antibodies were detected in 6/29 (20.7 per cent) of the DS mothers and in 23/87 (26.4 per cent) of the control mothers. Among the women with thyroid antibodies, 4/6 (66.7 per cent) of the DS mothers and 12/23 (52 per cent) of the control mothers had antibodies against both Tg and TPO. There was no increase in the relative risk of having a child with DS if the titre of either Tg or TPO antibodies or both were positive, i.e. ≥ 1/5. The results indicate that the presence of thyroid antibodies in the serum of a pregnant woman has no prognostic value for the birth of an infant with DS.  相似文献   
229.
Fifty-three patients who elected to reduce their pregnancies to a twin gestation in our centre are known to have subsequently undergone genetic amniocentesis. Five of these patients lost their entire pregnancy following the genetic amniocentesis procedure. This is equivalent to a 9·4 per cent pregnancy loss rate for reduced twin gestations in comparison with an expected loss rate of 2 per cent for non-reduced twin gestations.  相似文献   
230.
IntroductionTheprocessofmunicipalsolidwaste(MSW)isoneofthemostseriousissuesintermsofenvironmentalprotection.ProcessingofMSWwithoutfurtherdisastrouscontaminationcanbeachievedonlyinmodernizedmeasures,suchasincineratingandenergygeneratingconcurrently(Shen…  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