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   49989篇
  免费   543篇
  国内免费   424篇
安全科学   1436篇
废物处理   1873篇
环保管理   6736篇
综合类   8497篇
基础理论   13746篇
环境理论   34篇
污染及防治   12616篇
评价与监测   3091篇
社会与环境   2566篇
灾害及防治   361篇
  2022年   354篇
  2021年   347篇
  2020年   293篇
  2019年   372篇
  2018年   651篇
  2017年   712篇
  2016年   1009篇
  2015年   833篇
  2014年   1214篇
  2013年   3902篇
  2012年   1477篇
  2011年   2100篇
  2010年   1755篇
  2009年   1776篇
  2008年   2089篇
  2007年   2219篇
  2006年   1960篇
  2005年   1632篇
  2004年   1599篇
  2003年   1572篇
  2002年   1481篇
  2001年   1941篇
  2000年   1392篇
  1999年   864篇
  1998年   652篇
  1997年   667篇
  1996年   701篇
  1995年   757篇
  1994年   698篇
  1993年   647篇
  1992年   663篇
  1991年   619篇
  1990年   624篇
  1989年   626篇
  1988年   538篇
  1987年   485篇
  1986年   469篇
  1985年   500篇
  1984年   507篇
  1983年   521篇
  1982年   505篇
  1981年   455篇
  1980年   430篇
  1979年   448篇
  1978年   379篇
  1977年   341篇
  1976年   294篇
  1974年   298篇
  1973年   306篇
  1972年   333篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
671.
672.
673.
674.
The product service systems’ (PSS) sustainability potential is described in the framework of the new types of stakeholder relationships and/or partnerships, producing new convergence of economic interests, and a potential concomitant systemic resources optimization.In this perspective, it is argued that the design competencies should move towards those of the ‘strategic design’, thus introducing the concept of ‘strategic design for sustainability’: the design of an innovation strategy, shifting the business focus from designing (and selling) physical products only, to designing (and selling) a system of products and services which are jointly capable of fulfilling specific client demands, while re-orienting current unsustainable trends in production and consumption practices.Some examples of PSS are presented and discussed using the PSS categories ‘services providing added value to the product life cycle’, ‘services providing final results to customers’, and ‘services providing enabling platforms for customers’. The cases derive from an analysis of the ‘environmental friendly innovation’ yearly endowed prize submissions. The Politecnico di Milano University together with the Bocconi University and Legambiente (an environmental NGO) promotes the initiative in Italy.  相似文献   
675.
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   
676.
We report a 16-month-old boy with delayed psychomotor development, dysmorphic features, and failure to thrive. He had a mosaic karyotype detected prenatally: mos 46,XY/47,XY,+r(20)/47,XY,+20. After birth, the abnormal cell lines were confirmed in a number of tissues. The small ring chromosome was identified using fluorescence in situ hybridization as derived from chromosome 20. We compared our patient with previously reported cases of mosaic trisomy 20 detected prenatally and associated with an abnormal phenotype. In an attempt to characterize an r(20) syndrome, we also compared our case with two similar reports in the literature.  相似文献   
677.
678.
Many authors have suggested that individuals affected by a terminal 1q deletion display a phenotypically definable and recognizable syndrome. In all of the 27 cases reported to date, the breakpoints were at band q42 or distally to it. To our knowledge, we report the first case of a terminal 1q41 deletion. Diagnosis was made prenatally by amniocentesis, following ultrasonographic diagnosis of omphalocele, cerebral ventriculomegaly, and increased nuchal fold thickness in a 19-week female fetus. Multiple facial and extremity features were consistent with the proposed distal 1q deletion syndrome; omphalocele, however, has not been reported previously. The absence of liver herniation into the omphalocele sac in this case supports the previously reported association of this finding with chromosomal anomalies.  相似文献   
679.
680.
The main objective of this project was to evaluate the possibility of reducing the quantity of fibre wasted at one of many hydrocyclone (centrifugal) cleaning processes in a paper mill. It was found that the application of elutriation water to both the tertiary and quaternary cleaners was essential to minimise the fibre discharged to the sewer, and the pressure of this elutriation water had a dramatic effect of reducing the fibre wastage. Accordingly, it has been shown that 150–160 kPa as the optimum pressure range to apply elutriation water to minimise the product grade fibre wasted whilst sending undesired shive fibre to the sewer. Also, monitoring of the press uhle box wastewater revealed that the paper mill has the potential to make substantial cost savings by reducing the waste stream. Further investigation is necessary to determine the types of fibre that are being wasted, and the viability of a screen to recycle the wasted fibre to the process. However, these fibres may be unsuitable to reuse in the process and alternative uses must be found.  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