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   14393篇
  免费   102篇
  国内免费   155篇
安全科学   353篇
废物处理   592篇
环保管理   1574篇
综合类   3245篇
基础理论   3370篇
环境理论   6篇
污染及防治   3577篇
评价与监测   1104篇
社会与环境   759篇
灾害及防治   70篇
  2022年   128篇
  2021年   107篇
  2019年   102篇
  2018年   194篇
  2017年   202篇
  2016年   305篇
  2015年   226篇
  2014年   399篇
  2013年   1025篇
  2012年   452篇
  2011年   586篇
  2010年   467篇
  2009年   528篇
  2008年   567篇
  2007年   581篇
  2006年   536篇
  2005年   494篇
  2004年   454篇
  2003年   456篇
  2002年   432篇
  2001年   595篇
  2000年   373篇
  1999年   261篇
  1998年   147篇
  1997年   165篇
  1996年   171篇
  1995年   189篇
  1994年   182篇
  1993年   134篇
  1992年   168篇
  1991年   173篇
  1990年   170篇
  1989年   141篇
  1988年   156篇
  1987年   97篇
  1986年   128篇
  1985年   129篇
  1984年   124篇
  1983年   114篇
  1982年   122篇
  1981年   120篇
  1980年   88篇
  1979年   99篇
  1978年   102篇
  1976年   93篇
  1974年   105篇
  1972年   87篇
  1971年   86篇
  1967年   100篇
  1964年   92篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Holoprosencephaly is a congenital anomaly characterized by lack of cleavage of the prosencephalon. Although, relatively rare, it is the most common anomaly that involves both the brain and the face. Prenatal diagnosis of this anomaly using ultrasonography, particularly of the less severe forms, is difficult. Magnetic resonance imaging has recently become an important complement to US in prenatal diagnosis of CNS anomalies. We herein report a patient in whom, at 23 weeks of gestation, US suggested agenesis of the corpus callosum and in whom, at 24 weeks of gestation, MRI correctly diagnosed lobar holoprosencephaly, which was confirmed by a postnatal MRI at 3 weeks of age. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   
992.
Non-platinum-group metal antitumor agents are represented by inorganic and organometallic compounds which contain either main-group metals such as gallium, germanium, and tin, or transition metals such as titanium, vanadium, iron, copper, and gold. Their antiproliferative properties have been detected during the past years, the spectrum of antitumor activity not being identical with that of cytostatic platinum complexes. In the case of germanium complexes, the antitumor activity is obviously not based on direct cytotoxic effects, but on host-mediated immunopotentiating mechanisms. The toxic properties of most non-platinum-group metal antitumor agents differ fundamentally from those of platinum compounds. Thus, non-platinum-group metal antitumor agents may open new perspectives for the clinical therapy of human malignancies.  相似文献   
993.
Variation in the reproduction of Varroa jacobsoni mite was studied in relation to the expansion of the range of its parasitism on the honeybee. Geographic differences in the seasonal dynamics of mite reproduction in the nests of bee families were revealed. Variation in the sex ratio of mites and the factors inhibiting their reproduction at the northern boundary of the honeybee range are considered. The forms of parthenogenetic reproduction in V. jacobsoni are discussed.  相似文献   
994.
995.
The ability of surface flow and subsurface flow simulated wetlands to remove heavy metals from a NaCI-enriched wastewater was examined, employing bulrush (Scirpus validus) and cattail (Typha angustifolia) plants, and two organically amended substrates (mixtures of mushroom compost and leaf litter,with topsoil) with a limestone liner. A simulated wastewater solution containing Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn as chloride salts was added to the wetlands at a rate of 0.3 l h–1. During 12 weeks of surface flow, Fe was retained most efficiently (74%), and Mn the least (24%). Most metal retention occurred in residual forms, primarily in the upper 5 cm of the substrate. A subsequent 10 week subsurface flow treatment exhibited greater removal efficiencies for all metals, probably due to increased contact with the highly buffered lower substrate. During both treatments, bioaccumulation occurred in plants, but accounted for a very small portion of the total metal removal. Plant species did not significantly influence wetland performance with respect to metal retention. Substrate type did not affect removal efficiency for most metals, but did influence the forms of the metals retained in the wetland.To whom correspondence should be addressed.  相似文献   
996.
Males of the brush-legged wolf spider Schizocosa ocreata (Hentz) have conspicuously decorated forelegs used in courtship and agonistic displays. Approximately one in five juvenile males has a missing or regenerating foreleg, and regeneration of a leg lost during development usually results in the absence of a decorative tuft on that leg. The subsequent asymmetry in this male secondary character significantly decreases success in both courtship of females and male-male agonistic interactions. Experimental removal of tufts from one leg of previously successful symmetric males produces similar results. As a test for concomitant behavioral effects, female spiders were shown video images of a courting male with symmetric tufts and the same video image altered to have asymmetric tufts. Female receptivity to the asymmetric video image was lower. In contrast to fluctuating asymmetry resulting from developmental instability, leg tuft asymmetry in S. ocreata most likely arises from a single event during ontogeny – possibly leg loss from an aggressive or predator encounter  – and may serve as a quality indicator in female mate choice. Received: 27 July 1995/ Accepted after revision: 19 November 1995  相似文献   
997.
998.
The research related here focuses on municipal situations where problems of sustainability may be defined and tackled on the basis of bottom-up management procedures with the participation of organized society. The aim is to build management models that may be implemented with reasonable administrative effort and cost. Implementation pursues the target of approaching a sustainable situation in the municipality. Environmental parameters for an ideal municipality with undefined geographical location are presented. For each parameter, a set of indicators is developed that can measure the prospect of sustainability. The indicators are defined in terms of numbers or literal concepts according to the possibility of measurement. Examples of management models are presented, which are able to approach the situation defined as sustainable by the indicators. The basic management tool is the learning curve of targeted communities, which is experimentally developed and applied. The indicators are grouped according to their range of applicability.  相似文献   
999.
1000.
A 17-year monitoring programme of reef flats at Ko Phuket, Thailand afforded an opportunity to evaluate both univariate and multivariate measures of environmental stress in an assessment of change on coral reef ecosystems. The sites at Ko Phuket suffered the effects of dredging in 1986-1987 and then anomalously low sea levels in 1997-1998 as a result of climate-related events in the Indian Ocean. Univariate measures of species diversity and taxonomic distinctness ((*) increased across the reef flat, reflecting the greater effects of physical stresses on the inner reef flats (compared with outer reef flats) at all sites, with more congeneric species present on the inner reef and more confamilial species on the outer reef. Multivariate measures showed a clear breakdown in seriation patterns at all sites during the dredging in 1987 and in 1998, as a result of earlier negative sea-level anomalies. Recovery from environmental disturbances was obvious within 12 months in each case. The domination of the reefs by massive coral species, which are physiologically adapted to intertidal living and which display partial rather than total colony mortality, may be a factor contributing to the apparent resilience of the reef flats together with continued recruitment and survival of juvenile corals during adverse environmental conditions. Elevated sea temperatures and extensive bleaching of corals in 1991, 1995, and 1998 had no effect upon coral community measures, with many corals recovering their zooxanthellae numbers within 3-5 months of the bleaching events.  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