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   102459篇
  免费   1248篇
  国内免费   1200篇
安全科学   3963篇
废物处理   3815篇
环保管理   15388篇
综合类   21664篇
基础理论   28150篇
环境理论   77篇
污染及防治   20287篇
评价与监测   6178篇
社会与环境   4693篇
灾害及防治   692篇
  2022年   852篇
  2021年   861篇
  2020年   678篇
  2019年   890篇
  2018年   1365篇
  2017年   1408篇
  2016年   2341篇
  2015年   1882篇
  2014年   2628篇
  2013年   9335篇
  2012年   2698篇
  2011年   3412篇
  2010年   3542篇
  2009年   3687篇
  2008年   3092篇
  2007年   3045篇
  2006年   3141篇
  2005年   2916篇
  2004年   3165篇
  2003年   3074篇
  2002年   2600篇
  2001年   3148篇
  2000年   2427篇
  1999年   1702篇
  1998年   1445篇
  1997年   1437篇
  1996年   1568篇
  1995年   1650篇
  1994年   1545篇
  1993年   1394篇
  1992年   1405篇
  1991年   1368篇
  1990年   1318篇
  1989年   1288篇
  1988年   1128篇
  1987年   1034篇
  1986年   1015篇
  1985年   1100篇
  1984年   1193篇
  1983年   1205篇
  1982年   1196篇
  1981年   1116篇
  1980年   967篇
  1979年   974篇
  1978年   842篇
  1977年   746篇
  1976年   664篇
  1974年   672篇
  1973年   691篇
  1972年   704篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
941.
Laser-induced breakdown spectroscopy (LIBS) is a laser-based optical technique particularly suited for in situ surface analysis. A portable LIBS instrument was tested to detect surface chemical contamination by chemical warfare agents (CWAs). Test of detection of surface contamination was carried out in a toxlab facility with four CWAs, sarin (GB), lewisite (L1), mustard gas (HD), and VX, which were deposited on different substrates, wood, concrete, military green paint, gloves, and ceramic. The CWAs were detected by means of the detection of atomic markers (As, P, F, Cl, and S). The LIBS instrument can give a direct response in terms of detection thanks to an integrated interface for non-expert users or so called end-users. We have evaluated the capability of automatic detection of the selected CWAs. The sensitivity of our portable LIBS instrument was confirmed for the detection of a CWA at surface concentrations above 15 μg/cm2. The simultaneous detection of two markers may lead to a decrease of the number of false positive.  相似文献   
942.
Environmental Science and Pollution Research - The objective of this study was to monitor a newly constructed wetland (CW) in north Wales, UK, to assess whether it contributes to an improvement in...  相似文献   
943.
The population of foxes in the central regions of Yakutia has grown by a factor of four to five during the period from 2000 to 2011–2012, following an increase in the abundance of voles from the genus Microtus. A total of 130 carcasses of foxes taken in 2007–2012 have been examined. Age- and sex-related variation in morphological features has been described. The demographic structure of the population has been studied by estimating animal age from annual layers in the recording structures. Changes in female fertility and involvement in reproduction depending on age and feeding conditions have been analyzed. Changes in the composition of fox diet caused by long-term population depression in the mountain hare and their effect on the dynamics of fox abundance have been revealed. Age- and sex-related characteristics of the condition factor in foxes and sex-related differences in their dietary preferences have been demonstrated.  相似文献   
944.
Communities of benthic macroinvertebrates in drainless Lake Chany, the largest lake in Western Siberia, have been analyzed to estimate the effects of basic abiotic ecological factors (hydrophysical and hydrochemical parameters of water and the type of bottom ground) on their composition, structure, and dynamics. It has been shown that the level of development of these communities depends mainly on the water regime of the lake and also on the type of bottom ground, lake depth, and water mineral content.  相似文献   
945.
The spatial structure of 10 populations of rare orchid species (Dactylorhiza incarnata, D. traunsteineri, Listera ovata) has been studied in rich fens sporadically occurring in Murmansk oblast. Two levels of plant aggregation within populations have been distinguished: (1) clusters of individuals and (2) isolated population subsets consisting of clusters. General spatial demographic features of orchid populations in the fens are small area (77 m2) and low ecological density (0.009 ind./m2). Characteristics of the population subsets (their number, area, composition, and distance to the neighboring subset) are species-specific and reflect the degree of species rarity in plant communities.  相似文献   
946.
The role of ecotones with different (sharp or smooth) spatial boundaries between forest and meadow in ant biodiversity preservation was studied at the right-of-way of a power line in the Voronezh Reserve. The ecotone with a sharp boundary between forest and meadow (transitional zone 2 m wide) had higher species richness of ants compared to the ecotones (also 2 m wide) with smooth boundary between forest and meadow.  相似文献   
947.
A comparative analysis of epigenetic variation has been performed in nine European populations and population groups of the American mink. It has been shown that differentiation of samples in nonmetric characters is due mainly to endogenous processes that have occurred in introduced populations in the course of colonization of new territory by the invasive species. Environmental factors have played a secondary role, with the influence of the geographic (latitudinal) origin of a given sample being considerable and stronger than that of macroclimatic factors.  相似文献   
948.
The probable source of stone moroko, Pseudorasbora parva (Temminck & Schlegel, 1846), populations in lake- and stream-type Dnieper reservoirs was revealed. The dynamics and specific growth rates of these populations over 20 years were analyzed. The dynamic phase portrait method was used to determine the timing of stages in the process of invader naturalization and the periods when its populations were in equilibrium. The potential growth rates of P. parva populations in the Kremenchug and Dneprodzerzhinsk reservoirs were estimated.  相似文献   
949.
950.
This paper considers a two-echelon closed-loop supply chain consisting of a manufacturer and a remanufacturer at the upper echelon and a retailer at the lower echelon. The retailer faces a constant demand from customers, which is satisfied through recovered and new products received from the remanufacturer and the manufacturer, respectively. The manufacturer produces the product with finite rate, whereas the recovery of returned product is instantaneous at the remanufacturer. We develop three models to determine the optimal production-inventory policy of the players for minimizing the joint total cost of the system. In the first model, the retailer receives the product in batches from the manufacturer and the remanufacture simultaneously, whereas in the second and third models, the batches are received alternatively. In the third model, however, the procurement of raw material at the manufacturer is also considered. Numerical illustration is presented to examine the impact of certain key parameters.  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