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   5410篇
  免费   606篇
  国内免费   1778篇
安全科学   533篇
废物处理   287篇
环保管理   944篇
综合类   3529篇
基础理论   773篇
环境理论   1篇
污染及防治   966篇
评价与监测   341篇
社会与环境   292篇
灾害及防治   128篇
  2024年   12篇
  2023年   87篇
  2022年   177篇
  2021年   203篇
  2020年   211篇
  2019年   214篇
  2018年   211篇
  2017年   255篇
  2016年   320篇
  2015年   285篇
  2014年   375篇
  2013年   538篇
  2012年   502篇
  2011年   538篇
  2010年   402篇
  2009年   498篇
  2008年   296篇
  2007年   375篇
  2006年   369篇
  2005年   325篇
  2004年   241篇
  2003年   224篇
  2002年   181篇
  2001年   162篇
  2000年   143篇
  1999年   113篇
  1998年   89篇
  1997年   82篇
  1996年   69篇
  1995年   84篇
  1994年   49篇
  1993年   33篇
  1992年   31篇
  1991年   21篇
  1990年   15篇
  1989年   7篇
  1988年   8篇
  1987年   7篇
  1986年   6篇
  1985年   3篇
  1984年   5篇
  1983年   7篇
  1982年   6篇
  1981年   2篇
  1980年   6篇
  1978年   1篇
  1977年   3篇
  1976年   1篇
  1975年   1篇
  1972年   1篇
排序方式: 共有7794条查询结果,搜索用时 15 毫秒
941.
前驱物结晶体升华成膜法制备TiO2薄膜及其光催化性研究   总被引:2,自引:0,他引:2  
采用“前驱物结晶体升华成膜法”工艺,使含钛前驱物结晶体草酸氧钛酸以升华的方式,均匀地在玻璃表面形成前驱物薄膜;经过热处理,制备出外观平整透明的玻璃基TiO2薄膜,其薄膜厚度为80-100nm,粒度≤50nm。初步研究了制备条件、薄膜性能和本工艺制备的玻璃基TiO2纳米薄膜对甲基对硫磷的光催化降解性能。  相似文献   
942.
Populations of marine diatom Thalassiosira weissflogii were grown in continuous cultures enriched with f/2 medium. One of the two contrasting cultures (‘eutrophic’) received 5.6 times more nutrients than the other (‘oligotrophic’). Two mathematical models are analyzed to estimate eutrophication differences. The second model based on the Michaelis–Menten uptake and Droop growth shows that cells in the eutrophic culture should have about 56% higher content of silica which is the limiting nutrient. Diatom samples were prepared for the transmission electron microscopy after cells have been kept in chemostats for 37 days. The structure of diatom cells was investigated and a comparison is made between cells grown in oligotrophic and eutrophic conditions. In eutrophic culture, dividing cells were encountered more frequently while cell concentration was approximately equal in both chemostats. The central vacuole of cells in eutrophic culture accumulated dispersed and compact material from amorphous to spherical shape. In some cells the large central vacuole had fibrilar and peppered dense materials in addition to translucent granules, vesicules and multivesicular bodies. In the cytoplasm we found increased number of multivesicular bodies, dense and lucent granules some of which enclose membrane particles and lucent vesicules. Dense material depositions observed in the vacuole are also seen in the cytoplasm associated with organelles, mitochondria and plasmalemma. Cells have well-developed, active and slightly increased number of dictyosomes (5–6). Some dictyosomes with dense secretory material in the cistern are apparently engaged in a granule formation process. Functional significance of dense material in the central vacuole, which has not been observed in cells grown in oligotrophic condition, is discussed.  相似文献   
943.
Female choice on the basis of male traits has been described in an array of taxa but has rarely been demonstrated in reptiles. In the sand lizard (Lacerta agilis), and possibly in other non-territorial reptiles, a male's contribution to a female's fitness is restricted to his genes. In order to choose males of high genetic quality, females have to trade the fitness gain against the costs of active choice. In a Swedish population of sand lizards, long-lived males sired offspring with higher embryonic survival compared to offspring sired by short-lived males. In spite of this female sand lizards did not mate selectively with older and/or larger males. There appeared to be mo reliable cues to male longevity; age-specific male body size was highly variable. Furthermore, estimates of male nuptial coloration did not covary with ectoparasite load and, hence, females cannot use male coloration as a cue to heritable resistance to pathogenic parasite effects. When cues to male genetic quality are poor, or inaccurate, and males make no parental investment, we predict that female choice will be rare. Sand lizard females mating with many partners lay clutches with higher hatching success. Thus, females may obtain good genes for their young by multiple mating, thereby avoiding costs associated with mate choice.  相似文献   
944.
Wildlife management is limited by uncontrolled and often unrecognized environmental variation, by limited capabilities to observe and control animal populations, and by a lack of understanding about the biological processes driving population dynamics. In this paper I describe a comprehensive framework for management that includes multiple models and likelihood values to account for structural uncertainty, along with stochastic factors to account for environmental variation, random sampling, and partial controllability. Adaptive optimization is developed in terms of the optimal control of incompletely understood populations, with the expected value of perfect information measuring the potential for improving control through learning. The framework for optimal adaptive control is generalized by including partial observability and non-adaptive, sample-based updating of model likelihoods. Passive adaptive management is derived as a special case of constrained adaptive optimization, representing a potentially efficient suboptimal alternative that nonetheless accounts for structural uncertainty.  相似文献   
945.
边镜贸易作为我国作为开放的重要组成部分,进展显著。本文在概述我国边境贸易发展所产生的环境问题的基础上,以我国最大的陆边口岸--满州里市为例,运用灰色预测,动态规划等方法探讨边境贸易与环境保护协调发展的途径。  相似文献   
946.
Many methods that study the diversity within hierarchically structured populations have been developed in genetics. Among them, the analysis of molecular variance (AMOVA) (Excoffier et al., 1992) has the advantage of including evolutionary distances between individuals. AMOVA is a special case of a far more general statistical scheme produced by Rao (1982a; 1986) and called the apportionment of quadratic entropy (APQE). It links diversity and dissimilarity and allows the decomposition of diversity according to a given hierarchy. We apply this framework to ecological data showing that APQE may be very useful for studying diversity at various spatial scales. Moreover, the quadratic entropy has a critical advantage over usual diversity indices because it takes into account differences between species. Finally, the differences that can be incorporated in APQE may be either taxonomic or functional (biological traits), which may be of critical interest for ecologists.  相似文献   
947.
ABSTRACT

This article, through the use of political ecology perspectives on coercive conservation, aims to explain how in two separate Colombian Natural Parks and buffer zones, environmental policies designed to (re)take control of the frontier, have produced a similar territorial differentiation in the contention of illicit activities. Los Farallones in the Colombian Pacific and La Macarena/Puerto Rico in the Ariari region have experienced different stages of the armed conflict and are at the center of this analysis. I argue that in the contexts of both conflict escalation (1998–2007) and conflict de-escalation (2008–2016), the State in its attempt to control the frontier has not only had military intervention in areas of conservation but has also reinforced environmental programs that attack illegal mining and coca, producing both a territorially differentiated containment of illicit activities and an uneven progression of the illicit frontier.  相似文献   
948.
介孔纳米TiO2的超声化学法合成及其表征   总被引:3,自引:0,他引:3  
包南  马东  尚贞晓  孙剑  张锋  刘廷礼 《环境化学》2005,24(2):150-152
采用超声化学法制备介孔TiO2,并采用XRD,TEM,FT-IR等方法对样品进行了表征.结果表明,在超声波作用下,液相体系中能够一步合成锐钛矿相TiO2;添加有机模板剂并控制实验条件,则能直接合成具有介孔结构的锐钛矿相TiO2.超声化学法能更好地控制粒子的形貌和尺寸,所制备的TiO2晶型完整,孔径均匀,分散性好.  相似文献   
949.
In young-of-the-year perch (Perca fluviatilis), individuals within groups differed in the degree of boldness, estimated by habitat utilisation and feeding activity in visual contact with a potential predator. We looked at changes in individual behaviour in connection with change of group composition. During the first period, perch were randomly assigned to groups, and time spent in open habitat versus in vegetation and number of prey attacks were registered. The perch were then categorised into personality types (shy, bold, intermediate) according to their behaviour. During the second period, fish were observed when sorted into new groups, each containing only one personality type. Shy individuals showed the largest changes in behaviour, and increased both the time spent in the open and the number of prey attacks when placed into the new groups. Feeding activity in shy fish during the second period was affected by group composition during the first period. After regrouping, bold individuals decreased their time in the open, whereas intermediate individuals did not change behaviour. Time in the open habitat was, to some extent, influenced by the behaviour of the other members of the group, but number of prey attacks was not. The behaviour of fish of the different personality types we have defined in this study seemed to be based on innate traits, but also modified by the influence of other group members and by habituation to the environment.Communicated by J.Krause  相似文献   
950.
在低温和室温条件下,测定了两种规格日本沼虾(Macrobrachium nipponens)的耗氧率、排氨率和Na^ /K^ ATPase比活力.结果表明,低温条件下日本沼虾的耗氧率和排氨率均低于室温,且与体重呈负相关;而Na^ /K^ ATPase比活力高于室温,且与体重呈正相关.表4参21  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