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   5217篇
  免费   40篇
  国内免费   25篇
安全科学   79篇
废物处理   334篇
环保管理   375篇
综合类   769篇
基础理论   1092篇
环境理论   4篇
污染及防治   1803篇
评价与监测   486篇
社会与环境   328篇
灾害及防治   12篇
  2023年   54篇
  2022年   161篇
  2021年   147篇
  2020年   61篇
  2019年   73篇
  2018年   180篇
  2017年   134篇
  2016年   242篇
  2015年   146篇
  2014年   279篇
  2013年   469篇
  2012年   314篇
  2011年   344篇
  2010年   253篇
  2009年   207篇
  2008年   293篇
  2007年   299篇
  2006年   260篇
  2005年   195篇
  2004年   160篇
  2003年   139篇
  2002年   128篇
  2001年   102篇
  2000年   67篇
  1999年   47篇
  1998年   24篇
  1997年   20篇
  1996年   11篇
  1995年   36篇
  1994年   29篇
  1993年   15篇
  1992年   19篇
  1991年   12篇
  1990年   12篇
  1989年   13篇
  1988年   10篇
  1985年   8篇
  1967年   8篇
  1966年   13篇
  1965年   15篇
  1964年   30篇
  1963年   12篇
  1962年   18篇
  1961年   13篇
  1960年   10篇
  1959年   26篇
  1958年   28篇
  1957年   19篇
  1956年   13篇
  1955年   19篇
排序方式: 共有5282条查询结果,搜索用时 31 毫秒
871.
Global greenhouse gas emissions from air travel (GHG-A) are on the rise, and projections point towards a rapid growth in the coming decades. This study aims to examine how local government (cities), addresses GHG-A in their Sustainable Energy Action Plans (SEAP). To fulfil this aim, over 200 SEAPs were analysed focusing on three issues: (1) Treatment of GHG-A in local emissions inventories; (2) Policy initiatives within this domain; and (3) The cities’ perceptions of the conflicts of interests. Results showed that more than half of the cities acknowledge the challenge of GHG-A, around one third include GHG-A in their emissions inventories, and more than one quarter have initiated policy interventions. To categorise these interventions, we have added a mode ‘governing by agenda setting’ to an existing analytical framework, ‘Modes of governing’. With their authority limited to the local setting, this mode of governing is a common channel for cities to push changes at higher levels.  相似文献   
872.
Caesalpinea eriostachys seed oil, as a source of triglycerides with potential application for biodiesel production in Mexico is introduced. Its lipid profile obtained by Gas Chromatography-Mass Spectrometry (GC-MS) revealed saturated and unsaturated glycerol esters as the constituents. Therefore, heterogeneous and homogeneous catalyzed transesterification reactions were assayed employing ZnAl hydrotalcites and KOH, as the catalysts, respectively. The transesterification reactions yielded 59% for Zn/Al(2), 79% for Zn/Al(4), and 90% for KOH, depicting typical behavior, as in biodiesel production data from literature, where Zn-Al hydrotalcites or KOH were assayed. The caloric, density, viscosity values, and fatty acid methyl esters profile from reaction products were concordant to EN 14214, suggesting C. eriostachys as a promising feedstock for biodiesel production.  相似文献   
873.
When determining the effect of food processing on the infectivity of any contaminating virus, it is necessary to distinguish unambiguously between infectious and non-infectious viruses present. However, this can be difficult in the particular case of noroviruses (NoVs) because no reliable cell culture model is available. The aim of this study was to assess the use of molecular methods—RT real-time PCR (RT-qPCR) and enzymatic treatment (ET) coupled to RT-qPCR—to quantify the infectivity of NoV after application of various inactivating food-processing technologies. RT-qPCR and ET-RT-qPCR gave significantly different (P < 0.01) results concerning the reduction in viral genome counts by all inactivation procedures and conditions used, except for HHP treatment at 600 MPa for 5 min. These findings indicate that the ET prior to RT-qPCR has an effect on the estimation of the reduction of virus genome counts, and may eliminate genomes of affected virus particles. However, no correlation was found between the results obtained by ET-RT-qPCR and those obtained by cell culture. Therefore, the effect is presumably only partial, and not adequate to allow accurate estimation of virus inactivation. Consequently, our results indicate that the quantification of virus genomes by PCR, regardless of prior ET, is not adequate for establishing virus inactivation and/or infectivity. In addition, our results also illustrate that the general effect of virus inactivation is not directly correlated to effects on the integrity of virus genome and protein capsid. Presumably, inactivation by food processing is the consequence of effects on proteins involved in adhesion and invasion stages.  相似文献   
874.
Between 1988 and 1993 six surveys on the condition of forests in Navarra (North Spain) were carried out. The results, relating to 408 trees in 17 sampling points, showed that the overall percentage of damaged trees increased from 2.86% in 1988 to 18.6% in 1993, which indicates a general large-scale deterioration of forest condition. Among the most common groups of trees, the most severely affected species were Quercus faginea, Quercus robur and Pinus sylvestris. Furthermore, it was observed that defoliation and discoloration processes did not occur randomly between stand trees, but the trees that were damaged one year (1992) were more predisposed to suffer damage in the next year (1993).  相似文献   
875.
Arsenic and sulfur mineralization is a natural phenomenon occurring in hydrothermal systems where parameters like temperature and organic matter(OM) can influence the mobilization of the toxic metalloid in marine environments. In the present study we analyze the influence of temperature and OM(particularly sulfur-containing additives) on As and S precipitation based on the recent discovery of As-rich nanoparticles in the hydrothermal system near the coast of the Greek island Milos. To this end, ...  相似文献   
876.
Chirostoma charari and C. compressum, and they are presumed extinct. Twelve (63%) of the remaining species had declines in distribution. Sixteen (80%) of the 20 localities sampled had lost species. The greatest declines occurred in Lago de Cuitzeo proper and in the lower portion of the Río Grande de Morelia watershed. Species losses from the lake were attributable to drying and hypereutrophication of the lake because of substantial reductions in the amount and quality of tributary inputs, whereas losses from the Río Grande de Morelia watershed were the result of pollution from agricultural, municipal, and industrial sources, especially in the region around the city of Morelia. Three localities in the upper portion of the Río Grande de Morelia watershed—Cointzio reservoir, La Mintzita spring, and Insurgente Morelos stream—contained most of the remaining fish species diversity in the basin and deserve additional protection. Fish faunal changes indicated major declines in the health of aquatic ecosystems in the Morelia–Cuitzeo basin.  相似文献   
877.
Adult great spotted cuckoos, Clamator glandarius, frequently damage one or more eggs of their magpie host, Pica pica, without removing or eating them. The presence of damaged host eggs could signal parasitism thereby increasing the probability that the parasitic egg is ejected. This hypothesis was tested by experimentally introducing a model cuckoo egg with or without damaged host eggs. Magpie responses to experimental parasitism did not differ significantly between treatments implying that damaged host eggs are not used by magpies to assess parasitism. We followed the fate of magpie eggs naturally damaged by the great spotted cuckoo or experimentally damaged by us. Host response was very similar for naturally or experimentally damaged host eggs, but varied significantly according to the type of egg damage, eggs being removed more frequently when pecked than crushed, while cracked eggs were never removed. However, the egg damage that most readily causes egg removal is albumen leakage. Received: 30 November 1998 / Received in revised form: 7 June 1999 / Accepted: 12 June 1999  相似文献   
878.
Phenotype-limited interference models assume competitive asymmetries among conspecifics and unequal sharing of resources. Their main prediction is a correlation between dominance status and patch quality: dominant individuals should preferentially exploit better-quality habitats. We tested assumptions and predictions of the phenotype-limited interference model in Andean condors (Vultur gryphus), a New World vulture with strong sexual size dimorphism (males are 30–40% heavier than females). We recorded searching birds in habitats differing in quality: mountains and plains. We also observed scavenging behaviour at 20 sheep carcasses, and videotaped 5 of them. Intraspecific hierarchy at carcasses was based on size: males dominated females and, within each sex, older birds dominated younger ones. Adult males and juvenile females occupied extreme positions in the feeding hierarchy. Aggression was directed at those individuals belonging to lower hierarchical levels. In high-quality areas (mountains), more condors arrived at carcasses. Juvenile females were more often observed searching in low-quality areas (plains), far from breeding areas and main roost sites. GLM analyses of individual behaviour showed that the hierarchy did not influence time of arrival, but low-ranking individuals spent more time at carcasses, especially if the number of condors at arrival was high. Additionally, low-ranking condors spent less time feeding at carcasses when individuals of higher hierarchical levels were present. On the other hand, the number of condors present had a positive effect on feeding rates of dominant individuals, probably because of a reduction in individual vigilance. These results support most of the assumptions and predictions of the phenotype-limited distribution model, although a spatial truncated distribution between phenotypes was not observed. Asymmetric feeding pay-off, unequal parental roles and sexual selection constraints could favour sexual divergence in body size in Andean condors. Received: 6 April 1998 / Accepted after revision: 11 July 1998  相似文献   
879.
Queen mating frequency was studied in the European hornet, Vespa crabro, by analyzing four DNA microsatellite loci in 20 workers from each of 14 nests. Queens were found to be predominantly singly mated (9/14), although double (4/14) and triple mating (1/14) also occurred. For most multiply mated queens, paternity was significantly biased with the majority male fathering on average 80% of the female offspring. The population-wide effective mating frequency was therefore low (1.11), and sister-sister relatedness high (0.701 ± 0.023 SE). Low effective mating frequency in Vespa, in combination with data from other vespines, suggests that high paternity frequency is derived in the group. Some problems with the non-detection of fathers, where the queen was not sampled or shared alleles with males, are analyzed. Received: 16 November 1998 / Received in revised form: 29 March 1999 / Accepted: 12 April 1999  相似文献   
880.
Summary. Female Photuris fireflies sequester defensive steroidal pyrones (lucibufagins) from male fireflies of the genus Photinus. Lucibufagin analyses of Photuris females and Photinus ignitus males show that the lucibufagin mixtures of predator and prey differ in their composition. Analyses of whole body extracts showed that P. ignitus males contain a mixture of eight non-glycosylated lucibufagins, composed mostly of compounds with two oxygenated positions in the steroidal A-ring (C-3, C-5). After feeding on P. ignitus males, Photuris females contain six major lucibufagins. Three of these compounds are not present in the prey, including the novel lucibufagin glycoside 5β,11α-dihydroxy-12-oxo-3β-O-β-D-xylopyranosylbufalin, and two other lucibufagins with a trioxygenated A-ring (C-2, C-3, C-5). These results indicate that Photuris females transform the sequestered lucibufagins both by glycosylation and oxidation, which could affect the systemic transportability of these compounds due to an increase in their polarity. Received 18 February 1999; accepted 19 April 1999.  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