全文获取类型
收费全文 | 4029篇 |
免费 | 100篇 |
国内免费 | 53篇 |
专业分类
安全科学 | 250篇 |
废物处理 | 153篇 |
环保管理 | 831篇 |
综合类 | 468篇 |
基础理论 | 1006篇 |
环境理论 | 3篇 |
污染及防治 | 952篇 |
评价与监测 | 312篇 |
社会与环境 | 166篇 |
灾害及防治 | 41篇 |
出版年
2023年 | 28篇 |
2022年 | 40篇 |
2021年 | 46篇 |
2020年 | 57篇 |
2019年 | 70篇 |
2018年 | 85篇 |
2017年 | 123篇 |
2016年 | 140篇 |
2015年 | 109篇 |
2014年 | 134篇 |
2013年 | 351篇 |
2012年 | 185篇 |
2011年 | 236篇 |
2010年 | 182篇 |
2009年 | 203篇 |
2008年 | 210篇 |
2007年 | 221篇 |
2006年 | 205篇 |
2005年 | 178篇 |
2004年 | 156篇 |
2003年 | 138篇 |
2002年 | 136篇 |
2001年 | 97篇 |
2000年 | 69篇 |
1999年 | 63篇 |
1998年 | 48篇 |
1997年 | 64篇 |
1996年 | 50篇 |
1995年 | 54篇 |
1994年 | 56篇 |
1993年 | 46篇 |
1992年 | 39篇 |
1991年 | 31篇 |
1990年 | 29篇 |
1989年 | 27篇 |
1988年 | 23篇 |
1987年 | 17篇 |
1986年 | 17篇 |
1985年 | 23篇 |
1984年 | 18篇 |
1983年 | 28篇 |
1982年 | 22篇 |
1981年 | 32篇 |
1980年 | 19篇 |
1979年 | 18篇 |
1978年 | 13篇 |
1977年 | 5篇 |
1976年 | 6篇 |
1975年 | 5篇 |
1969年 | 4篇 |
排序方式: 共有4182条查询结果,搜索用时 295 毫秒
941.
Farming Endangered Turtles to Extinction in China 总被引:1,自引:0,他引:1
942.
Pat M. Fidopiastis Daniel J. Bezdek Michael H. Horn Judith S. Kandel 《Marine Biology》2006,148(3):631-642
The zebraperch, Hermosilla azurea Jenkins and Evermann, a warm-temperate marine fish species with a strictly macroalgal diet, has a relatively long digestive
tract with an enlarged hindgut and an associated blind caecum (HC). In zebraperch sampled off Santa Catalina Island, California
(33°19′42′′N; 118°18′37′′W) in years 1995 through 2001, direct cell counts, gut epithelium assessment of bacterial attachment,
and short-chain fatty acid (SCFA) analyses verified that the zebraperch HC possesses a dense and morphologically diverse,
fermentative microbiota. Bacterial cell counts and morphological diversity were significantly higher in HC contents compared
to anterior gut regions, suggesting that microbial populations were growing along the digestive tract. Similarly, electron
micrographs of the HC epithelium revealed attached microbes, further supporting the possibility that these organisms constitute
resident microbiota. Five different SCFAs were detected in all three regions of the digestive tract, but levels were up to
three times greater in HC contents. Acetate was consistently the prevailing SCFA in all gut regions. Sequence analysis of
bacterial 16S rDNA was used to identify predominant bacterial groups in HC contents. Of the seven main bacterial types identified,
Enterovibrio spp. were the dominant bacteria in HC contents followed by species of Bacteroides,Faecalibacterium, and Desulfovibrio. Taken together, our findings show that the zebraperch HC harbors a consortium of microbes that appears to assist in the
breakdown of algal polysaccharides in the herbivorous diet of the fish. 相似文献
943.
Alternative male mating tactics in a cichlid, Pelvicachromis pulcher: a comparison of reproductive effort and success 总被引:2,自引:0,他引:2
Pelvicachromis pulcher is a small African cichlid which breeds in holes. Males may either reproduce monogamously (pair males), polygynously (harem
males), or be tolerated as helpers in a harem territory (satellite males). These helpers share in defence of the territory
against conspecifics, heterospecific competitors and predators. There are two male colour morphs that are fixed for life and
are apparently genetically determined. These differ in their potential mating strategy. Red morph males may become harem owners,
while yellow morph males may become satellite males, and males of both morphs may alternatively pair up monogamously. We compared
the reproductive effort and success of these three male reproductive strategies. Effort was measured as attack rates, time
expenditure and the risk of being injured or killed when attacking competitors or predators of three sympatric fish species.
Reproductive success was measured by observing how many eggs were fertilized by each male when this was possible, and by using
genetic markers. The number of fry surviving to independence of parental care was used as a criterion of success. The reproductive
success of harem males was 3.3 times higher than that of pair males and 7 times higher than that of the average satellite
male. Dominant satellite males, however, were as successful as monogamous pair males, using the measure of fertilized eggs.
To our knowledge, this has not been found previously in any fish species. Both harem and pair males had lower parental defence
costs per sired offspring, however, than males using the alternative satellite tactic. Defence effort was significantly related
to the risk of injury.
Received: 17 January 1996 / Accepted after revision: 9 June 1997 相似文献
944.
Threats to Imperiled Freshwater Fauna 总被引:10,自引:0,他引:10
Brian D. Richter David P. Braun Michael A. Mendelson & Lawrence L. Master 《Conservation biology》1997,11(5):1081-1093
Threats to imperiled freshwater fauna in the U.S. were assessed through an experts survey addressing anthropogenic stressors and their sources. Specifically, causes of historic declines and current limits to recovery were identified for 135 imperiled freshwater species of fishes, crayfishes, dragonflies and damselflies, mussels, and amphibians. The survey was designed to identify threats with sufficient specificity to inform resource managers and regulators faced with translating information about predominant biological threats into specific, responsive actions. The findings point to altered sediment loads and nutrient inputs from agricultural nonpoint pollution; interference from exotic species; and altered hydrologic regimes associated with impoundment operations as the three leading threats nationwide, accompanied by many lesser but still significant threats. Variations in threats among regions and among taxa were also evident. Eastern species are most commonly affected by altered sediment loads from agricultural activities, whereas exotic species, habitat removal/damage, and altered hydrologic regimes predominate in the West. Altered sediment loading from agricultural activities and exotic species are dominant problems for both eastern mussels and fishes. However, eastern fishes also appear to be suffering from municipal nonpoint pollution (nutrients and sediments), whereas eastern mussels appear to be more severely affected by altered nutrient impacts from hydroelectric impoundments and agricultural runoff. Our findings suggest that control of nonpoint source pollution associated with agriculture activities should be a very high priority for agricultural producers and governmental support programs. Additonally, the large number of hydropower dams in the U.S. subject to federal re-licensing in coming years suggests a significant opportunity to restore natural hydrologic regimes in the affected rivers. 相似文献
945.
Michael G. Dalton 《Journal of Environmental Economics and Management》1997,33(3):221-239
This article analyzes the welfare effects of climatic variability from global warming in a stochastic economic growth model and shows that these may be significant. An empirical analysis indicates that the effects of climate change with variability are greater than the corresponding effects without it. Effects with variability are also shown to be more sensitive to variations in the rate of climate change. 相似文献
946.
Bighorn sheep ( Ovis canadensis ) are restricted in distribution and numbers relative to presettlement conditions. Some populations have alledgedly suffered losses of fitness resulting from small, insular populations and a breeding system that reduces effective population size. Large horns in rams, which confer breeding superiority, are absent from some populations, and this absence may result in part from loss of genetic variability. We investigated the relationship among allozyme variability, population history, and horn growth in bighorn sheep from the Rocky Mountains. Heterozygosity was higher for bighorn sheep than has been reported for Dall sheep ( O. dalli ). Heterozygosity and allelic variability were marginally related to effective population size for the proceeding 15 years. Horn growth was significantly higher in more heterozygous than in less heterozygous rams for years 6, 7, and 8 of life. By the end of year 8, more heterozygous rams had 13% higher horn volumes than less heterozygous rams. Most hunting of bighorn sheep involves selective removal of large-horned rams, which we hypothesize may reduce genetic variability of these populations and contribute to losses in fitness. 相似文献
947.
Summary Sibling recognition by spiny mice (Acomys cahirinus) was investigated by housing groups consisting of two pairs of littermates together and recording frequency of dyadic pairing. A total of 136 animals (68 pairs of siblings) were tested in three experiments. Sibling pairs were observed more often than pairings between nonsiblings; however, such preferences were no longer evident if the nonsiblings were exposed to one another prior to testing. Animals made anosmic through zinc sulfate treatment did not differ on their frequencies of sibling vs. nonsibling pairing and showed a higher incidence of group huddling (by all four animals) than did intact controls. Weanling A. cahirinus appear to be able to recognize (i.e., are attracted to) their littermate siblings through olfactory cues, which seems to be a modifiable attraction to odors to which the littermates were exposed rather than an irreversible imprinting-like process.The research project reported herein was supported by grant # 00973 from NICHD 相似文献
948.
949.
950.
Guang-yu Wang Michael D. Greenfield Todd E. Shelly 《Behavioral ecology and sociobiology》1990,27(3):191-198
Summary Males of the desert grasshopper Ligurotettix coquilletti typically eclose 3–5 weeks prior to females. Early-eclosed males experience more female encounters than the later-eclosed individuals. Evidence suggests that the number of encounters may be proportional to male lifetime mating success. Early-eclosed males enjoyed greater adult lifespans, occupied and defended higher quality territories (Larrea shrubs), and tended to be dominant on these shrubs if several males were present. The elevated number of female encounters were not conferred on early-eclosed males by their extended survivorship, but rather by the high quality of their territories, which retained numerous females, and their dominant behavior. We evaluate several female-benefit and male-benefit hypotheses for the evolution of protandry and propose that in L. coquilletti, the phenomenon arose due to male-male competition for female-encounter sites, a mechanism not considered in earlier models. Finally, we discuss several reasons for the high variance in the date of male eclosion. 相似文献