全文获取类型
收费全文 | 14176篇 |
免费 | 202篇 |
国内免费 | 164篇 |
专业分类
安全科学 | 485篇 |
废物处理 | 678篇 |
环保管理 | 2429篇 |
综合类 | 1563篇 |
基础理论 | 3659篇 |
环境理论 | 7篇 |
污染及防治 | 3792篇 |
评价与监测 | 1013篇 |
社会与环境 | 822篇 |
灾害及防治 | 94篇 |
出版年
2023年 | 59篇 |
2022年 | 118篇 |
2021年 | 121篇 |
2020年 | 92篇 |
2019年 | 125篇 |
2018年 | 212篇 |
2017年 | 220篇 |
2016年 | 333篇 |
2015年 | 267篇 |
2014年 | 329篇 |
2013年 | 1247篇 |
2012年 | 460篇 |
2011年 | 670篇 |
2010年 | 534篇 |
2009年 | 570篇 |
2008年 | 705篇 |
2007年 | 709篇 |
2006年 | 625篇 |
2005年 | 510篇 |
2004年 | 494篇 |
2003年 | 544篇 |
2002年 | 478篇 |
2001年 | 574篇 |
2000年 | 430篇 |
1999年 | 284篇 |
1998年 | 205篇 |
1997年 | 193篇 |
1996年 | 207篇 |
1995年 | 231篇 |
1994年 | 185篇 |
1993年 | 160篇 |
1992年 | 191篇 |
1991年 | 160篇 |
1990年 | 180篇 |
1989年 | 170篇 |
1988年 | 123篇 |
1987年 | 122篇 |
1986年 | 107篇 |
1985年 | 127篇 |
1984年 | 130篇 |
1983年 | 130篇 |
1982年 | 117篇 |
1981年 | 125篇 |
1980年 | 98篇 |
1979年 | 88篇 |
1978年 | 67篇 |
1977年 | 69篇 |
1976年 | 60篇 |
1975年 | 66篇 |
1973年 | 61篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
Darryl T. Gwynne Winston J. Bailey Amanda Annells 《Behavioral ecology and sociobiology》1998,42(3):157-162
In katydids such as Kawanaphilanartee, a female bias in the operational sex ratio (OSR) results in female competition for mates and male choice of mates. Previous
work showed that the excess of sexually active females occurs when food availability is low, in part because less food increases
the propensity of females to mate as they forage for the large edible spermatophores produced by males. In this study with
K.nartee, a pollen-feeding species, we estimate natural variation in numbers of sexually active males and females by assessing male
calling activity and the propensity of females to respond to experimental calling males. We found an excess of sexually active
males at a site with many flowers and an excess of sexually active females at a site with few flowers about 900 m away. Between-site
differences in gut masses of calling males were consistent with the hypothesis that pollen availability controls OSR. Finally,
at a third site where flowers were at first scarce, we found that the initial excess in sexually active females changed to
an excess of sexually active males after a clump of grass-trees flowered. The mean gut mass of all sampled males from this
site increased after flowering. The large variation in OSR that we document for K. nartee highlights the importance of identifying the appropriate spatial and temporal scales over which OSRs are measured in studies
of factors controlling sexual selection.
Received: 13 May 1997 / Accepted after revision: 27 October 1997 相似文献
952.
953.
954.
955.
An Ecology-Based Method for Defining Priorities for Large Mammal Conservation: The Tiger as Case Study 总被引:2,自引:0,他引:2
956.
957.
M. Zimmer J. P. Danko S. C. Pennings A. R. Danford A. Ziegler R. F. Uglow T. H. Carefoot 《Marine Biology》2001,138(5):955-963
Three isopod species (Crustacea: Isopoda), commonly found in the intertidal and supratidal zones of the North American Pacific
coast, were studied with respect to symbiotic microbiota in their midgut glands (hepatopancreas). Ligia pallasii (Oniscidea: Ligiidae) contained high numbers of microbial symbionts in its hepatopancreatic caeca. Numbers of endosymbionts
were strongly reduced by ingestion of antibiotics. By contrast, the hepatopancreas of Idotea wosnesenskii (Valvifera: Idoteidae) and Gnorimosphaeroma oregonense (Sphaeromatidea: Sphaeromatidae) did not contain any microbiota. Results of feeding experiments suggest that microbial endosymbionts
contribute to digestive processes in L. pallasii, the most terrestrial of the three isopods that we studied. The acquisition of digestion-enhancing endosymbionts may have
been an important evolutionary step allowing isopods to colonize terrestrial habitats where relatively indigestible leaf litter
is the primary food source. By contrast, the ability to digest phenolic compounds was most developed in one of the more marine
species, suggesting that this trait may have evolved independently in isopod species that consume a phenolic-rich diet, whether
in marine habitats or on land.
Received: 28 August 2000 / Accepted: 8 December 2000 相似文献
958.
Potential dietary effects on the fatty acid composition of the common jellyfish Aurelia aurita 总被引:2,自引:0,他引:2
Fatty acid composition of the natural and aquarium-reared common jellyfish Aurelia aurita was investigated. Fatty acid composition of the aquarium-reared A. aurita clearly reflected that of the diet, brine shrimp (Artemia). In the same way, fatty acid composition of the natural A. aurita was assumed to reflect those of natural diets. Samples of natural A. aurita were collected from April 1995 to September 1995 in the Seto Inland Sea, Japan, and their fatty acids were analyzed by gas
chromatography and mass spectrometry. Variation of fatty acid compositions was seasonal rather than dependent on body size.
Two major seasonal groups were divided by the cluster analysis of the A. aurita fatty acid composition: the April–June and the August–September clusters. The April–June cluster was characterized by high
contents of the (n − 3)-fatty acids of diatom origin, accumulated via the grazing food chain. By contrast, the August–September cluster was
characterized by an increase in (n − 6)-fatty acids of macroalgal origin, probably transferred via the detritus food chain. These results suggest that the diet
of natural A. aurita may shift between the diatom-based food chain and the detritus-based food chain.
Received: 12 April 2000 / Accepted: 1 December 2000 相似文献
959.
Effects of salinity on endogenous rhythm of the Manila clam, Ruditapes philippinarum (Bivalvia: Veneridae) 总被引:1,自引:0,他引:1
The Manila clam Ruditapes philippinarum, an intertidal bivalve, was exposed to different salinity regimes (from 31.0–31.7‰ down to 20‰, 15‰, 10‰, 5‰), and the endogenous
rhythm in its oxygen consumption was studied using an automatic intermittent-flow respirometer. When exposed to salinities
reduced from 31.5‰ to 20‰ and 15‰ under otherwise constant conditions, the clams recovered a clear endogenous circatidal rhythm
in their oxygen-consumption rate after having dampened periods of 12 h and 48 h, respectively. At salinities less than 10‰,
however, the oxygen-consumption rate was depressed greatly at the beginning of the experiment for about 36 h and then increased
to a level higher than normal, but the rhythm of oxygen consumption was not recovered. The results of this study indicate
that the Manila clam, a euryhaline organism, cannot maintain a normal metabolic activity at a salinity lower than 15‰. All
clams were dead after exposure at a salinity of 5‰ for 7 days.
Received: 28 February 2000 / Accepted: 26 August 2000 相似文献
960.