全文获取类型
收费全文 | 531417篇 |
免费 | 61488篇 |
国内免费 | 424篇 |
出版年
2016年 | 5538篇 |
2015年 | 7977篇 |
2014年 | 9177篇 |
2013年 | 13536篇 |
2012年 | 14890篇 |
2011年 | 15060篇 |
2010年 | 10152篇 |
2009年 | 9440篇 |
2008年 | 13652篇 |
2007年 | 13922篇 |
2006年 | 13265篇 |
2005年 | 13029篇 |
2004年 | 12736篇 |
2003年 | 12614篇 |
2002年 | 12160篇 |
2001年 | 21149篇 |
2000年 | 21292篇 |
1999年 | 17277篇 |
1998年 | 6555篇 |
1997年 | 6877篇 |
1996年 | 6791篇 |
1995年 | 6176篇 |
1994年 | 6166篇 |
1993年 | 6144篇 |
1992年 | 14876篇 |
1991年 | 14654篇 |
1990年 | 14160篇 |
1989年 | 14106篇 |
1988年 | 13058篇 |
1987年 | 12808篇 |
1986年 | 11798篇 |
1985年 | 12088篇 |
1984年 | 10098篇 |
1983年 | 8839篇 |
1982年 | 7009篇 |
1981年 | 6637篇 |
1980年 | 6124篇 |
1979年 | 10147篇 |
1978年 | 7923篇 |
1977年 | 7659篇 |
1976年 | 7179篇 |
1975年 | 7863篇 |
1974年 | 8609篇 |
1973年 | 8456篇 |
1972年 | 7776篇 |
1971年 | 7153篇 |
1970年 | 6346篇 |
1969年 | 6274篇 |
1968年 | 5708篇 |
1967年 | 4885篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
1. Metabolism is the fundamental process that powers life. Understanding what drives metabolism is therefore critical to our understanding of the ecology and behaviour of organisms in nature. 2. Metabolic rate generally scales with body size according to a power law. However, considerable unexplained variation in metabolic rate remains after accounting for body mass with scaling functions. 3. We measured resting metabolic rates (oxygen consumption) of 227 field‐caught wolf spiders. Then, we tested for effects of body mass, species, and body condition on metabolic rate. 4. Metabolic rate scales with body mass to the 0.85 power in these wolf spiders, and there are metabolic rate differences between species. After accounting for these factors, residual variation in metabolic rate is related to spider body condition (abdomen:cephalothorax ratio). Spiders with better body condition consume more oxygen. 5. These results indicate that recent foraging history is an important determinant of metabolic rate, suggesting that although body mass and taxonomic identity are important, other factors can provide helpful insights into metabolic rate variation in ecological communities. 相似文献
994.
1. Feeding behaviour of generalist and specialist predators is determined by a variety of trophic adaptations. Specialised prey‐capture adaptations allow specialists to catch relatively large prey on a regular basis. As a result, specialists might be adapted to exploit each item of prey more thoroughly than do generalists. 2. It was expected that obligatory specialist cursorial spiders would feed less frequently than generalists but for a longer time and, thus, that their foraging pause would be longer. First, the feeding frequencies of three generalist spider species (Cybaeodamus taim, Harpactea hombergi, Hersiliola sternbergsi) were compared with those three phylogenetically related specialist species: myrmecophagous Zodarion rubidum, and araneophagous Nops aff. variabilis and Palpimanus orientalis. 3. Generalists captured more prey, exploited each item of prey for a significantly shorter time, and had a shorter foraging pause than was the case for specialists. Generalists also gained significantly less relative amount of prey mass than did specialists. 4. Second, the study compared the prey DNA degradation rate in the gut of generalists and specialists by means of PCR. The degradation rate was not significantly different between specialists and generalists: the detectability half‐life was estimated to exist for 14.3 days after feeding. 5. This study shows that the feeding strategies of cursorial generalist and obligatory specialist spiders are different. Obligatory specialists have evolved a feeding strategy that is based on thorough exploitation of a few large prey, whereas generalists have evolved a strategy that is based on short exploitation of multiple small items of prey. 相似文献
995.
N W Cornell J J Stegeman M J Kerich B R Woodin 《Comparative biochemistry and physiology. B, Comparative biochemistry》1986,85(3):669-674
Hepatic metabolites and enzymes in the marine fish, scup or porgy (Stenotomus chrysops), were determined in freeze-clamped tissue taken either within a day of removing fish from their natural habitat or after scup were held in captivity for 6-8 months. The same determinations were made for liver from fed or 48 hr-starved rats (Mus norvegicus albinus). Compared with rat liver, both groups of fish had, per gram of liver, higher contents of AMP, inorganic phosphate, glucose, glucose-6-phosphate, malate, glutamate and NH4+. ATP was lower in fish liver, and ADP, lactate and pyruvate contents were similar in rats and fish. Fish held in captivity had significantly lower pyruvate, alpha-ketoglutarate, and cytosolic free NAD+/NADH and higher cytosolic free NADPH/NADP+. These decreases were similar to those seen when starved rats were compared with fed ones. In scup liver, glucose-6-phosphate dehydrogenase was 3-8 times, malic enzyme about 2 times, and alanine aminotransferase 2-4 times higher than those activities in rat liver. Those results and a higher cytosolic free NADPH/NADP+ are consistent with the liver being the major site of lipogenesis in fish. 相似文献
996.
Acrodipsas mortoni sp.n. from inland New South Wales and southern Queensland is described, figured, contrasted with the related A. arcana (Miller and Edwards) and assigned to the illidgei species-group. 相似文献
997.
The meningococcus and mechanisms of pathogenicity 总被引:32,自引:1,他引:31
I W DeVoe 《Microbiological reviews》1982,46(2):162-190
998.
Isolation and characterization of an insulin-degrading enzyme from Drosophila melanogaster 总被引:3,自引:0,他引:3
An insulin-degrading enzyme (IDE) from the cytoplasm of Drosophila Kc cells has been purified and characterized. The purified enzyme is a monomer with an s value of 7.2 S, an apparent Km for porcine insulin of 3 microM, and a specific activity of 3.3 nmol of porcine insulin degraded/(min.mg). N-Terminal sequence analysis of the gel-purified enzyme gave a single, serine-rich sequence. The Drosophila IDE shares a number of properties in common with its mammalian counterpart. The enzyme could be specifically affinity-labeled with [125I]insulin, has a molecular weight of 110K, and has a pI of 5.3. Although Drosophila Kc cells grow at room temperature, the optimal enzyme activity assay conditions parallel those of the mammalian IDE: 37 degrees C and a pH range of 7-8. The Drosophila IDE activity, like the mammalian enzymes, is inhibited by bacitracin and sulfhydryl-specific reagents. Similarly, the Drosophila IDE activity is insensitive to glutathione as well as protease inhibitors such as aprotinin and leupeptin. Insulin-like growth factor II, equine insulin, and porcine insulin compete for degradation of [125I]insulin at comparable concentrations (approximately 10(-6) M), whereas insulin-like growth factor I and the individual A and B chains of insulin are less effective. The high degree of evolutionary conservation between the Drosophila and mammalian IDE suggests an important role for this enzyme in the metabolism of insulin and also provides further evidence for the existence of a complete insulin-like system in invertebrate organisms such as Drosophila. 相似文献
999.
Virulent strains of Vibrio vulnificus isolated from estuaries of the United States West Coast 总被引:12,自引:0,他引:12
C A Kaysner C Abeyta M M Wekell A DePaola R F Stott J M Leitch 《Applied and environmental microbiology》1987,53(6):1349-1351
Vibrio vulnificus was isolated from United States West Coast estuaries at a low frequency (5.9%) from 529 samples of water, shellfish, and sediment. Four strains tested with iron-treated mice had 50% lethal dose values ranging from 7.6 to 360 CFU, compared with a 50% lethal dose of 4.9 CFU for a clinical isolate that caused the death of a septicemic patient. The presence of this pathogen may be a hazard to users of marine beaches and consumers of raw shellfish on the West Coast, especially to persons most susceptible to V. vulnificus septicemia. Species-specific antiflagellar serum and a gene probe for cytotoxin-hemolysin production were useful for screening these environmental isolates. 相似文献
1000.