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   12566篇
  免费   848篇
  国内免费   1141篇
  14555篇
  2024年   61篇
  2023年   276篇
  2022年   449篇
  2021年   501篇
  2020年   474篇
  2019年   501篇
  2018年   503篇
  2017年   401篇
  2016年   426篇
  2015年   502篇
  2014年   511篇
  2013年   724篇
  2012年   400篇
  2011年   438篇
  2010年   332篇
  2009年   497篇
  2008年   506篇
  2007年   593篇
  2006年   486篇
  2005年   426篇
  2004年   362篇
  2003年   390篇
  2002年   343篇
  2001年   251篇
  2000年   231篇
  1999年   228篇
  1998年   244篇
  1997年   214篇
  1996年   271篇
  1995年   211篇
  1994年   214篇
  1993年   209篇
  1992年   215篇
  1991年   193篇
  1990年   190篇
  1989年   177篇
  1988年   136篇
  1987年   148篇
  1986年   156篇
  1985年   173篇
  1984年   180篇
  1983年   113篇
  1982年   135篇
  1981年   126篇
  1980年   93篇
  1979年   101篇
  1978年   64篇
  1977年   59篇
  1976年   52篇
  1975年   23篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
In this study we have measured, under experimental conditions which maintained efficient coupling, respiratory intensity, respiratory control, oxidative phosphorylation capacity and protonmotive force. Succinate cytochrome-c reductase and cytochrome-c oxidase activities were also studied. These investigations were carried out using kidney mitochondria from cyclosporine-treated rats (in vivo studies) and from untreated rats in the presence of cyclosporine (in vitro studies). Inhibition of respiratory intensity by cyclosporine did not exceed 21.1% in vitro and 15.9% in vivo. Since there was no in vitro inhibition of succinate cytochrome-c reductase and cytochrome-c oxidase activities, the slowing of electron flow observed can be interpreted as a consequence of an effect produced by cyclosporine between cytochromes b and c1. Cyclosporine had no effect on respiratory control either in vitro or in vivo. Statistically significant inhibition of the oxidative phosphorylation was observed both in vitro (6.6%) and in vivo (12.1%). Moreover, cyclosporine did not induce any change of membrane potential either in vivo or in vitro. Our findings show that cyclosporine is neither a protonophore, nor a potassium ionophore. In cyclosporine-treated rats we noticed a decrease of protein in subcellular fraction, including the mitochondrial fraction. The role of the inhibition respiratory characteristics by cyclosporine in nephrotoxicity in vivo must take account of these two parameters: inhibition of the respiratory characteristics measured in vitro and diminution of mitochondrial protein in cyclosporine-treated rats.  相似文献   
22.
23.
The application of culture-dependent studies to quantify Fe-metabolizing microorganisms from the environment is a necessity, as there are so far no universal functional marker genes for application in culture-independent studies. Media composition can vary between studies, therefore, we determined the effects of three different growth media on the quantification (MPNs) and identity (via cloning and sequencing of dominant DGGE bands) of nitrate-reducing Fe(II)-oxidizers and lactate- or acetate-oxidizing Fe(III)-reducers from a lacustrine sediment: low sulphate freshwater medium (FWM), sterile filtered bicarbonate-buffered lake water (BLW) and a mixture of both (MIX). We consistently found fewer cells in the BLW than in the FWM and the MIX. The DGGE banding patterns of the microbial communities enriched in different media types clustered together according to the e? donor and acceptor couples and not according to the medium used. Thus, although the medium composition significantly influenced the quantification and thereby conclusions on the abundance and potential significance of the targeted group within the ecosystem, biodiversity assessments through enrichment cultures were less influenced by the medium, but instead were affected by the type and concentration of the e? donor/acceptor.  相似文献   
24.
Intrinsic processes are assumed to underlie life history expression and trade‐offs, but extrinsic inputs are theorised to shift trait expression and mask trade‐offs within species. Here, we explore application of this theory across species. We do this based on parentally induced embryo temperature as an extrinsic input, and mass‐specific embryo metabolism as an intrinsic process, underlying embryonic development rate. We found that embryonic metabolism followed intrinsic allometry rules among 49 songbird species from temperate and tropical sites. Extrinsic inputs via parentally induced temperatures explained the majority of variation in development rates and masked a relationship with metabolism; metabolism explained a minor proportion of the variation in development rates among species, and only after accounting for temperature effects. We discuss evidence that temperature further obscures the expected interspecific trade‐off between development rate and offspring quality. These results demonstrate the importance of considering extrinsic inputs to trait expression and trade‐offs across species.  相似文献   
25.
Based on literature, museum collections and three recent expeditions, an annotated species list of the Lake Edward, East Africa, drainage system is presented, excluding the endemic haplochromines. A total of 34 non-Haplochromis species belonging to 10 families and 21 genera are recorded from the system. Three of these are endemic and two others have been introduced in the region. Six species are new records for the Lake Edward system. A species accumulation curve indicates that we probably covered most of the non-Haplochromis species in the area sampled during the recent expeditions, but undetected species might still be present in the Congolese part of the system, which is poorly sampled. A comparison of the species list with those of neighbouring basins confirmed the placement of the Lake Edward system within the east-coast ichthyofaunal province.  相似文献   
26.
27.
The effects of a hot water extract and fractional extracts from rabbiteye blueberry (Vaccinium ashei reade) leaves (BBL) on lipid metabolism were studied in obese Otsuka Long-Evans Tokushima Fatty (OLETF) rats. Feeding the hot water extract and fractional extracts from BBL alleviated hepatic triglyceride accumulation in the rats. Additionally, feeding with the flavonol glycoside (FG) and proanthocyanidin (PA) fractions lowered serum cholesterol levels in the obese rats. The results from measurements of the hepatic enzyme activity indicate that the hypolipidemic effects of the hot water extract and the PA fraction might be attributable to enhanced lipolysis in the liver. The reduced serum levels of C-reactive protein, an inflammatory cytokine, by the chlorogenic acid + rutin fraction and FG fraction might be associated with alleviating the metabolic abnormalities in obese rats. These results indicate that the BBL extracts, and especially FG and PA, exerted hypolipidemic effects on obese OLETF rats and suggest that an infusion of BBL can be useful as a dietary hypolipidemic component.  相似文献   
28.
Among the materials excavated by the 1975 joint USSR–USA team in Siberia are two burials from Shaman's Cape, Olkhon Island, Lake Baikal. One is a middle-aged male of the Serovo culture, 6,000 B.C. , and the other is a young male of the Glaskovo culture of 2,000 B.C. This later burial displays an unusual pathology affecting the nose and post-cranial regions of the pelvic girdle and lower limbs. Osteon analysis confirms the determination of age at death and illustrates the difference between normal and pathological bone. Numerous cultural materials were associated with these burials, including harpoon heads, knives, a compound fishhook and a pestle with the Serovo man, and nephrite ornaments with the Glaskovo man. The skulls, though far apart in time, are pronouncedly Mongoloid and alike in their low cranial vaults. A low, broad and inclined ascending ramus resembles Chukchi, Eskimos and Aleuts. These two specimens document the Mongoloid character of the early inhabitants of Lake Baikal.  相似文献   
29.
30.
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