全文获取类型
收费全文 | 5415篇 |
免费 | 432篇 |
国内免费 | 1篇 |
专业分类
5848篇 |
出版年
2023年 | 24篇 |
2022年 | 59篇 |
2021年 | 101篇 |
2020年 | 65篇 |
2019年 | 72篇 |
2018年 | 100篇 |
2017年 | 96篇 |
2016年 | 172篇 |
2015年 | 223篇 |
2014年 | 245篇 |
2013年 | 346篇 |
2012年 | 417篇 |
2011年 | 400篇 |
2010年 | 246篇 |
2009年 | 218篇 |
2008年 | 335篇 |
2007年 | 334篇 |
2006年 | 293篇 |
2005年 | 290篇 |
2004年 | 245篇 |
2003年 | 229篇 |
2002年 | 226篇 |
2001年 | 70篇 |
2000年 | 46篇 |
1999年 | 60篇 |
1998年 | 66篇 |
1997年 | 34篇 |
1996年 | 52篇 |
1995年 | 51篇 |
1994年 | 39篇 |
1993年 | 48篇 |
1992年 | 41篇 |
1991年 | 35篇 |
1990年 | 27篇 |
1989年 | 25篇 |
1988年 | 25篇 |
1987年 | 35篇 |
1986年 | 32篇 |
1985年 | 30篇 |
1984年 | 28篇 |
1983年 | 23篇 |
1982年 | 23篇 |
1981年 | 23篇 |
1980年 | 26篇 |
1979年 | 18篇 |
1978年 | 17篇 |
1977年 | 19篇 |
1976年 | 25篇 |
1975年 | 23篇 |
1972年 | 17篇 |
排序方式: 共有5848条查询结果,搜索用时 15 毫秒
891.
Genetic and Functional Analysis of Polymorphisms in the Human Dopamine Receptor and Transporter Genes in Small Cell Lung Cancer 下载免费PDF全文
892.
Cytochromes P450 (P450) are hemoproteins encoded by a superfamily of genes nearly ubiquitously distributed in different organisms from all biological kingdoms. The reactions carried out by P450s are extremely diverse and contribute to the biotransformation of drugs, the bioconversion of xenobiotics, the bioactivation of chemical carcinogens, the biosynthesis of physiologically important compounds such as steroids, fatty acids, eicosanoids, fat-soluble vitamins and bile acids, the conversion of alkanes, terpenes and aromatic compounds as well as the degradation of herbicides and insecticides. Cytochromes P450 belong to the group of external monooxygenases and thus receive the necessary electrons for oxygen cleavage and substrate hydroxylation from different redox partners. The classical as well as the recently discovered P450 redox systems are compiled in this paper and classified according to their composition. 相似文献
893.
Bíró T Tóth BI Marincsák R Dobrosi N Géczy T Paus R 《Biochimica et biophysica acta》2007,1772(8):1004-1021
Itch (pruritus) is a sensory phenomenon characterized by a (usually) negative affective component and the initiation of a special behavioral act, i.e. scratching. Older studies predominantly have interpreted itch as a type of pain. Recent neurophysiological findings, however, have provided compelling evidence that itch (although it indeed has intimate connections to pain) rather needs to be understood as a separate sensory modality. Therefore, a novel pruriceptive system has been proposed, within which itch-inducing peripheral mediators (pruritogens), itch-selective receptors (pruriceptors), sensory afferents and spinal cord neurons, and defined, itch-processing central nervous system regions display complex, layered responses to itch. In this review, we begin with a current overview on the neurophysiology of pruritus, and distinguish it from that of pain. We then focus on the functional characteristics of the large family of transient receptor potential (TRP) channels in skin-coupled sensory mechanisms, including itch and pain. In particular, we argue that - due to their expression patterns, activation mechanisms, regulatory roles, and pharmacological sensitivities - certain thermosensitive TRP channels are key players in pruritus pathogenesis. We close by proposing a novel, TRP-centered concept of pruritus pathogenesis and sketch important future experimental directions towards the therapeutic targeting of TRP channels in the clinical management of itch. 相似文献
894.
De Simone F Guzzi R Sportelli L Marsh D Bartucci R 《Biochimica et biophysica acta》2007,1768(6):1541-1549
Human serum albumin (HSA) is an abundant plasma protein that transports fatty acids and also binds a wide variety of hydrophobic pharmacores. Echo-detected (ED) EPR spectra and D(2)O-electron spin echo envelope modulation (ESEEM) Fourier-transform spectra of spin-labelled free fatty acids and phospholipids were used jointly to investigate the binding of stearic acid to HSA and the adsorption of the protein on dipalmitoyl phosphatidylcholine (DPPC) membranes. In membranes, torsional librations are detected in the ED-spectra, the intensity of which depends on chain position at low temperature. Water penetration into the membrane is seen in the D(2)O-ESEEM spectra, the intensity of which decreases greatly at the middle of the membrane. Both the chain librational motion and the water penetration are only little affected by adsorption of serum albumin at the DPPC membrane surface. In contrast, both the librational motion and the accessibility of the chains to water are very different in the hydrophobic fatty acid binding sites of HSA from those in membranes. Indeed, the librational motion of bound fatty acids is suppressed at low temperature, and is similar for the different chain positions, at all temperatures. Correspondingly, all segments of the bound chains are accessible to water, to rather similar extents. 相似文献
895.
Regional versus local processes in determining zooplankton community composition of Little Rock Lake, Wisconsin, USA 总被引:3,自引:0,他引:3
The species present within a community result from a combination of local
and regional processes. We experimentally tested the importance of these
two processes for lake zooplankton communities by examining the ability of
additional species to persist when introduced into mesocosms in Little Rock
Lake, Wisconsin, from other nearby lakes in the Northern Highland Lake
District. We established a control treatment with only Little Rock Lake
zooplankton and two treatments that supplemented the Little Rock
communities with zooplankton from nearby lakes. Species richness declined
during the 3 weeks of the experiment so that, at the end of the third week,
the treatments with added zooplankton species had the same number of
species as the controls; increasing the initial number of species in the
community did not increase its final species richness. A plot of the mean
species richness in the local habitat against the mean species richness of
the regional pool fell below a 1:1 slope. This suggested that local
processes were more important in structuring Little Rock Lake zooplankton
communities.
相似文献
896.
897.
898.
899.
We used aerial counts to monitor the trend in numbers of harbor seals, Phoca vitulina richardsi, in Prince William Sound, Alaska, following the 1989 Exxon Valdez oil spill. Repetitive counts were made at 25 haul-out sites during the annual molt period each year from 1990 through 1997. A generalized linear model indicated that time of day, date, and time relative to low tide significantly affected seal counts. When Poisson regression was used to adjust counts to a standardized set of survey conditions, results showed a highly significant decline of 4.6% per year. Unadjusted counts indicated a slight, but not statistically significant, decline in the number of seals. The number of harbor seals on the trend-count route in eastern and central PWS has been declining since at least 1984, with an overall population reduction of 63% through 1997. Programs to monitor long-term changes in animal population sizes should account for factors that can cause short-term variations in indices of abundance. The inclusion of such factors as covariates in models can improve the accuracy of monitoring programs. 相似文献
900.