全文获取类型
收费全文 | 11588篇 |
免费 | 1063篇 |
国内免费 | 5篇 |
专业分类
12656篇 |
出版年
2023年 | 94篇 |
2022年 | 216篇 |
2021年 | 398篇 |
2020年 | 222篇 |
2019年 | 281篇 |
2018年 | 317篇 |
2017年 | 256篇 |
2016年 | 436篇 |
2015年 | 773篇 |
2014年 | 792篇 |
2013年 | 813篇 |
2012年 | 1120篇 |
2011年 | 1028篇 |
2010年 | 579篇 |
2009年 | 438篇 |
2008年 | 630篇 |
2007年 | 638篇 |
2006年 | 507篇 |
2005年 | 453篇 |
2004年 | 447篇 |
2003年 | 353篇 |
2002年 | 339篇 |
2001年 | 75篇 |
2000年 | 56篇 |
1999年 | 71篇 |
1998年 | 77篇 |
1997年 | 38篇 |
1996年 | 45篇 |
1995年 | 36篇 |
1994年 | 37篇 |
1993年 | 41篇 |
1992年 | 52篇 |
1991年 | 47篇 |
1990年 | 44篇 |
1989年 | 40篇 |
1988年 | 38篇 |
1987年 | 37篇 |
1986年 | 31篇 |
1985年 | 43篇 |
1984年 | 41篇 |
1983年 | 40篇 |
1982年 | 42篇 |
1981年 | 43篇 |
1980年 | 44篇 |
1979年 | 37篇 |
1978年 | 43篇 |
1977年 | 30篇 |
1976年 | 40篇 |
1975年 | 28篇 |
1974年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
11.
Nina Boiko Volodymyr Kucher Benjamin A. Eaton James D. Stockand 《The Journal of biological chemistry》2013,288(13):9418-9427
The voltage-gated K+ (Kv) channel blocker 4-aminopyridine (4-AP) is used to target symptoms of the neuroinflammatory disease multiple sclerosis (MS). By blocking Kv channels, 4-AP facilitates action potential conduction and neurotransmitter release in presynaptic neurons, lessening the effects of demyelination. Because they conduct inward Na+ and Ca2+ currents that contribute to axonal degeneration in response to inflammatory conditions, acid-sensing ion channels (ASICs) contribute to the pathology of MS. Consequently, ASICs are emerging as disease-modifying targets in MS. Surprisingly, as first demonstrated here, 4-AP inhibits neuronal degenerin/epithelial Na+ (Deg/ENaC) channels, including ASIC and BLINaC. This effect is specific for 4-AP compared with its heterocyclic base, pyridine, and the related derivative, 4-methylpyridine; and akin to the actions of 4-AP on the structurally unrelated Kv channels, dose- and voltage-dependent. 4-AP has differential actions on distinct ASICs, strongly inhibiting ASIC1a channels expressed in central neurons but being without effect on ASIC3, which is enriched in peripheral sensory neurons. The voltage dependence of the 4-AP block and the single binding site for this inhibitor are consistent with 4-AP binding in the pore of Deg/ENaC channels as it does Kv channels, suggesting a similar mechanism of inhibition in these two classes of channels. These findings argue that effects on both Kv and Deg/ENaC channels should be considered when evaluating the actions of 4-AP. Importantly, the current results are consistent with 4-AP influencing the symptoms of MS as well as the course of the disease because of inhibitory actions on Kv and ASIC channels, respectively. 相似文献
12.
John Llewelyn Benjamin L. Phillips Ross A. Alford Lin Schwarzkopf Richard Shine 《Oecologia》2010,162(2):343-348
Cane toads (Bufo marinus) are now moving about 5 times faster through tropical Australia than they did a half-century ago, during the early phases of toad invasion. Radio-tracking has revealed higher daily rates of displacement by toads at the invasion front compared to those from long-colonised areas: toads from frontal populations follow straighter paths, move more often, and move further per displacement than do toads from older (long-established) populations. Are these higher movement rates of invasion-front toads associated with modified locomotor performance (e.g. speed, endurance)? In an outdoor raceway, toads collected from the invasion front had similar speeds, but threefold greater endurance, compared to conspecifics collected from a long-established population. Thus, increased daily displacement in invasion-front toads does not appear to be driven by changes in locomotor speed. Instead, increased dispersal is associated with higher endurance, suggesting that invasion-front toads tend to spend more time moving than do their less dispersive conspecifics. Whether this increased endurance is a cause or consequence of behavioural shifts associated with rapid dispersal is unclear. Nonetheless, shifts in endurance between frontal and core populations of this invasive species point to the complex panoply of traits affected by selection for increased dispersal ability on expanding population fronts. 相似文献
13.
14.
15.
Joseph Bucukovski Neus Latorre-Margalef David E. Stallknecht Benjamin L. Miller 《PloS one》2015,10(8)
Influenza serology has traditionally relied on techniques such as hemagglutination inhibition, microneutralization, and ELISA. These assays are complex, challenging to implement in a format allowing detection of several types of antibody-analyte interactions at once (multiplex), and troublesome to implement in the field. As an alternative, we have developed a hemagglutinin microarray on the Arrayed Imaging Reflectometry (AIR) platform. AIR provides sensitive, rapid, and label-free multiplex detection of targets in complex analyte samples such as serum. In preliminary work, we demonstrated the application of this array to the testing of human samples from a vaccine trial. Here, we report the application of an expanded label-free hemagglutinin microarray to the analysis of avian serum samples. Samples from influenza virus challenge experiments in mallards yielded strong, selective detection of antibodies to the challenge antigen in most cases. Samples acquired in the field from mallards were also analyzed, and compared with viral hemagglutinin inhibition and microneutralization assays. We find that the AIR hemagglutinin microarray can provide a simple and robust alternative to standard methods, offering substantially greater information density from a simple workflow. 相似文献
16.
Benjamin Weiss 《Chemistry and physics of lipids》1977,19(4):347-355
Cerebroside analogues were synthesized from DL-threo-and DL-erythro-3-phenylserines by the following sequence of reactions: estirification, N-acylation, reduction with sodium bis (2-methoxyethoxy)-aluminum hydride (SMEAH), and condensation with acetobromoglucose followed by deacetylation. Mass spectrometry disclosed that the glycosidic bond was formed at the primary hydroxyl group. 相似文献
17.
Background
Many molecules are flexible and undergo significant shape deformation as part of their function, and yet most existing molecular shape comparison (MSC) methods treat them as rigid bodies, which may lead to incorrect shape recognition. 相似文献18.
Genes for serum amyloid A proteins map to Chromosome 7 in the mouse 总被引:10,自引:0,他引:10
Summary Several restriction fragment length variants have been detected among inbred strains using a mouse serum amyloid A cDNA clone. Five variants were shown to segregate as a single genetic unit and were mapped to Chromosome 7 between the glucose phosphate isomerase locus (Gpi-1) and the pink eye dilution locus (p) using recombinant inbred and congenic strains. The finding that no major MspI or BclI restriction fragments were shared between digests of DNAs from a Chromosome 7 congenic strain and its inbred partner, indicate that most, and probably all, sequences detected with the probe are clustered on Chromosome 7. Aneuploid mapping was used to show that the serum amyloid A gene complex (Saa) is proximal to the Chromosome 7 breakpoint in T(7;X)1Ct, a translocation in which the middle third of Chromosome 7 is inserted into the X-chromosome. A survey of inbred strains revealed a single common Saa haplotype and eight rare haplotypes. The complex distribution of 14 different variants suggests that recombination may have played a role in haplotype evolution.This work was supported by grants GM18684 and CA33093 from the National Institute of General Medical Sciences and the National Cancer Institute, respectively. 相似文献
19.
20.
Observed intensification of precipitation extremes, responsible for extensive societal impacts, are widely attributed to anthropogenic sources, which may include indirect effects of agricultural irrigation. However quantifying the effects of irrigation on far-downstream climate remains a challenge. We use three paired Community Earth System Model simulations to assess mechanisms of irrigation-induced precipitation trends and extremes in the conterminous US and the effect on the terrestrial carbon sink. Results suggest precipitation enhancement in the central US reduced drought conditions and increased regional carbon uptake, while further downstream, the heaviest precipitation events were more frequent and intense. Specifically, moisture advection from irrigation in the western U.S. and recycling of enhanced local convective precipitation produced very-heavy storm events that were 11% more intense and occurred 23% more frequently in the densely populated greater New York City region. 相似文献