全文获取类型
收费全文 | 5560篇 |
免费 | 529篇 |
国内免费 | 5篇 |
专业分类
6094篇 |
出版年
2023年 | 32篇 |
2022年 | 63篇 |
2021年 | 144篇 |
2020年 | 87篇 |
2019年 | 108篇 |
2018年 | 148篇 |
2017年 | 119篇 |
2016年 | 213篇 |
2015年 | 292篇 |
2014年 | 342篇 |
2013年 | 372篇 |
2012年 | 513篇 |
2011年 | 508篇 |
2010年 | 299篇 |
2009年 | 263篇 |
2008年 | 363篇 |
2007年 | 359篇 |
2006年 | 330篇 |
2005年 | 260篇 |
2004年 | 277篇 |
2003年 | 218篇 |
2002年 | 239篇 |
2001年 | 58篇 |
2000年 | 51篇 |
1999年 | 46篇 |
1998年 | 63篇 |
1997年 | 37篇 |
1996年 | 31篇 |
1995年 | 30篇 |
1994年 | 23篇 |
1993年 | 17篇 |
1992年 | 24篇 |
1991年 | 19篇 |
1990年 | 19篇 |
1989年 | 15篇 |
1988年 | 9篇 |
1987年 | 9篇 |
1986年 | 9篇 |
1985年 | 11篇 |
1984年 | 16篇 |
1983年 | 4篇 |
1982年 | 11篇 |
1981年 | 10篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1971年 | 4篇 |
排序方式: 共有6094条查询结果,搜索用时 15 毫秒
41.
42.
Minobe E Hao LY Saud ZA Xu JJ Kameyama A Maki M Jewell KK Parr T Bardsley RG Kameyama M 《Biochemical and biophysical research communications》2006,348(1):288-294
Calpastatin, an endogenous inhibitor of calpain, is composed of domain L and four repetitive homologous domains 1-4. Domains 1-4 inhibit calpain, whereas domain L partially reprimes L-type Ca2+ channels for voltage-gated activation. In the present study, the effects on Ca2+ channel activity of four isoforms and a series of fragments of calpastatin domain L were investigated in guinea-pig ventricular myocytes with the patch-clamp method. With one exception, all the isoforms and fragment peptides that contained amino acid residues 54-64 of domain L reprimed the Ca2+ channels to comparable levels (9-15% of control activity) to those observed previously with a full-length form of calpastatin. These results suggest that the region containing amino acid residues 54-64 (EGKPKEHTEPK) is responsible for the Ca2+ channel repriming function of calpastatin domain L. 相似文献
43.
Jessica R. Hale Kristin L. Laidre Steven J. Jeffries Jonathan J. Scordino Deanna Lynch Ronald J. Jameson M. Tim Tinker 《The Journal of wildlife management》2022,86(4):e22215
Sea otters (Enhydra lutris kenyoni) historically occurred in Washington State, USA, until their local extinction in the early 1900s as a result of the maritime fur trade. Following their extirpation, 59 sea otters were translocated from Amchitka Island, Alaska, USA, to the coast of Washington, with 29 released at Point Grenville in 1969 and 30 released at La Push in 1970. The Washington Department of Fish and Wildlife has outlined 2 main objectives for sea otter recovery: a target population level and a target geographic distribution. Recovery criteria are based on estimates of population abundance, equilibrium abundance (K), and geographic distribution; therefore, estimates of these parameters have important management implications. We compiled available survey data for sea otters in Washington State since their translocation (1977–2019) and fit a Bayesian state-space model to estimate past and current abundance, and equilibrium abundance at multiple spatial scales. We then used forward projections of population dynamics to explore potential scenarios of range recolonization and as the basis of a sensitivity analysis to evaluate the relative influence of movement behavior, frontal wave speed, intrinsic growth, and equilibrium density on future population recovery potential. Our model improves upon previous analyses of sea otter population dynamics in Washington by partitioning and quantifying sources of estimation error to estimate population dynamics, by providing robust estimates of K, and by simulating long-term population growth and range expansion under a range of realistic parameter values. Our model resulted in predictions of population abundance that closely matched observed counts. At the range-wide scale, the population size in our model increased from an average of 21 independent sea otters (95% CI = 13–29) in 1977 to 2,336 independent sea otters (95% CI = 1,467–3,359) in 2019. The average estimated annual growth rate was 12.42% and varied at a sub-regional scale from 6.42–14.92%. The overall estimated mean K density of sea otters in Washington was 1.71 ± 0.90 (SD) independent sea otters/km2 of habitat (1.96 ± 1.04 sea otters/km2, including pups), and estimated densities within the current range correspond on average to 87% of mean sub-regional equilibrium values (range = 66–111%). The projected value of K for all of Washington was 5,287 independent sea otters (95% CI = 2,488–8,086) and 6,080 sea otters including pups (95% CI = 2,861–9,300), assuming a similar range of equilibrium densities in currently un-occupied habitats. Sensitivity analysis of simulations of sea otter population growth and range expansion suggested that mean K density estimates in currently occupied sub-regions had the largest impact on predicted future population growth (r2 = 0.52), followed by the rate of southward range expansion (r2 = 0.26) and the mean K density estimate of currently unoccupied sub-regions to the south of the current range (r2 = 0.04). Our estimates of abundance and sensitivity analysis of simulations of future population abundance and geographic range help determine population status in relation to population recovery targets and identify the most influential parameters affecting future population growth and range expansion for sea otters in Washington State. 相似文献
44.
One approach to predicting non-target attack by potential biological control agents is to first describe their fundamental host ranges and then to predict how it will be expressed under postrelease field conditions. In this paper, we illustrate how the fundamental host range can be estimated experimentally by excluding possible limiting factors such as time-dependent effects. The example we use is a host-specificity study of a leaf-tying moth (Gelechiidae: Evippe sp. #1) which was being assessed for the biological control of mesquite (Leguminosae: Prosopis spp.) in Australia. Females oviposited all eggs on plants, mostly into cracks and fissures. First instar larvae leaf-mined and subsequent instars leaf-tied. Oviposition was not host-specific in cage trials, although ten times more eggs were laid on Prosopis than on non-targets. The fundamental host range for initiation of larval feeding was restricted to Prosopis and Leucaena leucocephala which both belong to the same tribe, and the fundamental host range for complete larval development was restricted to Prosopis . We predict that if released in Australia Evippe sp. #1 will only attack Prosopis spp., although low levels of 'indiscriminate' oviposition might occur on other taxa, and might result in initiation of feeding on L. leucocephala . 相似文献
45.
Il-Chan Kim Young Ja Kim Young-Mi Lee Bok-Geon Kim Tae-Jin Park Hyeung-Sin Kim Min-Min Jung Tim D Williams Wonchoel Lee Jae-Seong Lee 《DNA sequence》2004,15(2):159-163
We synthesized a cDNA library from the intertidal copepod Tigriopus japonicus, converted it to phagemids and sequenced expressed sequence tags (ESTs). Of these, Tigriopus translationally controlled tumor protein/histamine releasing factor (TCTP/HRF) was further characterized. The Tigriopus TCTP/HRF gene encoded 172 amino acid residues and showed high similarity to Drosophila but moderate similarity to other annelids (e.g. Brugia, Wuchereria and C. elegans). The Tigriopus TCTP/HRF gene appeared in the same clade as the annelids. Here, we describe the analysis of the Tigriopus TCTP/HRF gene. 相似文献
46.
Substrates of Energy Metabolism Attenuate Methamphetamine-Induced Neurotoxicity in Striatum 总被引:4,自引:2,他引:4
†Stacy E. Stephans ‡Tim S. Whittingham ‡Albertina J. Douglas ‡W. David Lust † Bryan K. Yamamoto 《Journal of neurochemistry》1998,71(2):613-621
Abstract: High doses of methamphetamine (METH) produce a long-term depletion in striatal tissue dopamine content. The mechanism mediating this toxicity has been associated with increased concentrations of dopamine and glutamate and altered energy metabolism. In vivo microdialysis was used to assess and alter the metabolic environment of the brain during high doses of METH. METH significantly increased extracellular concentrations of lactate in striatum and prefrontal cortex. This increase was significantly greater in striatum and coincided with the greater vulnerability of this brain region to the toxic effects of METH. To examine the effect of supplementing energy metabolism on METH-induced dopamine content depletions, the striatum was perfused directly with decylubiquinone or nicotinamide to enhance the energetic capacity of the tissue during or after a neurotoxic dosing regimen of METH. When decylubiquinone or nicotinamide was perfused into striatum during the administration of METH, there was no significant effect on METH-induced striatal dopamine efflux, glutamate efflux, or the long-term dopamine depletions measured 7 days later. However, a delayed perfusion with decylubiquinone or nicotinamide for 6 h beginning immediately after the last METH injection attenuated the METH-induced striatal dopamine depletions measured 1 week later. These results support the hypothesis that the compromised metabolic state produced by METH administration predisposes dopamine terminals to the neurotoxic effects of glutamate, dopamine, and/or free radicals. 相似文献
47.
Involvement of regulatory volume decrease in the migration of nasopharyngeal carcinoma cells 总被引:7,自引:0,他引:7
Mao JW Wang LW Jacob T Sun XR Li H Zhu LY Li P Zhong P Nie SH Chen LX 《Cell research》2005,15(5):371-378
The transwell chamber migration assay and CCD digital camera imaging techniques were used to investigate the relationship between regulatory volume decrease (RVD) and cell migration in nasopharyngeal carcinoma cells (CNE-2Z cells). Both migrated and non-migrated CNE-2Z cells, when swollen by 47% hypotonic solution, exhibited RVD which was inhibited by extracellular application of chloride channel blockers adenosine 5‘-triphosphate (ATP), 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB) and tamoxifen. However, RVD rate in migrated CNE-2Z cells was bigger than that of non-migrated cells and the sensitivity of migrated cells to NPPB and tamoxifen was higher than that of nonmigrated cells. ATP, NPPB and tamoxifen also inhibited migration of CNE-2Z cells. The inhibition of migration was positively correlated to the blockage of RVD, with a correlation coefficient (r) = 0.99, suggesting a functional relationship between RVD and cell migration. We conclude that RVD is involved in cell migration and RVD may play an important role in migratory process in CNE-2Z cells. 相似文献
48.
Tim Ammon ;Shravan Kumar Mishra ;Kaja Kowalska ;Grzegorz M. Popowicz ;Tad A. Holak ;Stefan Jentsch 《分子细胞生物学报》2014,(4):312-323
Different from canonical ubiquitin-like proteins, Hub1 does not form covalent conjugates with substrates but binds proteins noncovalently. In Socchoromyces cerevisioe, Hub1 associates with spUceosomes and mediates alternative splicing of SRCI, without affecting pre-mRNA splicing generaity. Human Hub1 is highty similar to its yeast homotog, but its cellular function remains largely unexplored. Here, we show that human Hub1 binds to the spliceosomal protein Snu66 as in yeast; however, unlike its 5. cerevisioe homolos, human Hub1 is essential for viability. Prolonged in vivo depletion of human Hub1 leads to various cellular defects, including splicing speckle abnormalities, partial nuclear retention of mRNAs, mitotic catastrophe, and consequently cell death by apoptosis. Early consequences of Hub1 depletion are severe splicing defects, however, only for specific splice sites leading to exon skipping and intron retention. Thus, the ubiquitin-iike protein Hub1 is not a canonlcal spliceosomal factor needed generally for splicing, but rather a modulator of spliceosome performance and facilitator of alternative splicing. 相似文献
49.
Pierre-Paul Lizotte Lana E Hanford Jan J Enghild Eva Nozik-Grayck Brenda-Louise Giles Tim D Oury 《BMC developmental biology》2007,7(1):15