全文获取类型
收费全文 | 100273篇 |
免费 | 924篇 |
国内免费 | 1733篇 |
专业分类
102930篇 |
出版年
2024年 | 40篇 |
2023年 | 174篇 |
2022年 | 343篇 |
2021年 | 453篇 |
2020年 | 334篇 |
2019年 | 467篇 |
2018年 | 12135篇 |
2017年 | 10872篇 |
2016年 | 7769篇 |
2015年 | 1096篇 |
2014年 | 862篇 |
2013年 | 903篇 |
2012年 | 4850篇 |
2011年 | 13329篇 |
2010年 | 12304篇 |
2009年 | 8517篇 |
2008年 | 10109篇 |
2007年 | 11634篇 |
2006年 | 535篇 |
2005年 | 702篇 |
2004年 | 1192篇 |
2003年 | 1215篇 |
2002年 | 933篇 |
2001年 | 407篇 |
2000年 | 274篇 |
1999年 | 116篇 |
1998年 | 81篇 |
1997年 | 75篇 |
1996年 | 89篇 |
1995年 | 66篇 |
1994年 | 56篇 |
1993年 | 56篇 |
1992年 | 62篇 |
1991年 | 69篇 |
1990年 | 38篇 |
1989年 | 28篇 |
1988年 | 42篇 |
1987年 | 30篇 |
1986年 | 12篇 |
1985年 | 18篇 |
1984年 | 13篇 |
1983年 | 24篇 |
1982年 | 7篇 |
1972年 | 246篇 |
1971年 | 274篇 |
1965年 | 13篇 |
1962年 | 24篇 |
1956年 | 5篇 |
1944年 | 12篇 |
1940年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Haag ES 《Genetica》2007,129(1):45-55
The evolution of molecules, developmental circuits, and new species are all characterized by the accumulation of incompatibilities
between ancestors and descendants. When specific interactions between components are necessary at any of these levels, this
requires compensatory coevolution. Theoretical treatments of compensatory evolution that only consider the endpoints predict
that it should be rare because intermediate states are deleterious. However, empirical data suggest that compensatory evolution
is common at all levels of molecular interaction. A general solution to this paradox is provided by plausible neutral or nearly
neutral intermediates that possess informational redundancy. These intermediates provide an evolutionary path between coadapted
allelic combinations. Although they allow incompatible end points to evolve, at no point was a deleterious mutation ever in
need of compensation. As a result, what appears to be compensatory evolution may often actually be “pseudocompensatory.” Both
theoretical and empirical studies indicate that pseudocompensation can speed the evolution of intergenic incompatibility,
especially when driven by adaptation. However, under strong stabilizing selection the rate of pseudocompensatory evolution
is still significant. Important examples of this process at work discussed here include the evolution of rRNA secondary structures,
intra- and inter-protein interactions, and developmental genetic pathways. Future empirical work in this area should focus
on comparing the details of intra- and intergenic interactions in closely related organisms. 相似文献
992.
The osmotolerant and cell wall properties of the two most studied wild-type Zygosaccharomyces rouxii strains (CBS 732 and ATCC 42981) were examined. Differences in their (1) tolerance to high salt content in the medium, (2) resistance to the lysing enzymes Lyticase and Zymolyase, (3) cell-wall polymer content and (4) cell wall micromorphology suggested that the less osmotolerant CBS 732 strain possesses a more rigid cell wall than the more osmotolerant ATCC 42981, whose cell wall seems to be more flexible and elastic. 相似文献
993.
Di Bonaventura G Stepanović S Picciani C Pompilio A Piccolomini R 《Folia microbiologica》2007,52(1):86-90
The influence of environmental factors (temperature, aerobiosis-anaerobiosis, static-dynamic conditions, pH) was determined on biofilm formation by 51 S. maltophilia clinical isolates. The strains produced more biofilm at 32 degrees C than at 37 or 18 degrees C. Aerobic and 6% CO2 atmosphere yielded comparable biofilm amounts, higher than under anaerobic conditions. Biofilm production was not affected by static vs. agitated culture conditions. Biofilm production at pH 7.5 and 8.5 was comparable but significantly higher than at pH 5.5. The capacity of individual strains to form biofilm and thus contribute to the severity of some diseases is influenced by host traits and environmental conditions at the site of infection, and play an important role in the pathogenesis of biomaterial-related disease caused by S. maltophilia. 相似文献
994.
The protein C (PC) pathway plays an important role in coagulation and inflammation. Many components of the PC pathway have been identified in epidermal keratinocytes, including endothelial protein C receptor (EPCR), which is the specific receptor for PC/activated PC (APC), but the core member of this pathway, PC, and its function in keratinocytes has not been defined. In this study, we reveal that PC is strongly expressed by human keratinocytes at both gene and protein levels. When endogenous PC was blocked by siRNA the proliferation of keratinocytes was significantly decreased. This inhibitory effect was restored by the addition of recombinant APC. PC siRNA treatment also increased cell apoptosis by 3-fold and inhibited cell migration by more than 20%. When keratinocytes were pretreated with RCR252, an EPCR-blocking antibody, or PD153035, an epidermal growth factor receptor (EGFR) inhibitor, cell proliferation was hindered by more than 30%. These inhibitors also completely abolished recombinant APC (10 mug/ml)-stimulated proliferation. Blocking PC expression or inhibiting its binding to EPCR/EGFR decreased the phosphorylation of ERK1/2 but increased p38 activation. Furthermore, inhibition of ERK decreased cell proliferation by approximately 30% and completely abolished the stimulatory effect of APC on proliferation. Taken together, these results indicate that keratinocyte-derived PC promotes cell survival, growth, and migration in an autocrine manner via EPCR, EGFR, and activation of ERK1/2. Our results highlight a novel role for the PC pathway in normal skin physiology and wound healing. 相似文献
995.
996.
Ann Margaret Grøndahl Ellen Margrete Skancke Cecilie Marie Mejdell Johan Høgset Jansen 《Acta veterinaria Scandinavica》2007,49(1):16
Over a period of two years, growth rate and health were measured for dairy calves allowed to suckle their mothers up to 6–8
weeks of age. Thirty-one calves were weighted weekly, and the mean daily growth rate was 1.2 ± 0.03 kg from birth up to 13
weeks of age. Illness in calves and young stock was not observed. In the cows, the mean incidences of ketosis, displaced abomasum,
puerperal paresis, mastitis, teat injury and retained placenta were 0, 0, 8, 22, 1 and 1%, respectively, during a 6-year period.
The mean daily gain of 56 growing bulls was 1.4 kg when slaughtered at 15 months of age, which is higher than the mean daily
gain of 0.95 kg in the population. Probiotics, hormones and vaccines were not used, and antibiotics were only used for treating
illness. The present study indicates many advantages and few problems when dairy calves are penned together with the cows
and allowed natural feeding up to 6–8 weeks of age. This production system was easy to manage, preferred by the farmer, and
may satisfy the public concern regarding the practice of immediate separation of cow and calf in commercial milk production. 相似文献
997.
Mycoplasma alkalescens is an arginine-metabolizing mycoplasma, which has been found in association with mastitis and arthritis in cattle. Routine
bacteriological examination of 17 bronchoalveolar lavage samples from calves with pneumonia in a single herd in Denmark, identified
M. alkalescens in eight samples. The organism was found as a sole bacterilogical findings in five of the samples as well as in combination
with Mannheimia haemolytica, Haemophilus somni and Salmonella Dublin. This is the first report of isolation of M. alkalescens in Denmark. 相似文献
998.
999.
1000.