全文获取类型
收费全文 | 18949篇 |
免费 | 1774篇 |
国内免费 | 8篇 |
专业分类
20731篇 |
出版年
2024年 | 27篇 |
2023年 | 117篇 |
2022年 | 269篇 |
2021年 | 621篇 |
2020年 | 340篇 |
2019年 | 443篇 |
2018年 | 501篇 |
2017年 | 444篇 |
2016年 | 705篇 |
2015年 | 1173篇 |
2014年 | 1239篇 |
2013年 | 1290篇 |
2012年 | 1767篇 |
2011年 | 1778篇 |
2010年 | 1098篇 |
2009年 | 951篇 |
2008年 | 1230篇 |
2007年 | 1229篇 |
2006年 | 1072篇 |
2005年 | 971篇 |
2004年 | 912篇 |
2003年 | 723篇 |
2002年 | 647篇 |
2001年 | 126篇 |
2000年 | 78篇 |
1999年 | 108篇 |
1998年 | 115篇 |
1997年 | 79篇 |
1996年 | 70篇 |
1995年 | 52篇 |
1994年 | 45篇 |
1993年 | 48篇 |
1992年 | 34篇 |
1991年 | 25篇 |
1990年 | 20篇 |
1989年 | 28篇 |
1988年 | 18篇 |
1987年 | 16篇 |
1986年 | 14篇 |
1985年 | 24篇 |
1984年 | 21篇 |
1983年 | 25篇 |
1982年 | 22篇 |
1981年 | 18篇 |
1980年 | 13篇 |
1979年 | 12篇 |
1978年 | 13篇 |
1976年 | 11篇 |
1963年 | 10篇 |
1960年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
Leilani M. Lehmann Sean E. Walker† & Matthew H. Persons 《Ethology : formerly Zeitschrift fur Tierpsychologie》2004,110(4):323-339
The wolf spider, Pardosa milvina, reduces activity in the presence of chemical cues (silk and excreta) from a larger predatory wolf spider, Hogna helluo. Hogna is sexually dimorphic in body size and males and females differ in their propensity to attack prey. Consequently, each sex may present different levels of risk to Pardosa. We measured predation risk of Pardosa in the presence of male or female Hogna. We also assessed Pardosa antipredator responses and survival in the presence or absence of previously deposited chemical cues from male or female Hogna. In the absence of predator chemical cues, Pardosa survived significantly longer in the presence of male Hogna compared with female Hogna. We then assessed Pardosa survival in the presence of chemical cues from each Hogna sex by placing Pardosa in containers previously occupied by a female Hogna, a male Hogna, or no Hogna (control). We then introduced a female Hogna into each container and measured predation latency. Pardosa survived significantly longer in the presence of female and male cues compared with the control treatment. Median survival time of Pardosa was over four times longer on substrates with female Hogna cues compared with male cues, but this difference was not statistically significant. We tested Pardosa activity levels in the presence of chemical cues from male or female Hogna. Both Hogna sexes were maintained in separate containers after which we placed an adult female Pardosa in one of the containers or a blank control container. Pardosa significantly decreased activity in the presence of chemical cues from either sex relative to the control. Activity was lowest on substrates with female Hogna cues, but not significantly lower than on substrates with male Hogna cues. Results suggest that chemical information from male or female Hogna significantly reduces Pardosa activity which results in increased survival. 相似文献
63.
De Cotiis DA Woll MP Fox TE Hill RB Levenson R Flanagan JM 《Protein expression and purification》2008,61(2):103-112
We have developed a protocol to produce large quantities of high purity myristoylated and non-myristoylated neuronal calcium sensor 1 (NCS-1) protein. NCS-1 is a member of the neuronal calcium sensor (NCS) family and plays an important role in modulating G-protein signaling and exocytosis pathways in cells. Many of these functions are calcium-dependent and require NCS-1 to be modified with an N-terminal myristoyl moiety. In our system, a C-terminally 6x His-tagged variant of NCS-1 was co-expressed with yeast N-myristoyltransferase (NMT) in ZYP-5052 auto-induction media supplemented with sodium myristate (100-200 microM). With optimized growth conditions and a high capacity metal affinity purification scheme, >50mg of homogenous myristoylated NCS-1 is obtained from 1L of culture in a single step. The properties of the C-terminally tagged NCS-1 variants are indistinguishable from those reported for untagged NCS-1. Using this system, we have also isolated and characterized mutant NCS-1 proteins that have attenuated (NCS-1 E120Q) and abrogated (NCS-1 DeltaEF) ability to bind calcium. The large quantities of NCS-1 proteins isolated from small culture volumes of auto-inducible media will provide the necessary reagents for further biochemical and structural characterization. The affinity tag at the C-terminus of the protein provides a suitable reagent for easily identifying binding partners of the various NCS-1 constructs. Additionally, this method could be used to produce other recombinant proteins of the NCS family, and may be extended to express and isolate myristoylated variants of other proteins. 相似文献
64.
Matthew A.J. Duncton Eugene L. Piatnitski Chekler Reeti Katoch-Rouse Dan Sherman Wai C. Wong Leon M. Smith Joel K. Kawakami Alexander S. Kiselyov Daniel L. Milligan Chris Balagtas Yaron R. Hadari Ying Wang Sheetal N. Patel Robin L. Rolster James R. Tonra David Surguladze Stan Mitelman Paul Kussie Peter Bohlen Jacqueline F. Doody 《Bioorganic & medicinal chemistry》2009,17(2):731-740
A series of arylphthalazine derivatives were synthesized and evaluated as antagonists of VEGF receptor II (VEGFR-2). IM-094482 57, which was prepared in two steps from commercially available starting materials, was found to be a potent inhibitor of VEGFR-2 in enzymatic, cellular and mitogenic assays (comparable activity to ZD-6474). Additionally, 57 inhibited the related receptor, VEGF receptor I (VEGFR-1), and showed excellent exposure when dosed orally to female CD-1 mice. 相似文献
65.
doi: 10.1111/j.1741‐2358.2011.00510.x Edentulism and dental caries in Victorian nursing homes Objectives: The aim of this project was to investigate edentulism and dental caries in nursing home residents in Victoria, Australia. Background: The Australian population is ageing with a growing number of people living in nursing homes. These residents are at increased risk for dental caries, have more teeth present now than at any time in the past 50 years and often have difficulty maintaining adequate oral hygiene. Materials and methods: Clinical dental examinations were conducted at 31 nursing homes in Melbourne and regional Victoria between May 2005 and June 2006. A total of 510 residents were examined out of 1345 eligible participants. Socio‐demographic and medical history was collected via questionnaire. Results: Just over half of the residents were dentate (53.9%), and dentate residents had a mean of 14.4 teeth present and 2.66 untreated decayed teeth. Residents who required total assistance with oral hygiene had more decayed teeth and fewer filled teeth than residents who did not require assistance. Conclusions: Nursing home residents in Victoria are retaining an increasing number of natural teeth and have more tooth surfaces at risk for dental caries. Untreated dental caries was a significant problem for residents, particularly for those who are dependent on others for their daily oral hygiene care. 相似文献
66.
Eric L. Stevens Joseph D. Baugher Matthew D. Shirley Laurence P. Frelin Jonathan Pevsner 《PloS one》2012,7(11)
Correct annotation of the genetic relationships between samples is essential for population genomic studies, which could be biased by errors or omissions. To this end, we used identity-by-state (IBS) and identity-by-descent (IBD) methods to assess genetic relatedness of individuals within HapMap phase III data. We analyzed data from 1,397 individuals across 11 ethnic populations. Our results support previous studies (Pemberton et al., 2010; Kyriazopoulou-Panagiotopoulou et al., 2011) assessing unknown relatedness present within this population. Additionally, we present evidence for 1,657 novel pairwise relationships across 9 populations. Surprisingly, significant Cotterman''s coefficients of relatedness K1 (IBD1) values were detected between pairs of known parents. Furthermore, significant K2 (IBD2) values were detected in 32 previously annotated parent-child relationships. Consistent with a hypothesis of inbreeding, regions of homozygosity (ROH) were identified in the offspring of related parents, of which a subset overlapped those reported in previous studies (Gibson et al. 2010; Johnson et al. 2011). In total, we inferred 28 inbred individuals with ROH that overlapped areas of relatedness between the parents and/or IBD2 sharing at a different genomic locus between a child and a parent. Finally, 8 previously annotated parent-child relationships had unexpected K0 (IBD0) values (resulting from a chromosomal abnormality or genotype error), and 10 previously annotated second-degree relationships along with 38 other novel pairwise relationships had unexpected IBD2 (indicating two separate paths of recent ancestry). These newly described types of relatedness may impact the outcome of previous studies and should inform the design of future studies relying on the HapMap Phase III resource. 相似文献
67.
Gareth Betts Hazel Poyntz Elena Stylianou Arturo Reyes-Sandoval Matthew Cottingham Adrian Hill Helen McShane 《PloS one》2012,7(12)
The Bacillus Calmette - Guerin (BCG) vaccine provides a critical but limited defense against Mycobacterium tuberculosis (M.tb). More than 60 years after the widespread introduction of BCG, there is an urgent need for a better vaccine. A large body of pre-clinical research continues to support ongoing clinical trials to assess whether viral vectors expressing M.tb antigens that are shared by BCG and M.tb, can be used alongside BCG to enhance protection. A major focus involves using multiple unique viral vectors to limit anti-vector immunity and thereby enhance responses to the insert antigen delivered. The successful introduction of viral vector vaccines to target M.tb and other pathogens will be reliant on reducing the costs when using multiple vectors and inhibiting the development of unwanted anti-vector responses that interfere with the response to insert antigen. This study examines methods to reduce the logistical costs of vaccination by mixing different viral vectors that share the same insert antigen in one vaccine; and whether combining different viral vectors reduces anti-vector immunity to improve immunogenicity to the insert antigen. Here we show that a homologous prime-boost regimen with a mixture of MVA (Modified Vaccinia virus Ankara) and Ad5 (human adenovirus type 5) vectors both expressing Ag85A in a single vaccine preparation is able to reduce anti-vector immunity, compared with a homologous prime-boost regimen with either vector alone. However, the level of immunogenicity induced by the homologous mixture remained comparable to that induced with single viral vectors and was less immunogenic than a heterologous Ad5 prime-MVA-boost regimen. These findings advance the understanding of how anti-vector immunity maybe reduced in viral vector vaccination regimens. Furthermore, an insight is provided to the impact on vaccine immunogenicity from altering vaccination methods to reduce the logistical demands of using separate vaccine preparations in the field. 相似文献
68.
69.
Andrew M. Griffiths David W. Sims Andrew Johnson Arve Lynghammar Matthew McHugh Torkild Bakken Martin J. Genner 《Conservation Genetics》2011,12(2):577-582
Sequencing of a partial region of the mitochondrial control region has revealed no shared haplotypes between longnose skate (Dipturus oxyrinchus L.) sampled in the north-eastern Atlantic (Norway and Rockall) and those sampled in the Mediterranean (Mallorca). Bayesian estimation of the migration rate suggests little, if any, gene flow occurs between the regions and that the populations separated 20,000?years ago. These conclusions provide a genetic basis for long-standing observations, based on egg capsule and adult size, that longnose skate in the Mediterranean may be genetically isolated from other stocks. This result has important conservation implications for the threatened longnose skate. 相似文献
70.