全文获取类型
收费全文 | 2628篇 |
免费 | 632篇 |
国内免费 | 1篇 |
出版年
2022年 | 27篇 |
2021年 | 30篇 |
2019年 | 24篇 |
2018年 | 33篇 |
2016年 | 39篇 |
2015年 | 75篇 |
2014年 | 85篇 |
2013年 | 107篇 |
2012年 | 118篇 |
2011年 | 115篇 |
2010年 | 76篇 |
2009年 | 56篇 |
2008年 | 77篇 |
2007年 | 101篇 |
2006年 | 158篇 |
2005年 | 145篇 |
2004年 | 161篇 |
2003年 | 143篇 |
2002年 | 143篇 |
2001年 | 140篇 |
2000年 | 76篇 |
1999年 | 70篇 |
1998年 | 30篇 |
1997年 | 35篇 |
1996年 | 29篇 |
1995年 | 27篇 |
1994年 | 29篇 |
1993年 | 24篇 |
1992年 | 49篇 |
1991年 | 53篇 |
1990年 | 48篇 |
1989年 | 37篇 |
1988年 | 48篇 |
1987年 | 50篇 |
1986年 | 62篇 |
1985年 | 51篇 |
1984年 | 33篇 |
1983年 | 37篇 |
1982年 | 22篇 |
1981年 | 33篇 |
1980年 | 30篇 |
1979年 | 49篇 |
1977年 | 30篇 |
1976年 | 30篇 |
1975年 | 32篇 |
1974年 | 34篇 |
1973年 | 37篇 |
1972年 | 33篇 |
1971年 | 36篇 |
1970年 | 24篇 |
排序方式: 共有3261条查询结果,搜索用时 15 毫秒
961.
This study examined the prevalence of behaviour problems exhibited by dogs within 4 weeks of acquisition from a rescue shelter in Northern Ireland. One thousand five hundred and forty-seven people who had purchased a dog from a rescue shelter in Northern Ireland were sent a postal questionnaire designed to collect information on the behaviours exhibited by their dog within the first month of acquisition. Five hundred and fifty-six people responded to the survey, representing a response rate of 37%. The majority of respondents (68.3%) reported that their dog exhibited a behaviour problem, the most common being fearfulness. Most of those respondents (89.7%) who returned their dog to the shelter did so because the animal exhibited behaviour that they considered undesirable. Male dogs showed more unacceptable behaviours than females, specifically inter-male aggression, sexual problems and straying tendencies. More stray dogs displayed undesirable behaviour than unwanteds, specifically straying tendencies. Puppies were less likely to exhibit unacceptable behaviours than juveniles or adults, particularly fearfulness, sexual problems and straying tendencies. More juvenile dogs showed excessive activity and excessive barking than puppies or adults. More adult dogs displayed aggression towards other dogs than juveniles or puppies. Findings indicate that dogs purchased from rescue shelters do exhibit behaviour problems that may lead to their return. The number of dogs admitted or returned to rescue shelters with behaviour problems may be reduced by raising public awareness regarding the value of behaviour therapy and introducing behaviour therapy schemes to rescue shelters. 相似文献
962.
Endoderm that forms the respiratory and digestive tracts is a sheet of approximately 500-1000 cells around the distal cup of an E7.5 mouse embryo. Within 2 days, endoderm folds into a primitive gut tube from which numerous organs will bud. To characterize the signals involved in the developmental specification of this early endoderm, we have employed an in vitro assay using germ layer explants and show that adjacent germ layers provide soluble, temporally specific signals that induce organ-specific gene expression in endoderm. Furthermore, we show that FGF4 expressed in primitive streak-mesoderm can induce the differentiation of endoderm in a concentration-dependent manner. We conclude that the differentiation of gastrulation-stage endoderm is directed by adjacent mesoderm and ectoderm, one of the earliest reported patterning events in formation of the vertebrate gut tube. 相似文献
963.
The creation of enduring modifications in synaptic efficacy requires new protein synthesis. Neurons face the formidable challenge of directing these newly made proteins to the appropriate subset of synapses. One attractive solution to this problem is the local translation of mRNAs that are targeted to dendrites and perhaps to synapses themselves. The molecular mechanisms mediating such local protein synthesis, notably CPEB-mediated cytoplasmic polyadenylation, are now being elucidated. 相似文献
964.
Developmental changes in time spent suckling and related mother-foal behaviour are described in an unmanaged herd of Camargue horses. Male foals spent about 40% more time suckling than females during the first 8 weeks. Body weight did not differ between the sexes but time-budgets did: males grazed less and were more active. If pregnant, the typical multiparous mare nursed her foals for 35–40 weeks, males and females alike, and weaned them 15 weeks before the next foaling. Primiparae lactated longer and weaned closer to the next foaling by 5 weeks. The mares played an active role in regulating the time spent suckling in early, and particularly in late lactation. 相似文献
965.
966.
967.
An IL-7 fusion protein that shows increased thymopoietic ability 总被引:2,自引:0,他引:2
Henson SM Snelgrove R Hussell T Wells DJ Aspinall R 《Journal of immunology (Baltimore, Md. : 1950)》2005,175(6):4112-4118
The role of IL-7 during thymopoiesis has led to it being the focus of a number of therapeutic interventions. However, its small size and pleiotropic nature present problems for thymus-directed therapies. We have created a fusion molecule between the extracellular N-terminal domain of CCR9 and IL-7, which has the potential to overcome these difficulties. This novel fusion protein retains the thymopoietic activity of IL-7 and the ligand-binding ability of CCR9. As a thymopoietic agent, compared with IL-7, it shows an enhanced retention in the thymus, increased de novo T cell production, and increased thymic output. Old mice receiving the fusion protein show improved CD8 T cell responses and reduced viral load after infection with influenza virus compared with those receiving IL-7. This chimeric molecule offers a novel therapeutic strategy that may result in the production of an effective immunorestorative agent. 相似文献
968.
Advances in mechanisms of genetic instability related to hereditary neurological diseases 总被引:11,自引:3,他引:8
下载免费PDF全文
![点击此处可从《Nucleic acids research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Substantial progress has been realized in the past several years in our understanding of the molecular mechanisms responsible for the expansions and deletions (genetic instabilities) of repeating tri-, tetra- and pentanucleotide repeating sequences associated with a number of hereditary neurological diseases. These instabilities occur by replication, recombination and repair processes, probably acting in concert, due to slippage of the DNA complementary strands relative to each other. The biophysical properties of the folded-back repeating sequence strands play a critical role in these instabilities. Non-B DNA structural elements (hairpins and slipped structures, DNA unwinding elements, tetraplexes, triplexes and sticky DNA) are described. The replication mechanisms are influenced by pausing of the replication fork, orientation of the repeat strands, location of the repeat sequences relative to replication origins and the flap endonuclease. Methyl-directed mismatch repair, nucleotide excision repair, and repair of damage caused by mutagens are discussed. Genetic recombination and double-strand break repair advances in Escherichia coli, yeast and mammalian models are reviewed. Furthermore, the newly discovered capacities of certain triplet repeat sequences to cause gross chromosomal rearrangements are discussed. 相似文献
969.
This note redescribes M. borneensis and describes M. traubi n. sp. based on the known specimens from the two sampling localities (holotype from Mount Murud and further recorded from Mount Kinabalu by Traub). The clearly allied, but clearly distinct species for the two localities, were recorded. 相似文献
970.
An in silico mining for simple sequence repeats from expressed sequence tags of zebrafish, medaka, Fundulus, and Xiphophorus 总被引:3,自引:0,他引:3
Teleost fish genome projects involving model species are resulting in a rapid accumulation of genomic and expressed DNA sequences in public databases. The expressed sequence tags (ESTs) collected in the databases can be mined for the analysis of both structural and functional genomics. In this study, we in silico analyzed 49,430 unigenes representing a total of 692,654 ESTs from four model fish for their potential use in developing simple sequence repeats (SSRs), or microsatellites. After bioinformatical mining, a total of 3,018 EST derived SSRs (EST-SSRs) were identified for 2,335 SSR containing ESTs (SSR-ESTs). The frequency of identified SSR-ESTs ranged from 1.5% for Xiphophorus to 7.3% for zebrafish. The dinucleotide repeat motif is the most abundant SSR, accounting for 47%, 52%, 64%, and 78% for medaka, Fundulus, zebrafish, and Xiphophorus, respectively. Simulation analysis suggests that a majority of these EST-SSRs have sufficient flanking sequences for polymerase chain reaction (PCR) primer design. Comparative DNA sequence analyses of SSR-ESTs identified several cross-species SSRs and sequences that may be used as cross-reference genes in comparative studies. For example, the flanking sequences of one SSR (CTG)n within the pituitary tumor-transforming gene (PTTG) 1 interacting protein (PTTGIP), showed conservation spanning the medaka, Fundulus, human, and mouse genomes. This study provides a large body of information on EST-SSRs that can be useful for the development of polymorphic markers, gene mapping, and comparative genome analysis. Functional analysis of these SSR-ESTs may reveal their role in metabolism and gene evolution of these model species. 相似文献