全文获取类型
收费全文 | 65193篇 |
免费 | 18747篇 |
国内免费 | 24篇 |
专业分类
83964篇 |
出版年
2023年 | 255篇 |
2022年 | 604篇 |
2021年 | 1476篇 |
2020年 | 2738篇 |
2019年 | 4383篇 |
2018年 | 4647篇 |
2017年 | 4770篇 |
2016年 | 5193篇 |
2015年 | 5958篇 |
2014年 | 5827篇 |
2013年 | 6395篇 |
2012年 | 5084篇 |
2011年 | 4533篇 |
2010年 | 4995篇 |
2009年 | 3445篇 |
2008年 | 3123篇 |
2007年 | 2663篇 |
2006年 | 2403篇 |
2005年 | 2360篇 |
2004年 | 2141篇 |
2003年 | 2046篇 |
2002年 | 1905篇 |
2001年 | 646篇 |
2000年 | 481篇 |
1999年 | 524篇 |
1998年 | 447篇 |
1997年 | 299篇 |
1996年 | 276篇 |
1995年 | 226篇 |
1994年 | 236篇 |
1993年 | 241篇 |
1992年 | 256篇 |
1991年 | 236篇 |
1990年 | 221篇 |
1989年 | 197篇 |
1988年 | 196篇 |
1987年 | 193篇 |
1986年 | 157篇 |
1985年 | 149篇 |
1984年 | 171篇 |
1983年 | 140篇 |
1982年 | 160篇 |
1981年 | 154篇 |
1980年 | 142篇 |
1979年 | 113篇 |
1978年 | 114篇 |
1977年 | 111篇 |
1976年 | 91篇 |
1975年 | 84篇 |
1973年 | 96篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
P. Cruz C. H. Mejia‐Ruiz R. Perez‐Enriquez A. M. Ibarra 《Molecular ecology resources》2002,2(3):239-241
Five polymorphic microsatellite loci were characterized for Penaeus (Litopenaeus) vannamei. Loci were isolated using a partial Sau3A1 genomic library by the sequencing of randomly selected clones and by a biotinylated (CT)10 and (GT)10 probes screening procedure. The last strategy resulted in the most useful data. About 40% of the clones showed a previously reported satellite/microsatellite (PVS1), reducing the chance of finding new microsatellite regions. Whereas two of the microsatellite loci with more than 10 alleles will be useful for mating analysis in a breeding program, the others might prove useful for population genetic studies. 相似文献
22.
23.
24.
25.
The phenotypic consequences in the house mouse (Mus musculus domesticus) of the transition from an ordinary field-dwelling rodent to a species that is dependent on human populations was studied by investigating the morphometric variation of non-commensal populations of M. m. domesticus from Syria, Jordan, SW Iran, and Libya and comparing them with that of conspecific commensal populations from Eastern Turkey, Greece, and Bulgaria. Commensal populations of M. musculus musculus from the Czech Republic were used as an outgroup. About 849 adult specimens of M. musculus were analysed by multivariate procedures based on standard molar, skull and body measurements. As expected, there was considerable variation among the studied populations and a good correspondence between morphometric and geographic distances. The resulting morphometric tree was consistent with the hypothesis that the original radiation of M. m. domesticus took place somewhere in the Near East. Commensal populations of M. m. domesticus form a single derived branch. Specimens originating from four different sites in eastern Syria showed the greatest similarity to one another and possessed relatively bigger molars than the other studied populations. Commensal populations were characterised by longer tails when compared to non-commensal populations, which suggests an adaptation for living in a more three-dimensionally heterogeneous environment for commensal populations. 相似文献
26.
27.
28.
Background
Eosinophilia plays the major role in the pathogenesis of asthma and correlates with the up‐regulation of eotaxin, which, together with interleukin (IL)‐5, is important for differentiation, chemo‐attraction, degranulation, and survival of eosinophils in local tissue. In a previous study, we found that administration of lentivirus‐delivered short hairpin RNA (shRNA) to suppress the expression of IL‐5 inhibited airway inflammation. The present study aimed to investigate the role of eotaxin shRNA and the synergistic effect of eotaxin and IL‐5 shRNAs on airway inflammation in an ovalbumin (OVA)‐induced murine model of asthma.Methods
Lentivirus‐delivered shRNAs were used to suppress the expression of eotaxin and/or IL‐5 in local tissue in an OVA‐induced murine asthma model.Results
Intra‐tracheal administration of lentivirus containing eotaxin shRNA expressing cassette (eoSEC3.3) efficiently moderated the characteristics of asthma, including airway hyper‐responsiveness, cellular infiltration of lung tissues, and eotaxin and IL‐5 levels in bronchio‐alveolar lavage fluid. Administration of lentiviruses expressing IL‐5 or eotaxin shRNAs (IL5SEC4 + eoSEC3.3) also moderated the symptoms of asthma in a mouse model.Conclusions
Local delivery of lentiviruses expressing IL‐5 and eotaxin shRNAs provides a potential tool in moderating airway inflammation and also has the potential for developing clinical therapy based on the application of shRNAs of chemokines and cytokines involved in T helper 2 cell inflammation and eosinophilia. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献29.
The economic viability of the wildlife based enterprises (bee-keeping and caterpillar utilization) in Malawi is discussed in relation to conventional agricultural enterprises (maize, beans and ground-nuts). A strong incentive emerges for rural people to adopt wildlife management as an adjunct to subsistence agriculture, and therefore, to promote conservation of natural ecosystems and wildlife habitats in the face of growing human population and demand for land. Dependence on agriculture has depleted the wildlife resource outside protected areas and has been less effective in improving the wealth and living standards of most rural people. This study illustrates that the Malawi Department of National Parks and Wildlife needs to introduce economic incentives that integrate biological conservation with economic development for the rural people. The management programme involves the adoption of a rotation burning policy that promotes vegetation coppicing, eases harvesting and promotes high caterpillar yields. 相似文献
30.
Daniel M. Wetzel Ursula L. Haerter Darcy B. Kelley 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1985,157(6):749-761
Vocalizations of South African clawed frogs are produced by contractions of laryngeal muscles innervated by motor neurons of the caudal medulla (within cranial nerve nucleus IX-X). We have traced afferents to laryngeal motor neurons in male and female frogs using retrograde axonal transport of horseradish peroxidase conjugated to wheat germ agglutinin (HRP-WGA). After iontophoretic injection of HRP-WGA into n. IX-X, retrogradely labelled neurons were seen in the contralateral n. IX-X, in rhombencephalic reticular nuclei, and in the pre-trigeminal nucleus of the dorsal tegmental area (DTAM) of both males and females. 相似文献