全文获取类型
收费全文 | 35058篇 |
免费 | 76篇 |
国内免费 | 118篇 |
专业分类
系统科学 | 338篇 |
丛书文集 | 720篇 |
教育与普及 | 87篇 |
理论与方法论 | 116篇 |
现状及发展 | 15312篇 |
研究方法 | 1398篇 |
综合类 | 16687篇 |
自然研究 | 594篇 |
出版年
2013年 | 201篇 |
2012年 | 486篇 |
2011年 | 1076篇 |
2010年 | 181篇 |
2008年 | 551篇 |
2007年 | 633篇 |
2006年 | 668篇 |
2005年 | 662篇 |
2004年 | 632篇 |
2003年 | 626篇 |
2002年 | 555篇 |
2001年 | 1067篇 |
2000年 | 1033篇 |
1999年 | 654篇 |
1992年 | 632篇 |
1991年 | 543篇 |
1990年 | 578篇 |
1989年 | 501篇 |
1988年 | 520篇 |
1987年 | 557篇 |
1986年 | 537篇 |
1985年 | 691篇 |
1984年 | 558篇 |
1983年 | 450篇 |
1982年 | 370篇 |
1981年 | 394篇 |
1980年 | 521篇 |
1979年 | 1119篇 |
1978年 | 916篇 |
1977年 | 882篇 |
1976年 | 701篇 |
1975年 | 782篇 |
1974年 | 1050篇 |
1973年 | 927篇 |
1972年 | 913篇 |
1971年 | 1113篇 |
1970年 | 1462篇 |
1969年 | 1098篇 |
1968年 | 914篇 |
1967年 | 1014篇 |
1966年 | 916篇 |
1965年 | 648篇 |
1964年 | 165篇 |
1959年 | 386篇 |
1958年 | 612篇 |
1957年 | 466篇 |
1956年 | 419篇 |
1955年 | 351篇 |
1954年 | 382篇 |
1948年 | 282篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
231.
Maller JB Fagerness JA Reynolds RC Neale BM Daly MJ Seddon JM 《Nature genetics》2007,39(10):1200-1201
The association of variants in complement factors H and B with age-related macular degeneration has led to more intense genetic and functional analysis of the complement pathway. We identify a nonsynonymous coding change in complement factor 3 that is strongly associated with risk of age-related macular degeneration in a large case-control sample. 相似文献
232.
MacArthur DG Seto JT Raftery JM Quinlan KG Huttley GA Hook JW Lemckert FA Kee AJ Edwards MR Berman Y Hardeman EC Gunning PW Easteal S Yang N North KN 《Nature genetics》2007,39(10):1261-1265
More than a billion humans worldwide are predicted to be completely deficient in the fast skeletal muscle fiber protein alpha-actinin-3 owing to homozygosity for a premature stop codon polymorphism, R577X, in the ACTN3 gene. The R577X polymorphism is associated with elite athlete status and human muscle performance, suggesting that alpha-actinin-3 deficiency influences the function of fast muscle fibers. Here we show that loss of alpha-actinin-3 expression in a knockout mouse model results in a shift in muscle metabolism toward the more efficient aerobic pathway and an increase in intrinsic endurance performance. In addition, we demonstrate that the genomic region surrounding the 577X null allele shows low levels of genetic variation and recombination in individuals of European and East Asian descent, consistent with strong, recent positive selection. We propose that the 577X allele has been positively selected in some human populations owing to its effect on skeletal muscle metabolism. 相似文献
233.
Risheg H Graham JM Clark RD Rogers RC Opitz JM Moeschler JB Peiffer AP May M Joseph SM Jones JR Stevenson RE Schwartz CE Friez MJ 《Nature genetics》2007,39(4):451-453
Opitz-Kaveggia syndrome (also known as FG syndrome) is an X-linked disorder characterized by mental retardation, relative macrocephaly, hypotonia and constipation. We report here that the original family for whom the condition is named and five other families have a recurrent mutation (2881C>T, leading to R961W) in MED12 (also called TRAP230 or HOPA), a gene located at Xq13 that functions as a thyroid receptor-associated protein in the Mediator complex. 相似文献
234.
Gout AM;ADPKD Gene Variant Consortium Ravine D Harris PC Rossetti S Peters D Breuning M Henske EP Koizumi A Inoue S Shimizu Y Thongnoppakhun W Yenchitsomanus PT Deltas C Sandford R Torra R Turco AE Jeffery S Fontes M Somlo S Furu LM Smulders YM Mercier B Ferec C Burtey S Pei Y Kalaydjieva L Bogdanova N McCluskey M Geon LJ Wouters CH Reiterova J Stekrová J San Millan JL Aguiari G Del Senno L 《Nature genetics》2007,39(4):427-428
235.
Early changes of cyclic nucleotide levels in a mitogenic reaction in the rat mesentery. 总被引:2,自引:0,他引:2
By measuring simultaneously cAMP and cGMP we found a biphasic time course with regard to cGMP and the cGMP/cAMP ratio very early in a mitogenic reaction in vivo. This is a new finding. 相似文献
236.
Information processing along the course of a visual interneuron. 总被引:1,自引:0,他引:1
Locust ocellar retinal cells are innervated by giant second order cells, 2 mm long, which show discrete zones of integration along their course, including a major zone in the axonal length of the neuron. The complex synaptic arrangements which exist between higher-order afferent and efferent cells and these second order cells along their course suggests that transmission takes place by the electrotonic spread of slow potentials. The size and accessibility of these visual interneurons offers a unique preparation for examining mechanisms of graded synaptic transmission. 相似文献
237.
Ethanol, 3 g/kg i.p., did not significantly alter the acute toxicity of amphetamine in the mouse. However, the urinary metabolite pattern was changed, suggesting that ethanol suppressed metabolism of the stimulant during the initial 6 h period. After 24 h, the mouse metabolized the same fraction of a given dose of amphetamine, whether it was given as amphetamine alone or amphetamine mixed with 2,3 or 4 g/kg ethanol. 相似文献
238.
Relation between total and exchangeable sodium in the body 总被引:1,自引:0,他引:1
239.
ATransportProtocolandItsFormalDescriptionforLocalNetworksLiLayuanWuhanTransportationUniversity,430063,P.R.China(ReceivedMay4... 相似文献
240.
In occupational therapy education in South Africa, community service (CS) focuses learning opportunities during fieldwork placements. CS therefore enabled the researcher to utilise successive small scale research projects to guide learning of students during fieldwork while simultaneously developing the occupational therapy service at a residential care facility. This community setting provided a powerful environment through which research, in combination with opportunities for reflection, contributed to nurturing skills needed by these future health professionals. A technical action research (AR) approach incorporated AR cycles and opportunities for structured reflection. Therefore situations were created for the students to embrace experiential learning. Experiential learning in the form of anticipatory reflection, reflection-in-action, reflection on reflection and retrospective reflection impacted on the quality of the students’ work. Besides encouraging unique leaning opportunities for students when engaging in research during their fieldwork placement, engagement in AR cycles simultaneously improved service delivery to residents in the facility. Key benefits of this investigation were that fieldwork education utilising AR cycles within a CS situation promoted students to identify voids in their theoretical background as well as practice skills; to apply reflective practice that could contribute to their personal and professional development; and to utilize learning opportunities optimally. Despite positive gains showed by this study, the role of power relations between the researcher as fieldwork educator and the students prohibited the AR cycles from being more emancipatory in nature and should be addressed in follow-up studies. 相似文献