全文获取类型
收费全文 | 7363篇 |
免费 | 30篇 |
国内免费 | 68篇 |
专业分类
系统科学 | 118篇 |
丛书文集 | 250篇 |
教育与普及 | 478篇 |
理论与方法论 | 98篇 |
现状及发展 | 305篇 |
研究方法 | 691篇 |
综合类 | 5519篇 |
自然研究 | 2篇 |
出版年
2023年 | 39篇 |
2022年 | 47篇 |
2021年 | 46篇 |
2020年 | 39篇 |
2019年 | 59篇 |
2018年 | 52篇 |
2016年 | 25篇 |
2015年 | 50篇 |
2014年 | 134篇 |
2013年 | 115篇 |
2012年 | 492篇 |
2011年 | 565篇 |
2010年 | 205篇 |
2009年 | 134篇 |
2008年 | 449篇 |
2007年 | 522篇 |
2006年 | 460篇 |
2005年 | 541篇 |
2004年 | 431篇 |
2003年 | 424篇 |
2002年 | 399篇 |
2001年 | 324篇 |
2000年 | 447篇 |
1999年 | 142篇 |
1998年 | 36篇 |
1997年 | 23篇 |
1996年 | 30篇 |
1995年 | 30篇 |
1994年 | 24篇 |
1993年 | 29篇 |
1992年 | 26篇 |
1991年 | 28篇 |
1990年 | 44篇 |
1989年 | 36篇 |
1988年 | 53篇 |
1987年 | 52篇 |
1986年 | 58篇 |
1985年 | 50篇 |
1984年 | 61篇 |
1983年 | 50篇 |
1982年 | 52篇 |
1981年 | 51篇 |
1979年 | 38篇 |
1970年 | 27篇 |
1959年 | 61篇 |
1958年 | 67篇 |
1957年 | 67篇 |
1956年 | 38篇 |
1955年 | 55篇 |
1954年 | 55篇 |
排序方式: 共有7461条查询结果,搜索用时 0 毫秒
981.
在论文[10—12](注:本文的引文,下同)里,依据论文[9]里采用过的蠕变稳定的定义,通过受压柱形薄壳的例题,分析了粘弹性的解题特点。结果表明,对指定的构件就表面摄动而言,轴对称变形的稳定性范围可分成几个部分,而其中的每一部分的稳定性程度也有质的不同。 相似文献
982.
石羊河流域早全新世湖泊孢粉记录及其环境意义 总被引:22,自引:3,他引:22
三角城剖面全新世地层中85个样(分辨率为40-50年)孢粉分析显示:孢粉组合中针叶树含量高达50%以上,以云杉属、圆柏属为主,两者之和达40%-60%左右,且含量互为消长。同流域其他湖相地层也有类似现象。通过对云杉属、圆柏属生态习性、传播性能、与其他组分的数量关系及表土花粉分析,认为孢粉组合中的云杉属、圆柏属等主要成分并不指示当地的植被状况,而指示流域上游祁连山山上的植被状况;云杉属和圆柏属含量与区域有效湿度关系密切,云杉属丰值指示湿润,圆柏属丰值指示干旱。并用该模式重建了石羊河流域全新世早期的环境演化过程。 相似文献
983.
984.
Gelsolin superfamily proteins: key regulators of cellular functions 总被引:10,自引:0,他引:10
Silacci P Mazzolai L Gauci C Stergiopulos N Yin HL Hayoz D 《Cellular and molecular life sciences : CMLS》2004,61(19-20):2614-2623
Cytoskeletal rearrangement occurs in a variety of cellular processes and involves a wide spectrum of proteins. Among these, the gelsolin superfamily proteins control actin organization by severing filaments, capping filament ends and nucleating actin assembly [1]. Gelsolin is the founding member of this family, which now contains at least another six members: villin, adseverin, capG, advillin, supervillin and flightless I. In addition to their respective role in actin filament remodeling, these proteins have some specific and apparently non-overlapping particular roles in several cellular processes, including cell motility, control of apoptosis and regulation of phagocytosis (summarized in table 1). Evidence suggests that proteins belonging to the gelsolin superfamily may be involved in other processes, including gene expression regulation. This review will focus on some of the known functions of the gelsolin superfamily proteins, thus providing a basis for reflection on other possible and as yet incompletely understood roles for these proteins. 相似文献
985.
986.
Tumour evolution inferred by single-cell sequencing 总被引:1,自引:0,他引:1
Navin N Kendall J Troge J Andrews P Rodgers L McIndoo J Cook K Stepansky A Levy D Esposito D Muthuswamy L Krasnitz A McCombie WR Hicks J Wigler M 《Nature》2011,472(7341):90-94
Genomic analysis provides insights into the role of copy number variation in disease, but most methods are not designed to resolve mixed populations of cells. In tumours, where genetic heterogeneity is common, very important information may be lost that would be useful for reconstructing evolutionary history. Here we show that with flow-sorted nuclei, whole genome amplification and next generation sequencing we can accurately quantify genomic copy number within an individual nucleus. We apply single-nucleus sequencing to investigate tumour population structure and evolution in two human breast cancer cases. Analysis of 100 single cells from a polygenomic tumour revealed three distinct clonal subpopulations that probably represent sequential clonal expansions. Additional analysis of 100 single cells from a monogenomic primary tumour and its liver metastasis indicated that a single clonal expansion formed the primary tumour and seeded the metastasis. In both primary tumours, we also identified an unexpectedly abundant subpopulation of genetically diverse 'pseudodiploid' cells that do not travel to the metastatic site. In contrast to gradual models of tumour progression, our data indicate that tumours grow by punctuated clonal expansions with few persistent intermediates. 相似文献
987.
988.
989.
990.
MC Turchin CW Chiang CD Palmer S Sankararaman D Reich;Genetic Investigation of ANthropometric Traits 《Nature genetics》2012,44(9):1015-1019
Strong signatures of positive selection at newly arising genetic variants are well documented in humans, but this form of selection may not be widespread in recent human evolution. Because many human traits are highly polygenic and partly determined by common, ancient genetic variation, an alternative model for rapid genetic adaptation has been proposed: weak selection acting on many pre-existing (standing) genetic variants, or polygenic adaptation. By studying height, a classic polygenic trait, we demonstrate the first human signature of widespread selection on standing variation. We show that frequencies of alleles associated with increased height, both at known loci and genome wide, are systematically elevated in Northern Europeans compared with Southern Europeans (P < 4.3 × 10(-4)). This pattern mirrors intra-European height differences and is not confounded by ancestry or other ascertainment biases. The systematic frequency differences are consistent with the presence of widespread weak selection (selection coefficients ~10(-3)-10(-5) per allele) rather than genetic drift alone (P < 10(-15)). 相似文献