全文获取类型
收费全文 | 55808篇 |
免费 | 598篇 |
国内免费 | 647篇 |
专业分类
系统科学 | 619篇 |
丛书文集 | 1092篇 |
教育与普及 | 440篇 |
理论与方法论 | 279篇 |
现状及发展 | 19374篇 |
研究方法 | 1707篇 |
综合类 | 33012篇 |
自然研究 | 530篇 |
出版年
2013年 | 591篇 |
2012年 | 963篇 |
2011年 | 1557篇 |
2010年 | 651篇 |
2009年 | 637篇 |
2008年 | 1266篇 |
2007年 | 1262篇 |
2006年 | 1182篇 |
2005年 | 1274篇 |
2004年 | 1111篇 |
2003年 | 1103篇 |
2002年 | 1115篇 |
2001年 | 1766篇 |
2000年 | 1613篇 |
1999年 | 1554篇 |
1998年 | 808篇 |
1997年 | 857篇 |
1996年 | 793篇 |
1995年 | 689篇 |
1994年 | 839篇 |
1993年 | 604篇 |
1992年 | 1170篇 |
1991年 | 1004篇 |
1990年 | 953篇 |
1989年 | 995篇 |
1988年 | 910篇 |
1987年 | 866篇 |
1986年 | 768篇 |
1985年 | 883篇 |
1984年 | 679篇 |
1983年 | 576篇 |
1982年 | 527篇 |
1980年 | 603篇 |
1979年 | 1398篇 |
1978年 | 1180篇 |
1977年 | 1114篇 |
1976年 | 836篇 |
1975年 | 909篇 |
1974年 | 1246篇 |
1973年 | 1075篇 |
1972年 | 1072篇 |
1971年 | 1332篇 |
1970年 | 1756篇 |
1969年 | 1332篇 |
1968年 | 1285篇 |
1967年 | 1278篇 |
1966年 | 1126篇 |
1965年 | 820篇 |
1958年 | 729篇 |
1957年 | 565篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
DNA fingerprinting transforms the art of cell authentication. 总被引:4,自引:0,他引:4
The increasing diversity of new cell cultures is seriously stretching the capabilities of traditional methods of identification. DNA fingerprinting is set to play an important role in increasing confidence in the authenticity of cultures in research and industry. 相似文献
92.
We recently reported on a linkage study within a Quarter Horse lineage segregating hyperkalaemic periodic paralysis (HYPP), an autosomal dominant condition showing potassium-induced attacks of skeletal muscle paralysis. HYPP co-segregated with the equine adult skeletal muscle sodium channel alpha subunit gene, the same gene that causes human HYPP. We now describe the Phe to Leu mutation in transmembrane domain IVS3 which courses the horse disease. This represents the first application of molecular genetics to an important horse disease, and the data will provide an opportunity for control or eradication of this condition. 相似文献
93.
估计两个单属性关系在连接属性上取相同值的个数的方法有两种:静态估计法和动态估计法.本文利用不精确性推理模型对这两种方法的可信度定量地进行讨论,并用具体例子进行说明. 相似文献
94.
95.
Targeted disruption of the mouse transforming growth factor-beta 1 gene results in multifocal inflammatory disease. 总被引:149,自引:0,他引:149
M M Shull I Ormsby A B Kier S Pawlowski R J Diebold M Yin R Allen C Sidman G Proetzel D Calvin 《Nature》1992,359(6397):693-699
Transforming growth factor-beta 1 (TGF-beta 1) is a multifunctional growth factor that has profound regulatory effects on many developmental and physiological processes. Disruption of the TGF-beta 1 gene by homologous recombination in murine embryonic stem cells enables mice to be generated that carry the disrupted allele. Animals homozygous for the mutated TGF-beta 1 allele show no gross developmental abnormalities, but about 20 days after birth they succumb to a wasting syndrome accompanied by a multifocal, mixed inflammatory cell response and tissue necrosis, leading to organ failure and death. TGF-beta 1-deficient mice may be valuable models for human immune and inflammatory disorders, including autoimmune diseases, transplant rejection and graft versus host reactions. 相似文献
96.
Short alanine peptides, containing 16 or 17 residues, appear to form alpha-helices in aqueous solution. But the main spectroscopic analyses used on helical peptides (circular dichroism and nuclear magnetic resonance) cannot distinguish between an alpha-helix (in which the ith residue is hydrogen-bonded to residue i + 4; ref. 9) and the next most common peptide helix, the 3(10)-helix10 (i-->i + 3 hydrogen-bonding). To address this problem we have designed single and doubly spin-labelled analogues of alanine-based peptides in which the nitroxide spin label forms an unbranched side chain extending from the sulphur atom of a cysteine residue. Here we report the circular dichroism, Fourier-transform infrared and electron-spin resonance spectra of these peptides under helix-forming conditions. The infrared absorbance gives an amide I' band with a frequency that is substantially different from that observed for alpha-helices. The electron-spin resonance spectra of doubly labelled helices show that the ranking of distances between side chains, around a single turn (residues 4-8), is inconsistent with an alpha-helical structure. Our experiments suggest that the more likely peptide geometry is a 3(10)-helix. 相似文献
97.
本文在系统阐述当代跨国经营战略调整与发展趋势的基础上,简要剖析了现阶段我国企业跨国经营的主要问题,重点探讨了我国跨国企业发展战略的基本构想。 相似文献
98.
韭菜凝集素的纯化及部分性质的研究 总被引:7,自引:0,他引:7
用葡聚糖凝胶柱层析法从韭菜的叶片组织分离出一种对新鲜兔红细胞有强烈凝集作用的凝集素,PAGE鉴定和高碘酸-Schiff试剂反应均显单一条带。SDS-PAGE分析表明该凝集素含有3个亚基,其相对分子质量分别约为31000、24000和21000。韭菜凝集素具有一定的热稳定性,在酸、碱处理中该凝集素对碱处理较酸处理稳定,氨基酸组成分析表明韭菜凝集素含有14种氨基酸,其中半胱氨酸含量较高。 相似文献
99.
Itknownthatsmallamountsoffluxonthesurfaceofstainlesssteelcanincreasethedepthofweldpene trationinTIGweldingbyafactorofthree[1] .Thisprocessisreferredtoas”ATIG”orTIGweldingacti vatedbyflux .Therehavebeenthreepublishedphys icalmechanismsthatarepossiblecontri… 相似文献
100.
Ana Cuesta Laia Pedrola Teresa Sevilla Javier García-Planells María José Chumillas Fernando Mayordomo Eric LeGuern Ignacio Marín Juan J Vílchez Francesc Palau 《Nature genetics》2002,30(1):22-25
We identified three distinct mutations and six mutant alleles in GDAP1 in three families with axonal Charcot-Marie-Tooth (CMT) neuropathy and vocal cord paresis, which were previously linked to the CMT4A locus on chromosome 8q21.1. These results establish the molecular etiology of CMT4A (MIM 214400) and suggest that it may be associated with both axonal and demyelinating phenotypes. 相似文献