全文获取类型
收费全文 | 32983篇 |
免费 | 83篇 |
国内免费 | 91篇 |
专业分类
系统科学 | 368篇 |
丛书文集 | 662篇 |
教育与普及 | 64篇 |
理论与方法论 | 164篇 |
现状及发展 | 15930篇 |
研究方法 | 1300篇 |
综合类 | 14309篇 |
自然研究 | 360篇 |
出版年
2012年 | 435篇 |
2011年 | 839篇 |
2010年 | 210篇 |
2009年 | 169篇 |
2008年 | 521篇 |
2007年 | 588篇 |
2006年 | 579篇 |
2005年 | 589篇 |
2004年 | 664篇 |
2003年 | 572篇 |
2002年 | 523篇 |
2001年 | 925篇 |
2000年 | 921篇 |
1999年 | 573篇 |
1992年 | 541篇 |
1991年 | 433篇 |
1990年 | 504篇 |
1989年 | 467篇 |
1988年 | 417篇 |
1987年 | 459篇 |
1986年 | 494篇 |
1985年 | 612篇 |
1984年 | 442篇 |
1983年 | 393篇 |
1982年 | 382篇 |
1981年 | 422篇 |
1980年 | 457篇 |
1979年 | 1085篇 |
1978年 | 887篇 |
1977年 | 874篇 |
1976年 | 656篇 |
1975年 | 734篇 |
1974年 | 1095篇 |
1973年 | 889篇 |
1972年 | 872篇 |
1971年 | 1039篇 |
1970年 | 1300篇 |
1969年 | 1092篇 |
1968年 | 1008篇 |
1967年 | 1034篇 |
1966年 | 879篇 |
1965年 | 681篇 |
1964年 | 210篇 |
1959年 | 375篇 |
1958年 | 584篇 |
1957年 | 418篇 |
1956年 | 350篇 |
1955年 | 352篇 |
1954年 | 346篇 |
1948年 | 212篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
孙智宏 《淮阴师范学院学报(自然科学版)》2002,1(1):13-15
设{Bn}为Bernoulli数,m、n为自然数,本文证明了同余式(2-22n)B2n≡1-4n ∑mk=1(2n)/(2k)24kB2k (mod 24m 3)与(3-32n)B2n≡2-6n 2∑mk=1(2n)/(2k)32kB2k (mod 32m 1).取m=1,2,得到[5]中宣布的(2-22n)B2n(mod 27)与(3-32n)B2n(mod 35)的简单同余式. 相似文献
32.
33.
Gösta Lindeberg 《Cellular and molecular life sciences : CMLS》1948,4(12):476-477
Zusammenfassung Es wurde die Zugkraft nasser Flachsfasern nach Behandlung mit verschiedenen Chemikalien geprüft. Es wurde gefunden, daß die Mittellamelle der Flachsfaser verschiedene miteinander verbundene Systeme enthält, nämlich Pektin, Lignin und eine im Oxalat unlös iche alkaliempfindliche Komponente. 相似文献
34.
煤矸石空心砖是一种新型环保墙体材料,符合国家及山西省出台的限制生产和使用实心黏土砖,鼓励发展新型建筑材料的政策。利用煤矸石制造的空心砖可以作为保温材料,既可节约建筑能耗,又可节约土地资源,减少环境污染。煤矸石空心砖同黏土实心砖相比,具有高强、轻质、隔音、隔热、保温、防震等优点,市场前景良好。 相似文献
35.
36.
Growth hormone signal transduction 总被引:1,自引:0,他引:1
Growth hormone (GH) promotes animal growth by stimulating bone and cartilage cell proliferation, and influences carbohydrate and lipid metabolism. Some of these effects are brought about indirectly via somatomedin induction in hepatocytes, others by acting directly on the target cells. In either case, GH first binds to specific receptors on cells to trigger a sequence of biochemical events culminating in a biological response. Recently much has been learnt about the molecular structure of GH receptor, its binding to ligand, and the ensuing signal transduction events. 相似文献
37.
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
38.
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
39.
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
40.
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