全文获取类型
收费全文 | 41990篇 |
免费 | 68篇 |
国内免费 | 121篇 |
专业分类
系统科学 | 254篇 |
丛书文集 | 919篇 |
教育与普及 | 112篇 |
理论与方法论 | 246篇 |
现状及发展 | 18388篇 |
研究方法 | 1703篇 |
综合类 | 19961篇 |
自然研究 | 596篇 |
出版年
2013年 | 264篇 |
2012年 | 591篇 |
2011年 | 1215篇 |
2010年 | 245篇 |
2008年 | 737篇 |
2007年 | 768篇 |
2006年 | 801篇 |
2005年 | 806篇 |
2004年 | 780篇 |
2003年 | 765篇 |
2002年 | 760篇 |
2001年 | 1256篇 |
2000年 | 1154篇 |
1999年 | 795篇 |
1992年 | 741篇 |
1991年 | 600篇 |
1990年 | 644篇 |
1989年 | 616篇 |
1988年 | 619篇 |
1987年 | 656篇 |
1986年 | 643篇 |
1985年 | 785篇 |
1984年 | 654篇 |
1983年 | 538篇 |
1982年 | 469篇 |
1981年 | 451篇 |
1980年 | 589篇 |
1979年 | 1324篇 |
1978年 | 1107篇 |
1977年 | 1118篇 |
1976年 | 795篇 |
1975年 | 857篇 |
1974年 | 1251篇 |
1973年 | 1066篇 |
1972年 | 1091篇 |
1971年 | 1330篇 |
1970年 | 1744篇 |
1969年 | 1278篇 |
1968年 | 1219篇 |
1967年 | 1315篇 |
1966年 | 1101篇 |
1965年 | 797篇 |
1964年 | 200篇 |
1959年 | 471篇 |
1958年 | 707篇 |
1957年 | 592篇 |
1956年 | 501篇 |
1955年 | 419篇 |
1954年 | 484篇 |
1948年 | 301篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
41.
S. J. Leybourne 《Journal of forecasting》1993,12(1):49-62
A linear regression model with random walk coefficients is extended to allow for linear restrictions between the coefficients to be satisfied at each point in time. Estimation in this model is shown to be no more involved than estimation in the standard model. It is also demonstrated how, after a slight modification to the testing problem, classical test procedures may be applied to the problem of testing for such restrictions. The performance of the Lagrange Multiplier test for a variety of different restrictions is then investigated via simulation. An empirical application involving testing for homogeneity in a random walk coefficient version of the AIDS model is given. 相似文献
42.
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
43.
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
44.
本文根据浙江省教委、省基金、舟山市科委关于浙江沿海虾蛄生物学及其开发利用研究的要求,对四年多来的研究进行总结,主要包括资源与分布、生物学习性、暂养及运输技术、营养成份分析、开发利用等诸方面 相似文献
45.
Thyroid cancer after Chernobyl. 总被引:17,自引:0,他引:17
46.
47.
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
48.
Itknownthatsmallamountsoffluxonthesurfaceofstainlesssteelcanincreasethedepthofweldpene trationinTIGweldingbyafactorofthree[1] .Thisprocessisreferredtoas”ATIG”orTIGweldingacti vatedbyflux .Therehavebeenthreepublishedphys icalmechanismsthatarepossiblecontri… 相似文献
49.
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
50.
Rui M Costa Nikolai B Federov Jeff H Kogan Geoffrey G Murphy Joel Stern Masuo Ohno Raju Kucherlapati Tyler Jacks Alcino J Silva 《Nature》2002,415(6871):526-530
Neurofibromatosis type I (NF1) is one of the most common single-gene disorders that causes learning deficits in humans. Mice carrying a heterozygous null mutation of the Nfl gene (Nfl(+/-) show important features of the learning deficits associated with NF1 (ref. 2). Although neurofibromin has several known properties and functions, including Ras GTPase-activating protein activity, adenylyl cyclase modulation and microtubule binding, it is unclear which of these are essential for learning in mice and humans. Here we show that the learning deficits of Nf1(+/-) mice can be rescued by genetic and pharmacological manipulations that decrease Ras function. We also show that the Nf1(+/-) mice have increased GABA (gamma-amino butyric acid)-mediated inhibition and specific deficits in long-term potentiation, both of which can be reversed by decreasing Ras function. Our results indicate that the learning deficits associated with NF1 may be caused by excessive Ras activity, which leads to impairments in long-term potentiation caused by increased GABA-mediated inhibition. Our findings have implications for the development of treatments for learning deficits associated with NF1. 相似文献