全文获取类型
收费全文 | 32591篇 |
免费 | 55篇 |
国内免费 | 101篇 |
专业分类
系统科学 | 188篇 |
丛书文集 | 731篇 |
教育与普及 | 82篇 |
理论与方法论 | 242篇 |
现状及发展 | 14037篇 |
研究方法 | 1416篇 |
综合类 | 15641篇 |
自然研究 | 410篇 |
出版年
2013年 | 208篇 |
2012年 | 450篇 |
2011年 | 893篇 |
2010年 | 198篇 |
2008年 | 574篇 |
2007年 | 573篇 |
2006年 | 631篇 |
2005年 | 627篇 |
2004年 | 556篇 |
2003年 | 642篇 |
2002年 | 672篇 |
2001年 | 1102篇 |
2000年 | 964篇 |
1999年 | 638篇 |
1992年 | 578篇 |
1991年 | 465篇 |
1990年 | 499篇 |
1989年 | 498篇 |
1988年 | 496篇 |
1987年 | 511篇 |
1986年 | 495篇 |
1985年 | 607篇 |
1984年 | 503篇 |
1983年 | 409篇 |
1982年 | 353篇 |
1981年 | 347篇 |
1980年 | 460篇 |
1979年 | 992篇 |
1978年 | 870篇 |
1977年 | 868篇 |
1976年 | 600篇 |
1975年 | 654篇 |
1974年 | 949篇 |
1973年 | 808篇 |
1972年 | 828篇 |
1971年 | 1045篇 |
1970年 | 1349篇 |
1969年 | 1018篇 |
1968年 | 960篇 |
1967年 | 1008篇 |
1966年 | 852篇 |
1965年 | 627篇 |
1964年 | 150篇 |
1959年 | 362篇 |
1958年 | 529篇 |
1957年 | 449篇 |
1956年 | 368篇 |
1955年 | 319篇 |
1954年 | 369篇 |
1948年 | 197篇 |
排序方式: 共有10000条查询结果,搜索用时 804 毫秒
941.
人类学在聚焦世界各地人们的生活及其方式的过程中,一直致力于成为一门客观性的科学。最近,女性人类学者们的一些活动则为表达主观观点,传达个人情感及检验人类学者和研究群体间的关系开辟了道路。这篇文章审视了我个人一生对中国的美好情感,而我的这种情感于 2000 年参加在北京举行的IUAES(国际人类学民族学联合会中期会议)时达到高潮。 相似文献
942.
Microbial starch-binding domains (SBD) and granule-bound starch synthase I (GBSSI) are proteins which are accumulated in potato starch granules. The efficiency of SBD and GBSSI for targeting active luciferase reporter proteins to granules during starch biosynthesis was compared. GBSSI or SBD sequences were fused to the N- or C-terminus of the luciferase (LUC) gene, via an artificial Pro-Thr encoding linker sequence. The genes were introduced into an amylose-free (amf) potato mutant. It appeared that SBD was superior to GBSSI as a targeting sequence, mainly because the luciferase retained higher activity in the SBD-containing fusion proteins than in the GBSSI-containing ones. 相似文献
943.
新疆西天山西段位于哈萨克斯坦 -伊犁板块的东南部边缘 ,包括伊犁石炭纪裂谷、那拉提地块、哈尔克早古生代被动陆缘褶皱带。主要已知矿床 (点 )按其容矿围岩可分为镁铁 -超镁铁岩型、斑岩型、花岗岩型、矽卡岩型、陆相火山岩型、陆相沉积岩型、浅变质含碳碎屑岩型。根据区内成矿地质条件、矿化特征 ,区内以找金矿主 ,兼顾铜镍矿等。金矿以穆龙套型和火山岩型金矿为主 ,同时注意卡林型和中 -酸性侵入岩内外接触带型 ;铜矿以镁铁 -超镁铁岩型和火山岩型为主。地质与成矿条件与中亚成矿域具有可比性 ,因此 ,新疆西天山西段金铜成矿带应为中亚成矿域东延部分 相似文献
944.
945.
Mark de Rooij 《Journal of Classification》2002,19(1):161-178
p similarity function, the L
p
-transform and the Minkowski-p distance. For triadic distance models defined by the L
p
-transform we will prove that they do not model three-way association. Moreover, triadic distance models defined by the L
p
-transform are restricted multiple dyadic distances, where each dyadic distance is defined for a two-way margin of the three-way
table. Distance models for three-way two-mode data, called three-way distance models, do succeed in modeling three-way association. 相似文献
946.
We have developed technologies that simplify genomic library construction and screening, substantially reducing both the time and the cost associated with traditional library screening methods and facilitating the generation of gene-targeting constructs. By taking advantage of homologous recombination in Escherichia coli, we were able to use as little as 80 bp of total sequence homology to screen for a specific gene from a genomic library in plasmid or phage form. This method, called recombination cloning (REC), takes only a few days instead of the several weeks required for traditional plaque-lift methods. In addition, because every clone in the mouse genomic library we have constructed has a negative selection marker adjacent to the genomic insert, REC screening can generate gene-targeting vectors in one step, from library screening to finished construct. Conditional targeting constructs can be generated easily with minimal additional manipulation. 相似文献
947.
The extent of linkage disequilibrium in Arabidopsis thaliana. 总被引:20,自引:0,他引:20
Magnus Nordborg Justin O Borevitz Joy Bergelson Charles C Berry Joanne Chory Jenny Hagenblad Martin Kreitman Julin N Maloof Tina Noyes Peter J Oefner Eli A Stahl Detlef Weigel 《Nature genetics》2002,30(2):190-193
Linkage disequilibrium (LD), the nonrandom occurrence of alleles in haplotypes, has long been of interest to population geneticists. Recently, the rapidly increasing availability of genomic polymorphism data has fueled interest in LD as a tool for fine-scale mapping, in particular for human disease loci. The chromosomal extent of LD is crucial in this context, because it determines how dense a map must be for associations to be detected and, conversely, limits how finely loci may be mapped. Arabidopsis thaliana is expected to harbor unusually extensive LD because of its high degree of selfing. Several polymorphism studies have found very strong LD within individual loci, but also evidence of some recombination. Here we investigate the pattern of LD on a genomic scale and show that in global samples, LD decays within approximately 1 cM, or 250 kb. We also show that LD in local populations may be much stronger than that of global populations, presumably as a result of founder events. The combination of a relatively high level of polymorphism and extensive haplotype structure bodes well for developing a genome-wide LD map in A. thaliana. 相似文献
948.
949.
利用Buch的方法构造出了一类处处连续,但处处不可微函数,该函数是Buch所构造出的函数的推广,并对该函数图像的盒(Bouligand)维数进行了估计,得出了Buch函数的盒维数只是其中的一种特殊情况. 相似文献
950.
微量Mg对纯Ag的性能影响 总被引:1,自引:0,他引:1
在99.995%Ag中添加8×10-5Mg制成99.99%纯Ag,进行机械性能测试试验.当ε=98%时,在25℃下保存200d,其强度和硬度稳定不变.即在99.995%的高纯Ag中存在有微量镁,使Ag在结晶过程中出现少量Ag溶Mg的固溶体颗粒,细化Ag的晶粒,晶界增多,变形抗力增大.起到强化和稳定机械性能的作用. 相似文献