全文获取类型
收费全文 | 43841篇 |
免费 | 769篇 |
国内免费 | 976篇 |
专业分类
系统科学 | 860篇 |
丛书文集 | 865篇 |
教育与普及 | 326篇 |
理论与方法论 | 187篇 |
现状及发展 | 12736篇 |
研究方法 | 1391篇 |
综合类 | 28701篇 |
自然研究 | 520篇 |
出版年
2015年 | 457篇 |
2014年 | 644篇 |
2013年 | 781篇 |
2012年 | 1139篇 |
2011年 | 1809篇 |
2010年 | 951篇 |
2009年 | 953篇 |
2008年 | 1394篇 |
2007年 | 1448篇 |
2006年 | 1310篇 |
2005年 | 1230篇 |
2004年 | 1092篇 |
2003年 | 920篇 |
2002年 | 979篇 |
2001年 | 1330篇 |
2000年 | 1226篇 |
1999年 | 1116篇 |
1998年 | 580篇 |
1997年 | 567篇 |
1996年 | 571篇 |
1995年 | 555篇 |
1994年 | 504篇 |
1993年 | 445篇 |
1992年 | 800篇 |
1991年 | 699篇 |
1990年 | 700篇 |
1989年 | 631篇 |
1988年 | 622篇 |
1987年 | 589篇 |
1986年 | 507篇 |
1985年 | 607篇 |
1984年 | 466篇 |
1980年 | 401篇 |
1979年 | 899篇 |
1978年 | 693篇 |
1977年 | 678篇 |
1976年 | 552篇 |
1975年 | 625篇 |
1974年 | 836篇 |
1973年 | 752篇 |
1972年 | 756篇 |
1971年 | 882篇 |
1970年 | 1160篇 |
1969年 | 860篇 |
1968年 | 793篇 |
1967年 | 862篇 |
1966年 | 727篇 |
1965年 | 516篇 |
1958年 | 533篇 |
1957年 | 376篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
C. Ambrogi Lorenzini C. Bucherelli A. Giachetti G. Tassoni 《Cellular and molecular life sciences : CMLS》1991,47(10):1019-1026
Several aspects of spontaneous and conditioned behavior (food and water intake, locomotion and emotionality, passive and active avoidance acquisition and retention) of standard (albino and pigmented) rats, and rats heterozygous (HEDI) and homozygous (HODI) for diabetes insipidus, are reviewed. As would be expected, HODI rats have been repeatedly found to consume far more fluid than either HEDI or control rats. Pigmented rats appear to be more active than albinos. HODI rats exhibit less marked emotional responses than do control rats, among which the pigmented ones exhibit the highest emotionality. Light aversion is more evident in albino than in pigmented rats. No differences are found among HEDI, HODI and normal Long Evans rats. It is quite difficult to provide a clear-cut statement concerning inter-strain differences in passive avoidance behavior, possibly because of the variety of techniques employed. In any case, HODI rats do not perform worse than normal controls do. In one-way active avoidance paradigms, pigmented rats perform better than albinos, and the performance of HODI rats does not differ from that of controls. In two-way avoidance paradigms, albinos appear to outperform pigmented rats. Once again, there are no obvious differences between HODI and control animals.In addition to indicating that HODI rats may actually be less emotional than the other groups of rats reviewed here, the studies described once again fail to confirm the previously alleged functions of vasopressin in memory consolidation. 相似文献
52.
53.
54.
1 .INTRODUCTIONDuetotheireconomicsignificanceandclosenesstopersons,productionsystemsmustbemodeledbeforetheirimplementationanduse,thus,amethodwhichspecifies ,analyzesandsynthesizestheproductionsys tems—discreteeventsystems (DES)hasbeenestab lishedanddevelopedstepbystepinrecentyears.DESmethodspecifiestheplantbasedonitsdiscretecharacters,however,intherealworld ,therearefewplantsthatcanbemodeledbypurelydiscretemathe maticalmodelbecausetherearealwayssomecontinu ousparametersforstudyinnearlya… 相似文献
55.
The genetic engineering of production traits in domestic animals 总被引:1,自引:0,他引:1
56.
金属间化合物Ni3Al中的硼晶界偏聚特性的AES研究 总被引:1,自引:0,他引:1
本文应用俄歇能谱仪研究了不同化学计量比NiAl金属间化合物硼在晶界偏聚的特性。研究结果表明:硼在Ni3Al的各个晶界偏聚存在着不均匀性,硼在晶界的偏聚范围只有几个原子层,晶界结构及晶界化学环境是影响在晶界偏聚的决定因素。 相似文献
57.
Aeromonas caviae isolated from stools of diarrheic formula-fed infants and environmental sources produce acetic acid when grown in glucose broth, which is bactericidal (suicide phenomenon). A. caviae grows anaerobically in a minimal medium or under permissive conditions such as the intestinal tract of formula-fed infants. These isolates adhered to HEp-2 cells and produced a cytotoxic and a cytotonic enterotoxin which underscore their enteropathogenicity. 相似文献
58.
Low-molecular-weight GTP-binding proteins are strong candidates for regulators of membrane traffic. In yeast, mutations in the sec4 or ypt1 genes encoding small GTP-binding proteins inhibit constitutive membrane flow at the plasma membrane or Golgi complex, respectively. It has been suggested that membrane fusion-fission events are regulated by cycling of small GTP-binding proteins between a membrane-bound and free state, but although most of these small proteins are found in both soluble and tightly membrane-bound forms, there is no direct evidence to support such cycling. In rat brain a small GTP-binding protein, rab3A, is exclusively associated with synaptic vesicles, the secretory organelles of nerve terminals. Here we use isolated nerve terminals to study the fate of rab3A during synaptic vesicle exocytosis. We find that rab3A dissociates quantitatively from the vesicle membrane after Ca2(+)-dependent exocytosis and that this dissociation is partially reversible during recovery after stimulation. These results are direct evidence for an association-dissociation cycle of a small GTP-binding protein during traffic of its host membrane. 相似文献
59.
张临 《科技情报开发与经济》2004,14(7):302-303
摘要:阐述了焦炭整粒在高炉冶炼中的必要性和重要性。针对临钢双齿辊切焦机的缺点进行了改造,研制出了CQD-80型齿圈式切焦机,介绍了CQD-80型齿圈式切焦机设备构造及改进,CQD-80型切焦机使用情况说明,其性能安全可靠,效果显著。 相似文献
60.
M E MacDonald A Novelletto C Lin D Tagle G Barnes G Bates S Taylor B Allitto M Altherr R Myers 《Nature genetics》1992,1(2):99-103
Analysis of 78 Huntington's disease (HD) chromosomes with multi-allele markers revealed 26 different haplotypes, suggesting a variety of independent HD mutations. The most frequent haplotype, accounting for about one third of disease chromosomes, suggests that the disease gene is between D4S182 and D4S180. However, the paucity of an expected class of chromosomes that can be related to this major haplotype by assuming single crossovers may reflect the operation of other mechanisms in creating haplotype diversity. Some of these mechanisms sustain alternative scenarios that do not require a multiple mutational origin for HD and/or its positioning between D4S182 and D4S180. 相似文献