全文获取类型
收费全文 | 39085篇 |
免费 | 114篇 |
国内免费 | 143篇 |
专业分类
系统科学 | 180篇 |
丛书文集 | 691篇 |
教育与普及 | 63篇 |
理论与方法论 | 155篇 |
现状及发展 | 18017篇 |
研究方法 | 1549篇 |
综合类 | 18087篇 |
自然研究 | 600篇 |
出版年
2013年 | 260篇 |
2012年 | 529篇 |
2011年 | 1100篇 |
2010年 | 221篇 |
2008年 | 620篇 |
2007年 | 737篇 |
2006年 | 697篇 |
2005年 | 737篇 |
2004年 | 810篇 |
2003年 | 658篇 |
2002年 | 689篇 |
2001年 | 1116篇 |
2000年 | 1054篇 |
1999年 | 751篇 |
1992年 | 711篇 |
1991年 | 511篇 |
1990年 | 571篇 |
1989年 | 562篇 |
1988年 | 515篇 |
1987年 | 547篇 |
1986年 | 631篇 |
1985年 | 786篇 |
1984年 | 557篇 |
1983年 | 493篇 |
1982年 | 440篇 |
1981年 | 462篇 |
1980年 | 527篇 |
1979年 | 1240篇 |
1978年 | 1015篇 |
1977年 | 972篇 |
1976年 | 752篇 |
1975年 | 821篇 |
1974年 | 1181篇 |
1973年 | 986篇 |
1972年 | 1047篇 |
1971年 | 1171篇 |
1970年 | 1584篇 |
1969年 | 1240篇 |
1968年 | 1105篇 |
1967年 | 1171篇 |
1966年 | 1038篇 |
1965年 | 807篇 |
1964年 | 263篇 |
1959年 | 435篇 |
1958年 | 794篇 |
1957年 | 567篇 |
1956年 | 430篇 |
1955年 | 421篇 |
1954年 | 469篇 |
1948年 | 292篇 |
排序方式: 共有10000条查询结果,搜索用时 422 毫秒
921.
M. L. Mousavi Gargari R. C. Bansal K. Singh A. Mahmood 《Cellular and molecular life sciences : CMLS》1994,50(9):833-836
10 mM isatin (2,3-dioxoindole) inhibited glucose influx into human erythrocytes by over 30%. The inhibition is of the competitive type, where the affinity constant (Kt) was increased from 5.71 (control) to 11.11 mM in the presence of isatin with no change in Vmax (130 nmol/min/ml packed cells). The observed inhibition of sugar transport by isatin was not mediated through membrane–SH groups accessible to iodoacetate, iodoacetamide, DTNB, DNP or sodium arsenite. Isatin inhibited sugar transport in the presence of 2 mM harmaline, an alkaloid inhibitor of Na+, K+–ATPase activity. The inhibition was non additive which suggests that these two compounds interact with the same or a similar site on the erythrocyte membrane. 相似文献
922.
Hsp70 and aging 总被引:1,自引:0,他引:1
A. R. Heydari R. Takahashi A. Gutsmann S. You A. Richardson 《Cellular and molecular life sciences : CMLS》1994,50(11-12):1092-1098
923.
罗廷和 《武汉科技大学学报(自然科学版)》1995,(2)
还原合金化,即当炼钢或铸造过程需要进行合金化时,不用添加铁合金,而是直接添加所需合金元素的氧化物,通过还原使其合金化。研究结果表明:在等离子体条件下,30min内可以达到合锰目标值为12%~18%的还原合金化。这一新的冶炼工艺特有可能从根本上改变铁合金的生产现状. 相似文献
924.
925.
926.
927.
Calcium/calmodulin-dependent protein kinase II increases glutamate and noradrenaline release from synaptosomes 总被引:28,自引:0,他引:28
A variety of evidence indicates that calcium-dependent protein phosphorylation modulates the release of neurotransmitter from nerve terminals. For instance, the injection of rat calcium/calmodulin-dependent protein kinase II (Ca2+/CaM-dependent PK II) into the preterminal digit of the squid giant synapse leads to an increase in the release of a so-far unidentified neurotransmitter induced by presynaptic depolarization. But until now, it has not been demonstrated that Ca2+/CaM-dependent PK II can also regulate neurotransmitter release in the vertebrate nervous system. Here we report that the introduction of Ca2+/CaM-dependent PK II, autoactivated by thiophosphorylation, into rat brain synaptosomes (isolated nerve terminals) increases the initial rate of induced release of two neurotransmitters, glutamate and noradrenaline. We also show that introduction of a selective peptidergic inhibitor of Ca2+/CaM-dependent PK II inhibits the initial rate of induced glutamate release. These results support the hypothesis that activation of Ca2+/CaM-dependent PK II in the nerve terminal removes a constraint on neurotransmitter release. 相似文献
928.
R D Salter R J Benjamin P K Wesley S E Buxton T P Garrett C Clayberger A M Krensky A M Norment D R Littman P Parham 《Nature》1990,345(6270):41-46
Adhesion measurements between CD8 and 48 point mutants of HLA-A2.1 show that the CD8 alpha-chain binds to the alpha 3 domain of HLA-A2.1. Three clusters of alpha 3 residues contribute to the binding, with an exposed, negatively charged loop (residues 223-229) playing a dominant role. CD8 binding correlates with cytotoxic T-cell recognition and sensitivity to inhibition by anti-CD8 antibodies. Impaired alloreactive T-cell recognition of an HLA-A2.1 mutant with reduced affinity for CD8 is not restored by functional CD8 binding sites on an antigenically irrelevant class I molecule. Therefore, complexes of CD8 and the T-cell receptor bound to the same class I major histocompatibility complex molecule seem to be necessary for T-cell activation. 相似文献
929.
Nonlinear forecasting as a way of distinguishing chaos from measurement error in time series 总被引:49,自引:0,他引:49
An approach is presented for making short-term predictions about the trajectories of chaotic dynamical systems. The method is applied to data on measles, chickenpox, and marine phytoplankton populations, to show how apparent noise associated with deterministic chaos can be distinguished from sampling error and other sources of externally induced environmental noise. 相似文献
930.
Genetic mapping of chronic childhood-onset spinal muscular atrophy to chromosome 5q11.2-13.3 总被引:16,自引:0,他引:16
L M Brzustowicz T Lehner L H Castilla G K Penchaszadeh K C Wilhelmsen R Daniels K E Davies M Leppert F Ziter D Wood 《Nature》1990,344(6266):540-541
SPINAL muscular atrophy (SMA) describes a group of heritable degenerative diseases that selectively affect the alpha-motor neuron. Childhood-onset SMAs rank second in frequency to cystic fibrosis among autosomal recessive disorders, and are the leading cause of heritable infant mortality. Predictions that genetic heterogeneity underlies the differences between types of SMA, together with the aggressive nature of the most-severe infantile form, make linkage analysis of SMA potentially complex. We have now analysed 13 clinically heterogeneous SMA families. We find that 'chronic' childhood-onset SMA (including intermediate SMA or SMA type II, and Kugelberg-Welander or SMA type III) is genetically homogeneous, mapping to chromosomal region 5q11.2-13.3. 相似文献