全文获取类型
收费全文 | 13427篇 |
免费 | 90篇 |
国内免费 | 175篇 |
专业分类
系统科学 | 122篇 |
丛书文集 | 62篇 |
教育与普及 | 28篇 |
理论与方法论 | 55篇 |
现状及发展 | 5792篇 |
研究方法 | 626篇 |
综合类 | 6871篇 |
自然研究 | 136篇 |
出版年
2014年 | 85篇 |
2012年 | 242篇 |
2011年 | 347篇 |
2010年 | 109篇 |
2009年 | 103篇 |
2008年 | 242篇 |
2007年 | 285篇 |
2006年 | 295篇 |
2005年 | 286篇 |
2004年 | 281篇 |
2003年 | 361篇 |
2002年 | 541篇 |
2001年 | 631篇 |
2000年 | 555篇 |
1999年 | 369篇 |
1992年 | 251篇 |
1991年 | 207篇 |
1990年 | 222篇 |
1989年 | 197篇 |
1988年 | 211篇 |
1987年 | 227篇 |
1986年 | 201篇 |
1985年 | 267篇 |
1984年 | 238篇 |
1983年 | 178篇 |
1982年 | 185篇 |
1981年 | 189篇 |
1980年 | 181篇 |
1979年 | 421篇 |
1978年 | 359篇 |
1977年 | 268篇 |
1976年 | 307篇 |
1975年 | 270篇 |
1974年 | 292篇 |
1973年 | 236篇 |
1972年 | 261篇 |
1971年 | 323篇 |
1970年 | 403篇 |
1969年 | 272篇 |
1968年 | 321篇 |
1967年 | 306篇 |
1966年 | 268篇 |
1965年 | 194篇 |
1964年 | 109篇 |
1959年 | 89篇 |
1958年 | 163篇 |
1957年 | 105篇 |
1956年 | 95篇 |
1955年 | 85篇 |
1954年 | 77篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
Thyroid cancer after Chernobyl. 总被引:17,自引:0,他引:17
22.
估计两个单属性关系在连接属性上取相同值的个数的方法有两种:静态估计法和动态估计法.本文利用不精确性推理模型对这两种方法的可信度定量地进行讨论,并用具体例子进行说明. 相似文献
23.
In myelinated nerves, segregation of voltage-dependent sodium channels to nodes of Ranvier is crucial for saltatory conduction along axons. As sodium channels associate and colocalize with ankyrin at nodes of Ranvier, one possibility is that sodium channels are recruited and immobilized at axonal sites which are specified by the subaxolemmal cytoskeleton, independent of glial cell contact. Alternatively, segregation of channels at distinct sites along the axon may depend on glial cell contact. To resolve this question, we have examined the distribution of sodium channels, ankyrin and spectrin in myelination-competent cocultures of sensory neurons and Schwann cells by immunofluorescence, using sodium channel-, ankyrin- and spectrin-specific antibodies. In the absence of Schwann cells, sodium channels, ankyrin and spectrin are homogeneously distributed on sensory axons. When Schwann cells are introduced into these cultures, the distribution of sodium channels dramatically changes so that channel clusters on axons are abundant, but ankyrin and spectrin remain homogeneously distributed. Addition of latex beads or Schwann cell membranes does not induce channel clustering. Our results suggest that segregation of sodium channels on axons is highly dependent on interactions with active Schwann cells and that continuing axon-glial interactions are necessary to organize and maintain channel distribution during differentiation of myelinated axons. 相似文献
24.
Heat-shock proteins are normal constituents of cells whose synthesis is increased on exposure to various forms of stress. They are interesting because of their ubiquity and high conservation during evolution. Two families of heat-shock proteins, hsp60s and hsp70s, have been implicated in accelerating protein folding and oligomerization and also in maintaining proteins in an unfolded state, thus facilitating membrane transport. The Escherichia coli hsp70 analogue, DnaK, and two other heat-shock proteins, DnaJ and GrpE, are required for cell viability at high temperatures and are involved in DNA replication of phage lambda and plasmids P1 and F. These three proteins are involved in replication in vitro of P1 DNA along with many host replication proteins and the P1 RepA initiator protein. RepA exists in a stable protein complex with DnaJ containing a dimer each of RepA and DnaJ. We report here that DnaK and DnaJ mediate an alteration in the P1 initiator protein, rendering it much more active for oriP1 DNA binding. 相似文献
25.
K K Leong K M Yu W B Lee 《厦门大学学报(自然科学版)》2002,(Z1)
Product data management (PDM) has been accepted as an important tool for the manufacturing industries. In recent years, more and mor e researches have been conducted in the development of PDM. Their research area s include system design, integration of object-oriented technology, data distri bution, collaborative and distributed manufacturing working environment, secur ity, and web-based integration. However, there are limitations on their rese arches. In particular, they cannot cater for PDM in dis... 相似文献
26.
赵德建 《江苏技术师范学院学报》2003,9(2):65-67,74
现行《化学教学论》教材将典型教学示例放在化学教学原则之后,致使整本教材缺乏逻辑性,不符合当前创新能力培养的要求,不利于坚定师范生从事教育事业的信心,笔者认为应先讲教学示例、后授教学原则。 相似文献
27.
A. Fernández-Guasti K. Larsson C. Beyer 《Cellular and molecular life sciences : CMLS》1985,41(11):1414-1416
Summary Intracerebral infusion of (+) bicuculline methiodide, but not of its (–) isomer, in the preoptic area, stimulated masculine sexual behavior in rat as evidenced by a decrease in the number of intromissions preceding ejaculation and a shortening of the ejaculation latency and postejaculatory interval. Data suggest a role of the GABAergic system in mediating masculine sexual behavior.Acknowledgments. Authors wish to thank Ms Elisabeth Wallin for excellent technical assistance and Ms Madelene Kröning for preparing the figures. 相似文献
28.
Summary The nature of antigen Dd, an antigen present in the extracts of human dandruff which precipitates human sera selectively, and antibodies reacting with it are reported.This work was supported through U.G.C. Grant No. F.23-230/75/SR II. H.K. participated in this study, first as J.R.F. of U.G.C. and then as S.R.F. of I.C.M.R. We are grateful to Dr Baruch S. Blumberg for his invaluable suggestions and to Professor H. Walter for the gift of IgG, IgM and IgA immune sera. 相似文献
29.
30.
廖德仲 《湖南理工学院学报:自然科学版》2002,(1)
自制了一种新固体酸催化剂SO2 -4MoO3 -TiO2 ,FT -IR谱图表明 ,催化剂表面具有强酸中心 ,该催化剂对苹果酯合成的活性高 ,并得到该反应的优化条件如下 :乙酰乙酸乙酯 0 .3mol,乙二醇 0 .6mol,环己烷 30ml,催化剂 3g ,反应温度 110℃ ,反应时间 1.5h ,在此条件下 ,苹果酯产率达 90 % ,且催化剂易回收 ,具有较好的重复使用性能 相似文献