全文获取类型
收费全文 | 21356篇 |
免费 | 1790篇 |
国内免费 | 7656篇 |
专业分类
化学 | 25402篇 |
晶体学 | 462篇 |
力学 | 505篇 |
综合类 | 220篇 |
数学 | 1678篇 |
物理学 | 2535篇 |
出版年
2024年 | 18篇 |
2023年 | 256篇 |
2022年 | 347篇 |
2021年 | 588篇 |
2020年 | 726篇 |
2019年 | 697篇 |
2018年 | 672篇 |
2017年 | 747篇 |
2016年 | 787篇 |
2015年 | 701篇 |
2014年 | 1080篇 |
2013年 | 1670篇 |
2012年 | 1929篇 |
2011年 | 1338篇 |
2010年 | 1118篇 |
2009年 | 1308篇 |
2008年 | 1553篇 |
2007年 | 1640篇 |
2006年 | 1494篇 |
2005年 | 1455篇 |
2004年 | 1426篇 |
2003年 | 1148篇 |
2002年 | 974篇 |
2001年 | 851篇 |
2000年 | 852篇 |
1999年 | 755篇 |
1998年 | 665篇 |
1997年 | 629篇 |
1996年 | 496篇 |
1995年 | 530篇 |
1994年 | 465篇 |
1993年 | 402篇 |
1992年 | 375篇 |
1991年 | 266篇 |
1990年 | 222篇 |
1989年 | 159篇 |
1988年 | 115篇 |
1987年 | 81篇 |
1986年 | 74篇 |
1985年 | 56篇 |
1984年 | 38篇 |
1983年 | 22篇 |
1982年 | 25篇 |
1981年 | 13篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1959年 | 2篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 162 毫秒
61.
The association of complex formation with static quenching in CT systems was investigated. Evaluation of the data made evident
that the inner filter effect must be allowed for. Time-resolved and temperature-dependent stationary measurements of fluorescence
led to the separation of dynamic and static quenching components. The static quenching constant is discussed with respect
to the equilibrium constant of complex formation determined by absorption spectroscopy. 相似文献
62.
63.
Maria Marques Zhengtian Yu Marvin D. Rausch James C. W. Chien 《Journal of polymer science. Part A, Polymer chemistry》1995,33(16):2787-2793
4-Vinylcyclohexene (VCH) and cyclooctadiene (COD) were investigated as termonomers in EPDM (ethylene/propylene/diene) synthesis by using rac-ethylenebis (1-η5-indenyl) zir-conium dichloride ( 1 ) as a catalyst precursor. Homopolymerizations of VCH, vinylcycloh-exane and cyclohexene were compared. The parameter Kπκp, which is the apparent rate constant for Ziegler-Natta polymerization, is about the same for VCH and vinylcyclohexanebut is 10 times smaller for cyclohexene. Therefore, the linear olefinic double bond is more active than the cyclic internal double bond. VCH reduces ethylene polymerization rate but not propylene polymerization rate in copolymerizations. In terpolymerizations, VCH tends to suppress ethylene incorporation especially at elevated polymerization temperature and Lowers the polymer MW by about two-fold. COD has very low activity as a termonomer. © 1995 John Wiley & Sons, Inc. 相似文献
64.
Daniele Cauzzi Roberto Giordano Enrico Sappa Antonio Tiripicchio Marisa Tiripicchio Camellini 《Journal of Cluster Science》1993,4(3):279-296
The title complex (complex1) was the first alkyne-substituted triruthenium dihydrido cluster to be reported and was characterized by spectroscopy as a triangular cluster with the alkyne parallel to a Ru-Ru edge. Recently, we have found that1 is a key intermediate in the homogeneous hydrogenation of diphenylacetylene catalyzed by tetrahedral Ru4 and FeRu3 clusters. Since the discovery of1, a great number of complexes with alkynes parallel to a cluster edge have been reported; at present this is the more common bonding mode for alkynes on trinuclear clusters. The structural features of1 allow a comparison with those of other ruthenium-containing derivatives and help to draw suggestions of the role of1 in hydrogenation catalysis. 相似文献
65.
66.
67.
68.
王胜奎 《数学的实践与认识》2006,36(5):5-10
根据松纵坑切梢小蠹的主要生物学特征,通过分析抚育间伐持续控制松纵坑切梢小蠹虫害的机理,应用复杂适应系统(CA S)理论,建立了模拟松纵坑切梢小蠹虫害的一种动态演化数学模型,并讨论了模型的收敛性.然后选用昆明小哨林场为背景,进行了各种抚育间伐决策的仿真,从中优选抚育间伐决策.结果表明:模拟优化方案与实际调查统计分析结果一致:均为弱度间伐与中弱度间伐控制蠹害效果最好.最后通过森林积材量与虫害程度之间的优化,给出了抚育间伐的优化策略. 相似文献
69.
GAO Xing-Ru 《理论物理通讯》2006,46(11)
In this paper, we propose a modified traffic model in which a single car moves through a sequence of traffic lights controlled by a step function instead of a sine function. In contrast to the previous work [Phys. Rev. E 70 (2004)016107], we have investigated in detail the dependence of the behavior on four parameters, ω, α, η, and a1, and given three kinds of bifurcation diagrams, which show three kinds of complex behaviors. We have found that in this model there are chaotic and complex periodic motions, as well as special singularities. We have also analyzed the characteristic of the complex period motion and the essential feature of the singularity. 相似文献
70.
Yong LU Hong WANG Ye LIU Ming Yuan HE 《中国化学快报》2006,17(10):1397-1400
Recently, miniature H2 generator to power fuel cells for portable/micro electronic devices and passenger propulsion has been the focus of intense research activities1-3. One of the strategies is to find simple CO-free H2 production with novel microreactor… 相似文献