全文获取类型
收费全文 | 19024篇 |
免费 | 3559篇 |
国内免费 | 2610篇 |
专业分类
化学 | 11169篇 |
晶体学 | 602篇 |
力学 | 1431篇 |
综合类 | 214篇 |
数学 | 683篇 |
物理学 | 11094篇 |
出版年
2024年 | 40篇 |
2023年 | 151篇 |
2022年 | 405篇 |
2021年 | 538篇 |
2020年 | 565篇 |
2019年 | 556篇 |
2018年 | 580篇 |
2017年 | 684篇 |
2016年 | 852篇 |
2015年 | 712篇 |
2014年 | 890篇 |
2013年 | 2060篇 |
2012年 | 1227篇 |
2011年 | 1259篇 |
2010年 | 1067篇 |
2009年 | 1226篇 |
2008年 | 1175篇 |
2007年 | 1192篇 |
2006年 | 1138篇 |
2005年 | 1044篇 |
2004年 | 939篇 |
2003年 | 879篇 |
2002年 | 748篇 |
2001年 | 601篇 |
2000年 | 658篇 |
1999年 | 571篇 |
1998年 | 431篇 |
1997年 | 378篇 |
1996年 | 376篇 |
1995年 | 280篇 |
1994年 | 289篇 |
1993年 | 268篇 |
1992年 | 237篇 |
1991年 | 168篇 |
1990年 | 142篇 |
1989年 | 131篇 |
1988年 | 138篇 |
1987年 | 82篇 |
1986年 | 87篇 |
1985年 | 63篇 |
1984年 | 61篇 |
1983年 | 22篇 |
1982年 | 55篇 |
1981年 | 45篇 |
1980年 | 29篇 |
1979年 | 35篇 |
1978年 | 24篇 |
1977年 | 19篇 |
1976年 | 14篇 |
1973年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
XiaoMinSUN DaChengFENG ZhengTingCAI 《中国化学快报》2004,15(6):749-752
For the Na I2 collision system, theoretical study is performed on the QCISD(T) level by using ab initio method. The ab initio potential energy surfaces are got and on them the long-lived complexes are found and optimized. These results verify the crossed molecule beam experimental phenomenon and the detailed geometry structures are given for the first time. The role of the complexes in the reaction path is also described in detail. 相似文献
63.
K. S. Birdi 《Colloid and polymer science》1997,275(6):561-566
The surface tension versus temperature data of homologous series of n-alkanes and n-alkenes is analyzed. Critical temperatures are shown to be predicted from these data, with a very high precision, after some
corrections are made. The corrections are shown to arise from the effect of the critical pressure on the extrapolated data
to surface tension approaching zero.
Received: 29 October 1996 Accepted: 13 December 1996 相似文献
64.
随机化交通灯的二维元胞自动机交通模型 总被引:8,自引:0,他引:8
元胞自动机交通模型以简单的规则反映交通系统中的多种因素,可以分析各种交通现象,且可在计算机上方便、高效地运作·Biham-Middleton-Levine模型(BML模型)实现了二维交通问题的元胞自动机模型的模拟研究·本文对BML模型作了改进,解除了该模型中关于交通灯同步变化的限制·在新模型中,每个路口的交通灯可以自由选定起始工作时间和变化节奏,于是可以更全面、准确地反映交通灯对交通系统性能的影响·本文还对新模型中出现的若干新效应作了解释· 相似文献
65.
Paul阱内的压缩效应与量子跃迁 总被引:1,自引:1,他引:0
处理一个一维Paul阱系统中的压缩现象与量子跃迁现象,对于阱内的最强压缩态和共振跃迁(一种极不稳定状态)之间的关系作了阐述,并对利用压缩性质在阱内进行精密测量的可能性作了讨论 相似文献
66.
67.
提出了折射率温敏式光纤温度传感器的理论模型,包括子午光线和偏射光线的影响,讨论了多模光纤的弯曲损耗,理论的分析和结果与实验相当一致。 相似文献
68.
69.
Benjamin S. Hsiao Rong-Ming Ho Stephen Z. D. Cheng 《Journal of Polymer Science.Polymer Physics》1995,33(17):2439-2447
Unique crystallization and melting behavior in poly(aryl ether ketone ketone) containing alternated terephthalic and isophthalic moieties were studied by time-resolved synchrotron x-ray methods. Recently, this material has been shown to exhibit three polymorphs (forms I, II, and III). In this work, we further investigated their distinctive thermal properties and found that form I is the dominating and the most thermally stable phase while form II is favored by fast nucleation conditions and is the least stable phase. On the other hand, form III represents a minor intermediate phase that usually coexists with form I and can be transferred from form II and to form I. Structural and morphological changes in form I have been followed by simultaneous wide-angle x-ray diffraction (WAXD)/small-angle x-ray scattering (SAXS) measurements during cold- or melt-crystallization and subsequent melting. In all cases, a larger dimensional change was found in the crystallographic a-axis than the b-axis during heating and cooling. This may be due to the greater lateral stress variation with respect to temperature along the a direction of the primary lamellae which is induced by either the formation of secondary lamellae or the preferential chain-folding direction in poly(aryl ether ketone ketone)s. During the phase transitions of form II ← III in the cold-crystallized specimen and form III ← I in the melt-crystallized samples, lamellar variables (long period, lamellar thickness, and invariant) obtained from SAXS remain almost constant. This indicates that the density distribution in the long spacing is independent of the melting in form II or III. For melt-crystallization, the corresponding changes in unit-cell dimensions and lamellar morphology during the annealing-induced low endotherm are most consistent with the argument that these changes are due to the melting of thin lamellar population. © 1995 John Wiley & Sons, Inc. 相似文献
70.