全文获取类型
收费全文 | 4576篇 |
免费 | 646篇 |
国内免费 | 628篇 |
专业分类
化学 | 3665篇 |
晶体学 | 34篇 |
力学 | 264篇 |
综合类 | 61篇 |
数学 | 604篇 |
物理学 | 1222篇 |
出版年
2024年 | 4篇 |
2023年 | 64篇 |
2022年 | 109篇 |
2021年 | 105篇 |
2020年 | 144篇 |
2019年 | 150篇 |
2018年 | 138篇 |
2017年 | 121篇 |
2016年 | 221篇 |
2015年 | 198篇 |
2014年 | 273篇 |
2013年 | 360篇 |
2012年 | 381篇 |
2011年 | 336篇 |
2010年 | 317篇 |
2009年 | 273篇 |
2008年 | 271篇 |
2007年 | 247篇 |
2006年 | 253篇 |
2005年 | 204篇 |
2004年 | 187篇 |
2003年 | 189篇 |
2002年 | 299篇 |
2001年 | 256篇 |
2000年 | 137篇 |
1999年 | 120篇 |
1998年 | 86篇 |
1997年 | 50篇 |
1996年 | 53篇 |
1995年 | 44篇 |
1994年 | 51篇 |
1993年 | 13篇 |
1992年 | 25篇 |
1991年 | 31篇 |
1990年 | 27篇 |
1989年 | 17篇 |
1988年 | 15篇 |
1987年 | 19篇 |
1986年 | 13篇 |
1985年 | 11篇 |
1984年 | 9篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1977年 | 3篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1887年 | 1篇 |
1886年 | 1篇 |
排序方式: 共有5850条查询结果,搜索用时 0 毫秒
991.
线接触弹性接触变形的解析算法 总被引:13,自引:1,他引:13
以一般光滑性体接触理论为基础,结合有限长弹性体接触的特点,求出线接触弹性接蟹变形的解析公式,并发现其解析解与数值解具有很好的一致性,所得公式可以对赫兹线接触理论加以补充,与经验公式相比,它能够确切反映材料、载荷以及曲率半径等对接触变形的影响,为工程中的精确计算提供了方便。 相似文献
992.
Cui Hua XUE Qi Ming MU Shu Hua CHEN* The Faculty of chemistry Sichuan University Chengdu 《中国化学快报》2001,(5)
Molecular tweezers is a novel type of artificial receptors, which not only offer the advantage of efficient construction but also their surfaces can be tailored for specific applications. The clefts of molecular tweezers are particularly effective in regard to complementarity with substrates since functional groups attached to the interior of the cleft converge on substrates held inside1. So, in recent years, the molecular tweezers receptors have attracted more and more attention in molecular … 相似文献
993.
In this paper, an optimal criterion is presented for adaptive Kalman filter in a control system with unknown variances of
stochastic vibration by constructing a function of noise variances and minimizing the function. We solve the model and measure
variances by using DFP optimal method to guarantee the results of Kalman filter to be optimized. Finally, the control of vibration
can be implemented by LQG method. 相似文献
994.
Synthesis of Calix[4]pyrroles: A Class of New Molecular Receptor 总被引:1,自引:0,他引:1
RecentlySesslerandco-workersdiscoveredthatthemeso-octaalkylporphyrinogensshowedinterestinganionandneutralsubstratebindingpropertiesandmightserveasaclassofneweasy-to-makemolecularreceptorintheareaofsupramolecularchemistry'.However,themeso-octaalkylpor... 相似文献
995.
996.
Wei Li YANG Jun TIAN Qiang ZHANG Shu Lin PENG Li Sheng DING* Chengdu Institute of Biology Chinese Academy of Sciences Chengdu School of Pharmacy West China University of Medical Sciences Chengdu 《中国化学快报》2001,(2)
There are only three species in the genus Diuranthera (Liliaceae), which is endemic in the southwest of China1. Four steroidal saponins, diuranthosides A-C and chloromalo-side A were isolated from the fresh roots of D. major. This paper deals with the structure elucidation of two new steroidal saponins, diuranthosides D and E, which were isolated from the methanolic extract of whole plant of D. inarticulata Wang et K. Y. Lang.Diuranthoside D (1), [(]-38 (c 0.08, pyridine), afforded galac… 相似文献
997.
In the title complex, {[Ag(C20H20N2S2)](NO3)·CHCl3}n, the coordination about the Ag atom is a slightly distorted tetrahedron, involving the two S atoms of the ligand and two N‐atom donors from two amine groups of two adjacent complexes related by centrosymmetry, so building up a chain running all along the crystal structure. 相似文献
998.
Shu Nakamura 《Letters in Mathematical Physics》1986,11(4):337-340
It is shown that the bound obtained by the WKB-method gives a correct lower bound on eigenvalue splittings for one-dimensional double-well Hamiltonians in the semiclassical limit. A modified version of the argument of Kirsch and Simon is employed. 相似文献
999.
Mario Primicerio Weiqing Xie Muzeng Shu 《Mathematical Methods in the Applied Sciences》1990,12(6):519-531
An exothermic binary chemical reaction of first order is studied, assuming that one of the reactants can undergo a change of phase. In the limit of low activation energy, a one-dimensional problem is considered and the well-posedness of the corresponding system of two parabolic equations with a free boundary is proved in a classical sense. 相似文献
1000.
Studies on the Synthesis of Morphinan Alkaloid: Preparation of the Key Allylic Silyl Ether Precursor
Zhen Lei SONG Yong Qiang TU Shuan Hu GAO Yi Jun JIANG Shu Yu ZHANG 《中国化学快报》2005,16(11):1445-1447
Morphinan alkaloid consisting of many diverse molecules has been attracting much attention of synthetic chemists because of their biologically significant activities and the intriguing structures1. As shown in the common nucleus 1 of these polycyclic frameworks, there is a unique quaternary carbon center with an aryl substituent representing a central synthetic challenge2. In connection with our constant investigations on the quaternary carbon chemistry3, we proposed a general and conceptually… 相似文献