全文获取类型
收费全文 | 59822篇 |
免费 | 11741篇 |
国内免费 | 20253篇 |
专业分类
化学 | 44780篇 |
晶体学 | 2470篇 |
力学 | 4409篇 |
综合类 | 2163篇 |
数学 | 9171篇 |
物理学 | 28823篇 |
出版年
2024年 | 162篇 |
2023年 | 652篇 |
2022年 | 2215篇 |
2021年 | 2139篇 |
2020年 | 2071篇 |
2019年 | 2076篇 |
2018年 | 1847篇 |
2017年 | 2758篇 |
2016年 | 2122篇 |
2015年 | 3062篇 |
2014年 | 3721篇 |
2013年 | 5060篇 |
2012年 | 5061篇 |
2011年 | 5300篇 |
2010年 | 5150篇 |
2009年 | 5362篇 |
2008年 | 5955篇 |
2007年 | 5152篇 |
2006年 | 5062篇 |
2005年 | 4447篇 |
2004年 | 3682篇 |
2003年 | 2722篇 |
2002年 | 2709篇 |
2001年 | 2475篇 |
2000年 | 2454篇 |
1999年 | 1462篇 |
1998年 | 863篇 |
1997年 | 665篇 |
1996年 | 609篇 |
1995年 | 510篇 |
1994年 | 574篇 |
1993年 | 541篇 |
1992年 | 457篇 |
1991年 | 351篇 |
1990年 | 317篇 |
1989年 | 359篇 |
1988年 | 274篇 |
1987年 | 235篇 |
1986年 | 181篇 |
1985年 | 148篇 |
1984年 | 132篇 |
1983年 | 145篇 |
1982年 | 120篇 |
1981年 | 108篇 |
1980年 | 79篇 |
1979年 | 69篇 |
1978年 | 33篇 |
1977年 | 21篇 |
1976年 | 23篇 |
1971年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
A new constant-pressure molecular dynamics (MD) method is developed to simulate the dynamic behavior and structure transition of finite system under external pressure. In this method, no artificial parameter is introduced and the computation overheads are very small. As an application, a hard-soft transition of single wall carbon nanotube (SWCNT) under external pressure is found, which is in agreement with the experiments.
相似文献92.
93.
5‐Methylene‐2‐oxazolidinone (1) and 5‐methylene‐1,3‐thiazolidine‐2‐thione (4) react with various isocyanates to give the corresponding urethanes 3 and 5 in high yields in the presence of palladium(0) or palladium(II) catalyst under mild reaction conditions. A mechanism is proposed. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
94.
A facile, rapid and regioselective method for the 1-O-deacylation of peracylated glycopyranoses is described which occurs under mild conditions by absorption onto alumina using microwave irradiation. 相似文献
95.
Under dielectric continuum approximation, interface optical (IO) phonon modes and the Frohlich electron-IO phonon interaction Hamiltonian in a multi-shell spherical nanoheterosystem were derived and studied. Numericalcalculations on three-layer and four-layer CdS/HgS spherical nanoheterosystems have been performed. Results revealthat there are four IO phonon modes for the three-layer system and six IO phonon modes for the four-layer system.On each interface, there are two IO phonon modes, the frequency of one is between WTO,CdS and WLO,CdS, and that ofthe other is between WTO,HgS and WLO,HgS. With the increasing of quantum number l, the frequency of each IO modeapproaches one of the two frequency values of the single CdS/HgS heterostructure, and the potential for each IO modeis more and more localized at a certain interface, furthermore, the coupling between the electron-lO phonons becomes weaker. 相似文献
96.
Comment on “A Hierarchy of Integrable Nonlinear Lattice Equations and New Integrable Symplectic Map“
Comment on a recent paper on Commun. Theor. Phys. (Beijing, China) 38 (2002) pp. 523-528. 相似文献
97.
马科维兹资产组合选择模型的旋转算法 总被引:2,自引:0,他引:2
提出线性不等式组的一种旋转算法,并用其求解马科维兹资产组合选择模型,此算法每次迭代约需n^2次乘法和加法,其中n是模型中变量的数目,在微机上运行Delphi程序的实验结果表明,从上海和深圳股市1072支股票70期周末收盘价计算出20个最优投资组合仅需314次迭代和45s。 相似文献
98.
99.
A convenient and large-scale preparation of retinoic acid 1 from β-ionone in five steps with 38% overall yield is described.The key steps are the epoxidization of 2 with a new methylated agent and the condensation 4 with tetraethyl methylenediphophonate in one-pot procedure to prepare 6. 相似文献
100.
Hyun Chul Choi Min Kyu Lee Hyun Joon Shin Seung Bin Kim 《Journal of Electron Spectroscopy and Related Phenomena》2003,130(1-3):85-96
To investigate the formation of a solid electrolyte interface (SEI) on the Li1+xV3O8 electrode surface in the thermodynamic stability range of the organic electrolyte, we applied scanning photoelectron microscopy (SPEM) to a pristine electrode and to an electrode after ten cycles. The F K-edge absorption spectrum of the cycled electrode showed that LiF forms on the electrode surface during the lithium insertion–extraction process in the Li1+xV3O8/Li cell. The photoelectron spectrum for the cycled electrode showed intense spectral features corresponding to Li 1s, F 2s, F 2p, and P 2p electron signals, whereas these spectral features were of negligible intensity for the pristine electrode. The above results give strong support for the formation of an SEI that consists of LiF and compounds containing phosphorus during operation of the battery. The SPEM images also revealed that the fluorine distribution on the surface of the cycled electrode was inhomogeneous. 相似文献