全文获取类型
收费全文 | 30504篇 |
免费 | 5384篇 |
国内免费 | 4704篇 |
专业分类
化学 | 22539篇 |
晶体学 | 448篇 |
力学 | 1851篇 |
综合类 | 423篇 |
数学 | 3494篇 |
物理学 | 11837篇 |
出版年
2024年 | 105篇 |
2023年 | 573篇 |
2022年 | 1116篇 |
2021年 | 1159篇 |
2020年 | 1336篇 |
2019年 | 1330篇 |
2018年 | 1091篇 |
2017年 | 1096篇 |
2016年 | 1425篇 |
2015年 | 1550篇 |
2014年 | 1837篇 |
2013年 | 2332篇 |
2012年 | 2720篇 |
2011年 | 2879篇 |
2010年 | 2047篇 |
2009年 | 1987篇 |
2008年 | 2210篇 |
2007年 | 1860篇 |
2006年 | 1764篇 |
2005年 | 1483篇 |
2004年 | 1235篇 |
2003年 | 966篇 |
2002年 | 1001篇 |
2001年 | 816篇 |
2000年 | 692篇 |
1999年 | 573篇 |
1998年 | 439篇 |
1997年 | 438篇 |
1996年 | 396篇 |
1995年 | 349篇 |
1994年 | 325篇 |
1993年 | 248篇 |
1992年 | 177篇 |
1991年 | 179篇 |
1990年 | 155篇 |
1989年 | 124篇 |
1988年 | 106篇 |
1987年 | 91篇 |
1986年 | 77篇 |
1985年 | 71篇 |
1984年 | 53篇 |
1983年 | 44篇 |
1982年 | 37篇 |
1981年 | 28篇 |
1980年 | 20篇 |
1979年 | 8篇 |
1976年 | 6篇 |
1975年 | 8篇 |
1959年 | 7篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Nanocrystalline FeS2 cathode material of lithium cell was synthesized from cheap materials of FeSO4, Na2S2O3, and sulfur by a hydrothermal process. The scanning electron microscopy analysis showed the obtained material was nano-sized,
about 500 nm. The X-ray powder diffraction analysis showed that the synthetic FeS2 material had two phases of the crystalline structure, pyrite and marcasite. The phase of marcasite seems to have no negative
effect on the electrochemical performance of the material. The synthetic FeS2 showed a significant improvement of electrochemical performance for Li/FeS2 cells. 相似文献
42.
Fuzzy random vector is a measurable map from a probability space to a collection of fuzzy vectors. Our aim in this paper is
to discuss the measurability criteria for fuzzy random vectors, and show that under mild assumption, the measurability criteria
for upper semicontinuous fuzzy random vectors can be expressed in several different but equivalent formulations. Finally,
applying the obtained results, we resolve an open problem about the relationship between fuzzy random vectors and fuzzy random
variables. 相似文献
43.
44.
900 MHz 1H NMR (nuclear magnetic resonance) spectroscopy was used to analyze metabolites in allantoic fluid of the chicken embryo in
the 9th incubation day without any chemical or physical sample separation. The result showed that superhigh spectral dispersion
and sensitivity at 900 MHz are useful in directly analyzing a complex mixture, particularly in resolving the overlapped NMR
resonances. In this study, we had assigned 61 metabolites and 26 chemical fragments in the allantoic fluid. The relative concentrations
of the major metabolites were also measured. Among the assigned metabolites, some were detected by NMR in chicken embryo allantoic
fluids for the first time. The biological functions of these compounds were briefly discussed.
Authors' address: Maili Liu, State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute
of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, People's Republic of China 相似文献
45.
46.
提出了一种基于增强现实的室内漫游系统,在这个系统中用户通过HMD观察增强的视景。在这个视景中不但包含真实布景的图像,还包含有计算机生成的虚拟物体的图像。为了实现虚实场景之间的注册,在HMD上安装有两个摄像机:场景摄像机与跟踪摄像机。并且在用户所在房间的顶部安装了一系列的红外标志点,这些标志点的图像由跟踪摄像机获取,并通过位置估计算法计算用户头部的位置和姿态。另外,通过一对安装有ARtoolKit标志点的手套,实现用户与虚拟环境之间的交互。最后,一套海底漫系统被开发出来,以验证整个漫游系统的可用性 相似文献
47.
J. Jiang B.Y. Jiang C.X. Ren F.M. Zhang T. Feng X. Wang X.H. Liu S.C. Zou 《Applied Surface Science》2006,252(10):3642-3646
Hafnium and platinum were deposited onto molybdenum grids by ion-beam assisted deposition method. Electron-emission characteristics from molybdenum grids with Hf and Pt films, which were contaminated by active electron-emission substances (Ba, BaO) of the cathode, were measured using analogous diode method. The surfaces of grids were analyzed by X-ray diffraction. The results revealed that the reaction between BaO and Hf formed BaHfO3 compound, which greatly reduced the accumulation of BaO on the surface and accordingly decreased grid emission. In contrast, Ba were formed by the decomposition of BaO on the surface of Pt film under high temperature and re-evaporated from its surface, which reduced the active electron-emission substances on the surface of the grid and effectively restrained grid emission. Their mechanisms for grid-emission suppression are discussed and a good method to develop new grid-coating materials is suggested. 相似文献
48.
49.
50.