全文获取类型
收费全文 | 35813篇 |
免费 | 5824篇 |
国内免费 | 3544篇 |
专业分类
化学 | 25137篇 |
晶体学 | 358篇 |
力学 | 2206篇 |
综合类 | 201篇 |
数学 | 4026篇 |
物理学 | 13253篇 |
出版年
2024年 | 113篇 |
2023年 | 707篇 |
2022年 | 1211篇 |
2021年 | 1306篇 |
2020年 | 1339篇 |
2019年 | 1378篇 |
2018年 | 1232篇 |
2017年 | 1112篇 |
2016年 | 1702篇 |
2015年 | 1600篇 |
2014年 | 1997篇 |
2013年 | 2538篇 |
2012年 | 3201篇 |
2011年 | 3241篇 |
2010年 | 2177篇 |
2009年 | 1987篇 |
2008年 | 2238篇 |
2007年 | 1981篇 |
2006年 | 1936篇 |
2005年 | 1550篇 |
2004年 | 1181篇 |
2003年 | 948篇 |
2002年 | 967篇 |
2001年 | 783篇 |
2000年 | 618篇 |
1999年 | 740篇 |
1998年 | 556篇 |
1997年 | 554篇 |
1996年 | 575篇 |
1995年 | 473篇 |
1994年 | 409篇 |
1993年 | 368篇 |
1992年 | 308篇 |
1991年 | 331篇 |
1990年 | 254篇 |
1989年 | 216篇 |
1988年 | 166篇 |
1987年 | 141篇 |
1986年 | 147篇 |
1985年 | 113篇 |
1984年 | 110篇 |
1983年 | 73篇 |
1982年 | 64篇 |
1981年 | 54篇 |
1980年 | 55篇 |
1978年 | 37篇 |
1977年 | 37篇 |
1976年 | 39篇 |
1975年 | 33篇 |
1973年 | 41篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Chien-Hsin Cheng 《中国化学会会志》1994,41(1):33-38
Dynamic and static scattering of light was employed to investigate mixed micelles of two homologous anionic surfactants-sodium octyl sulfate and sodium hexadecyl sulfate, above the phase boundary temperature and critical micelle concentrations (cmc). The results indicate that the mixed micelles change from prolate to sphcrical as the molar ratio SOS/SHS increases from 1 to 8. Below 1 or above 8, the formation of micelles is due to one surfactant dissolving the other. 相似文献
3.
Ma Jiangle Yang Hong-shen Zhang Zhongxi Lu Zhong-zuo 《International Journal of Infrared and Millimeter Waves》1993,14(5):1069-1076
A simple method is introduced to improve the analysing accuracy of circular groove guide. With this method, the characteristic equation of circular groove guide is derived and its solution is given and discussed.The Project Supported by National Natural Science Foundation of P.R.China 相似文献
4.
Gang Wang Xiulin Zhu Zhenping Cheng Jian Zhu 《Journal of polymer science. Part A, Polymer chemistry》2006,44(9):2912-2921
A series of (di)picolinic acids and their derivates are investigated as novel complexing tridentate or bidentate ligands in the iron‐mediated reverse atom transfer radical polymerization of methyl methacrylate in N,N‐dimethylformamide at 100 °C with 2,2′‐azobisisobutyrontrile as an initiator. The polymerization rates and polydispersity indices (1.32–1.8) of the resulting polymers are dependent on the structures of the ligands employed. Different iron complexes may be involved in iron‐mediated reverse atom transfer radical polymerization, depending on the type of acid used. 1H NMR spectroscopy has been used to study the structure of the resulting polymers. Chain‐extension reactions have been performed to further confirm the living nature of this catalytic system. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2912–2921, 2006 相似文献
5.
A two-dimensional, nonlinear, compressible, diabatic, nonhydrostatic photochemical-dynamical gravity wave model has been advanced. The model includes diabetic process produced by photochemistry and the effect of gravity wave on atmospheric chemical species. In the horizontal direction, the pseudospectral method is used. The finite difference approximations are used in vertical direction z and time t. The FICE method is used to solve the model. The model results on small amplitude fluctuation are very close to those of linear theory, which demonstrates the correctness of the model.
相似文献6.
The structural evolution in amorphous silicon and germanium thin films has been investigated by high-resolution transmission electron microscopy (HRTEM) in conjunction with autocorrelation function (ACF) analysis. The results established that the structure of as-deposited semiconductor films is of a high density of nanocrystallites embedded in the amorphous matrix. In addition, from ACF analysis, the structure of a-Ge is more ordered than that of a-Si. The density of embedded nanocrystallites in amorphous films was found to diminish with annealing temperature first, then to increase. The conclusions also corroborate well with the results of diminished medium-range order in annealed amorphous films determined previously by a variable coherence microscopy method. 相似文献
7.
A convenient route was developed to synthesize S-oxo-[(methylthio)-methyl]cysteinols on a large scale from cheap l-serine as the starting material. The structures of diastereoisomers were determined by NMR, CD spectra, and X-ray diffraction analysis. All four diastereoisomers were examined for their ability to inhibit certain bacteria from growing. 相似文献
8.
A nonlinear, compressible, non-isothermal gravity wave model that involves photochemistry is used to study the effects of gravity wave on atmospheric chemical species distributions in this paper. The changes in the distributions of oxygen compound and hydrogen compound density induced by gravity wave propagation are simulated. The results indicate that when a gravity wave propagates through a mesopause region, even if it does not break, it can influence the background distributions of chemical species. The effect of gravity wave on chemical species at night is larger than in daytime. 相似文献
9.
Wang Qing-Lun Zhao Bin Liao Dai-Zheng Yan Shi-Ping Cheng Peng Jiang Zong-Hui 《Transition Metal Chemistry》2003,28(3):326-330
The copper(II) complex Na2[Cu(pba)] · 6H2O has been synthesized and its structure determined. It consists of a novel two-dimensional network of [Cu(pba)]2– anions connected to each other through the sodium ion as a bridge. Spectroscopic and magnetic properties have been measured and a spin distribution calculation has been carried out with the GAUSSIAN-94. Theoretical calculations indicate the rather larger spin density on nitrogen atoms should be responsible for the satellite lines appearing beside the main hyperfine coupling signs of copper(II). The antiferromagnetic interaction may be due to the intermolecular interaction and/or different copper(II) ions through the Na+ bridge in the same layer. 相似文献
10.
Mingbao Zhang Raymond Reeves Cheng Bi Robert Dally Gaetan Ladouceur William Bullock Jefferson Chin 《Tetrahedron letters》2004,45(27):5229-5231
Three novel, optically active, 6-substituted 2-(aminomethyl)chromans were synthesized from readily available chroman 2-carboxylic acid precursors. These chroman-containing primary amines are useful building blocks for the synthesis of chroman-derived pharmaceutical agents. 相似文献