全文获取类型
收费全文 | 6468篇 |
免费 | 1795篇 |
国内免费 | 478篇 |
专业分类
化学 | 1210篇 |
晶体学 | 57篇 |
力学 | 961篇 |
综合类 | 145篇 |
数学 | 1261篇 |
物理学 | 5107篇 |
出版年
2024年 | 24篇 |
2023年 | 56篇 |
2022年 | 153篇 |
2021年 | 157篇 |
2020年 | 164篇 |
2019年 | 160篇 |
2018年 | 186篇 |
2017年 | 242篇 |
2016年 | 274篇 |
2015年 | 237篇 |
2014年 | 493篇 |
2013年 | 458篇 |
2012年 | 440篇 |
2011年 | 488篇 |
2010年 | 387篇 |
2009年 | 424篇 |
2008年 | 457篇 |
2007年 | 435篇 |
2006年 | 424篇 |
2005年 | 372篇 |
2004年 | 319篇 |
2003年 | 282篇 |
2002年 | 267篇 |
2001年 | 276篇 |
2000年 | 229篇 |
1999年 | 187篇 |
1998年 | 197篇 |
1997年 | 153篇 |
1996年 | 150篇 |
1995年 | 117篇 |
1994年 | 77篇 |
1993年 | 62篇 |
1992年 | 62篇 |
1991年 | 67篇 |
1990年 | 37篇 |
1989年 | 32篇 |
1988年 | 32篇 |
1987年 | 29篇 |
1986年 | 21篇 |
1985年 | 17篇 |
1984年 | 17篇 |
1983年 | 9篇 |
1982年 | 13篇 |
1981年 | 17篇 |
1980年 | 13篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1973年 | 2篇 |
1971年 | 4篇 |
排序方式: 共有8741条查询结果,搜索用时 15 毫秒
151.
Lucifer yellow and lissamine rhodamine sulfonyl hydrazine were used as the donor and the receptor, respectively, for Förster energy transfer measurements to determine the location of the subunit in the native Na,K-ATPase from pig kidney. It was found that (1) the subunits are located in one functional complex, i.e., the dimer ()2 appears to be the functional complex of Na,K-ATPase, and (2) the subunits in the functional enzyme complex in the membrane are not located next to each other but are rather well separated. The distance between fluorophores covalently attached to the subunits was found to be 5.3 nm. 相似文献
152.
The cutoff frequency f_(max) of radiation from earthquakes is one of the important parameters for studying the source process. By theoretical analysis and numerical experiments on acceleration Fourier spectrum it is suggested that f_(max) mainly depends on the lower values of slip rise time. This result can be used to explain the observational fact that the greater the earthquake magnitude, the smaller the value of f_(max). 相似文献
153.
Samuel O. Asekomhe Janet A. W. Elliott 《Colloids and surfaces. A, Physicochemical and engineering aspects》2003,220(1-3):271-278
Much research has been done on line tension measurement and interpretation, and attempts have also been made to measure line tension with simple, cheap and reliable methods that do not require excessive sophistication. Of particular interest is the method of determining line tensions of solid–liquid–vapor systems from the capillary rise in a conical tube. This simple and relatively inexpensive method gives line tension values comparable to those reported in the literature obtained via highly sophisticated instruments or techniques such as the well known axisymmetric drop shape analysis technique. The absolute value of line tension obtained using the conical tube method and assuming a spherical liquid–vapor interface is larger but of the same order of magnitude (1 μJ m−1) as that reported in the literature. A theoretical analysis presented herein shows that by including the deformation of the liquid–vapor interface due to gravity in the conical capillary analysis, the line tension value inferred from the experimental data is reduced by approximately 50% and compares better with values in the literature obtained using other sophisticated methods. Thus a relatively simple, cheap, accurate and reliable method of line tension measurement has been advanced. 相似文献
154.
E. C. C. Vasconcellos K. M. Evenson 《International Journal of Infrared and Millimeter Waves》1985,6(11):1157-1167
We have obtained laser action on 34 far infrared lines for the first time in fully deuterated methyl alcohol with the13C isotope (13CD3OD), and we have measured the frequency of 13 lines. The molecule was pumped by a cw CO2 laser. We have measured the wavelength, the relative polarization, the relative intensity of most lines, the frequency, and the CO2 pump frequency offset of the strongest lines. The new lines are distributed in the wavelength region from 75.27 m to 464.7 m.Supported in part by a joint grant with the U.S. National Science Foundation grant # INT 80-19014 and the Brazilian Conselho Nacional de Pesquisas (CNPq). 相似文献
155.
用ab initio方法研究NaN_3的几何构型、电子结构和热力学、动力学性质 总被引:2,自引:0,他引:2
用abinitioMO方法,在MP2(ful)/6311G水平下,全优化计算了叠氮化钠(NaN3)分子的线状和环状两种稳定构型及其转化过渡态的几何参数、电荷分布、分子总能量和振动频率,并研究了它们的热力学性质及转化速率常数和平衡常数.结果表明,线状比环状构型稍稳定(能量低6.04kJ/mol);两者相互转化的能垒分别为13.15kJ/mol(线型→环状)和7.11kJ/mol(环状→线型).热力学和动力学计算均表明:NaN3通常主要以线型结构存在(占85%以上),且随温度升高而增多(在1000K大于91%). 相似文献
156.
Sm2+-doped glasses in the system of Al2O3-SiO2 were prepared by sol-gel processing of metal alkoxides and reacting with H2 gas at 800°C. The hole burning properties of these glasses were investigated. The holes were burned in the 7F0 5D0 line of the Sm2+ ions using a DCM dye laser at 77 K. The hole depth increased with increasing the laser irradiation time, reaching up to 15% of the total intensity within a few hundred seconds. The hole width was 3 cm–1 full width at half maximum. Fluorescence line narrowing spectra of the 5D0 7 F1 transition were analyzed to study the local structure surrounding the Sm2+ ion. It is concluded that the Sm2+ ions are closely coordinated with nine oxygens of the AlO6 group in aluminosilicate glasses and that the addition of Al3+ ions into glass induces an increase in the coordination number of the Sm2+. 相似文献
157.
158.
159.
烷基极化效应与X=O键伸缩振动频率 总被引:2,自引:0,他引:2
烷基取代物R’X=0的X=0键伸缩振动频率ν与烷基R的极化效应指数PEI(R)的关系可表示为:ν=a bPEI(R)。研究结果表明,烷基的极化效应使X=0键的伸缩振动频率降低。 相似文献
160.
Summary Four most frequently used presentation forms of the ECD response are described. Equations describing the dependence of the
sensitivity, linearity and minimum detectable concentration of the ECD working under constant frequency mode of operation
on the pulse period are derived from Wenthworth’s kinetic model for all four forms mentioned above. The forms presented are
compared on the basis of equations derived. Results of the calculations are given and some predictions are experimentally
tested for sulphur hexafluoride. Good agreement was found between the predicted and observed relationships.
Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984 相似文献