全文获取类型
收费全文 | 436747篇 |
免费 | 4842篇 |
国内免费 | 1245篇 |
专业分类
化学 | 234132篇 |
晶体学 | 6506篇 |
力学 | 18787篇 |
综合类 | 13篇 |
数学 | 50088篇 |
物理学 | 133308篇 |
出版年
2021年 | 3771篇 |
2020年 | 4196篇 |
2019年 | 4523篇 |
2018年 | 5858篇 |
2017年 | 5748篇 |
2016年 | 8844篇 |
2015年 | 5573篇 |
2014年 | 8554篇 |
2013年 | 20210篇 |
2012年 | 15684篇 |
2011年 | 19303篇 |
2010年 | 13520篇 |
2009年 | 13384篇 |
2008年 | 17678篇 |
2007年 | 17570篇 |
2006年 | 16284篇 |
2005年 | 14585篇 |
2004年 | 13544篇 |
2003年 | 11914篇 |
2002年 | 11764篇 |
2001年 | 13437篇 |
2000年 | 10100篇 |
1999年 | 7922篇 |
1998年 | 6575篇 |
1997年 | 6320篇 |
1996年 | 6096篇 |
1995年 | 5485篇 |
1994年 | 5404篇 |
1993年 | 5204篇 |
1992年 | 5832篇 |
1991年 | 5932篇 |
1990年 | 5672篇 |
1989年 | 5479篇 |
1988年 | 5501篇 |
1987年 | 5384篇 |
1986年 | 5099篇 |
1985年 | 6568篇 |
1984年 | 6697篇 |
1983年 | 5308篇 |
1982年 | 5397篇 |
1981年 | 5380篇 |
1980年 | 4966篇 |
1979年 | 5359篇 |
1978年 | 5502篇 |
1977年 | 5390篇 |
1976年 | 5333篇 |
1975年 | 4923篇 |
1974年 | 4897篇 |
1973年 | 4886篇 |
1972年 | 3461篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
971.
Andrew D. Abell Bruce M. Clark Kathryn B. Morris Jane M. Taylor 《Journal of mass spectrometry : JMS》1993,28(1):27-29
Positive-ion fast atom bombardment mass spectra of 13 keto acid and keto ester phosphoranes were examined. All compounds gave a protonated molecular ion and characteristic peaks at m/z 303, 279, 262 and 201. 相似文献
972.
A technique is proposed for improving the accuracy of the heat of fusion of semicrystalline polymers by DSC. The results of three commercially available instruments are compared. 相似文献
973.
S. A. J. Wiegers B. Tieke U. Zeitler R. Fletcher A. K. Geim J. C. Maan M. Henini 《Czechoslovak Journal of Physics》1996,46(5):2461-2462
We have investigated the interaction of phonons with a 2DEG in the FQH regime with phonon drag thermoelectric power (TEP). We find that the TEP at filling factors with the same even denominator is identical and at other even denominator filling factors they differ only by a constant. Assuming these states to be Composite Fermions (CF), we can explain our observations by extending a zero magnetic field theory for phonon drag to the CF-phonon interaction. This analysis is further corroborated by the observed T4 dependence of the CF TEP. 相似文献
974.
We generalize literature data and our own experimental data on using 1,3-dipolar cycloaddition reactions for synthesis of fullerene C60 derivatives containing annelated heterocyclic moieties.M. V. Lomonosov Moscow State University, Moscow 119899, Russia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 291–297, March, 1998. 相似文献
975.
Thermally induced phase conjugation by degenerate four-wave mixing in solutions of Rhodamine 6G in ethanol in the weak absorption region, low-reflectivity regime, and nonosecond time domain is reported. Evidence of oscillatory acoustic modes in the nonlinear medium is presented and existing theories are shown to explain satisfactorily the experimental results. 相似文献
976.
The X-ray patterns for the nematic phase in a series of side-on fixed polysiloxanes show different kinds of diffuse elements which imply complex short range ordering. A systematic structural study of the evolution of the patterns versus two molecular parameters, namely the spacer length and the length of the terminal aliphatic tails, suggests the possible occurrence of a smectic C phase for certain values of these parameters. Taking into account these tendencies, new synthesis led to a nematic-smectic C polymorphism observed for the first time in side-on fixed polysiloxanes. 相似文献
977.
The temperature dependence of the NMR chemical shift of129Xe dissolved in liquid alkanes is examined in the context of the reaction field model. An essential feature of the theory is the inclusion of the temperature dependence of the density of thesolvent. The theory of free volume for liquids is incorporated into the reaction field model to account for this temperature dependence. Comparison of the theory with previously reported measurements indicates the sensitivity of the129Xe chemical shift to the free volume of liquids. Incorporation of free volume improves the agreement between measurement and theory for branched alkane solvents, and resolves the origin of the 62 ppm intercept in the plot of reaction field as a function of129Xe chemical shift for the n-alkanes. 相似文献
978.
979.
980.
A generalized Gibbs-ensemble methodology with a fluctuating particle is used to determine the coexistence vapor-liquid densities for a square-well fluid. It is shown that the presence of the fluctuating particle in sub-states of the Markov chain of states supresses considerably density fluctuations which makes it possible to carry out simulations efficiently even for temperatures very close to the critical temperature. 相似文献