全文获取类型
收费全文 | 1350315篇 |
免费 | 29731篇 |
国内免费 | 7697篇 |
专业分类
化学 | 672843篇 |
晶体学 | 20458篇 |
力学 | 75123篇 |
综合类 | 105篇 |
数学 | 242712篇 |
物理学 | 376502篇 |
出版年
2021年 | 13515篇 |
2020年 | 15928篇 |
2019年 | 16055篇 |
2018年 | 13828篇 |
2016年 | 28426篇 |
2015年 | 20876篇 |
2014年 | 30458篇 |
2013年 | 74409篇 |
2012年 | 38581篇 |
2011年 | 36275篇 |
2010年 | 37772篇 |
2009年 | 40098篇 |
2008年 | 35082篇 |
2007年 | 31143篇 |
2006年 | 36000篇 |
2005年 | 29017篇 |
2004年 | 30135篇 |
2003年 | 28265篇 |
2002年 | 29198篇 |
2001年 | 29055篇 |
2000年 | 24972篇 |
1999年 | 22602篇 |
1998年 | 21097篇 |
1997年 | 21090篇 |
1996年 | 21130篇 |
1995年 | 19199篇 |
1994年 | 18653篇 |
1993年 | 18189篇 |
1992年 | 18234篇 |
1991年 | 18503篇 |
1990年 | 17711篇 |
1989年 | 17762篇 |
1988年 | 17321篇 |
1987年 | 17326篇 |
1986年 | 16264篇 |
1985年 | 22672篇 |
1984年 | 23877篇 |
1983年 | 20054篇 |
1982年 | 21694篇 |
1981年 | 20919篇 |
1980年 | 20273篇 |
1979年 | 20505篇 |
1978年 | 21749篇 |
1977年 | 21355篇 |
1976年 | 21064篇 |
1975年 | 19721篇 |
1974年 | 19370篇 |
1973年 | 19820篇 |
1972年 | 14304篇 |
1967年 | 12554篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
811.
Brian R. Hunt 《Proceedings of the American Mathematical Society》1998,126(3):791-800
The Weierstrass nowhere differentiable function, and functions constructed from similar infinite series, have been studied often as examples of functions whose graph is a fractal. Though there is a simple formula for the Hausdorff dimension of the graph which is widely accepted, it has not been rigorously proved to hold. We prove that if arbitrary phases are included in each term of the summation for the Weierstrass function, the Hausdorff dimension of the graph of the function has the conjectured value for almost every sequence of phases. The argument extends to a much wider class of Weierstrass-like functions.
812.
NaY zeolite samples loaded with sodium metal by vapor phase deposition have been investigated using129Xe NMR spectroscopy. At low sodium concentration, the129Xe NMR spectrum showed three resonance lines which clearly indicate the existence of distinct domains in the zeolite sample. Such an observation suggests that the diffusion of the xenon atoms into each domain only occurs with respect to the NMR time scale (2.9 ms). As the sodium concentration increases, observation of a single broad line indicate a macroscopic homogenization of the system. The shift of this line is explained in part due to a paramagnetic interaction between the xenon atoms and the unpaired electrons of particles containing an odd number of sodium atoms. The linewidth is due to the distribution of the local magnetic fields partially averaged by the rapid motion of the xenon atoms and to the statistical distribution of the sodium particles in the supercage cavities. The paramagnetic interaction vanishes with the oxidation of the sample leading to a narrowing and a shift of the line to higher magnetic fields. 相似文献
813.
We have recently demonstrated that polarization transfer using an adiabatic passage through the Hartmann-Hahn condition (APHH-CP) by a variation of the radio-frequency amplitude can substantially improve the transfer efficiency over Hartmann-Hahn cross polarization. Here we show that APHH-CP can be combined with fast magic angle sample spinning (MAS). The heteronuclear dipolar order, established in the course of the transfer, can indeed be created and preserved. 相似文献
814.
A. Negr n-Mendoza G. Albarran S. Ramos-Bernal 《Radiation Physics and Chemistry》1993,42(4-6):1003-1006
The effect of clay on the radiolysis of malonic acid solutions was studied. The results showed an enhanced of decarboxylation rather than condensation reactions. 相似文献
815.
Peter J. Grabner 《Random Structures and Algorithms》1993,4(1):99-110
We investigate the following process: N people select b losers by flipping coins. The 0-party continues until there are less than b losers; then the 1-party has to find the other losers by the same process. The average time for this process is about long2 N, but this result requires rather advanced methods. Furthermore, the average size of a binary tree associated to this process and the average number of coin flippings are computed. The method used in this article can be used to give asympotical solutions of a special type of bivariate recurrences. © 1993 John Wiley & Sons, Inc. 相似文献
816.
V. I. Verkhoturov O. S. Grafodatskii V. I. Simanchuk A. V. Kargapol'tsev 《Russian Physics Journal》1993,36(9):865-869
Experimental results are presented on acoustic probing of electric fields in solid insulators. An experimental apparatus and methods are described for acoustic measurements of the bulk space charge density and electric field strength in solid insulators. The sensitivity and spatial resolution of the acoustic probe technique are determined.Institute of Introscopy Research, Polytechnical University, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 62–67, September, 1993. 相似文献
817.
The optical absorption coefficient γ of a thin film of a Peierls semiconductor has been calculated in the dipole approximation for direct interband transitions as a function of intensity I and central frequency ω0 of a quasi-monochromatic frequency spectrum near the lower optical transition edge. It is shown that the γ(I, ω0) dependence is strongly nonlinear, and within a certain region of I and ω0 variation, not single-valued, which indicates the onset of resonator-free optical bistability with increasing absorption. 相似文献
818.
Peter A. McCoy 《Journal of Mathematical Analysis and Applications》2002,275(2):761-770
An integral transform based method is given for determining information about the locating and properties of singularities of electromagnetic fields associated with axially symmetric radiating sources. 相似文献
819.
We study spectral properties of discrete Schrödinger operators with potentials obtained via dimerization of a class of aperiodic sequences. It is shown that both the nature of the autocorrelation measure of a regular sequence and the presence of generic (full probability) singular continuous spectrum in the hull of primitive and palindromic (four block substitution) potentials are robust under dimerization. Generic results also hold for circle potentials. We illustrate these results with numerical studies of the quantum mean square displacement as a function of time. The numerical techniques provide a very fast algorithm for the time evolution of wave packets. 相似文献
820.
An M/G/1 retrial queueing system with additional phase of service and possible preemptive resume service discipline is considered. For an arbitrarily distributed retrial time distribution, the necessary and sufficient condition for the system stability is obtained, assuming that only the customer at the head of the orbit has priority access to the server. The steady-state distributions of the server state and the number of customers in the orbit are obtained along with other performance measures. The effects of various parameters on the system performance are analysed numerically. A general decomposition law for this retrial queueing system is established. 相似文献