全文获取类型
收费全文 | 8556篇 |
免费 | 200篇 |
国内免费 | 57篇 |
专业分类
化学 | 4980篇 |
晶体学 | 86篇 |
力学 | 212篇 |
数学 | 1417篇 |
物理学 | 2118篇 |
出版年
2023年 | 31篇 |
2022年 | 157篇 |
2021年 | 198篇 |
2020年 | 150篇 |
2019年 | 207篇 |
2018年 | 238篇 |
2017年 | 207篇 |
2016年 | 303篇 |
2015年 | 230篇 |
2014年 | 271篇 |
2013年 | 533篇 |
2012年 | 497篇 |
2011年 | 627篇 |
2010年 | 438篇 |
2009年 | 381篇 |
2008年 | 498篇 |
2007年 | 459篇 |
2006年 | 417篇 |
2005年 | 398篇 |
2004年 | 332篇 |
2003年 | 281篇 |
2002年 | 255篇 |
2001年 | 129篇 |
2000年 | 124篇 |
1999年 | 117篇 |
1998年 | 108篇 |
1997年 | 74篇 |
1996年 | 109篇 |
1995年 | 65篇 |
1994年 | 62篇 |
1993年 | 73篇 |
1992年 | 56篇 |
1991年 | 47篇 |
1990年 | 32篇 |
1989年 | 34篇 |
1988年 | 26篇 |
1987年 | 30篇 |
1986年 | 41篇 |
1985年 | 32篇 |
1984年 | 34篇 |
1983年 | 34篇 |
1982年 | 33篇 |
1981年 | 30篇 |
1979年 | 28篇 |
1977年 | 35篇 |
1975年 | 32篇 |
1972年 | 28篇 |
1971年 | 25篇 |
1970年 | 30篇 |
1969年 | 27篇 |
排序方式: 共有8813条查询结果,搜索用时 0 毫秒
1.
A finite support product of clones of Jensen's minimal singleton forcing is used to define a model in which any non-empty analytically definable set of reals contains an analytically definable real (the full basis theorem), but there is no analytically definable wellordering of the reals. 相似文献
2.
3.
4.
Yoel Shkolnisky Mark Tygert Vladimir Rokhlin 《Applied and Computational Harmonic Analysis》2006,21(3):413-420
Many signals encountered in science and engineering are approximated well by bandlimited functions. We provide suitable error bounds for the approximation of bandlimited functions by linear combinations of certain special functions—the prolate spheroidal wave functions of order 0. The coefficients in the approximating linear combinations are given explicitly via appropriate quadrature formulae. 相似文献
5.
Vladimir Kogan 《Tetrahedron letters》2006,47(43):7515-7518
Mild Ni-catalyzed homogeneous reductions of aryl tosylates are described for the first time. The catalytic system Ni(PPh3)2Cl2 and PCy3 is shown to be general for hydrogenolysis of a wide range of tosylates, including hindered, deactivated, heterocyclic, and bifunctional examples. 相似文献
6.
A. R. Volkov B. V. Shul'gin T. I. Polupanova V. N. Lebedev A. A. Nagornyi V. L. Petrov Yu. F. Kargin 《Journal of Applied Spectroscopy》1991,54(6):585-590
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 6, pp. 970–975, June, 1991. 相似文献
7.
A (w,r) cover‐free family is a family of subsets of a finite set such that no intersection of w members of the family is covered by a union of r others. A (w,r) superimposed code is the incidence matrix of such a family. Such a family also arises in cryptography as the concept of key distribution pattern. In the present paper, we give some new results on superimposed codes. First we construct superimposed codes from super‐simple designs which give us results better than superimposed codes constructed by other known methods. Next we prove the uniqueness of the (1,2) superimposed code of size 9 × 12, the (2,2) superimposed code of size 14 × 8, and the (2,3) superimposed code of size 30 × 10. Finally, we improve numerical values of upper bounds for the asymptotic rate of some (w,r) superimposed codes. © 2004 Wiley Periodicals, Inc. 相似文献
8.
Quasi-wavelets (QWs) are a representation of turbulence consisting of self-similar, eddy-like structures with random orientations and positions in space. They are used in this paper to calculate the scattering, due to turbulent velocity fluctuations, of sound behind noise barriers as a function of the size and spatial location of the eddies. The sound scattering cross-section for QWs of an individual size class (eddy size) is derived and shown to reproduce results for the von Kármán spectrum when the scattered energies from a continuous distribution of QW sizes are combined. A Bragg resonance condition is derived for the eddy size that scatters most strongly for a given acoustic wavenumber and scattering angle. Results for scattering over barriers show that, for typical barrier conditions, most of the scattered energy originates from eddies in the size range of approximately one-half to twice the size of the eddies responsible for maximum scattering. The results also suggest that scattering over the barrier due to eddies with a line of sight to both the source and receiver is generally significant only for frequencies above several kilohertz, for sources and receivers no more than a few meters below the top of the barrier, and for very turbulent atmospheric conditions. 相似文献
9.
10.
Experimental studies of the scattering of a monochromatic sound signal by a rough sea surface are carried out. The signal is produced by a point source in a shallow-water basin. The measurements are performed with the use of horizontal and vertical linear receiving arrays. The experimental data are compared with the estimates obtained on the basis of the model developed by the authors for resonant sound scattering by surface roughness. A satisfactory agreement between the experiments and the calculations is achieved. It is shown that the scattered signal is formed within small surface areas, whose sizes have the same order of magnitude as the first Fresnel zone with respect to the source and the receiving system. 相似文献