全文获取类型
收费全文 | 17011篇 |
免费 | 344篇 |
国内免费 | 313篇 |
专业分类
化学 | 1670篇 |
晶体学 | 29篇 |
力学 | 119篇 |
综合类 | 15篇 |
数学 | 14525篇 |
物理学 | 1310篇 |
出版年
2023年 | 29篇 |
2022年 | 49篇 |
2021年 | 43篇 |
2020年 | 79篇 |
2019年 | 393篇 |
2018年 | 427篇 |
2017年 | 237篇 |
2016年 | 154篇 |
2015年 | 218篇 |
2014年 | 429篇 |
2013年 | 1297篇 |
2012年 | 593篇 |
2011年 | 1128篇 |
2010年 | 1010篇 |
2009年 | 1185篇 |
2008年 | 1337篇 |
2007年 | 1349篇 |
2006年 | 1017篇 |
2005年 | 599篇 |
2004年 | 539篇 |
2003年 | 483篇 |
2002年 | 372篇 |
2001年 | 358篇 |
2000年 | 353篇 |
1999年 | 402篇 |
1998年 | 328篇 |
1997年 | 282篇 |
1996年 | 305篇 |
1995年 | 370篇 |
1994年 | 349篇 |
1993年 | 274篇 |
1992年 | 212篇 |
1991年 | 131篇 |
1990年 | 112篇 |
1989年 | 104篇 |
1988年 | 84篇 |
1987年 | 78篇 |
1986年 | 85篇 |
1985年 | 117篇 |
1984年 | 106篇 |
1983年 | 56篇 |
1982年 | 89篇 |
1981年 | 88篇 |
1980年 | 84篇 |
1979年 | 63篇 |
1978年 | 89篇 |
1977年 | 61篇 |
1976年 | 53篇 |
1975年 | 26篇 |
1974年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
We consider the Dirichlet problem for a class of anisotropic degenerate elliptic equations. New a priori estimates for solutions and for the gradient of solutions are established. Based on these estimates sufficient conditions guaranteeing the solvability of the problem are formulated. The results are new even in the semilinear case when the principal part is the Laplace operator. 相似文献
82.
We study the domain of existence of a solution to a Riemann problem for the pressure gradient equation in two space dimensions. The Riemann problem is the expansion of a quadrant of gas of constant state into the other three vacuum quadrants. The global existence of a smooth solution was established in Dai and Zhang [Z. Dai, T. Zhang, Existence of a global smooth solution for a degenerate Goursat problem of gas dynamics, Arch. Ration. Mech. Anal. 155 (2000) 277-298] up to the free boundary of vacuum. We prove that the vacuum boundary is the coordinate axes. 相似文献
83.
Piotr Borodulin-Nadzieja 《Topology and its Applications》2007,154(18):3107-3124
We investigate properties of minimally generated Boolean algebras. It is shown that all measures defined on such algebras are separable but not necessarily weakly uniformly regular. On the other hand, there exist Boolean algebras small in terms of measures which are not minimally generated. We prove that under CH a measure on a retractive Boolean algebra can be nonseparable. Some relevant examples are indicated. Also, we give two examples of spaces satisfying some kind of Efimov property. 相似文献
84.
A. Cavallini B. Fraboni W. Dusi N. Auricchio M. Zanarini P. Chirco 《Applied Physics A: Materials Science & Processing》2002,75(3):427-429
The time recovery of the spectroscopic capabilities of CdZnTe and CdTe detectors, irradiated with increasing doses of high-
and low-energy neutrons, as well as electrons, has been investigated by studying their spectroscopic behavior at different
photon energies using leakage current measurements and PICTS (photo-induced current transient spectroscopy) analysis. The
detectors were stored at room temperature for up to one year to study the time evolution of their spectroscopic performance
and to correlate it with the presence of defective states in the material. We have observed a clear improvement in the material’s
detection properties with time, though only in those detectors which have not been severely degraded by the irradiation. The
recovery can be associated with a decrease in the concentration of some defective states, thus allowing the assessment of
the crucial role these play in determining the charge collection processes in the material and its spectroscopic capabilities.
Received: 1 August 2001 / Accepted: 3 August 2001 / Published online: 20 December 2001 相似文献
85.
We study the multiplicity of critical points for functionals which are only differentiable along some directions. We extend to this class of functionals the three critical point theorem of Pucci and Serrin and we apply it to a one-parameter family of functionals Jλ, λ∈I⊂R. Under suitable assumptions, we locate an open subinterval of values λ in I for which Jλ possesses at least three critical points. Applications to quasilinear boundary value problems are also given. 相似文献
86.
Robert Hochberg 《Combinatorica》2006,26(1):47-64
We prove that the class of homogeneous quasi-arithmetic progressions has unbounded discrepancy. That is, we show that given any 2-coloring of the natural numbers and any positive integer D, one can find a real number α≥1 and a set of natural numbers of the form {0, [α], [2α], [3α], . . . , [kα]} so that one color appears at least D times more than the other color. This was already proved by Beck in 1983, but the proof given here is somewhat simpler and
gives a better bound on the discrepancy. 相似文献
87.
A magic labelling of a set system is a labelling of its points by distinct positive integers so that every set of the system has the same sum,
the magic sum. Examples are magic squares (the sets are the rows, columns, and diagonals) and semimagic squares (the same, but without
the diagonals). A magilatin labelling is like a magic labelling but the values need be distinct only within each set. We show that the number of n × n magic or magilatin labellings is a quasipolynomial function of the magic sum, and also of an upper bound on the entries in
the square. Our results differ from previous ones because we require that the entries in the square all be different from
each other, and because we derive our results not by ad hoc reasoning but from a general theory of counting lattice points in rational inside-out polytopes. We also generalize from
set systems to rational linear forms.
Dedicated to the memory of Claudia Zaslavsky, 1917–2006
Received August 10, 2005 相似文献
88.
Scanning electron microscopy (SEM), Fourier transform infrared (FTIR) transmission, and Hall effect measurements were performed to investigate the structural, optical, and electrical properties of as-grown and in situ-annealed Hg0.7Cd0.3Te epilayers grown on CdTe buffer layers by using molecular beam epitaxy. After the Hg0.7Cd0.3Te epilayers had been annealed in a Hg-cell flux atmosphere, the SEM images showed that the surface morphologies of the Hg0.7Cd0.3Te thin films were mirror-like with no indication of pinholes or defects, and the FTIR spectra showed that the transmission intensities had increased in comparison to that of the as-grown Hg0.7Cd0.3Te epilayer. Hall-effect measurements showed that n-Hg0.7Cd0.3Te epilayers were converted to p-Hg0.7Cd0.3Te epilayers. These results indicate that the surface, optical, and electrical properties of the Hg1 − xCdxTe epilayers are improved by annealing and that as-grown n-Hg1 − xCdxTe epilayers can be converted to p-Hg1 − xCdxTe epilayers by in situ annealing. 相似文献
89.
Application of Electron-Shelving Detection via 423 nm Transition in Calcium-Beam Optical Frequency Standard
下载免费PDF全文
![点击此处可从《中国物理快报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A new scheme of small compact optical frequency standard based on thermal calcium beam with application of 423 nm shelving detection and sharp-angle velocity selection detection is proposed. Combining these presented techniques, we conclude that a small compact optical frequency standard based on thermal calcium beam will outperform the commercial caesium-beam microwave dock, like the 5071 Cs clock (from Hp to Agilent, now Symmetricom company), both in accuracy and stability. 相似文献
90.