全文获取类型
收费全文 | 5176篇 |
免费 | 117篇 |
国内免费 | 13篇 |
专业分类
化学 | 2709篇 |
晶体学 | 131篇 |
力学 | 230篇 |
数学 | 691篇 |
物理学 | 1545篇 |
出版年
2022年 | 73篇 |
2021年 | 78篇 |
2020年 | 89篇 |
2019年 | 97篇 |
2018年 | 72篇 |
2017年 | 89篇 |
2016年 | 136篇 |
2015年 | 115篇 |
2014年 | 132篇 |
2013年 | 370篇 |
2012年 | 264篇 |
2011年 | 292篇 |
2010年 | 184篇 |
2009年 | 166篇 |
2008年 | 213篇 |
2007年 | 238篇 |
2006年 | 183篇 |
2005年 | 185篇 |
2004年 | 147篇 |
2003年 | 95篇 |
2002年 | 94篇 |
2001年 | 65篇 |
2000年 | 51篇 |
1999年 | 52篇 |
1998年 | 50篇 |
1996年 | 55篇 |
1995年 | 49篇 |
1994年 | 56篇 |
1993年 | 71篇 |
1992年 | 63篇 |
1991年 | 48篇 |
1990年 | 58篇 |
1989年 | 53篇 |
1988年 | 62篇 |
1987年 | 51篇 |
1986年 | 33篇 |
1985年 | 73篇 |
1984年 | 96篇 |
1983年 | 57篇 |
1982年 | 63篇 |
1981年 | 70篇 |
1980年 | 72篇 |
1979年 | 72篇 |
1978年 | 68篇 |
1977年 | 62篇 |
1976年 | 57篇 |
1975年 | 46篇 |
1974年 | 48篇 |
1973年 | 55篇 |
1972年 | 34篇 |
排序方式: 共有5306条查询结果,搜索用时 15 毫秒
21.
The coupling of visible nanosecond laser pulses to metallic targets irradiated in vacuum is studied. The expressions of the vapour and plasma ignition times are obtained. Two cases for vapour breakdown in the plasma ignition process are considered. The first case is that 40 generations of new electrons are born in vapour generation time before plasma formation as assumed in the literature. The second case is that 10 generations of new electrons are born in vapour generation time. Molybdenum (Mo), niobium (Nb) and aluminium (Al) targets are considered for illustrations of our results. The expression of the plasma ignition time for the Al target is substantially different from that reported in the literature. The vapour and plasma ignition threshold laser intensities are calculated and compared with those reported in the literature. Reasons for disagreement are discussed. The plasma ignition threshold estimated in the second case is noted to be in good agreement with the reported experimental result. 相似文献
22.
The present paper deals with the study of a Durrmeyer-type integral modification of certain modified Baskakov operators. Here
we study simultaneous approximation properties for these operators by using the iterative combinations. We obtain an asymptotic
formula and an error estimation in terms of higher order modulus of continuity for these operators.
相似文献
23.
In the present paper, we study the rate of convergence in simultaneous approximation for the Bézier variant of the Baskakov-Beta operators by using the decomposition technique of functions of bounded variation. 相似文献
24.
Apurba Bhattacharya Nitin C. Patel Ritesh Tichkule Jiejun Wu 《Tetrahedron letters》2006,47(4):565-567
A simple, surfactant-mediated, one-pot, solvent-free dealkylative cleavage of aryl ethers and esters followed by subsequent optional trans-alkylation under essentially neutral conditions has been developed. 相似文献
25.
Pure adaptive search constructs a sequence of points uniformly distributed within a corresponding sequence of nested regions of the feasible space. At any stage, the next point in the sequence is chosen uniformly distributed over the region of feasible space containing all points that are equal or superior in value to the previous points in the sequence. We show that for convex programs the number of iterations required to achieve a given accuracy of solution increases at most linearly in the dimension of the problem. This compares to exponential growth in iterations required for pure random search. 相似文献
26.
JPC – Journal of Planar Chromatography – Modern TLC - A high-performance thin-layer chromatographic (HPTLC) method has been established for simple and rapid quantification of two... 相似文献
27.
We present exact numerical results for a symmetric layered medium (prism/Ag film/nonlinear dielectric/Ag film/prism) where
the middle dielectric slab is assumed to have a saturation-type nonlinearity. We show bistable behaviour in the power dependence
of the reflectivity ofp-polarized light under the condition when coupled surface modes are excited in the structure. Moreover, we study the effect
of saturation on the bistable behaviour to show that multivalued character is inhibited by saturation effects. The field distributions
corresponding to the minimum reflectivity states of the nonlinear structure are also presented. 相似文献
28.
Gamma ray bursts (GRBs) have been proposed as one possible class of sources of the ultrahigh energy cosmic ray (UHECR) events
observed up to energies ≳ 1020 eV. The synchrotron radiation of the highest energy protons accelerated within the GRB source should produce gamma rays up
to TeV energies. Here we briefly discuss the implications on the energetics of the GRB from the point of view of the detectability
of the prompt TeV γ-rays of proton-synchrotron origin in GRBs in the up-coming ICECUBE muon detector in the south pole. 相似文献
29.
In survival or reliability studies, the mean residual life or life expectancy is an important characteristic of the model. Whereas the failure rate can be expressed quite simply in terms of the mean residual life and its derivative, the inverse problem—namely that of expressing the mean residual life in terms of the failure rate—typically involves an integral of a complicated expression. In this paper, we obtain simple expressions for the mean residual life in terms of the failure rate for certain classes of distributions which subsume many of the standard cases. Several results in the literature can be obtained using our approach. Additionally, we develop an expansion for the mean residual life in terms of Gaussian probability functions for a broad class of ultimately increasing failure rate distributions. Some examples are provided to illustrate the procedure. 相似文献
30.
Alick KT Law Deepak Gupta Shawn Levy Douglas C Wallace Robert J McKeon Charles R Buck 《BMC neuroscience》2004,5(1):1