全文获取类型
收费全文 | 30294篇 |
免费 | 793篇 |
国内免费 | 191篇 |
专业分类
化学 | 20634篇 |
晶体学 | 241篇 |
力学 | 785篇 |
综合类 | 1篇 |
数学 | 4942篇 |
物理学 | 4675篇 |
出版年
2022年 | 160篇 |
2021年 | 250篇 |
2020年 | 312篇 |
2019年 | 383篇 |
2018年 | 302篇 |
2017年 | 264篇 |
2016年 | 578篇 |
2015年 | 458篇 |
2014年 | 603篇 |
2013年 | 1560篇 |
2012年 | 1479篇 |
2011年 | 1872篇 |
2010年 | 936篇 |
2009年 | 759篇 |
2008年 | 1674篇 |
2007年 | 1725篇 |
2006年 | 1710篇 |
2005年 | 1648篇 |
2004年 | 1444篇 |
2003年 | 1228篇 |
2002年 | 1164篇 |
2001年 | 406篇 |
2000年 | 330篇 |
1999年 | 281篇 |
1998年 | 319篇 |
1997年 | 352篇 |
1996年 | 447篇 |
1995年 | 332篇 |
1994年 | 309篇 |
1993年 | 319篇 |
1992年 | 296篇 |
1991年 | 271篇 |
1990年 | 251篇 |
1989年 | 255篇 |
1988年 | 282篇 |
1987年 | 264篇 |
1986年 | 257篇 |
1985年 | 410篇 |
1984年 | 464篇 |
1983年 | 336篇 |
1982年 | 445篇 |
1981年 | 420篇 |
1980年 | 364篇 |
1979年 | 345篇 |
1978年 | 372篇 |
1977年 | 348篇 |
1976年 | 291篇 |
1975年 | 286篇 |
1974年 | 273篇 |
1973年 | 245篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
51.
John Strantzen 《Journal of Geometry》1989,36(1-2):160-172
52.
53.
Given a1,a2,...,an ∈ ℤ^d$, we examine the set, G, of all non-negative integer combinations of these ai. In particular, we examine the generating function f(z) = ∑b ∈ Gzb. We prove that one can write this generating function as a rational function using the neighborhood complex (sometimes called
the complex of maximal lattice-free bodies or the Scarf complex) on a particular lattice in ℤn. In the generic case, this follows from algebraic results of Bayer and Sturmfels. Here we prove it geometrically in all
cases, and we examine a generalization involving the neighborhood complex on an arbitrary lattice. 相似文献
54.
55.
Frank H.G.M. Wijnands Charles G. Crookes Paul M. Charles Richard M. Ash Ian F. Lealman Michael J. Robertson Anthony E. Kelly Kevin A. Williams Aeneas B. Massara Richard V. Penty Ian H. White 《Optical and Quantum Electronics》2002,34(10):959-973
An anomalous modulation in the wavelength spectrum has been observed in lasers with spot-size converters. This intensity modulation is shown to be caused by beating between the fundamental lasing mode and radiation modes in the taper. This results in a periodic modulation in the net gain spectrum, which causes wavelength jumps between adjacent net gain maxima, and a drive current dependent spectral width that is expected to affect system performance. The amplitude of this spectral modulation is reduced significantly by either using an angled rear-facet which reflects the beating radiation modes away from the laser axis, or by using a nonlinear, adiabatic taper. 相似文献
56.
57.
In an earlier paper on a malignant cell invasion model (Marchantet al., SIAM J. Appl. Math, 60, 2000) we introduced a novelform of discontinuous travelling wave solution. These solutionscould be studied easily by combining behaviour within a phaseplane with the RankineHugoniot shock conditions, whichdescribe properties (such as the ratio of the jump discontinuitiesto the speed of propagation) that solutions may possess. Theseresults were new for several reasons. The shock conditions relateto hyperbolic equations (which the model is) but were appliedin a travelling wave ordinary differential equation phase planeusing techniques that usually apply to parabolic reactiondiffusionsystems. In addition the solutions possess singular behaviournear several points in the phase plane but in spite of thisthere exists a robust and stable family of physically interestingsolutions. In this paper we discuss two previously studied models, oneof detonation theory and one of angiogenesis. We show that eachof these models also possesses a family of discontinuous travellingwave solutions which was not previously discovered. Of particularinterest is the solution which has a blunt interface at thefront of the invading profile. In all three models it is thissolution that is seen to stably evolve from physically relevantinitial data, and for physically relevant parameter values. This work confirms the robustness of these novel travellingwave solutions and their applicability to a wider range of mathematicalmodelling situations. 相似文献
58.
Apurba Bhattacharya Nitin C. Patel Michael Peddicord Luca Parlanti John A. Grosso 《Tetrahedron letters》2006,47(30):5341-5343
An efficient, one-pot, phase transfer N-amination technology was developed. The protocol utilizes chloramine, an inexpensive and safe electrophilic aminating agent potentially viable for commercial manufacturing. 相似文献
59.
John T. Herron 《国际化学动力学杂志》1987,19(2):129-142
The gas phase chemical kinetics of SF4, SF5, and S2F10 are reviewed with particular emphasis on relevance to the general problem of the dielectric breakdown of SF6. Specific reaction systems treated are SF4 + F2, SF5 + SF5, and the pyrolysis of S2F10. Computer modeling calculations were carried out to arrive at the best estimates of rate parameters. Based on the results of these calculations, sets of recommended rate parameters are provided. The major discrepancies and problems in establishing the kinetic data base are described. Thermochemical consequences of different model calculations are given. 相似文献
60.
John A. Ryan 《Discrete Applied Mathematics》2006,154(2):399-412
We consider irreducible Goppa codes over Fq of length qn defined by polynomials of degree r, where q is a prime power and n,r are arbitrary positive integers. We obtain an upper bound on the number of such codes. 相似文献