全文获取类型
收费全文 | 21578篇 |
免费 | 698篇 |
国内免费 | 118篇 |
专业分类
化学 | 15528篇 |
晶体学 | 191篇 |
力学 | 408篇 |
综合类 | 1篇 |
数学 | 3187篇 |
物理学 | 3079篇 |
出版年
2022年 | 163篇 |
2021年 | 230篇 |
2020年 | 341篇 |
2019年 | 321篇 |
2018年 | 215篇 |
2017年 | 204篇 |
2016年 | 466篇 |
2015年 | 424篇 |
2014年 | 509篇 |
2013年 | 1070篇 |
2012年 | 1076篇 |
2011年 | 1414篇 |
2010年 | 717篇 |
2009年 | 607篇 |
2008年 | 1128篇 |
2007年 | 1198篇 |
2006年 | 1200篇 |
2005年 | 1162篇 |
2004年 | 969篇 |
2003年 | 824篇 |
2002年 | 808篇 |
2001年 | 266篇 |
2000年 | 269篇 |
1999年 | 249篇 |
1998年 | 243篇 |
1997年 | 275篇 |
1996年 | 309篇 |
1995年 | 247篇 |
1994年 | 229篇 |
1993年 | 260篇 |
1992年 | 220篇 |
1991年 | 196篇 |
1990年 | 186篇 |
1989年 | 145篇 |
1988年 | 154篇 |
1987年 | 174篇 |
1986年 | 148篇 |
1985年 | 207篇 |
1984年 | 256篇 |
1983年 | 188篇 |
1982年 | 225篇 |
1981年 | 247篇 |
1980年 | 190篇 |
1979年 | 191篇 |
1978年 | 219篇 |
1977年 | 167篇 |
1976年 | 166篇 |
1975年 | 154篇 |
1974年 | 168篇 |
1973年 | 144篇 |
排序方式: 共有10000条查询结果,搜索用时 390 毫秒
51.
52.
53.
Paul Fabel 《Topology and its Applications》2007,154(3):635-638
With a certain natural topology, the fundamental group of a locally path connected metric space X becomes discrete if and only if X is semilocally simply connected. We include some related material and offer a counterexample to a similar result. 相似文献
54.
55.
Paul Rohland 《Colloid and polymer science》1911,9(1):21-22
Ohne Zusammenfassung 相似文献
56.
What features characterize complex system dynamics? Power laws and scale invariance of fluctuations are often taken as the hallmarks of complexity, drawing on analogies with equilibrium critical phenomena. Here we argue that slow, directed dynamics, during which the system's properties change significantly, is fundamental. The underlying dynamics is related to a slow, decelerating but spasmodic release of an intrinsic strain or tension. Time series of a number of appropriate observables can be analyzed to confirm this effect. The strain arises from local frustration. As the strain is released through “quakes,” some system variable undergoes record statistics with accompanying log‐Poisson statistics for the quake event times. We demonstrate these phenomena via two very different systems: a model of magnetic relaxation in type II superconductors and the Tangled Nature model of evolutionary ecology and show how quantitative indications of aging can be found. © 2004 Wiley Periodicals, Inc. Complexity 10: 49–56, 2004 相似文献
57.
David S. Dummit Brett A. Tangedal Paul B. van Wamelen. 《Mathematics of Computation》2004,73(247):1525-1546
Systematic computation of Stark units over nontotally real base fields is carried out for the first time. Since the information provided by Stark's conjecture is significantly less in this situation than the information provided over totally real base fields, new techniques are required. Precomputing Stark units in relative quadratic extensions (where the conjecture is already known to hold) and coupling this information with the Fincke-Pohst algorithm applied to certain quadratic forms leads to a significant reduction in search time for finding Stark units in larger extensions (where the conjecture is still unproven). Stark's conjecture is verified in each case for these Stark units in larger extensions and explicit generating polynomials for abelian extensions over complex cubic base fields, including Hilbert class fields, are obtained from the minimal polynomials of these new Stark units.
58.
We initiate the study of a new measure of approximation. This measure compares the performance of an approximation algorithm to the random assignment algorithm. This is a useful measure for optimization problems where the random assignment algorithm is known to give essentially the best possible polynomial time approximation. In this paper, we focus on this measure for the optimization problems Max‐Lin‐2 in which we need to maximize the number of satisfied linear equations in a system of linear equations modulo 2, and Max‐k‐Lin‐2, a special case of the above problem in which each equation has at most k variables. The main techniques we use, in our approximation algorithms and inapproximability results for this measure, are from Fourier analysis and derandomization. © 2004 Wiley Periodicals, Inc. Random Struct. Alg., 2004 相似文献
59.
The thermal migration of cyclic and acyclic organoboranes were studied. In most cases, a stereoselective 1,2-dyotropic migration was observed, allowing the stereocontrol of three contiguous chiral centers. Scope and limitations of this thermal migration are presented. 相似文献
60.
The periodic precipitation pattern formation in gelatinous media is interpreted as a moving boundary problem. The time law,
spacing law and width law are revisited on the basis of the new scenario. The explicit dependence of the geometric structure
on the initial concentrations of the reactants is derived. Matalon—Packter law, which relates the spacing coefficient with
the initial concentrations is reformulated removing many ambiguities and impractical parameters. Experimental results are
discussed to establish the significance of moving boundary concept in the diffusion controlled pattern forming systems 相似文献