全文获取类型
收费全文 | 6929篇 |
免费 | 503篇 |
国内免费 | 585篇 |
专业分类
化学 | 623篇 |
晶体学 | 3篇 |
力学 | 95篇 |
综合类 | 167篇 |
数学 | 6736篇 |
物理学 | 393篇 |
出版年
2024年 | 16篇 |
2023年 | 127篇 |
2022年 | 159篇 |
2021年 | 153篇 |
2020年 | 231篇 |
2019年 | 255篇 |
2018年 | 249篇 |
2017年 | 252篇 |
2016年 | 166篇 |
2015年 | 132篇 |
2014年 | 229篇 |
2013年 | 631篇 |
2012年 | 271篇 |
2011年 | 367篇 |
2010年 | 373篇 |
2009年 | 528篇 |
2008年 | 493篇 |
2007年 | 381篇 |
2006年 | 415篇 |
2005年 | 312篇 |
2004年 | 290篇 |
2003年 | 264篇 |
2002年 | 259篇 |
2001年 | 222篇 |
2000年 | 219篇 |
1999年 | 206篇 |
1998年 | 164篇 |
1997年 | 120篇 |
1996年 | 94篇 |
1995年 | 80篇 |
1994年 | 65篇 |
1993年 | 38篇 |
1992年 | 37篇 |
1991年 | 30篇 |
1990年 | 19篇 |
1989年 | 27篇 |
1988年 | 21篇 |
1987年 | 12篇 |
1986年 | 8篇 |
1985年 | 24篇 |
1984年 | 17篇 |
1983年 | 5篇 |
1982年 | 18篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1975年 | 6篇 |
1974年 | 2篇 |
排序方式: 共有8017条查询结果,搜索用时 921 毫秒
51.
R. Thomas conjectured, 20 years ago, that the presence of a positive circuit in the interaction graph of a dynamical system is a necessary condition for the presence of several stable states. Recently, E. Remy et al. stated and proved the conjecture for Boolean dynamical systems. Using a similar approach, we generalize the result to discrete dynamical systems, and by focusing on the asynchronous dynamics that R. Thomas used in the course of his analysis of genetic networks, we obtain a more general variant of R. Thomas’ conjecture. In this way, we get a necessary condition for genetic networks to lead to differentiation. 相似文献
52.
53.
The Efficient Determination Criterion (EDC) generalizes the AIC and BIC criteria and provides a class of consistent estimators
for the order of a Markov chain with finite state space. In this note, we derive rates of convergence for the EDC estimates.
*Partially supported by CNPq, CAPES/PROCAD, FAPDF/PRONEX, FINATEC and FUNPE/UnB.
**Partially supported by CAPES. 相似文献
54.
Valentin Brimkov 《Discrete Applied Mathematics》2007,155(14):1812-1825
We consider the problem of computing the Lovász theta function for circulant graphs Cn,J of degree four with n vertices and chord length J, 2?J?n. We present an algorithm that takes O(J) operations if J is an odd number, and O(n/J) operations if J is even. On the considered class of graphs our algorithm strongly outperforms the known algorithms for theta function computation. We also provide explicit formulas for the important special cases J=2 and J=3. 相似文献
55.
Influence of annealing and chain defects on the melting behaviour of poly(vinylidene fluoride) 总被引:2,自引:0,他引:2
C. Marega 《European Polymer Journal》2003,39(8):1713-1720
The melting behaviour of poly(vinylidene fluoride) (PVDF) was investigated by differential scanning calorimetry (DSC) and small- and wide-angle X-ray scattering in order to study the influence of the chain defects content and of the temperature of annealing on the crystallization and melting behaviour.All the DSC scans show a double endotherm and the analysis of the data suggests that the low temperature endotherm is due to the melting of a population of thin lamellae, whose thickness increases during the annealing, but a high content of chain defects prevents the lamellar thickening and the main effect in this case is the crystallization of thin lamellae from a portion of polymer which did not crystallize during the quenching from the melt. Furthermore, the two melting endotherms, which are observed, can be partially ascribed to a melting-recrystallization process.Furthermore, stepwise isothermal cooling was performed in a differential scanning calorimeter followed by melting scans of fractionated PVDF samples to point out the possible presence of a series of endothermic peaks. 相似文献
56.
Using Lagrange's multiplier rule, we find upper and lower bounds of the energy of a bipartite graph G, in terms of the number of vertices, edges and the spectral moment of fourth order. Moreover, the upper bound is attained in a graph G if and only if G is the graph of a symmetric balanced incomplete block design (BIBD). Also, we determine the graphs for which the lower bound is sharp. 相似文献
57.
An m‐covering of a graph G is a spanning subgraph of G with maximum degree at most m. In this paper, we shall show that every 3‐connected graph on a surface with Euler genus k ≥ 2 with sufficiently large representativity has a 2‐connected 7‐covering with at most 6k ? 12 vertices of degree 7. We also construct, for every surface F2 with Euler genus k ≥ 2, a 3‐connected graph G on F2 with arbitrarily large representativity each of whose 2‐connected 7‐coverings contains at least 6k ? 12 vertices of degree 7. © 2003 Wiley Periodicals, Inc. J Graph Theory 43: 26–36, 2003 相似文献
58.
设{Xni:1≤i≤n,n≥1}为行间独立的B值r.v.阵列,g(z)是指数为1/p的正则变化函数,r>0,{ani 1≤t≤n,n≥1}为实数阵列,本文得到了使(?)成立的条件,推广并改进了Stout及Sung等的著名结论. 相似文献
59.