全文获取类型
收费全文 | 31135篇 |
免费 | 5579篇 |
国内免费 | 3277篇 |
专业分类
化学 | 22036篇 |
晶体学 | 351篇 |
力学 | 1813篇 |
综合类 | 137篇 |
数学 | 2983篇 |
物理学 | 12671篇 |
出版年
2024年 | 135篇 |
2023年 | 697篇 |
2022年 | 1207篇 |
2021年 | 1380篇 |
2020年 | 1397篇 |
2019年 | 1380篇 |
2018年 | 1167篇 |
2017年 | 1051篇 |
2016年 | 1599篇 |
2015年 | 1514篇 |
2014年 | 1950篇 |
2013年 | 2400篇 |
2012年 | 2860篇 |
2011年 | 2883篇 |
2010年 | 1873篇 |
2009年 | 1785篇 |
2008年 | 1998篇 |
2007年 | 1740篇 |
2006年 | 1625篇 |
2005年 | 1284篇 |
2004年 | 983篇 |
2003年 | 766篇 |
2002年 | 757篇 |
2001年 | 589篇 |
2000年 | 469篇 |
1999年 | 594篇 |
1998年 | 511篇 |
1997年 | 499篇 |
1996年 | 492篇 |
1995年 | 426篇 |
1994年 | 342篇 |
1993年 | 282篇 |
1992年 | 280篇 |
1991年 | 224篇 |
1990年 | 203篇 |
1989年 | 151篇 |
1988年 | 92篇 |
1987年 | 79篇 |
1986年 | 104篇 |
1985年 | 73篇 |
1984年 | 37篇 |
1983年 | 44篇 |
1982年 | 28篇 |
1981年 | 22篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1957年 | 4篇 |
1923年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
Nd:LMA自锁模飞秒激光器腔结构最佳化设计 总被引:1,自引:0,他引:1
Nd:LMA晶体相对低的非线性折射率n2,使得针对Ti:Sapphire自锁模激光器设计的腔,对Nd:LMA介质而言并没有提供足够的自幅度调制(SAM).为了在Nd:LMA激光器上实现自锁模,在腔内引入一个具有大的非线性系数n2、快的响应时间的SF57介质,这样就使得激光腔的结构比较特殊.在这篇文章里利用ABCD传输矩阵对该激光器的结构从理论上进行了分析和计算,使腔结构达到了最佳化设计. 相似文献
962.
A multicone graph is defined to be the join of a clique and a regular graph. Based on Zhou and Cho’s result [B. Zhou, H.H. Cho, Remarks on spectral radius and Laplacian eigenvalues of a graph, Czech. Math. J. 55 (130) (2005), 781–790], the spectral characterization of multicone graphs is investigated. Particularly, we determine a necessary
and sufficient condition for two multicone graphs to be cospectral graphs and investigate the structures of graphs cospectral
to a multicone graph. Additionally, lower and upper bounds for the largest eigenvalue of a multicone graph are given. 相似文献
963.
964.
Weihua Zhao Riquan Zhang Zhensheng HuangJingyan Feng 《Journal of multivariate analysis》2012,103(1):116-123
An important model in handling the multivariate data is the partially linear single-index regression model with a very flexible distribution—beta distribution, which is commonly used to model data restricted to some open intervals on the line. In this paper, the score test is extended to the partially linear single-index beta regression model. The penalized likelihood estimation based on P-spline is proposed. Based on the estimation, the score test statistics about varying dispersion parameter is given. Its asymptotical property is investigated. Both simulated examples are used to illustrate our proposed methods. 相似文献
965.
In this paper, we consider a renewal risk model with stochastic premiums income. We assume that the premium number process and the claim number process are a Poisson process and a generalized Erlang (n) processes, respectively. When the individual stochastic premium sizes are exponentially distributed, the Laplace transform and a defective renewal equation for the Gerber-Shiu discounted penalty function are obtained. Furthermore, the discounted joint distribution of the surplus just before ruin and the deficit at ruin is given. When the claim size distributions belong to the rational family, the explicit expression of the Gerber-Shiu discounted penalty function is derived. Finally, a specific example is provided. 相似文献
966.
967.
In this paper, we investigate some properties of the unital quantale Q[e], in terms of the quantic quotients of Q[e] we study the extensions of quantic nuclei of Q to Q[e] and prove that for any non-trivial quantale Q\textbf{Q}, Q[e] is not simple. Also, we give some applications for the unital quantale Q[e]. 相似文献
968.
969.
In this paper, we study a generalized Nicholson??s Blowflies model with feedback control and multiple time-varying delays. Under proper conditions, we employ a novel proof to establish some criteria to guarantee the global exponential convergence and permanence of this model. Moreover, we give two examples to illustrate our main results. 相似文献
970.
In the present paper, we mainly discuss the (??,?)-generalized fuzzy rough sets introduced by B.Q. Hu and Z.H. Huang with both constructive approach and axiomatic approach considered. In the former, we started from the investigation of the properties of the ??-upper and ?-lower approximation operators generated by binary fuzzy relations. In the latter, by defining a pair of fuzzy set-theoretic operators, we show (??,?)-fuzzy rough approximation operators can be characterized by different sets of axioms. 相似文献