全文获取类型
收费全文 | 108796篇 |
免费 | 8971篇 |
国内免费 | 6810篇 |
专业分类
化学 | 40514篇 |
晶体学 | 1944篇 |
力学 | 4057篇 |
综合类 | 1059篇 |
数学 | 28220篇 |
物理学 | 48783篇 |
出版年
2023年 | 463篇 |
2022年 | 669篇 |
2021年 | 1612篇 |
2020年 | 1434篇 |
2019年 | 1699篇 |
2018年 | 1525篇 |
2017年 | 1268篇 |
2016年 | 1226篇 |
2015年 | 1249篇 |
2014年 | 2165篇 |
2013年 | 3779篇 |
2012年 | 2461篇 |
2011年 | 3286篇 |
2010年 | 3835篇 |
2009年 | 8635篇 |
2008年 | 9594篇 |
2007年 | 8019篇 |
2006年 | 7074篇 |
2005年 | 4894篇 |
2004年 | 4715篇 |
2003年 | 4739篇 |
2002年 | 7806篇 |
2001年 | 4240篇 |
2000年 | 3945篇 |
1999年 | 3693篇 |
1998年 | 3132篇 |
1997年 | 2273篇 |
1996年 | 2124篇 |
1995年 | 2577篇 |
1994年 | 2500篇 |
1993年 | 2011篇 |
1992年 | 1523篇 |
1991年 | 1109篇 |
1990年 | 906篇 |
1989年 | 800篇 |
1988年 | 792篇 |
1987年 | 579篇 |
1986年 | 383篇 |
1985年 | 1226篇 |
1984年 | 827篇 |
1983年 | 610篇 |
1982年 | 891篇 |
1981年 | 1047篇 |
1980年 | 943篇 |
1979年 | 824篇 |
1978年 | 743篇 |
1977年 | 635篇 |
1976年 | 615篇 |
1974年 | 376篇 |
1973年 | 514篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
1.
2.
《Discrete Mathematics》2022,345(12):113083
Let G be a graph, the order of G, the connectivity of G and k a positive integer such that . Then G is said to be k-extendable if it has a matching of size k and every matching of size k extends to a perfect matching of G. A Hamiltonian path of a graph G is a spanning path of G. A bipartite graph G with vertex sets and is defined to be Hamiltonian-laceable if such that and for every pair of vertices and , there exists a Hamiltonian path in G with endpoints p and q, or and for every pair of vertices , there exists a Hamiltonian path in G with endpoints p and q. Let G be a bipartite graph with bipartition . Define to be a maximum integer such that and (1) for each non-empty subset S of X, if , then , and if , then ; and (2) for each non-empty subset S of Y, if , then , and if , then ; and (3) if there is no non-negative integer satisfying (1) and (2).Let G be a bipartite graph with bipartition such that and . In this paper, we show that if , then G is Hamiltonian-laceable; or if , then for every pair of vertices and , there is an -path P in G with . We show some of its corollaries in k-extendable, bipartite graphs and a conjecture in k-extendable graphs. 相似文献
3.
本文设计了一种梯形的周期极化掺镁铌酸锂(PPMgLN)波导,并通过在传播方向上引入温度梯度来拓宽其倍频(SHG)过程的泵浦光源可接收带宽。通过有限差分的光束传输法,计算波导的有效折射率,并进行波导尺寸的设计。结果表明,通过改变梯形波导不同位置的温度,使其形成一个温度梯度,可拓宽泵浦光源的波长可接收带宽。本文所设计的PPMgLN波导最大泵浦光源可接收带宽为C波段,即1 530~1 565 nm,该波导可倍频C波段,得到输出波段带宽为765~782.5 nm,温度调谐范围为30~150 ℃。 相似文献
4.
5.
6.
7.
A general framework for describing photofission observables of actinides at an average excitation energy below 30 MeV 下载免费PDF全文
Guan-Lin Wang Hao-Yang Lan Xiao-Ming Shi Zhi-Chao Zhu Wen Luo 《中国物理C(英文版)》2022,46(8):084102-084102-14
A reasonable prediction of photofission observables plays a paramount role in understanding the photofission process and guiding various photofission-induced applications, such as short-lived isotope production, nuclear waste disposal, and nuclear safeguards. However, the available experimental data for photofission observables are limited, and the existing models and programs have mainly been developed for neutron-induced fission processes. In this study, a general framework is proposed for characterizing the photofission observables of actinides, including the mass yield distributions (MYD) and isobaric charge distributions (ICD) of fission fragments and the multiplicity and energy distributions of prompt neutrons (np) and prompt γ rays (γp). The framework encompasses various systematic neutron models and empirical models considering the Bohr hypothesis and does not rely on the experimental data as input. These models are then validated individually against experimental data at an average excitation energy below 30 MeV, which shows the reliability and robustness of the general framework. Finally, we employ this framework to predict the characteristics of photofission fragments and the emissions of prompt particles for typical actinides including 232Th, 235, 238U and 240Pu. It is found that the 238U(γ, f) reaction is more suitable for producing neutron-rich nuclei compared to the 232Th(γ, f) reaction. In addition, the average multiplicity number of both np and γp increases with the average excitation energy. 相似文献
8.
铋基卤化物材料因其无毒和优良的光电性能而显示出巨大的应用潜力。BiI3作为一种层状重金属半导体,已被用于X射线检测、γ射线检测和压力传感器等领域,最近其作为一种薄膜太阳能电池吸收材料备受关注。本文采用简单的气相输运沉积(VTD)法,以BiI3晶体粉末作为蒸发源,在玻璃基底上得到高质量c轴择优取向的BiI3薄膜。并通过研究蒸发源温度和沉积距离对薄膜物相和形貌的影响,分析了BiI3薄膜择优生长的机理。结果表明VTD法制备的BiI3薄膜属于三斜晶系,其光学带隙为~1.8 eV。沉积温度对薄膜的择优取向有较大影响,在沉积温度低于270 ℃时,沉积的薄膜具有沿c轴择优取向生长的特点,超过此温度,c轴择优取向生长消失。在衬底温度为250 ℃、沉积距离为15 cm时制备的薄膜结晶性能最好,晶体形貌为片状八面体。 相似文献
9.
Based on the primal mixed variational formulation, a stabilized nonconforming mixed finite element method is proposed for the linear elasticity on rectangular and cubic meshes. Two kinds of penalty terms are introduced in the stabilized mixed formulation, which are the jump penalty term for the displacement and the divergence penalty term for the stress. We use the classical nonconforming rectangular and cubic elements for the displacement and the discontinuous piecewise polynomial space for the stress, where the discrete space for stress are carefully chosen to guarantee the well-posedness of discrete formulation. The stabilized mixed method is locking-free. The optimal convergence order is derived in the $L^2$-norm for stress and in the broken $H^1$-norm and $L^2$-norm for displacement. A numerical test is carried out to verify the optimal convergence of the stabilized method. 相似文献
10.
Given a graph sequence denote by T3(Gn) the number of monochromatic triangles in a uniformly random coloring of the vertices of Gn with colors. In this paper we prove a central limit theorem (CLT) for T3(Gn) with explicit error rates, using a quantitative version of the martingale CLT. We then relate this error term to the well-known fourth-moment phenomenon, which, interestingly, holds only when the number of colors satisfies . We also show that the convergence of the fourth moment is necessary to obtain a Gaussian limit for any , which, together with the above result, implies that the fourth-moment condition characterizes the limiting normal distribution of T3(Gn), whenever . Finally, to illustrate the promise of our approach, we include an alternative proof of the CLT for the number of monochromatic edges, which provides quantitative rates for the results obtained in [7]. 相似文献