全文获取类型
收费全文 | 6124篇 |
免费 | 362篇 |
国内免费 | 279篇 |
专业分类
化学 | 1018篇 |
晶体学 | 9篇 |
力学 | 1107篇 |
综合类 | 60篇 |
数学 | 3843篇 |
物理学 | 728篇 |
出版年
2024年 | 3篇 |
2023年 | 25篇 |
2022年 | 63篇 |
2021年 | 88篇 |
2020年 | 100篇 |
2019年 | 250篇 |
2018年 | 260篇 |
2017年 | 105篇 |
2016年 | 146篇 |
2015年 | 169篇 |
2014年 | 317篇 |
2013年 | 374篇 |
2012年 | 305篇 |
2011年 | 518篇 |
2010年 | 416篇 |
2009年 | 485篇 |
2008年 | 487篇 |
2007年 | 544篇 |
2006年 | 419篇 |
2005年 | 264篇 |
2004年 | 222篇 |
2003年 | 220篇 |
2002年 | 116篇 |
2001年 | 76篇 |
2000年 | 81篇 |
1999年 | 89篇 |
1998年 | 69篇 |
1997年 | 65篇 |
1996年 | 64篇 |
1995年 | 58篇 |
1994年 | 56篇 |
1993年 | 53篇 |
1992年 | 46篇 |
1991年 | 30篇 |
1990年 | 20篇 |
1989年 | 24篇 |
1988年 | 20篇 |
1987年 | 19篇 |
1986年 | 14篇 |
1985年 | 24篇 |
1984年 | 14篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1977年 | 2篇 |
1971年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有6765条查询结果,搜索用时 15 毫秒
1.
In this paper we study the domain of the generator of stable processes, stable-like processes and more general pseudo- and integro-differential operators which naturally arise both in analysis and as infinitesimal generators of Lévy- and Lévy-type (Feller) processes. In particular we obtain conditions on the symbol of the operator ensuring that certain (variable order) Hölder and Hölder–Zygmund spaces are in the domain. We use tools from probability theory to investigate the small-time asymptotics of the generalized moments of a Lévy or Lévy-type process , for functions f which are not necessarily bounded or differentiable. The pointwise limit exists for fixed if f satisfies a Hölder condition at x. Moreover, we give sufficient conditions which ensure that the limit exists uniformly in the space of continuous functions vanishing at infinity. As an application we prove that the domain of the generator of contains certain Hölder spaces of variable order. Our results apply, in particular, to stable-like processes, relativistic stable-like processes, solutions of Lévy-driven SDEs and Lévy processes. 相似文献
2.
3.
Zihua Guo Xingxing Liu Luc Molinet Zhaoyang Yin 《Journal of Differential Equations》2019,266(2-3):1698-1707
We prove norm inflation and hence ill-posedness for a class of shallow water wave equations, such as the Camassa–Holm equation, Degasperis–Procesi equation and Novikov equation etc., in the critical Sobolev space and even in the Besov space for . Our results cover both real-line and torus cases (only real-line case for Novikov), solving an open problem left in the previous works ([5], [14], [16]). 相似文献
4.
Tomasz Przebinda 《Journal of Functional Analysis》2018,274(5):1284-1305
We relate the distribution characters and the wave front sets of unitary representation for real reductive dual pairs of type I in the stable range. 相似文献
5.
6.
Mark Prendergast Cormac Breen Aibhin Bray Fiona Faulkner Brian Carroll Dominic Quinn 《International Journal of Mathematical Education in Science & Technology》2018,49(8):1203-1218
Many studies over the past 30 years have highlighted the important role of students’ beliefs for successful problem-solving in mathematics. Given the recent emphasis afforded to problem-solving on the reformed Irish secondary school mathematics curriculum, the main aim of this study was to identify Irish students’ (n = 975) beliefs about the field. A quantitative measure of these beliefs was attained through the use of the Indiana Mathematical Belief Scale, an existing 30-item (five-scale) self-report questionnaire. A statistical analysis of the data revealed that students who were further through their secondary education had a stronger belief that not all problems could be solved by applying routine procedures. In contrast, the same students held less positive beliefs than their younger counterparts that they could solve time-consuming problems and that conceptual understanding was important. The analysis also indicated that gender had a significant impact on three of the five belief scales. 相似文献
7.
This work deals with a study of the dynamic and buckling analysis of polymer hybrid composite(PHC) beam. The beam has variable thickness and is reinforced by carbon nanotubes(CNTs) and nanoclay(NC) simultaneously. The governing equations are derived based on the first shear deformation theory(FSDT). A three-phase HalpinTsai approach is used to predict the mechanical properties of the PHC. We focus our attention on the effect of the simultaneous addition of NC and CNT on the vibration and buckling analysis of the PHC beam with variable thickness. Also a comparison study is done on the sensation of three impressive parameters including CNT, NC weight fractions, and the shape factor of fillers on the mechanical properties of PHC beams,as well as fundamental frequencies of free vibrations and critical buckling load. The results show that the increase of shape factor value, NC, and CNT weight fractions leads to considerable reinforcement in mechanical properties as well as increase of the dimensionless fundamental frequency and buckling load. The variation of CNT weight fraction on elastic modulus is more sensitive rather than shear modulus but the effect of NC weight fraction on elastic and shear moduli is fairly the same. The shape factor values more than the medium level do not affect the mechanical properties. 相似文献
8.
应用Hamilton原理建立了双路传力的无轴承旋翼运动方程。采用均匀入流模型,基于直升机飞行平衡条件,建立了无轴承旋翼柔性梁载荷的计算模型,并通过算例验证了模型的精度。利用该模型,研究了全机重心位置、机身气动阻力以及平尾安装角对柔性梁载荷特性的影响,给出了各因素对柔性梁载荷的影响趋势,得出了降低柔性梁载荷的方法。数值结果表明:2cm左右重心位置的变化能够引起9%~11%的柔性梁载荷变化量,15%气动阻力的增加会导致约9%的柔性梁载荷的增大;2°平尾安装角的变化引起约10%柔性梁载荷的变化量,3°平尾安装角的变化引起约26%柔性梁载荷的变化。 相似文献
9.
Understanding the complicated failure mechanisms of hierarchical composites such as fiber yarns is essential for advanced materials design. In this study, we developed a new Monte Carlo model for predicting the mechanical properties of fiber yarns that includes statistical variation in fiber strength. Furthermore, a statistical shear load transfer law based on the shear lag analysis was derived and implemented to simulate the interactions between adjacent fibers and provide a more accurate tensile stress distribution along the overlap distance. Simulations on two types of yarns, made from different raw materials and based on distinct processing approaches, predict yarn strength values that compare favorably with experimental measurements. Furthermore, the model identified very distinct dominant failure mechanisms for the two materials, providing important insights into design features that can improve yarn strength. 相似文献
10.