全文获取类型
收费全文 | 2391篇 |
免费 | 105篇 |
国内免费 | 22篇 |
专业分类
化学 | 1481篇 |
晶体学 | 15篇 |
力学 | 81篇 |
数学 | 435篇 |
物理学 | 364篇 |
无线电 | 142篇 |
出版年
2023年 | 22篇 |
2022年 | 51篇 |
2021年 | 54篇 |
2020年 | 59篇 |
2019年 | 62篇 |
2018年 | 60篇 |
2017年 | 43篇 |
2016年 | 91篇 |
2015年 | 86篇 |
2014年 | 106篇 |
2013年 | 160篇 |
2012年 | 189篇 |
2011年 | 249篇 |
2010年 | 128篇 |
2009年 | 111篇 |
2008年 | 169篇 |
2007年 | 132篇 |
2006年 | 140篇 |
2005年 | 113篇 |
2004年 | 96篇 |
2003年 | 84篇 |
2002年 | 65篇 |
2001年 | 28篇 |
2000年 | 24篇 |
1999年 | 11篇 |
1998年 | 13篇 |
1997年 | 14篇 |
1996年 | 16篇 |
1995年 | 8篇 |
1994年 | 9篇 |
1993年 | 9篇 |
1992年 | 8篇 |
1990年 | 5篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1978年 | 8篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1975年 | 3篇 |
1973年 | 4篇 |
1971年 | 3篇 |
1961年 | 3篇 |
1942年 | 6篇 |
1940年 | 3篇 |
排序方式: 共有2518条查询结果,搜索用时 9 毫秒
191.
A mathematical two-phase model is used to numerically investigate physical and rheological effects on small, individual bubbles in high-viscosity liquids under pressure impact. It is found out that bubbles remain stable over time at high viscosity and surface tension. The steady case is considered and connected to the stability behavior of the bubble. An upper bound for the bubble radius is derived and the new equilibrium state of the bubble can be predicted by means of stability theorems of differential equations. Finally, the interaction of a limited number of well separated bubbles in an Hele-Shaw flow is mathematically analyzed to visualize and physically interpret their trajectories. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
192.
In the view of robotics or granular media mechanics, we ask for the statement of the dynamical evolution problem for multibody systems with contacts and friction. The “event driven” approach does not allow to state an evolution problem in a systematic way: it gives a peculiar status to the instants of impact and to the contact points although they are unknowns of the problem. This matter of fact has given rise to a new approach in the frictionless case [4, 6] we generalize to the case including friction. Following to the point of view of Lagrange on the equation of the dynamics, we emphasize the systematic use of virtual powers and duality. This bias suggests to put emphasis on generalized reaction forces in the statement of the evolution problem and not on local reaction forces of the real world. This point of view allows to escape from pathologies e.g. Painlevé paradox [5] and Kane Paradox [3]. The proposed evolution problem accounts for impacts and friction in case of multiple unilateral constraints. We prove the existence and uniqueness of the solution to the associated rate problem. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
193.
In a multi-secret sharing scheme (MSSS), \(\ell \) different secrets are distributed among the players in some set \(\mathcal{P }=\{P_1,\ldots ,P_n\}\) , each one according to an access structure. The trivial solution to this problem is to run \(\ell \) independent instances of a standard secret sharing scheme, one for each secret. In this solution, the length of the secret share to be stored by each player grows linearly with \(\ell \) (when keeping all other parameters fixed). Multi-secret sharing schemes have been studied by the cryptographic community mostly from a theoretical perspective: different models and definitions have been proposed, for both unconditional (information-theoretic) and computational security. In the case of unconditional security, there are two different definitions. It has been proved that, for some particular cases of access structures that include the threshold case, a MSSS with the strongest level of unconditional security must have shares with length linear in \(\ell \) . Therefore, the optimal solution in this case is equivalent to the trivial one. In this work we prove that, even for a more relaxed notion of unconditional security, and for some kinds of access structures (in particular, threshold ones), we have the same efficiency problem: the length of each secret share must grow linearly with \(\ell \) . Since we want more efficient solutions, we move to the scenario of MSSSs with computational security. We propose a new MSSS, where each secret share has constant length (just one element), and we formally prove its computational security in the random oracle model. To the best of our knowledge, this is the first formal analysis on the computational security of a MSSS. We show the utility of the new MSSS by using it as a key ingredient in the design of two schemes for two new functionalities: multi-policy signatures and multi-policy decryption. We prove the security of these two new multi-policy cryptosystems in a formal security model. The two new primitives provide similar functionalities as attribute-based cryptosystems, with some advantages and some drawbacks that we discuss at the end of this work. 相似文献
194.
195.
Brian N. Figgis Alexandre N. Sobolev Edward S. Kucharski Vanessa Broughton 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(6):e228-e229
The crystal structure of tripotassium sodium hexachloroferrate(II) has been determined by X‐ray diffraction at 293, 84 and 9.5 K. The accurate and extensive data sets collected should be suitable for charge–density analysis studies. 相似文献
196.
Alexandre Lumbroso Isabelle Beaudet Thierry Besson Erwan Le Grognec 《Tetrahedron》2009,65(45):9180-45
An efficient and reproducible synthesis of various α-ethoxycarbamates is described via a microwave heating mode. Compared to the thermal process, the microwave dielectric heating induces a dramatic reduction of the reaction time and the improvement of the yields. The reaction is general since applicable to aromatic and aliphatic aldehydes with various primary amines. Several examples involving chiral aldehydes have also been considered. 相似文献
197.
Gerd Finke Pierre Lemaire Jean-Marie Proth Maurice Queyranne 《European Journal of Operational Research》2009,199(3):702-705
In this paper, we present a new objective function for scheduling on parallel machines: minimizing the number of machines for schedules of minimum length. We study its complexity and we prove the NP-completeness of this problem, even if there is no precedences or for unitary execution times. We propose several polynomial algorithms for various particular cases. 相似文献
198.
199.
Javier Mazuela Oscar Pàmies Montserrat Diéguez Laetitia Palais Stephane Rosset Alexandre Alexakis 《Tetrahedron: Asymmetry》2010,21(17):2153-2157
A biaryl-based monophosphoroamidite L1–L4a–f and aminophosphine L5–L7a–f ligand library was screened in the Rh-catalyzed asymmetric hydroformylation of several vinylarenes and heterocyclic olefins. Our results indicate that the selectivity is strongly dependent on the ligand parameters and on the substrate type. Enantioselectivities (up to 46%) were moderate in the hydroformylation of several vinylarenes S1–S5 and promising (up to 58%) for the more challenging heterocyclic olefins S6–S9. 相似文献
200.