全文获取类型
收费全文 | 109261篇 |
免费 | 5111篇 |
国内免费 | 5602篇 |
专业分类
化学 | 22409篇 |
晶体学 | 432篇 |
力学 | 4002篇 |
综合类 | 594篇 |
数学 | 11796篇 |
物理学 | 21554篇 |
综合类 | 59187篇 |
出版年
2024年 | 264篇 |
2023年 | 878篇 |
2022年 | 1866篇 |
2021年 | 1950篇 |
2020年 | 1974篇 |
2019年 | 1870篇 |
2018年 | 1637篇 |
2017年 | 1967篇 |
2016年 | 2228篇 |
2015年 | 2555篇 |
2014年 | 4777篇 |
2013年 | 5430篇 |
2012年 | 5672篇 |
2011年 | 6423篇 |
2010年 | 5134篇 |
2009年 | 6499篇 |
2008年 | 6840篇 |
2007年 | 8008篇 |
2006年 | 7043篇 |
2005年 | 5815篇 |
2004年 | 5119篇 |
2003年 | 5176篇 |
2002年 | 5155篇 |
2001年 | 4029篇 |
2000年 | 3419篇 |
1999年 | 2800篇 |
1998年 | 2409篇 |
1997年 | 1677篇 |
1996年 | 1563篇 |
1995年 | 1370篇 |
1994年 | 1302篇 |
1993年 | 992篇 |
1992年 | 1032篇 |
1991年 | 773篇 |
1990年 | 703篇 |
1989年 | 591篇 |
1988年 | 493篇 |
1987年 | 411篇 |
1986年 | 322篇 |
1985年 | 251篇 |
1984年 | 242篇 |
1983年 | 142篇 |
1982年 | 191篇 |
1981年 | 183篇 |
1980年 | 121篇 |
1979年 | 152篇 |
1978年 | 127篇 |
1977年 | 120篇 |
1976年 | 75篇 |
1973年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
XIE Fu-Ding Xiao-Shan LIU Feng 《理论物理通讯》2004,42(11)
Based on the rank analysis method, algorithmization idea, and symbolic computation, in this paper we have presented a method to construct the conservation laws for nonlinear evolution equations. The polynomial conservation laws for K (n 2, n) equations and mnK(m, n) equations are found by using of this approach and some new results have been obtained. 相似文献
993.
The three-dimensional structure of the calcite (104)-water interface has been determined with surface X-ray scattering. Nine crystal truncation rods (including specular and non-specular rods) were measured providing both vertical and lateral sensitivity to the interfacial structure. The results reveal that calcite is nearly ideally terminated with a single surface hydration layer that includes two inequivalent water molecules having distinct heights of 2.3 ± 0.1 and 3.5 ± 0.2 Å, each with a well-defined lateral registry with respect to the calcite surface. No additional layering of water is observed beyond this surface hydration layer. Small displacements in the outer two calcium carbonate layers were also observed. These results are compared with previous experimental and computational results. 相似文献
994.
Yoshihide Yoshimoto 《Surface science》2004,556(1):52-62
A conception of a structure formation suitable for nano-technology is proposed, which is programmable and suitable for mass production-like lithography. This conception utilizes the controlled folding of chains like the scan-lines of television. Its possibility and property were studied theoretically using the modeled chains consist of beads. By adopting the interaction among the beads which can distinguish the kind of the partner by its polarity and is chiral to break the chiral symmetry of the folded state, the special chains which have the unique ground states could be designed. In these ground states, the chains are folded like the scan-lines of television. The thermodynamic properties of the suggested chains were studied by the Monte Carlo simulations and the suggested chains showed the phase-transition-like behavior which is distinct compared to both the random chains and the chain that has only the non-specific attraction. The size dependence and the effects of adding the non-specific attraction and modifying the border of the folded conformation were also studied. 相似文献
995.
Doubly tunable sum frequency generation (SFG) spectra demonstrate that the water molecules at gold/electrolyte interface change their orientation with applied potential. At negative potentials, water molecules in the double layer align with their oxygen atom pointing to the solution. As potential became positive to be close to the potential of zero charge (PZC), the SFG signal decreased, suggesting the OH groups of the water molecule are either in random orientation or parallel to the electrode. As potential became more positive than the PZC, the SFG signal increased again with the oxygen-up orientation as same as in the negative potential region, indicating that water molecules interact with the adsorbed sulfate anions. The peak position of the SFG spectra indicates a relatively disordered state of water molecules at the gold electrode surface, in contrast to the previously observed ice-like structure of water at electrolyte/oxide interfaces. 相似文献
996.
WU Jiada WU Changzheng ZHONG Xiaoxia SONG Zhoumo LI Fuming 《Chinese Journal of Lasers》1997,6(2):161-168
l.IntroductionowingtotheirpromisingproPertiesandPOtentialapplications,transitionmetalni-trideshavedrawngreatattentionandthepreparationandinvestigationofthesecom-poundshavebeenasubjectbothofscientificandoftechnologicalinterest.Transitionmetalnitridescombineadvantagesofexce1lenthardness,highmeltingPOint,goodchemi-calstabilityandhigheIectricalconductivity[11,henceoverlaySofthesecompoundshavefoundwideappIicationsinvariousfie1ds.Molybdenumnitrides,inparticular,havealsoemergedasverypromisingcandi… 相似文献
997.
Contingent epiderivatives and set-valued optimization 总被引:24,自引:0,他引:24
In this paper we introduce the concept of the contingent epiderivative for a set-valued map which modifies a notion introduced by Aubin [2] as upper contingent derivative. It is shown that this kind of a derivative has important properties and is one possible generalization of directional derivatives in the single-valued convex case. For optimization problems with a set-valued objective function optimality conditions based on the concept of the contingent epiderivative are proved which are necessary and sufficient under suitable assumptions. 相似文献
998.
999.
1000.
资源共享方式若干问题的研讨 总被引:3,自引:1,他引:2
社会公用服务系统和工程技术系统,存在共同的资源共享问题。本文通过典例就资源共享方式的若干问题加以探究:讨论广义的多用户系统中人工资源共享方式的分类;阐述常用的共享方式的特点、优缺点;分析系统时间性能及其改进与共享方式的关系等。文章还提出在系统工程范畴里,应对社会公用服务和工程技术两类系统的资源共享方式予以综合研究,并相互借鉴和移植。 相似文献