首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   98456篇
  免费   5189篇
  国内免费   5322篇
化学   21803篇
晶体学   416篇
力学   3906篇
综合类   532篇
数学   11020篇
物理学   20967篇
综合类   50323篇
  2024年   202篇
  2023年   734篇
  2022年   1477篇
  2021年   1617篇
  2020年   1663篇
  2019年   1683篇
  2018年   1515篇
  2017年   1788篇
  2016年   2007篇
  2015年   2403篇
  2014年   4366篇
  2013年   5201篇
  2012年   5097篇
  2011年   5570篇
  2010年   4441篇
  2009年   5747篇
  2008年   6049篇
  2007年   7088篇
  2006年   6300篇
  2005年   5224篇
  2004年   4527篇
  2003年   4653篇
  2002年   4787篇
  2001年   3770篇
  2000年   3281篇
  1999年   2696篇
  1998年   2320篇
  1997年   1627篇
  1996年   1519篇
  1995年   1325篇
  1994年   1268篇
  1993年   980篇
  1992年   1021篇
  1991年   769篇
  1990年   692篇
  1989年   590篇
  1988年   473篇
  1987年   399篇
  1986年   307篇
  1985年   244篇
  1984年   238篇
  1983年   139篇
  1982年   189篇
  1981年   184篇
  1980年   122篇
  1979年   157篇
  1978年   129篇
  1977年   119篇
  1976年   77篇
  1973年   59篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
931.
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   
932.
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   
933.
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   
934.
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   
935.
MEASUREMENTSOFFeANDCuK-ShelIONIZATIONCROSSSECTIONSBYSLOWELECTRONIMPACTLiTaihuaAnZhuLuoZhengmingCenterforRadiationPhysics,Ins...  相似文献   
936.
电子被HF和HCl分子散射总截面的计算   总被引:1,自引:1,他引:0  
利用光学势方法计算了能量在10eV—1000eV范围内电子被H、F和Cl原子散射的总截面,并与已有的实验结果和理论计算进行了比较;又利用可加性规则(additivityrule)计算得到了电子被HF和HCl分子散射的总截面,计算结果也与已有的实验结果和理论计算进行了比较  相似文献   
937.
l.IntroductionowingtotheirpromisingproPertiesandPOtentialapplications,transitionmetalni-trideshavedrawngreatattentionandthepreparationandinvestigationofthesecom-poundshavebeenasubjectbothofscientificandoftechnologicalinterest.Transitionmetalnitridescombineadvantagesofexce1lenthardness,highmeltingPOint,goodchemi-calstabilityandhigheIectricalconductivity[11,henceoverlaySofthesecompoundshavefoundwideappIicationsinvariousfie1ds.Molybdenumnitrides,inparticular,havealsoemergedasverypromisingcandi…  相似文献   
938.
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   
939.
本文在左截断右删失数据下获得了概论密度的核估计的L1距离的一个上界.  相似文献   
940.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号