全文获取类型
收费全文 | 58554篇 |
免费 | 10522篇 |
国内免费 | 8540篇 |
专业分类
化学 | 29260篇 |
晶体学 | 767篇 |
力学 | 2577篇 |
综合类 | 506篇 |
数学 | 4493篇 |
物理学 | 16328篇 |
无线电 | 23685篇 |
出版年
2024年 | 255篇 |
2023年 | 1276篇 |
2022年 | 1931篇 |
2021年 | 2268篇 |
2020年 | 2167篇 |
2019年 | 2135篇 |
2018年 | 1942篇 |
2017年 | 2167篇 |
2016年 | 2491篇 |
2015年 | 3089篇 |
2014年 | 3703篇 |
2013年 | 4581篇 |
2012年 | 5223篇 |
2011年 | 5189篇 |
2010年 | 4395篇 |
2009年 | 4461篇 |
2008年 | 4700篇 |
2007年 | 4154篇 |
2006年 | 3832篇 |
2005年 | 3046篇 |
2004年 | 2345篇 |
2003年 | 1954篇 |
2002年 | 1890篇 |
2001年 | 1567篇 |
2000年 | 1404篇 |
1999年 | 1005篇 |
1998年 | 701篇 |
1997年 | 580篇 |
1996年 | 534篇 |
1995年 | 447篇 |
1994年 | 425篇 |
1993年 | 314篇 |
1992年 | 257篇 |
1991年 | 194篇 |
1990年 | 188篇 |
1989年 | 116篇 |
1988年 | 111篇 |
1987年 | 81篇 |
1986年 | 88篇 |
1985年 | 67篇 |
1984年 | 33篇 |
1983年 | 46篇 |
1982年 | 25篇 |
1981年 | 30篇 |
1980年 | 19篇 |
1979年 | 24篇 |
1978年 | 12篇 |
1977年 | 12篇 |
1973年 | 9篇 |
1925年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
由于混凝土材料理化特性的差异,高强混凝土的弯压极限应变明显地小于普通混凝土,依据试验结果分析了高强混凝土的弯压极限应变变化规律,并给出了它的计算公式. 相似文献
172.
A graph G is 3‐domination critical if its domination number γ is 3 and the addition of any edge decreases γ by 1. Let G be a 3‐connected 3‐domination critical graph of order n. In this paper, we show that there is a path of length at least n?2 between any two distinct vertices in G and the lower bound is sharp. © 2002 John Wiley & Sons, Inc. J Graph Theory 39: 76–85, 2002 相似文献
173.
Films of polytetrafluoroethylene (PTFE) were exposed to sodium naphthalenide (Na/naphtha) etchant so as to defluorinate the surface for obtaining hydroxyl functionality. Surface-initiators were immobilized on the PTFE films by esterification of 4,4′-azobis(4-cyanopentanoic acid) (ACP) and the hydroxyl groups covalently linked to the surface. Grafting of polymer brushes on the PTFE films was carried out by the surface-initiated free radical polymerization. Homopolymers brushes of methyl methacrylate (MMA) were prepared by free radical polymerization from the azo-functionalized PTFE surface. The chemical composition and topography of the graft-functionalized PTFE surfaces were characterized by X-ray photoelectron spectroscopy (XPS), attenuated total reflectance (ATR) FT-IR spectroscopy and atomic force microscopy (AFM). Water contact angles on PTFE films were reduced by surface grafting of MMA. 相似文献
174.
We propose a new lens scheme to focus cold atoms by using a controllable inhomogeneous magnetic field from a square current-carrying wire fabricated on a chip. The spatial distributions of the magnetic field are calculated, and the results show that the generated magnetic field is a two-dimensional (2D) quadrupole one and can be used to focus cold atoms or a cold atomic beam. The dynamic processes of cold atoms passing through our square wire layout and its focusing properties are studied by using Monte Carlo simulations. Our study shows that the atomic clouds can be focused effectively by our magnetic lens scheme, and the focal length of the atomic lens and its radius of focused spot can be continuously changed by adjusting the current in the wires. 相似文献
175.
176.
常规双极晶体管在77K下电流增益和频率性能都严重退化。本文首先分析了低温双极晶体管基区Gummel数,基区方块电阻,渡越时间和穿通电压等参数与温度及基区掺杂的关系,然后讨论了低温双极器件基区的优化设计问题。 相似文献
177.
K0.9Li0.1(Ta0.5Nb0.5)O3晶体压电应变系数的测量 总被引:4,自引:2,他引:2
用准静态d_(33)测量仪和干涉法相结合。测量了K_(0.9)Li_(0.1)(Ta_(0.5)Nb_(0.5)Nb_(0.5))O_3晶体的压电应变系数。结果为:d_(33)=86.0,d_(33)=一29.5,d_(15)=112.9×10 ̄(-12)C/N. 相似文献
178.
Dierk Knittel Qinxue Wei Eckhard Schollmeyer 《Fresenius' Journal of Analytical Chemistry》1994,348(12):820-824
Different strategies are presented for the development of a voltammetric sensor for in-line measurement and monitoring of H2O2 in high concentrations (up to 30 g/l) as used in textile bleaching systems. When using macroelectrodes, signal saturation is observed even at medium concentrations. Some improvement can be achieved by hydrodynamic electrodes like ring-disk electrodes. Satisfactory results up to the desired level in practical solutions (possessing only limited conductivity) are obtained with Pt-microelectrodes. 相似文献
179.
180.
Wei Guoqiang 《数学年刊B辑(英文版)》1998,19(4):465-472
1.IntroductionInwhatfollows,allofHilbertspacesappearedinthispaperareinfinite-dimensionalseparablecomplexHilbertspace.IfHisaHilbertspace,thenC(n)denotestheC*--algebraofallboundedlinearoperatorsonHandK(H)denotesthesetofcompactoperatorsonn.TwooperatorsSandTarecalledapproximatelyequivalentifthereisasequenc{Un}ofunitaryoperatorssuchthatlIU:SUn--Tll-0(n-- co).SimilarlytwooperatosSandTareapproximatelysimilarifthereisasequence{Vn}ofinvertibleoperatorswithsup(llVn11,11VJ'11)相似文献