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   37283篇
  免费   5492篇
  国内免费   3656篇
化学   25783篇
晶体学   358篇
力学   2227篇
综合类   241篇
数学   4280篇
物理学   13542篇
  2024年   111篇
  2023年   759篇
  2022年   1224篇
  2021年   1400篇
  2020年   1443篇
  2019年   1329篇
  2018年   1150篇
  2017年   1067篇
  2016年   1611篇
  2015年   1633篇
  2014年   2004篇
  2013年   2580篇
  2012年   3253篇
  2011年   3210篇
  2010年   2180篇
  2009年   2050篇
  2008年   2203篇
  2007年   1961篇
  2006年   1843篇
  2005年   1541篇
  2004年   1305篇
  2003年   985篇
  2002年   895篇
  2001年   739篇
  2000年   691篇
  1999年   829篇
  1998年   693篇
  1997年   635篇
  1996年   705篇
  1995年   601篇
  1994年   550篇
  1993年   470篇
  1992年   449篇
  1991年   364篇
  1990年   324篇
  1989年   236篇
  1988年   216篇
  1987年   198篇
  1986年   141篇
  1985年   156篇
  1984年   135篇
  1983年   116篇
  1982年   80篇
  1981年   59篇
  1980年   49篇
  1979年   33篇
  1978年   26篇
  1976年   27篇
  1975年   31篇
  1974年   23篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
231.
Wrinkling and buckling of nano-films on the compliant substrate are always induced due to thermal deformation mismatch.This paper proposes effective means to control the surface wrinkling of thin film on the compliant substrate,which exploits the curvatures of the curve cracks designed on the stiff film.The procedures of the method are summarized as:1)curve patterns are fabricated on the surface of PDMS(Polydimethylsiloxane)substrate and then the aluminum film with the thickness of several hundred nano-meters is deposited on the substrate;2)the curve patterns are transferred onto the aluminum film and lead to cracking of the film along the curves.The cracking redistributes the stress in the compressed film on the substrate;3)on the concave side of the curve,the wrinkling of the film surface is suppressed to be identified as shielding effect and on the convex side the wrinkling of the film surface is induced to be identified as inductive effect.The shielding and inductive effects make the dis-ordered wrinkling and buckling controllable.This phenomenon provides a potential application in the fabrication of flexible electronic devices.  相似文献   
232.
Investigation of remelting and cladding processing with laminar plasma jets on several metals has been conducted looking for possible development of a new surface modification technique. The remelting tests illustrated that the new method could evidently improve the material microstructure and properties of cast iron. The cladding was done with Al2O3 ceramic powder on stainless steel. The energy dispersive spectra (EDS) analysis was used to determine the distribution of the major cladding element in the plasma-processed layers, for which the microstructure observations and hardness measurements were also performed.  相似文献   
233.
A new terahertz dispersive device designed for single-shot spectral measurements of broadband terahertz pulses is proposed. With two-dimensional quasi-randomly distributed element design, the device exhibits approximately the dispersive property of single-order diffraction in far field. Its far-field diffraction pattern is experimentally verified employing a continuous terahertz source centered at 2.52 THz and a pyroelectric focal-plane-array camera, which is in good agreement with the numerical result. The device provides a new approach for direct single-shot spectral measurements of broadband terahertz waves.  相似文献   
234.
Zn1-xCdx O films are grown on c-sapphire substrates by laser molecular beam epitaxy(LMBE) at different temperatures. Their crystallographic structures, compositions, surface electronic structures are investigated. The a-axis lattice constant of Zn0.95Cd0.05 O is 3.20. Moreover, the epitaxial relationship shows a 30°-in-plane rotation of the film with respect to the c-sapphire substrate. When the substrate temperatures arrives at 500℃, the in situ reflection high-energy electron diffraction(RHEED) pattern of Zn Cd O film shows sharp streaky pattern. The maximum Cd content of Zn Cd O film grown at low substrate temperatures increases up to about 29.6 at.%, which is close to that of the ceramic target. In situ ultraviolet photoelectron spectroscopy(UPS) measurements demonstrate that Zn Cd O film exhibits intense peaks at 4.7 e V and 10.7 e V below the Fermi level, which are assigned to the O 2p and Zn 3p states. Energetic distance between Zn 3d and Cd 4d is 0.60 e V. Above 470 nm, the thin film shows excellent optical transmission.  相似文献   
235.
提出一种利用谱编辑的方法来简化二维谱的探测,使得一张二维谱可以被简化为N条一维谱(N等于二维谱中F1维上的谱线总数),从而达到缩短数据采集时间和减少数据贮存空间的目的。文中给出了运用此方法探测二维碳氢异核相关实验的实例,并分析了由于F1维的谱线不为δ函数而产生的编辑误差的大小,最后将此方法推广到三维的简化探测,即通过对N张二维谱的编辑获得三维谱的信息。  相似文献   
236.
The LNYAB self-doubling laser pumped by (LD) has been developed for the first time. The properties of the lasers are much better than those of NYAB self-doubling lasers pumped by LD. The LNYAB self-doubling laser pumped by LD can be operated in TEM_(00) mode with threshold pumping power of 3.6mW which is lower than that of LD pumped NYAB self-doubling lasers by 74%. The output power is 29mW at 0.531μm in green region with optical-to-optical efficiency of 4.8% which is higher than that of NYAB self-doubling laser by 20%.  相似文献   
237.
文章描述了荧光级氧化钇中痕量稀土铈的测定方法,在溴酸钾存在下,5摩尔/升HNO_3介质中,以P507萃取微量铈,然后有机相用硝酸、过氧化氢反萃取、再将水相浓缩定容,然后以电感耦合等离子体原子发射光谱法分析。同时用铈的离子选择电极以二次标准加入法作第二种手段分析。样品溶液以乙醇预去溶方式引入等离子体,测定下限为2微克/克,方法简单、快速、准确。离子选择电极法测定铈离子下限1×10~(-5)摩尔/升,回收率为94-101%,方法简单,结果满意、价格便宜。  相似文献   
238.
本文介绍李代数的非简谐振子的表示。运用这样的表示可以方便地讨论局域模与简正模之关系及其半经典图象。  相似文献   
239.
240.
吴震  李志扬 《光子学报》1993,22(4):375-381
本文简述了用电视摄象机进行工业尺寸测量的微分法与拟合法的基本原理,同时详细的讨论了各自所能达到的精度极限。本文用实验验证了理论计算的结果,最后对二维工件测量时,如何根据工件的不同形状与位置以及光学系统的特点,提出了在测量时工件的放置应该注意的问题以及对工件拐角处如何进行处理的方法。  相似文献   
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