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   48669篇
  免费   2910篇
  国内免费   1463篇
化学   29820篇
晶体学   415篇
力学   1914篇
综合类   76篇
数学   6747篇
物理学   14070篇
  2023年   444篇
  2022年   767篇
  2021年   1029篇
  2020年   1136篇
  2019年   993篇
  2018年   1015篇
  2017年   880篇
  2016年   1484篇
  2015年   1377篇
  2014年   1490篇
  2013年   2595篇
  2012年   2814篇
  2011年   3088篇
  2010年   1911篇
  2009年   1839篇
  2008年   2532篇
  2007年   2336篇
  2006年   2135篇
  2005年   2480篇
  2004年   2347篇
  2003年   1737篇
  2002年   1372篇
  2001年   1094篇
  2000年   1016篇
  1999年   774篇
  1998年   592篇
  1997年   564篇
  1996年   705篇
  1995年   590篇
  1994年   557篇
  1993年   593篇
  1992年   563篇
  1991年   495篇
  1990年   411篇
  1989年   374篇
  1988年   368篇
  1987年   400篇
  1986年   359篇
  1985年   455篇
  1984年   427篇
  1983年   339篇
  1982年   364篇
  1981年   371篇
  1980年   344篇
  1979年   320篇
  1978年   329篇
  1977年   291篇
  1976年   274篇
  1975年   278篇
  1974年   253篇
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
81.
Blood serum samples were irradiated by monochromatic synchrotron radiation (15 keV) and by 2.4-MeV protons to compare their performance for the detection of trace elements by x-ray fluorescence (XRF) spectrometry. Absolute concentration assignment was based on the addition of an internal standard and on a method which uses the incoherent and coherent radiation as a flux monitor of the incoming beam. Preliminary experiments with a synchrotron XRF microprobe are reported.  相似文献   
82.
Suppose μ is a Radon measure on ℝ d , which may be non doubling. The only condition assumed on μ is a growth condition, namely, there is a constant C0>0 such that for all x∈supp(μ) and r>0, μ(B(x, r))⪯C0rn, where 0<n⪯d. We prove T1 theorem for non doubling measures with weak kernel conditions. Our approach yields new results for kernels satisfying weakened regularity conditions, while recovering previously known Tolsa’s results. We also prove T1 theorem for Besov spaces on nonhomogeneous spaces with weak kernel conditions given in [7].  相似文献   
83.
We present an interpolating, univariate subdivision scheme which preserves the discrete curvature and tangent direction at each step of subdivision. Since the polygon have a geometric information of some original (in some sense) curve as a discrete curvature, we can expect that the limit curve has the same curvature at each vertex as the control polygon. We estimate the curvature bound of odd vertices and give an error estimate for restoring a curve from sampled vertices on curves.  相似文献   
84.
在本文中,给定一组有序空间数据点列及每个数据点的切矢向量,利用加权二次有理Bézier曲线对数据点作插值曲线,使该曲线具有C1连续性,并且权因子只是对相应顶点曲线附近产生影响,同调整两个相邻的权因子可以调整这两个相邻顶点之间的曲线和它的控制多边形.  相似文献   
85.
YBa2Cu3O7-x (YBCO) bulk is one of the most important high temperature superconducting materials for magnetic levitation applications, because it has a high magnetic irreversibility field Hirr at liquid nitrogen temperature, and can grow into large grains. The levitation force of YBCO bulk is proportional to the critical current density (Jc) and grain radius (r)[1], so higher Jc and r are appreciated for YBCO bulks to achieve higher levitation force. Now single-domain YBCO bulks up to s…  相似文献   
86.
Affine Arithmetic: Concepts and Applications   总被引:2,自引:0,他引:2  
Affine arithmetic is a model for self-validated numerical computation that keeps track of first-order correlations between computed and input quantities. We explain the main concepts in affine arithmetic and how it handles the dependency problem in standard interval arithmetic. We also describe some of its applications.  相似文献   
87.
88.
We have synthesized a blue‐light‐emitting polyfluorene (PF) derivative ( PF‐CBZ‐OXD ) that presents bulky hole‐transporting carbazole and electron‐transporting oxadiazole pendent groups functionalized at the C‐9 positions of alternating fluorene units. The results from photoluminescence and electrochemical measurements indicate that both the side chains and the PF main chain retain their own electronic characteristics in the copolymer. An electroluminescent device incorporating this polymer as the emitting layer was turned on at 4.5 V; it exhibited a stable blue emission with a maximum external quantum efficiency of 1.1%. Moreover, we doped PF‐CBZ‐OXD and its analogue PF‐TPA‐OXD with a red‐light‐emitting iridium phosphor for use as components of phosphorescent red‐light emitters to investigate the effect of the host's HOMO energy level on the degree of charge trapping and on the electrophosphorescent efficiency. We found that spectral overlap and individual energy level matching between the host and guest were both crucial features affecting the performance of the electroluminescence devices. Atomic force microscopy measurements indicated that the dipolar nature of PF‐CBZ‐OXD , in contrast to the general nonpolarity of polydialkylfluorenes, provided a stabilizing environment that allowed homogeneous dispersion of the polar iridium triplet dopant. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2925–2937, 2007  相似文献   
89.
90.
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