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   633422篇
  免费   6078篇
  国内免费   1695篇
化学   323092篇
晶体学   9505篇
力学   30955篇
综合类   19篇
数学   82855篇
物理学   194769篇
  2021年   5694篇
  2020年   6229篇
  2019年   7057篇
  2018年   9409篇
  2017年   9578篇
  2016年   13397篇
  2015年   7374篇
  2014年   12265篇
  2013年   28498篇
  2012年   21838篇
  2011年   26038篇
  2010年   19382篇
  2009年   19291篇
  2008年   24571篇
  2007年   24344篇
  2006年   22334篇
  2005年   19917篇
  2004年   18511篇
  2003年   16708篇
  2002年   16519篇
  2001年   17747篇
  2000年   13719篇
  1999年   10605篇
  1998年   9132篇
  1997年   8968篇
  1996年   8403篇
  1995年   7611篇
  1994年   7574篇
  1993年   7289篇
  1992年   7858篇
  1991年   8235篇
  1990年   7884篇
  1989年   7790篇
  1988年   7584篇
  1987年   7423篇
  1986年   7088篇
  1985年   9103篇
  1984年   9485篇
  1983年   8068篇
  1982年   8455篇
  1981年   7841篇
  1980年   7490篇
  1979年   8089篇
  1978年   8354篇
  1977年   8200篇
  1976年   8144篇
  1975年   7833篇
  1974年   7677篇
  1973年   8082篇
  1972年   5756篇
排序方式: 共有10000条查询结果,搜索用时 39 毫秒
31.
Mathematical Notes - Subspaces of the space of analytic functions on a convex domain in the complex plane that are invariant with respect to the differentiation operator are studied. The problem of...  相似文献   
32.
The requirement of green and sustainable materials to prepare heterogeneous catalysts has intensified for practical reasons over the past few decades. Carbohydrates are possibly the most plentiful and renewable organic materials in nature with inimitable physiochemical properties, plausible low-cost and large-scale production, and sustainability features could be exploited in the generation of nanostructured heterogeneous catalysts. This review article outlines the organic transformations catalyzed by diverse carbohydrate-based nanostructured catalysts in greener and environmentally friendly processes. Selected examples are highlighted for a variety of organic reactions exploiting the proposed catalysts’ reactivity and reusability, and interactions with the intrinsic nature of the applied carbohydrate supports; advantages and speculated challenges of the introduced catalysts are deliberated as well.  相似文献   
33.
Nonlinear Dynamics - Given a data-set of Ribonucleic acid (RNA) sequences we can infer the phylogenetics of the samples and tackle the information for scientific purposes. Based on current data and...  相似文献   
34.

We show that near periodic rivet chains that connect two Kirchhoff plates and are modeled by point Sobolev transmission conditions, Rayleigh waves arise, propagate along the chains, and decay exponentially in the orthogonal direction. Under additional geometric conditions we discover the standing (periodic) waves that carry no energy.

  相似文献   
35.
Physics of Atomic Nuclei - The muon puzzle is an excess of muon bundles generated by primary cosmic rays (PCR) at energies above 10 $${}^{17}$$ eV compared to estimations that assume even a heavy...  相似文献   
36.
Taherian  A.  Toutounian  F. 《Numerical Algorithms》2021,88(4):1831-1850
Numerical Algorithms - In this paper, the block generalized product-type bi-conjugate gradient (GPBi-CG) method for solving large, sparse nonsymmetric linear systems of equations with multiple...  相似文献   
37.
Crystallography Reports - The crystal and molecular structures of Cl–C6H4–O–C16H33 (I) have been studied, and its differential scanning calorimetry (DSC) study is performed....  相似文献   
38.
Gawad  Dina A.  Elnaggar  Mai M.  Belal  Tarek S. 《Chromatographia》2022,85(7):617-628
Chromatographia - The present work deals with the optimization, validation and application of a versatile HPLC–DAD method for concurrent estimation of nine antimicrobials and proton pump...  相似文献   
39.
We investigate the possibility of phantom crossing in the dark energy sector and the solution for the Hubble tension between early and late universe observations. We use robust combinations of different cosmological observations, namely the Cosmic Microwave Background (CMB), local measurement of Hubble constant (H0), Baryon Acoustic Oscillation (BAO) and SnIa for this purpose. For a combination of CMB+BAO data that is related to early universe physics, phantom crossing in the dark energy sector was confirmed at a 95% confidence level and we obtained the constraint H0=71.03.8+2.9 km/s/Mpc at a 68% confidence level, which is in perfect agreement with the local measurement by Riess et al. We show that constraints from different combinations of data are consistent with each other and all of them are consistent with phantom crossing in the dark energy sector. For the combination of all data considered, we obtained the constraint H0=70.25±0.78 km/s/Mpc at a 68% confidence level and the phantom crossing happening at the scale factor am=0.8510.031+0.048 at a 68% confidence level.  相似文献   
40.
Algebra and Logic - Unary functions definable in o-stable ordered groups of nonvaluational type are studied. Such functions are proved to be piecewise monotone and continuous.  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