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   635106篇
  免费   6118篇
  国内免费   1703篇
化学   324315篇
晶体学   9527篇
力学   30980篇
综合类   19篇
数学   83094篇
物理学   194992篇
  2021年   5711篇
  2020年   6253篇
  2019年   7076篇
  2018年   9424篇
  2017年   9591篇
  2016年   13422篇
  2015年   7399篇
  2014年   12310篇
  2013年   28587篇
  2012年   21915篇
  2011年   26142篇
  2010年   19450篇
  2009年   19329篇
  2008年   24662篇
  2007年   24447篇
  2006年   22430篇
  2005年   20018篇
  2004年   18605篇
  2003年   16787篇
  2002年   16593篇
  2001年   17772篇
  2000年   13739篇
  1999年   10624篇
  1998年   9153篇
  1997年   8987篇
  1996年   8429篇
  1995年   7626篇
  1994年   7588篇
  1993年   7307篇
  1992年   7869篇
  1991年   8255篇
  1990年   7898篇
  1989年   7802篇
  1988年   7599篇
  1987年   7432篇
  1986年   7101篇
  1985年   9121篇
  1984年   9507篇
  1983年   8081篇
  1982年   8474篇
  1981年   7859篇
  1980年   7506篇
  1979年   8106篇
  1978年   8366篇
  1977年   8213篇
  1976年   8157篇
  1975年   7840篇
  1974年   7688篇
  1973年   8089篇
  1972年   5760篇
排序方式: 共有10000条查询结果,搜索用时 15 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