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   52500篇
  免费   2140篇
  国内免费   38篇
化学   34708篇
晶体学   256篇
力学   1598篇
数学   7884篇
物理学   10232篇
  2023年   403篇
  2022年   324篇
  2021年   695篇
  2020年   794篇
  2019年   743篇
  2018年   1070篇
  2017年   898篇
  2016年   1661篇
  2015年   1541篇
  2014年   1553篇
  2013年   3138篇
  2012年   3686篇
  2011年   3787篇
  2010年   2303篇
  2009年   1920篇
  2008年   3229篇
  2007年   3253篇
  2006年   2842篇
  2005年   2756篇
  2004年   2352篇
  2003年   1906篇
  2002年   1664篇
  2001年   937篇
  2000年   786篇
  1999年   569篇
  1998年   426篇
  1997年   389篇
  1996年   488篇
  1995年   316篇
  1994年   356篇
  1993年   362篇
  1992年   386篇
  1991年   338篇
  1990年   321篇
  1989年   309篇
  1988年   249篇
  1987年   259篇
  1986年   225篇
  1985年   383篇
  1984年   357篇
  1983年   243篇
  1982年   330篇
  1981年   314篇
  1980年   276篇
  1979年   268篇
  1978年   254篇
  1976年   263篇
  1975年   241篇
  1974年   247篇
  1973年   238篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
A new strategy for the synthesis of tetrahydroisoquinolines based on the Pd0‐catalyzed intramolecular α‐arylation of sulfones is reported. The combination of this Pd‐catalyzed reaction with intermolecular Michael and aza‐Michael reactions allows the development of two‐ and three‐step domino processes to synthesize diversely functionalized scaffolds from readily available starting materials.  相似文献   
12.
13.
14.
15.
16.
17.
Development of biocompatible porous supports is a promising strategy in the field of tissue engineering for the repair and regeneration of bone tissues with severe damage. Graphene oxide aerogels (GOAs) are excellent candidates for the manufacture of these systems due to their porosity, ability to imitate bone structure, and mechanical resistance, and according to their surface chemical reactivity, they can facilitate osseointegration, osteogenesis, osteoinduction and osteoconduction. In this review, synthesis of GOAs from the most primary source is described, and recent studies on the use of these functionalized carbonaceous foams as scaffolding for bone tissue regeneration are presented.  相似文献   
18.
The synthesis and characterisation of a family of block codendrimers consisting of highly versatile mesogenic and carbazole‐containing 2,2‐bis(hydroxymethyl)propionic acid (bis‐MPA) dendrons are reported. The liquid‐crystal behaviour was investigated by means of differential scanning calorimetry, polarised‐light optical microscopy and X‐ray diffraction. Depending on the chemical structure of the constituent dendrons, the codendrimers show lamellar or columnar mesophases. On the basis of the experimental results, models both at the molecular level and in the mesophase are proposed. The physical properties of the block codendrimers derived from the presence of the carbazole moiety in their structure were investigated: photoluminescence in solution and in the mesophase, electrochemical behaviour and hole transport. Electrodeposition of carbazole dendrons afforded a globular supramolecular conformation in which the mesogenic molecular side plays a key role.  相似文献   
19.
20.
In this paper, we study the local linear convergence properties of a versatile class of Primal–Dual splitting methods for minimizing composite non-smooth convex optimization problems. Under the assumption that the non-smooth components of the problem are partly smooth relative to smooth manifolds, we present a unified local convergence analysis framework for these methods. More precisely, in our framework, we first show that (i) the sequences generated by Primal–Dual splitting methods identify a pair of primal and dual smooth manifolds in a finite number of iterations, and then (ii) enter a local linear convergence regime, which is characterized based on the structure of the underlying active smooth manifolds. We also show how our results for Primal–Dual splitting can be specialized to cover existing ones on Forward–Backward splitting and Douglas–Rachford splitting/ADMM (alternating direction methods of multipliers). Moreover, based on these obtained local convergence analysis result, several practical acceleration techniques are discussed. To exemplify the usefulness of the obtained result, we consider several concrete numerical experiments arising from fields including signal/image processing, inverse problems and machine learning. The demonstration not only verifies the local linear convergence behaviour of Primal–Dual splitting methods, but also the insights on how to accelerate them in practice.  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