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   59016篇
  免费   13626篇
  国内免费   5005篇
化学   57566篇
晶体学   605篇
力学   1936篇
综合类   227篇
数学   5571篇
物理学   11742篇
  2024年   59篇
  2023年   479篇
  2022年   617篇
  2021年   953篇
  2020年   2177篇
  2019年   3430篇
  2018年   1840篇
  2017年   1511篇
  2016年   4443篇
  2015年   4618篇
  2014年   4723篇
  2013年   5828篇
  2012年   5142篇
  2011年   4464篇
  2010年   4418篇
  2009年   4302篇
  2008年   3991篇
  2007年   3238篇
  2006年   2778篇
  2005年   2783篇
  2004年   2433篇
  2003年   2118篇
  2002年   2920篇
  2001年   2122篇
  2000年   1896篇
  1999年   928篇
  1998年   517篇
  1997年   453篇
  1996年   417篇
  1995年   362篇
  1994年   312篇
  1993年   217篇
  1992年   214篇
  1991年   204篇
  1990年   172篇
  1989年   122篇
  1988年   88篇
  1987年   72篇
  1986年   87篇
  1985年   61篇
  1984年   37篇
  1983年   33篇
  1982年   19篇
  1981年   15篇
  1980年   6篇
  1977年   3篇
  1976年   2篇
  1975年   3篇
  1957年   4篇
  1936年   7篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Hua  Saixiang  Zhu  Huichao  Wang  Xiao  Wu  Mingyuan  Wu  Qingyun  Liu  Jiuyi  Yang  Jianjun  Zhang  Jianan 《Cellulose (London, England)》2022,29(13):7465-7475
Cellulose - Ultraviolet (UV) protective cotton fabric is a convenient and reliable way to protect human body from sunlight. Herein, a polymerizable UV-absorber,...  相似文献   
3.
Journal of Radioanalytical and Nuclear Chemistry - The simplified 8-oxide system (SiO2-B2O3-Na2O-Al2O3-CaO-TiO2-MoO3-La2O3) has been prepared under two types of cooling methods, and analyzed with...  相似文献   
4.
A graphic sequence π =(d1, d2,..., dn) is said to be forcibly k-edge-connected if every realization of π is k-edge-connected. In this paper, we obtain a new sufficient degree condition for π to be forcibly k-edgeconnected. We also show that this new sufficient degree condition implies a strongest monotone degree condition for π to be forcibly 2-edge-connected and a conjecture about a strongest monotone degree condition for π to be forcibly 3-edge-connected due to...  相似文献   
5.
In this article,we study the initial boundary value problem of coupled semi-linear degenerate parabolic equations with a singular potential term on manifolds with corner singularities.Firstly,we introduce the corner type weighted p-Sobolev spaces and the weighted corner type Sobolev inequality,the Poincare′inequality,and the Hardy inequality.Then,by using the potential well method and the inequality mentioned above,we obtain an existence theorem of global solutions with exponential decay and show the blow-up in finite time of solutions for both cases with low initial energy and critical initial energy.Significantly,the relation between the above two phenomena is derived as a sharp condition.Moreover,we show that the global existence also holds for the case of a potential well family.  相似文献   
6.
Gao  Zhigen  Guo  Jianhua  Ma  Yanyuan 《中国科学 数学(英文版)》2021,64(8):1905-1916
Science China Mathematics - Linear factor models are familiar tools used in many fields. Several pioneering literatures established foundational theoretical results of the quasi-maximum likelihood...  相似文献   
7.
8.
In the paper, the authors establish several integral representations for the generating functions of the large and little Schröder numbers and for the large and little Schröder numbers.  相似文献   
9.
The development of high‐surface‐area carbon electrodes with a defined pore size distribution and the incorporation of pseudo‐active materials to optimize the overall capacitance and conductivity without destroying the stability are at present important research areas. Composite electrodes of carbon nano‐onions (CNOs) and polypyrrole (Ppy) were fabricated to improve the specific capacitance of a supercapacitor. The carbon nanostructures were uniformly coated with Ppy by chemical polymerization or by electrochemical potentiostatic deposition to form homogenous composites or bilayers. The materials were characterized by transmission‐ and scanning electron microscopy, differential thermogravimetric analyses, FTIR spectroscopy, piezoelectric microgravimetry, and cyclic voltammetry. The composites show higher mechanical and electrochemical stabilities, with high specific capacitances of up to about 800 F g?1 for the CNOs/SDS/Ppy composites (chemical synthesis) and about 1300 F g?1 for the CNOs/Ppy bilayer (electrochemical deposition).  相似文献   
10.
A two‐step synthesis of structurally diverse pyrrole‐containing bicyclic systems is reported. ortho‐Nitro‐haloarenes coupled with vinylic N‐methyliminodiacetic acid (MIDA) boronates generate ortho‐vinyl‐nitroarenes, which undergo a “metal‐free” nitrene insertion, resulting in a new pyrrole ring. This novel synthetic approach has a wide substrate tolerance and it is applicable in the preparation of more complex “drug‐like” molecules. Interestingly, an ortho‐nitro‐allylarene derivative furnished a cyclic β‐aminophosphonate motif.  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