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   65780篇
  免费   14764篇
  国内免费   5189篇
化学   61626篇
晶体学   582篇
力学   2474篇
综合类   241篇
数学   6237篇
物理学   14573篇
  2024年   87篇
  2023年   694篇
  2022年   1129篇
  2021年   1269篇
  2020年   2544篇
  2019年   3624篇
  2018年   2014篇
  2017年   1641篇
  2016年   4720篇
  2015年   4809篇
  2014年   5067篇
  2013年   6187篇
  2012年   5615篇
  2011年   5043篇
  2010年   4711篇
  2009年   4567篇
  2008年   4342篇
  2007年   3505篇
  2006年   3012篇
  2005年   3000篇
  2004年   2518篇
  2003年   2227篇
  2002年   3034篇
  2001年   2192篇
  2000年   1998篇
  1999年   1100篇
  1998年   681篇
  1997年   628篇
  1996年   612篇
  1995年   524篇
  1994年   467篇
  1993年   356篇
  1992年   348篇
  1991年   309篇
  1990年   253篇
  1989年   204篇
  1988年   129篇
  1987年   113篇
  1986年   117篇
  1985年   96篇
  1984年   58篇
  1983年   50篇
  1982年   32篇
  1981年   25篇
  1980年   13篇
  1978年   8篇
  1977年   7篇
  1976年   8篇
  1975年   7篇
  1974年   10篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
International Journal of Theoretical Physics - A new quantum watermark algorithm is presented by combining maximum pixel difference partitioning with the least significant bit substitution...  相似文献   
3.
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   
4.
Acridone as a new kind of visible light photocatalyst has been developed to catalyze metal free atom transfer radical polymerization (ATRP). The photocatalyst possess low excited state potential as can undergo an oxidative quenching pathway to initiate ATRP of vinyl monomers. Kinetic study and light on/off reaction demonstrate the “living”/controlled nature of the polymerization by light. Block copolymers can be achieved by using PMMA as macroinitiator to reinitiate polymerization of other vinyl monomers, which shows highly preserved Br chain-end functionality in the synthesized polymers. Moreover, the polymerization can be conducted under air atmosphere as most photocatalysts need anaerobic condition, which may give inspiration of further application of this kind of photocatalyst.  相似文献   
5.
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   
6.
7.
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   
8.
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   
9.
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   
10.
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