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   52320篇
  免费   4111篇
  国内免费   4231篇
化学   28777篇
晶体学   605篇
力学   2413篇
综合类   313篇
数学   11413篇
物理学   17141篇
  2023年   483篇
  2022年   642篇
  2021年   819篇
  2020年   1042篇
  2019年   1043篇
  2018年   2040篇
  2017年   2353篇
  2016年   1909篇
  2015年   1819篇
  2014年   2043篇
  2013年   2581篇
  2012年   5520篇
  2011年   4729篇
  2010年   3550篇
  2009年   3131篇
  2008年   2339篇
  2007年   2254篇
  2006年   2042篇
  2005年   5540篇
  2004年   4688篇
  2003年   2910篇
  2002年   1119篇
  2001年   882篇
  2000年   563篇
  1999年   609篇
  1998年   433篇
  1997年   335篇
  1996年   288篇
  1995年   276篇
  1994年   218篇
  1993年   196篇
  1992年   298篇
  1991年   253篇
  1990年   223篇
  1989年   183篇
  1988年   153篇
  1987年   112篇
  1986年   87篇
  1985年   82篇
  1984年   47篇
  1983年   44篇
  1982年   37篇
  1976年   86篇
  1975年   37篇
  1974年   41篇
  1973年   49篇
  1972年   40篇
  1969年   38篇
  1968年   35篇
  1966年   37篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Fuzzy Optimization and Decision Making - Seepage equation in fissured porous media is a partial differential equation describing the variation of pressure of a given area over time. In traditional...  相似文献   
2.
Crystal engineering, as a burgeoning technology, has been widely used to construct metalloporphyrins biomimetic catalysts. Herein, a bimetallic metal-organic framework (MOF) was constructed by 4-(4-carboxyphenyl)-1,2,4-triazole ligand, Co2+ and Zr4+ metal ions by solvothermal reaction(named PFC-88). A N,N-chelation site was found between the two adjacent ligands in PFC-88, consequently a porphyrin-like structure was obtained through chelating Fe3+ in this site by post-modification, named PFC-88-Fe. The result of a single crystal X-ray technology verified that Fe ions were successfully metalated in the N,N-chelation site of PFC-88, which is assisted by the X-ray absorption near-edge structure(XANES) spectra. An o-phenylenediamine oxidation reaction was applied to assessing the catalytic activity of PFC-88-Fe, in which the absorbance increases of phenazine-2,3-diamine at λ=418 nm were recorded by absorption spectroscopy in kinetic mode, exhibiting the application potential as a biomimetic catalyst.  相似文献   
3.
4.
International Journal of Theoretical Physics - Quantum state sharing (QSS) plays significant role in transmitting quantum secret information. However, in practical quantum communication situation,...  相似文献   
5.
Zhao  Tianqi  Luo  Tianzi  Fang  Bo  Shi  Lijiang  Jin  Yongxing  Zhou  Pengwei  Yao  Dong  Li  Chenxia  Jing  Xufeng  Hong  Zhi 《Journal of Russian Laser Research》2021,42(5):586-597
Journal of Russian Laser Research - The zero-refractive-index metamaterials have excellent electromagnetic properties, which provide new ideas and methods to realize the control of electromagnetic...  相似文献   
6.
International Journal of Theoretical Physics - In this paper, we will consider the exact calculation of differential entropy of induced random state ensemble by partial tracing a subsystem over...  相似文献   
7.
Wang  Xiaoshen  Ye  Xiu  Zhang  Shangyou 《Numerical Algorithms》2021,88(3):1361-1381

The purpose of this paper is to investigate the connections between the weak Galerkin (WG) methods with and without stabilizers. The choices of stabilizers directly affect the convergence rates of the corresponding WG methods in general. However, we observed that the convergence rates are independent of the choices of stabilizers for these WG elements with stabilizers being optional. In this paper, we will verify such phenomena theoretically as well as numerically.

  相似文献   
8.
International Journal of Theoretical Physics - In this paper, we investigate Einstein-Podolsky-Rosen steering, Bell non-locality, first-order coherence and concurrence in the spin- $\frac {1}{2}$...  相似文献   
9.
化学工业生产中,用氢气为还原剂,通过选择性加氢可以制备多种重要化学品。5-羟甲基糠醛是重要的生物质基平台化合物,而5-甲基糠醛是用途广泛的化学品。由5-羟甲基糠醛加氢得到5-甲基糠醛是一条非常理想的路径,但是选择性活化C-OH非常困难。本文设计并制备了Pt@PVP/Nb2O5(PVP: 聚乙烯吡咯烷酮)催化剂,该催化体系巧妙地结合了位阻效应、氢溢流和催化剂界面的电子效应,系统研究了该催化剂对5-羟甲基糠醛选择性加氢制备5-甲基糠醛催化性能,在最优条件下,5-甲基糠醛的选择性可达92%。利用密度泛函理论计算研究了5-羟甲基糠醛选择性加氢制备5-甲基糠醛反应路径。  相似文献   
10.
One important prerequisite for the fabrication of molecular functional device strongly relies on the understanding the conducting behaviors of the metal-molecule-metal junction that can respond to an external stimulus. The model Lewis basic molecule 4,4′-(pyridine-3,5-diyl)dibenzonitrile (DBP), which can react with Lewis acid and protic acid, was synthesized. Then, the molecular conducting behavior of DBP, DBP-B(C6F5)3, and DBP-TfOH (DBP-B(C6F5)3, and DBP-TfOH were produced by Lewis acid and protonic acid treatment of DBP) was researched and compared. Given that their identical physical paths for DBP, DBP-B(C6F5)3, and DBP-TfOH to sustain charge transport, our results indicate that modifying the molecular electronic structure, even not directly changing the conductive physical backbone, can tune the charge transporting ability by nearly one order of magnitude. Furthermore, the addition of another Lewis base triethylamine (of stronger alkaline than DBP), to Lewis acid-base pair reverts the electrical properties back to that of a single DBP junction, that is constructive to propose a useful but simple strategy for the design and construction of reversible and controllable molecular device based on pyridine derived molecule.  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