全文获取类型
收费全文 | 35306篇 |
免费 | 5957篇 |
国内免费 | 4227篇 |
专业分类
化学 | 25249篇 |
晶体学 | 536篇 |
力学 | 2180篇 |
综合类 | 257篇 |
数学 | 3975篇 |
物理学 | 13293篇 |
出版年
2024年 | 55篇 |
2023年 | 664篇 |
2022年 | 1094篇 |
2021年 | 1195篇 |
2020年 | 1417篇 |
2019年 | 1373篇 |
2018年 | 1155篇 |
2017年 | 1086篇 |
2016年 | 1683篇 |
2015年 | 1646篇 |
2014年 | 1958篇 |
2013年 | 2567篇 |
2012年 | 3395篇 |
2011年 | 3514篇 |
2010年 | 2376篇 |
2009年 | 2306篇 |
2008年 | 2434篇 |
2007年 | 2231篇 |
2006年 | 2063篇 |
2005年 | 1754篇 |
2004年 | 1272篇 |
2003年 | 939篇 |
2002年 | 928篇 |
2001年 | 715篇 |
2000年 | 653篇 |
1999年 | 694篇 |
1998年 | 583篇 |
1997年 | 551篇 |
1996年 | 536篇 |
1995年 | 436篇 |
1994年 | 370篇 |
1993年 | 293篇 |
1992年 | 287篇 |
1991年 | 246篇 |
1990年 | 200篇 |
1989年 | 159篇 |
1988年 | 109篇 |
1987年 | 115篇 |
1986年 | 95篇 |
1985年 | 94篇 |
1984年 | 58篇 |
1983年 | 47篇 |
1982年 | 39篇 |
1981年 | 22篇 |
1980年 | 14篇 |
1979年 | 13篇 |
1978年 | 7篇 |
1976年 | 9篇 |
1975年 | 11篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
许多乙酰芳胺类化合物具有优异的生物活性,例如除草剂苯噻草胺,可抑制细胞生长和分裂,防除稻田中禾本科杂草[1];杀菌剂甲霜灵可防治作物霜霉病[2]。本文将具有多种生物活性的嘧啶基团引入到乙酰芳胺结构中[3],合成下列10个未见文献报道的标题化合物Ⅰ,通... 相似文献
93.
The Existence of Solutions to Sturm-Liouville Boundary Value Problems with Laplacian-like Operator 总被引:2,自引:0,他引:2
Wei-ping Sun Wei-gao GeDepartment of Applied Mathematics Beijing Institute of Technology Beijing China 《应用数学学报(英文版)》2002,18(2):341-348
Abstract The existence of infinitely many solutions to Sturm-Liouville boundary value problem with aLaplacian-like operator is studied by applying generalized polar coordinates. 相似文献
94.
To incorporate an acceptor type polythiophene segment onto a supramolecular block copolymer for potential light harvesting applications, effective synthetic routes for the end‐functionalized and acceptor‐substituted polythiophenes are critical. The Ullmann coupling reaction can be utilized to obtain electron‐deficient polythiophenes and to attach terminal thiophene units that carry functional groups. In this article, the reactions involving a 2,5‐dibromothiophene monomer containing an electron‐withdrawing fluorinated ester and 5‐bromo‐2‐thiophenecarboxaldehyde (the end‐capper) were studied in detail. It was found that the Ullmann coupling reaction of the dibromide is very fast (completed in a few minutes) and the terminal bromine group does not survive long under the reaction condition. These findings lead to the development of an effective procedure for aldehyde end‐capping of electron‐deficient polythiophenes. Polymers with molecular weights around 4000 Da are routinely obtained. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 41–47, 2007 相似文献
95.
三种群食物链交错扩散模型的整体 总被引:1,自引:0,他引:1
本文应用能量估计方法和Gagliardo-Nirenberg型不等式证明了一类强耦合反应扩散系统整体解的存在性和一致有界性,该系统是带自扩散和交错扩散项的三种群Lotka-Volterra食物链模型.通过构造Lyapunov函数给出了该模型正平衡点全局渐近稳定的充分条件. 相似文献
96.
97.
For vertical-cavity surface-emitting lasers (VCSELs) with polarization-rotated feedback, there exist several synchronization
types such as synchronizations between total powers and synchronizations between separate polarization modes. Based on the
two-mode rate equations, we study and compare numerically the performances of different synchronization types. Our results
show that three synchronization types exhibit good performances when their synchronization conditions are satisfied. They
are the complete synchronization between total powers, complete synchronization between x-polarized modes, and generalized synchronization between x-polarized and y-polarized modes. The former two types are sensitive to the injection rate and spontaneous emission, while the third type
is contrary. Synchronization type with the best performance may switch from one to another, with changing of injection rate
and spontaneous emission factor. 相似文献
98.
Bing Yong HSIE 《数学学报(英文版)》2006,22(2):507-514
This paper gives a p-adic analogue of the Mackey theory, which relates representations of a group of type G - H × t A to systems of imprimitivity. 相似文献
99.
A novel field emission pressure sensor has been achieved utilizing carbon nanotubes (CNTs) as the electron source. The sensor consists of the anode sensing film fabricated by wet etching process and multi-wall carbon nanotubes (MWNTs) cathode in the micro-vacuum chamber. MWNTs on the silicon substrate were grown by thermal CVD. The prototype pressure sensor has a measured sensitivity of about 0.17-0.77 nA/Pa (101-550 KPa). The work shows the potential use of CNTs-based field-emitter in microsensors, such as accelerometers and tactile sensors. 相似文献
100.