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   6665篇
  免费   517篇
  国内免费   516篇
化学   3880篇
晶体学   40篇
力学   219篇
综合类   72篇
数学   2283篇
物理学   1204篇
  2025年   3篇
  2024年   34篇
  2023年   55篇
  2022年   76篇
  2021年   98篇
  2020年   183篇
  2019年   185篇
  2018年   175篇
  2017年   225篇
  2016年   187篇
  2015年   206篇
  2014年   285篇
  2013年   979篇
  2012年   277篇
  2011年   305篇
  2010年   261篇
  2009年   319篇
  2008年   340篇
  2007年   359篇
  2006年   349篇
  2005年   288篇
  2004年   276篇
  2003年   252篇
  2002年   854篇
  2001年   179篇
  2000年   187篇
  1999年   117篇
  1998年   145篇
  1997年   83篇
  1996年   87篇
  1995年   78篇
  1994年   59篇
  1993年   36篇
  1992年   28篇
  1991年   17篇
  1990年   17篇
  1989年   16篇
  1988年   16篇
  1987年   12篇
  1986年   9篇
  1985年   5篇
  1984年   9篇
  1983年   2篇
  1982年   3篇
  1981年   3篇
  1980年   2篇
  1979年   5篇
  1978年   3篇
  1973年   3篇
  1936年   1篇
排序方式: 共有7698条查询结果,搜索用时 88 毫秒
61.
硅像素传感器上的保护环结构有利于提高传感器的耐高电压性能,为评估保护环结构对硅像素传感器的保护效果,仿真分析了三种保护环结构。通过计算机辅助设计技术对三种保护环结构进行二维建模,利用TACD内置的电学模型对三种保护环结构的I-V特性进行了仿真。研究结果表明,电流收集环会提高像素的耐高电压性能,同时不等间距保护环、保护环的内外等距离Al悬挂以及多个保护环结构有利于进一步提高传感器的击穿电压。  相似文献   
62.
我们得到了环的稳定度为2或∞的一个充分条件,并进给出了SBN环的稳定度  相似文献   
63.
In this paper, we define a class of extended quantum enveloping algebras U q (f(K, J)) and some new Hopf algebras, which are certain extensions of quantum enveloping algebras by a Hopf algebra H. This construction generalizes some well-known extensions of quantum enveloping algebras by a Hopf algebra and provides a large of new noncommutative and noncocommutative Hopf algebras.  相似文献   
64.
杂多酸引发四氢呋喃聚合反应Ⅱ.水的反应行为   总被引:5,自引:2,他引:3  
前报我们对低腐蚀性非均相的磷钨杂多酸H3PW12O40(PW12)引发体系进行了研究[1],发现环氧乙烷(EO)可有效地促进PW12引发的四氢呋喃(THF)聚合反应,大幅度地降低了引发剂用量,聚合物收率显著提高,并发现聚合过程中不存在链终止反应.产物...  相似文献   
65.
一种多波长窄线宽环形掺铒光纤激光器   总被引:3,自引:2,他引:1  
本文提出了一种利用多个光纤光栅串接来实现环形掺铒光纤多波长,窄线宽激光器的新颖方法,并在实验中验证了这一设计的合理性,得到了稳定的双波长输出。  相似文献   
66.
Novel elastomeric A‐B‐A triblock copolymers were successfully synthesized in a new two‐step process: controlled ring‐opening polymerization of the cyclic ether–ester 1,5‐dioxepan‐2‐one as the amorphous middle block (B‐block) followed by addition and polymerization of the two semicrystalline L ‐lactide blocks (A‐block). A 1,1,6,6‐tetra‐n‐butyl‐1,6‐distanna‐2,5,7,10‐tetraoxacyclodecane initiator system was utilized and the reaction was performed in chloroform at 60 °C. A good control of the synthesis was obtained, resulting in well defined triblock copolymers. The molecular weight and chemical composition were easily adjusted by the monomer‐to‐initiator ratio. The triblock copolymers formed exhibited semicrystallinity up to a content of 1,5‐dioxepan‐2‐one as high as 89% as determined by differential scanning calorimetry. WAXS investigation of the triblock copolymers showed a crystal structure similar to that of the pure poly(L ‐lactide). © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1774–1784, 2000  相似文献   
67.
The reaction of p-toluidine with 2,3-dichloromaleic anhydride in the presence of added 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) does not give the known compound 2-chloro-3-p-toluidino-N-p-tolylmaleimide (1), but rather 2-p-toluidino-N-p-tolylmaleimide (2) in low yields. Repeating this same reaction with Et3N, pyridine, tmeda, and 4-Me2Npyridine in place of DBU furnishes the expected product 2-chloro-3-p-toluidino-N-p-tolylmaleimide, without the presence of 2-p-toluidino-N-p-tolylmaleimide. The participation of DBU in the chlorine for hydrogen exchange reaction in compound 1 has been demonstrated from the independent thermolysis reaction of 1 with DBU in toluene, where 2 was obtained as the sole isolable product. Compound 2 was isolated and fully characterized in solution, and the molecular structure was established by X-ray diffraction analysis. 2-p-Toluidino-N-p-tolylmaleimide crystallizes in the monoclinic space C2/c, a = 33.630(5), b = 12.508(2), c = 7.381(1), = 90.668(3), V = 3104.3(8)3, Z = 8, and D calc = 1.251 Mg/m3; R = 0.0357, R w = 0.0896 for 2011 reflections with I > 2(I).  相似文献   
68.
The effect of NH4Cl on the temperature dependence of deuterium oxide splitting (water order) and proton line width (surfactant order) in decylammonium chloride (DACl), D2O systems is reported. The molar ratio of DACl to D2O was held constant at .085 and the molar ratio of NH4Cl to D2O was varied from .012 to .029. We find for the above concentration ranges that in the nematic range the relative temperature dependence of the D2O splitting is little affected by changes on salt concentration. The slopes of the proton line widths as a function of temperature decrease with increasing salt concentration. The results are compared with earlier data on salt effects on order obtained with the disodium cromoglycate system.  相似文献   
69.
Abstract

Electronic states in junctions of nanotubes with different circumferences are studied in an effective-mass approximation. The junction is characterized by boundary conditions which mix wave functions associated with K and K′ points. At ε=0, they decay linearly with the distance from the thicker nanotube, showing that the conductance decays with the junction length in proportion to its third power.  相似文献   
70.
The structure of (5S)-3,4-dichloro-5-menthoxy-2(5H)-furanone is reported. The title compound crystallizes in the monoclinic space group P21: a = 6.650(2) Å, b = 8.038(3) Å, c = 14.858(8) Å, = 97.01(3), V = 788.3(6) Å3, Z = 2, R = 0.0718, R w = 0.0795 for 735 observed reflections with I > 3 (I), and the absolute configuration at C-5 of the furanone ring is shown to be (S).  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