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   1508篇
  免费   32篇
  国内免费   2篇
化学   941篇
晶体学   14篇
力学   13篇
数学   42篇
物理学   532篇
  2022年   9篇
  2021年   10篇
  2020年   16篇
  2019年   14篇
  2018年   14篇
  2017年   10篇
  2016年   20篇
  2015年   25篇
  2014年   18篇
  2013年   64篇
  2012年   60篇
  2011年   66篇
  2010年   41篇
  2009年   34篇
  2008年   76篇
  2007年   102篇
  2006年   79篇
  2005年   85篇
  2004年   80篇
  2003年   66篇
  2002年   70篇
  2001年   49篇
  2000年   30篇
  1999年   12篇
  1998年   13篇
  1997年   12篇
  1996年   24篇
  1995年   13篇
  1994年   21篇
  1993年   14篇
  1992年   18篇
  1991年   21篇
  1990年   15篇
  1989年   17篇
  1988年   18篇
  1986年   15篇
  1985年   29篇
  1984年   27篇
  1983年   17篇
  1982年   13篇
  1981年   20篇
  1980年   20篇
  1979年   26篇
  1978年   22篇
  1977年   23篇
  1976年   15篇
  1975年   11篇
  1974年   9篇
  1973年   10篇
  1965年   7篇
排序方式: 共有1542条查询结果,搜索用时 15 毫秒
151.
152.
Several 5-substituted derivatives of 7-ethoxycarbonyl-6,8-dimethyl-1(2H)- phthalazinone were prepared by means of nitration, reductive amination, and diazonium decomposition. The substituents introduced included NO2, NH2, F, Cl, CN. Among the derivatives, the fluorine compound was obtained only in poor yield because intramolecular cyclization occurred predominantly.  相似文献   
153.
It was found that a beta-fructofuranosidase produced by Microbacterium sp. H-1 has potent trans-beta-fructofuranosylation activity from sucrose (donor). By means of this enzyme system, rebaudioside A (RA), the second major sweet steviol glycoside of the leaves of Stevia rebaudiana, was subjected to transfructosylation, affording a mono-beta-fructofuranosylated product (RA-F) in a high yield. The structure of RA-F was elucidated as beta-D-fructofuranosyl-(2----6)-beta-D-glucopyranosyl ester of steviol-13-O-[beta-D-glucopyranosyl-(1----2)]- [beta-D-glucopyranosyl-(1----3)]-beta-D-glucopyranoside. Some improvement in the quality of sweetness was observed for RA-F.  相似文献   
154.
A new technique for preparing anti-reflection/anti-static thin films for CRTs at low temperature has been developed. Double-layered films of SiO2/SnO2 were formed on a CRT panel surface by the sol-gel method using photoirradiation. The new method makes it possible to reduce heat treatment temperature (°C) by almost 50% and treatment time to approximately 33% of the conventional levels.  相似文献   
155.
A series of 4-furyl-2-guanidinothiazole derivatives and related compounds were synthesized and evaluated for histamine H2-receptor antagonist and gastric acid antisecretory activities. Among them, compounds I-17, I-48 and I-49 showed high activities in these tests. In addition, compound I-17 possessed potent inhibitory activities on each of the gastric ulcers induced by stress, ethanol and HCl-aspirin. On the other hand, compound I-48 demonstrated antimicrobial activity against Helicobacter Pylori and the potency was far stronger than that of clinically used H2-antagonists. Some structure-activity relationships are discussed.  相似文献   
156.
Phonon-assisted interchain hopping of negatively charged solitons in polyacetylene has been studied using a local chemical reaction model CH + CH4 → CH4 + CH. Quantum chemical characteristics of the electron transfer process have been analyzed in terms of the dynamic electron density and the mutual polarization moment. The CH stretching vibrational motion of CH4, which is a local model of the sp3 defect, has been found to play a significant role for the electron transfer. The excitation of the corresponding vibrational mode of the sp3 defect would promote the interchain hopping of the charged soliton. The electron transfer process has also been studied in terms of the “regional” density functional theory. It has been shown that the driving force of the electron transfer is represented by the regional chemical potentials.  相似文献   
157.
158.
Masaharu Ishikawa 《Topology》2004,43(1):215-232
In the present paper we generalize the divide lying in the unit disk, introduced by A'Campo, to compact, oriented, smooth surfaces, and prove a fibration theorem for generalized divides. As a consequence, we will show that, for any link L in the tangent circle bundle Y to the compact surface, there exists an additional knot K such that the link LK is the binding of a “positive” open book decomposition of Y.  相似文献   
159.
In this paper we introduce a certain sum by using Dirichlet characters. We investigate the Riesz mean of the sum using the analytic properties of the MultipleL-function systematically. Eine überarbeitete Fassung ging am 6. 8. 2001 ein  相似文献   
160.
Our main interest in this paper is to translate from “natural language” into “system theoretical language”. This is of course important since a statement in system theory can be analyzed mathematically or computationally. We assume that, in order to obtain a good translation, “system theoretical language” should have great power of expression. Thus we first propose a new frame of system theory, which includes the concepts of “measurement” as well as “state equation”. And we show that a certain statement in usual conversation, i.e., fuzzy modus ponens with the word “very”, can be translated into a statement in the new frame of system theory. Though our result is merely one example of the translation from “natural language” into “system theoretical language”, we believe that our method is fairly general.  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