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   18451篇
  免费   2106篇
  国内免费   784篇
化学   5216篇
晶体学   103篇
力学   1174篇
综合类   104篇
数学   7872篇
物理学   6872篇
  2024年   23篇
  2023年   174篇
  2022年   314篇
  2021年   419篇
  2020年   485篇
  2019年   482篇
  2018年   352篇
  2017年   395篇
  2016年   638篇
  2015年   533篇
  2014年   854篇
  2013年   1416篇
  2012年   822篇
  2011年   875篇
  2010年   806篇
  2009年   1106篇
  2008年   1256篇
  2007年   1260篇
  2006年   1060篇
  2005年   828篇
  2004年   693篇
  2003年   748篇
  2002年   781篇
  2001年   587篇
  2000年   607篇
  1999年   524篇
  1998年   499篇
  1997年   355篇
  1996年   273篇
  1995年   239篇
  1994年   233篇
  1993年   192篇
  1992年   179篇
  1991年   126篇
  1990年   110篇
  1989年   114篇
  1988年   130篇
  1987年   96篇
  1986年   95篇
  1985年   132篇
  1984年   97篇
  1983年   33篇
  1982年   69篇
  1981年   56篇
  1980年   54篇
  1979年   46篇
  1978年   42篇
  1977年   44篇
  1976年   41篇
  1973年   10篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
982.
The Device is composed of the basic microdensitometer, the control computer, the magnetic tape unit, the teletype, the interface, and the software package.

This apparatus is designated for digitalization of image data point by point (system “flying spot”) and for their record on magnetic tape for further data processing. The software package makes possible to realize some basic evaluation only by using configuration mentioned above — for example recording of measured values, determination of numbers of occurrences particular optical density (histogram), tresholding and mapping of measured values.

This paper describes the instrument and its using for autoradiographs evaluating.  相似文献   
983.
984.
985.
We address theoretically the electronic transport through graphene quantum dots with the emphasis on the transmission phase. Analytical and numerical results are presented regarding the existence – or not – of a π lapse of the transmittance phase (and, consequentially, a Fano zero in the transmittance) at the charge neutrality point. A simple universal criterium is found, the phase lapses being always present if the contact sites belong to the same sub‐lattice. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)  相似文献   
986.
The ladderane family of natural products are well known for their linearly concatenated cyclobutane skeletal structure. Owing to their unique carbocyclic framework, several chemical syntheses have been reported since their discovery in 2002. The focus of this review is to showcase the novel tactics that have been used to generate the ladderane core and the challenges that are associated with the synthesis of these unusual and complex natural products.  相似文献   
987.
This work reports a detailed structure–property relationship study of a series of efficient host materials based on the donor–spiro–acceptor (D‐spiro‐A) design for green and sky‐blue phosphorescent organic light‐emitting diodes (PhOLEDs). The electronic and physical effects of the indoloacridine (IA) fragment connected through a spiro bridge to different acceptor units, namely, fluorene, dioxothioxanthene or diazafluorene moiety, have been investigated in depth. The resulting host materials have been easily synthesised through short, efficient, low‐cost, and highly adaptable synthetic routes by using common intermediates. The dyes possess a very high triplet energy (ET) and tuneable HOMO/LUMO levels, depending on the strength of the donor/acceptor combination. The peculiar electrochemical and optical properties of the IA moiety have been investigated though a fine comparison with their phenylacridine counterparts to study the influence of planarisation. Finally, these molecules have been incorporated as hosts in green and sky‐blue PhOLEDs. For the derivative SIA‐TXO2 as a host, external quantum efficiencies as high as 23 and 14 % have been obtained for green and sky‐blue PhOLEDs, respectively.  相似文献   
988.
The proposed anti-synchronization conditions of coupled chaotic systems are based, in this Letter, on the use of aggregation techniques for the stability study of the error dynamics. The schemes are, successfully, applied to coupled Rössler and Chen chaotic systems making the instantaneous characteristic matrix under the arrow form. Numerical simulations are performed to illustrate the efficiency of the proposed approach.  相似文献   
989.
A Complex Adaptive System is a collection of autonomous, heterogeneous agents, whose behavior is defined with a limited number of rules. A Game Theory is a mathematical construct that assumes a small number of rational players who have a limited number of actions or strategies available to them. The CAS method has the potential to alleviate some of the shortcomings of GT. On the other hand, CAS researchers are always looking for a realistic way to define interactions among agents. GT offers an attractive option for defining the rules of such interactions in a way that is both potentially consistent with observed real‐world behavior and subject to mathematical interpretation. This article reports on the results of an effort to build a CAS system that utilizes GT for determining the actions of individual agents. © 2009 Wiley Periodicals, Inc. Complexity, 16,24–42, 2010  相似文献   
990.
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