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   8208篇
  免费   357篇
  国内免费   73篇
化学   5965篇
晶体学   88篇
力学   368篇
综合类   4篇
数学   1109篇
物理学   1104篇
  2024年   9篇
  2023年   69篇
  2022年   385篇
  2021年   399篇
  2020年   286篇
  2019年   326篇
  2018年   312篇
  2017年   244篇
  2016年   430篇
  2015年   288篇
  2014年   344篇
  2013年   772篇
  2012年   544篇
  2011年   566篇
  2010年   355篇
  2009年   319篇
  2008年   365篇
  2007年   366篇
  2006年   292篇
  2005年   251篇
  2004年   207篇
  2003年   187篇
  2002年   190篇
  2001年   70篇
  2000年   78篇
  1999年   55篇
  1998年   53篇
  1997年   59篇
  1996年   59篇
  1995年   47篇
  1994年   53篇
  1993年   50篇
  1992年   43篇
  1991年   35篇
  1990年   54篇
  1989年   43篇
  1988年   36篇
  1987年   39篇
  1986年   34篇
  1985年   51篇
  1984年   31篇
  1983年   26篇
  1982年   44篇
  1981年   26篇
  1980年   24篇
  1979年   23篇
  1978年   15篇
  1977年   15篇
  1976年   14篇
  1975年   12篇
排序方式: 共有8638条查询结果,搜索用时 31 毫秒
11.
The fractional order evolutionary integral equations have been considered by the first author in [6], the existence, uniqueness and some other properties of the solution have been proved. Here we study the continuation of the solution and its fractional order derivative. Also we study the generality of this problem and prove that the fractional order diffusion problem, the fractional order wave problem and the initial value problem of the equation of evolution are special cases of it. The abstract diffusion-wave problem will be given also as an application.  相似文献   
12.
In this study, lead sulphide (PbS) was prepared by the chemical bath deposition technique. The sample was characterized by X-ray diffraction (XRD), Energy Dispersive Analysis of X-rays (EDAX) and cyclic voltammetry. EDAX spectrum shows peaks attributable to lead and sulphur. The EDAX analysis also shows that the prepared sample is stoichiometric. Cyclic voltammetry experiments were recorded at 100 mV·s−1 and 400 mV·s−1 scan rates. Results show that the rate controlling electrochemical reaction is electron transfer. The presence of redox waves shows that the lithium intercalation and deintercalation can occur as a result of lattice expansion in PbS. There were no differences in the PbS XRD data before and after the cyclic voltammetry experiments indicating that the PbS structure is not modified upon lithium ion intercalation and deintercalation in PbS. The discharge characteristics for 35 cycles of the cell using the LiCoO2/PbS couple is presented indicating the possible development of such materials as anode in lithium ion cells.  相似文献   
13.
The Aza-Diels-Alder reaction of aldimines with isoeugenol is described. New 1,2,3,4-tetrahydroquinoline and quinoline structures are reported. The stereo- and regioselectivities of the [4+2] cycloaddition are discussed.  相似文献   
14.
Using a double Suzuki cross-coupling reaction ortho- or para-bromobenzyl bromides are easily transformed into unsymmetrical diaryl (or heteroaryl) methanes  相似文献   
15.

Background  

The aim of the present study was to characterize the activation profiles of 15 opioid ligands in transfected human embryonic kidney cells expressing only δ opioid receptors. Activation profiles of most of these ligands at δ opioid receptors had not been previously characterized in vitro. Receptor activation was assessed by measuring the inhibition of forskolin-stimulated cAMP production.  相似文献   
16.
The behaviour of several 2-amino-3-cyano-4H-pyran derivatives toward a variety of nucleophilic reagents is reported.  相似文献   
17.
18.
针对基于Web的图书馆管理系统资源访问控制的动态性问题,提出了一种基于角色的访问控制策略描述方案.通过对基于Web的图书馆管理系统访问控制管理影响因素和访问控制需求的分析,结合NIST基于角色的访问控制统一模型标准,构造了一种基于角色的访问控制元模型.并在这一元模型的基础上,提出了一种紧凑的基于角色的访问控制XML策略描述语言框架.结果表明该访问控制策略描述语言框架适合表述动态环境下对图书馆资源的访问策略,提高了基于Web的图书馆管理系统资源访问的安全性.  相似文献   
19.
In this paper, we introduce a new concept of semi-preemptive scheduling and we show how it can be used to derive a maximum-flow-based lower bound for the P|rj|Lmax which dominates the well-known preemptive lower bound. We show that, in some cases, the proposed bound strictly dominates the preemptive one while having the same complexity.  相似文献   
20.
There are few techniques available to numerically solve sixth-order boundary-value problems with two-point boundary conditions. In this paper we show that the Sinc-Galerkin method is a very effective tool in numerically solving such problems. The method is then tested on examples with homogeneous and nonhomogeneous boundary conditions and a comparison with the modified decomposition method is made. It is shown that the Sinc-Galerkin method yields better results.

  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