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   15188篇
  免费   871篇
  国内免费   456篇
系统科学   1417篇
丛书文集   324篇
教育与普及   433篇
理论与方法论   301篇
现状及发展   903篇
研究方法   32篇
综合类   13104篇
自然研究   1篇
  2024年   43篇
  2023年   126篇
  2022年   179篇
  2021年   206篇
  2020年   137篇
  2019年   44篇
  2018年   794篇
  2017年   806篇
  2016年   511篇
  2015年   257篇
  2014年   335篇
  2013年   284篇
  2012年   589篇
  2011年   1276篇
  2010年   1143篇
  2009年   874篇
  2008年   929篇
  2007年   1175篇
  2006年   365篇
  2005年   348篇
  2004年   401篇
  2003年   563篇
  2002年   661篇
  2001年   538篇
  2000年   371篇
  1999年   502篇
  1998年   441篇
  1997年   409篇
  1996年   349篇
  1995年   342篇
  1994年   299篇
  1993年   248篇
  1992年   195篇
  1991年   177篇
  1990年   168篇
  1989年   158篇
  1988年   129篇
  1987年   77篇
  1986年   44篇
  1985年   12篇
  1984年   5篇
  1982年   3篇
  1980年   1篇
  1967年   1篇
排序方式: 共有10000条查询结果,搜索用时 297 毫秒
871.
In this paper,domain decomposition method(DDM) for numerical solutions of mathematical physics equations is improved into dynamic domain decomposition method(DDDM) . The main feature of the DDDM is that the number,shape and volume of the sub-domains are all flexibly changeable during the iterations,so it suits well to be implemented on a reconfigurable parallel computing system. Convergence analysis of the DDDM is given,while an application approach to a weak nonlinear elliptic boundary value problem and a ...  相似文献   
872.
Within the framework of the regularization theory, a spectral regularization method is introduced and analyzed. The convergence estimate under an appropriate choice of regularization parameter is obtained. A numerical implementation is described. Numerical examples show that the proposed method is effective and stable.  相似文献   
873.
Classical network reliability problems assume both networks and components have only binary states,fully working or fully failed states.But many actual networks are multi-state,such as communication networks and transportation networks.The nodes and arcs in the networks may be in intermediate states which are not fully working either fully failed.A simulation approach for computing the two-terminal reliability of a multi-state network is described.Two-terminal reliability is defined as the probability that d units of demand can be supplied from the source to sink nodes under the time threshold T.The capacities of arcs may be in a stochastic state following any discrete or continuous distribution.The transmission time of each arc is also not a fixed number but stochastic according to its current capacity and demand.To solve this problem,a capacitated stochastic coloured Petri net is proposed for modelling the system behaviour.Places and transitions respectively stand for the nodes and arcs of a network.Capacitated transition and self-modified token colour with route information are defined to describe the multi-state network.By the simulation,the two-terminal reliability and node importance can be estimated and the optimal route whose reliability is highest can also be given.Finally,two examples of different kinds of multistate networks are given.  相似文献   
874.
郭全胜 《太原科技》2014,(1):105-107
列车运行监控装置是确保列车安全运行的重要设备,具有监控和记录两大功能,如果记录文件丢失,将给后续的分析工作造成不便,为列车安全运行造成隐患。针对列车运行监控装置记录文件丢失故障问题,分析了故障产生的原因,探讨了解决办法。  相似文献   
875.
The approach of available transfer capability (denoted as ATC) incorporating wind generation has been paid very high attention since the development of wind generation. Based on the maximum function, this paper presents an ATC model. The characteristic of the new model is twofold. First, it considers wind turbines connected to power system and static security of power system simultaneously. Second, it is a system of semismooth equations and can be solved easily. By using the smoothing strategy, a smoothing Newton method is adopted for solving the proposed new ATC model. Numerical simulation results of the IEEE 30-bus and 118-bus system show that the new model and algorithm are feasible and effective. The impact of wind turbines connected to power system on ATC is also analyzed.  相似文献   
876.
Mobile genomic islands (GIs) can be excised from the chromosome, then form a circular intermediate and be reintegrated into the chromosome by the GI internal integrase. Some mobile GIs can also be transferred into a new receptor cell by transformation, conjugation, or transduction. The action sites of the integrase are usually flanked direct repeats (DRs) of the GIs. Accurate localization of the flanking sequences is a precondition for determining the mobility of the GI. Mobile GIs are generally associated with transfer RNAs (tRNAs). Based on the correlation between flanking sequences and tRNA sequences, the flanking sequences of 11 putative mobile GIs in Pseudomonas aeruginosa PAO1, P. aeruginosa PA14, P. fluorescens Pf-5 and P. fluorescens Pf0-1 were identified. Among the 11 GIs, Pf0-1GI-1 is responsible for benzoate degradation. PAO1GI-1, Pf5GI-2, Pf5GI-3, and Pf5GI-4 were confirmed experimentally to be excised from a chromosome to form a circular intermediate. The action sites of the integrases are these GIs direct repeats. Due to distinct DRs, cutting sites for the internal integrase of PAO1GI-1, Pf5GI-2, Pf5GI-3 and Pf5GI-4 were determined outside the T-loop of the tRNAGly gene, outside the anticodon loop of the tRNASer gene and tRNALys gene, and at the asymmetric 3′-end of the tRNALeu gene, respectively. PAO1GI-1 and other mobile GIs may be transferred into many different strains that belong to different phyla because of the clear flanking sequences. This study describes basic information about the action sites of the integrases, assesses the mobility of GIs, and can help design and transfer mobile GIs to candidate strains.  相似文献   
877.
The shock compression experiment of liquid helium is an available way to gain properties of specimen at high temperatures and pressures.Based on Fluent,a thermal insulation analysis and design of a liquid helium temperature target in the environment condition of 100 Pa for shock compression experiment is performed.Then,a cryogenic target with a 10 K helium vapor shield and a separated vacuum interval is particularly developed.A lowest temperature of 3.63 K and a stable temperature of 3.70 K in the specimen cavity with an accuracy of 0.1 K are obtained by means of continuous flow and vacuum cooling.Both time-consuming and temperature stability are well-suited to the requirements of the shock compression experiment.The results show that the calculated and experimental data well-matched each other.The simulation method may be effective and feasible for the optimal design of the cryogenic target.  相似文献   
878.
DNA is the genetic material that contains the "instructions" to not only guide the continuation of life but also govern the development, metabolism and functioning of living organisms. DNA damage occurs daily due to various exogenous (environ-  相似文献   
879.
A new class of media with abnormal electromagnetic parameters has been attracting increasing attention because of its exotic properties and potential application. Currently, typical metamaterials are mainly composed of artificially designed metallic periodic structures. However, due to the limitations of available fabrication technologies, physical size and material effects, it is difficult to realize these abnormal properties by these artificial structures in the high-frequency regime. Therefore, it is important to find materials with intrinsic abnormal electromagnetic responses. In this field, a new mechanism based on the interaction between polar lattice vibrations and electromagnetic waves has been proposed. In this paper, we review progress in this field.  相似文献   
880.
Langevin equation is widely used to study the stochastic effects in molecular networks, as it often approximates well the underlying chemical master equation. However, frequently it is not clear when such an approximation is applicable and when it breaks down. This paper studies the simple Schnakenberg model consisting of three reversible reactions and two molecular species whose concentrations vary. To reduce the residual errors from the conventional formulation of the Langevin equation, the authors propose to explicitly model the effective coupling between macroscopic concentrations of different molecular species. The results show that this formulation is effective in correcting residual errors from the original uncoupled Langevin equation and can approximate the underlying chemical master equation very accurately.  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