全文获取类型
收费全文 | 27068篇 |
免费 | 764篇 |
国内免费 | 987篇 |
专业分类
电工技术 | 714篇 |
综合类 | 515篇 |
化学工业 | 2997篇 |
金属工艺 | 2403篇 |
机械仪表 | 1170篇 |
建筑科学 | 714篇 |
矿业工程 | 210篇 |
能源动力 | 952篇 |
轻工业 | 1646篇 |
水利工程 | 247篇 |
石油天然气 | 442篇 |
武器工业 | 40篇 |
无线电 | 3181篇 |
一般工业技术 | 6923篇 |
冶金工业 | 4003篇 |
原子能技术 | 388篇 |
自动化技术 | 2274篇 |
出版年
2024年 | 9篇 |
2023年 | 65篇 |
2022年 | 171篇 |
2021年 | 250篇 |
2020年 | 181篇 |
2019年 | 284篇 |
2018年 | 463篇 |
2017年 | 478篇 |
2016年 | 524篇 |
2015年 | 472篇 |
2014年 | 797篇 |
2013年 | 1785篇 |
2012年 | 1236篇 |
2011年 | 1754篇 |
2010年 | 1428篇 |
2009年 | 1620篇 |
2008年 | 1648篇 |
2007年 | 1681篇 |
2006年 | 1476篇 |
2005年 | 1319篇 |
2004年 | 1021篇 |
2003年 | 866篇 |
2002年 | 808篇 |
2001年 | 779篇 |
2000年 | 762篇 |
1999年 | 744篇 |
1998年 | 1471篇 |
1997年 | 1047篇 |
1996年 | 909篇 |
1995年 | 565篇 |
1994年 | 457篇 |
1993年 | 373篇 |
1992年 | 239篇 |
1991年 | 245篇 |
1990年 | 156篇 |
1989年 | 170篇 |
1988年 | 120篇 |
1987年 | 86篇 |
1986年 | 58篇 |
1985年 | 59篇 |
1984年 | 37篇 |
1983年 | 31篇 |
1982年 | 26篇 |
1981年 | 29篇 |
1980年 | 16篇 |
1979年 | 9篇 |
1977年 | 8篇 |
1976年 | 19篇 |
1975年 | 11篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
HOU Xiao-lin LI Shu-bo YIN Chang-chuan YUE Guang-xin School of Telecommunication Engineering Beijing University of Posts Telecommunications Beijing P.R. China 《中国邮电高校学报(英文版)》2004,11(3)
1 Introduction Linkadaptationtechniqueisnowwidelyrecognizedasakeysolutiontoincreasethespectralefficiencyofwire lesssystems[1~ 3] .GPRS ,EDGE ,cdma2 0 0 0andWCDMAallincludelinkadaptationasameanstopro videhigherdatarates[4~ 5] .Torealizethepotentialoflinkadaptation ,reliablechannel predictionisneces sary[6 ] . Therearemanydifferentchannelpredictionmethodsavailablenow ,suchasLongRangePrediction(LRP) [6 ] ,predictionbasedonsubspacesignalprocess ingalgorithms[7] ,predictionbasedonFinit… 相似文献
152.
153.
154.
155.
156.
157.
High spatial order finite element method to solve Maxwell's equations in time domain 总被引:2,自引:0,他引:2
Pernet S. Ferrieres X. Cohen G. 《Antennas and Propagation, IEEE Transactions on》2005,53(9):2889-2899
This paper presents a finite element method with high spatial order for solving the Maxwell equations in the time domain. In the first part, we provide the mathematical background of the method. Then, we discuss the advantages of the new scheme compared to a classical finite-difference time-domain (FDTD) method. Several examples show the advantages of using the new method for different kinds of problems. Comparisons in terms of accuracy and CPU time between this method, the FDTD and the finite-volume time-domain methods are given as well. 相似文献
158.
X. Liang X. Wang J. Zhuang Y. Chen D. Wang Y. Li 《Advanced functional materials》2006,16(14):1805-1813
Uniform magnetite, hematite, and goethite nanocrystals were prepared through an attractive method based on an oleic acid/alcohol/water system. By adjusting the synthetic parameters (base concentration, alcohol content, categories of alcohols, etc.), the controlled synthesis of uniform magnetite, hematite, and goethite nanocrystals can be easily achieved. Detailed investigations on the effect of the experimental parameters on the morphology of the final products and the phase transitions among the magnetite, hematite, and goethite phases were carried out. Finally, a method of doping other metal ions into magnetite was developed and the magnetic properties of magnetite doped with different metal elements were studied. 相似文献
159.
An improved coupled-mode equation for nonlinear directional couplers (NLDC) with Kerr-like nonlinear media is proposed. The method is based on the generalized reciprocity relation in which two sets of field solutions satisfying Maxwell's equations are for the NLDC and for the isolated nonlinear waveguide. That leads to a reasonable result that all the coefficients in the coupled-mode equations, including the coupling coefficient, become power dependent. For the NLDC with a self-focusing or self-defocusing nonlinear material, the authors examine how the coupling coefficient, the coupling length, and the guided power depend on the input power in the range of coupling stronger than in previous reports. It is found that the critical power at which the coupling length becomes infinity does not increase as much with the two guides for the case of self-focusing media 相似文献
160.
Zhang X.B. Lam S.S. Dong-Young Lee Yang Y.R. 《Networking, IEEE/ACM Transactions on》2003,11(6):908-922
We present the design and specification of a protocol for scalable and reliable group rekeying together with performance evaluation results. The protocol is based upon the use of key trees for secure groups and periodic batch rekeying. At the beginning of each rekey interval, the key server sends a rekey message to all users consisting of encrypted new keys (encryptions, in short) carried in a sequence of packets. We present a scheme for identifying keys, encryptions, and users, and a key assignment algorithm that ensures that the encryptions needed by a user are in the same packet. Our protocol provides reliable delivery of new keys to all users eventually. It also attempts to deliver new keys to all users with a high probability by the end of the rekey interval. For each rekey message, the protocol runs in two steps: a multicast step followed by a unicast step. Proactive forward error correction (FEC) multicast is used to reduce delivery latency. Our experiments show that a small FEC block size can be used to reduce encoding time at the server without increasing server bandwidth overhead. Early transition to unicast, after at most two multicast rounds, further reduces the worst-case delivery latency as well as user bandwidth requirement. The key server adaptively adjusts the proactivity factor based upon past feedback information; our experiments show that the number of NACKs after a multicast round can be effectively controlled around a target number. Throughout the protocol design, we strive to minimize processing and bandwidth requirements for both the key server and users. 相似文献