全文获取类型
收费全文 | 177116篇 |
免费 | 12000篇 |
国内免费 | 9124篇 |
专业分类
化学 | 70971篇 |
晶体学 | 1420篇 |
力学 | 11024篇 |
综合类 | 531篇 |
数学 | 39805篇 |
物理学 | 40170篇 |
无线电 | 34319篇 |
出版年
2024年 | 368篇 |
2023年 | 2131篇 |
2022年 | 2626篇 |
2021年 | 3332篇 |
2020年 | 3174篇 |
2019年 | 3003篇 |
2018年 | 13837篇 |
2017年 | 13322篇 |
2016年 | 10147篇 |
2015年 | 4726篇 |
2014年 | 4980篇 |
2013年 | 6448篇 |
2012年 | 11234篇 |
2011年 | 18532篇 |
2010年 | 11787篇 |
2009年 | 11780篇 |
2008年 | 12558篇 |
2007年 | 14484篇 |
2006年 | 5233篇 |
2005年 | 5906篇 |
2004年 | 5048篇 |
2003年 | 4831篇 |
2002年 | 3479篇 |
2001年 | 2349篇 |
2000年 | 2339篇 |
1999年 | 2348篇 |
1998年 | 2144篇 |
1997年 | 1823篇 |
1996年 | 1881篇 |
1995年 | 1624篇 |
1994年 | 1433篇 |
1993年 | 1288篇 |
1992年 | 1114篇 |
1991年 | 957篇 |
1990年 | 786篇 |
1989年 | 652篇 |
1988年 | 537篇 |
1987年 | 459篇 |
1986年 | 404篇 |
1985年 | 398篇 |
1984年 | 287篇 |
1983年 | 251篇 |
1982年 | 225篇 |
1981年 | 177篇 |
1980年 | 152篇 |
1979年 | 115篇 |
1978年 | 101篇 |
1977年 | 84篇 |
1976年 | 82篇 |
1973年 | 93篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
An experimental study of an optical burst switching network based on wavelength-selective optical switches 总被引:1,自引:0,他引:1
Li Xinwan Chen Jianping Wu Guiling Wang Hui Ye Ailun 《Communications Magazine, IEEE》2005,43(5):S3-10
In this article we report the system structure and test results of an experimental optical burst switching network with three edge router's and one core node. Wavelength-selective switches developed for this system and their characteristics are depicted. The implementation and performance of our new scheme for the just-in-time protocol are described. We also report experimental results of FTP and VOD services on this system. Some parameters, including traffic rate, average burst data length, and assembly time, are studied. 相似文献
62.
63.
M. K. Bakhadyrkhanov O. É. Sattarov Kh. M. Iliev K. S. Ayupov Tuérdi Umaier 《Semiconductors》2005,39(7):789-791
It is experimentally ascertained that light stimulates the negative magnetoresistance observed in a high electric field in silicon doped with boron and manganese. The optimum conditions (the electric field, temperature, illumination, and resistivity of the material) for observation of the largest magnitude of negative magnetoresistance in (Si:B):Mn are determined. The dependence of the negative magnetoresistance on the concentration of compensating impurity is established. 相似文献
64.
On effective offloading services for resource-constrained mobile devices running heavier mobile internet applications 总被引:1,自引:0,他引:1
Kun Yang Shumao Ou Hsiao-Hwa Chen 《Communications Magazine, IEEE》2008,46(1):56-63
Rapid advances in wireless mobile network technologies and mobile handsets (MHs) facilitate ubiquitous infrastructure that can support a range of mobile services and applications in addition to conventional mobile Internet access. One recent trend is to effectively run desktop PC-oriented heavier applications on MHs. However, due to their miniature, portable size, MHs are resource-constrained and therefore, running these applications directly on an MH is not satisfactory given a user's expectations. To cope with this problem, this article proposes a novel offloading service that can seamlessly offload some of the tasks of a mobile application from an MH to nearby, resource-rich PCs (called surrogates). The system architecture and key components of the proposed offloading service are presented, prototyped, and evaluated. The results of experiments and simulations have demonstrated the effectiveness and efficiency of this offloading service for mobile applications. 相似文献
65.
Chris Hope 《The Journal of the Operational Research Society》2003,54(11):1167-1176
What strategy should a football (soccer, in American parlance) club adopt when deciding whether to sack its manager? This paper introduces a simple model assuming that a club's objective is to maximize the number of league points that it scores per season. The club's strategy consists of three choices: the length of the honeymoon period during which it will not consider sacking a new manager, the level of the performance trapdoor below which the manager get the sack, and the weight that it will give to more recent games compared to earlier ones. Some data from the last six seasons of the English Premiership are used to calibrate the model. At this early stage of the research, the best strategy appears to have only a short honeymoon period of eight games (much less than the actual shortest period of 12 games), to set the trapdoor at 0.74 points per game, and to put 47% of the weight on the last five games. A club adopting this strategy would obtain on average 56.8 points per season, compared to a Premiership average of 51.8 points. 相似文献
66.
67.
Dominique Fourdrinier William E. Strawderman 《Annals of the Institute of Statistical Mathematics》2003,55(4):803-816
We consider estimation of loss for generalized Bayes or pseudo-Bayes estimators of a multivariate normal mean vector, θ. In
3 and higher dimensions, the MLEX is UMVUE and minimax but is inadmissible. It is dominated by the James-Stein estimator and by many others. Johnstone (1988,
On inadmissibility of some unbiased estimates of loss,Statistical Decision Theory and Related Topics, IV (eds. S. S. Gupta and J. O. Berger), Vol. 1, 361–379, Springer, New York) considered the estimation of loss for the usual
estimatorX and the James-Stein estimator. He found improvements over the Stein unbiased estimator of risk. In this paper, for a generalized
Bayes point estimator of θ, we compare generalized Bayes estimators to unbiased estimators of loss. We find, somewhat surprisingly,
that the unbiased estimator often dominates the corresponding generalized Bayes estimator of loss for priors which give minimax
estimators in the original point estimation problem. In particular, we give a class of priors for which the generalized Bayes
estimator of θ is admissible and minimax but for which the unbiased estimator of loss dominates the generalized Bayes estimator
of loss. We also give a general inadmissibility result for a generalized Bayes estimator of loss.
Research supported by NSF Grant DMS-97-04524. 相似文献
68.
A one-dimensional bulk reaction model for the oxidation of nickeltitanium is formulated, with preferential oxidation of titaniumbeing included. The modelling is directed at the better understandingof the dominant mechanisms involved in the oxidation processand their significance for the biocompatibility of the alloy.Two different regimes for the relative diffusivities of oxygenand the metals are investigated. By assuming fast bulk reactions,different asymptotic structures emerge in different parameterregimes and the resulting models take the form of moving boundaryproblems. Different profiles of nickel concentration are obtained:in particular a nickel-rich layer (observed in practice) ispresent below the oxide/metal interface for the case when oxygenand the metals diffuse at comparable rates. 相似文献
69.
A lithium(I) coordination polymer has been formed from LiClO4 and the 2,2′‐bipyrimidine (bpym) ligand in which each square pyramidal lithium(I) atom is coordinated in the basal plane by four nitrogen donor atoms derived from two bpym ligands and one water molecule at the apical position. These are connected into a layer structure via hydrogen‐bonding interactions involving the perchlorate anions. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
70.
Briand et al. (Electron. Comm. Probab. 5 (2000) 101–117) gave a counterexample and proposition to show that given g,g-expectations usually do not satisfy Jensen's inequality for most of convex functions. This yields a natural question, under which conditions on g, do g-expectations satisfy Jensen's inequality for convex functions? In this paper, we shall deal with this question in the case that g is convex and give a necessary and sufficient condition on g under which Jensen's inequality holds for convex functions. To cite this article: Z. Chen et al., C. R. Acad. Sci. Paris, Ser. I 337 (2003). 相似文献