全文获取类型
收费全文 | 813669篇 |
免费 | 11078篇 |
国内免费 | 2453篇 |
专业分类
电工技术 | 14821篇 |
综合类 | 825篇 |
化学工业 | 121866篇 |
金属工艺 | 29764篇 |
机械仪表 | 23141篇 |
建筑科学 | 21108篇 |
矿业工程 | 2936篇 |
能源动力 | 22223篇 |
轻工业 | 75096篇 |
水利工程 | 7354篇 |
石油天然气 | 10699篇 |
武器工业 | 49篇 |
无线电 | 97217篇 |
一般工业技术 | 153285篇 |
冶金工业 | 160154篇 |
原子能技术 | 14249篇 |
自动化技术 | 72413篇 |
出版年
2021年 | 6658篇 |
2020年 | 4823篇 |
2019年 | 6131篇 |
2018年 | 10299篇 |
2017年 | 10121篇 |
2016年 | 10729篇 |
2015年 | 7871篇 |
2014年 | 12917篇 |
2013年 | 37876篇 |
2012年 | 21084篇 |
2011年 | 29565篇 |
2010年 | 23177篇 |
2009年 | 26063篇 |
2008年 | 27120篇 |
2007年 | 27036篇 |
2006年 | 23929篇 |
2005年 | 21991篇 |
2004年 | 21197篇 |
2003年 | 20901篇 |
2002年 | 19964篇 |
2001年 | 19970篇 |
2000年 | 18537篇 |
1999年 | 19775篇 |
1998年 | 49550篇 |
1997年 | 35185篇 |
1996年 | 27182篇 |
1995年 | 20769篇 |
1994年 | 18217篇 |
1993年 | 17782篇 |
1992年 | 12858篇 |
1991年 | 12254篇 |
1990年 | 11799篇 |
1989年 | 11449篇 |
1988年 | 10788篇 |
1987年 | 9390篇 |
1986年 | 9242篇 |
1985年 | 10802篇 |
1984年 | 10096篇 |
1983年 | 8866篇 |
1982年 | 8305篇 |
1981年 | 8386篇 |
1980年 | 7931篇 |
1979年 | 7733篇 |
1978年 | 7337篇 |
1977年 | 8893篇 |
1976年 | 11970篇 |
1975年 | 6291篇 |
1974年 | 5988篇 |
1973年 | 5977篇 |
1972年 | 4870篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
901.
Javier Roca-Pardiñas Carmen Cadarso-Suárez María J. Lado 《Computational statistics & data analysis》2008,52(4):1958-1970
In many applications, the joint effect of two continuous covariates on the target binary response may vary across groups defined by levels of a given factor. A testing procedure that would enable this type of surface-by-factor interactions to be detected has been designed. To accomplish this goal, a logistic generalized additive model (GAM) with bivariate continuous interactions varying across groups defined by levels of a factor is considered. A local scoring algorithm based on local linear kernel smoothers was implemented to estimate the proposed logistic GAM. Bootstrap resampling techniques were used for the purpose of testing for factor-by-surface interactions. Given the high computational cost involved, binning techniques were used to speed up computation in the estimation and testing processes. The adequacy of the bootstrap-based test was assessed by means of a simulation study. If a factor-by-surface interaction is detected in the model, it is then established that the use of the odds-ratio curves is very useful in obtaining a direct interpretation of the fitted model. The benefits of using this methodology when analyzing real data are illustrated by applying the technique to the outputs produced by a computerized system dedicated to the early detection of breast cancer. 相似文献
902.
M. I. Surin V. E. Keilin S. M. Miklyaev S. A. Shevchenko 《Instruments and Experimental Techniques》2008,51(4):634-637
Within the framework of the “International Thermonuclear Experimental Reactor” (ITER) program, a prototype of a superconducting magnet for a 170-GHz gyrotron has been developed, manufactured, and tested. The operating induction value (7.1 T at the center of a 219-mm-diameter cold hole and 8.1 T on the winding) is reached at a current of 185.2 A. In the final version of the magnet, the required induction value was reached without aging. Special requirements are imposed on the distribution of the magnetic field along the axis, including an abrupt field decrease on both sides of the magnet. Axial forces are additionally taken by a special device. The magnet’s sections are wound with multifiber conductors based on niobium-tin and niobium-titanium alloys. Seventeen resistive shunts are provided for protecting sections during their transition to the normal state. The magnet is equipped with a device for removing a part of energy from the sections. Mechanical stresses in the magnet’s sections and the structure’s power elements have been measured during tests. 相似文献
903.
M. E. Borodyanskii I. M. Borodyanskii T. A. Martyshchenko 《Instruments and Experimental Techniques》2008,51(3):392-395
A device for measuring the active resistance of a direct current energized circuit section is described. Owing to the use of up-to-date electronic components, an iteration measurement algorithm, and a sinusoidal signal as a test one, the following performance characteristics have been obtained: the measurement time is <1 s, and the error varies from 0.3 to 2.0% in a 100-Ω to 1-MΩ range and ≤25% in 10-to 100-Ω and 1-to 10-MΩ ranges. 相似文献
904.
van Driel W.D. van Gils M.A.J. Xuejun Fan Zhang G.Q. Ernst L.J. 《Components and Packaging Technologies, IEEE Transactions on》2008,31(2):260-268
Exposed pad packages were introduced in the late 1980s and early 1990s because of their excellent thermal and electrical performance. Despite these advantages, the exposed pad packages experience a lot of thermo-hygro-mechanical related reliability problems during qualification and testing. Examples are die lift, which occurs predominantly after moisture sensitivity level conditions, and die-attach to leadframe delamination leading to downbond stitch breaks during temperature cycling. In this chapter, nonlinear finite element (FE) models using fracture mechanics based J-integral calculations are used to assess the reliability problems of the exposed pad package family. Using the parametric FE models any geometrical and material effects can be explored to their impact on the occurrence diepad delamination, and dielift. For instance the impact of diepad size is found to be of much less importance as the impact of die thickness is. Using the fracture mechanics approach, the starting location for the delamination from thermo-hygro-mechanical point of view is deducted. The results indicate that when diepad delamination is present, cracks are likely to grow beneath the die and dielift will occur. The interaction between dielift and other failure modes, such as lifted ball bonds, are not found to be very significant. The FE models are combined with simulation-based optimization methods to deduct design guidelines for optimal reliability of the exposed pad family. 相似文献
905.
M E Rentschler S R Platt K Berg J Dumpert D Oleynikov S M Farritor 《IEEE transactions on information technology in biomedicine》2008,12(1):66-75
Long-term human space exploration will require contingencies for emergency medical procedures including some capability to perform surgery. The ability to perform minimally invasive surgery (MIS) would be an important capability. The use of small incisions reduces surgical risk, but also eliminates the ability of the surgeon to view and touch the surgical environment directly. Robotic surgery, or telerobotic surgery, may provide emergency surgical care in remote or harsh environments such as space flight, or extremely forward environments such as battlefields. However, because current surgical robots are large and require extensive support personnel, their implementation has remained limited in forward environments, and they would be difficult, or impossible, to use in space flight or on battlefields. This paper presents experimental analysis of miniature fixed-base and mobile in vivo robots to support MIS surgery in remote and harsh environments. The objective is to develop wireless imaging and task-assisting robots that can be placed inside the abdominal cavity during surgery. Such robots will provide surgical task assistance and enable an on-site or remote surgeon to view the surgical environment from multiple angles. This approach is applicable to long-duration space flight, battlefield situations, and for traditional medical centers and other remote surgical locations. 相似文献
906.
Inter-vehicle communication systems: a survey 总被引:1,自引:0,他引:1
Inter-vehicle communication (IVC) systems (i.e., systems not relying on roadside infrastructure) have the potential to radically improve the safety, efficiency, and comfort of everyday road travel. Their main advantage is that they bypass the need for expensive infrastructure; their major drawback is the comparatively complex networking protocols and the need for significant penetration before their applications can become effective. In this article we present several major classes of applications and the types of services they require from an underlying network. We then proceed to analyze existing networking protocols in a bottom-up fashion, from the physical to the transport layers, as well as security aspects related to IVC systems. We conclude the article by presenting several projects related to IVC as well as a review of common performance evaluation techniques for IVC systems. 相似文献
907.
E. M. Zobov M. E. Zobov F. S. Gabibov I. K. Kamilov F. I. Manyakhin E. K. Naimi 《Semiconductors》2008,42(3):277-280
The results of the effect of ultrasonic treatment of ZnSe crystals on the structure of the energy spectrum of electronic states of centers with deep levels forming photoelectric and luminescent properties of this compound are presented. It is for the first time proved experimentally that the climb of edge dislocations under the effect of ultrasound leads to regrouping and generation of defects forming deep levels, which manifest themselves in phenomena of photosensitivity and radiative recombination. 相似文献
908.
Charalambous C.D. Bultitude R.J.C. Li X. Zhan J. 《Wireless Communications, IEEE Transactions on》2008,7(2):434-439
This paper is concerned with modeling and identification of wireless channels using noisy measurements. The models employed are governed by stochastic differential equations (SDEs) in state space form, while the identification method is based on the expectation-maximization (EM) algorithm and Kalman filtering. The algorithm is tested against real channel measurements. The results presented include state space models for the channels, estimates of inphase and quadrature components, and estimates of the corresponding Doppler power spectral densities (DPSDs), from sample noisy measurements. Based on the available measurements, it is concluded that state space models of order two are sufficient for wireless flat fading channel characterization. 相似文献
909.
Jun-Guo Lu Hill D.J. 《Circuits and Systems II: Express Briefs, IEEE Transactions on》2008,55(6):586-590
Sampled-data feedback control for master-slave synchronization schemes that consist of identical chaotic Lur'e systems is studied. Sufficient conditions for global asymptotic synchronization of such chaotic Lur'e systems are obtained using the free-weighting matrix approach and expressed in terms of linear matrix inequalities (LMIs). With the help of the LMI solvers, the sampled-data feedback control law can easily be obtained to globally asymptotically synchronize Lur'e chaotic systems. The effectiveness of the proposed method is finally illustrated via numerical simulations of chaotic Chua's circuits. 相似文献
910.
Sebastián López Gustavo M. Callicó Félix Tobajas Valentín de Armas José F. López Roberto Sarmiento 《ETRI Journal》2008,30(6):862-864
This letter presents a novel approach for organizing computational resources into groups within H.264/AVC motion estimation architectures, leading to reductions of up to 75% in the equivalent gate count with respect to state‐of‐the‐art designs. 相似文献