全文获取类型
收费全文 | 274605篇 |
免费 | 6496篇 |
国内免费 | 2708篇 |
专业分类
电工技术 | 7094篇 |
技术理论 | 1篇 |
综合类 | 2269篇 |
化学工业 | 40812篇 |
金属工艺 | 12601篇 |
机械仪表 | 9075篇 |
建筑科学 | 8768篇 |
矿业工程 | 1467篇 |
能源动力 | 7136篇 |
轻工业 | 26533篇 |
水利工程 | 2417篇 |
石油天然气 | 3000篇 |
武器工业 | 274篇 |
无线电 | 34875篇 |
一般工业技术 | 48815篇 |
冶金工业 | 51397篇 |
原子能技术 | 4268篇 |
自动化技术 | 23007篇 |
出版年
2022年 | 2108篇 |
2021年 | 3084篇 |
2020年 | 2246篇 |
2019年 | 2388篇 |
2018年 | 3383篇 |
2017年 | 3421篇 |
2016年 | 3425篇 |
2015年 | 3274篇 |
2014年 | 4875篇 |
2013年 | 12664篇 |
2012年 | 7497篇 |
2011年 | 9896篇 |
2010年 | 8066篇 |
2009年 | 8756篇 |
2008年 | 9317篇 |
2007年 | 9199篇 |
2006年 | 8633篇 |
2005年 | 7833篇 |
2004年 | 7098篇 |
2003年 | 7120篇 |
2002年 | 7051篇 |
2001年 | 7090篇 |
2000年 | 6524篇 |
1999年 | 7193篇 |
1998年 | 17179篇 |
1997年 | 12128篇 |
1996年 | 9410篇 |
1995年 | 7108篇 |
1994年 | 6222篇 |
1993年 | 5964篇 |
1992年 | 4274篇 |
1991年 | 4136篇 |
1990年 | 3705篇 |
1989年 | 3616篇 |
1988年 | 3518篇 |
1987年 | 2958篇 |
1986年 | 2872篇 |
1985年 | 3445篇 |
1984年 | 3067篇 |
1983年 | 2764篇 |
1982年 | 2570篇 |
1981年 | 2573篇 |
1980年 | 2441篇 |
1979年 | 2277篇 |
1978年 | 2241篇 |
1977年 | 2813篇 |
1976年 | 4173篇 |
1975年 | 1902篇 |
1974年 | 1796篇 |
1973年 | 1784篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
This paper proposes an original method for obtaining analytical approximations of the invariant probability density function of multi-dimensional Hamiltonian dissipative dynamic systems under Gaussian white noise excitations, with linear non-conservative parts and nonlinear conservative parts. The method is based on an exact result and a heuristic argument. Its pertinence is attested by numerical tests. 相似文献
192.
Derivation of a second-order switching surface in the boundary control of buck converters 总被引:1,自引:0,他引:1
A second-order switching surface in the boundary control of buck converters is derived in this letter. The formulated switching surface can make the overall converter exhibit better steady-state and transient behaviors than the one with a first-order switching surface. The switching surface is derived by estimating the state trajectory movement after a switching action, resulting in a high state trajectory velocity along the switching surface. This phenomenon accelerates the trajectory moving toward the target operating point. The proposed control scheme has been successfully applied to a 120-W buck converter. The large-signal performance and a comparison with the first-order switching surface have been studied. 相似文献
193.
Kilchytska V. Neve A. Vancaillie L. Levacq D. Adriaensen S. van Meer H. De Meyer K. Raynaud C. Dehan M. Raskin J.-P. Flandre D. 《Electron Devices, IEEE Transactions on》2003,50(3):577-588
This work presents a systematic comparative study of the influence of various process options on the analog and RF properties of fully depleted (FD) silicon-on-insulator (SOI), partially depleted (PD) SOI, and bulk MOSFET's with gate lengths down to 0.08 /spl mu/m. We introduce the transconductance-over-drain current ratio and Early voltage as key figures of merits for the analog MOS performance and the gain and the transition and maximum frequencies for RF performances and link them to device engineering. Specifically, we investigate the effects of HALO implantation in FD, PD, and bulk devices, of film thickness in FD, of substrate doping in SOI, and of nonstandard channel engineering (i.e., asymmetric Graded-channel MOSFETs and gate-body contacted DTMOS). 相似文献
194.
We consider the problem of designing a network of optical cross-connects (OXCs) to provide end-to-end lightpath services to large numbers of label switched routers (LSRs). We present a set of heuristic algorithms to address the combined problem of physical topology design (i.e., determine the number of OXCs required and the fiber links among them) and logical topology design (i.e., determine the routing and wavelength assignment for the lightpaths among the LSRs). Unlike previous studies which were limited to small topologies with a handful of nodes and a few tens of lightpaths, we have applied our algorithms to networks with hundreds or thousands of LSRs and with a number of lightpaths that is an order of magnitude larger than the number of LSRs. In order to characterize the performance of our algorithms, we have developed lower bounds which can be computed efficiently. We present numerical results for up to 1000 LSRs and for a wide range of system parameters such as the number of wavelengths per fiber, the number of transceivers per LSR, and the number of ports per OXC. The results indicate that it is possible to build large-scale optical networks with rich connectivity in a cost-effective manner, using relatively few but properly dimensioned OXCs. 相似文献
195.
196.
Static energy reduction techniques for microprocessor caches 总被引:1,自引:0,他引:1
Hanson H. Hrishikesh M.S. Agarwal V. Keckler S.W. Burger D. 《Very Large Scale Integration (VLSI) Systems, IEEE Transactions on》2003,11(3):303-313
Microprocessor performance has been improved by increasing the capacity of on-chip caches. However, the performance gain comes at the price of static energy consumption due to subthreshold leakage current in cache memory arrays. This paper compares three techniques for reducing static energy consumption in on-chip level-1 and level-2 caches. One technique employs low-leakage transistors in the memory cell. Another technique, power supply switching, can be used to turn off memory cells and discard their contents. A third alternative is dynamic threshold modulation, which places memory cells in a standby state that preserves cell contents. In our experiments, we explore the energy and performance tradeoffs of these techniques. We also investigate the sensitivity of microprocessor performance and energy consumption to additional cache latency caused by leakage-reduction techniques. 相似文献
197.
2-D symmetry: theory and filter design applications 总被引:1,自引:0,他引:1
In this comprehensive review article, we present the theory of symmetry in two-dimensional (2-D) filter functions and in 2-D Fourier transforms. It is shown that when a filter frequency response possesses symmetry, the realization problem becomes relatively simple. Further, when the frequency response has no symmetry, there is a technique to decompose that frequency response into components each of which has the desired symmetry. This again reduces the complexity of two-dimensional filter design. A number of filter design examples are illustrated. 相似文献
198.
Shi-Jin Ding Hang Hu Lim H.F. Kim S.J. Yu X.F. Chunxiang Zhu Li M.F. Byung Jin Cho Chan D.S.H. Rustagi S.C. Yu M.B. Chin A. Dim-Lee Kwong 《Electron Device Letters, IEEE》2003,24(12):730-732
For the first time, we successfully fabricated and demonstrated high performance metal-insulator-metal (MIM) capacitors with HfO/sub 2/-Al/sub 2/O/sub 3/ laminate dielectric using atomic layer deposition (ALD) technique. Our data indicates that the laminate MIM capacitor can provide high capacitance density of 12.8 fF//spl mu/m/sup 2/ from 10 kHz up to 20 GHz, very low leakage current of 3.2 /spl times/ 10/sup -8/ A/cm/sup 2/ at 3.3 V, small linear voltage coefficient of capacitance of 240 ppm/V together with quadratic one of 1830 ppm/V/sup 2/, temperature coefficient of capacitance of 182 ppm//spl deg/C, and high breakdown field of /spl sim/6 MV/cm as well as promising reliability. As a result, the HfO/sub 2/-Al/sub 2/O/sub 3/ laminate is a very promising candidate for next generation MIM capacitor for radio frequency and mixed signal integrated circuit applications. 相似文献
199.
200.
The problem of operating freeze drying of pharmaceutical products in vials placed in trays of a freeze dryer to remove free water (in frozen state) at a minimum time was formulated as an optimal control problem. Two different types of freeze dryer designs were considered. In type I freeze dryer design, upper and lower plate temperatures were controlled together, while in type II freeze dryer design, upper and lower plate temperatures were controlled independently. The heat input to the material being dried and the drying chamber pressure were considered as control variables. Constraints were placed on the system state variables by the melting and scorch temperatures during primary drying stage. Necessary conditions of optimality for the primary drying stage of freeze drying process in vials are derived and presented. Furthermore, an approach for constructing the optimal control policies that would minimize the drying time for the primary drying stage was given. In order to analyze optimal control policy for the primary drying stage of the freeze-drying process in vials, a rigorous multi-dimensional unsteady state mathematical model was used. The theoretical approach presented in this work was applied in the freeze drying of skim milk. Significant reductions in the drying times of primary drying stage of freeze drying process in vials were obtained, as compared to the drying times obtained from conventional operational policies. 相似文献