全文获取类型
收费全文 | 92023篇 |
免费 | 7624篇 |
国内免费 | 4089篇 |
专业分类
电工技术 | 5693篇 |
技术理论 | 2篇 |
综合类 | 5777篇 |
化学工业 | 14020篇 |
金属工艺 | 4959篇 |
机械仪表 | 5216篇 |
建筑科学 | 6721篇 |
矿业工程 | 1853篇 |
能源动力 | 2647篇 |
轻工业 | 7090篇 |
水利工程 | 1811篇 |
石油天然气 | 3878篇 |
武器工业 | 675篇 |
无线电 | 12045篇 |
一般工业技术 | 11656篇 |
冶金工业 | 5963篇 |
原子能技术 | 1029篇 |
自动化技术 | 12701篇 |
出版年
2024年 | 370篇 |
2023年 | 1371篇 |
2022年 | 2574篇 |
2021年 | 3572篇 |
2020年 | 2503篇 |
2019年 | 2107篇 |
2018年 | 2360篇 |
2017年 | 2801篇 |
2016年 | 2455篇 |
2015年 | 3397篇 |
2014年 | 4445篇 |
2013年 | 5667篇 |
2012年 | 6040篇 |
2011年 | 6752篇 |
2010年 | 5858篇 |
2009年 | 5649篇 |
2008年 | 5586篇 |
2007年 | 5347篇 |
2006年 | 5122篇 |
2005年 | 4180篇 |
2004年 | 2846篇 |
2003年 | 2352篇 |
2002年 | 2370篇 |
2001年 | 2026篇 |
2000年 | 1912篇 |
1999年 | 1976篇 |
1998年 | 2203篇 |
1997年 | 1798篇 |
1996年 | 1577篇 |
1995年 | 1261篇 |
1994年 | 998篇 |
1993年 | 824篇 |
1992年 | 625篇 |
1991年 | 486篇 |
1990年 | 406篇 |
1989年 | 306篇 |
1988年 | 266篇 |
1987年 | 205篇 |
1986年 | 166篇 |
1985年 | 152篇 |
1984年 | 100篇 |
1983年 | 79篇 |
1982年 | 80篇 |
1981年 | 70篇 |
1980年 | 64篇 |
1979年 | 36篇 |
1978年 | 35篇 |
1977年 | 82篇 |
1976年 | 159篇 |
1973年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 21 毫秒
71.
Lianshan Yan Yeh C. Yang G. Lin L. Chen Z. Shi Y.Q. Willner A.E. Yao X.S. 《Lightwave Technology, Journal of》2003,21(7):1676-1684
We demonstrate the first programmable group-delay module based on polarization switching. With a unique binary tuning mechanism, the device can generate any differential group delay value from -45 to +45 ps with a resolution of 1.40 ps, or any true-time-delay value from 0 to 45 ps with a resolution of 0.7 ps. The delay varying speeds for both applications are under 1 ms and can be as fast as 0.1 ms. We evaluate both the dynamic and static performances of the device while paying special attention to its dynamic figures of merit for polarization-mode dispersion emulation and compensation applications. Our experiment shows that the device exhibits a negligible transient-effect induced power penalty (<0.2 dB) in a 10-Gb/s nonreturn-to-zero system. 相似文献
72.
Stabilization of singularly perturbed fuzzy systems 总被引:6,自引:0,他引:6
This paper presents some novel results for stabilizing singularly perturbed (SP) nonlinear systems with guaranteed control performance. By using Takagi-Sugeno fuzzy model, we construct the SP fuzzy (SPF) systems. The corresponding fuzzy slow and fast subsystems of the original SPF system are also obtained. Two fuzzy control designs are explored. In the first design method, we propose the composite fuzzy control to stabilize the SPF subsystem with H/sup /spl infin// control performance. Based on the Lyapunov stability theorem, the stability conditions are reduced to the linear matrix inequality (LMI) problem. The composite fuzzy control will stabilize the original SP nonlinear systems for all /spl epsiv//spl isin/(0,/spl epsiv//sup */) and the upper bound /spl epsiv//sup */ can be determined. For the second design method, we present a direct fuzzy control scheme to stabilize the SP nonlinear system with H/sup /spl infin// control performance. By utilizing the Lyapunov stability theorem, the direct fuzzy control can guarantee the stability of the original SP nonlinear systems for a given interval /spl epsiv//spl isin/[/spl epsiv/_,/spl epsiv/~]. The stability conditions are also expressed in the LMIs. Two SP nonlinear systems are adopted to demonstrate the feasibility and effectiveness of the proposed control schemes. 相似文献
73.
74.
A highly linear electrooptic modulator has been designed, fabricated, and evaluated. The design of this modulator consists of only a simple modification to the directional coupler. Two-tone testing has demonstrated that, for an optical modulation depth of 30% per channel, the third-order intermodulation distortion is more than 30 dB lower than that of the conventional directional coupler or Mach-Zehnder modulators. This improvement was not observed to be accompanied by any increase in second harmonic distortion. Also included are results of two-tone computer simulations which predict the improvement in linearity of this device for a range of modulation depths.<> 相似文献
75.
From the rhizomes of Polygonatum alte-lobatum, two new homologous series of 1,4-benzoquinones, polygonaquinones A and B, a novel homoisoflavanone, a new gentrogenin glycoside and 13 known compounds were isolated and characterized. The structures of the new compounds were determined as two homologous series of three 2,5-dihydroxy-3-methyl-6-alkyl-1,4-benzoquinones and three 2-hydroxy-3-methyl-6-alkyl-1,4-benzoquinones, with chain lengths C21 to C23, and 4',5,7-trihydroxy-6,8-dimethylhomoisoflavanone and gentrogenin 3-O-beta-D-glucopyranosyl(1-->2)-[beta-D-xylopyranosyl(1-->3)] -beta-D-glucopyranosyl(1-->4)-beta-D-galactopyranoside. 相似文献
76.
In this paper we report the fabrication of ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT) thin films on Si-on-Insulator (SOI) substrates with and without an electrode by pulsed excimer laser deposition combined with rapid thermal annealing. Based on the structural and interfacial characteristics analysis by X-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS), cross-sectional transmission electron microscopy (XTEM) and automatic spreading resistance measurement (ASR), the film structure and orientation were revealed to be dependent on the annealing time and annealing temperature as well as deposition temperature. From RBS spectra and XTEM observation it is shown that the PZT thin films did not interact with the top silicon layers of SOI and that the composition of the film was similar to the target. The ASR measurements showed that the electrical properties of PZT/SOI as well as PZT/Pt/SOI were abrupt, and that the electrical properties of the SOI substrates were still good after the PZT growth. 相似文献
77.
This paper deals with the non-steady-state kinetics of direct thermal initiated polymerization. The initiation is assumed to be a bimolecular reaction of the monomer. The relationship between the radical concentration and the monomer conversion is rigorously derived. In further treatment a few very close approximations are introduced based on the fact that the number of monomer molecules reacting in the initiation step is much less than that consumed in the propagation step for a process producing high polymer, and the value of the rate constant for propagation or chain transfer is much lower than that for chain termination. Expressions for various molecular parameters, such as molecular weight distribution, number-average and weight-average degrees of polymerization, and dispersity, are given. Several numerical examples are provided. 相似文献
79.
The aim of this study was to determine the actual prevalence of diabetes mellitus and to investigate the contribution of various risk factors to the diabetes mellitus among the population in a methyl mercury polluted area. The study was a population based cross sectional mass screening survey. A case-control study was designed to estimate the role of various risk factors including methyl mercury exposure for diabetes mellitus. The study was confined to a small rural town 10 km north of Minamata City; 1,087 persons older than 40 years were examined. Measurement of glucose metabolism was made on the basis of urine and haematological examinations. Data on risk factors were collected by questionnaire, and by measurement of body height and weight (obesity). The prevalence rate of the diabetes mellitus was 8.4% in males and 5.3% in females. The odds ratio of family history was significantly higher, 4.63. The odds ratio of residential history in a methyl mercury high polluted area was 0.58. The prevalence of the diabetes mellitus in this methyl mercury polluted area was not increased, contrary to what was expected based on the pathological findings. 相似文献
80.