全文获取类型
收费全文 | 18198篇 |
免费 | 1295篇 |
国内免费 | 52篇 |
专业分类
电工技术 | 246篇 |
综合类 | 21篇 |
化学工业 | 4150篇 |
金属工艺 | 681篇 |
机械仪表 | 1170篇 |
建筑科学 | 346篇 |
矿业工程 | 3篇 |
能源动力 | 835篇 |
轻工业 | 1424篇 |
水利工程 | 55篇 |
石油天然气 | 19篇 |
武器工业 | 1篇 |
无线电 | 3415篇 |
一般工业技术 | 3906篇 |
冶金工业 | 1169篇 |
原子能技术 | 225篇 |
自动化技术 | 1879篇 |
出版年
2024年 | 9篇 |
2023年 | 203篇 |
2022年 | 245篇 |
2021年 | 567篇 |
2020年 | 392篇 |
2019年 | 461篇 |
2018年 | 563篇 |
2017年 | 567篇 |
2016年 | 676篇 |
2015年 | 546篇 |
2014年 | 785篇 |
2013年 | 1146篇 |
2012年 | 1212篇 |
2011年 | 1444篇 |
2010年 | 1076篇 |
2009年 | 1111篇 |
2008年 | 999篇 |
2007年 | 801篇 |
2006年 | 741篇 |
2005年 | 638篇 |
2004年 | 595篇 |
2003年 | 541篇 |
2002年 | 524篇 |
2001年 | 405篇 |
2000年 | 409篇 |
1999年 | 397篇 |
1998年 | 562篇 |
1997年 | 347篇 |
1996年 | 274篇 |
1995年 | 205篇 |
1994年 | 193篇 |
1993年 | 128篇 |
1992年 | 114篇 |
1991年 | 100篇 |
1990年 | 86篇 |
1989年 | 79篇 |
1988年 | 55篇 |
1987年 | 62篇 |
1986年 | 47篇 |
1985年 | 29篇 |
1984年 | 27篇 |
1983年 | 30篇 |
1982年 | 17篇 |
1981年 | 24篇 |
1980年 | 14篇 |
1979年 | 8篇 |
1977年 | 25篇 |
1976年 | 27篇 |
1975年 | 9篇 |
1974年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
Oh Seung-Jun Yoon Jeong-Hwan Kim Si-Pom 《Journal of Mechanical Science and Technology》2021,35(3):1065-1073
Journal of Mechanical Science and Technology - In the industry, globe valves, which are commonly used to precise control the flow rate along with opening and closing flow in pipes, are technically... 相似文献
23.
Jaehoon Lee Seongha Kim Yonghoon Kim Yunje Oh Seongtaek Hwang Jichai Jeong 《Lightwave Technology, Journal of》2003,21(2):521-527
Optically preamplified receiver performance according to the vestigial sideband (VSB) filtering has been numerically investigated for 40-Gb/s optical signals modulated with nonreturn-to-zero, duobinary nonreturn-to-zero (NRZ), return-to-zero (RZ), carrier-suppressed RZ, and duobinary carrier-suppressed RZ formats. The VSB filtering enables the spectral widths of NRZ, duobinary NRZ, and RZ signals to be reduced without severe power penalties at the receiver. On the other hand, carrier-suppressed RZ and duobinary carrier-suppressed RZ signals have no large advantages over VSB filtering because of the characteristics of their signals. Our results suggest that RZ signals are the most suitable modulation format for VSB filtering, without considering the filter loss, because of the tolerance of the intersymbol interference and a large spectral width. However, duobinary NRZ signals are the most suitable modulation format for VSB filtering, considering the filter loss, because of their narrow spectral width. 相似文献
24.
Jokerst N.M. Gaylord T.K. Glytsis E. Brooke M.A. Cho S. Nonaka T. Suzuki T. Geddis D.L. Shin J. Villalaz R. Hall J. Chellapa A. Vrazel M. 《Advanced Packaging, IEEE Transactions on》2004,27(2):376-385
This paper explores design options for planar optical interconnections integrated onto boards, discusses fabrication options for both beam turning and embedded interconnections to optoelectronic devices, describes integration processes for creating embedded planar optical interconnections, and discusses measurement results for a number of integration schemes that have been demonstrated by the authors. In the area of optical interconnections with beams coupled to and from the board, the topics covered include integrated metal-coated polymer mirrors and volume holographic gratings for optical beam turning perpendicular to the board. Optical interconnections that utilize active thin film (approximately 1-5 /spl mu/m thick) optoelectronic components embedded in the board are also discussed, using both Si and high temperature FR-4 substrates. Both direct and evanescent coupling of optical signals into and out of the waveguide are discussed using embedded optical lasers and photodetectors. 相似文献
25.
A route to synthesize ZSM‐5 crystals with a bimodal micro/mesoscopic pore system has been developed in this study; the successful incorporation of the mesopores within the ZSM‐5 structure was performed using tetrapropylammonium hydroxide (TPAOH)‐impregnated mesoporous materials containing carbon nanotubes in the pores, which were encapsulated in the ZSM‐5 crystals during a solid rearrangement process within the framework. Such mesoporous ZSM‐5 zeolites can be readily obtained as powders, thin films, or monoliths. 相似文献
26.
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
27.
Theoretical analysis of cladding-mode waveguide dispersion and its effects on the spectra of long-period fiber grating 总被引:2,自引:0,他引:2
A new method to control the free spectral range (FSR) of a long-period fiber grating (LPFG) is proposed and theoretically analyzed. As the refractive index decreases radially outward in the silica cladding by graded doping of fluorine, waveguide dispersion in the cladding modes was modified to result in the effective indexes change and subsequently the phase-matching conditions for coupling with the core mode in a LPFG. Enlargement of the FSR in a LPFG was theoretically confirmed. 相似文献
28.
H.S. Seo Y.G. Choi B.J. Park D.H. Cho K.H. Kim 《Photonics Technology Letters, IEEE》2003,15(9):1198-1200
A flat signal gain over in the entire C- and L-bands by erbium (Er) ions' radiative transition and stimulated Raman scattering in an Er-doped germano-silica fiber can be obtained if proper values of the concentration of Er and background loss in a fiber core are obtained during the fiber fabrication process. The optimized conditions for the flat C- and L-band gain are analyzed as functions of Er concentrations. Even for a low-gain value provided by a germano-silica core fiber with a low Er concentration and an optimum fiber length, a relatively low pump is required to obtain the flat gain band. 相似文献
29.
Estimation of the Longitudinal Dispersion Coefficient Using the Velocity Profile in Natural Streams 总被引:2,自引:0,他引:2
In this study, a theoretical method for predicting the longitudinal dispersion coefficient is developed based on the transverse velocity distribution in natural streams. Equations of the transverse velocity profile for irregular cross sections of the natural streams are analyzed. Among the velocity profile equations tested in this study, the beta distribution equation, which is a probability density function, is considered to be the most appropriate model for explaining the complex behavior of the transverse velocity structure of irregular natural streams. The new equation for the longitudinal dispersion coefficient that is based on the beta function for the transverse velocity profile is developed. A comparison of the proposed equation with existing equations and the observed longitudinal dispersion coefficient reveals that the proposed equation shows better agreement with the observed data compared to other existing equations. 相似文献
30.
Wallace A.M. Sung R.C.W. Buller G.S. Harkins R.D. Warburton R.E. Lamb R.A. 《Vision, Image and Signal Processing, IEE Proceedings -》2006,153(2):160-172
A new multi-spectral laser radar (ladar) system based on the time-correlated single photon counting, time-of-flight technique has been designed to detect and characterise distributed targets at ranges of several kilometres. The system uses six separated laser channels in the visible and near infrared part of the electromagnetic spectrum. The authors present a method to detect the numbers, positions, heights and shape parameters of returns from this system, used for range profiling and target classification. The algorithm has two principal stages: non-parametric bump hunting based on an analysis of the smoothed derivatives of the photon count histogram in scale space, and maximum likelihood estimation using Poisson statistics. The approach is demonstrated on simulated and real data from a multi-spectral ladar system, showing that the return parameters can be estimated to a high degree of accuracy. 相似文献