全文获取类型
收费全文 | 103206篇 |
免费 | 1456篇 |
国内免费 | 1229篇 |
专业分类
电工技术 | 1926篇 |
综合类 | 138篇 |
化学工业 | 10567篇 |
金属工艺 | 5456篇 |
机械仪表 | 3189篇 |
建筑科学 | 2039篇 |
矿业工程 | 160篇 |
能源动力 | 2983篇 |
轻工业 | 6158篇 |
水利工程 | 707篇 |
石油天然气 | 670篇 |
武器工业 | 15篇 |
无线电 | 15966篇 |
一般工业技术 | 21834篇 |
冶金工业 | 25322篇 |
原子能技术 | 1383篇 |
自动化技术 | 7378篇 |
出版年
2022年 | 460篇 |
2021年 | 708篇 |
2020年 | 526篇 |
2019年 | 683篇 |
2018年 | 1141篇 |
2017年 | 1099篇 |
2016年 | 1195篇 |
2015年 | 936篇 |
2014年 | 1500篇 |
2013年 | 4684篇 |
2012年 | 2595篇 |
2011年 | 3868篇 |
2010年 | 3114篇 |
2009年 | 3747篇 |
2008年 | 3915篇 |
2007年 | 4097篇 |
2006年 | 3709篇 |
2005年 | 3337篇 |
2004年 | 3188篇 |
2003年 | 3038篇 |
2002年 | 2678篇 |
2001年 | 2973篇 |
2000年 | 2727篇 |
1999年 | 3083篇 |
1998年 | 9467篇 |
1997年 | 6171篇 |
1996年 | 4771篇 |
1995年 | 3176篇 |
1994年 | 2795篇 |
1993年 | 2733篇 |
1992年 | 1629篇 |
1991年 | 1597篇 |
1990年 | 1520篇 |
1989年 | 1322篇 |
1988年 | 1171篇 |
1987年 | 862篇 |
1986年 | 888篇 |
1985年 | 916篇 |
1984年 | 803篇 |
1983年 | 699篇 |
1982年 | 699篇 |
1981年 | 681篇 |
1980年 | 567篇 |
1979年 | 476篇 |
1978年 | 414篇 |
1977年 | 535篇 |
1976年 | 958篇 |
1975年 | 299篇 |
1974年 | 277篇 |
1973年 | 256篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
881.
M.H. Song B. Park S. Nishimura T. Toyooka I.J. Chung Y. Takanishi K. Ishikawa H. Takezoe 《Advanced functional materials》2006,16(14):1793-1798
A liquid crystal (LC) photonic device with an anisotropic optical heterojunction structure has been fabricated. The device has a phase‐retarding nematic LC (NLC) layer sandwiched between two polymer cholesteric LC films with right‐handed helices of different pitches. Electrotunable non‐reciprocal light transmittance and unidirectional circularly polarized (CP) lasing emission have been successfully demonstrated for this device structure. Two left CP (LCP) lasing emission peaks are observed at the edges of the overlapping region between the two photonic bands in the structure and are shifted upon the application of a voltage. In contrast, a non‐reciprocal right CP (RCP) lasing emission peak emerges at one of the band edges and diminishes upon the application of a voltage. These phenomena are interpreted based on the selective reflection of RCP light and the reorientation of the NLC molecules by the application of a voltage. 相似文献
882.
Tsubone K. Wakana H. Tarutani Y. Adachi S. Ishimaru Y. Nakayama K. Tanabe K. 《Applied Superconductivity, IEEE Transactions on》2006,16(4):2011-2017
Toggle-flip-flop (T-FF) is one of the most important high-Tc superconducting single-flux quantum (HTS SFQ) circuit components and has been designed and fabricated by using YBa2Cu3 O7-delta ramp-edge junction technology. The circuit layout of the T-FF was improved to suppress the junction critical current (Ic) spread in the circuit. Test circuits, which include a T-FF with a single output for evaluating the logic operation and measuring the operating frequency, were fabricated and their operation characteristics were investigated. The T-FF circuit with a single output was successfully operated and finite direct current (dc) supply current margins were obtained at temperatures from 27 to 34 K. Moreover, the maximum operating frequency of the T-FF was estimated to be 360 GHz at 4.2 K and 114 GHz at 41 K. In addition, reduction of dc supply current margins due to thermal noise was also investigated. According to the numerical simulation in which parasitic inductances were taken into account, the narrowest margin in the T-FF circuit wider than plusmn10% was maintained with a bit-error rate (BER) of 10-6 up to 40 K 相似文献
883.
884.
Dolgin Y. Zeheb E. 《Circuits and Systems II: Express Briefs, IEEE Transactions on》2004,51(8):406-411
Model reduction of high-order polynomial systems is considered. The main novelty of the paper is that the polynomial coefficients are assumed to be known only within given intervals. The resulted reduced system is characterized by a fixed-coefficients polynomial. First, the meaning of such a model reduction is defined. Then, applying a novel approach, the maximal "distance" (error) between the polygon in the complex plane which represents, at each frequency, the original uncertain system and the point which represents the resulted reduced-order fixed-coefficients system, is minimized. By a smart definition of this "distance" and by a formulation of the "closest" distance to the polygon as a "maximum" in some sense, the problem is formulated as linear semi-infinite programming with linear constraints, thus reducing significantly the computational complexity. A numerical example is provided. 相似文献
885.
Y.F. Li D. Bi 《Mechatronics, IEEE/ASME Transactions on》2003,8(4):476-482
Realistic dynamics models are important for haptic display for virtual reality systems. Such dynamic models are desirably obtained via experimental identification. However, traditional dynamics identification methods normally require large sized training data sets, which maybe difficult to meet in many practical applications. To obtain the dynamics models, we present, in this paper, an identification method using support vector machines regression algorithm which is more effective than traditional methods for sparse training data. This method can be used as a generic learning machine or as a special learning technique that can make full use of the available knowledge about the dynamics structure. The experimental results show the application of our method for identifying friction models for haptic display. 相似文献
886.
An efficient electromagnetic-physics-based numerical technique for modeling and optimization of high-frequency multifinger transistors 总被引:1,自引:0,他引:1
We present a fast wavelet-based time-domain modeling technique to study the effect of electromagnetic (EM)-wave propagation on the performance of high-power and high-frequency multifinger transistors. The proposed approach solves the active device model that combines the transport physics, and Maxwell's equations on nonuniform self-adaptive grids, obtained by applying wavelet transforms followed by hard thresholding. This allows forming fine and coarse grids in the locations where variable solutions change rapidly and slowly, respectively. A CPU time reduction of 75% is achieved compared to a uniform-grid case, while maintaining the same degree of accuracy. After validation, the potential of the developed technique is demonstrated by EM-physical modeling of multifinger transistors. Different numerical examples are presented, showing that accurate modeling of high-frequency devices should incorporate the effect of EM-wave propagation and electron-wave interactions within and around the device. Moreover, high-frequency advantages of multifinger transistors over single-finger transistors are underlined through numerical examples. To our knowledge, this is the first time in the literature a fully numerical EM-physics-based simulator for accurate modeling of high-frequency multifinger transistors is introduced and implemented. 相似文献
887.
The effect of deformation speed on defect structures introduced into bulk gold specimens at 298 K has been investigated systematically over a wide range of strain rate from ′=10−2 to 106 s−1. As strain rate increased, dislocation structure changed from heterogeneous distribution, so-called cell structure, to random distribution. Also, stacking fault tetrahedra (SFTs) were produced at anomalously high density by deformation at high strain rate. The anomalous production of SFTs observed at high strain rate is consistent with the characteristic microstructure induced by dislocation-free plastic deformation, which has been recently reported in deformation of gold thin foils. Thus, the results of the present study indicate that high-speed deformation induces an abnormal mechanism of plastic deformation, which falls beyond the scope of dislocation theory. Numerical analysis of dislocation structure and SFTs revealed that the transition point of variation of deformation mode is around the strain rate of 103 s−1. 相似文献
888.
G. Kulcsar Y. Jaouen G. Canat E. Olmedo G. Debarge 《Photonics Technology Letters, IEEE》2003,15(6):801-803
Cascaded Stokes waves generation due to stimulated Brillouin scattering (SBS) of coherent optical pulses in a double-cladding Er/sup 3+/-Yb/sup 3+/ codoped fiber amplifier is reported. The highest attainable output power strongly depends on the amplifier pumping arrangement. A maximum of 40-W peak power has been obtained in counterpumping configuration. The highest energy extracted from the single-mode fiber amplifier in 1-/spl mu/s pulses is limited SBS to 15 /spl mu/J. Theses results have been theoretically confirmed using coupled-waves SBS model. 相似文献
889.
A. Kadashchuk A. Andreev H. Sitter N.S. Sariciftci Y. Skryshevski Y. Piryatinski I. Blonsky D. Meissner 《Advanced functional materials》2004,14(10):970-978
We report on photoluminescence (PL) and thermally stimulated luminescence (TSL) in highly ordered nanostructures of para‐sexiphenyl (PSP) grown by hot wall epitaxy (HWE). A low‐energy broad band is observed in the PL spectra that can be attributed to the emission from molecular aggregates. While the intrinsic exciton emission in steady‐state PL dominates at low temperatures, the emission from aggregates increases with elevating temperature and its magnitude depends sensitively on film preparation conditions. Time‐resolved PL measurements showed that the aggregate emission decays with a life‐time of ≈ 4 ns, which is approximately an order of magnitude larger than the lifetime of singlet excitons. TSL data suggests the presence of an energetically disordered distribution of localized states for charge carriers in PSP films, which results from an intrinsic disorder in this material. A low‐temperature TSL peak with the maximum at around 30 K evidences for a weak energy disorder in PSP films, and has been interpreted in terms of a hopping model of TSL in disordered organic materials. 相似文献
890.