全文获取类型
收费全文 | 755192篇 |
免费 | 8711篇 |
国内免费 | 2303篇 |
专业分类
电工技术 | 13796篇 |
综合类 | 1146篇 |
化学工业 | 116983篇 |
金属工艺 | 30363篇 |
机械仪表 | 23668篇 |
建筑科学 | 17434篇 |
矿业工程 | 5187篇 |
能源动力 | 19604篇 |
轻工业 | 60895篇 |
水利工程 | 8938篇 |
石油天然气 | 18073篇 |
武器工业 | 92篇 |
无线电 | 82651篇 |
一般工业技术 | 152903篇 |
冶金工业 | 132647篇 |
原子能技术 | 18568篇 |
自动化技术 | 63258篇 |
出版年
2021年 | 6965篇 |
2020年 | 5133篇 |
2019年 | 6569篇 |
2018年 | 11337篇 |
2017年 | 11514篇 |
2016年 | 12072篇 |
2015年 | 7746篇 |
2014年 | 13005篇 |
2013年 | 34512篇 |
2012年 | 20262篇 |
2011年 | 27503篇 |
2010年 | 21974篇 |
2009年 | 24645篇 |
2008年 | 25025篇 |
2007年 | 24709篇 |
2006年 | 21414篇 |
2005年 | 19568篇 |
2004年 | 18962篇 |
2003年 | 18478篇 |
2002年 | 17855篇 |
2001年 | 17408篇 |
2000年 | 16614篇 |
1999年 | 16794篇 |
1998年 | 39373篇 |
1997年 | 28483篇 |
1996年 | 22086篇 |
1995年 | 17023篇 |
1994年 | 15237篇 |
1993年 | 15053篇 |
1992年 | 11435篇 |
1991年 | 11100篇 |
1990年 | 10801篇 |
1989年 | 10553篇 |
1988年 | 10050篇 |
1987年 | 9105篇 |
1986年 | 8920篇 |
1985年 | 10011篇 |
1984年 | 9139篇 |
1983年 | 8666篇 |
1982年 | 7857篇 |
1981年 | 7975篇 |
1980年 | 7694篇 |
1979年 | 7628篇 |
1978年 | 7571篇 |
1977年 | 8335篇 |
1976年 | 10600篇 |
1975年 | 6698篇 |
1974年 | 6436篇 |
1973年 | 6501篇 |
1972年 | 5532篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
A set of poly[N‐oligo(ethylene oxide)yl 4‐vinylpyridinium tosylate] (P4VOEOOTs) has been prepared by spontaneous polymerization of 4‐vinylpyridine. This method gives a grafted polyelectrolyte having a positive charge on every backbone pyridinic moiety. The P4VP15Ts, P4VP164Ts, P4VP350Ts and P4VP750Ts aqueous solution conductivities were determined in the concentration range from 6 × 10?4 to 10?2 M at 25 °C. The variation of the conductivity versus concentration of the investigated system exhibits typical polyelectrolyte behaviour. The polyelectrolyte mobility was found to be dependent on the oligo(ethylene oxide) (OEO) side‐chain length. Manning's rod‐like model fails to describe these results. A simple steric effect is proposed to explain the influence of the OEO length. Copyright © 2003 Society of Chemical Industry 相似文献
32.
The activation of safety valves causes the development of flow reaction forces that have to be transferred in an adequate way via the piping to the steel structure or via the connected vessel into the foundation. If the safety valve outlet piping is connected to a blowdown system or, in case of blowing off into the atmosphere, are equipped with a T‐piece at the outlet, the stationary reaction forces are compensated completely. The transient opening process, however, develops flow reaction forces which culminate in peaks of short duration. In this article, a simple method will be proposed for the estimation of the resulting reaction forces as a function of the length of the pipe at the safety valve outlet. CFD calculations and blowdown tests executed with a full‐lift safety valve have confirmed this method on principle. Special importance is attributed to the short duration of the effect of the reaction forces which seems to have only a negligible impact on the supporting steel structure. 相似文献
33.
Korolev I. A. Alekseenko N. N. Porodnov B. T. Sapunov V. A. Savel'ev D. V. 《Measurement Techniques》2003,46(9):865-871
The design of a sylphon bellows sensor and the basic circuits of an LC-generator and of a microprocessor unit are presented. An analytical pressure–frequency conversion function and a special method of adjusting the sensor ensure an error of less than 0.05%. The dynamic range is up to 105. The instruments developed cover the ranges 103, 104, and 105 Pa. 相似文献
34.
35.
Chloride doped polyaniline conducting polymer films have been prepared in a protic acid medium (HCl) by potentiodynamic method
in an electrochemical cell and studied by cyclic voltammetry and FTIR techniques. The FTIR spectra confirmed Cl- ion doping in the polymers. The polymerization rate was found to increase with increasing concentration of aniline monomer.
But the films obtained at high monomer concentration were rough having a nonuniform flaky polyaniline distribution. Results
showed that the polymerization rate did not increase beyond a critical HCl concentration. Cyclic voltammetry suggested that,
the oxidation-reduction current increased with an increase in scan rate and that the undoped polyaniline films were not hygroscopic
whereas chloride doped polyaniline films were found to be highly hygroscopic. 相似文献
36.
Tanabe A. Nakahara Y. Furukawa A. Mogami T. 《Solid-State Circuits, IEEE Journal of》2003,38(1):107-113
A redundant multivalued logic is proposed for high-speed communication ICs. In this logic, serial binary data are received and converted into parallel redundant multivalued data. Then they are restored into parallel binary data. Because of the multivalued data conversion, this logic makes it possible to achieve higher operating speeds than that of a conventional binary logic. Using this logic, a 1:4 demultiplexer (DEMUX, serial-parallel converter) IC was fabricated using a 0.18-/spl mu/m CMOS process. The IC achieved an operating speed of 10 Gb/s with a supply voltage of only 1.3 V and with power consumption of 38 mW. This logic may achieve CMOS communication ICs with an operating speed several times greater than 10 Gb/s. 相似文献
37.
B. Pantchev P. Danesh K. Antonova B. Schmidt D. Grambole J. Baran 《Journal of Materials Science: Materials in Electronics》2003,14(10-12):751-752
The hydrogen content, its depth distribution, and its bonding configuration have been studied in hydrogenated amorphous silicon prepared by plasma-enhanced chemical vapor deposition with hydrogen-diluted silane. Nuclear reaction analysis and infrared spectroscopy were used to determine the total amount of hydrogen and its bonded component, respectively. It has been established that the total concentration of hydrogen does not depend on the film thickness, and has a uniform depth profile. The concentration of bonded hydrogen changes with the film thickness within the measurement accuracy. The data obtained suggest the presence of molecular (non-bonded) hydrogen, uniformly distributed in concentration across the film thickness. 相似文献
38.
Hook T.B. Brown J. Cottrell P. Adler E. Hoyniak D. Johnson J. Mann R. 《Electron Devices, IEEE Transactions on》2003,50(9):1946-1951
Lateral scattering of retrograde well implants is shown to have an effect on the threshold voltage of nearby devices. The threshold voltage of both NMOSFETs and PMOSFETs increases in magnitude for conventional retrograde wells, but for triple-well isolated NMOSFETs the threshold voltage decreases for narrow devices near the edge of the well. Electrical data, SIMS, and SUPREM4 simulations are shown that elucidate the phenomenon. 相似文献
39.
A common computing-core representation of the discrete cosine transform and discrete sine transform is derived and a reduced-complexity algorithm is developed for computation of the proposed computing-core. A parallel architecture based on the principle of distributed arithmetic is designed further for the computation of these transforms using the common-core algorithm. The proposed scheme not only leads to a systolic-like regular and modular hardware for computing these transforms, but also offers significant improvement in area-time efficiency over the existing structures. The structure proposed here is devoid of complicated input/output mapping and does not involve any complex control. Unlike the convolution-based structures, it does not restrict the transform length to be a prime or multiple of prime and can be utilized as a reusable core for cost-effective, memory-efficient, high-throughput implementation of either of these transforms 相似文献
40.
N. P. Yeliseyeva 《Journal of Communications Technology and Electronics》2006,51(4):380-384
Rigorous analytic expressions for radiation resistance R Σ of an electric dipole are obtained for three mutually orthogonal orientations of the dipole’s axis with respect to a plane metal screen or right-angle corner of infinite dimensions. Radiation resistance R Σ of the dipole oriented arbitrarily in space is calculated and analyzed as a function of the distance from the screen. 相似文献