全文获取类型
收费全文 | 690228篇 |
免费 | 7343篇 |
国内免费 | 1174篇 |
专业分类
电工技术 | 12317篇 |
综合类 | 525篇 |
化学工业 | 109525篇 |
金属工艺 | 30542篇 |
机械仪表 | 22505篇 |
建筑科学 | 15192篇 |
矿业工程 | 6005篇 |
能源动力 | 16884篇 |
轻工业 | 51731篇 |
水利工程 | 9034篇 |
石油天然气 | 20029篇 |
武器工业 | 48篇 |
无线电 | 70233篇 |
一般工业技术 | 146760篇 |
冶金工业 | 112407篇 |
原子能技术 | 18895篇 |
自动化技术 | 56113篇 |
出版年
2021年 | 6629篇 |
2019年 | 6298篇 |
2018年 | 11245篇 |
2017年 | 11416篇 |
2016年 | 11960篇 |
2015年 | 7328篇 |
2014年 | 12501篇 |
2013年 | 31252篇 |
2012年 | 19016篇 |
2011年 | 25302篇 |
2010年 | 20318篇 |
2009年 | 22712篇 |
2008年 | 23015篇 |
2007年 | 22578篇 |
2006年 | 19411篇 |
2005年 | 17505篇 |
2004年 | 16783篇 |
2003年 | 16450篇 |
2002年 | 15921篇 |
2001年 | 15381篇 |
2000年 | 14816篇 |
1999年 | 14336篇 |
1998年 | 32103篇 |
1997年 | 23526篇 |
1996年 | 18299篇 |
1995年 | 14148篇 |
1994年 | 12958篇 |
1993年 | 12687篇 |
1992年 | 9987篇 |
1991年 | 9816篇 |
1990年 | 9686篇 |
1989年 | 9380篇 |
1988年 | 9029篇 |
1987年 | 8335篇 |
1986年 | 8066篇 |
1985年 | 9024篇 |
1984年 | 8298篇 |
1983年 | 8027篇 |
1982年 | 7287篇 |
1981年 | 7440篇 |
1980年 | 7187篇 |
1979年 | 7406篇 |
1978年 | 7385篇 |
1977年 | 8043篇 |
1976年 | 9718篇 |
1975年 | 6669篇 |
1974年 | 6579篇 |
1973年 | 6646篇 |
1972年 | 5820篇 |
1971年 | 5399篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
102.
It is demonstrated that the density of binary glasses upon variation of the molar content of the modifier in their compositions obeys a parabolic dependence, whose parameters can be used to estimate the extent and type of reactions between the components. The reaction parameters in glasses that are prone to liquation are lower by an order of magnitude and have the negative sign. 相似文献
103.
In studying a series of fibre samples spun in steady-state conditions, the following was found: as a function of the conditions of processing Armos fibre, two structural modifications of the polymer can form; intensive crystallization of the modification corresponding to the 28.7° reflection begins in heat treatment above 220°C; above 320°C, intensive crystallization of the modification corresponding to the 14.25° reflection is observed; at 360°C, symbatic enhancement of the intensities of both reflections with a weak change in the other structural parameters of the fibre is observed. 相似文献
104.
N. Jongen M. Donnet P. Bowen J. Lemaître H. Hofmann R. Schenk C. Hofmann M. Aoun‐Habbache S. Guillemet‐Fritsch J. Sarrias A. Rousset M. Viviani M.T. Buscaglia V. Buscaglia P. Nanni A. Testino J.R. Herguijuela 《化学工程与技术》2003,26(3):303-305
The synthesis of powders with controlled shape and narrow particle size distributions is still a major challenge for many industries. A continuous Segmented Flow Tubular Reactor (SFTR) has been developed to overcome homogeneity and scale‐up problems encountered when using batch reactors. Supersaturation is created by mixing the co‐reactants in a micromixer inducing precipitation; the suspension is then segmented into identical micro‐volumes by a non‐miscible fluid and sent through a tube. These micro‐volumes are more homogeneous when compared to large batch reactors leading to narrower size distributions, better particle morphology, polymorph selectivity and stoichiometry. All these features have been demonstrated on single tube SFTR for different chemical systems. To increase productivity for commercial application the SFTR is being “scaled‐out” by multiplying the number of tubes running in parallel instead of scaling‐up by increasing their size. The versatility of the multi‐tube unit will allow changes in type of precipitate with a minimum of new investment as new chemistry can be researched, developed and optimised in a single tube SFTR and then transferred to the multi‐tube unit for powder production. 相似文献
105.
Chou Y.C. Leung D. Lai R. Grundbacher R. Barsky M. Kan Q. Tsai R. Wojtowicz M. Eng D. Tran L. Block T. Liu P.H. Nishimoto M. Oki A. 《Electron Device Letters, IEEE》2003,24(6):378-380
The authors have investigated the reliability performance of G-band (183 GHz) monolithic microwave integrated circuit (MMIC) amplifiers fabricated using 0.07-/spl mu/m T-gate InGaAs-InAlAs-InP HEMTs with pseudomorphic In/sub 0.75/Ga/sub 0.25/As channel on 3-in wafers. Life test was performed at two temperatures (T/sub 1/ = 200 /spl deg/C and T/sub 2/ = 215 /spl deg/C), and the amplifiers were stressed at V/sub ds/ of 1 V and I/sub ds/ of 250 mA/mm in a N/sub 2/ ambient. The activation energy is as high as 1.7 eV, achieving a projected median-time-to-failure (MTTF) /spl ap/ 2 /spl times/ 10/sup 6/ h at a junction temperature of 125 /spl deg/C. MTTF was determined by 2-temperature constant current stress using /spl Delta/G/sub mp/ = -20% as the failure criteria. The difference of reliability performance between 0.07-/spl mu/m InGaAs-InAlAs-InP HEMT MMICs with pseudomorphic In/sub 0.75/Ga/sub 0.25/As channel and 0.1-/spl mu/m InGaAs-InAlAs-InP HEMT MMICs with In/sub 0.6/Ga/sub 0.4/As channel is also discussed. The achieved high-reliability result demonstrates a robust 0.07-/spl mu/m pseudomorphic InGaAs-InAlAs-InP HEMT MMICs production technology for G-band applications. 相似文献
106.
Polycrystalline Cu(In,Ga)Se2 (CIGS) films with various ratios of Cu, In, and Ga were grown by codeposition of all elements in vacuum. The X-ray diffraction
study showed that the films are single-phase and possess a chalcopyrite structure with predominant [112] orientation. The
films exhibited a mirror smooth surface and had a close-packed structure composed of crystallites with clear faceting and
a transverse size of 0.1–0.3 μm. Related surface barrier structures of the (In,Ag)/Cu(In,Ga)Se2 type were obtained and their spectra of the quantum efficiency of photoconversion were studied. The obtained structures can
be used for optimization of the CIGS film technology. 相似文献
107.
108.
Previously unknown compounds AI
I(BUO5)2·nH2O (AI
I = Mg, Ca, Sr, Ba; n = 0-7) were synthesized. Their structure and thermal decomposition were studied by X-ray diffraction, IR spectroscopy, and thermal analysis. 相似文献
109.
V. S. Butylkin G. A. Kraftmakher 《Journal of Communications Technology and Electronics》2006,51(5):484-497
A new composite medium based on waveguiding structures loaded with bianisotropic gratings of planar double split rings (PDSRs) and planar helices is considered. The microwave transmission spectra of this medium are studied experimentally. The effective parameters of the medium are determined theoretically, and its passbands are investigated. The characteristics of the medium are compared to those of infinite homogeneous bianisotropic media. A relationship between the spectral transmission characteristics and the type of resonance excitation is established. The transparency bands and overforbidden bands of the composite medium are revealed. The combinations of the medium’s effective parameters that correspond to these bands are determined. It is shown that the transparency bands where the medium is characterized simultaneously by negative permittivity and negative permeability can be identified. 相似文献
110.
Kumar R. Kursun V. 《Circuits and Systems II: Express Briefs, IEEE Transactions on》2006,53(10):1078-1082
The supply voltage to threshold voltage ratio is reduced with each new technology generation. The gate overdrive variation with temperature plays an increasingly important role in determining the speed characteristics of CMOS integrated circuits. The temperature-dependent propagation delay characteristics, as shown in this brief, will experience a complete reversal in the near future. Contrary to the older technology generations, the speed of circuits in a 45-nm CMOS technology is enhanced when the temperature is increased at the nominal supply voltage. Operating an integrated circuit at the prescribed nominal supply voltage is not preferable for reliable operation under temperature fluctuations. A design methodology based on optimizing the supply voltage for temperature-variation-insensitive circuit performance is proposed in this brief. The optimum supply voltage is 45% to 53% lower than the nominal supply voltage in a 180-nm CMOS technology. Alternatively, the optimum supply voltage is 15% to 35% higher than the nominal supply voltage in a 45-nm CMOS technology. The speed and energy tradeoffs in the supply voltage optimization technique are also presented 相似文献