全文获取类型
收费全文 | 433695篇 |
免费 | 5103篇 |
国内免费 | 1330篇 |
专业分类
电工技术 | 8042篇 |
综合类 | 467篇 |
化学工业 | 64161篇 |
金属工艺 | 19001篇 |
机械仪表 | 14153篇 |
建筑科学 | 9555篇 |
矿业工程 | 2988篇 |
能源动力 | 10378篇 |
轻工业 | 33479篇 |
水利工程 | 5104篇 |
石油天然气 | 10510篇 |
武器工业 | 87篇 |
无线电 | 51693篇 |
一般工业技术 | 88009篇 |
冶金工业 | 76386篇 |
原子能技术 | 10867篇 |
自动化技术 | 35248篇 |
出版年
2021年 | 3732篇 |
2019年 | 3634篇 |
2018年 | 6435篇 |
2017年 | 6548篇 |
2016年 | 6948篇 |
2015年 | 4179篇 |
2014年 | 7103篇 |
2013年 | 18615篇 |
2012年 | 11239篇 |
2011年 | 14863篇 |
2010年 | 11818篇 |
2009年 | 13257篇 |
2008年 | 14060篇 |
2007年 | 13922篇 |
2006年 | 12358篇 |
2005年 | 11296篇 |
2004年 | 10697篇 |
2003年 | 10498篇 |
2002年 | 10022篇 |
2001年 | 10152篇 |
2000年 | 9585篇 |
1999年 | 9780篇 |
1998年 | 23123篇 |
1997年 | 16483篇 |
1996年 | 12874篇 |
1995年 | 9981篇 |
1994年 | 8801篇 |
1993年 | 8930篇 |
1992年 | 7091篇 |
1991年 | 6749篇 |
1990年 | 6509篇 |
1989年 | 6228篇 |
1988年 | 6081篇 |
1987年 | 5319篇 |
1986年 | 5313篇 |
1985年 | 6068篇 |
1984年 | 5684篇 |
1983年 | 5241篇 |
1982年 | 4844篇 |
1981年 | 4901篇 |
1980年 | 4783篇 |
1979年 | 4692篇 |
1978年 | 4558篇 |
1977年 | 5058篇 |
1976年 | 6059篇 |
1975年 | 4186篇 |
1974年 | 4086篇 |
1973年 | 4188篇 |
1972年 | 3482篇 |
1971年 | 3218篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
We have analyzed degradation of N-channel thin-film-transistor (TFT) under dynamic stress using a pico-second time-resolved emission microscope. We have successfully detected emission at pulse fall edge for the first time. Emission intensity increased with the decrease of pulse fall time. As the degradation depended on the pulse fall time, this dependence clearly illustrates that hot electrons are the dominant cause of the degradation under dynamic stress. Based on these dependences, we proposed a model considering electron traps in the poly-Si. 相似文献
102.
M. Ganschow C. Hellriegel E. Kneuper M. Wark C. Thiel G. Schulz‐Ekloff C. Bruchle D. Whrle 《Advanced functional materials》2004,14(3):269-276
Dye‐loaded AlPO4‐5 single crystals were prepared by microwave‐assisted hydrothermal synthesis from a batch, containing a mixture of three chromophores (Coumarin 40, Rhodamine BE50, and Oxazine 1) differing in their absorption range, molecular dimensions, and solubilities. Confocal fluorescence images reveal a spatial separation effect of the dye molecules, where the slimmer, more‐soluble dye molecule (Coumarin 40) is uniformly distributed in the body of the single crystal, and the bulky and/or less‐soluble ones (Rhodamine BE50, Oxazine 1) are situated in distinct domains. Visible spectra show good panchromatic absorption of visible light. Fluorescence lifetime measurements indicate the presence of an energy transfer cascade of the entirely fixed dye molecules from Coumarin 40 to Oxazine 1. The transfer mechanism is predominantly radiative. 相似文献
103.
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
104.
Barch Deanna M.; Mitropoulou Vivian; Harvey Philip D.; New Antonia S.; Silverman Jeremy M.; Siever Larry J. 《Canadian Metallurgical Quarterly》2004,113(4):556
Research suggests that schizotypal personality disorder (SPD) is a part of the spectrum of schizophrenia-related illnesses. This article hypothesizes that a deficit in the representation and maintenance of context is a core cognitive disturbance in schizophrenia and that SPD individuals should demonstrate context-processing deficits. To test this hypothesis, the authors administered 3 versions of their AX-CPT task, designed to assess context processing, to 35 healthy controls and 26 individuals with DSM-IV SPD. They also administered working memory and selective attention tasks. SPD individuals displayed context representation deficits similar to those found in schizophrenia but did not show the same additional deficits in context maintenance. Context processing was strongly associated with working memory and selective attention performance in the SPD individuals. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
105.
E. A. Gurieva P. P. Konstantinov L. V. Prokof D. A. Pshenaĭ-Severin M. I. Fedorov Yu. I. Ravich 《Semiconductors》2006,40(7):763-767
The coefficients of thermopower and electrical and thermal conductivity in the PbTe0.8Se0.1 S 0.1 solid solution with electron concentration (4.6–54) × 1018 cm?3 are studied in the range of 85–300 K (and in some cases up to 700 K). The temperature dependences of electrical and thermal conductivity indicate that the low-temperature electron and phonon scattering initiated by the off-center impurity of sulfur exists. The temperature dependences of the electronic and lattice components of thermal conductivity are calculated in the approximation of a parabolic spectrum and electron scattering by acoustic phonons and neutral substitutional impurities. The lattice thermal conductivity is found to have a feature in the form of a shallow minimum in the range of 85–250 K. A similar feature, while not so clearly pronounced, is found to exist also in Pb1?x SnxTe1?x Sex alloys (x≥0.15) with an off-center tin impurity. An analysis of the possible origins of this effect suggests that, at low temperatures, the Lorentz numbers L of the materials under study are smaller than the L0 numbers employed which correspond to the above scattering mechanisms. The cause of the decrease in L is related to electron scattering at two-level systems, a mechanism whose effect grows with increasing electron energy. An analysis of experimental data obtained at high temperatures, as well as on undoped samples with the lowest possible carrier concentrations, yields the values of L for samples with different electron densities. The minimum value L/L0 = 0.75 is obtained for a lightly doped sample at ~130 K. 相似文献
106.
Solar cells based on SnO2/Cd0.4Zn0.6S/CdTe heterostructures are fabricated by electrochemical deposition, and the dependences of their electrical and photoelectric properties on the thermal annealing conditions are studied. It is shown that thermal annealing reduces the tunnel currents by almost two orders of magnitude. The best conditions of thermal annealing are determined (t = 300°C and τ = 9 min). These conditions provide the highest photosensitivity of the heterostructures under study (I sc ≈ 21.2 mA/cm2, U oc ≈ 813 mV, and η = 14.7%). 相似文献
107.
The variation of current density with bias or temperature is examined for DNA molecules of different configuration. To this end, the DNA molecule is represented as an equivalent electrical network whose behavior is then simulated with PSPICE. The results are found to be in close agreement with ones obtained within a physical model. It is established that the electrical response of a DNA molecule to an applied electric field depends on the boundary conditions and the potential profile along the molecule. This finding should contribute to the creation of a complete library of DNA-molecule configurations with prescribed electrical properties. 相似文献
108.
Self-induced effects in a passive polarization-independent vertical-cavity semiconductor gate are investigated numerically and experimentally. We demonstrate all-optical seed-pulse extraction for synchronization of differential phase-shift keying and ON-OFF keying packets at 10 Gb/s. Our results provide evidence that vertical-cavity gates, exploiting saturable absorption in semiconductor quantum-wells, exhibit attractive performances in terms of efficiency, power consumption, and polarization independency. 相似文献
109.
Seidel A.R. Bisogno F.E. Pinheiro H. do Prado R.N. 《Industrial Electronics, IEEE Transactions on》2003,50(6):1267-1274
This paper presents a simple alternative for an electronic ballast operating in self-sustained oscillating mode with dimming capability for fluorescent lamps. A simple modification in one of the gate drivers side circuit allows the lamp to dim without compromising the simplicity, reliability, and low cost which characterize the self-oscillating electronic ballast (SOEB). A qualitative analysis is presented to explain the behavior of the proposed self-oscillating electronic ballast with dimming feature. In addition, the stability and the key equations for the design are derived using the extended Nyquist criterion and describing function method. Experimental results from two 40-W electronic ballasts are presented to demonstrate the performance and to validate the analysis carried out. 相似文献
110.
A series of novel thermoplastic elastomers, based on poly(dimethylsiloxane) (PDMS) as the soft segment and poly(butylene terephthalate) (PBT) as the hard segment, were synthesized by catalyzed two‐step, melt transesterification reactions of dimethyl terephthalate and methyl esters of carboxypropyl‐terminated poly(dimethylsiloxane)s (M?n = 550–2170 g mol?1) with 1,4‐butanediol. The lengths of both the hard and soft segments were varied while the weight ratio of the hard to soft segments in the reaction mixture was maintained constant (57/43). The molecular structure, composition and molecular weights of the poly(ester–siloxane)s were examined by 1H NMR spectroscopy. The effectiveness of the incorporation of the methyl‐ester‐terminated poly(dimethylsiloxane)s into the copolymer chains was verified by chloroform extraction. The effect of the segment length on the transition temperatures (Tm and Tg) and the thermal and thermo‐oxidative degradation stability, as well as the degree of crystallinity and hardness properties of the synthesized TPESs, were studied. Copyright © 2003 Society of Chemical Industry 相似文献