全文获取类型
收费全文 | 26915篇 |
免费 | 1716篇 |
国内免费 | 26篇 |
专业分类
电工技术 | 167篇 |
综合类 | 10篇 |
化学工业 | 5650篇 |
金属工艺 | 420篇 |
机械仪表 | 565篇 |
建筑科学 | 823篇 |
矿业工程 | 52篇 |
能源动力 | 518篇 |
轻工业 | 5514篇 |
水利工程 | 312篇 |
石油天然气 | 121篇 |
武器工业 | 1篇 |
无线电 | 1057篇 |
一般工业技术 | 4371篇 |
冶金工业 | 5415篇 |
原子能技术 | 69篇 |
自动化技术 | 3592篇 |
出版年
2024年 | 67篇 |
2023年 | 281篇 |
2022年 | 298篇 |
2021年 | 734篇 |
2020年 | 660篇 |
2019年 | 674篇 |
2018年 | 1245篇 |
2017年 | 1213篇 |
2016年 | 1269篇 |
2015年 | 975篇 |
2014年 | 1114篇 |
2013年 | 2323篇 |
2012年 | 1776篇 |
2011年 | 1594篇 |
2010年 | 1285篇 |
2009年 | 1100篇 |
2008年 | 1158篇 |
2007年 | 1068篇 |
2006年 | 676篇 |
2005年 | 564篇 |
2004年 | 535篇 |
2003年 | 508篇 |
2002年 | 437篇 |
2001年 | 326篇 |
2000年 | 262篇 |
1999年 | 310篇 |
1998年 | 1897篇 |
1997年 | 1198篇 |
1996年 | 732篇 |
1995年 | 395篇 |
1994年 | 306篇 |
1993年 | 318篇 |
1992年 | 87篇 |
1991年 | 74篇 |
1990年 | 60篇 |
1989年 | 60篇 |
1988年 | 82篇 |
1987年 | 74篇 |
1986年 | 63篇 |
1985年 | 73篇 |
1984年 | 62篇 |
1983年 | 35篇 |
1982年 | 36篇 |
1981年 | 61篇 |
1980年 | 59篇 |
1978年 | 31篇 |
1977年 | 106篇 |
1976年 | 207篇 |
1975年 | 33篇 |
1973年 | 38篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
122.
J Pokorny J Davídek V Chocholatá J Pánek H Bulantová W Janitz H Valentová M Vierecklová 《Die Nahrung》1990,34(2):159-169
The reaction of ethyl linoleate with collagen proceeded at 60 degrees C following the first order kinetics but during the hydroperoxide decomposition the rate constant of the first order decomposition was substantially lower than that of the second order decomposition. Contrary to cellulose, collagen catalyzed the hydroperoxide decomposition. The amount of total oxidation products rose rapidly at the stage of rapid hydroperoxide formation, and slowly afterwards. The browning reaction was fasted in the stage of maximum hydroperoxide content, and both ether-insoluble and ether-soluble pigments were formed, the latter low in nitrogen. The amount of lipid oligomers increased mainly in the reaction stage following the hydroperoxide maximum. Soluble collagen was converted into insoluble forms by the reaction with oxidized lipids. Basic amino acids were blocked by reaction with oxidized lipids but the bonds formed became resistant to acid hydrolysis only in the stage following the hydroperoxide maximum. Changes of sensory profiles could be explained by reactions of flavour-active carbonylic oxidation products with protein. 相似文献
123.
Rafael López-Ahumada Rafael Rodríguez-Macías 《Analog Integrated Circuits and Signal Processing》2003,37(2):103-111
A strategy is presented to evaluate the statistical means and standard deviations of the transient characteristics of CMOS analog cells. Based upon the Monte Carlo analysis of electrical simulations, this strategy follows a circuit-theory based approach achieving an important reduction on matrix ranges and consequently on the number of operations involved in the resolution of the circuit. The CPU time-consuming reduction is achieved also by saving information corresponding to the nominal transient analysis. We include comparative results for several CMOS cells showing the advantages of the proposed strategy. 相似文献
124.
R.G. Carvajal A. Torralba J. Tombs F. Muñoz J. Ramírez-Angulo 《Analog Integrated Circuits and Signal Processing》2003,36(3):245-249
A new class AB output stage for CMOS op-amps is proposed with simple and accurate quiescent current control using floating gate transistors. The proposed stage can be operated with a supply voltage close to a transistor's threshold voltage. Experimental results are provided showing a 15 MHz gain-bandwidth product when it is used as the second stage of an op-amp with 1.5 V supply voltage in a standard 0.8 m CMOS technology. 相似文献
125.
José R. Sendra Javier del Pino Antonio Hernández Benito González Javier García Andrés García-Alonso Antonio Nunez 《Analog Integrated Circuits and Signal Processing》2003,35(2-3):121-132
In this work we propose a modification to the conventional lumped equivalent circuit model for integrated inductors. Also the widely used parametric model is modified. The proposed models expand the frequency range where the integrated inductor behavior is accurately predicted. They are useful in developing automatic tools to assist the designers in selecting and automatically laying-out integrated inductors [1]. This work is based on measurements from integrated inductors fabricated in a standard silicon process. 相似文献
126.
Martín-Guerrero JD Camps-Valls G Soria-Olivas E Serrano-López AJ Pérez-Ruixo JJ Jiménez-Torres NV 《IEEE transactions on bio-medical engineering》2003,50(10):1136-1142
The external administration of recombinant human erythropoietin is the chosen treatment for those patients with secondary anemia due to chronic renal failure in periodic hemodialysis. The objective of this paper is to carry out an individualized prediction of the EPO dosage to be administered to those patients. The high cost of this medication, its side-effects and the phenomenon of potential resistance which some individuals suffer all justify the need for a model which is capable of optimizing dosage individualization. A group of 110 patients and several patient factors were used to develop the models. The support vector regressor (SVR) is benchmarked with the classical multilayer perceptron (MLP) and the Autoregressive Conditional Heteroskedasticity (ARCH) model. We introduce a priori knowledge by relaxing or tightening the epsilon-insensitive region and the penalization parameter depending on the time period of the patients' follow-up. The so-called profile-dependent SVR (PD-SVR) improves results of the standard SVR method and the MLP. We perform sensitivity analysis on the MLP and inspect the distribution of the support vectors in the input and feature spaces in order to gain knowledge about the problem. 相似文献
127.
E. Fernández A. Beriain H. Solar I. Rebollo A. García-Alonso J. Sosa J.M Monzón S. García-Alonso J.A. Montiel-Nelson R. Berenguer 《Microelectronics Journal》2012,43(10):708-713
This paper presents a low power voltage limiter design for avoiding possible damages in the analog front-end of a RFID sensor due to voltage surges whenever readers and tags are close. The proposed voltage limiter design takes advantage of the implemented bandgap reference and voltage regulator blocks in order to provide low deviation of the limiting voltage due to temperature variation and process dispersion. The measured limiting voltage is 2.9 V with a voltage deviation of only ±0.065 V for the 12 measured dies. The measured current consumption is only 150 nA when the reader and the tag are far away, not limiting the sensitivity of the tag due to an undesired consumption in the voltage limiter. The circuit is implemented on a low cost 2P4M 0.35 μm CMOS technology. 相似文献
128.
G. García Salgado R. Hernández J. Martínez T. Díaz H. Juárez E. Rosendo R. Galeazzi A. García G. Juárez 《Microelectronics Journal》2008,39(3-4):489-493
Porous silicon photodetectors obtained by electrochemical etching of p-type non-polished crystalline silicon were studied. A metal-porous silicon structure was used to obtain the rectifying behavior. The geometry of the metal layer deposited by thermal evaporation on the porous zone was modified with different masks fabricated using a photolithographic method. The samples obtained under different anodization conditions were characterized by PL. The sample that showed the best intensity in photoluminescence, centered on 675 nm, was selected and five samples obtained under these conditions were prepared to compare the difference in the photoresponse because of the geometry of the evaporated metal layer. The responsivities obtained show us an important difference between the devices and allow us to propose a specific geometrical pattern to obtain a better response in this kind of devices. 相似文献
129.
Faouzi Bouali Oriol Sallent Jordi Pérez-Romero Ramon Agustí 《Wireless Personal Communications》2013,72(3):1675-1689
In order to increase cognitive radios (CRs) operation efficiency, there has been an increasing interest in strengthening awareness level about spectrum utilisation. In this respect, this paper proposes to exploit the fittingness factor concept to capture the suitability of spectral resources exhibiting time-varying characteristics to support a set of heterogeneous CR applications. First, a new knowledge management functional architecture for optimizing spectrum management has been constructed. It integrates a set of advanced statistics capturing the influence of the dynamic radio environment on the fittingness factor. Then, a knowledge manager (KM) exploiting these statistics to monitor time-varying suitability of spectrum resources has been proposed to support the spectrum selection (SS) decision-making process. In particular, a new Fittingness Factor-based strategy combining two SS and spectrum mobility (SM) functionalities has been proposed, following either a greedy or a proactive approach. Results have shown that, with a proper fittingness factor function, the greedy approach efficiently exploits the KM support at low loads and the SM functionality at high loads to introduce significant gains in terms of the user dissatisfaction probability. The proactive approach has been shown to maintain the introduced performance gain while minimizing the signalling requirements in terms of spectrum handover rate. 相似文献
130.
E.J. Suárez-Domínguez J.F. Pérez-Sánchez A. Palacio-Pérez A. Rodríguez-Valdes E. Izquierdo-Kulich S. González-Santana 《Petroleum Science and Technology》2018,36(2):166-172
Considering that high viscosity of extra-heavy crudes is related to the formation of a dispersed phase of asphaltenes, a dynamic interaction model is proposed which explains the mechanism to achieve viscosity reduction based on the molecular interacting energies between the ester active principle of a viscosity bio-reducer and the asphaltene fraction of crude oil. A qualitative comparison is made between the theoretical and experimental results observed in relation to the rheological behavior of Mexican extra-heavy crudes in the presence of the enhancer. Both, theoretical and experimental data, described a decrease in the asphaltenes dispersed fraction in relation to the ester concentration mainly because of polarity in asphaltenic crudes. 相似文献