全文获取类型
收费全文 | 909370篇 |
免费 | 11158篇 |
国内免费 | 2108篇 |
专业分类
电工技术 | 16553篇 |
综合类 | 807篇 |
化学工业 | 139178篇 |
金属工艺 | 35299篇 |
机械仪表 | 27534篇 |
建筑科学 | 21573篇 |
矿业工程 | 5561篇 |
能源动力 | 23702篇 |
轻工业 | 75981篇 |
水利工程 | 10117篇 |
石油天然气 | 19120篇 |
武器工业 | 64篇 |
无线电 | 99570篇 |
一般工业技术 | 178906篇 |
冶金工业 | 171372篇 |
原子能技术 | 20018篇 |
自动化技术 | 77281篇 |
出版年
2021年 | 8346篇 |
2020年 | 6145篇 |
2019年 | 7873篇 |
2018年 | 13443篇 |
2017年 | 13479篇 |
2016年 | 14191篇 |
2015年 | 9375篇 |
2014年 | 15603篇 |
2013年 | 41503篇 |
2012年 | 24389篇 |
2011年 | 33426篇 |
2010年 | 26654篇 |
2009年 | 29750篇 |
2008年 | 30384篇 |
2007年 | 29989篇 |
2006年 | 26051篇 |
2005年 | 23765篇 |
2004年 | 22734篇 |
2003年 | 22393篇 |
2002年 | 21456篇 |
2001年 | 21139篇 |
2000年 | 19971篇 |
1999年 | 20562篇 |
1998年 | 51141篇 |
1997年 | 36435篇 |
1996年 | 28146篇 |
1995年 | 21285篇 |
1994年 | 18854篇 |
1993年 | 18479篇 |
1992年 | 13706篇 |
1991年 | 12985篇 |
1990年 | 12867篇 |
1989年 | 12455篇 |
1988年 | 11824篇 |
1987年 | 10629篇 |
1986年 | 10380篇 |
1985年 | 11683篇 |
1984年 | 10679篇 |
1983年 | 9910篇 |
1982年 | 9138篇 |
1981年 | 9276篇 |
1980年 | 8842篇 |
1979年 | 8783篇 |
1978年 | 8590篇 |
1977年 | 9913篇 |
1976年 | 12843篇 |
1975年 | 7584篇 |
1974年 | 7215篇 |
1973年 | 7371篇 |
1972年 | 6175篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
941.
M. I. Mazurkov V. S. Dmitrenko S. N. Kropachev 《Radioelectronics and Communications Systems》2008,51(2):106-111
It is proposed a rule of total classes of composition systems of discrete frequency signals (CDF-signals) construction in extended Galois fields. It is carried out modeling and research a correlation properties of CDF-signals, and determined their practical attraction. 相似文献
942.
Ricardo Beristain‐Cardoso Anne‐Claire Texier Reyes Sierra‐Álvarez Jim A Field Elías Razo‐Flores Jorge Gómez 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(9):1197-1203
BACKGROUND: Simultaneous removal of sulfur, nitrogen and carbon compounds from wastewaters is a commercially important biological process. The objective was to evaluate the influence of the CH3COO?/NO3? molar ratio on the sulfide oxidation process using an inverse fluidized bed reactor (IFBR). RESULTS: Three molar ratios of CH3COO?/NO3? (0.85, 0.72 and 0.62) with a constant S2?/NO3? molar ratio of 0.13 were evaluated. At a CH3COO?/NO3? molar ratio of 0.85, the nitrate, acetate and sulfide removal efficiencies were approximately 100%. The N2 yield (g N2 g?1 NO3?‐N consumed) was 0.81. Acetate was mineralized, resulting in a yield of 0.65 g inorganic‐C g?1 CH3COO?‐C consumed. Sulfide was partially oxidized to S0, and 71% of the S2? consumed was recovered as elemental sulfur by a settler installed in the IFBR. At a CH3COO?/NO3? molar ratio of 0.72, the efficiencies of nitrate, acetate and sulfide consumption were of 100%, with N2 and inorganic‐C yields of 0.84 and 0.69, respectively. The sulfide was recovered as sulfate instead of S0, with a yield of 0.92 g SO42?‐S g?1 S2? consumed. CONCLUSIONS: The CH3COO?/NO3? molar ratio was shown to be an important parameter that can be used to control the fate of sulfide oxidation to either S0 or sulfate. In this study, the potential of denitrification for the simultaneous removal of organic matter, sulfide and nitrate from wastewaters was demonstrated, obtaining CO2, S0 and N2 as the major end products. Copyright © 2008 Society of Chemical Industry 相似文献
943.
Different and alternative methods for the preparation of Ni/pillared clays based on impregnation and encapsulation procedures are reported. Several nickel precursors and metal loadings are considered in order to evaluate their influence on the structural, textural and catalytic properties of the resulting solids. The behaviour of the optimum solids as catalysts has been proved in the selective catalytic reduction of nitrogen oxides with propene, and the relevance of the oxidant nature was checked by changing the composition of the oxidant mixture. Of all the factors studied, the nature of the nickel precursors appears as the most important one, owing to the formation of different active nickel species during the synthesis procedure. 相似文献
944.
In this work, the kinetics and mechanism of free-radical polymerisation of glycidyl methacrylate (GMA) using potassium peroxydisulphate
(PDS) as water soluble initiator in the presence of synthesized 1, 4-Bis (tributyl methyl ammonium) benzene dichloride (TBMABDC)
as multi-site phase transfer catalyst (MPTC) was studied. The polymerisation reactions were carried out under inert and unstirred
conditions at constant temperature of 60 ± 1°C in cyclohexane/water biphase media. The role of concentrations of monomer,
initiator, catalyst and volume fraction of aqueous phase, solvent polarity and temperature on the rate of polymerisation (Rp)
was ascertained. The order with respect to monomer and initiator was found to be unity. The order with respect to catalyst
was found to be 0.51. The rate of polymerisation is independent of ionic strength and pH of the medium. However, an increase
in the polarity of solvent has slightly increased the Rp value. Based on the results obtained, a suitable kinetic scheme has
been proposed to account for the experimental observations and its significance discussed. 相似文献
945.
The specific features of SPPA-T3000, a new instrumentation and control system intended for automation of processes in power engineering, are briefly described. Distinctive features of the system architecture, central to which is using the model of web systems, are singled out. 相似文献
946.
An analogy is established between the solutions of the problems of singularities of stresses in linear and bilinear elastic isotropic media. It is shown that the distributions of stresses and displacements in the vicinity of singular points on the boundary of the body (characterized by the singularities of stresses) are described, in both cases, by the same functional dependences on the space coordinates but with different characteristics of the material. We deduce expressions for the effective moduli of elasticity and Poisson's ratio of the bielastic medium including the parameter of hardening of the material. The solution of the problem of singularities of stresses in bilinear materials is obtained from the solution of the corresponding problem for the linear elastic medium by replacing the elastic constants with the corresponding effective values depending on the parameter of hardening of the material. The cases of wedge-shaped notches (for various boundary conditions imposed on their edges), two-component wedges, plane wedge-shaped cracks, and circular conic notches or rigid inclusions in the bielastic space are studied in detail. 相似文献
947.
Hiding biometric data 总被引:5,自引:0,他引:5
Jain A.K. Uludag U. 《IEEE transactions on pattern analysis and machine intelligence》2003,25(11):1494-1498
With the wide spread utilization of biometric identification systems, establishing the authenticity of biometric data itself has emerged as an important research issue. The fact that biometric data is not replaceable and is not secret, combined with the existence of several types of attacks that are possible in a biometric system, make the issue of security/integrity of biometric data extremely critical. We introduce two applications of an amplitude modulation-based watermarking method, in which we hide a user's biometric data in a variety of images. This method has the ability to increase the security of both the hidden biometric data (e.g., eigen-face coefficients) and host images (e.g., fingerprints). Image adaptive data embedding methods used in our scheme lead to low visibility of the embedded signal. Feature analysis of host images guarantees high verification accuracy on watermarked (e.g., fingerprint) images. 相似文献
948.
Production pipelines of manufactory industries present several machines and robots in which the movements of interpolated axes are managed by computerized numerical controls (CNCs). These are typically synchronized with several other simpler actuators along the pipeline of production. CNCs have to be flexible, easily expandable, and reusable, when pipelines of production are frequently reconfigured to realize different arranged pipelines with different technical requirements. In this paper, the assessment of a flexible CNC for such reconfigurable pipelines is presented. The analysis has been focused on defining objective metrics that can be applied for assessing performance and feasibility of distributed controls for pipelines. The method proposed has been applied on the distributed control architecture defined in the MUPAAC ESPRIT HPCN (Multi Processor Architecture for Automatic Control, High Performance Computer Networking of the European Commission). MUPAAC architecture and prototype has been assessed in order to identify the critical configurations and the limits of the architecture. 相似文献
949.
950.