全文获取类型
收费全文 | 525237篇 |
免费 | 7666篇 |
国内免费 | 1468篇 |
专业分类
电工技术 | 9563篇 |
综合类 | 526篇 |
化学工业 | 78759篇 |
金属工艺 | 19961篇 |
机械仪表 | 15196篇 |
建筑科学 | 12676篇 |
矿业工程 | 2269篇 |
能源动力 | 14519篇 |
轻工业 | 47156篇 |
水利工程 | 5221篇 |
石油天然气 | 9334篇 |
武器工业 | 37篇 |
无线电 | 59925篇 |
一般工业技术 | 101813篇 |
冶金工业 | 103604篇 |
原子能技术 | 10559篇 |
自动化技术 | 43253篇 |
出版年
2022年 | 3162篇 |
2021年 | 4901篇 |
2020年 | 3481篇 |
2019年 | 4564篇 |
2018年 | 7819篇 |
2017年 | 7623篇 |
2016年 | 7942篇 |
2015年 | 5563篇 |
2014年 | 9250篇 |
2013年 | 24079篇 |
2012年 | 14642篇 |
2011年 | 20156篇 |
2010年 | 15810篇 |
2009年 | 17709篇 |
2008年 | 18108篇 |
2007年 | 17791篇 |
2006年 | 15508篇 |
2005年 | 14216篇 |
2004年 | 13609篇 |
2003年 | 13403篇 |
2002年 | 12643篇 |
2001年 | 12845篇 |
2000年 | 11875篇 |
1999年 | 12601篇 |
1998年 | 32847篇 |
1997年 | 22920篇 |
1996年 | 17459篇 |
1995年 | 13047篇 |
1994年 | 11294篇 |
1993年 | 10986篇 |
1992年 | 7923篇 |
1991年 | 7419篇 |
1990年 | 7263篇 |
1989年 | 7017篇 |
1988年 | 6474篇 |
1987年 | 5768篇 |
1986年 | 5663篇 |
1985年 | 6268篇 |
1984年 | 5904篇 |
1983年 | 5179篇 |
1982年 | 4905篇 |
1981年 | 4970篇 |
1980年 | 4708篇 |
1979年 | 4613篇 |
1978年 | 4411篇 |
1977年 | 5338篇 |
1976年 | 6977篇 |
1975年 | 3803篇 |
1974年 | 3552篇 |
1973年 | 3672篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
E. E. Mukhin G. T. Razdobarin M. M. Kochergin S. Yu. Tolstyakov V. V. Semenov G. S. Kurskiev K. A. Podushnikova 《Instruments and Experimental Techniques》2008,51(2):220-225
A diagnostic array has been developed for studying the operating modes of the divertor in the ITER tokamak-reactor using the Thomson scattering technique. The aim of this study is to measure the spatial profiles of the electron temperature and density. The structure of the diagnostic setup was selected on the basis of a classical diagnostic geometry and the high-resolution LIDAR system, which provide access to different regions of the divertor plasma. A severe radiation environment, limited access to the plasma in the ITER divertor, and a high-dust environment (the divertor plate erosion material) in the divertor volume pose many problems for performing diagnostics under unique conditions having no analogs in the tokamaks that are now in operation. Different methods for protecting optical surfaces from plasma-enriched deposition are proposed and analyzed. The efficiency of these methods has been demonstrated in bench tests. The concept of laser and detector systems and diffraction polychromators capable of operating at different electron temperatures with a lower limit of 1 eV, has been justified and approved. 相似文献
992.
Lean philosophy: implementation in a forging company 总被引:2,自引:2,他引:0
Ajit Kumar Sahoo N. K. Singh Ravi Shankar M. K. Tiwari 《The International Journal of Advanced Manufacturing Technology》2008,36(5-6):451-462
This research addresses the implementation of lean philosophy in a forging company with a focus on radial forging production
flow lines. Here, the prime motive is to evolve and test several strategies to eliminate waste on the shop floor. In this
research, a systematic approach is suggested for the implementation of lean principles. This paper describes an application
of value stream mapping (VSM). Consequently, the present and future states of value stream maps are constructed to improve
the production process by identifying waste and its sources. Furthermore, Taguchi’s method of design of experiments is pursued
here to minimize the forging defects produced due to imperfect operating conditions. A noticeable reduction in set-up time
and work-in-process (WIP) inventory level is substantiated. Finally, we conclude with a discussion of managerial implications
and the future scope of research. 相似文献
993.
M. M. Zverev N. A. Gamov D. V. Peregoudov V. B. Studionov E. V. Zdanova I. V. Sedova S. V. Gronin S. V. Sorokin S. V. Ivanov P. S. Kop’ev 《Semiconductors》2008,42(12):1440-1444
Emission characteristics of an electron-beam-pumped Cd(Zn)Se/ZnMgSSe semiconductor laser are studied. The laser’s active region consists of a set of ten equidistant ZnSe quantum wells containing fractional-monolayer CdSe quantum-dot inserts and a waveguide formed by a short-period superlattice with the net thickness of ~0.65 μm. Lasing occurs at room temperature at a wavelength of 542 nm. Pulsed power as high as 12 W per cavity face and an unprecedentedly high efficiency of ~8.5% are attained for the electron-beam energy of 23 keV. 相似文献
994.
Seyeong Choi Alouini M.-S. Qaraqe K.A. Hong-Chuan Yang 《Wireless Communications, IEEE Transactions on》2008,7(2):495-499
We propose and analyze new finger assignment techniques that are applicable for RAKE receivers in the soft handover (SHO) region. Specifically, extending the results for the case of two-base station (BS), we consider the multi-BS situation, attack the statistics of several correlated generalized selection combining (GSC) stages, and provide closed-form expressions for the statistics of the output signal-to-noise ratio (SNR). By investigating the tradeoff among the error performance, the average number of required path estimations/comparisons, and the SHO overhead, we show through numerical examples that the new schemes offer commensurate performance in comparison with more complicated GSC-based diversity systems while requiring a smaller estimation load and SHO overhead. 相似文献
995.
S. K. Chen A. Serquis G. Serrano K. A. Yates M. G. Blamire D. Guthrie J. Cooper H. Wang S. Margadonna J. L. MacManus‐Driscoll 《Advanced functional materials》2008,18(1):113-120
By applying a combination of characterisation tools, changes in structural and superconducting properties with nominal Mg non‐stoichiometry in MgxB2 are found. The non‐stoichiometry produces enhanced in‐field critical current densities (Jc's) and upper critical field / irreversibility field (Hc2/Hirr(T)) values. Upper critical fields of ~ 21 T (4.2 K) were obtained in nominal Mg‐deficient samples compared to ~ 17 T (4.2 K) for near‐stoichiometric samples. 相似文献
996.
997.
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
998.
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
999.
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
1000.
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