全文获取类型
收费全文 | 5310篇 |
免费 | 105篇 |
国内免费 | 20篇 |
专业分类
电工技术 | 267篇 |
综合类 | 7篇 |
化学工业 | 1040篇 |
金属工艺 | 158篇 |
机械仪表 | 99篇 |
建筑科学 | 74篇 |
矿业工程 | 2篇 |
能源动力 | 111篇 |
轻工业 | 313篇 |
水利工程 | 11篇 |
石油天然气 | 17篇 |
无线电 | 555篇 |
一般工业技术 | 1023篇 |
冶金工业 | 1291篇 |
原子能技术 | 160篇 |
自动化技术 | 307篇 |
出版年
2023年 | 14篇 |
2022年 | 50篇 |
2021年 | 99篇 |
2020年 | 38篇 |
2019年 | 56篇 |
2018年 | 59篇 |
2017年 | 59篇 |
2016年 | 77篇 |
2015年 | 55篇 |
2014年 | 87篇 |
2013年 | 188篇 |
2012年 | 170篇 |
2011年 | 243篇 |
2010年 | 159篇 |
2009年 | 165篇 |
2008年 | 180篇 |
2007年 | 191篇 |
2006年 | 159篇 |
2005年 | 159篇 |
2004年 | 146篇 |
2003年 | 141篇 |
2002年 | 109篇 |
2001年 | 111篇 |
2000年 | 107篇 |
1999年 | 138篇 |
1998年 | 539篇 |
1997年 | 293篇 |
1996年 | 216篇 |
1995年 | 167篇 |
1994年 | 130篇 |
1993年 | 120篇 |
1992年 | 80篇 |
1991年 | 82篇 |
1990年 | 67篇 |
1989年 | 74篇 |
1988年 | 51篇 |
1987年 | 58篇 |
1986年 | 63篇 |
1985年 | 59篇 |
1984年 | 54篇 |
1983年 | 37篇 |
1982年 | 44篇 |
1981年 | 47篇 |
1980年 | 45篇 |
1979年 | 31篇 |
1978年 | 29篇 |
1977年 | 30篇 |
1976年 | 74篇 |
1975年 | 17篇 |
1974年 | 14篇 |
排序方式: 共有5435条查询结果,搜索用时 15 毫秒
991.
Helton José Alves Cícero Bley Junior Rafael Rick Niklevicz Elisandro Pires Frigo Michelle Sato Frigo Carlos Henrique Coimbra-Araújo 《International Journal of Hydrogen Energy》2013
Traditionally, H2 is a large-scale production by the reforming process of light hydrocarbons, mainly natural gas, used by the chemical industry. However, the reforming technologies currently used encounter numerous technical/scientific challenges, which depend on the quality of raw materials, the conversion efficiency and security needs for the integration of H2 production, purification and use, among others. Biogas is a high-potential versatile raw material for reforming processes, which can be used as an alternative CH4 source. The production of H2 from renewable sources, such as biogas, helps to largely reduce greenhouse gas emissions. Within this context, the integration of biogas reforming processes and the activation of fuel cell using H2 represent an important route for generating clean energy, with added high-energy efficiency. This work expounds a literature review of the biogas reforming technologies, emphasizing the types of fuel cells available, the advantages offered by each route and the main problems faced. 相似文献
992.
The structural response of an austenitic stainless steel single crystal to friction stir welding (FSW) was examined. The microstructural changes induced by FSW were found to essentially vary around the rotating tool. This effect was attributed to variable orientation of the shear plane and shear direction inherent to the FSW process, which significantly influenced slip activity of the single crystal. 相似文献
993.
W. Jiang R. Devanathan C.J. Sundgren M. Ishimaru K. Sato T. Varga S. Manandhar A. Benyagoub 《Acta Materialia》2013,61(20):7904-7916
Tetragonally structured barium titanate (BaTiO3) single crystals were irradiated using 635 MeV 238U+ ions to fluences of 1 × 107, 5 × 1010 and 1.4 × 1012 ions cm?2 at room temperature. Irradiated samples were characterized using ion channeling, X-ray diffraction, helium ion microscopy and transmission electron microscopy. The results show that the ion-entry spot on the surface has an amorphous core of up to ~10 nm in diameter, surrounded by a strained lattice structure. Satellite-like defects around smaller cores are also observed and are attributed to the imperfect epitaxial recrystallization of thermal-spike-induced amorphization. The critical value of the electronic stopping power for creating observable amorphous cores is determined to be ~22 keV nm?1. Molecular dynamics simulations show an amorphous track of ~1.2 nm in radius under thermal energy deposition at 5 keV nm?1; the radius increases to ~4.5 nm at 20 keV nm?1. A linear fit of the core diameter as a function of the square root of the energy deposition rate suggests a reduction in the diameter by an average of ~8.4 nm due to thermal recrystallization if electron–phonon coupling efficiency of 100% is assumed. The simulation also reveals details of the bonding environments and shows different densities of the amorphous zones produced at different energy deposition rates. 相似文献
994.
995.
Advanced resonance self-shielding method for gray resonance treatment in lattice physics code GALAXY
Hiroki Koike Kazuya Yamaji Kazuki Kirimura Daisuke Sato Hideki Matsumoto Akio Yamamoto 《Journal of Nuclear Science and Technology》2013,50(7):725-747
A new resonance self-shielding method based on the equivalence theory is developed for general application to the lattice physics calculations. The present scope includes commercial light water reactor (LWR) design applications which require both calculation accuracy and calculation speed. In order to develop the new method, all the calculation processes from cross-section library preparation to effective cross-section generation are reviewed and reframed by adopting the current enhanced methodologies for lattice calculations. The new method is composed of the following four key methods: (1) cross-section library generation method with a polynomial hyperbolic tangent formulation, (2) resonance self-shielding method based on the multi-term rational approximation for general lattice geometry and gray resonance absorbers, (3) spatially dependent gray resonance self-shielding method for generation of intra-pellet power profile and (4) integrated reaction rate preservation method between the multi-group and the ultra-fine-group calculations. From the various verifications and validations, applicability of the present resonance treatment is totally confirmed. As a result, the new resonance self-shielding method is established, not only by extension of a past concentrated effort in the reactor physics research field, but also by unification of newly developed unique and challenging techniques for practical application to the lattice physics calculations. 相似文献
996.
Takayuki Sasaki Yuu Takeno Akira Kirishima Nobuaki Sato 《Journal of Nuclear Science and Technology》2013,50(2):147-151
The leaching behaviors of gamma-ray radionuclides, Cs-137, Ru-103, and Zr-95, produced by neutron irradiation of UO2/ZrO2 solid solutions, in real surface seawater were investigated under atmospheric conditions. The fraction of radionuclide inventory leached in the seawater was in the order of Cs > Ru (~U) ? Zr, indicating that the fraction was significantly affected by the chemical state of the radionuclides. However, the amount of soluble nuclides was proportional to that of uranium regardless of whether the solid solutions were prepared under an oxidative or reductive environment. A tiny fraction of Ru was filtered out by a 3 kDa nominal molecular weight cut-off filter after the 160 d leaching test, suggesting a different behavior from its ionic form, but Cs and U did not form a colloid-like species in seawater. 相似文献
997.
We discuss the mode I energy release rate of a rectangular piezoelectric material with a crack under electromechanical loading at cryogenic temperatures. A crack was created normal or parallel to the poling direction, and electric fields were applied parallel or normal to the poling. A plane strain finite element analysis was carried out, and the effects of electric field and localized polarization switching on the energy release rate were discussed for the piezoelectric ceramics at cryogenic temperatures. 相似文献
998.
In this paper, we conduct an analytical comparison of three pull production control systems: Kanban, CONWIP and Base-stock in multi-stage production processes. First, we compare the three control systems in a multi-stage serial production process. Then, we compare them in multi-stage assembly production processes, and present guidelines that allow us to select the best system. As a result, we show which structural parameters decide the superiority of one control scheme to the others, and how they are related. A key for superiority is a configuration of parameters, such as processing times and number of cards employed in the system. We show that there is no general superiority amongst the analysed concepts. Finally, we verify the effect of variability on the system performance, and generalise the analytical results of deterministic cases by conducting numerical experiments. 相似文献
999.
Summary Conformational analyses using quantum chemical calculations were carried out for 1- to 4-mers of ethylene
oxide (EO) and ethylene imine (EI) oligomer models (EO-x and EI-x, x = 1 - 4) in the liquid phase using
four solvents (permittivity: ε = 2.0 ~80.1). The results were compared against those obtained in
the gaseous phase. The calculations involved either RHF/6-31+G(d,p) or B3LYP/6-31G(d) // SCRF/IPCM,
based on the observed and calculated results for the energy difference between trans-
and cis-dichloroethane. The conformations repeated for a unit of
X-C, C-C and C-X bonds (X: O or N) were examined. For both oligomers, the energies of every conformer
decreased with increasing ε values, and were linear against the Kirkwood function (Kf
= (ε-1)/(2ε+1)). For the EO oligomers, the (ttt)x conformer was most
stable in the gaseous phase. In liquid phases, however, the preference for the gauche-conformation
(gauche preference) of the C-C bonds increased with higher values of ε. In the case of EO-3, the
(tg+t)x conformer was most stable above an ε value
of 8.9, which were in good agreement with those observed for triglyme solutions using NMR analysis.
For the EI oligomers, the (tg+t)x conformer was most
stable in either gaseous or liquid phase, and the gauche preference of the C-C bonds in both phases
were comparable. These results were in good agreement with those observed for di-MEDA solutions using
NMR analysis. It was estimated that such small solvent effects on gauche preferences of the EI oligomers
result in weakening for hydrogen bonds (NH-N) of neighboring imino groups by solvents. 相似文献
1000.
Dense BaTiO3 ceramics with 1 1 1-texture were prepared by the TGG process. Platelike BaTiO3 particles with their 1 1 1 direction perpendicular to the plate face were prepared by the reaction of platelike Ba6Ti17O40 particles with BaCO3 particles in molten NaCl. A green compact was composed of the aligned, platelike BaTiO3 template particles dispersed in the matrix of small, equiaxed BaTiO3 particles. Sintering caused densification and also the growth of template particles at the expense of matrix particles, resulting in texture development. Densification prior to grain growth was found to be necessary to obtain highly textured ceramics, and the effect of pre-sintering conditions on texture development was examined. 相似文献