全文获取类型
收费全文 | 1008篇 |
免费 | 30篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 16篇 |
化学工业 | 198篇 |
金属工艺 | 29篇 |
机械仪表 | 27篇 |
建筑科学 | 18篇 |
矿业工程 | 3篇 |
能源动力 | 41篇 |
轻工业 | 78篇 |
水利工程 | 7篇 |
石油天然气 | 1篇 |
无线电 | 76篇 |
一般工业技术 | 270篇 |
冶金工业 | 155篇 |
原子能技术 | 5篇 |
自动化技术 | 117篇 |
出版年
2024年 | 4篇 |
2023年 | 8篇 |
2022年 | 23篇 |
2021年 | 41篇 |
2020年 | 38篇 |
2019年 | 42篇 |
2018年 | 36篇 |
2017年 | 31篇 |
2016年 | 24篇 |
2015年 | 26篇 |
2014年 | 34篇 |
2013年 | 64篇 |
2012年 | 30篇 |
2011年 | 41篇 |
2010年 | 48篇 |
2009年 | 44篇 |
2008年 | 32篇 |
2007年 | 28篇 |
2006年 | 18篇 |
2005年 | 21篇 |
2004年 | 12篇 |
2003年 | 18篇 |
2002年 | 21篇 |
2001年 | 14篇 |
2000年 | 12篇 |
1999年 | 12篇 |
1998年 | 44篇 |
1997年 | 24篇 |
1996年 | 21篇 |
1995年 | 10篇 |
1994年 | 14篇 |
1993年 | 16篇 |
1992年 | 8篇 |
1990年 | 14篇 |
1989年 | 11篇 |
1988年 | 10篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1985年 | 20篇 |
1984年 | 11篇 |
1983年 | 9篇 |
1982年 | 10篇 |
1981年 | 12篇 |
1980年 | 15篇 |
1979年 | 11篇 |
1977年 | 5篇 |
1976年 | 11篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 3篇 |
排序方式: 共有1041条查询结果,搜索用时 15 毫秒
71.
72.
An electronically tunable microstrip bandpass filter using thin-film Barium-Strontium-Titanate (BST) varactors 总被引:2,自引:0,他引:2
Nath J. Ghosh D. Maria J.-P. Kingon A.I. Fathelbab W. Franzon P.D. Steer M.B. 《Microwave Theory and Techniques》2005,53(9):2707-2712
A tunable third-order combline bandpass filter using thin-film barium-strontium-titanate varactors and fabricated on a sapphire substrate is reported. Application of 0-200-V bias varied the center frequency of the filter from 2.44 to 2.88 GHz (16% tuning) while achieving a 1-dB bandwidth of 400 MHz. The insertion loss varied from 5.1 dB at zero bias to 3.3 dB at full bias, while the return loss exceeded 13 dB over the range. The third-order intercept of the filter was found to be 41 dBm. 相似文献
73.
M. R. Ramesh S. Prakash S. K. Nath Pawan Kumar Sapra N. Krishnamurthy 《Journal of Thermal Spray Technology》2011,20(5):992-1000
High velocity oxy-fuel (HVOF) spray process has grown into a well-accepted industrial technology for obtaining coatings resistant
to significant surface degradation processes. In the present study, HVOF process was used to deposit Ni-based hardfacing NiCrFeSiB
alloy powder on kinds of boiler tube steels designated as SA210 grade-A1, SA213-T11, and SA213-T22. The microstructures and
several properties of the as-sprayed coatings have been investigated. Thermocyclic oxidation studies were performed in static
air at 900 °C. NiCrFeSiB-coated steels showed slow oxidation kinetics and considerably lower weight gains than that of uncoated
steels. The superior performance of NiCrFeSiB coatings can be attributed to continuous and protective thin oxide scale of
amorphous SiO2 and Cr2O3 formed on the surface of the oxidized coatings. The combined technique of x-ray diffraction, scanning electron microscopy,
energy dispersive x-ray analysis, and electron probe microanalysis are used to characterize reaction products of the oxidized
surfaces. 相似文献
74.
Fastow R. Ahmed K. Haddad S. Randolph M. Huster C. Hom P. 《Electron Device Letters, IEEE》2000,21(4):184-186
Charge gain, caused by localized defects in the tunnel oxide of floating gate devices, is one of the central reliability concerns of flash memory. In this work, we show that charge motion in the poly sidewall spacers of flash cells can also result in substantial charge gain, for nonoptimized processes. Data showing the time, temperature, and field dependencies of this charge gain mechanism are presented. It is shown that the threshold voltage shift caused by charge motion in the poly sidewall spacers follows the simple factorial expression: ΔV th=C·Vfg·tα ·e-ϵ(a)kT/ 相似文献
75.
Commonly used aging measures such as the proportion of older people, the proportion of people aged less than 15 years, and the aging index (aged-child ratio) are based on a simple head count ratio (HCR). The HCR is a crude measure as it fails to give any idea about the tail distribution of the population age. Here an attempt has been made to develop new aging indices (age gap, age distribution sensitive and generalized) taking into account both tails of the population age distribution i.e., distribution of the population aged under fifteen and over sixty. These new indices have been applied to the Bangladesh population based on data collected from secondary sources: the international data base, US Census Bureau and Bangladesh Bureau of Statistics (BBS), for the years 1961, 1981 and 2001 and for some selected Asian countries for 1960, 1980 and 2000 using data from the international UN data base. Conventional aging indices have also been calculated and compared with new ones. Cross-country analysis has also been performed to study the sensitivity of aging indices. Analysis shows an increasing in the speed of aging and new indices indicate the process is faster than conventional ones. For example, relative increases in the speed of aging in 2001 compared to 1981 for conventional and new aging indices (aged-young age gap and aged-young distribution sensitive) are 28.97, 39.19 and 42.04% respectively. The findings also indicate that population aging at the peak is not clear but at the base it is evident. Again the aging process with respect to sex and urban-rural dwelling is also different. From cross-country analysis it is found that the new indices are more sensitive than conventional ones. 相似文献
76.
Summary Nonsimilar solution of the unsteady laminar incompressible magneto-hydrodynamic boundary layer flow and heat transfer for an electrically conducting fluid over two-dimensional and axisymmetric bodies in the presence of an applied magnetic field has been obtained. The effects of surface mass transfer, Joule heating and viscous dissipation are included in the analysis. Numerical computation have been carried out for the flow over a circular cylinder and a sphere using an implicit finite difference scheme in combination with a quasi-linearization technique. It is observed that magnetic field and suction cause the location of vanishing skin friction to move downstream while, the effect of injection is just the opposite. The effect of magnetic field on the skin friction is more pronounced as compared to its effect on the heat transfer. On the other hand, the heat transfer is strongly affected by the viscous dissipation and the effect is more for larte times. However, heat transfer responds comparatively less to the fluctuations of the free stream than the skin friction. 相似文献
77.
Anil Kumar Mandeep Kaur Rajeev Kumar Pinaki Ranjan Sengupta Vasantha Raman Gopal Bhatia Kedar Nath Sood 《Journal of Materials Science》2010,45(5):1393-1400
Carbon–copper composites with varying copper to carbon ratio of 0.66–1.5 (by weight) were developed from coal-tar-pitch-derived
green coke (as such or modified with natural graphite) as carbon source and electrolytic grade copper powder at different
heat treatment temperatures (HTTs) of 1000–1400 °C. The physical, mechanical, and electrical properties differ depending upon
the HTT and also on copper to carbon ratio (Cu/C). The composites prepared at HTT of 1100 °C having Cu/C ratio of 0.66 and
0.9 exhibited a high bending strength of 150 and 140 MPa, bulk density of 2.63 and 2.81 gm/cm3, electrical resistivity of 1.6 and 0.96 m Ω cm and shore hardness of 88 and 84, respectively, in spite of well-known inadequate
wettability between copper and carbon. Increasing the temperature from 1100 °C for processing of the composites deteriorated
the properties mainly due to the loss of copper through melting above 1100 °C as revealed by X-ray, scanning electron microscopy,
thermal analysis and EDAX studies. 相似文献
78.
Sumbit Chaliha Mothura Nath Borah P. C. Sarmah A. Rahman 《International Journal of Thermophysics》2010,31(10):2030-2039
Schottky barrier junctions of Al-doped n-type Zinc selenide (ZnSe) thin films of doping concentrations up to 9.7 × 1014 cm ?3 have been fabricated with Au and Ni electrodes on glass substrates by sequential thermal evaporation. All of the junctions of different doping concentrations exhibited rectifying current-voltage characteristics with a non-saturating reverse current. From the current-voltage characteristics, the different junction parameters such as ideality factor, saturation current density, series resistance, etc., were measured. Both types of junctions were found to possess a high ideality factor and a high series resistance. The barrier heights of the junctions were measured from Richardson plots and found to be around 0.8 eV. The structures were found to exhibit a poor photovoltaic effect with a fill factor not greater than 0.4. The diode quality as well as the photovoltaic performance of the diodes were improved following a short heat treatment in vacuum. 相似文献
79.
The unsteady laminar mixed convection boundary layer flow of a thermomicropolar fluid over a long thin vertical cylinder has been studied when the free stream velocity varies with time. The coupled nonlinear partial differential equations with three independent variables governing the flow have been solved numerically using an implicit finite difference scheme in combination with the quasilinearization technique. The results show that the buoyancy, curvature and suction parameters, in general, enhance the skin friction, heat transfer and gradient of microrotation, but the effect of injection is just opposite. The skin friction and heat transfer for the micropolar fluid are considerably less than those for the Newtonian fluids. The effect of microrotation parameter is appreciable only on the microrotation gradient. The effect of the Prandtl number is appreciable on the skin friction, heat transfer and gradient of microtation. 相似文献
80.
The thermal boundary layer along an isothermal cylinder in a porous 3edium is studied numerically by a finite difference scheme and also using the method of extended perturbation series. The series in terms of the transverse curvature parameter ξ extended to seven terms and is subsequently improved by applying the Shanks transformation twice and thrice, respectively. Results for heat transfer characteristics are found in very good agreement. 相似文献