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121.
采用低压化学气相沉积法系统研究了H2S/Zn流量比、沉积温度、沉积速率及衬底材料对ZnS体材料红外透过率的影响规律,在本实验研究的条件下认为采用低的H2S/Zn流量比及低的沉积速率,适宜的沉积温度可以提高ZnS的透过率。同时高沉积温度及高H2S/Zn流量比可减少ZnS对波长6.2μm光的吸收。在优化的工艺下获得了高红外透过率的ZnS体材料。 相似文献
122.
Sang Joon Seo 《Electrochimica acta》2006,52(4):1676-1682
Cr-modified Pt/C catalysts were prepared by the chemical vapour deposition (CVD) of Cr on Pt/C, and their performance as a cathode of phosphoric acid fuel cell (PAFC) was compared with the case of catalysts containing Cr added by impregnation (IMP).The catalyst prepared by CVD showed a higher activity for oxygen reduction reaction (ORR) than one prepared by IMP. There was an optimum amount of Cr that yielded the maximum mass activity of the catalyst because the gain in the intrinsic activity due to the promotional effect of Cr was counterbalanced by the loss of exposed Pt surface area as a result of the Cr introduction. Nevertheless, the activity increase at the optimum amount of Cr was greater for the CVD catalyst than for the IMP catalyst. Also, the optimum amount of Cr to yield the maximum activity was smaller for the former catalyst [Cr/Pt]CVD = 0.6, than for the latter, [Cr/Pt]IMP = 1.0.The enhancement of the Pt catalyst activity by Cr addition is attributed to two factors: changes in the surface Pt-Pt spacing and the electronic modification of the Pt surface. The formation of a Pt-Cr alloy, as confirmed by X-ray diffraction, decreased the lattice parameter of Pt, which was beneficial to the catalyst activity for ORR. X-ray photoelectron spectroscopy results showed that the binding energies of Pt electrons were shifted to higher energies due to Cr modification. Accordingly, the electron density of Pt was lowered and the Pt-O bond became weak on the Cr-modified catalysts, which was also beneficial to the catalyst activity for ORR.The promotion of oxygen reduction on Cr-modified catalysts was confirmed by measuring the cyclic voltammograms of the catalysts. All the above changes were made more effectively for catalysts prepared by CVD than for those prepared by IMP because the former method allowed Cr to interact more closely with the Pt surface than the latter, which was demonstrated by the characterization of catalysts in this study. 相似文献
123.
124.
The electrical properties of sets of simultaneously grown p-type polycrystalline Si films, deposited by SiH4 pyrolysis on polycrystalline high-purity alumina substrates and B-doped during growth, were determined by Hall-effect measurements
in the temperature range 77-420K as functions both of impurity doping concentration N (~10l5 to ~1020cm−3) and average grain size (≈1 to ≈125μm) in the film. Room temperature data showed rapidly increasing resistivities and rapidly
decreasing free-carrier concentrations for doping below a critical concentration Nm and distinct mobility minima at that concentration, with the value of Nm being larger the smaller the average grain size. Measurements as a function of sample temperature showed the intergrain barrier
height Eb, decreasing from a maximum value of ~0.4eV at the critical concentration to very small values (~0.01eV) for concentrations
above 1019cm−3, with a functional dependence close to Eb ∝l/N1/2 and Eb for any given concentration being larger the smaller the average grain size. Results are interpreted in terms of the grain-boundary
trapping model. Trapped carrier densities in the grain boundaries were calculated to range from ~5×l011cm−2 at N≈Nm to ~5×l012cm−2 for N>1019cm−3, the density being higher the smaller the grain size, and evidence was found for an energy distribution of traps in the Si
bandgap, rather than a fixed density at a single discrete energy level. The observed relationship between Nm and average grain size nearly coincides with that of the model for films with ~lμm grain size but sharply departs from it
for larger grain sizes, indicating probable applicability of the model for grain sizes up to that range.
aThis work was supported by the U.S. Department of Energythrough its San Francisco Operations Office under Contract DE-AC03-79ET23045
and monitored by the Solar Energy Research Institute, Golden, CO.
bThese results were first described at the 22nd Electronic Materials Conference, Ithaca, NY, June 21–27, 1980, Paper No. M4. 相似文献
125.
Wentao?HuangEmail author Changchun?Chen Xiyou?Li Xiaoyi?Xiong Zhihong?Liu Wei?Zhang Jun?Xu Pei-hsin?Tsien 《Metals and Materials International》2004,10(5):435-438
Ultra-high-vacuum chemical vapor deposition (UHV/CVD) system displays excellent performance for the growth of high-quality
SiGe film. Investigations have shown that have shown that SiGe film grown by this system has high quality. A 10-finger SiGe
hetero-junction bipolar transistor (HBT) device displayed good electrical performance. The current gain was about 500, and
the fT was 5.4 GHz with fmax 7.5 GHz under VCB=3 V, IC=10 mA.
This article is based on a presentation in “The 7th Korea-China Workshop on Advanced Materials” organized by the Korea-China
Advanced Materials Cooperation Center and the China-Korea Advanced Materials Cooperation Center, held at Ramada Plaza Jeju
Hotel, Jeju Island, Korea on August 24–27, 2003. 相似文献
126.
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129.
通过编制C语言程序在CFD商业软件FLUENT中引入颗粒动力学模型,实现对颗粒成长的数学模拟。首先在FLUENT中计算得到丙烷与空气反应的湍流火焰场(含四氯化钛氧化反应),在此基础上将气体中的颗粒或者颗粒聚集块看成一种假定的气体组分,忽略颗粒相对流体的影响,通过UDF导入颗粒模型进行计算,对颗粒尺寸进行了预测,结果显示该模型对颗粒尺寸的预测与实验数据相差不大。进一步分析了火焰温度、氧化剂流量等对生成颗粒或者颗粒聚集块尺寸的影响,结果表明:温度越高颗粒成长越快,单位空间内氧化产物越多越容易长大。 相似文献
130.
R. M. Dey M. Pandey D. Bhattacharyya D. S. Patil S. K. Kulkarni 《Bulletin of Materials Science》2007,30(6):541-546
Diamond-like carbon (DLC) films were deposited by microwave assisted chemical vapour deposition system using d.c. bias voltage
ranging from −100 V to −300 V. These films were characterized by X-ray photoelectron spectroscopy (XPS) and spectroscopic
ellipsometry techniques for estimating sp
3/sp
2 ratio. The sp
3/sp
2 ratio obtained by XPS is found to have an opposite trend to that obtained by spectroscopic ellipsometry. These results are
explained using sub-plantation picture of DLC growth. Our results clearly indicate that the film is composed of two different
layers, having entirely different properties in terms of void percentage and sp
3/sp
2 ratio. The upper layer is relatively thinner as compared to the bottom layer. 相似文献