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In this paper, we present some new results of our work in a novel polymerization process (called the free-radical retrograde precipitation polymerization, or FRRPP, process) that occurs at temperatures above the lower critical solution temperature. Our polymerization experiments basically involve the methacrylic acid–poly(methacrylic acid)–water system. Experimental results indicate a gradual increase in conversion with time after what seemingly is the onset of phase separation. In an equivalent solution polymerization system, conversion of methacrylic acid reaches almost 100% at a much shorter time than in the FRRPP system. Molecular weights of poly(methacrylic acid) at different times for the FRRPP system are not dramatically different from those obtained in the solution system. However, the FRRPP system yields a relatively narrow molecular weight distribution at a wide range of conversion compared to that obtained in the equivalent solution system. The unique characteristics of the FRRPP process is shown in the asymptotic time behavior of the free-radical concentration compared to the decay behavior in other polymerization systems. © 1996 John Wiley & Sons, Inc. 相似文献
33.
Nagabhatla Viswanadham Sandeep K. Saxena M.O. Garg 《Journal of Industrial and Engineering Chemistry》2013,19(3):950-955
An Indian industrial naphtha containing mixture of various hydrocarbons belong to n-paraffins, isoparaffins, naphthenes and aromatics falling in C5 to C9 carbon range has been studied for its octane boosting through the production of isoparaffins over various Pt loaded zeolite catalysts possessing different acidity and porosity properties. Optimum balance of acid and metal functionalities in 0.6 wt.% Pt loaded on BEA zeolite helped in achieving highest increase in research octane number (RON) from 44 to 80, suitable for gasoline applications, through the production of lower isoparaffins (iC4-iC6) along with C7+ isoparaffins. 相似文献
34.
Zirconium oxide (ZrO2) nanostructures were synthesized by hydrothermal route. Surface morphology analysis depicts the formation of the nanobars and hexagonal-shaped nanodiscs at different synthesis conditions. The structural analysis confirms that the as-synthesized ZrO2 product is of pure monoclinic phase (m-ZrO2) with crystallite size of about 25 nm. The product consists of monodispersed nanoparticles of uniform composition, high purity, and crystallinity. The Raman spectra are quantitatively analyzed and the observed peaks are attributed to various vibration modes of the m-ZrO2. The UV–vis absorption spectrum showed a strong absorption peak at about 292 nm and the estimated optical band gap was around 3.57 eV. Photoluminescence (PL) spectrum of ZrO2 nanostructure showed a strong and broad emission peak at around 410 nm at room temperature, which can be attributed to the ionized oxygen vacancy in the material. 相似文献
35.
Lyci George Vadym DrozdAndriy Durygin Jiuhua ChenSurendra K. Saxena 《International Journal of Hydrogen Energy》2009
Mg2FeH6 was synthesized by ball milling MgH2 and Fe (2:1 molar ratio) mixture for 72 h followed by heating at 400 °C under H2 pressure. The hydride formation, its structure and homogeneity were investigated by scanning electron microscopy, X-ray diffraction, transmission electron microscopy and Raman spectroscopy. High pressure in situ synchrotron X-ray diffraction and Vienna ab initio simulation were used to determine bulk modulus of the sample. The bulk modulus of Mg2FeH6 was found to be 75.4(4) GPa by optimized experiment and 76.3 GPa by theoretical simulation. From high temperature in situ X-ray diffraction study the volumetric thermal expansion coefficient of Mg2FeH6 was found to be αv = 5.85(3) × 10−5 + 7.47(7) × 10−8 (T − To)/°C. Decomposition of Mg2FeH6 was observed at 425 °C and the decomposition products were Mg, Fe and H2. 相似文献
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Use of the nanoindentation technique for studying microstructure/crack interactions in the fatigue of 4340 steel 总被引:2,自引:0,他引:2
Fan Yang Ashok Saxena Laura Riester 《Metallurgical and Materials Transactions A》1998,29(12):3029-3036
The objectives of this research are to study the influence of microstructure on the fatigue crack growth behavior in 4340
steel and to explore the application of the nanoindentation technique for determining the plastic deformation zone at a fatigue
crack tip. Two heat treatment conditions were chosen for the steel: annealed and quenched plus tempered. The annealed steel
consists of coarse pearlite and proeutectoid ferrite, while the quenched and tempered steel consists of fine tempered martensite.
Fatigue crack propagation tests were conducted on disklike compact (DCT) specimens. Subsequently, the nanoindentation technique
was applied to quantitatively determine the plastic deformation zone at fatigue crack tips. The plastic deformation zone size
determined by the nanoindentation test seems larger than the cyclic deformation zone calculated using the fracture mechanics
equation, which involves many assumptions. The fatigue crack growth test results show that the annealed steel has a higher
resistance to crack growth than the quenched and tempered steel. The fatigue crack in the annealed steel tends to grow along
pearlite domain boundaries, or the cementite/ferrite interfaces within a pearlite domain. In contrast, the fatigue crack in
the quenched and tempered steel tends to traverse the fine martensite laths. Consequently, the actual crack path in the annealed
steel is rougher than in the quenched and tempered steel and more secondary cracks are observed in the annealed steel. 相似文献
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