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101.
Polycrystalline Ag treated with O2 at pressures up to 1 bar and at temperatures up to 920 K was examined by TDS. It was found that the peak commonly observed at 595±25 K and assigned to adsorbed atomic oxygen (Oa) is shifted to higher desorption temperatures with rising dosing temperatures. Since saturation of the uptake was not possible either, this peak was identified as dissolved atomic oxygen (Od). The existence of a maximum for the O2 uptake after exposure at 820 K was found. Hence, under conditions of formaldehyde synthesis ( 920 K) the ability of the catalyst to dissolve oxygen is near its maximum. 相似文献
102.
Masashi Shou Hiroyuki Takekawa Dong-Ying Ju Tokio Hagiwara Da-ling Lu Ken-ichi Tanaka 《Catalysis Letters》2006,108(3-4):119-124
Catalytic activity of a 1 wt% Au/TiO2 catalyst is markedly improved by loading a large amount of FeOx, on which the oxidation of CO in excess H2 is selectively promoted at temperature lower than 60 °C. Oxidation of CO with O2 on the FeOx/Au/TiO2 catalyst is markedly enhanced by H2, and H2O moisture also enhances the oxidation of CO but its effect is not so large as the promotion by H2. We deduced that activation of Au/TiO2 catalyst by loading FeOx is not caused by the size effect of Au particles but a new reaction path via hydroxyl carbonyl intermediate is responsible
for the superior activity of the FeOx/Au/TiO2 catalyst. 相似文献
103.
Evolution with heat treatment of crystallinity in carbons 总被引:1,自引:0,他引:1
F. G. Emmerich 《Carbon》1995,33(12)
The variation with heat treatment of the dimensions La and Lc of the graphite-like crystallites of graphitizable and non-graphitizable carbons is studied. The increases of La and Lc with heat treatment temperature (HTT) owing to three processes (crystallite growth in-plane, coalescence of crystallites along the c-axis and coalescence of crystallites along the a-axis) are functionally separated. The evolution with HTT of the number of crystallites (Ncr), the mean volume of the crystallites (vcr) and the total volume occupied by the crystallites (Vcr) are determined in terms of the changes of La, Lc and d002. Since among other characteristics the crystallites form the electrical and thermal conducting phase of the carbon, Ncr, vcr and Vcr are important parameters in many physical properties of these materials. The developed expressions were applied to a non-graphitizable and to a graphitizable carbon. 相似文献
104.
105.
A simulation model for winter wheat growth, crop nitrogen dynamics and soil nitrogen supply was tested against experimental data. When simulations of dry matter production agreed with measurements, nitrogen uptake was simulated accurately. The total amount of soil mineral nitrogen as well as the distribution of mineral nitrogen over the various soil layers were generally simulated well, except for experiments in which fertilizer was applied late in spring. In these experiments, applied nitrogen disappeared because it could not be accounted for by the model. Some explanations for this disappearance are briefly discussed. 相似文献
106.
1993年化工系统完成总产值1796.3亿元,比上年增长7.3%。全年完成固定资产投资230多亿元,比上年增长19%。全年进出口总额达187亿美元,比上年增长16.1%。但化学工业发展速度低于全国工业的增长速度。 相似文献
107.
Ragnar Larsson 《Catalysis Letters》1991,10(3-4):317-324
Kinetic data on the exchange reaction betwee hexane and deuterium have recently been reported by Maier and coworkers [1]. The reaction was catalysed by a series of platinum or rhodium systems, some of which had the property that the upper surface was shielded by a silica overlayer. The data are reinterpreted to indicate an isokinetic temperature of 580 K. This observation indicates that all the catalysts behave in a similar manner, which means that the exchange reaction does not require a free metal surface. 相似文献
108.
The phenomenon of slow stable crack growth in polyethylene is investigated using notched specimens subject to constant load and the concepts of fracture mechanics. The effect of specimen geometry and dimension, the loading and the mode of loading on the applied stress intensity factor versus crack speed () curves has been studied to demonstrate that Kc is the controlling stress parameter for crack growth under suitable conditions. curves are obtained for a high density polyethylene homopolymer in distilled water and in a diluted detergent solution at four different temperatures. Results are also obtained for a much tougher medium density polyethylene copolymer whenever possible. Several mechanisms can be identified from the form of the curves. Two, in particular, have been observed but not explained before: (i) crack growth with a time dependence of 0.25, and (ii) the high slopes for crack growth in a tough copolymer. With the help of scanning electron microscopic studies of the fracture surfaces, (i) is postulated to be due to diffusion controlled void growth process and (ii) is considered to be the result of crack tip blunting effects. From the temperature dependence of crack growth, the activation energy of the diffusion controlled crack growth process is found to coincide with that of the x-relaxation process in polyethylene implying that diffusion controlled crack growth may be related to the motion of main chains in the polymer. 相似文献
109.
F. Figueras J. L. Flores G. Delahay A. Bourane J.-M. Clacens A. Desmartin-Chomel B. Coq A. Giroir-Fendler 《Topics in Catalysis》2006,39(1-2):59-64
Titanias of different surface areas have been sulfated and used as supports of Rh oxide for the selective catalytic reduction
of nitrogen oxides. Only the sulfation of TiO2 of large surface areas gives strong Br?nsted acid sites, retaining pyridine up to 773 K. Low surface area anatase is unable
to retain sulfates. The catalytic activities measured at 523 K, increase with the number of acid sites, and then reach a plateau,
showing the intervention of acidity in the SCR. This is true only for Rh but not for Pt. The investigation of the elemental
steps on Rh/sulfated TiO2 by in situ diffuse reflectance spectroscopy permits to clarify a few points: the oxidation of propene, presumably to acetaldehyde, occurs
by the reaction with nitrates adsorbed on the support. The further oxidation of this intermediate by NO2 yields an isocyanate, which can be hydrolysed to ammonia. 相似文献
110.