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71.
72.
Summary This article deals with the handy synthesis of sulfonyl resins, which were produced by the treatment of a commercial sulfonic resin (Lewatit VPOC1812® based at divinylbenzene (DVB) and styrene (STY). The preliminary chemical modification was based on the reaction of the Lewatit VPOC1812® with thionyl chloride aiming to produce the sulfonyl chloride groups. The best conditions to obtain the sulfonyl chloride groups were: SOCl2/SO3H (molar ratio) =13 at 79 °C during 72 h. The resin chlorinated was afterward treated with urea, thiourea or guanidine. The functionalized resins with urea, thiourea or guanidine were produced with 56, 68 and 93% yield, respectively. The commercial and modified resins were characterized by apparent density, swelling degree, elemental analysis (CHNS), FTIR, optical microscopy (OM) and scanning electron microscopy (SEM).  相似文献   
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The Piracicaba river basin is a subtropical watershed located in the southeastern region of Brazil. With an area of 12 400 km2, the basin is a typical example of new landscape resulting from development in tropical and sub-tropical regions: establishment of intensive industrial and agricultural processes were followed by significant population growth and water management. This scenario has led to significant increase in water demand and decrease in water quality. The main objective of this study is the detection of changes in the patterns of flow and precipitation in the basin, and its possible relation to man-induced changes. Statistical analyses were performed on records of precipitation, evapotranspiration and streamflow, from 1947 to 1991. Precipitation and evapotranspiration totals showed significant increasing trends for the entire basin. From eight streamflow gauge stations, half showed significant decreasing trend. The most probable cause of such trends is the export of water from the basin to the metropolitan region of São Paulo city.  相似文献   
75.
The liquid-phase hydrodechlorination of 3-chloropyridine and chlorobenzene has been studied over alkali-modified zirconia-supported palladium catalysts. The modification of the ZrO2 with alkali metal carbonates improves the catalytic activity of the final palladium catalyst. Therefore, the larger the ionic radii (Li+ < Na+ < K+), the greater the catalytic activity (TOF) of the palladium catalyst. For 3-chloropyridine, hydrodechlorination proceeds without catalyst deactivation. This is explained as the result of the interaction of reaction products (pyridine and HCl) forming pyridinium chloride, thus avoiding the detrimental effect of HCl on the palladium particles. Catalytic hydrodechlorination of chlorobenzene over Pd catalysts exhibits an initial catalytic activity (TOF) much lower than that of 3-chloropyridine and the Pd catalysts deactivate as the reaction proceeds. Finally, chlorobenzene hydrodehalogenation has also been carried out in the presence of an equimolecular amount of pyridine resulting in a decrease in the initial reaction rate on the one hand, but also in an increase in final conversion on the other.  相似文献   
76.
Infrared and UV–vis studies of metallocene immobilization on silica are reported here. The results have indicated changes in the Zr coordination sphere of metallocene depending on the immobilization route used. The reaction of [(Cp)2ZrCl2] with silica formed [(Cp)2ZrCl]+[SiO] species. The same metallocene, reacting with TMA modified silica, formed monomethylated and dimethylated species by the substitution of chloro for methyl ligands, stabilized on the surface by interaction with “MAO-like” species (methylaluminoxane, MAO). These monomethylated and dimethylated cationic zirconium species are the active centers for the polymerization reaction. Different order of TMA addition in the silica modification step generated surface species of a similar nature, differing in their relative quantities. The highest amount of these active species was obtained when the support was added to the TMA solution rather than adding the TMA solution to the silica support. This was the most significant parameter affecting catalytic activity in ethylene polymerization.  相似文献   
77.
Detailed representations of the reactor core generate computational meshes with a high number of cells where the fluid dynamics equations must be solved. An exhaustive analysis of the CPU times needed by the thermal-hydraulic subchannel code COBRA-TF for different stages in the solution process has revealed that the solution of the linear system of pressure equations is the most time consuming process. To improve code efficiency two optimized matrix solvers, Super LU library and Krylov non-stationary iterative methods have been implemented in the code and their performance has been tested using a suite of five test cases. The results of performed comparative analyses have demonstrated that for large cases, the implementation of the Bi-Conjugate Gradient Stabilized (Bi-CGSTAB) Krylov method combined with the incomplete LU factorization with dual truncation strategy (ILUT) pre-conditioner reduced the time used by the code for the solution of the pressure matrix by a factor of 20. Both new solvers converge smoothly regardless of the nature of simulated cases and the mesh structures and improve the stability and accuracy of results compared to the classic Gauss–Seidel iterative method. The obtained results indicate that the direct inversion method is the best option for small cases.  相似文献   
78.
79.
As in today’s knowledge society the Internet is playing an important role in the information literacy of university students the goal of this paper is to analyse, after its first year on the Web, the informational impact of an e-learning resource developed by Granada’s University lecturers (the e-COMS educational portal), a pioneer in Spain for training in information literacy. From the objective and subjective data provided by the own portal and by it users, two different and complementary kinds of analysis (functional and users’) are performed. Assessment of various capabilities, among which visibility and usability stand out, is provided. The highly positive but improvable results offer a detailed analysis of the functional aspects of the portal itself and of the users’ relations with this information resource. From these analyses strengths and weaknesses are extracted and some proposals for improvement are derived.  相似文献   
80.
Test data on the residual fracture energy of two significantly different concrete types are presented. About 80 beams of high performance basalt concrete and ordinary gravel concrete have been tested in accordance with the RILEM work of fracture method. The beams are heated at 1°C per minute up to a certain maximum temperature and kept at this temperature for 8 hours before cooling them back to room temperature and testing in three-point bending. The tests show that the two concretes behave almost identifical when the fracture energyG F is considered as a function of maximum temperature. It is found that the damage introduced by a maximum temperature of 300 to 400°C increases the fracture energy by 50% compared with the reference tests at room temperature. A more tortuous crack surface is one plausible explanation for the significant increase inG F. The article also presents temperature and weight loss recordings from the heating scenarios and finally, the characteristic length and the cohesive tensile softening curve are shown to depend on the maximum temperature. Basically it is demonstrated that the temperature exposure makes the concrete significantly more ductile.
Résumé Des données sur l'énergie résiduelle de rupture de deux bétons différents sont présentées. Environ 80 poutres de béton à base de basalte de très haute performance et de béton à base de gravier ordinaire ont été examinées conformément au travaux de la RILEM sur l'énergie de rupture. Les poutres sont chauffées à 1°C par minute jusqu'à une température maximale, puis maintenues à cette température pendant 8 heures avant d'être refroidies de nouveau à la température ambiante. Les poutres sont ensuite testées en flexion (système de flexion en trois points). Les essais prouvent que les deux bétons se comportent d'une manière presque identique quandG F est considéré comme une fonction de la température maximale. On peut aussi constater que le dommage occasionné par une température maximale de 300 à 400°C augmente l'énergie de rupture de 50% par comparaison aux essais de référence réalisés à la température ambiante. Une surface de rupture plus tortueuse semble être une explication plausible pour l'augmentation significative deG F. L'article présente également les évolutions de la température et de la perte de poids pour les scénarios de chauffage utilisés. En conclusion, cette étude montre que la longueur caractéristique et la courbe de post pic dépendent de la température maximale. Fondamentalement cela démontre que l'exposition à la température rend le béton sensiblement plus ductile.
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