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101.
Jae-Bok Seol Dierk Raabe P. Choi Hyung-Seok Park J.-H. Kwak Chan-Gyung Park 《Scripta materialia》2013,68(6):348-353
We study the structure and chemical composition of the κ-carbide formed as a result of isothermal transformation in an Fe–3.0Mn–5.5Al–0.3C alloy using transmission electron microscopy and atom probe tomography. Both methods reveal the evolution of κ-particle morphology as well as the partitioning of solutes. We propose that the κ-phase is formed by a eutectoid reaction associated with nucleation growth. The nucleation of κ-carbide is controlled by both the ordering of Al partitioned to austenite and the carbon diffusion at elevated temperatures. 相似文献
102.
In the Friedel–Crafts alkylation of xylene to prepare 1-phenyl-1-xylyl ethane (PXE), α-methylbenzyl alcohol was used as an alkylating agent over a mordenite catalyst. The catalyst was characterized by MAS-NMR, N2 adsorption/desorption, NH3-TPD, and various other techniques and was found to possess strong Brønsted acid sites. When temperature was low, the main product was bis-(α-methylbenzyl) ether. However, as the temperature went up, PXE and heavies, styrene trimers and heavier oligomers, became main products. The formation of PXE, occurring on strong acid sites, is favored by raising temperature, space velocity, pressure, and xylene/MBA ratio within the experimental ranges. As the catalyst deactivates, the selectivities to PXE and heavies decrease and those to linear dimer and styrene increase. A reaction mechanism is proposed. 相似文献
103.
Changsoo Jang Geun Sik Ahn Yung Joon Kim Dong Ok Kwak Seong Woon Booh Jae Ok Kim 《Electronics Packaging Manufacturing, IEEE Transactions on》2003,26(1):46-53
The joint structure of a transducer horn-holder assembly for a wire bonder was examined through finite element contact analysis. Three-dimensional modeling and analysis was carried out to survey the internal physics of this structure and to verify the accuracy of a proposed computation relative to measurement. After validation, a two-dimensional model was built to conduct parametric studies and improve the efficiency and speed of the computation. Several factors such as boundary conditions, modeling boundary, and mesh density, were considered to obtain consistency with the three-dimensional analysis. Arc angle and the position of each holder boss were chosen as design parameters. A designed computation approach was applied for efficiency in computation. As a result, a guideline for holder boss design was suggested, and the main factors and their influence on stress concentration in the transducer horn were surveyed. 相似文献
104.
A plate-fin type recuperator for a gas turbine/fuel cell hybrid power generation system was designed, manufactured, and tested.
Performance analysis shows that the performance of the system is directly affected by the performance of the recuperator.
Therefore, the recuperator should be designed and manufactured carefully, and its performance should be tested and verified
before it is integrated into the system. In this paper, the developing procedure including designing, manufacturing, and testing
of a cross flow plate-fin type recuperator was presented. Performance test results showed that the design requirements of
the recuperator were almost satisfied. Based on the test results, improved design to reduce the size of the recuperator was
suggested. 相似文献
105.
Fluorinated NiW/Al2O3 catalysts with different orders of fluorine addition have been prepared, tested for hydrodesulfurization (HDS) of thiophene,
and characterized using nitric oxide chemisorption and temperature-programmed sulfidation. The catalyst surface area has been
affected by fluorine addition but not by the order of fluorination. The fluorine addition-order does not affect the amount
of fluorine retained in the catalysts after the calcination and the reaction steps, either. On the other hand, the order of
fluorine addition changes the dispersion of the nickel and the tungsten species, incorporation of nickel with the tungsten
edge sites, and consequently the HDS activity of the catalysts. The catalyst fluorinated in the last step, i.e., after addition
of both tungsten and nickel, shows the highest activity in thiophene HDS, which is supported by other experimental results
indicating the most nitric oxide chemisorption and the largest incorporation of nickel with the tungsten species. Accordingly,
enhancement of the catalyst activity by fluorination is due to the repartition of the metal species rather than to partial
solubilization of alumina in the fluorine-addition step. 相似文献
106.
We investigate the inherent scalability problem of ad hoc networks originated from the nature of multihop networks. First, the expected packet traffic at the center of a network is analyzed. The result shows that the expected packet traffic at the center of a network is linearly related with the network size, that is, the expected packet traffic at the center of a network is O(k), where k is the radius of a network. From the result, the upper bound of the diameter of a network D=2k, that guarantees the network is scalable, is obtained. The upper bound is given by C/r-1, where C is the channel capacity available to each node and r is the packet arrival rate at each node. 相似文献
107.
Identification and Characterization of a Welwitindolinone Alkaloid Biosynthetic Gene Cluster in the Stigonematalean Cyanobacterium Hapalosiphon welwitschii
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Dr. Matthew L. Hillwig Heather A. Fuhrman Kuljira Ittiamornkul Tyler J. Sevco Daniel H. Kwak Prof. Dr. Xinyu Liu 《Chembiochem : a European journal of chemical biology》2014,15(5):665-669
The identification of a 36 kb welwitindolinone (wel) biosynthetic gene cluster in Hapalosiphon welwitschii UTEX B1830 is reported. Characterization of the enzymes responsible for assembling the early biosynthetic intermediates geranyl pyrophosphate and 3‐((Z)‐2′‐isocyanoethenyl)indole as well as a dedicated N‐methyltransferase in the maturation of N‐methylwelwitindolinone C isothiocyanate solidified the link between the wel pathway and welwitindolinone biosynthesis. Comparative analysis of the ambiguine and welwitindolinone biosynthetic pathways in two different organisms provided insights into the origins of diverse structures within hapalindole‐type molecules. 相似文献
108.
Jeon-Hee Kim Seung-Joon Yoo Dong-Heui Kwak Heung-Joe Jung Tae-Young Kim Kyung-Hee Park Jae-Wook Lee 《Nanoscale research letters》2014,9(1):44
Alumina nanofibers were prepared by a technique that combined the sol–gel and electrospinning methods. The solution to be electrospun was prepared by mixing aluminum isopropoxide (AIP) in ethanol, which was then refluxed in the presence of an acid catalyst and polyvinylpyrolidone (PVP) in ethanol. The characterization results showed that alumina nanofibers with diameters in the range of 102 to 378 nm were successfully prepared. On the basis of the results of the XRD and FT-IR, the alumina nanofibers calcined at 1,100°C were identified as comprising the α-alumina phase, and a series of phase transitions such as boehmite → γ-alumina → α-alumina were observed from 500°C to 1,200°C. The pore size of the obtained γ-alumina nanofibers is approximately 8 nm, and it means that they are mesoporous materials. The kinetic study demonstrated that MO adsorption on alumina nanofibers can be seen that the pseudo-second-order kinetic model fits better than the pseudo-first-order kinetic model. 相似文献
109.
We have investigated the effect of electron beam irradiation as well as insertion of a Ag layer on the electrical and optical properties of the ITO or IZO films. The results show that electron beam irradiation as well as inserting a very thin Ag layer can significantly reduce sheet resistance of the ITO/Ag/ITO and IZO/Ag/IZO films. The electron beam irradiation also increases light transmittance and optical band gap of the ITO/Ag/ITO multilayer films; meanwhile, it has not influence on the transmittance of the IZO/Ag/IZO films. These results can be explained by that In and Zn cation in IZO film have strong tendency to preserve their coordination with oxygen. 相似文献
110.
Seung-Joon Yoo Dong-Heui Kwak Se-II Lee Jin-Geol Kim Jai Koo Park Ho Sung Yoon Hee Dong Jang 《Advanced Powder Technology》2011,22(5):617-622
Al sec-butoxide (ASB) has been used as a precursor for activated aluminas but its cost is higher than any other type of precursor. This study was carried out on the dissolution kinetics for synthesis of the ASB from Al dross waste. The reaction was performed under the molar ratio of Al dross and sec-butyl alcohol (SBA) of 3 mol SBA/mol Al with a catalyst of 10?3 mol HgI2/mol Al and three different dissolution temperatures of 80, 90 and 100 °C. The Al reactant was used with Al dross of 3–5 mm size range. As a result of the experiment, the dissolution reaction gave a 65% yield after 24 h. The dissolution mechanism was determined by the shrinking core model assumed by the shape of spherical particles. Especially, the kinetic data were well fitted by a chemical reaction in the model. By the Arrhenius equation, the apparent activation energy was determined to be 40.9 kJ mol?1 at the given reaction temperatures. 相似文献