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51.
Paula Bracco Hein J. Wijma Bastian Nicolai Jhon Alexander Rodriguez Buitrago Thomas Klünemann Agustina Vila Patrick Schrepfer Wulf Blankenfeldt Dick B. Janssen Prof. Dr. Anett Schallmey 《Chembiochem : a European journal of chemical biology》2021,22(6):1099-1110
CYP154C5 from Nocardia farcinica is a P450 monooxygenase able to hydroxylate a range of steroids with high regio- and stereoselectivity at the 16α-position. Using protein engineering and substrate modifications based on the crystal structure of CYP154C5, an altered regioselectivity of the enzyme in steroid hydroxylation had been achieved. Thus, conversion of progesterone by mutant CYP154C5 F92A resulted in formation of the corresponding 21-hydroxylated product 11-deoxycorticosterone in addition to 16α-hydroxylation. Using MD simulation, this altered regioselectivity appeared to result from an alternative binding mode of the steroid in the active site of mutant F92A. MD simulation further suggested that the entrance of water to the active site caused higher uncoupling in this mutant. Moreover, exclusive 15α-hydroxylation was observed for wild-type CYP154C5 in the conversion of 5α-androstan-3-one, lacking an oxy-functional group at C17. Overall, our data give valuable insight into the structure–function relationship of this cytochrome P450 monooxygenase for steroid hydroxylation. 相似文献
52.
Jessica M. Groenevelt Daniel J. Corey Prof. Charlie Fehl 《Chembiochem : a European journal of chemical biology》2021,22(11):1854-1870
All human cells use O-GlcNAc protein modifications (O-linked N-acetylglucosamine) to rapidly adapt to changing nutrient and stress conditions through signaling, epigenetic, and proteostasis mechanisms. A key challenge for biologists in defining precise roles for specific O-GlcNAc sites is synthetic access to homogenous isoforms of O-GlcNAc proteins, a result of the non-genetically templated, transient, and heterogeneous nature of O-GlcNAc modifications. Toward a solution, this review details the state of the art of two strategies for O-GlcNAc protein modification: advances in “bottom-up” O-GlcNAc peptide synthesis and direct “top-down” installation of O-GlcNAc on full proteins. We also describe key applications of synthetic O-GlcNAc peptide and protein tools as therapeutics, biophysical structure–function studies, biomarkers, and as disease mechanistic probes to advance translational O-GlcNAc biology. 相似文献
53.
Rodriguez J. S. Duran J. F. Aguilar Y. Alcazar G. A. Perez Souza R. M. Zambrano O. A. 《Metallurgical and Materials Transactions A》2022,53(8):2961-2976
Metallurgical and Materials Transactions A - In the present work, the dynamic recrystallization and microstructural evolution of the family of advanced high-strength steels Fe18MnxAl0.74C are... 相似文献
54.
Peter Meszmer Karla Hiller Steffen Hartmann Alexey Shaporin Daniel May Raul David Rodriguez Jörg Arnold Gianina Schondelmaier Jan Mehner Dietrich R. T. Zahn Bernhard Wunderle 《Microsystem Technologies》2014,20(6):1041-1050
In this paper, a novel concept of a thermo-mechanical MEMS actuator using aluminum thin-film heaters on a thermal oxide for electrical insulation is presented. The actuator is part of an universal tensile testing platform for thermo-mechanical material characterization of one dimensional materials on a micro- and nano-scopic scale under different environmental conditions, as varying temperatures, pressure, moisture or even vacuum and is realised in BDRIE technology. It is shown, that the actuator concept fulfills the requirements for the use in a tensile loading stage along with heterogeneously integrated nanofunctional elements, following a specimen centered approach in line with bottom-up self-assembly processes. Simulation and experiment agree very well in the thermal and mechanical domain and allow subsequent optimisation of the actuator performance. 相似文献
55.
Entrepreneurship and the carbon market: opportunities and challenges for South African entrepreneurs
The Kyoto Protocol and its implementation brought forward issues of climate change and its mitigation strategy by national measures through the creation of market mechanisms in carbon trading. The trading of emission certificates has become an important trade commodity worldwide, and its markets have diversified. While this opportunity has created new markets for entrepreneurs and actors that range from farmers to brokers, unequal involvement in most developing countries is noted. This has been mostly observed in those countries where entrepreneurship is often regarded as the cornerstone of economic growth and social improvement. South Africa has spearheaded other African countries in its implementation of Clean Development Mechanism (CDM) projects leading to carbon trading. Based on our research on South African entrepreneurship and its involvement in the carbon market, we conclude that albeit a number of opportunities, the biggest challenge for entrepreneurial participation in the carbon market remains in the nature and processes of CDM project implementation, the lack of a clear supportive system, limited access to financing and—more importantly—general ignorance of the trading opportunities by entrepreneurs. The complex nature of CDM projects themselves limits participation due to lack of the necessary skills on the national level leading to uneven distribution of CDM projects on provincial levels in South Africa. Recommendations are provided to overcome the obstacles and to promote entrepreneurial activity in the carbon market. 相似文献
56.
The effect of potential catalysts on the curing reaction of a new type of phenolic resins obtained from benzoxazine precursors is studied. These novel resins solve the shortcomings of traditional phenolics because they cure by a ring-opening mechanism that avoids the release of volatiles. Isothermal and nonisothermal differential scanning calorimetry (DSC) data is used to determine the influence of the catalysts on the curing kinetics. Fourier transform infrared (FTIR) spectroscopy is also applied. The benzoxazine chosen for this study is a purified benzoxazine monomer based on bisphenol-A, formaldehyde, and aniline. The as-synthesized benzoxazine precursor is also studied to determine the influence of the dimers and higher oligomers in the curing mechanism. The presence of these structures seems to catalyze the curing reactions. The activation energy and overall reaction order of the as-synthesized precursor are determined. Among the catalysts tested, adipic acid shows the most promising results. For all the cases studied the curing reaction is autocatalyzed up to a diffusion-controlled stage. © 1995 John Wiley & Sons, Inc. 相似文献
57.
J. A. Rodriguez X. Wang P. Liu W. Wen J. C. Hanson J. Hrbek M. Pérez J. Evans 《Topics in Catalysis》2007,44(1-2):73-81
Synchrotron-based techniques (high-resolution photoemission, in-situ X-ray absorption spectroscopy, and time-resolved X-ray diffraction) have been used to study the destruction of SO2 and the water-gas shift (WGS, CO + H2O → H2 + CO2) reaction on a series of gold/ceria systems. The adsorption and chemistry of SO2 was investigated on Au/CeO2(111) and AuO
x
/CeO2 surfaces. The heat of adsorption of the molecule on Au nanoparticles supported on stoichiometric CeO2(111) was 4–7 kcal/mol larger than on Au(111). However, there was negligible dissociation of SO2 on the Au/CeO2(111) surfaces. The full decomposition of SO2 was observed only after introducing O vacancies in the ceria support. AuO
x
/CeO2 surfaces were found to be much less chemically active than Au/CeO2(111) or Au/CeO2−x
(111) surfaces. In a separate set of experiments, in-situ time-resolved X-ray diffraction and X-ray absorption spectroscopy were used to monitor the behavior of nanostructured {Au + AuO
x
}–CeO2 catalysts under the WGS reaction. At temperatures above 250 °C, a complete AuO
x
→ Au transformation was observed with high catalytic activity. Photoemission results for the oxidation and reduction of Au
nanoparticles supported on rough ceria films or a CeO2(111) single crystal corroborate that cationic Auδ+ species cannot be the key sites responsible for the WGS activity at high temperatures. The active sites in {Au + AuO
x
}/ceria catalysts should involve pure gold nanoparticles in contact with O vacancies of the oxide. 相似文献
58.
The present paper summarizes a comprehensive Second-Law analysis of the SYNTHANE process of coal gasification(1), based on the available-energy concept as applied to design conditions and data. The analysis yields an overall process efficiency of 46%. For every 100 MJ of useful energy supplied with coal, 51 MJ are consumed during the various unit operations while effluents carry 3 MJ. Unit 30, Steam and Power Production, consumes nearly 20 MJ; Unit 15, Gasification, used up nearly 16 MJ; Units 12 and 14, Coal Preparation and Feeding, about 5 MJ; Units 16 and 17, Raw Gas Quenching and Shift Conversion, 4 MJ; Unit 32, Oxygen Plant, approximately 2 MJ; other miscellaneous units contribute a combined available-energy destruction of 4 MJ. The Second-Law analysis unveils the inefficiencies present in the process and their sources, thus pinpointing the opportunities for improvement in the SYNTHANE process. 相似文献
59.
60.
The preparation of amorphous silica by acid treatment of a natural magnesium silicate and its use as reinforcing filler for NR and SBR compounds are studied. Limited to the treatment with nitric acid, the rate constants at different temperatures and acid concentrations and the activation energy are calculated, as a function of percentage of extracted magnesium. The resulting material is basically an amorphous silica (92.5% SiO2), as shown by X-ray analysis, that keeps the fibrous morphology of the original mineral. According to a preliminary technological study the resulting silica is a suitable reinforcing filler for general purpose rubbers; a comparison between the experimental results and those obtained with a commercial fine particle precipitated silica was made. Using a SBR compound the effect of silane coupling agents on the new silica was studied. 相似文献