全文获取类型
收费全文 | 4083篇 |
免费 | 91篇 |
国内免费 | 8篇 |
专业分类
电工技术 | 37篇 |
综合类 | 1篇 |
化学工业 | 604篇 |
金属工艺 | 124篇 |
机械仪表 | 100篇 |
建筑科学 | 117篇 |
矿业工程 | 5篇 |
能源动力 | 71篇 |
轻工业 | 279篇 |
水利工程 | 19篇 |
石油天然气 | 8篇 |
无线电 | 537篇 |
一般工业技术 | 696篇 |
冶金工业 | 1241篇 |
原子能技术 | 33篇 |
自动化技术 | 310篇 |
出版年
2021年 | 32篇 |
2019年 | 25篇 |
2018年 | 38篇 |
2017年 | 28篇 |
2016年 | 37篇 |
2015年 | 30篇 |
2014年 | 52篇 |
2013年 | 147篇 |
2012年 | 90篇 |
2011年 | 95篇 |
2010年 | 99篇 |
2009年 | 116篇 |
2008年 | 121篇 |
2007年 | 114篇 |
2006年 | 101篇 |
2005年 | 99篇 |
2004年 | 85篇 |
2003年 | 99篇 |
2002年 | 75篇 |
2001年 | 91篇 |
2000年 | 114篇 |
1999年 | 108篇 |
1998年 | 349篇 |
1997年 | 238篇 |
1996年 | 164篇 |
1995年 | 135篇 |
1994年 | 100篇 |
1993年 | 108篇 |
1992年 | 55篇 |
1991年 | 62篇 |
1990年 | 80篇 |
1989年 | 75篇 |
1988年 | 51篇 |
1987年 | 59篇 |
1986年 | 42篇 |
1985年 | 60篇 |
1984年 | 68篇 |
1983年 | 59篇 |
1982年 | 44篇 |
1981年 | 61篇 |
1980年 | 45篇 |
1979年 | 42篇 |
1978年 | 26篇 |
1977年 | 67篇 |
1976年 | 71篇 |
1975年 | 36篇 |
1974年 | 36篇 |
1973年 | 45篇 |
1972年 | 23篇 |
1970年 | 24篇 |
排序方式: 共有4182条查询结果,搜索用时 15 毫秒
81.
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
82.
T. S. Wilson J. P. Bearinger J. L. Herberg J. E. Marion III W. J. Wright C. L. Evans D. J. Maitland 《应用聚合物科学杂志》2007,106(1):540-551
Aliphatic urethane polymers have been synthesized and characterized, using monomers with high molecular symmetry, to form amorphous networks with very uniform supermolecular structures, which can be used as photo‐thermally actuable shape memory polymers (SMPs). The monomers used include hexamethylene diisocyanate (HDI), trimethylhexamethylenediamine (TMHDI), N,N,N′,N′‐tetrakis(hydroxypropyl)ethylenediamine (HPED), triethanolamine (TEA), and 1,3‐butanediol (BD). The new polymers were characterized by solvent extraction, NMR, XPS, UV/VIS, DSC, DMTA, and tensile testing. The resulting polymers were found to be single phase amorphous networks with very high gel fraction, excellent optical clarity, and extremely sharp single glass transitions in the range of 34–153°C. Thermomechanical testing of these materials confirms their excellent shape memory behavior, high recovery force, and low mechanical hysteresis (especially on multiple cycles), effectively behaving as ideal elastomers above Tg. We believe these materials represent a new and potentially important class of SMPs, and should be especially useful in applications such as biomedical microdevices. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 相似文献
83.
C. D. Evans Helen A. Moser G. R. List H. J. Dutton J. C. Cowan 《Journal of the American Oil Chemists' Society》1971,48(11):711-714
Room odors developed on heating edible fats in open vessels were evaluated and characterized by a 20 member odor panel. Edible
fats tested were: special soybean salad and cooking oils, hydrogenated soybean oil and some commercial salad and cooking oils.
Factors were investigated that affect reliability and reproducibility of the test and the acuity of the panel members. The
effects of fry temperature and size of sample were investigated. The method has been applied to a study of hydrogenated and
unhydrogenated soybean oil samples.
Presented at the AOCS Meeting, Chicago, September 1970.
No. Market. Nutr. Res. Div., ARS, USDA. 相似文献
84.
Narayana BirakayalaEdward A Evans 《Carbon》2002,40(5):675-683
Carbon-carbon composites are produced by chemical vapor deposition/chemical vapor infiltration (CVD/CVI) processes. Models of carbon-carbon composite production processes will help reduce production costs. Reliable process models must, however, include details of the gas phase kinetics in order to identify optimal conditions. We have combined detailed gas phase kinetics, surface kinetics, and a pore closure model to predict pore geometry changes with respect to time. To determine the dominant gas phase kinetics, we reduced a large set of reactions to a minimal set using a sensitivity, rate, and dimensional analysis approach. These robust and relatively fast techniques can be used under a variety of conditions, including those within the pores of the composite. The process model shows that the deposition profile depends on the kinetic model chosen. Using the more realistic reaction model, conditions for uniform, or inside-out, densification can be suggested. 相似文献
85.
Robert C. Pullar Yong Zhang Lifeng Chen Shoufeng Yang Julian R.G. Evans Peter Kr. Petrov Andrei N. Salak Dmitry A. Kiselev Andrei L. Kholkin Victor M. Ferreira Neil McN. Alford 《Journal of the European Ceramic Society》2007,27(16):4437-4443
Applying combinatorial methods to materials science offers the opportunity to accelerate the discovery of more efficient dielectric ceramics. High-throughput methods have the potential to investigate the effects of a wide range of dopants on the dielectric properties, and to optimise existing systems, encouraging the short innovation cycles that the communications technology industry requires. The London University Search Instrument (LUSI) is a fully automated, high-throughput combinatorial robot that has the potential capability to produce large numbers of sintered bulk ceramic samples with varying composition in 1 day, as combinatorial libraries on alumina substrates. Ba1−xSrxTiO3 (BST) libraries were produced by LUSI as a proof-of-principle, with x = 0–1 in steps of 0.1, and fired to 1350 and 1400 °C for 1 h. Part I of this paper described the manufacture and physical characterisation of BST libraries, showing a regular change in composition with x across the libraries. In this second part, the dielectric properties of BST libraries produced by LUSI are assessed at frequencies between 100 Hz and 1 MHz, and at temperatures between 150 and 500 K. Local piezoelectric properties were also characterised by scanning probe microscope (SPM). All measurements showed evidence of a clear functional gradient varying with x across the library, with measured r corresponding to expected values for BST. 相似文献
86.
Damage Mechanisms and the Mechanical Properties of a Laminated 0/90 Ceramic/Matrix Composite 总被引:2,自引:0,他引:2
Douglas S. Beyerle S. Mark Spearing Anthony G. Evans 《Journal of the American Ceramic Society》1992,75(12):3321-3330
The tensile properties of a 0/90 laminated CAS matrix composite reinforced with Nicalon fibers have been measured. Some effects of notches have also been explored. Changes in modulus and permanent strain caused by matrix cracking have been measured and compared with available models. For this comparison, independent measurements have been made of the constituent properties and the residual stress. The ultimate tensile strength has also been measured and compared with a global load-sharing model. It is concluded that lower-bound matrix cracking models provide good predictability of the stresses at which various matrix cracking mechanisms first operate. Also, the ultimate tensile strength is found to be consistent with a global load-sharing model, based on the in situ strength properties of the fibers. Conversely, the evolution of matrix cracks at stresses above the lower bound has yet to be adequately modeled. In addition, a need is identified for improved models relating elastic properties and permanent strains to matrix crack spacing. 相似文献
87.
Shuttleworth Wendy A.; Hough Colleen D.; Bertrand Kevin P.; Evans Jeremy N.S. 《Protein engineering, design & selection : PEDS》1992,5(5):461-466
5-Enolpyruvylshikimate-3-phosphate (EPSP) synthase, the productof the Escherichia coli aroA gene, has been overproduced inE.coli BL21(DE3) under the control of the T7 gene 10 promoterand ribosome binding site, to a level of {small tilde}50% oftotal cell protein. EPSP synthase is the primary target of thepost-emergence herbicide, glyphosate, commonly known as RoundupTM.A simple two step purification is described, which results in99% pure homogeneous protein (as determined by PAGE). The integrityof the protein has been compared with previously characterizedprotein from .E.coli AB2829(pKD501) by determination of itskinetic parameters, N-terminal protein and DNA sequences, aminoacid analysis and 13C-NMR spectroscopy. This new overproducingstrain readily provides the gram quantities of highly pure proteinrequired for NMR studies of the active site and the developmentof novel time-resolved solid-state NMR techniques currentlyunderway in this laboratory. 相似文献
88.
E. N. Frankel D. G. McConnell C. D. Evans 《Journal of the American Oil Chemists' Society》1962,39(6):297-301
A liquid-partition chromatographic procedure was used to separate hydroxy fatty acids, their methyl esters, and reduced fatty
ester hydroperoxides. Mixtures of methyl stearate, mono- and dihydroxystearate, and mixtures of the corresponding free fatty
acids were easily separated. Chromatographic determinations for ricinoleate in castor oils compared favorably with the chemical
and infrared analyses.
The chromatographic procedure was used to separate hydroxy fatty acids inDimorphotheca andStrophanthus seed oils. The methyl ester of dimorphecolic acid, the principal hydroxy fatty ester ofDimorphotheca oil, behaved like reduced methyl linoleate hydroperoxide and showed a polarity intermediate between methyl 12-hydroxystearate
and methyl 9,10-dihydroxystearate. The 9-hydroxy-12-octadecenoic ester ofStrophanthus oil had a larger retention volume than methyl ous hydroxy fatty esters isolated chromatographically. The diene content of
the reduced hydroperoxides agrees well with values reported in the literature (1,5,16). The diene content of the chromatographed
methyl dimorphecolate is higher than reported by Smithet al. (20) for their preparations but agrees well with the value reported by Chipault and Hawkins (6) for puretrans-trans conjugated methyl linoleate. The extinction coefficient of methyl 12-hydroxystearate at 2.8 μ is higher than that reported
for ricinoleate and the absorption band is much sharper. Because of these two conditions no association of the hydroxyl groups
is indicated. These results also confirm the purity of the hydroxy fatty esters obtained by LPC. This method has been a valuable
adjunct to the study of various oxygen-containing fatty acid and esters and was used to characterize the hydroxy esters obtained
from the hydrogenation of methyl linolenate hydroperoxides (9). This work offers a basis for the development of analytical
methods to determine the hydroxy and other polar acid content of fatty glycerides and their derivatives. 相似文献
89.
H. A. Lloyd M. S. Blum R. R. Snelling S. L. Evans 《Journal of chemical ecology》1989,15(11):2589-2599
Males of several species ofMyrmecocystus produce mandibular gland secretions that contain 2,4-dimethyl-2-hexenoic acid and a variety of monoterpenes that include neral, geranial, citronellol, limonene, and 2,6-dimethyl-5-hepten-1-ol. Other components identified include methyl anthranilate, octanal, octanol, octyl octanoate, and 2-hexyl-2-decenal. Methyl salicylate has been identified as a mandibular gland constituent of workers of several species in addition to mellein and monoterpenes such as cymene, limonene, and the isomers of citral. The Dufour's gland secretions of workers and females of 14 species contain typical formicine alkanes (e.g., undecane), 2-alkanols (e.g., 2-tridecanol), and 2-alkanones (e.g., 2-tridecanone). Two species in the subgenusEremnocystus produce secretions that are distinguished by the presence of significant quantities of tridecyl esters. The functions of these compounds as well as their possible chemosystematic significance in the genusMyrmecocystus are discussed. 相似文献
90.
In order to get good adhesion between polyethylene and copper previous workers have oxidized the metal in alkaline solution to give a matt black oxide film. In this paper it is shown that the good adhesion obtained is associated with the very rough, fibrous nature of the matt black oxide film. Adhesion rises as the layer develops on the copper. If the fibres are damaged to alter the topography without changing the chemical nature of the substrate, the adhesion falls markedly. If the chemical nature of the oxide film is changed by electrolytic reduction, with minimum change in topography, the adhesion is still substantial. Adhesion to these matt black oxide films is still good if oxidation of the polymer is suppressed either by incorporation of stabilizers or by coating in a nitrogen atmosphere. This further points to the importance of topography in adhesion to these surfaces. 相似文献