全文获取类型
收费全文 | 4338篇 |
免费 | 224篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 68篇 |
综合类 | 3篇 |
化学工业 | 1164篇 |
金属工艺 | 95篇 |
机械仪表 | 72篇 |
建筑科学 | 173篇 |
矿业工程 | 5篇 |
能源动力 | 149篇 |
轻工业 | 336篇 |
水利工程 | 21篇 |
石油天然气 | 13篇 |
武器工业 | 1篇 |
无线电 | 540篇 |
一般工业技术 | 766篇 |
冶金工业 | 336篇 |
原子能技术 | 29篇 |
自动化技术 | 800篇 |
出版年
2023年 | 25篇 |
2022年 | 64篇 |
2021年 | 78篇 |
2020年 | 69篇 |
2019年 | 79篇 |
2018年 | 103篇 |
2017年 | 95篇 |
2016年 | 121篇 |
2015年 | 107篇 |
2014年 | 158篇 |
2013年 | 274篇 |
2012年 | 228篇 |
2011年 | 292篇 |
2010年 | 222篇 |
2009年 | 182篇 |
2008年 | 220篇 |
2007年 | 203篇 |
2006年 | 184篇 |
2005年 | 151篇 |
2004年 | 130篇 |
2003年 | 117篇 |
2002年 | 129篇 |
2001年 | 60篇 |
2000年 | 75篇 |
1999年 | 69篇 |
1998年 | 69篇 |
1997年 | 86篇 |
1996年 | 71篇 |
1995年 | 69篇 |
1994年 | 65篇 |
1993年 | 44篇 |
1992年 | 44篇 |
1991年 | 38篇 |
1990年 | 47篇 |
1989年 | 40篇 |
1988年 | 27篇 |
1987年 | 26篇 |
1986年 | 24篇 |
1985年 | 40篇 |
1984年 | 41篇 |
1983年 | 38篇 |
1982年 | 44篇 |
1981年 | 33篇 |
1980年 | 17篇 |
1979年 | 28篇 |
1978年 | 18篇 |
1977年 | 18篇 |
1976年 | 19篇 |
1974年 | 15篇 |
1970年 | 15篇 |
排序方式: 共有4571条查询结果,搜索用时 15 毫秒
41.
Ccile Donze Pavel Korovchenko Pierre Gallezot Michle Besson 《Applied catalysis. B, Environmental》2007,70(1-4):621-629
The synthesis of substituted benzaldehydes, benzoic acids, heterocyclic aromatic aldehydes and acids has been studied via the oxidation of the aromatic alcohols with air under mild pressure (<20 bar) at 100 °C, in the presence of a 1.95 wt.% Pt/C catalyst. The solvent was found to play the most important role in determining the selectivity of the oxidation products. Changing the solvent enabled tuning the reaction either to the aldehyde (pure dioxane), or the carboxylic acid (dioxane/aqueous solution without or with addition of sodium hydroxide). This oxidation method allowed to effectively oxidize many substituted benzylalcohols with various electron-releasing or -attracting groups (NO2, Me, OMe, Cl, Br, OH, phenyl, …) and heterocyclic alcohols including nitrogen and sulphur atoms (2-thiophenemethanol, 2- and 4-pyridine methanol compounds). 相似文献
42.
Jacques Jupille Anne-Marie Flank Pierre Lagarde 《Journal of the American Ceramic Society》2002,85(5):1041-1046
The local structure centered on sodium after diffusion in silica (Na-SiO2 samples) has been determined by means of extended X-ray absorption fine structure (EXAFS) studies. The Na-SiO2 samples are of particular interest because (i) their sodium content can be varied over a wide range of concentration and (ii) their local structure is representative of that of soda–silica glass. EXAFS analyses reveal the existence of a well-defined local structure involving oxygen, sodium, and silicon neighbors. The Na-O, Na-Na, and Na-Si bonds lengths, which amount to 0.23, 0.30, and 0.38 nm, respectively, do not depend on sodium concentration. This environment closely resembles that found in soda–silica glass. Moreover, it is compatible with the "target site" and "the site memory effect" suggested by recent theories of the ionic conductivity in oxide glasses. 相似文献
43.
Ming-Cheng Guo Marie-Claude Heuzey Pierre J. Carreau 《Polymer Engineering and Science》2007,47(7):1070-1081
The cell structure and properties of branched and linear polypropylene (PP) foams containing organically modified nanoclay and maleic anhydride grafted polypropylene (PPMA) have been thoroughly investigated. X-ray diffraction (XRD) and melt rheometry were used to identify the structure and linear viscoelastic properties of the nanocomposites, as well as the effectiveness of two different compatibilizers. These nanocomposites were used in injection molding to investigate their foamability and the influence of experimental conditions such as chemical foaming agent concentration, shot size, back pressure, injection speed, as well as melt temperature and different injection methods on the resulting cell structure of the foams. Quite different results were obtained with the linear and the branched PP. While the foamability of the branched PP was intrinsically good, that of the linear one could largely be improved by modifying its rheological properties and favoring nucleation through the addition of nanoclay. The effect of cell structure on the dynamic mechanical properties of the foams was also investigated using dynamic mechanical analysis (DMA). POLYM. ENG. SCI., 47:1070–1081, 2007. © 2007 Society of Plastics Engineers 相似文献
44.
Corinne Leprince Eric Vivier Dominique Treton Pierre Galanaud Jacques Benveniste Yolande Richard Yolene Thomas 《Lipids》1991,26(12):1204-1208
The role of paf-acether (paf), a phospholipid cytokine, in the modulation of human B cell function was investigated. Paf,
from 1×10−5 M to 10−6 M, decreased B cell proliferation induced by both phorbol myristate acetate (PMA) and anti-IgM antibodies (anti-IgM Ab).
By contrast, 1×10−7 M to 1×10−9 M paf enhanced PMA triggered, but not anti-IgM triggered B cell proliferation. B cell proliferation was modulated between
24 and 72 hr of culture indicating that the effect of paf did not merely reflect a shift in proliferation kinetics. Interestingly,
paf also enhanced the spontaneous proliferation of a Burkitt lymphoma-derived B cell line, Raji, which suggests that paf can
directly act on B cells. The modulatory effect of paf on peripheral blood B cells was independent of PMA concentration, yet
the effect on Raji cells was dependent upon cell density. The data suggest that paf is a potent modulator of B cell function,
and may be involved in the control of humoral immune response.
Based on a paper presented at the Third International Conference on Platelet-Activating Factor and Structurally Related Alkyl
Ether Lipids, Tokyo, Japan, May 1989. 相似文献
45.
The effects of the non-Newtonian properties on the effective deformation rate, mixing and circulation times and flow behaviour have been investigated in the transition flow regime of mixing systems. Based on the equivalent Couette flow, three models are proposed and are shown to predict similar and drastic increases of the effective deformation rate with the impeller rotational speed in the transition regime. The predictions are shown to fit very well data obtained for various non-Newtonian fluids mixed with helical ribbon agitators, and with literature data for anchor, blade turbine and flat disc agitators. The elasticity along with shear-thinning properties appear to have slight effects on the dimensionless mixing and circulation times in the transition regime, whereas their effects in the laminar regime are quite drastic, as reported by others. 相似文献
46.
The paper gives a general survey of the factors contributing to the deactivation of metal catalysts employed in liquid phase reactions for the synthesis of fine or intermediate chemicals. The main causes of catalyst deactivation are particle sintering, metal and support leaching, deposition of inactive metal layers or polymeric species, and poisoning by strongly adsorbed species. Weakly adsorbed species, poisons at low surface coverage and solvents, may act as selectivity promoters or modifiers. Three examples of long term stability studies carried out in trickle-bed reactor (glucose to sorbitol hydrogenation on Ru/C catalysts, hydroxypropanal to 1,3-propanediol hydrogenation on Ru/TiO2 catalysts, and wet air oxidation of paper pulp effluents on Ru/TiO2) are discussed. 相似文献
47.
Pierre Colomb Alexis Irlande Olivier Raynaud Yoan Renaud 《Annals of Mathematics and Artificial Intelligence》2014,70(1-2):107-122
A collection of sets on a ground set U n (U n ?=?{1,2,...,n}) closed under intersection and containing U n is known as a Moore family. The set of Moore families for a fixed n is in bijection with the set of Moore co-families (union-closed families containing the empty set) denoted ${\mathbb{M}}_n$ . This paper follows the work initiated in Colomb et al. (Ann Math Artif Intell 67(2):109–122, 2013) in which we have given an inductive definition of the lattice of Moore co-families. In the present paper we use this definition to define a recursive decomposition tree of any Moore co-family and we design an original algorithm to compute the closure under union of any family. Then we compare performance of this algorithm to performance of Ganter’s algorithm and Norris’ algorithm. 相似文献
48.
This paper addresses the distributed control by input–output linearization of a nonlinear diffusion equation that describes a particular but important class of distributed parameter systems. Both manipulated and controlled variables are assumed to be distributed in space. The control law is designed using the concept of characteristic index from geometric control by using directly the PDE model without any approximation or reduction. The main idea consists in the control design in assuming an equivalent linear diffusion equation obtained by use of the Cole–Hopf transformation. This framework helps to demonstrate the closed‐loop stability using some concepts from the powerful semigroup theory. The performance of the proposed controller is successfully tested, through simulation, by considering a nonlinear heat conduction problem concerning the control of the temperature of a steel plate modeled by a nonlinear heat equation with Dirichlet boundary conditions. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
49.
50.
Racemic -methyl--n-propyl--propiolactone is readily polymerized with zinc and cadmium chiral glycolates leading to optically active polyesters. The stereoelectivities observed are lower than for oxiranes and thiiranes with the same initiator system. A value of rotatory power for pure enantiomer o, is deduced from NMR measurements in the presence of chiral solvent. The structure of polymers is discussed on the basis of NMR results. 相似文献