全文获取类型
收费全文 | 4337篇 |
免费 | 215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 | 71篇 |
建筑科学 | 173篇 |
矿业工程 | 5篇 |
能源动力 | 149篇 |
轻工业 | 337篇 |
水利工程 | 21篇 |
石油天然气 | 13篇 |
武器工业 | 1篇 |
无线电 | 531篇 |
一般工业技术 | 765篇 |
冶金工业 | 344篇 |
原子能技术 | 29篇 |
自动化技术 | 792篇 |
出版年
2023年 | 25篇 |
2022年 | 63篇 |
2021年 | 78篇 |
2020年 | 69篇 |
2019年 | 79篇 |
2018年 | 103篇 |
2017年 | 96篇 |
2016年 | 122篇 |
2015年 | 107篇 |
2014年 | 157篇 |
2013年 | 276篇 |
2012年 | 228篇 |
2011年 | 291篇 |
2010年 | 222篇 |
2009年 | 181篇 |
2008年 | 220篇 |
2007年 | 201篇 |
2006年 | 180篇 |
2005年 | 150篇 |
2004年 | 130篇 |
2003年 | 116篇 |
2002年 | 129篇 |
2001年 | 60篇 |
2000年 | 74篇 |
1999年 | 67篇 |
1998年 | 68篇 |
1997年 | 86篇 |
1996年 | 70篇 |
1995年 | 71篇 |
1994年 | 62篇 |
1993年 | 44篇 |
1992年 | 44篇 |
1991年 | 38篇 |
1990年 | 47篇 |
1989年 | 42篇 |
1988年 | 27篇 |
1987年 | 27篇 |
1986年 | 24篇 |
1985年 | 40篇 |
1984年 | 40篇 |
1983年 | 37篇 |
1982年 | 45篇 |
1981年 | 33篇 |
1980年 | 18篇 |
1979年 | 28篇 |
1978年 | 17篇 |
1977年 | 20篇 |
1976年 | 19篇 |
1974年 | 15篇 |
1970年 | 15篇 |
排序方式: 共有4561条查询结果,搜索用时 15 毫秒
41.
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
42.
Maud Cansell Noredine Moussaoui Alain Pierre Petit Alain Denizot Nicole Combe 《European Journal of Lipid Science and Technology》2006,108(6):459-467
Two n‐3 polyunsaturated fatty acid (PUFA)‐rich diets differing in their chemical and physical forms were given to rats during 2 wk. Liposomes [phospholipids (PL) organized in bilayer structures] made from a natural marine lipid extract or a mixture of fats containing fish oil [similar fatty acids esterified in triacylglycerols (TAG)] were used. The influence of n‐3 PUFA dietary sources on plasma parameters, i.e. TAG, cholesterol and PL concentrations, was investigated. A similar hypotriglyceridemic effect of n‐3 PUFA from liposomes or fish oil was observed. In contrast, feeding rats with liposomes led to different PL and cholesterol patterns. In the plasma of rats fed liposomes, total cholesterol amounts were positively correlated with PL levels. Liposome and fish oil feedings caused a marked increase in the amounts of n‐3 PUFA, which occurred mainly at the expense of n‐6 PUFA. However, the enrichment in n‐3 PUFA in the different plasma lipid classes differed substantially when ingested in the form of fish oil or liposomes. These results were interpreted in terms of different lipid bioavailability and metabolic fate during the digestive steps and in the liver, with the dietary source. 相似文献
43.
Amy E. Childress Pierre Le-Clech Joanne L. Daugherty Caifeng Chen Greg L. Leslie 《Desalination》2005,180(1-3):5-14
In order to gain insight into membrane fiber failure (i.e., loss of integrity), properties of five hollow fiber membranes and four hollow fiber modules were evaluated. Specifically, membrane material, membrane symmetry, fiber modulus of elasticity, fiber diameter and thickness, module potting technique, module flow pattern (inside-out or outside-in), and coliform breakthrough were investigated. The approach combined evaluation of the above properties with mathematical modeling of structure-fluid interactions to comprehensively evaluate the properties most important for maintaining hollow fiber membrane integrity. Tensile strength testing revealed that the strongest fiber was an asymmetric polyacrylonitrile membrane fiber. The weakest fiber was a symmetric polyethylene membrane fiber. Pilot plant testing on the four membrane modules revealed that membrane symmetry may be a more important factor than potting technique for hollow fiber integrity. Results from the SEM and tensile testing were used as input to a finite element analysis model used to evaluate time-dependent structure-fluid interactions. It was found that additional stresses at the juncture of the potting material and the hollow fiber membranes exist. These stresses likely lead to the formation of fractures. 相似文献
44.
Laurie Pesant Joseph Matta Cuong Pham-Huu François Garin Pierre Bernhardt Charlotte Pham Marc-Jacques Ledoux 《Topics in Catalysis》2004,(1):281-286
Platinum catalyst supported on a medium surface area -SiC was successfully used for the catalytic combustion of model carbon particles and compared to a catalyst supported on a low surface area -SiC. The -SiC-based catalyst showed no deactivation as a function of cycling tests while a strong deactivation was observed on the -SiC-based catalyst. This deactivation was attributed to the progressive encapsulation of the platinum particles by a layer of silica which built up during the combustion cycle. These results render possible the use of Pt/-SiC catalyst as a diesel carbon particle catalytic filter with continuous regeneration. 相似文献
45.
Elevated temperature Mg-Al-Sr: Creep resistance,mechanical properties,and microstructure 总被引:13,自引:0,他引:13
Eric Baril Pierre Labelle Mihriban Pekguleryuz 《JOM Journal of the Minerals, Metals and Materials Society》2003,55(11):34-39
Mg-Al-Sr-based alloys (AJ alloys) have shown superior creep performance and tensile strength at temperatures as high as 175°
with stresses up to 70 MPa. Mg-6Al-2.4Sr (AJ62x) exhibits an optimum combination of creep resistance and excellent castability,
while AJ62Lx (strontium <2.1) has better ductility than other AJ formulations. The AJ alloy microstructure is characterized
by the Al4Sr-α(Mg) lamellar phase that forms at the interdendritic/grain boundary region of the primary magne sium matrix. Mg-5Al-2Sr
(AJ52x) contains a ternary phase that was tentatively named Al3Mg13Sr. When the strontium level is low in AJ62x, the volume fraction of Al4Sr is reduced, the aluminum supersaturation of the magnesium primary phase increases, and Mg17Al12 forms. In this article, a mechanism is proposed whereby the creep resistance decreases with the strontium level but the tensile
strength and ductility increase.
For more information, contact Eric Baril, Noranda, Noranda Technologies Centre, 240 Hymus Pointe-Claire (Montréal), Québec,
H9R 1G5 Canada; (514) 630-9347; fax (514) 630-9379; e-mail eric.baril@ntc.noranda.com. 相似文献
46.
47.
The problem of determining whether several finite automata accept a word in common is closely related to the well-studied membership problem in transformation monoids. We raise the issue of limiting the number of final states in the automata intersection problem. For automata with two final states, we show the problem to be \({\oplus}\)L-complete or NP-complete according to whether a nontrivial monoid other than a direct product of cyclic groups of order 2 is allowed in the automata. We further consider idempotent commutative automata and (Abelian, mainly) group automata with one, two, or three final states over a singleton or larger alphabet, elucidating (under the usual hypotheses on complexity classes) the complexity of the intersection nonemptiness and related problems in each case. 相似文献
48.
Andre Suslik Spritzer Jeremy Boy Pierre Dragicevic Jean‐Daniel Fekete Carla Maria Dal Sasso Freitas 《Computer Graphics Forum》2015,34(3):461-470
Node‐link infographics are visually very rich and can communicate messages effectively, but can be very difficult to create, often involving a painstaking and artisanal process. In this paper we present an investigation of node‐link visualizations for communication and how to better support their creation. We begin by breaking down these images into their basic elements and analyzing how they are created. We then present a set of techniques aimed at improving the creation workflow by bringing more flexibility and power to users, letting them manipulate all aspects of a node‐link diagram (layout, visual attributes, etc.) while taking into account the context in which it will appear. These techniques were implemented in a proof‐of‐concept prototype called GraphCoiffure, which was designed as an intermediary step between graph drawing/editing software and image authoring applications. We describe how GraphCoiffure improves the workflow and illustrate its benefits through practical examples. 相似文献
49.
Matrix models are ubiquitous for constraint problems. Many such problems have a matrix of variables $\mathcal{M}$ , with the same constraint C defined by a finite-state automaton $\mathcal{A}$ on each row of $\mathcal{M}$ and a global cardinality constraint $\mathit{gcc}$ on each column of $\mathcal{M}$ . We give two methods for deriving, by double counting, necessary conditions on the cardinality variables of the $\mathit{gcc}$ constraints from the automaton $\mathcal{A}$ . The first method yields linear necessary conditions and simple arithmetic constraints. The second method introduces the cardinality automaton, which abstracts the overall behaviour of all the row automata and can be encoded by a set of linear constraints. We also provide a domain consistency filtering algorithm for the conjunction of lexicographic ordering constraints between adjacent rows of $\mathcal{M}$ and (possibly different) automaton constraints on the rows. We evaluate the impact of our methods in terms of runtime and search effort on a large set of nurse rostering problem instances. 相似文献
50.
Fabrice Rousselle Petrik Clarberg Luc Leblanc Victor Ostromoukhov Pierre Poulin 《The Visual computer》2008,24(7-9):465-474
We present an efficient method for importance sampling the product of multiple functions. Our algorithm computes a quick approximation of the product on the fly, based on hierarchical representations of the local maxima and averages of the individual terms. Samples are generated by exploiting the hierarchical properties of many low-discrepancy sequences, and thresholded against the estimated product. We evaluate direct illumination by sampling the triple product of environment map lighting, surface reflectance, and a visibility function estimated per pixel. Our results show considerable noise reduction compared to existing state-of-the-art methods using only the product of lighting and BRDF. 相似文献