全文获取类型
收费全文 | 3186篇 |
免费 | 148篇 |
国内免费 | 12篇 |
专业分类
电工技术 | 28篇 |
综合类 | 2篇 |
化学工业 | 649篇 |
金属工艺 | 71篇 |
机械仪表 | 86篇 |
建筑科学 | 144篇 |
矿业工程 | 12篇 |
能源动力 | 127篇 |
轻工业 | 277篇 |
水利工程 | 32篇 |
石油天然气 | 6篇 |
无线电 | 207篇 |
一般工业技术 | 655篇 |
冶金工业 | 630篇 |
原子能技术 | 25篇 |
自动化技术 | 395篇 |
出版年
2023年 | 51篇 |
2022年 | 71篇 |
2021年 | 104篇 |
2020年 | 107篇 |
2019年 | 103篇 |
2018年 | 101篇 |
2017年 | 92篇 |
2016年 | 92篇 |
2015年 | 69篇 |
2014年 | 100篇 |
2013年 | 181篇 |
2012年 | 145篇 |
2011年 | 208篇 |
2010年 | 143篇 |
2009年 | 143篇 |
2008年 | 185篇 |
2007年 | 150篇 |
2006年 | 107篇 |
2005年 | 101篇 |
2004年 | 75篇 |
2003年 | 70篇 |
2002年 | 44篇 |
2001年 | 48篇 |
2000年 | 47篇 |
1999年 | 54篇 |
1998年 | 52篇 |
1997年 | 43篇 |
1996年 | 51篇 |
1995年 | 43篇 |
1994年 | 28篇 |
1993年 | 19篇 |
1992年 | 26篇 |
1991年 | 15篇 |
1990年 | 26篇 |
1989年 | 25篇 |
1988年 | 17篇 |
1987年 | 21篇 |
1986年 | 23篇 |
1985年 | 27篇 |
1984年 | 15篇 |
1983年 | 18篇 |
1982年 | 21篇 |
1981年 | 23篇 |
1980年 | 28篇 |
1979年 | 18篇 |
1978年 | 24篇 |
1977年 | 19篇 |
1976年 | 20篇 |
1975年 | 16篇 |
1973年 | 18篇 |
排序方式: 共有3346条查询结果,搜索用时 281 毫秒
51.
System Modularity has positive effects on software maintainability, reusability, and understandability. One factor that can affect system modularity is code tangling due to code clones. Code tangling can have serious cross-cutting effects on the source code and thereby affect maintainability and reusability of the code. In this research we have developed an algorithmic approach to convert code clones to aspects in order to improve modularity and aid maintainability. Firstly, we use an existing code-clone detection tool to identify code clones in a source code. Secondly, we design algorithms to convert the code clones into aspects and do aspect composition with the original source code. Thirdly, we implement a prototype based on the algorithms. Fourthly, we carry out a performance analysis on the aspects composed source code and our analysis shows that the aspect composed code performs as well as the original code and even better in terms of execution times. 相似文献
52.
Alexander Böhm Franz Carstens Christian Trieb Samuel Schabel Markus Biesalski 《Microfluidics and nanofluidics》2014,16(5):789-799
In the present study, we introduce a novel approach to control and modulate fluid transport inside microfluidic papers using lab-engineered paper sheets. Lab-sheets consisting of different fiber sources (eucalyptus sulfate and cotton linters pulp) and varying porosities were designed and further modified with small millimeter-scaled channels using hydrophobic barriers consisting of fiber-attached, hydrophobic polymers. The capillary-driven transport of an aqueous solution was monitored visually, and the influence of parameters such as fiber source, paper grammage, and channel width on the flow rates through the channel was investigated. The experimental results were compared with those obtained with commercially available filter papers. Our findings suggest that accurate control of fluid transport processes with standard filter papers is complex. Additionally, if the channel width is smaller than the mean fiber length, flow rates become dependent on the geometric parameters of the channel because of the formation of dead-end pores at the hydrophobic barriers. Finally, control of the paper sheets porosity, by varying the fiber density of the lab-made paper, affords the fabrication of chemically identical sheets whereby capillary flow is largely influenced and can be modulated accordingly by simple papermaking processes. 相似文献
53.
Depolymerization of the biopolymer chitosan by an autoclaving process at 121°C and 15 psi was investigated using various treatments. Acetic acid was found to be the most effective solvent in decreasing chitosan viscosity among the six organic acids tested. The rate of viscosity decrease increased with increasing chitosan concentration. The viscosity of 1% chitosan in 1% acetic acid decreased rapidly to 91% of the initial viscosity following the initial 15 min of autoclaving. This decreased gradually to 93% and 94% in 30 and 60 min, respectively, without being adversely affected by the chitosan solution volume. The degree of deacetylation was comparable before and after autoclaving for 60 min. Chitosan at three molecular weights (Mr = 1597, 1110, and 789 kDa) decreased in molecular weight by 46%–51% in the 15‐min treatment, 55%–60% in the 30‐min treatment, and 60%–62% in the 60‐min treatment. The addition of 0.1%–1.0% (v/v) concentrations of hydrogen peroxide to the chitosan solution autoclaved for 15 min decreased viscosity by 94%–98% and molecular weight by 69%–83%. This process is a simple, timesaving, homogeneous depolymerization procedure, and it is possible to prepare partially hydrolyzed chitosan with specified molecular weights by regulating the time of treatment. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1890–1894, 2003 相似文献
54.
Covalent grafting of mesogenic chains on carbon fiber surfaces was attempted as part of a study on composite materials containing liquid crystal polymer matrices. Grafting in these composite systems is viewed not only as a mechanism to achieve interfacial bonding but also as an approach to modify the interphase physical structure. The synthetic approach to grafting involved the in-situ polymerization of monomers in the presence of functionalized fibers in order to grow chains covalently attached to the fibers. The chemical mechanism may be viewed as the “transesterification of car boxy lated fibers” with acetylated monomers. The monomers used were pimelic acid, p-acetoxybenzoic acid and diacetoxy hydroquinone which are known to yield upon condensation a chemically aperiodic nematic polymer. Evidence for grafting was obtained from X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) analysis on fibers retrieved from composite samples. Interestingly, SEM micrographs of fractured composite specimens containing the mesogen-grafted fibers reveal excellent wetting and interfacial bonding of a liquid crystalline matrix on the carbon surfaces. Based on theoretical considerations for end-adsorbed macromolecules and the nematogenic nature of the grafted chains we infer that dense layers of adsorbed polymer may form at the interfaces studied. From a materials point of view the in situ growth of liquid crystal polymer chains on fibers may offer mechanisms to control composite properties through both bonding and molecular orientation in interfacial regions. 相似文献
55.
Thibaut Lécrivain Ashleigh Kimberlin Devon E. Dodd Samuel Miller Ian Hobbs Emily Campbell 《溶剂提取与离子交换》2019,37(3-4):284-296
ABSTRACTBecause there are fewer tools available to probe the interactions therein, the effect of the fundamental chemistry of the organic diluent on solvent extraction equilibria has been under-characterized relative to the aqueous. As a result, diluents for solvent extraction are often selected for an application not for their utility as a medium for reaction, but for other (often equally) important reasons (like low flammability). To begin to improve this imbalance in the science, twenty different diluents have been used in a study of the extraction of radiotracer 152/154Eu3+ from dilute nitric acid solutions using the extractant 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEH[EHP]). To increase the utility of the study and to honor the memory of Professor Jan Rydberg, this investigation was conducted by a cadre of comparatively inexperienced separation scientists (who are as a result no longer inexperienced separation scientists) as a radioanalytical chemistry and solvent extraction educational exercise. Slope analysis was used to determine the apparent stoichiometry of the extracted metal complex. The results discussed in the following indicate that, while the pH dependence exhibits the expected three H+ exchanged per metal ion extracted, the extractant dependence suggests that the number of protonated extractant molecules in the extracted complex changes with the organic diluent. The experimentally observed “extractant dependency” ranges from 2.5 to 3.0 dimer equivalent molecules per extracted metal ion. Ironically, in the diluents exhibiting the highest apparent M:(HA)3 stoichiometry, HEH[EHP] extracts Eu3+ less efficiently. Europium luminescence spectroscopy was used to probe for changes in the first coordination sphere of the complex in different diluents. A model and conceptual framework for understanding these observations is described. 相似文献
56.
Darryl P. Butt Klaus S. Lackner Christopher H. Wendt Samuel D. Conzone Harriet Kung Yung-Cheng Lu Julie K. Bremser 《Journal of the American Ceramic Society》1996,79(7):1892-1898
The kinetics of simultaneous dehydroxylation and carbonation of precipitated Mg(OH)2 were studied using isothermal and nonisothermal thermogravimetric analyses. Specimens were analyzed using X-ray diffraction, transmission electron microscopy, and through measurements of the volume of carbon dioxide evolved in a subsequent reaction with hydrochloric acid. From 275° to 475°C, the kinetics of isothermal dehydroxylation in helium were best fit to a contracting-sphere model, yielding an activation energy of 146 kJ/mol, which was greater than values reported in the literature for isothermal dehydroxylation under vacuum (53–126 kJ/mol). The carbonation kinetics were complicated by the fact that dehydroxylation occurred simultaneously. The overall kinetics also could be fit to a contracting-sphere model, yielding a net activation energy of 304 kJ/mol. The most rapid carbonation kinetics occurred near 375°C. At this temperature, Mg(OH)2 underwent rapid dehydroxylation and subsequent phase transformation, whereas thermodynamics favored the formation of carbonate. During carbonation, MgCO3 precipitated on the surface of disrupted Mg(OH)2 crystals acting as a kinetic barrier to both the outward diffusion of H2 O and the inward diffusion of CO2 . 相似文献
57.
Hamza El Marouazi Benoit van der Schueren Damien Favier Anaëlle Bolley Samuel Dagorne Thierry Dintzer Izabela Janowska 《应用聚合物科学杂志》2021,138(44):51300
Four series of polylactide (PLA) based composite films containing horizontally aligned few layer graphene (FLG) flakes of high aspect ratio and adsorbed albumin are prepared. The mechanical and thermal properties varies with percentage, dispersion degree and size of FLG flakes. Great improvement up to 290% and 360% of tensile modulus and strength respectively were obtained for the composite containing high lateral size of FLG at 0.17% wt, and up to 60% and 80% for the composite with very well dispersed 0.02% wt FLG. The composites of PLA and PEG-PLLA containing very well dispersed FLG flakes at 0.07% wt are ductile showing enhancement of elongation at break up to respectively 80% and 88%. Relatively high electrical conductivity, 5 × 10−3 S/cm, is measured for PLA film charged with 3% of FLG. 相似文献
58.
Anshu Dubey Klaus Weide Dongwook Lee John Bachan Christopher Daley Samuel Olofin Noel Taylor Paul M. Rich Lynn B. Reid 《Software》2015,45(2):233-244
When developing a complex, multi‐authored code, daily testing on multiple platforms and under a variety of conditions is essential. It is therefore necessary to have a regression test suite that is easily administered and configured, as well as a way to easily view and interpret the test suite results. We describe the methodology for verification of FLASH, a highly capable multiphysics scientific application code with a wide user base. The methodology uses a combination of unit and regression tests and an in‐house testing software that is optimized for operation under limited resources. Although our practical implementations do not always comply with theoretical regression‐testing research, our methodology provides a comprehensive verification of a large scientific code under resource constraints.Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
59.
Lourenço André Rota Bulò Samuel Rebagliati Nicola Fred Ana L. N. Figueiredo Mário A. T. Pelillo Marcello 《Machine Learning》2015,98(1-2):331-357
Machine Learning - Clustering ensemble methods produce a consensus partition of a set of data points by combining the results of a collection of base clustering algorithms. In the evidence... 相似文献
60.
Samuel Mascarenhas Nick Degens Ana Paiva Rui Prada Gert Jan Hofstede Adrie Beulens Ruth Aylett 《Autonomous Agents and Multi-Agent Systems》2016,30(5):931-962
This work addresses the challenge of creating virtual agents that are able to portray culturally appropriate behavior when interacting with other agents or humans. Because culture influences how people perceive their social reality it is important to have agent models that explicitly consider social elements, such as existing relational factors. We addressed this necessity by integrating culture into a novel model for simulating human social behavior. With this model, we operationalized a particular dimension of culture—individualism versus collectivism—within the context of an interactive narrative scenario that is part of an agent-based tool for intercultural training. Using this scenario we conducted a cross-cultural study in which participants from a collectivistic country (Portugal) were compared with participants from an individualistic country (the Netherlands) in the way they perceived and interacted with agents whose behavior was either individualistic or collectivistic, according to the configuration of the proposed model. In the obtained results, Portuguese subjects rated the collectivistic agents more positively than the Dutch but both countries had a similarly positive opinion about the individualistic agents. This experiment sheds new light on how people from different countries differ when assessing the social appropriateness of virtual agents, while also raising new research questions on this matter. 相似文献