全文获取类型
收费全文 | 4569篇 |
免费 | 124篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 46篇 |
综合类 | 4篇 |
化学工业 | 1055篇 |
金属工艺 | 84篇 |
机械仪表 | 77篇 |
建筑科学 | 156篇 |
矿业工程 | 17篇 |
能源动力 | 126篇 |
轻工业 | 339篇 |
水利工程 | 66篇 |
石油天然气 | 19篇 |
无线电 | 233篇 |
一般工业技术 | 750篇 |
冶金工业 | 1153篇 |
原子能技术 | 30篇 |
自动化技术 | 541篇 |
出版年
2021年 | 70篇 |
2020年 | 42篇 |
2019年 | 53篇 |
2018年 | 63篇 |
2017年 | 70篇 |
2016年 | 72篇 |
2015年 | 63篇 |
2014年 | 102篇 |
2013年 | 264篇 |
2012年 | 137篇 |
2011年 | 214篇 |
2010年 | 189篇 |
2009年 | 166篇 |
2008年 | 192篇 |
2007年 | 176篇 |
2006年 | 187篇 |
2005年 | 155篇 |
2004年 | 139篇 |
2003年 | 142篇 |
2002年 | 113篇 |
2001年 | 86篇 |
2000年 | 84篇 |
1999年 | 87篇 |
1998年 | 118篇 |
1997年 | 103篇 |
1996年 | 97篇 |
1995年 | 94篇 |
1994年 | 98篇 |
1993年 | 83篇 |
1992年 | 89篇 |
1991年 | 43篇 |
1990年 | 65篇 |
1989年 | 58篇 |
1988年 | 59篇 |
1987年 | 50篇 |
1986年 | 52篇 |
1985年 | 82篇 |
1984年 | 77篇 |
1983年 | 65篇 |
1982年 | 51篇 |
1981年 | 46篇 |
1980年 | 38篇 |
1979年 | 50篇 |
1978年 | 51篇 |
1977年 | 39篇 |
1976年 | 45篇 |
1975年 | 33篇 |
1974年 | 36篇 |
1973年 | 27篇 |
1972年 | 29篇 |
排序方式: 共有4696条查询结果,搜索用时 0 毫秒
31.
The last decade has placed the superiority of graphical user interfaces over traditional text-based approaches beyond dispute. In almost all contexts, users have found graphical interfaces easier to learn, faster to use, and less error-prone. However, it has been shown that the creation of powerful graphical interfaces takes up to 80% of the time required to develop an application. In our work, we seek to extend the benefits of graphical interaction to the next layer of computer user—the interface designer. Our work in this area is distinguished from other efforts by two important differences. First, while other efforts focus primarily on the design of standard user interfaces, our approach emphasizes the creation of unique and innovative interfaces by supporting, among other things, arbitrary user-designed graphical representations, direct specification of animation, and digitized sound. Second, our goal is to cater to the nonprogrammer. Thus, we address a challenging trade-off: maximizing power and flexibility in an extremely simple environment. We explore the utility of the prototype object-oriented paradigm, a high-level userinterface language, and a direct-manipulation programming environment in this context. 相似文献
32.
Assessment of contaminant releases during utilization of used oils is essential for the determination of environmental acceptability. These paper reports the results of the study examining a toxic metal leachability from used engine oil and sludge samples employing leaching test (TCLP). The leaching test indicated that lead in oil samples exceeded 5-ppm concentration level what qualified them as a toxic waste. The samples of contaminated sludge were found to contain high concentration of total lead, barium and chromium, but the leaching test showed concentration below regulatory limit. The total content of benzene, ethylbenzene, toluene, and xylenes (BETX), and naphthalene in used oil and sludge samples was also determined and was found not to be a significant factor to contamination. 相似文献
33.
The overall non-isothermal crystallization kinetics for nucleated and non-nucleated isotactic polypropylene (iPP) in dotriacontane systems was investigated. Adipic acid was used as the nucleating agent. Crystallization peak temperature was determined via differential scanning calorimetry as a function of the experimentally controlled variables iPP concentration, cooling rate, and nucleating agent concentration. The influence of these variables on crystallization mechanism and spherulitic structure as implied by the Ozawa and Ziabicki analyses was determined. The non-isothermal crystallization kinetics presented here are the first for iPP-diluent systems with and without nucleating agent. 相似文献
34.
Maltose long-chain fatty acid esters (MFAE), esterified at the 6 and 6′ position, were synthesized with stearic, palmitic,
myristic, and oleic groups. Synthesis yields were 15–20% based on initial maltose present, and structural confirmation was
obtained using plasma desorption mass spectrometry and nuclear magnetic resonance spectroscopy. These surfactants have surface
tensions in the range of 34–36 dyn/cm at their critical micelle concentrations (CMC) of approximately 10−5–10−6 mol/L. The increased chain lengths have a marked effect, reducing CMC values for MFAE by approximately three orders of magnitude
over similar carbohydrate-based dodecyl chain sources. Within chain lengths between 14 and 18 carbons, the rate of change
in CMC is significant and decreases with increasing chain length for MFAE. The melting points of MFAE are approximately 40°C,
and the heat capacities range from 1.6 to 1.9 J/g·K. These numbers are comparable to those of sucrose esters, indicating their
applicability in similar uses. However, because MFAE, unlike sucrose, possess an anomeric carbohydrate carbon position, these
surfactants maintain their reducing nature and are susceptible to further derivatization. They are also synthesized from renewable,
economical carbohydrates and lipids and may provide an excellent alternative to pertrochemical-derived products. 相似文献
35.
Murray S. Blum Ray F. Severson Richard F. Arrendale Douglas W. Whitman Pierre Escoubas Olushola Adeyeye Clive G. Jones 《Journal of chemical ecology》1990,16(1):223-244
Adults of a generalist herbivore, the lubber grasshopper,Romalea guttata, can be converted to functional specialists by feeding them exclusively on catnip,Nepeta cataria. No obvious adverse effects on adult development resulted from this enforced monophagy. Notwithstanding the fact thatR. guttata has had no coevolutionary relationship with this Eurasian mint, it readily sequesters compounds that are identical to or derived from the terpenoid lactones that are characteristic ofN. cataria. R. guttata appears to both biomagnify minor allelochemicals and to sequester metabolites of theNepeta terpenes in its paired defensive glands. The levels of autogenously produced phenolics are not affected by feeding onN. cataria and the defensive secretions of catnip-fed grasshoppers are more repellent to ants than those of wild-fed acridids. Metabolites of theN. cataria monoterpenes are sequestered in the defensive glands when catnip is added to the natural diet ofR. guttata. The ability of a generalist,R. guttata, to facilely bioaccumulate a potpourri of foreign allelochemicals when feeding in a specialist mode is analyzed in terms of its biochemical, physiological, and functional significance. Sequestration is examined as a response to the enteric effronteries represented by the phytochemicals that can be characteristic of the overload in a monophagous diet. 相似文献
36.
Douglas Walton 《Artificial Intelligence and Law》2014,22(4):423-449
This paper applies two argumentation schemes, argument from fairness and argument from lack of knowledge (along with other schemes of lesser prominence) to model the reasoning given by Judge McCarthy supporting his decision to divide the proceeds of a homerun baseball in the case of Popov v. Hayashi. Several versions of both schemes are explained and discussed, and then applied to the argumentation given by Judge McCarthy as the basis of the reasoning used to arrive at his decision. The scheme for argument from fairness is shown to be based on a special principle in Perelman’s theory of justice. 相似文献
37.
A simple method has been developed to optimally design a distillation sequence with a fixed degree of flexibility in feed composition and flowrate, and accounts for uncertainty in stage efficiency, K-value and beat transfer coefficient calculations. The method minimizes a weighted cost function and ensures both optimal and feasible operation in the range of flexibility/uncertainty by using an approach termed “practical feasibility”. The method was tested on a 4 column distillation sequence separating a 5 component light alkane feed mixture. Results are presented to illustrate the effect of uncertainty on sequence cost and column overdesign. 相似文献
38.
Gordon B. A. Lim Kenneth S. McGuire Douglas R. Lloyd 《Polymer Engineering and Science》1993,33(9):537-542
Non-isothermal crystallization growth rates of nucleated and non-nucleated isotactic polypropylene (iPP) in dotriacontane were determined experimentally by thermal optical microscopy. Adipic acid was used as the nucleating agent. The non-isothermal growth rates of the nucleated and non-nucleated systems were compared with experimentally determined isothermal growth rates. The Lauritzen and Hoffman growth rate equation, originally developed for isothermal crystallization, was modified to describe the non-isothermal growth. The modified Lauritzen-Hoffman equation was used to predict isothermal growth rates from non-isothermal crystallization for the nucleated and non-nucleated polymer-diluent mixtures. This study is the first to deal with polymer-diluent-nucleating agent systems vital to membrane production. 相似文献
39.
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
40.
Douglas D. Frey 《Chemical Engineering Communications》1992,117(1):143-162
A local equilibrium theory for nonisothermal gas adsorption is developed which accounts for variations in interstitial gas velocity induced by adsorption. Also presented are expressions describing the entropy admissibility criterion. A solution is developed for a Riemann's problem involving adiabatic gas-phase adsorption where there is no inert diluent and where Langmuir isotherms apply. 相似文献