全文获取类型
收费全文 | 11958篇 |
免费 | 136篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 74篇 |
综合类 | 4篇 |
化学工业 | 1089篇 |
金属工艺 | 123篇 |
机械仪表 | 208篇 |
建筑科学 | 234篇 |
矿业工程 | 33篇 |
能源动力 | 188篇 |
轻工业 | 534篇 |
水利工程 | 47篇 |
石油天然气 | 11篇 |
武器工业 | 2篇 |
无线电 | 640篇 |
一般工业技术 | 1174篇 |
冶金工业 | 6982篇 |
原子能技术 | 120篇 |
自动化技术 | 638篇 |
出版年
2021年 | 63篇 |
2020年 | 49篇 |
2019年 | 52篇 |
2018年 | 59篇 |
2017年 | 70篇 |
2016年 | 71篇 |
2015年 | 59篇 |
2014年 | 105篇 |
2013年 | 239篇 |
2012年 | 162篇 |
2011年 | 263篇 |
2010年 | 181篇 |
2009年 | 187篇 |
2008年 | 214篇 |
2007年 | 207篇 |
2006年 | 218篇 |
2005年 | 156篇 |
2004年 | 168篇 |
2003年 | 161篇 |
2002年 | 142篇 |
2001年 | 144篇 |
2000年 | 135篇 |
1999年 | 328篇 |
1998年 | 2074篇 |
1997年 | 1129篇 |
1996年 | 842篇 |
1995年 | 459篇 |
1994年 | 424篇 |
1993年 | 464篇 |
1992年 | 146篇 |
1991年 | 183篇 |
1990年 | 167篇 |
1989年 | 197篇 |
1988年 | 159篇 |
1987年 | 159篇 |
1986年 | 165篇 |
1985年 | 155篇 |
1984年 | 104篇 |
1983年 | 89篇 |
1982年 | 97篇 |
1981年 | 141篇 |
1980年 | 149篇 |
1979年 | 95篇 |
1978年 | 91篇 |
1977年 | 231篇 |
1976年 | 444篇 |
1975年 | 81篇 |
1974年 | 47篇 |
1973年 | 68篇 |
1972年 | 46篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
C Chryssanthopoulos C Williams W Wilson L Asher L Hearne 《Canadian Metallurgical Quarterly》1994,4(4):374-386
The purpose of this study was to compare the effects of a carbohydrate-electrolyte solution, ingested during exercise, with the effects of a preexercise carbohydrate meal on endurance running performance. Ten endurance-trained males completed two 30-km treadmill runs. In one trial subjects consumed a placebo solution 4 hr before exercise and a carbohydrate-electrolyte solution immediately before exercise and every 5 km (C). In the other trial, subjects consumed a 4-hr preexercise high-carbohydrate meal and water immediately before exercise and every 5 km (M). Performance times were identical for M and C, and there was no difference in the self-selected speeds. Oxygen uptake, heart rates, perceived rate of exertion, and respiratory exchange ratios were also similar. However, blood glucose concentration was higher in C during the first 20 km of the 30-km run. In M, blood glucose concentration was maintained above 4.5 mmol.L-1 throughout exercise. Thus, the two conditions produced the same 30-km treadmill running performance time. 相似文献
22.
J. C. Williams R. G. Baggerly N. E. Paton 《Metallurgical and Materials Transactions A》2002,33(3):837-850
Single crystals of Ti-Al alloys containing 1.4, 2.9, 5, and 6.6 pct Al (by weight) were oriented for 〈a〉 slip on either basal or prism planes or loaded parallel along the c-axis to enforce a nonbasal deformation mode. Most of the tests were conducted in compression and at temperatures between
77 and 1000 K. Trace analysis of prepolished surfaces enabled identification of the twin or slip systems primarily responsible
for deformation. Increasing the deformation temperature, Al content, or both, acted to inhibit secondary twin and slip systems,
thereby increasing the tendency toward strain accommodation by a single slip system having the highest resolved stress. In
the crystals oriented for basal slip, transitions from twinning to multiple slip and, finally, to basal slip occurred with
increasing temperature in the lower-Al-content alloys, whereas for Ti-6.6 pct Al, only basal slip was observed at all temperatures
tested. A comparison of the critically resolved shear stress (CRSS) values for basal and prism slip as a function of Al content
shows that prism slip is favored at room temperature in pure Ti, but the stress to activate these two systems becomes essentially
equal in the Ti-6.6 pct Al crystals over a wide range of temperatures.
Compression tests on crystals oriented so that the load was applied parallel to the c-axis showed extensive twinning in lower Al concentrations and 〈c+a〉 slip at higher Al concentrations, with a mixture of 〈c+a〉 slip and twinning at intermediate compositions. A few tests also were conducted in tension, with the load applied parallel
to the c-axis. In these cases, twinning was observed, and the resolved shear for plastic deformation by twinning was much lower that
that for 〈c+a〉 slip observed in compression loading.
This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals
and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following
ASM committees: Materials Science and Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic
Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee. 相似文献
23.
24.
25.
26.
Structure-property relationships in a series of thermoset organotin polymers have been investigated. The tri-n-butyltin esters of glycine, 4-aminobutanoic, 6-aminohexanoic, and 11-aminoundecanoic acids were synthesized and reacted with diepoxides to prepare prepolymers carrying epoxide end groups. The prepolymers were crosslinked by diethylenetriamine or metaphenylenediamine. Similar epoxy network polymers were prepared directly from the tributyltin ester of 3,5-diaminobenzoic acid which was also synthesized. The strength, moduli, toughness, glass transition and dynamic mechanical response of the polymers were investigated, and correlated with structural changes introduced in the network. The results establish the utility of the adopted synthesis schemes in exercising considerable control over the bulk polymer properties, and consequently, in modifying the controlled release of organotin groups from the crosslinked network. 相似文献
27.
S.J. Curran R.E. Hayes A. Afacan M.C. Williams P.A. Tanguy 《Journal of food science》2002,67(1):176-180
ABSTRACT: The effect of pH on the non-Newtonian viscosity (η)of aqueous Carbopol 940 solutions is presented with high resolution (pH increments about 0.4) between pH = 2.8 and 12.7. Aqueous NaOH was used to adjust pH of 1.48 wt % Carbopol solutions. A Contraves viscometer was used to measure steady-flow shear stress at known shear rate (γ) over the range γ= 8 to 195 s−1 . Yield stresses and shear-thinning η(γ) were observed. Data were fitted with a Herschel-Bulkley model, whose parameters (including yield stress) were expressed as functions of pH. Comparisons were made of η(γ) to the dynamic viscometric properties η'(ω) and η*(ω) for comparable ranges of γ and frequency (ω): A fairly close match was found between η and η* but η«η'. pH dependence included previously unreported extrema of h(pH) in the range of pH = 6.2 to 6.6. Because of sensitive control of rheological properties with pH, Carbopol solutions can be used to mimic a great range of shear-thinning and yield-stress behavior that should make them useful for model studies directed toward process and equipment design and evaluation. 相似文献
28.
29.
The miscibility and phase behavior of ternary blends containing dimethylpolycarbonate (DMPC), tetramethylpolycarbonate (TMPC) and poly[styrene‐co‐(methyl methacrylate)] copolymer (SMMA) have been explored. Ternary blends containing polystyrene (PS) instead of SMMA were also examined. Blends of DMPC with SMMA copolymers (or PS) did not form miscible blends regardless of methyl methacrylate (MMA) content in copolymers. However, DMPC blends with SMMA (or PS) blends become miscible by adding TMPC. The miscible region of ternary blends is compared with the previously determined miscibility region of binary blends having the same chemical components and compositions. The region where the ternary blends are miscible is much narrower than that of binary blends. Based on lattice fluid theory, the observed phase behavior of ternary blends was analyzed. Even though the term representing the Gibbs free energy change of mixing for certain ternary blends had a negative value, blends were immiscible. It was revealed that a negative value of the Gibbs free energy change of mixing was not a sufficient condition for miscible ternary blends because of the asymmetry in the binary interactions involved in ternary blends. Copyright © 2004 Society of Chemical Industry 相似文献
30.
In this paper we suggest a new statistical method of correcting the results of hot-line experiments for the effects of background sources and we use the new method to reassess the adequacy of three probability distributions proposed in the literature for image spread from line sources. The data are from sources labelled with 125I in semi-thin resin sections 0·4-0·8 μm in thickness. The new method reveals that two of the models describe the empirical distributions more closely than earlier analysis had suggested, and it confirms an increasing relationship between half distance of image spread and the thickness of the source. However, it also confirms that considerable ‘inter hot-line’ experimental variation remains, even after background correction. This suggests that multiple experiments are needed to produce reliable estimates of half distance. 相似文献