全文获取类型
收费全文 | 8377篇 |
免费 | 241篇 |
国内免费 | 10篇 |
专业分类
电工技术 | 88篇 |
综合类 | 13篇 |
化学工业 | 1760篇 |
金属工艺 | 136篇 |
机械仪表 | 112篇 |
建筑科学 | 484篇 |
矿业工程 | 47篇 |
能源动力 | 207篇 |
轻工业 | 807篇 |
水利工程 | 107篇 |
石油天然气 | 38篇 |
无线电 | 528篇 |
一般工业技术 | 1169篇 |
冶金工业 | 2118篇 |
原子能技术 | 95篇 |
自动化技术 | 919篇 |
出版年
2022年 | 82篇 |
2021年 | 121篇 |
2020年 | 98篇 |
2019年 | 100篇 |
2018年 | 107篇 |
2017年 | 109篇 |
2016年 | 126篇 |
2015年 | 112篇 |
2014年 | 164篇 |
2013年 | 435篇 |
2012年 | 285篇 |
2011年 | 355篇 |
2010年 | 280篇 |
2009年 | 306篇 |
2008年 | 366篇 |
2007年 | 350篇 |
2006年 | 307篇 |
2005年 | 261篇 |
2004年 | 233篇 |
2003年 | 238篇 |
2002年 | 212篇 |
2001年 | 147篇 |
2000年 | 143篇 |
1999年 | 144篇 |
1998年 | 122篇 |
1997年 | 119篇 |
1996年 | 115篇 |
1995年 | 140篇 |
1994年 | 132篇 |
1993年 | 123篇 |
1992年 | 134篇 |
1991年 | 91篇 |
1990年 | 109篇 |
1989年 | 122篇 |
1988年 | 116篇 |
1987年 | 113篇 |
1986年 | 117篇 |
1985年 | 146篇 |
1984年 | 135篇 |
1983年 | 118篇 |
1982年 | 130篇 |
1981年 | 126篇 |
1980年 | 89篇 |
1979年 | 123篇 |
1978年 | 120篇 |
1977年 | 103篇 |
1976年 | 87篇 |
1975年 | 84篇 |
1974年 | 90篇 |
1973年 | 99篇 |
排序方式: 共有8628条查询结果,搜索用时 15 毫秒
91.
92.
Charles Merritt Jr. D. A. Forss Pio Angelini M. L. Bazinet 《Journal of the American Oil Chemists' Society》1967,44(2):144-146
Anhydrous butterfat was irradiated at 6 megarads in a special glass reaction flask, and the headspace and total condensate
samples were examined by wide-range (−180C to 125C) gas chromatography combined with mass spectrometry. The nature and amounts
of volatile compounds were not greatly influenced by whether the butterfat was irradiated under oxygen or under vacuum, nor
(apart fromn-alkanoic acids) by storage for 1 and 9 weeks.
Carbon dioxide was produced in greatest amount. Of the remaining compounds, aliphatic hydrocarbons predominated both in number
and amount. Aliphatic oxygenated compounds including carbonyl compounds were isolated in relatively small amounts. The following
compounds were identified positively: C1–13
n-alkanes; C4–9 2-methylalkanes; C2–14 alk-l-enes; C2–9 alk-l-ynes; C2–5
n-alkanoic acids; C1–5
n-alkan-l-ols and propan-2-ol; C2–8
n-alkanals and 2-methylbut-2-enal; C3–5,7 alkan-2-ones; C1–4
n-alkyl formates, vinyl and isoamyl formate, methyl acetate and methyln-hexanoate; and carbon dioxide.
Visiting Scientist from Division of Dairy Research, C.S.I.R.O., Highett, Victoria, Australia. 相似文献
93.
James Charles Tomas Pfister Mark Everingham Andrew Zisserman 《International Journal of Computer Vision》2014,110(1):70-90
We present a fully automatic arm and hand tracker that detects joint positions over continuous sign language video sequences of more than an hour in length. To achieve this, we make contributions in four areas: (i) we show that the overlaid signer can be separated from the background TV broadcast using co-segmentation over all frames with a layered model; (ii) we show that joint positions (shoulders, elbows, wrists) can be predicted per-frame using a random forest regressor given only this segmentation and a colour model; (iii) we show that the random forest can be trained from an existing semi-automatic, but computationally expensive, tracker; and, (iv) introduce an evaluator to assess whether the predicted joint positions are correct for each frame. The method is applied to 20 signing footage videos with changing background, challenging imaging conditions, and for different signers. Our framework outperforms the state-of-the-art long term tracker by Buehler et al. (International Journal of Computer Vision 95:180–197, 2011), does not require the manual annotation of that work, and, after automatic initialisation, performs tracking in real-time. We also achieve superior joint localisation results to those obtained using the pose estimation method of Yang and Ramanan (Proceedings of the IEEE conference on computer vision and pattern recognition, 2011). 相似文献
94.
Joseph C. McBride Xiaopeng Zhao Nancy B. Munro Charles D. Smith Gregory A. Jicha Lee Hively Lucas S. Broster Frederick A. Schmitt Richard J. Kryscio Yang Jiang 《Computer methods and programs in biomedicine》2014
Amnestic mild cognitive impairment (aMCI) often is an early stage of Alzheimer's disease (AD). MCI is characterized by cognitive decline departing from normal cognitive aging but that does not significantly interfere with daily activities. This study explores the potential of scalp EEG for early detection of alterations from cognitively normal status of older adults signifying MCI and AD. Resting 32-channel EEG records from 48 age-matched participants (mean age 75.7 years)—15 normal controls (NC), 16 early MCI, and 17 early stage AD—are examined. Regional spectral and complexity features are computed and used in a support vector machine model to discriminate between groups. Analyses based on three-way classifications demonstrate overall discrimination accuracies of 83.3%, 85.4%, and 79.2% for resting eyes open, counting eyes closed, and resting eyes closed protocols, respectively. These results demonstrate the great promise for scalp EEG spectral and complexity features as noninvasive biomarkers for detection of MCI and early AD. 相似文献
95.
W. Charles Cooper 《Journal of Applied Electrochemistry》1985,15(6):789-805
In recent years research on the electrowinning of copper has led to a number of significant advances. These developments include improved mass transfer and higher current density operation through air sparging, reduced anode overvoltage in the conventional cell as a result of cobalt(II) addition to the electrolyte or the use of alternative types of anodes, and the production of high quality cathodes in the electrowinning of copper from solvent extraction strip liquor. The fluidized-bed cathode offers the possibility of continuous electrowinning as well as the direct electrowinning of copper from dilute solutions. The problem of high power consumption may find its solution in the adoption of an alternate anode reaction or in the electrowinning of copper (I) electrolytes. Noteworthy is the development of unique electrowinning cells in conjunction with the hydrometallurgical treatment of copper concentrates. These cells utilize cuprous or ferrous anodic oxidation with the resulting cupric or ferric ions being active lixiviants of sulphide copper minerals. The numerous advances combined with the increasing tonnage of copper being produced by the electrowinning route ensure an interesting and promising future for this process. 相似文献
96.
CLATHRATE HYDRATE FORMATION ENHANCES NEAR-CRITICAL AND SUPERCRITICAL SOLVENT EXTRACTION EQUILIBRIA 总被引:3,自引:0,他引:3
Richard C. Willson Eric Bulot Charles L. Cooney 《Chemical Engineering Communications》1990,95(1):47-55
Pre-concentration of dilute aqueous solutions by hydrate formation can improve the effective distribution coefficient and selectivity of solvent extraction. Many solvents can serve simultaneously to promote solution concentration by hydrate formation and also to extract non-polar solutes from the resulting concentrated solution. This concept is illustrated for systems with supercritical ethylene and with near-critical liquid carbon dioxide, and its application to conventional solvents is discussed. 相似文献
97.
In our previous research, we found that crosslinking paper using poly(carboxylic acid)s with different molecular weight or using the combination of glutaraldehyde and poly(vinyl alcohol) (PVA) significantly improved the wet strength of the paper. In this research, we studied the mechanism of paper wet strength development using crosslinking systems with different molecular weight by measuring scanning electron microscopic (SEM) images, wet strength, folding endurance, wet thickness, water retention, and Z‐direction tensile strength of the treated paper. The paper crosslinked by a high‐molecular weight (MW) poly(carboxylic acid) shows more swelling by water than that crosslinked by a low‐MW polycarboxylic acid in the SEM micrographs even though both treated paper samples have similar wet strength. Thus, the data suggest that high‐MW poly(carboxylic acid)s promote the formation of interfiber crosslinking. Crosslinking paper by glutaraldehyde, a crosslinking agent of small molecular size, improves wet strength and reduces flexibility and swellability of paper because of the formation of intrafiber crosslinking. Combining glutaraldehyde with PVA as a coreactant increases wet strength and also retains flexibility and swellability of the treated paper because of the formation of interfiber crosslinking. The hypothesis that PVA reacts with glutaraldehyde to form a polymeric pentanedialated‐PVA crosslinking system and promotes the formation of interfiber crosslinking on the paper is supported by the data of wet strength, folding endurance, wet thickness, water retention, and Z‐direction tensile strength of the treated paper. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 277–284, 2006 相似文献
98.
Sykes EC Han P Kandel SA Kelly KF McCarty GS Weiss PS 《Accounts of chemical research》2003,36(12):945-953
Adsorbate interactions and reactions on metal surfaces have been investigated using scanning tunneling microscopy. The manners in which adsorbates perturb the surface electronic structure in their vicinity are discussed. The effects these perturbations have on other molecules are shown to be important in overlayer growth. Interactions of molecules with surface steps are addressed, and each molecule's electron affinity is shown to dictate its adsorption sites at step edges. Standing waves emanating from steps are demonstrated to effect transient molecular adsorption up to 40 A away from the step edge. Halobenzene derivatives are used to demonstrate how the surface is important in aligning reactive intermediates. 相似文献
99.
Linear low‐density polyethylene (LLDPE), based on butene‐1 or hexene‐1, was irradiated with γ‐rays under vacuum or in the presence of air. The study focused on the influence of the dose rate and the γ‐dose on the thermal properties of LLDPE. Differential scanning calorimetry, thermogravimetric analysis (TGA), and TGA/FTIR techniques were used to address the thermal behavior as a result of γ‐irradiation. During this irradiation, competition between crosslinking and scission reactions, subsequent to oxidation reactions, occurred in the polymeric material, which strongly depends on the experimental conditions. A decrease of the crystallinity for γ‐irradiated samples was observed in particular for samples irradiated under vacuum. This observation may be explained by increased hindrance of segment mobility due to crosslinking reactions that prevent crystal growth. TGA investigations revealed an enhancement of the thermal stability for samples irradiated under vacuum but not for those irradiated in air. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2790–2795, 2006 相似文献
100.
Thomas J. Brumm Charles R. Hurburgh Jr 《Journal of the American Oil Chemists' Society》1990,67(5):302-307
Interest in marketing soybeans on the basis of protein and oil content is increasing. Producers, breeders, handlers and buyers
of soybeans need a method of evaluating soybean lots of different composition. A model is presented that predicts, given soybean
composition and processing conditions, the yield of crude soybean oil and soybean meal from the processing of soybeans in
a solvent extraction plant. From these yields, an estimated processed value (EPV) was calculated. For one set of price conditions,
the EPV of typical soybeans had a range of $0.93 per bushel if premiums were paid for meal protein in excess of specifications
and a range of $0.53 per bushel if meal protein premiums were not paid. Trading rules established by the National Oilseed
Processors Association for domestic meal markets have a significant effect on the value and composition of soybean meal. 相似文献