全文获取类型
收费全文 | 14951篇 |
免费 | 1374篇 |
国内免费 | 656篇 |
专业分类
电工技术 | 427篇 |
综合类 | 1000篇 |
化学工业 | 3758篇 |
金属工艺 | 1287篇 |
机械仪表 | 459篇 |
建筑科学 | 841篇 |
矿业工程 | 383篇 |
能源动力 | 228篇 |
轻工业 | 5081篇 |
水利工程 | 178篇 |
石油天然气 | 726篇 |
武器工业 | 213篇 |
无线电 | 552篇 |
一般工业技术 | 961篇 |
冶金工业 | 456篇 |
原子能技术 | 70篇 |
自动化技术 | 361篇 |
出版年
2024年 | 103篇 |
2023年 | 289篇 |
2022年 | 610篇 |
2021年 | 626篇 |
2020年 | 521篇 |
2019年 | 407篇 |
2018年 | 347篇 |
2017年 | 412篇 |
2016年 | 432篇 |
2015年 | 425篇 |
2014年 | 630篇 |
2013年 | 714篇 |
2012年 | 976篇 |
2011年 | 1039篇 |
2010年 | 787篇 |
2009年 | 808篇 |
2008年 | 697篇 |
2007年 | 972篇 |
2006年 | 995篇 |
2005年 | 884篇 |
2004年 | 714篇 |
2003年 | 616篇 |
2002年 | 523篇 |
2001年 | 456篇 |
2000年 | 398篇 |
1999年 | 303篇 |
1998年 | 235篇 |
1997年 | 214篇 |
1996年 | 158篇 |
1995年 | 139篇 |
1994年 | 129篇 |
1993年 | 88篇 |
1992年 | 109篇 |
1991年 | 45篇 |
1990年 | 33篇 |
1989年 | 37篇 |
1988年 | 20篇 |
1987年 | 10篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1984年 | 7篇 |
1983年 | 10篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1977年 | 6篇 |
1976年 | 4篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
941.
Preparation of elevated-temperature intermetallic powders via a novel reaction ball milling technique 总被引:1,自引:0,他引:1
Chen Zhenhua Chen Ding Chen Gang Yan Hongge Huang Peiyun 《Journal of Alloys and Compounds》2004,370(1-2):43-46
The synthesis of elevated-temperature intermetallic powders was carried out using a novel solid–liquid reaction milling technique. As opposed to the conventional mechanical milling, the direct formation of nanometer-sized elevated-temperature intermetallic powders such as Fe1.3Sn and Fe3Sn2, at relatively low temperatures and an enhanced solid solubility extension of iron in lead were realized. 相似文献
942.
943.
矿物及化合物微波化学理论与应用研究进展述评 总被引:3,自引:0,他引:3
综述了矿物及化合物(有色金属矿物及原煤)的微波加热特性、微波化学机理及微波加热应用研究进展,评述了各类有色金属矿物微波化学理论研究的程度及应用前景。 相似文献
944.
Leafy spurge (Euphorbia esula) is an introduced forb that is invading western rangelands. Goats (Capra hircus) readily graze the plant, but cattle (Bos tarus) generally and sheep (Ovis aries) locally appear to develop conditioned flavor aversions to leafy spurge. They either avoid the plant entirely or graze it reluctantly. We hypothesized that: (1) a diterpene diester that can occur in leafy spurge was an aversive agent, and (2) diet selection differences among ruminant species may be partly a function of differential ruminai metabolism of aversive phytochemicals, and further that cattle and sheep may be reluctant to graze leafy spurge because their ruminai microbes do not metabolize certain leafy spurge chemicals as do ruminai microbes in goats. Sheep did not develop an aversion to a novel food when its consumption was followed by an intravenous injection of ingenol 3,20-dibenzoate (P=0.34). Sheep did develop an aversion to a novel food when its intake was followed by a dose of leafy spurge fermented with sheep ruminai digesta, but not when followed by a dose of leafy spurge fermented with goat ruminai digesta (P= 0.03). This suggests that goat ruminai microbes may modify leafy spurge such that it does not elicit an aversion in sheep.This research was supported in part by a grant from the Cooperative States Research Service (91-38300-6158). All experimental procedures with ruminants followed a protocol approved by the U.S. Sheep Experiment Station's Animal Care and Use Committee. Mention of trade names or companies does not constitute an implied warranty by USDA or the authors. 相似文献
945.
946.
ADSA Foundation Scholar Award: defining dairy flavors 总被引:4,自引:0,他引:4
Drake M 《Journal of dairy science》2004,87(4):777-784
Production and consumption of dairy foods continue to increase annually. Further, new ingredient applications for dairy foods continue to expand. With continued production and consumption, there is also increased competition. Increased competition exists regionally, nationally, and globally. Processors as well as product developers must find ways to maximize existing markets and expand into new markets. A consistent high quality product is necessary to maintain competitiveness. Although microbial safety and stability are key ways to define quality, flavor is one method of defining quality that is often assumed or overlooked. The aggressive and competitive nature of today's market demands more precise and powerful tools for defining flavor and flavor quality. Traditional as well as more recent methods for evaluating dairy flavor are reviewed. The application of defining sensory flavors to fundamental research on flavor chemistry, product understanding, and effective marketing is addressed. 相似文献
947.
The aroma of a deacidified cheese medium is the result of the overall perception of a large number of molecules belonging to different classes. The volatile compound composition of (60%) cheese medium (pH 5.8) deacidified by Debaryomyces hansenii (DCM(Dh)) was compared with the one deacidified by Kluyveromyces marxianus (DCM(Km)). It was determined by dynamic headspace extraction, followed by gas chromatography separation and quantification as well as by mass spectrometry identification. Whatever the media tested, a first class of volatile compounds can be represented by the ones not produced by any of the yeasts, but some of them are affected by K. marxianus or by D. hansenii. A second class of volatile compounds can be represented by the ones produced by K. marxianus, which were essentially esters. Their concentrations were generally higher than their thresholds, explaining the DCM(Km) global fruity odor. A third class can be represented by the ones generated by D. hansenii, which were essentially methyl ketones with fruity, floral (rose), moldy, cheesy, or wine odor plus 2-phenylethanol with a faded-rose odor. The impact of methyl ketones on the DCMDh global flavor was lower than the impact of 2-phenylethanol and even negligible. Therefore, the global faded-rose odor of D. hansenii DCM can be explained by a high concentration of 2-phenylethanol. 相似文献
948.
大民屯凹陷油品性质复杂,既有含蜡量小于20%的正常油,又富含蜡量>20%的特高蜡油。经过原油物性、甾萜等分析,认为高蜡油油源岩沉积环境为较正常油贫粘土、盐度相对较高、相对闭塞的弱还原环境,其母质应由陆源高等植物和低等水生生物共同构成,且经微生物改造较强烈。正常油油源以高等植物为主体,处于相对氧化且富粘土的沉积环境。通过精细油源对比认为:大民屯凹陷高蜡油主要来源于沙四下部的"油页岩",而正常油母质主要为沙四上部和沙三四的厚层泥岩。综合分析认为高蜡油成因主要受控于沉积母质和沉积环境的双重控制,且因整个大民屯凹陷较低的热演化程度而使高蜡油得以保存。 相似文献
949.
A method is described whereby the precursors of 2-trans-nonenal may be estimated in worts and beers. Treatment of malt grist or malt with a variety of polar substances is shown to reduce or eliminate the production of nonenal precursors during mashing. Beers made from worts so treated have enhanced flavour stability over those made conventionally. 相似文献
950.
K Badarinarayana S Srinivasa Murthy M.V Krishna Murthy 《International Journal of Refrigeration》1982,5(2):115-119
The concentration-enthalpy chart for R 21-DMF refrigerant-absorbent combination is presented for the temperature range of interest for solar-driven cooling applications. A thermodynamic analysis of the vapour absorption refrigeration system (VARS) working with R 21-DMF is made to study the theoretical performance characteristics. At evaporator temperatures lower than about 0°C, R 21-DMF has a distinct advantage over R 22-DMF systems in being able to operate at lower generator temperatures. Also R 21-DMF systems perform better than R 22-DMETEG systems. 相似文献