全文获取类型
收费全文 | 40585篇 |
免费 | 6120篇 |
国内免费 | 2433篇 |
专业分类
电工技术 | 3218篇 |
技术理论 | 4篇 |
综合类 | 3860篇 |
化学工业 | 4853篇 |
金属工艺 | 1607篇 |
机械仪表 | 2566篇 |
建筑科学 | 4087篇 |
矿业工程 | 2279篇 |
能源动力 | 2400篇 |
轻工业 | 6909篇 |
水利工程 | 1942篇 |
石油天然气 | 2734篇 |
武器工业 | 508篇 |
无线电 | 2827篇 |
一般工业技术 | 3655篇 |
冶金工业 | 2053篇 |
原子能技术 | 387篇 |
自动化技术 | 3249篇 |
出版年
2024年 | 417篇 |
2023年 | 1189篇 |
2022年 | 1960篇 |
2021年 | 2264篇 |
2020年 | 2305篇 |
2019年 | 1822篇 |
2018年 | 1607篇 |
2017年 | 1825篇 |
2016年 | 1857篇 |
2015年 | 1897篇 |
2014年 | 2672篇 |
2013年 | 2524篇 |
2012年 | 2926篇 |
2011年 | 3111篇 |
2010年 | 2262篇 |
2009年 | 2237篇 |
2008年 | 1881篇 |
2007年 | 2272篇 |
2006年 | 1943篇 |
2005年 | 1684篇 |
2004年 | 1415篇 |
2003年 | 1216篇 |
2002年 | 974篇 |
2001年 | 800篇 |
2000年 | 748篇 |
1999年 | 653篇 |
1998年 | 451篇 |
1997年 | 337篇 |
1996年 | 336篇 |
1995年 | 301篇 |
1994年 | 254篇 |
1993年 | 196篇 |
1992年 | 139篇 |
1991年 | 112篇 |
1990年 | 107篇 |
1989年 | 72篇 |
1988年 | 54篇 |
1987年 | 38篇 |
1986年 | 28篇 |
1985年 | 24篇 |
1984年 | 24篇 |
1983年 | 18篇 |
1982年 | 22篇 |
1980年 | 20篇 |
1979年 | 9篇 |
1964年 | 15篇 |
1962年 | 7篇 |
1961年 | 9篇 |
1959年 | 13篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
WANG Jiqing 《声学技术》2004,23(Z3)
This paper gives an overview of the research at Institute of Acoustics, Tongji University, on functional absorbers and experience acquired in practical applications over the past three decades. Experiments and analysis of the absorption characteristics of three different geometrical forms of functional absorbers, i.e., panels, cubes and tubes, were conducted with different arrangements. The resulting esthetical effects are illustrated with pictures. Several non-fiber materials are used to compose functional absorbers with advantages both in acoustic properties and in architectural features. Cost effectiveness analysis is also given in order to provide design guidelines. 相似文献
62.
63.
Effect of the absence of lipoxygenase isoenzymes on the storage characteristics of rice grains 总被引:1,自引:0,他引:1
Three varieties of paddy rice with and three varieties without lipoxygenase (LOX) isoenzymes were stored at room temperature, in dark conditions for 42 months. Insect damage and viability were investigated during that time. Varieties without LOX-1,2 and their offspring were screened with a rapid method of estimating LOX isoenzymes, and subjected to an accelerated-ageing experiment. The results indicated that in varieties without LOX-1,2, after long storage, rice quality was normal, but for varieties with LOX-1,2, rice quality deteriorated. With increase of storage time, the germination rate of the seed of most varieties decreased greatly except for varieties without LOX-1,2 where there was almost no change in the germination rate. In varieties without LOX-1,2 and their offspring, after an accelerated ageing experiment the germination rate of some varieties changed slowly, but with others, the germination rate changed quickly. This indicated that a definitive factor, which influenced the life of seeds, may be the loss of LOX-1,2. During storage, there was also a significant difference in the degree of insect damage. In varieties without LOX-3 insect damage was lower, but in varieties with LOX-3 insect damage was higher. Therefore, the absence of LOX-3 may be very important in insect resistance in rice grain. 相似文献
64.
埕岛油田东部斜坡带下第三系油藏以三角洲、浊积扇砂体隐蔽油气藏为主,储层埋藏深、厚度变化大,油气成藏复杂。通过对该带的沉积特征、沉积体系和沉积物源的研究,指出其东下段砂体的分布主要受物源和沉积相带两方面控制,砂体只有在有效圈闭情况下才能成藏,并且从构造上总结了三种油藏类型。最后指出该带下一步勘探重点是沿主物源方向展布的、成藏条件良好的各种砂体。 相似文献
65.
The radical copolymerization of acyclic terpene namely geraniol [GER] with acrylonitrile [AN] in DMF at (70 ± 0.1)°C for 1 h, using benzoylperoxide (BPO) as an initiator has been carried out under inert atmosphere of nitrogen. The kinetic expression for reaction is Rp ∝ [BPO]0.5 [AN]1.0 [GER]1.0. The IR spectrum of the copolymer shows bands at 3432 and at 2244 cm?1 due to ? OH group of GER and ? CN group of AN, respectively. The 13C‐NMR spectrum shows peaks at 73–75 δ ppm and 116–120 δ ppm due to ? OH group of GER and ? CN group of AN, respectively. The thermogravimetric analysis and differential scanning calorimetry study shows that copolymer is thermally stable up to 407°C and has glass transition temperatures (Tg) 56°C. The reactivity ratios r1 (AN) and r2 (GER) have been calculated as 0.05 and 0.005, respectively. The Alfrey‐Price Q‐e parameter for GER has been calculated as 0.094 and ?2.0, respectively. The molecular weights of the copolymers have been evaluated by gel‐permeation chromatography. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
66.
O. L. Perevozchikova V. G. Tul'chinskii A. V. Kharchenko 《Cybernetics and Systems Analysis》2003,39(4):501-508
A statistical learning model is considered within the framework of the theory of uniform convergence of frequencies of errors in the case where the convergence is violated as a result of increasing the informativeness of training examples. Drawbacks of nonconstructive refinements of Vapnik-Chervonenkis estimates based on an assumption on the distribution law of violations are shown. A new approach to obtaining constructive estimates for mass data sets is proposed. 相似文献
67.
L. F. Fitzgerald, C. L. Hulin. and F. Drasgow (1995) proposed that victim characteristics, such as race, might moderate the relationships between sexual harassment and its job, psychological, and health status outcomes. This study describes 2 theoretical positions, tokenism and double jeopardy, that could account for this possible moderation by race, as well as the alternative view that no moderating effects exist. The effects of race are empirically examined through simultaneous path analysis. Results indicate that whereas, mean levels of harassment differ across race, the phenomenon of sexual harassment unfolds similarly across races; race is not a moderator of the relationships between sexual harassment and the variables proposed as its antecedents and outcomes. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
68.
Summary Recent progress in the modelling of exchanged Cu sites and their interactions with small molecules, based on DFT cluster calculations, is briefly reviewed. 相似文献
69.
东海西湖凹陷探井钻井完井液技术 总被引:2,自引:2,他引:0
介绍了东海西湖凹陷的储层特征。在分析探井储层损害原因的基础上,提出了优化的海水钻井完井液体系。两口井应用表明,储层保护效果明显。 相似文献
70.
本文报导了采用一种新型高温陶瓷发热体高温管状炉,通以氩气保护,测量WRe合金丝的电阻-温度(1600℃)特性试验方法,该方法较真空炉简便、实用且试验费用低而准确,测量数据与美国研究报导一致。 相似文献