全文获取类型
收费全文 | 20350篇 |
免费 | 2000篇 |
国内免费 | 1350篇 |
专业分类
电工技术 | 818篇 |
综合类 | 3033篇 |
化学工业 | 4319篇 |
金属工艺 | 2151篇 |
机械仪表 | 842篇 |
建筑科学 | 1242篇 |
矿业工程 | 598篇 |
能源动力 | 702篇 |
轻工业 | 1013篇 |
水利工程 | 385篇 |
石油天然气 | 854篇 |
武器工业 | 127篇 |
无线电 | 1117篇 |
一般工业技术 | 2748篇 |
冶金工业 | 1247篇 |
原子能技术 | 232篇 |
自动化技术 | 2272篇 |
出版年
2024年 | 43篇 |
2023年 | 235篇 |
2022年 | 365篇 |
2021年 | 539篇 |
2020年 | 560篇 |
2019年 | 540篇 |
2018年 | 465篇 |
2017年 | 620篇 |
2016年 | 680篇 |
2015年 | 694篇 |
2014年 | 1084篇 |
2013年 | 1282篇 |
2012年 | 1459篇 |
2011年 | 1543篇 |
2010年 | 1112篇 |
2009年 | 1213篇 |
2008年 | 1097篇 |
2007年 | 1308篇 |
2006年 | 1268篇 |
2005年 | 1103篇 |
2004年 | 960篇 |
2003年 | 856篇 |
2002年 | 716篇 |
2001年 | 585篇 |
2000年 | 517篇 |
1999年 | 447篇 |
1998年 | 338篇 |
1997年 | 326篇 |
1996年 | 285篇 |
1995年 | 263篇 |
1994年 | 260篇 |
1993年 | 177篇 |
1992年 | 158篇 |
1991年 | 147篇 |
1990年 | 111篇 |
1989年 | 92篇 |
1988年 | 68篇 |
1987年 | 37篇 |
1986年 | 19篇 |
1985年 | 21篇 |
1984年 | 25篇 |
1983年 | 15篇 |
1982年 | 22篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 9篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1959年 | 2篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
51.
Evaluation of the Hubbell integral for an omnidirectional detector response to a rectangular plaque gamma emitting radiation source using a different numerical computation method on a personal computer was made. For a plaque consisting of several strip gamma emitters, exposure rates at different positions above the source were calculated using 'exact' evaluation and an approximate method. Optimization method is used to find source activity of each strip, so as to acquire desirable dose uniformity of the irradiated products. In uses of the Hubbell integral, by introducing appropriate programming, computation time can be saved. 相似文献
52.
The high-temperature crystallization of poly(p-phenylene terephthalamide) (PPTA) from dilute organic solutions was achieved through the introduction of a non-solvent, or precipitating agent, at the desired crystallization temperature. The morphology and crystal structure were examined for crystals produced from PPTA polymer with two different molecular weights (Mw = 46000 and 3430 g mol−1), using transmission electron microscopy. For the high-molecular-weight polymer, ribbon-like crystals were produced, while the low-molecular-weight polymer yielded small needles or platelets. In both cases, electron diffraction showed that the Northolt allomorph was obtained. For the high-molecular-weight polymer, the molecular axes were parallel to the ribbon axes in a chain-extended type structure. A hypothesis for the orientation of the low-molecular-weight PPTA in the small platelets, is also given. 相似文献
53.
54.
55.
We describe a formal language/notation for DNA molecules that may contain nicks and gaps. The elements of the language, DNA
expressions, denote formal DNA molecules. Different DNA expressions may denote the same formal DNA molecule. We analyse the
shortest DNA expressions denoting a given formal DNA molecule. We determine lower bounds on their lengths and explain how
we construct these minimal DNA expressions. 相似文献
56.
在氧化铝生产过程中,熟料折合比是烧结法一项重要的综合性指标,本文通过对熟料折合比的定义、计算公式的剖析,分析了生产过程中影响熟料折合比的主要因素,对有效降低熟料折合比的措施进行了探讨。 相似文献
57.
The viscometric, turbidimetric and potentiometric properties of copolymers of acrylamide (AM) with 2-acrylamido-2-methylpropanedimethylammonium chloride (AMPDAC) were studied in aqueous solutions. The AMPDAC polymers exhibit poor salt tolerance and large, negative viscosity/temperature coefficients. Furthermore, the polymers were found to be sensitive to changes in pH. The AMPDAC polymers undergo phase separation in the presence of dianions as a function of temperature and AMPDAC composition. 相似文献
58.
Songping Wu 《Materials Letters》2007,61(16):3526-3530
In this paper, non-agglomerated monodispersed ultra-fine copper metallic powders have been synthesized with chemical reduction method. Fine lead-free glass powders were also prepared by solid synthesis process. Thick film paste prepared by above-mentioned copper metallic powders and lead-free glass powders was applied as conductive paste of MLCC. Mixture of glass and zinc oxide give the thick film a high adhesion strength which is attributed to the rough interface from interfacial reaction between glass and chip, and a good densification. Diffusion of metal between copper thick film and nickel thick film is clear. Ni-Cu solid solution appears under high temperature firing. 相似文献
59.
外转子电机关键技术及解决措施 总被引:1,自引:0,他引:1
对外转子电机的关键技术和主要工艺问题进行了探讨分析,并提出了解决措施。 相似文献
60.