全文获取类型
收费全文 | 7356篇 |
免费 | 84篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 44篇 |
综合类 | 2篇 |
化学工业 | 721篇 |
金属工艺 | 58篇 |
机械仪表 | 59篇 |
建筑科学 | 53篇 |
矿业工程 | 3篇 |
能源动力 | 91篇 |
轻工业 | 204篇 |
水利工程 | 12篇 |
石油天然气 | 7篇 |
无线电 | 302篇 |
一般工业技术 | 528篇 |
冶金工业 | 5030篇 |
原子能技术 | 27篇 |
自动化技术 | 308篇 |
出版年
2023年 | 27篇 |
2022年 | 61篇 |
2021年 | 76篇 |
2020年 | 70篇 |
2019年 | 66篇 |
2018年 | 85篇 |
2017年 | 60篇 |
2016年 | 62篇 |
2015年 | 57篇 |
2014年 | 84篇 |
2013年 | 176篇 |
2012年 | 108篇 |
2011年 | 108篇 |
2010年 | 75篇 |
2009年 | 89篇 |
2008年 | 84篇 |
2007年 | 74篇 |
2006年 | 86篇 |
2005年 | 58篇 |
2004年 | 44篇 |
2003年 | 53篇 |
2002年 | 45篇 |
2001年 | 22篇 |
2000年 | 43篇 |
1999年 | 190篇 |
1998年 | 1587篇 |
1997年 | 981篇 |
1996年 | 589篇 |
1995年 | 327篇 |
1994年 | 313篇 |
1993年 | 335篇 |
1992年 | 73篇 |
1991年 | 80篇 |
1990年 | 95篇 |
1989年 | 103篇 |
1988年 | 101篇 |
1987年 | 93篇 |
1986年 | 71篇 |
1985年 | 57篇 |
1984年 | 21篇 |
1983年 | 26篇 |
1982年 | 42篇 |
1981年 | 60篇 |
1980年 | 70篇 |
1979年 | 23篇 |
1978年 | 24篇 |
1977年 | 121篇 |
1976年 | 243篇 |
1975年 | 16篇 |
1973年 | 24篇 |
排序方式: 共有7449条查询结果,搜索用时 15 毫秒
1.
2.
Patel Sapna Kumar Dushyant Chaurasiya Nitesh Kumar Tripathi Shweta 《Semiconductors》2019,53(13):1797-1803
Semiconductors - In the present paper, analytical modeling of surface potential and drain current for hetero-dielectric double gate tunnel FET (HDG-TFET) has been done. The two dimensional (2D)... 相似文献
3.
Parsania P. H. Sankhavara Dharmesh B. Chopda Jalpa Patel Jignesh P. 《Polymer Bulletin》2020,77(6):3111-3128
Polymer Bulletin - Jute and glass composites of epoxy resin of (2E, 6E)-bis(4-hydroxybenzylidene)cyclohexanone (EBHBC) were prepared by compressing molding technique using three different hardeners... 相似文献
4.
TC Cope AJ Sokoloff SM Dacko R Huot E Feingold 《Canadian Metallurgical Quarterly》1997,78(6):3077-3082
To further test the hypothesis that some fixed property of motoneurons determines their recruitment order, we quantified the variation in force threshold (FT) for motoneurons recruited in muscle stretch reflexes in the decerebrate cat. Motor axons supplying the medial gastrocnemius (MG) muscle were penetrated with micropipettes and physiological properties of the motoneuron and its muscle fibers, i.e., the motor unit, were measured. FT, defined as the amount of MG force produced when the isolated motor unit was recruited, was measured from 20 to 93 consecutive stretch trials for 29 motor units. Trials were selected for limited variation in base force and rate of rise of force, which have been shown to covary with FT, and in peak stretch force, which gives some index of motor-pool excitability. Under these restricted conditions, large variation in FT would have been inconsistent with the hypothesis. Analysis of the variation in FT employed the coefficient of variation (CV), because of the tendency for FT variance and mean to increase together. We found that CV was distributed with a median value of 10% and with only 2 of 29 units exceeding 36%. Some of this variation was associated with measurement error and with intertrial fluctuations in base, peak, and the rate of change of muscle force. CV was not significantly correlated with motor-unit axonal conduction velocity, contraction time, or force. In three cases FT was measured simultaneously from two motor units in the same stretch trials. Changes in recruitment order were rarely observed (5 of 121 stretch trials), even when FT ranges for units in a pair overlapped. We suggest that the large variation in recruitment threshold observed in some earlier studies resulted not from wide variation in the recruitment ranking of motoneurons within one muscle, but rather from variation in the relative activity of different pools of motoneurons. Our findings are consistent with the hypothesis that recruitment order is determined by some fixed property of alpha-motoneurons and/or by some unvarying combination of presynaptic inputs that fluctuate in parallel. 相似文献
5.
In summary, recent literature indicates that the complications of chronic otitis media have been decreasing. However, even with the advent of modern and more powerful antimicrobials and aggressive surgical eradication of disease, the morbidity and mortality are still high. Some complications may initially be quite obvious and some complications may be quite subtle. Therefore, the most important tools in making early diagnosis are careful history and physical examination, and a high index of suspicion for impending complications. 相似文献
6.
7.
8.
Assuming that the chemical reactions used to synthesize a combinatorial library member are successful, then knowledge of the specific reaction sequence is equivalent to knowing the member's chemical identity. Because the determination of chemical identity is typically not automatable and requires a substantial amount of material, schemes that encode a member's reaction history onto the reaction platform are of value. The primary benefits of encoding are relational nomenclature (all methods) and automated handling (some methods). Encoding methods evaluated to date are spatial, graphical, chemical, spectrometric, electronic, and physical. 相似文献
9.
IG Sumner A Vaughan R Eisenthal RW Pickersgill AJ Owen PW Goodenough 《Canadian Metallurgical Quarterly》1993,1164(3):243-251
Papaya proteinase omega (pp omega) has been purified from dried latex both by immunoaffinity and traditional methods. Kinetic analysis revealed that (1), the pp omega-catalysed hydrolysis of N-benzoyl-L-arginine p-nitroanilide (BApNA) has a lower specificity (kcat/Km) than the same reaction catalysed by papain; (2), the pp omega-catalysed hydrolysis of a tripeptide substrate having phenylalanine at the second position (S2-site) showed a more similar specificity to that catalysed by papain; (3), the significant difference between the two enzymes is that steady state kinetics with both L-BApNA and a tripeptide enables the identification in pp omega of other ionizations affecting binding. The active sites of papain and pp omega can therefore be distinguished by pH-dependence of kcat/Km. 相似文献
10.
We describe a case of a hyperplastic anterior choroidal artery (AChA) with double persistent anastomotic channels. This hyperplastic AChA, which was detected at vertebral angiography, is different from previously reported cases, because it has an unusual, secondary anastomotic channel. 相似文献