全文获取类型
收费全文 | 127209篇 |
免费 | 2226篇 |
国内免费 | 456篇 |
专业分类
电工技术 | 1294篇 |
综合类 | 2344篇 |
化学工业 | 19589篇 |
金属工艺 | 5417篇 |
机械仪表 | 3783篇 |
建筑科学 | 4122篇 |
矿业工程 | 926篇 |
能源动力 | 2182篇 |
轻工业 | 7178篇 |
水利工程 | 1725篇 |
石油天然气 | 614篇 |
无线电 | 12535篇 |
一般工业技术 | 22374篇 |
冶金工业 | 14089篇 |
原子能技术 | 657篇 |
自动化技术 | 31062篇 |
出版年
2022年 | 390篇 |
2021年 | 669篇 |
2020年 | 397篇 |
2019年 | 546篇 |
2018年 | 14960篇 |
2017年 | 13829篇 |
2016年 | 10566篇 |
2015年 | 1229篇 |
2014年 | 1201篇 |
2013年 | 2467篇 |
2012年 | 4665篇 |
2011年 | 11326篇 |
2010年 | 9661篇 |
2009年 | 7027篇 |
2008年 | 8447篇 |
2007年 | 9304篇 |
2006年 | 1629篇 |
2005年 | 2591篇 |
2004年 | 2324篇 |
2003年 | 2315篇 |
2002年 | 1643篇 |
2001年 | 918篇 |
2000年 | 879篇 |
1999年 | 937篇 |
1998年 | 2422篇 |
1997年 | 1628篇 |
1996年 | 1306篇 |
1995年 | 932篇 |
1994年 | 925篇 |
1993年 | 901篇 |
1992年 | 642篇 |
1991年 | 494篇 |
1990年 | 601篇 |
1989年 | 577篇 |
1988年 | 538篇 |
1987年 | 532篇 |
1986年 | 476篇 |
1985年 | 620篇 |
1984年 | 601篇 |
1983年 | 496篇 |
1982年 | 481篇 |
1981年 | 407篇 |
1980年 | 382篇 |
1979年 | 448篇 |
1978年 | 377篇 |
1977年 | 371篇 |
1976年 | 364篇 |
1975年 | 321篇 |
1974年 | 288篇 |
1973年 | 270篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
Imre T.G. Cronje W.A. van Wyk J.D. Ferreira J.A. 《Industry Applications, IEEE Transactions on》2002,38(6):1613-1621
This paper covers the experimental investigation and theoretical calculation of losses in a planar inductor under load. Finite-element software is used to perform the loss calculations. Thermally controlled experiments are performed for a range of frequencies to validate the corresponding finite-element method loss calculations. The thermal dependence of the loss mechanisms is also considered. 相似文献
102.
103.
Pure cardiolipins (1,3-diphosphatidylglycerol) were prepared from mitochondria of heart, liver and kidney from 21-day-old
male Wistar rats and submitted toNaja naja venom phospholipase A2 (EC 3.1.1.4) action. Incubation conditions were controlled carefully, and a complete hydrolysis of cardiolipin to lysocardiolipin
{di [1 (1″) acylsn-glycero-3-phosphoryl] 1′, 3′-sn-glycerol} and fatty acids from positions 2 (2″) was obtained in less than two hr practically without side reactions. Cardiolipins
from the three organs contained low levels of saturated fatty acids; stearic acid accounted for 0.4–0.7% and palmitic acid
for 1.4–3.5% of total fatty acids. These percentages apparently depended on the organ. In all three cases, linoleic acid was
the major component, but its percentage varied from 62–78% of total fatty acids. Acyl chains linked to positions 1 (1″) of
all three cardiolipin preparations exhibited a similar pattern; they were composed of linoleic acid for 85–89%. This fatty
acid also was the main component esterified at position 2 (2″), but its percentage was much more variable: from 39.8% in heart
to 51.2% in kidney and 67.8% in liver mitochondria. The remaining acids comprised octadecenoic and polyunsaturated fatty acids
with more than 18 carbon atoms in different proportions. As opposed to other phospholipids,cis-vaccenic acid, and not oleic acid, was the main octadecenoic acid present in cardiolipins.
Octadecenoic acids were nine- to 10-fold more concentrated at positions 2 (2″) than at positions 1 (1″). The percentage ofcis-vaccenic acid was four- to five-fold higher than that of oleic acid at positions 2 (2″), whereas oleic acid dominated at
positions 1 (1″). From results presented in this study and selected literature data, it may be concluded that fatty acids
are asymmetrically distributed in cardiolipins of different origins, with linoleic acid showing a definite preference for
position 1 (1″). 相似文献
104.
Joseph A Wehrmeyer Zhongxian ChengDavid M Mosbacher Robert W PitzRobin Osborne 《Combustion and Flame》2002,128(3):232-241
Several opposed jet flames, produced by a lean H2-air jet opposing a rich or lean C3H8-air jet, are investigated. Spontaneous Raman spectroscopy is used for major species concentration and temperature measurements along the opposed jet centerline. The hot products of the H2-air flame simulate the burnt gases of strong-burning near-stoichiometric reactants as they impinge upon a weak-burning lean or rich hydrocarbon-fueled reactant mix, a situation encountered in stratified charge operation of direct injection spark ignition engines. In addition the H2-air flame hot products facilitate experimental data interpretation through the absence of carbon-bearing species. Good agreement between numerical and experimental data are obtained for a rich (equivalence ratio, φ = 1.25) C3H8-air jet versus a lean (φ = 0.4) H2-air jet. Two lean C3H8-air jets (φ = 0.64 or 0.60), versus the φ = 0.4 H2-air jet, are also investigated. For both of these flames, the amount of CO2 production strongly depends upon φ, with the φ = 0.64 flame having a peak CO2 mole fraction an order of magnitude higher than for the φ = 0.60 flame, and the C3H8 flames burning either as a normal flame (high CO2) or as a “negative flame speed” flame producing little CO2 and then only through diffusion of C3H8 into the hot products jet. The numerically predicted and experimental CO2 profiles agree well for the positive flame speed flame, but the large discrepancy between predicted and measured peak CO2 in the negative flame speed flame suggests modeling improvements are needed for this type of flame. 相似文献
105.
Less may not be more,but it still counts: The state of social capital in Yeoville,Johannesburg 总被引:2,自引:2,他引:0
Kirsten Harrison 《Urban Forum》2002,13(1):67-84
106.
107.
Yanqiu Shao Jiqing Han Ting Liu Yongzhen Zhao 《International Journal of Speech Technology》2007,10(1):45-55
In real speech, not like lexical words (LWs), prosodic words (PWs) are basic rhythmic units. The naturalness of a Text-to-Speech
(TTS) system is directly influenced by the segmentation of the PWs. Most of the PWs are the combination of several LWs. In
this paper, three Lexical Combination Models are proposed to combine LWs into PWs, including a Directed Acyclic Graph Model,
a Segmentation Model and a Markov Model (MM). To cope with the situation where some long LWs should be segmented into two
or more PWs, a Lexical Split Model (LSM) is applied to the long LWs. Experimental results prove that relatively constant results
with various training data can be obtained from a MM. The Transformation-Based Error Driven Learning (TBED) algorithm, for
its high performance of individual property, is applied in combination with the MM to improve the precision of PW segmentation.
Experiments show that among the three proposed models, the MM combined with TBED and LSM, leads to the best performance, in
which a precision of 93.00% and a recall of 93.23% are achieved. The perception test indicates that by using PWs as the lowest
prosodic units a speech sounds more natural and acceptable than by using LWs.
This paper is supported by NSFC Project (60503071); 973 Natural Basic Research Program of China (2004CB318102); Postdoctor
Science Foundation of P. R. China (20070420275). 相似文献
108.
The physical gestures that operate music instruments are responsible for the qualities of the sound being produced in a performance.
Gestural information is thereby crucial for a model of music performance, paired with a model of sound synthesis where this
information is applied. The highly constrained nature of performers gestures makes this task suitable to be modeled via a
constraint-based approach, coupled with a strategy aimed at maximizing the gestural comfort of performers. We illustrate the
problem representation, the search strategy and a validation of the model against human performance. 相似文献
109.
Approximately 80% of the international transport of goods is carried on by means of ships. A large portion of the transport
capacity is represented by Roll-on-Roll-off (RoRo) ships. Especially in Europe this is a relevant potential for the RoRo segment.
Consequently, the design and construction of RoRo ships plays an increasing role for German shipyards and their suppliers.
In order to make the loading and unloading procedure of trailer economically more competitive, ship owners would like to improve
the lashing of trailers on the ship. On the basis of a multibody system formalism, a software tool has been developed which
allows for an optimization of the loading of trailers on RoRo ships.
Commemorative Contribution. 相似文献
110.
Structural engineers use design codes formulated to consider uncertainty for both reinforced concrete and structural steel
design. For a simple one-bay structural steel frame, we survey typical uncertainties and compute an interval solution for
displacements and forces. The naive solutions have large over-estimations, so we explore the Mullen-Muhanna assembly strategy,
scaling, and constraint propagation to achieve tight enclosures of the true ranges for displacements and forces in a fraction
of the CPU time typically used for simulations. That we compute tight enclosures, even for large parameter uncertainties used
in practice, suggests the promise of interval methods for much larger structures. 相似文献