全文获取类型
收费全文 | 13469篇 |
免费 | 985篇 |
国内免费 | 48篇 |
专业分类
电工技术 | 263篇 |
综合类 | 69篇 |
化学工业 | 3482篇 |
金属工艺 | 359篇 |
机械仪表 | 458篇 |
建筑科学 | 426篇 |
矿业工程 | 42篇 |
能源动力 | 559篇 |
轻工业 | 2393篇 |
水利工程 | 131篇 |
石油天然气 | 87篇 |
无线电 | 913篇 |
一般工业技术 | 2164篇 |
冶金工业 | 1217篇 |
原子能技术 | 92篇 |
自动化技术 | 1847篇 |
出版年
2024年 | 45篇 |
2023年 | 154篇 |
2022年 | 369篇 |
2021年 | 614篇 |
2020年 | 435篇 |
2019年 | 522篇 |
2018年 | 550篇 |
2017年 | 580篇 |
2016年 | 560篇 |
2015年 | 409篇 |
2014年 | 599篇 |
2013年 | 1035篇 |
2012年 | 842篇 |
2011年 | 939篇 |
2010年 | 716篇 |
2009年 | 742篇 |
2008年 | 619篇 |
2007年 | 571篇 |
2006年 | 480篇 |
2005年 | 336篇 |
2004年 | 312篇 |
2003年 | 353篇 |
2002年 | 337篇 |
2001年 | 266篇 |
2000年 | 195篇 |
1999年 | 177篇 |
1998年 | 353篇 |
1997年 | 273篇 |
1996年 | 203篇 |
1995年 | 136篇 |
1994年 | 107篇 |
1993年 | 116篇 |
1992年 | 54篇 |
1991年 | 52篇 |
1990年 | 58篇 |
1989年 | 39篇 |
1988年 | 63篇 |
1987年 | 27篇 |
1986年 | 39篇 |
1985年 | 29篇 |
1984年 | 21篇 |
1983年 | 19篇 |
1982年 | 12篇 |
1981年 | 13篇 |
1980年 | 12篇 |
1978年 | 12篇 |
1977年 | 16篇 |
1976年 | 35篇 |
1975年 | 11篇 |
1974年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Eduardo Freire Teodiano Bastos-Filho Mário Sarcinelli-Filho Ricardo Carelli 《IEEE transactions on systems, man, and cybernetics. Part B, Cybernetics》2004,34(1):419-429
This paper proposes an alternative approach to address the problem of coordinating behaviors in mobile robot navigation: fusion of control signals. Such approach is based on a set of two decentralized information filters, which accomplish the data fusion involved. Besides these two fusion engines, control architectures designed according to this approach also embed a set of different controllers that generate reference signals for the robot linear and angular speeds. Such signals are delivered to the two decentralized information filters, which estimate suitable overall reference signals for the robot linear and angular speeds, respectively. Thus, the background for designing such control architectures is provided by the nonlinear systems theory, which makes this approach different from any other yet proposed. This background also allows checking control architectures designed according to the proposed approach for stability. Such analysis is carried out in the paper, and shows that the robot always reaches its final destination, in spite of either obstacles along its path or the environment layout. As an example, a control architecture is designed to guide a mobile robot in an experiment, whose results allows checking the good performance of the control architecture and validating the design approach proposed as well. 相似文献
42.
Recently, preemption techniques have attracted considerable attention as a means to provide differentiated quality of service
in optical burst switching (OBS) networks. This paper is focused on the analysis of preemption probabilities for bursts within
the same priority class. As proposed by Vokkarane and Jue ((2003)* IEEE J Select Areas Commun 21(7): 1198–1209) an incoming
burst will preempt the burst in service, within the same priority class, if the residual length of the burst in service is
smaller than the incoming burst length. For a general case with wavelength conversion, the preemption probability of contending
bursts with a generic service distribution, not necessarily exponential, is analyzed. First, we show that the size distribution
for the preempting bursts is shifted to larger values, in comparison to the original burst size distribution. Second, we obtain
an upper and lower bound for the preemption probability. Finally, the asymptotic behavior of the OBS switch is analyzed showing
that preemption will always occur for a very large number of wavelengths. 相似文献
43.
Marcia Cristina Kaezer Fran a Rosane Aguiar da Silva San Gil Jean-Guillaume Eon 《Catalysis Today》2003,78(1-4):105-115
γ-Al2O3 supported vanadium oxides were modified by tungsten and molybdenum oxides in order to improve dispersion and selectivity towards olefins in propane oxidative dehydrogenation (ODH). Both vanadium–tungsten and vanadium–molybdenum catalysts were obtained by adsorption of mixed isopolyanions (VW5O195−, V2W4O194−, VMo5O195− and V2Mo4O194−) from aqueous solutions. The isopolyanion solutions were characterized by UV-Vis and 51V NMR spectroscopy. Vanadium, vanadium–tungsten and vanadium–molybdenum precursors and catalysts were also characterized by UV-Vis (diffuse reflectance) and solid state 51V NMR spectroscopy. An improved selectivity to propene in the presence of tungsten and molybdenum in VOx/γ-Al2O3 was observed and attributed to dilution of vanadium by tungsten or molybdenum oxides on the γ-Al2O3 surface. 相似文献
44.
Oliveira F.D.C. Passos C.A.C. Fardin J.F. Simonetti D.S.L. Passamai J.L. Jr. Belich H. de Medeiros E.F. Orlando M.T.D. Ferreira M.M. Jr. 《Applied Superconductivity, IEEE Transactions on》2006,16(1):15-20
Hg/sub 0.82/Re/sub 0.18/Ba/sub 2/Ca/sub 2/Cu/sub 3/O/sub 8+/spl delta// polycrystalline samples were successfully obtained by using different oxygen partial pressure in the annealing treatment of the precursor ceramic. The doping state was confirmed by X-ray powder diffraction pattern analysis and by observing distinct thermopower values at room temperature. Also, the intergrain regions have shown an improvement in the critical current density when using the precursor preparation with 10% O/sub 2/ and 90% Ar (optimal doped). The optimal doped sample has presented the highest /spl alpha/ exponent of the J/sub c//spl prop/[1-(T/T/sub c/)/sup 2/]/sup /spl alpha// dependence. For the case of (Hg,Re)-1223 polycrystalline superconductor applications, the /spl alpha/ exponent can be used as a junction quality parameter. 相似文献
45.
46.
47.
A Abeliovich C Chen Y Goda AJ Silva CF Stevens S Tonegawa 《Canadian Metallurgical Quarterly》1993,75(7):1253-1262
Calcium-phospholipid-dependent protein kinase (PKC) has long been suggested to play an important role in modulating synaptic efficacy. We have created a strain of mice that lacks the gamma subtype of PKC to evaluate the significance of this brain-specific PKC isozyme in synaptic plasticity. Mutant mice are viable, develop normally, and have synaptic transmission that is indistinguishable from wild-type mice. Long-term potentiation (LTP), however, is greatly diminished in mutant animals, while two other forms of synaptic plasticity, long-term depression and paired-pulse facilitation, are normal. Surprisingly, when tetanus to evoke LTP was preceded by a low frequency stimulation, mutant animals displayed apparently normal LTP. We propose that PKC gamma is not part of the molecular machinery that produces LTP but is a key regulatory component. 相似文献
48.
49.
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
50.