全文获取类型
收费全文 | 44886篇 |
免费 | 5540篇 |
国内免费 | 4063篇 |
专业分类
电工技术 | 4990篇 |
技术理论 | 2篇 |
综合类 | 5924篇 |
化学工业 | 4296篇 |
金属工艺 | 1041篇 |
机械仪表 | 2355篇 |
建筑科学 | 5048篇 |
矿业工程 | 1261篇 |
能源动力 | 1464篇 |
轻工业 | 2062篇 |
水利工程 | 1550篇 |
石油天然气 | 2798篇 |
武器工业 | 456篇 |
无线电 | 4680篇 |
一般工业技术 | 5500篇 |
冶金工业 | 1454篇 |
原子能技术 | 757篇 |
自动化技术 | 8851篇 |
出版年
2024年 | 210篇 |
2023年 | 615篇 |
2022年 | 1245篇 |
2021年 | 1468篇 |
2020年 | 1550篇 |
2019年 | 1305篇 |
2018年 | 1304篇 |
2017年 | 1601篇 |
2016年 | 1846篇 |
2015年 | 1816篇 |
2014年 | 2575篇 |
2013年 | 3238篇 |
2012年 | 3275篇 |
2011年 | 3472篇 |
2010年 | 2613篇 |
2009年 | 2761篇 |
2008年 | 2676篇 |
2007年 | 3141篇 |
2006年 | 2720篇 |
2005年 | 2404篇 |
2004年 | 1943篇 |
2003年 | 1658篇 |
2002年 | 1442篇 |
2001年 | 1304篇 |
2000年 | 1132篇 |
1999年 | 918篇 |
1998年 | 737篇 |
1997年 | 670篇 |
1996年 | 558篇 |
1995年 | 460篇 |
1994年 | 374篇 |
1993年 | 263篇 |
1992年 | 232篇 |
1991年 | 180篇 |
1990年 | 165篇 |
1989年 | 126篇 |
1988年 | 113篇 |
1987年 | 48篇 |
1986年 | 37篇 |
1985年 | 26篇 |
1984年 | 44篇 |
1983年 | 15篇 |
1982年 | 28篇 |
1981年 | 22篇 |
1980年 | 28篇 |
1979年 | 15篇 |
1978年 | 12篇 |
1977年 | 15篇 |
1964年 | 10篇 |
1959年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
92.
Kernel Spectral Matched Filter for Hyperspectral Imagery 总被引:1,自引:0,他引:1
In this paper a kernel-based nonlinear spectral matched filter is introduced for target detection in hyperspectral imagery,
which is implemented by using the ideas in kernel-based learning theory. A spectral matched filter is defined in a feature
space of high dimensionality, which is implicitly generated by a nonlinear mapping associated with a kernel function. A kernel
version of the matched filter is derived by expressing the spectral matched filter in terms of the vector dot products form
and replacing each dot product with a kernel function using the so called kernel trick property of the Mercer kernels. The proposed kernel spectral matched filter is equivalent to a nonlinear matched filter in the original input space,
which is capable of generating nonlinear decision boundaries. The kernel version of the linear spectral matched filter is
implemented and simulation results on hyperspectral imagery show that the kernel spectral matched filter outperforms the conventional
linear matched filter. 相似文献
93.
功率因数校正技术越来越成为电源行业研究的热点。文中介绍了适用于雷达等设备的250W带功率因数校正整流电源模块的设计,分析了其中升压电感器设计、主开关管保护、控制电路消振、散热设计和表面贴装等关键技术,完成了实验研究,获得了满意的试验结果。 相似文献
94.
95.
Sangkwon Jeong 《低温学》2004,44(4):241-248
This paper describes transient numerical modeling for thermal characteristic of vapor-cooled current leads under pulse operation. The transient thermal analysis considers the temperature difference between a helium gas flow and a copper lead with temperature dependent properties of helium gas, copper and stainless steel. The numerical analysis was validated by an experiment with commercially available 100 A vapor-cooled current leads. A proper overloading factor calculation and the effect of intermediate cooling are presented for the current leads under pulse operation, which can significantly reduce heat input to a cryostat. 相似文献
96.
D. A. Gubaidullin R. G. Zaripov R. G. Galiullin E. R. Galiullina L. A. Tkachenko 《High Temperature》2004,42(5):794-802
Nonlinear oscillation of aerosol in the vicinity of a resonance frequency that is twice lower than the first eigenfrequency (subharmonic resonance) is experimentally investigated in tubes with different conditions at the ends. The time dependence of the number density of aerosol droplets is determined, and the effect of the frequency and intensity of oscillation on the process of coagulation of droplets is studied. The nonmonotonic pattern of the dependence of the time of coagulation of aerosol droplets on the frequency of excitation with a minimal value at resonance is found. Ordered space-time structures (alternation of denser and looser regions of aerosol) are revealed in the visible region in the vicinity of the middle of a closed tube. 相似文献
97.
裂缝性油气藏采收率:100个裂缝性油气田实例的经验总结 总被引:5,自引:2,他引:3
通过对世界上100个裂缝性油气藏的综合评价,研究储集层及流体本身的性质(包括孔隙度、渗透率、黏度、可动油比例、含水饱和度、润湿性及裂缝分布特征等)和驱动机制及油藏管理战略(优化日产量和采用不同类型的提高采收率技术)对其最终采收率的影响。将裂缝性油气藏分为4类:I类的基质几乎没有孔隙度和渗透率,裂缝是储存空间和流体流动的通道;Ⅱ类的基质有较低的孔隙度和渗透率,基质提供储存空间,裂缝提供流动通道;Ⅲ类(微孔隙)的基质具有高孔隙度和低渗透率,基质提供储存空间,裂缝提供流动通道;Ⅳ类(大孔隙)的基质具有高的孔隙度和渗透率,基质提供储存空间和流动通道,裂缝仅增加渗透率。对26个Ⅱ类油气藏和20个Ⅲ类油气藏的开采历史的研究表明:Ⅱ类油气藏的采收率受水驱强度和最优日产量控制,日产量过高会很容易破坏Ⅱ类油气藏,一些Ⅱ类油气藏如果管理得当,采收率可以很高,不需要二次或三次采油;Ⅲ类油气藏的采收率主要受岩石和流体本身性质的影响,特别是基质渗透率、流体重度、润湿性以及裂缝强度等,不进行二次或三次采油不可能完全开采,往往需要采用一些提高采收率的专门技术。以往将Ⅱ类和Ⅲ类裂缝性油气藏归为一类,认识它们的区别将有助于选择更好的开发策略。 相似文献
98.
对称非线性系统的无交互控制 总被引:1,自引:0,他引:1
本文讨论了具有对称性的非线性系统的无交互控制问题。通过定义对称系统的导出分布族的新概念,我们得出了问题可解的条件。我们取得的结果较不具对称性的情况要简单一些。从而说明,对称性不仅使得系统具有较好的结构,而且使得它的其它一些问题的研究得到简化。 相似文献
99.
Y. MURAKAMI K. TAKAHASHI R. KUSUMOTO 《Fatigue & Fracture of Engineering Materials & Structures》2003,26(6):523-531
ABSTRACT The fatigue crack growth behaviour of 0.47% carbon steel was studied under mode II and III loadings. Mode II fatigue crack growth tests were carried out using specially designed double cantilever (DC) type specimens in order to measure the mode II threshold stress intensity factor range, ΔKIIth. The relationship ΔKIIth > ΔKIth caused crack branching from mode II to I after a crack reached the mode II threshold. Torsion fatigue tests on circumferentially cracked specimens were carried out to study the mechanisms of both mode III crack growth and of the formation of the factory‐roof crack surface morphology. A change in microstructure occurred at a crack tip during crack growth in both mode II and mode III shear cracks. It is presumed that the crack growth mechanisms in mode II and in mode III are essentially the same. Detailed fractographic investigation showed that factory‐roofs were formed by crack branching into mode I. Crack branching started from small semi‐elliptical cracks nucleated by shear at the tip of the original circumferential crack. 相似文献
100.
E. I. Mashinskii 《Journal of Mining Science》2003,39(1):8-14
Using the theory of microplasticity as the base, it is shown that the curvature of graph for the function describing the equation of state of rocks can change its sign depending on the value of the mechanical energy applied. The experiments on dolomites under the strains of order of 10-6 reveal an increase in wave velocities as the amplitude grows. 相似文献