全文获取类型
收费全文 | 1485156篇 |
免费 | 28286篇 |
国内免费 | 7843篇 |
专业分类
电工技术 | 35348篇 |
技术理论 | 5篇 |
综合类 | 7391篇 |
化学工业 | 271722篇 |
金属工艺 | 64517篇 |
机械仪表 | 42066篇 |
建筑科学 | 46352篇 |
矿业工程 | 11777篇 |
能源动力 | 50317篇 |
轻工业 | 112358篇 |
水利工程 | 14948篇 |
石油天然气 | 38326篇 |
武器工业 | 367篇 |
无线电 | 196713篇 |
一般工业技术 | 280018篇 |
冶金工业 | 146147篇 |
原子能技术 | 33926篇 |
自动化技术 | 168987篇 |
出版年
2021年 | 16012篇 |
2020年 | 12087篇 |
2019年 | 14802篇 |
2018年 | 15285篇 |
2017年 | 14586篇 |
2016年 | 21199篇 |
2015年 | 17797篇 |
2014年 | 29133篇 |
2013年 | 88429篇 |
2012年 | 35785篇 |
2011年 | 47989篇 |
2010年 | 42961篇 |
2009年 | 51329篇 |
2008年 | 44971篇 |
2007年 | 42222篇 |
2006年 | 45299篇 |
2005年 | 39517篇 |
2004年 | 41198篇 |
2003年 | 41028篇 |
2002年 | 40319篇 |
2001年 | 36851篇 |
2000年 | 35481篇 |
1999年 | 34059篇 |
1998年 | 39145篇 |
1997年 | 35851篇 |
1996年 | 33071篇 |
1995年 | 29352篇 |
1994年 | 27733篇 |
1993年 | 27588篇 |
1992年 | 25987篇 |
1991年 | 22938篇 |
1990年 | 23311篇 |
1989年 | 22381篇 |
1988年 | 20923篇 |
1987年 | 19191篇 |
1986年 | 18531篇 |
1985年 | 21874篇 |
1984年 | 22259篇 |
1983年 | 20186篇 |
1982年 | 19179篇 |
1981年 | 19280篇 |
1980年 | 17841篇 |
1979年 | 18479篇 |
1978年 | 17695篇 |
1977年 | 17115篇 |
1976年 | 17742篇 |
1975年 | 15957篇 |
1974年 | 15509篇 |
1973年 | 15553篇 |
1972年 | 13044篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
991.
番禺30-1砂岩强水驱气藏储层非均质性研究 总被引:7,自引:5,他引:2
针对垂向非均质性严重且边底水能量强的番禺30-1气田面临的潜在开发问题,通过岩心分析及测井二次解释,对其夹层特征及储层非均质性等进行了研究,划分出19个流动单元并定量描述了各流动单元的特征参数,建立了该气田的精细地质模型。综合评价表明,新建的地质模型具有较高的精度,为该气藏合理开发提供了坚实的地质基础。 相似文献
992.
涡轮搅拌桨反应器混合过程的数值计算 总被引:1,自引:1,他引:0
利用CFD方法计算单层涡轮反应器搅拌槽内流体混合过程的速度场和浓度场,研究物料在搅拌槽内的混合过程,以及不同监测点对混合时间的影响。结果表明,搅拌槽内物料的混合主要受槽内流体的流动形式所影响;混合时间的长短与监测点位置有关;在搅拌桨的桨叶附近进行监测所得到的混合时间较短,在液面附近进行监测所得的混合时间较长。在实际生产和试验中,应注意对监测点位置的选取。 相似文献
993.
Reducing CIC filter complexity 总被引:1,自引:0,他引:1
This paper provides several tricks to reduce the complexity and enhance the usefulness of cascaded integrator-comb (CIC) filters. The first trick shows a way to reduce the number of adders and delay elements in a multi-stage CIC interpolation filter. The result is a multiplierless scheme that performs high-order linear interpolation using CIC filters. The second trick shows a way to eliminate the integrators from CIC decimation filters. The benefit is the elimination of unpleasant data word growth problems. 相似文献
994.
W. Shieh R. Hui X. Yi 《Photonics Technology Letters, IEEE》2006,18(10):1122-1124
We perform a systematic measurement of the degree-of-polarization (DOP) and eye-closure penalty for optical signals with orthogonal polarizations. We find that the symmetry of DOP is maintained for the orthogonal polarizations under both first and higher order polarization-mode dispersion (PMD), whereas the symmetry of eye-closure penalty is broken under second-order PMD. An orthogonal polarization pair can have large disparity of eye-closure penalty despite an identical DOP. We also demonstrate a novel approach to estimate the maximum eye-closure penalty asymmetry with three orthogonal polarizations on the Poincare/spl acute/ sphere. 相似文献
995.
A common computing-core representation of the discrete cosine transform and discrete sine transform is derived and a reduced-complexity algorithm is developed for computation of the proposed computing-core. A parallel architecture based on the principle of distributed arithmetic is designed further for the computation of these transforms using the common-core algorithm. The proposed scheme not only leads to a systolic-like regular and modular hardware for computing these transforms, but also offers significant improvement in area-time efficiency over the existing structures. The structure proposed here is devoid of complicated input/output mapping and does not involve any complex control. Unlike the convolution-based structures, it does not restrict the transform length to be a prime or multiple of prime and can be utilized as a reusable core for cost-effective, memory-efficient, high-throughput implementation of either of these transforms 相似文献
996.
Piedade M. Sousa L. A. de Almeida T. M. Germano J. da Costa B. A. Lemos J. M. Freitas P. P. Ferreira H. A. Cardoso F. A. 《IEEE transactions on circuits and systems. I, Regular papers》2006,53(11):2384-2395
This paper presents a hand-held microsystem based on new fully integrated magnetoresistive biochips for biomolecular recognition (DNA hybridization, antibody antigen interaction, etc.). Magnetoresistive chip surfaces are chemically treated, enabling the immobilization of probe biomolecules such as DNA or antibodies. Fluid handling is also integrated in the biochip. The proposed microsystem not only integrates the biochip, which is an array of 16times16 magnetoresistive sensors, but it also provides all the electronic circuitry for addressing and reading out each transducer. The proposed architecture and circuits were specifically designed for achieving a compact, programmable and portable microsystem. The microsystem also integrates a hand-held analyzer connected through a wireless channel. A prototype of the system was already developed and detection of magnetic nanoparticles was obtained. This indicates that the system may be used for magnetic label based bioassays 相似文献
997.
WiFi access point pricing as a dynamic game 总被引:1,自引:0,他引:1
We study the economic interests of a wireless access point owner and his paying client, and model their interaction as a dynamic game. The key feature of this game is that the players have asymmetric information - the client knows more than the access provider. We find that if a client has a "web browser" utility function (a temporal utility function that grows linearly), it is a Nash equilibrium for the provider to charge the client a constant price per unit time. On the other hand, if the client has a "file transferor" utility function (a utility function that is a step function), the client would be unwilling to pay until the final time slot of the file transfer. We also study an expanded game where an access point sells to a reseller,which in turn sells to a mobile client and show that if the client has a web browser utility function, that constant price is a Nash equilibrium of the three player game. Finally, we study a two player game in which the access point does not know whether he faces a web browser or file transferor type client, and show conditions for which it is not a Nash equilibrium for the access point to maintain a constant price. 相似文献
998.
Wu-An Kuo TingTing Hwang Wu A.C.-H. 《Very Large Scale Integration (VLSI) Systems, IEEE Transactions on》2006,14(1):81-85
This paper presents a novel power-driven multiplication instruction-set design method for application-specific instruction-set processors (ASIPs). Based on a dual-and-configurable-multiplier structure, our proposed method devises a multiplication instruction set for low-power ASIPs. Our method exploits the execution sequences of multiplication instructions and effective bit widths of variables to reduce power consumed by redundant multiplication bits while minimizing the multiplication execution time. Experimental results on a set of DSP programs demonstrate that our proposed method achieves significant power reduction (up to 18.53%) and execution time improvement (up to 10.43%) with 18% area overhead. 相似文献
999.
The phenomenon of persistent tunneling photoconductivity was studied using the tunneling spectroscopy technique at liquid-helium temperature: the separation between the unoccupied levels in a δ-doped layer at the GaAs surface decreased after illumination. This decrease was due to an increase in the width of the quantum well of the δ-doped layer. For photon energies hv exceeding the GaAs band gap E g , this increase in the width of the quantum well was related to the accumulation of positive charge in the depth of GaAs induced by the generation of the electron-hole pairs and photoionization of deep centers. For hv < E g (including the case of CO2 laser), only photoionization is important. The experimental data agree with the self-consistent calculations. The critical temperature for the effect has been determined (T c = 45 K); at higher temperatures, the effect disappears. 相似文献
1000.
The problem of synthesis of an isotropic reradiator providing for the transparency of a circular perfectly conducting cylinder illuminated by a TE-polarized plane wave is investigated. A general solution to the problem of diffraction from the cylinder with a reradiator is obtained, and a system of nonlinear equations for the synthesis problem is derived. Numerical solution of the synthesis problem is illustrated by a number of examples. 相似文献