全文获取类型
收费全文 | 62121篇 |
免费 | 5142篇 |
国内免费 | 2727篇 |
学科分类
工业技术 | 69990篇 |
出版年
2024年 | 275篇 |
2023年 | 963篇 |
2022年 | 1598篇 |
2021年 | 2357篇 |
2020年 | 1753篇 |
2019年 | 1557篇 |
2018年 | 1750篇 |
2017年 | 1907篇 |
2016年 | 1636篇 |
2015年 | 2288篇 |
2014年 | 2822篇 |
2013年 | 3461篇 |
2012年 | 3740篇 |
2011年 | 4102篇 |
2010年 | 3622篇 |
2009年 | 3520篇 |
2008年 | 3351篇 |
2007年 | 3203篇 |
2006年 | 3526篇 |
2005年 | 3027篇 |
2004年 | 2184篇 |
2003年 | 2109篇 |
2002年 | 2274篇 |
2001年 | 1956篇 |
2000年 | 1645篇 |
1999年 | 1790篇 |
1998年 | 1338篇 |
1997年 | 1145篇 |
1996年 | 1115篇 |
1995年 | 938篇 |
1994年 | 726篇 |
1993年 | 579篇 |
1992年 | 435篇 |
1991年 | 299篇 |
1990年 | 238篇 |
1989年 | 205篇 |
1988年 | 174篇 |
1987年 | 106篇 |
1986年 | 64篇 |
1985年 | 44篇 |
1984年 | 32篇 |
1983年 | 30篇 |
1982年 | 43篇 |
1981年 | 20篇 |
1980年 | 23篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1977年 | 6篇 |
1976年 | 2篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
A Subcarriers Allocation Scheme for Cognitive Radio Systems Based on Multi-Carrier Modulation 总被引:1,自引:0,他引:1
Tao Luo Tao Jiang Weidong Xiang Hsiao-Hwa Chen 《Wireless Communications, IEEE Transactions on》2008,7(9):3335-3340
Cognitive radio (CR) is a dynamic spectrum access technology as a solution to spectrum under-utilization problem in some licensed bands. Operating over an exceedingly wide spectrum, CR systems usually adopt multi-carrier modulation (MCM) to implement flexible channelization. Consequently, efficient channel allocation scheme becomes extremely important to an MCM based CR (MCM-CR) system. In this paper, a maximum likelihood detection model is developed to detect the presence and locations of licensed users (LUs) signals in the frequency domain. Performance of the detection model, including the optimal detection region, detection probability and false alarm probability, is analyzed. A one-order two-state Markovian chain model is proposed to predict channel status information. In particular, a novel subcarrier allocation scheme for MCM-CR systems is proposed, taking into account the confidence of channel estimation, quality of services (QoS) of rental users (RUs) and throughput. To validate the analytical results, simulations have been conducted to show effectiveness of the proposed scheme. 相似文献
62.
高速线材生产的弹簧钢盘卷的表面脱碳分析 总被引:1,自引:0,他引:1
从金相角度对高线生产的弹簧钢盘卷的表面脱碳进行了分析,找出相关的影响因素,并针对实际情况提出了相应的改进方法。 相似文献
63.
The Karlsruhe Tritium Neutrino experiment (KATRIN) is going to use a very large electro-static tandem spectrometer to measure the electron spectrum from the tritium beta decay, where several kilometers of non-evaporable getter (NEG) strips (type ST707) are to be used to achieve the UHV requirements. Different geometrical configurations of the NEG strips have been studied by Monte Carlo simulations. It is shown that the resulting pumping speed of the getter pumps will allow to get a pressure below 10−11 mbar in the huge vessel with a volume of 1400 m3. By systematic assessment of the statistics of the pumping surfaces, it could be demonstrated that the design is sound. 相似文献
64.
奥里油在电力工业的应用及环保处理 总被引:1,自引:0,他引:1
委内瑞拉富藏奥里油约469亿t,中国政府与委内瑞拉政府签订了合作生产和供应每年650万t奥里油的合作协议。介绍了奥里油的特性和在全球以及中国的应用情况,分析了奥里油燃烧发电带来的特殊的环保问题和处理方法。 相似文献
65.
Fan Jing yu Wang Dao zeng Zhong Bao chang Shanghai Institute of Applied Mathematics Mechanics Shanghai University Shanghai China 《水动力学研究与进展(B辑)》2003,15(2)
1 . INTRODUCTIONUndertheinfluenceofnaturaltides,theinterac tionsbetweenflowfeaturesandpollutantlongitudinaldiffusionintidalriversareimportantforwaterenvi ronmentrectificationinestuarineregions.Thediffu sionandtransportofpollutantinnaturalriversfallin tom… 相似文献
66.
67.
Elastic solutions of a cylindrical rod containing periodically distributed inclusions with axisymmetric eigenstrains 总被引:1,自引:0,他引:1
Summary. In this paper, we give the elastic solution for a special type of microstructure – a circular cylindrical rod containing periodically distributed inclusions along its axial direction. Each inclusion has the same uniform axisymmetric transformation strain (eigenstrain). Analytical elastic solutions are obtained for the displacements, stresses and elastic strain energy of the rod. The effects of microstructure and its evolution (growth of inclusions) on the elastic stress and strain fields as well as the strain energy of the rod are quantitatively demonstrated. As a result of such microstructure evolution nominal stress-strain relation with strain softening is derived for a rod under uniaxial tension. 相似文献
68.
本文采用粘滞流模型试验对青海桥头电厂河子沟灰场拦洪坝设计方案进行了论证,分析了多种防渗条件下的渗流场特点,提出了满足工程运作的既经济又合理的建议。 相似文献
69.
Huang Yuying Zhong Weifang Qin Qinghua 《Computer Methods in Applied Mechanics and Engineering》1992,100(3):315-323
The postbuckling behavior of plates on an elastic foundation is studied by using the boundary element method (BEM). A new fundamental solution of lateral deflection is derived through the resolution theory of a differential operator, and a set of boundary element formulae in incremental form is presented. By using these formulae, the BEM solution procedure becomes relatively simple. The results of a number of numerical examples are compared with existing solutions and good agreement is observed. It shows that the proposed method is effective for solving the postbuckling problems of plates with arbitrary shape and various boundary conditions. 相似文献
70.
The effect of heat treatments on the tensile properties and microstructures of wrought Mg–Zn–Zr-Rare earth alloys MB25 and MB26 have been studied in this paper. It was shown that the homogenization of the cast ingots decreased the strength of the extruded bars because some grain boundary phases were dissolved during the process of this treatment, while the ageing treatment of the extruded bars increased the strength due to the dispersive precipitation of MgZn2 phase. The quenching + ageing treatments of the extruded bars decreases the strength and plasticity because of the growing up of the grains.Abbreviations ED
electron diffraction
- GB
grain boundary
- RE
rare earth
- TEM
transmission electron microscope 相似文献