全文获取类型
收费全文 | 41690篇 |
免费 | 4900篇 |
国内免费 | 4172篇 |
专业分类
电工技术 | 3244篇 |
技术理论 | 3篇 |
综合类 | 5467篇 |
化学工业 | 3737篇 |
金属工艺 | 4104篇 |
机械仪表 | 2701篇 |
建筑科学 | 1842篇 |
矿业工程 | 1203篇 |
能源动力 | 694篇 |
轻工业 | 1171篇 |
水利工程 | 492篇 |
石油天然气 | 727篇 |
武器工业 | 482篇 |
无线电 | 4707篇 |
一般工业技术 | 6448篇 |
冶金工业 | 1808篇 |
原子能技术 | 259篇 |
自动化技术 | 11673篇 |
出版年
2024年 | 140篇 |
2023年 | 599篇 |
2022年 | 1083篇 |
2021年 | 1344篇 |
2020年 | 1335篇 |
2019年 | 1283篇 |
2018年 | 1144篇 |
2017年 | 1481篇 |
2016年 | 1541篇 |
2015年 | 1864篇 |
2014年 | 2731篇 |
2013年 | 2901篇 |
2012年 | 3025篇 |
2011年 | 3203篇 |
2010年 | 2520篇 |
2009年 | 2682篇 |
2008年 | 2384篇 |
2007年 | 2887篇 |
2006年 | 2507篇 |
2005年 | 2140篇 |
2004年 | 1778篇 |
2003年 | 1502篇 |
2002年 | 1247篇 |
2001年 | 1106篇 |
2000年 | 1006篇 |
1999年 | 814篇 |
1998年 | 691篇 |
1997年 | 632篇 |
1996年 | 533篇 |
1995年 | 513篇 |
1994年 | 461篇 |
1993年 | 336篇 |
1992年 | 288篇 |
1991年 | 239篇 |
1990年 | 210篇 |
1989年 | 177篇 |
1988年 | 122篇 |
1987年 | 66篇 |
1986年 | 38篇 |
1985年 | 38篇 |
1984年 | 32篇 |
1983年 | 29篇 |
1982年 | 22篇 |
1981年 | 21篇 |
1980年 | 13篇 |
1979年 | 10篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
本文较系统、通俗地介绍了模拟视频特技切换台的矩阵输入、混合/效果放大器(M/E)、下游键、系统控制和同步发生器等电路单元,介绍了特技切换台的切换、混合、扫变、键控的基本原理和功能。 相似文献
72.
Detection of multiple cracks using frequency measurements 总被引:2,自引:0,他引:2
D.P. Patil 《Engineering Fracture Mechanics》2003,70(12):1553-1572
A method for detection of multiple open cracks in a slender Euler-Bernoulli beams is presented based on frequency measurements. The method is based on the approach given by Hu and Liang [J. Franklin Inst. 330 (5) (1993) 841], transverse vibration modelling through transfer matrix method and representation of a crack by rotational spring. The beam is virtually divided into a number of segments, which can be decided by the analyst, and each of them is considered to be associated with a damage parameter. The procedure gives a linear relationship explicitly between the changes in natural frequencies of the beam and the damage parameters. These parameters are determined from the knowledge of changes in the natural frequencies. After obtaining them, each is treated in turn to exactly pinpoint the crack location in the segment and determine its size. The forward, or natural frequency determination, problems are examined in the passing. The method is approximate, but it can handle segmented beams, any boundary conditions, intermediate spring or rigid supports, etc. It eliminates the need for any symbolic computation which is envisaged by Hu and Liang [J. Franklin Inst. 330 (5) (1993) 841] to obtain mode shapes of the corresponding uncracked beams. The proposed method gives a clear insight into the whole analysis. Case studies (numerical) are presented to demonstrate the method effectiveness for two simultaneous cracks of size 10% and more of section depth. The differences between the actual and predicted crack locations and sizes are less than 10% and 15% respectively. The numbers of segments into which the beam is virtually divided limits the maximum number of cracks that can be handled. The difference in the forward problem is less than 5%. 相似文献
73.
J. Clausen L. Damkilde L. Andersen 《International journal for numerical methods in engineering》2006,66(6):1036-1059
A new return method for implicit integration of linear isotropic yield criteria is presented. The basic idea is to perform all the manipulations in the principal stress space and thereby achieve very simple formulae for calculating the plastic corrector stresses, based on the constant gradient of such criteria. The return formulae are in closed form and no iteration is required. The method accounts for three types of stress return: return to a single yield plane, to a discontinuity line at the intersection of two yield planes and to a discontinuity point at the intersection between three or more yield planes. The infinitesimal and the consistent elastoplastic constitutive matrix are calculated for each type of stress return, as are the conditions to ascertain which type of return is required. The method is exemplified with the Mohr–Coulomb yield criterion. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
74.
罗月泓 《湖南工业大学学报》2006,20(3)
首先分析了城市私房区带来的问题和改造的必然性,然后讨论了国内外私房区改造的经验和启示,最后提出了城市私房区改造的基本思路。 相似文献
75.
Transformations in machining. Part 1. enhancement of wavelet transformation neural network (WT-NN) combination with a preprocessor 总被引:2,自引:0,他引:2
X. Wang P. Chen I.N. Tansel Yenilmez A 《International Journal of Machine Tools and Manufacture》2006,46(1):36-42
Properly selected transformation methods obtain the most significant characteristics of metal cutting data efficiently and simplify the classification. Wavelet Transformation (WT) and Neural Networks (NN) combination was used to classify the experimental cutting force data of milling operations previously. Preprocessing (PreP) of the approximation coefficients of the WT is proposed just before the classification by using the Adaptive Resonance Theory (ART2) type NNs. Genetic Algorithm (GA) was used to estimate the weights of each coefficient of the PreP. The WT-PreP-NN (ART2) combination worked at lower vigilances by creating only a few meaningful categories without any errors. The WT-NN (ART2) combination could obtain the same error rate only if very high vigilances are used and many categories are allowed. 相似文献
76.
Jun Rong Li Jun Wang Jia Rui Xu Ming Qiu Zhang Min Zhi Rong Qiang Zheng 《Composites Science and Technology》2006,66(16):3126-3131
The authors of this paper synthesized a series of amphiphilic triblock copolymers of polystyrene-b-poly(ethylene glycol)-b-polystyrene (PS-PEG-PS) having different PEG/PS ratios with nearly identical molecular weights of the entire copolymers. The interfacial interactions in the composites consisting of carbon black and the copolymers can thus be tailored. When these conducting composites are exposed to certain solvent vapors, their electrical resistances greatly increase, showing the gas sensitivity. The present work indicated that this switching behavior is controlled by the structural relaxation of the composites because matrix swelling acts as the main mechanism. The response time has been correlated with absolute temperature by Arrhenius equation, and the estimated activation energy reflects mobility of the fillers involved in the solvent induced expansion of the surrounding polymer. Therefore, by using the gas sensibility of the conductive composites, the structure evolution of the composite materials in solid state and the effect of filler/matrix interfacial interaction on the relaxation property of the matrix polymer has been inspected. It was found that lower activation energy represents stronger interfacial interaction in case good solvent of the matrix was used for the test. 相似文献
77.
以δ-FeOOH为前驱体,用氨水调节溶液的pH值,分别采用(1)90℃水浴加热动态转化、(2)沸腾回流动态转化,(3)90℃静态转化及(4)200℃水热法四种方法合成了锰锌铁氧体纳米粉体.采用X射线衍射仪(XRD),透射电子显微镜(TEM)、振动样品磁强计(VSM)和X射线荧光光谱仪(XRF)等方法对粉体进行了表征,对四种液相法制备的锰锌铁氧体纳米粉体的结构和性能等进行了对比和分析.结果表明,四种方法中沸腾回流相转化法得到的产物具有磁性能较好、形状较规则、粒径可控等优点. 相似文献
78.
Solving regularized least squares with qualitatively controlled adaptive cross‐approximated matrices
The adaptive cross‐approximation (ACA) technique is applied to accelerating an inverse‐problem solver that estimates charge distribution on a dielectric spacer. The ACA generates an approximated system‐matrix that enables us to carry out high‐speed inverse calculation. We designed an approximation procedure based on ACA with some additional concepts, that is, (a) partitioning of matrix based on algebraic information, (b) approximation quality control based on matrix norms, and so on. The tested solver (LSQR for regularized least squares) with ACA demonstrates about 10 times faster performance than that without ACA. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(3): 10–18, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20326 相似文献
79.
80.