全文获取类型
收费全文 | 100447篇 |
免费 | 5462篇 |
国内免费 | 2455篇 |
专业分类
电工技术 | 3606篇 |
技术理论 | 5篇 |
综合类 | 3916篇 |
化学工业 | 14494篇 |
金属工艺 | 4126篇 |
机械仪表 | 4387篇 |
建筑科学 | 4967篇 |
矿业工程 | 2293篇 |
能源动力 | 2218篇 |
轻工业 | 6057篇 |
水利工程 | 1570篇 |
石油天然气 | 4246篇 |
武器工业 | 446篇 |
无线电 | 8011篇 |
一般工业技术 | 10168篇 |
冶金工业 | 24535篇 |
原子能技术 | 904篇 |
自动化技术 | 12415篇 |
出版年
2024年 | 325篇 |
2023年 | 1153篇 |
2022年 | 1893篇 |
2021年 | 2635篇 |
2020年 | 1815篇 |
2019年 | 1591篇 |
2018年 | 2216篇 |
2017年 | 2574篇 |
2016年 | 2742篇 |
2015年 | 3014篇 |
2014年 | 3312篇 |
2013年 | 3789篇 |
2012年 | 5693篇 |
2011年 | 6276篇 |
2010年 | 4089篇 |
2009年 | 3852篇 |
2008年 | 3639篇 |
2007年 | 3546篇 |
2006年 | 3722篇 |
2005年 | 5977篇 |
2004年 | 4250篇 |
2003年 | 3524篇 |
2002年 | 2240篇 |
2001年 | 1879篇 |
2000年 | 1643篇 |
1999年 | 2247篇 |
1998年 | 7389篇 |
1997年 | 4870篇 |
1996年 | 3570篇 |
1995年 | 2382篇 |
1994年 | 1817篇 |
1993年 | 1577篇 |
1992年 | 638篇 |
1991年 | 614篇 |
1990年 | 556篇 |
1989年 | 481篇 |
1988年 | 468篇 |
1987年 | 336篇 |
1986年 | 291篇 |
1985年 | 228篇 |
1984年 | 126篇 |
1983年 | 118篇 |
1982年 | 158篇 |
1981年 | 205篇 |
1980年 | 208篇 |
1979年 | 68篇 |
1978年 | 102篇 |
1977年 | 615篇 |
1976年 | 1329篇 |
1975年 | 101篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Using a corrected sum rule and a generalized virial identity, we study the analytical expression for entire modes of the collective elementary excitation spectrum in a trapped Bose–Einstein condensate at any atom number. Explicit analytical formulas for the spectrum are obtained for the harmonic traps with both spherical symmetry and axial symmetry using the gaussian approximation for the N-body ground-state wave function of the condensate. These formulas give the simple dependence of all energy levels on the atom numbers, their interaction strength and trap geometry parameters. 相似文献
12.
Sébastien Ambellouis Fran?ois Cabestaing Jack-Gérard Postaire 《IEEE transactions on image processing》2006,15(6):1601-1609
Energy-based methods for motion estimation in image sequences process the input data either in the spatiotemporal or in the frequency domain. In both cases, the algorithms already described in the literature often require a huge number of elementary operations. In this paper, we describe a class of velocity selective filters which yield an accurate detection of the edges moving in the sequence. We first present a filtering scheme based on a convolution operation computed on a finite size neighborhood and describe its properties in the spatiotemporal and frequency domains. Then, we show that filters with similar properties can be implemented recursively, i.e., as convolutions computed on infinite-size neighborhoods. As an example, we finally show the filters' responses in the case of two superimposed translational motions. 相似文献
13.
Presents an obituary and information about the life and accomplishments of Josef Maria Bro?ek. Born August 14, 1913, in the ancient town of Melnik, in central Bohemia, today the Czech Republic, Josef spent his childhood in Poland (Warsaw, 1913- 1915) and in Siberia (1915-1920). His education in Czechoslovakia culminated with a thesis on "Memory, Its Measurement and Structure" and a PhD awarded in June 1937. In the history of psychology, his lifetime project bore the title "Historiography of Psychology Around the World," and it covered about 20 geographical areas. Extensive attention was devoted to institutional and organizational developments as journals, academic settings, archives, museums, research groups, conferences, and institutes. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
14.
基于模式理论光栅椭偏参数反演的数值模拟 总被引:5,自引:2,他引:3
将一种广泛用于求解系统优化问题的方法——正单纯形法,求解光栅的椭偏方程。首先,利用求解光栅的傅立叶模式理论对TE和TM波的复反射系数进行求解。然后计算出其相应的椭偏参数(△,Ψ),并在该值的基础上加入不同偏差的随机高斯噪声,将加入噪声后的值(△m,Ψm)作为模拟测量值。最后使用优化算法进行反演。通过对几种常用面形光栅椭偏参数的数值模拟,一方面表明傅立叶模式理论计算光栅的椭偏参数不仅精度高。而且速度快;另一方面表明利用正单纯形法得到的光栅参数值很接近于正演时假设的参数值,从而从理论上证明了利用椭偏法测量光栅各种光学参数的可行性。 相似文献
15.
A note on the Gauss-Jacobi quadrature formulae for singular integral equations of the second kind 总被引:1,自引:0,他引:1
A fast and efficient numerical method based on the Gauss-Jacobi quadrature is described that is suitable for solving Fredholm
singular integral equations of the second kind that are frequently encountered in fracture and contact mechanics. Here we
concentrate on the case when the unknown function is singular at both ends of the interval. Quadrature formulae involve fixed
nodal points and provide exact results for polynomials of degree 2n − 1, where n is the number of nodes. Finally, an application of the method to a plane problem involving complete contact is presented. 相似文献
16.
优化项目管理MIS系统方案设计 总被引:2,自引:0,他引:2
按照工程项目“五制”管理的要求 ,以规范管理和提升工程质量为系统开发的基础和前提 ,探索适合本行业使用的项目MIS系统设计方案 ,并对其功能模型、数据规划、构造处理模型、数学模型进行分析 相似文献
17.
18.
19.
20.
Phospholamban (PLN) was expressed in Escherichia coli as a protein fusion with glutathione S-transferase (GST). GST-PLN was mostly present in the insoluble protein fraction and accounted for approximately 50% of total insoluble protein. Attempts to suppress inclusion body formation or to use GST as an affinity-purification tag failed. A successful purification method is based on preparative SDS/PAGE and electrodialysis. From 1 g cells we typically purified 13.5 mg fusion protein with a PLN content of 2.8 mg. We genetically inserted an enterokinase (EK) protease site just in front of the PLN sequence and demonstrated the proteolytical liberation of PLN from the carrier protein. The approach described represents a substantial advancement in PLN expression and purification. 相似文献