全文获取类型
收费全文 | 18461篇 |
免费 | 1601篇 |
国内免费 | 1210篇 |
专业分类
电工技术 | 820篇 |
技术理论 | 1篇 |
综合类 | 3797篇 |
化学工业 | 1700篇 |
金属工艺 | 624篇 |
机械仪表 | 1028篇 |
建筑科学 | 906篇 |
矿业工程 | 337篇 |
能源动力 | 497篇 |
轻工业 | 608篇 |
水利工程 | 584篇 |
石油天然气 | 1303篇 |
武器工业 | 248篇 |
无线电 | 1426篇 |
一般工业技术 | 2891篇 |
冶金工业 | 489篇 |
原子能技术 | 371篇 |
自动化技术 | 3642篇 |
出版年
2024年 | 57篇 |
2023年 | 164篇 |
2022年 | 279篇 |
2021年 | 297篇 |
2020年 | 390篇 |
2019年 | 440篇 |
2018年 | 459篇 |
2017年 | 492篇 |
2016年 | 535篇 |
2015年 | 503篇 |
2014年 | 811篇 |
2013年 | 1183篇 |
2012年 | 1232篇 |
2011年 | 1226篇 |
2010年 | 991篇 |
2009年 | 981篇 |
2008年 | 1025篇 |
2007年 | 1121篇 |
2006年 | 1083篇 |
2005年 | 914篇 |
2004年 | 827篇 |
2003年 | 755篇 |
2002年 | 652篇 |
2001年 | 531篇 |
2000年 | 529篇 |
1999年 | 534篇 |
1998年 | 462篇 |
1997年 | 418篇 |
1996年 | 387篇 |
1995年 | 385篇 |
1994年 | 303篇 |
1993年 | 258篇 |
1992年 | 225篇 |
1991年 | 199篇 |
1990年 | 160篇 |
1989年 | 135篇 |
1988年 | 100篇 |
1987年 | 57篇 |
1986年 | 43篇 |
1985年 | 34篇 |
1984年 | 25篇 |
1983年 | 12篇 |
1982年 | 15篇 |
1981年 | 17篇 |
1980年 | 3篇 |
1979年 | 8篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1959年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
大牛地气田为低渗-致密气田,因存在启动压力梯度等因素,修正等时试井曲线按常规方法处理出现异常,无法准确获取气井的产能方程.采用LIT法和异常曲线校正法对气田异常试井资料进行了重新处理,最终获得气井产能方程,为同类气藏产能试井可能出现的异常资料处理解释探索了新的途径. 相似文献
2.
Barbara M. Johnston Peter R. Johnston 《International journal for numerical methods in engineering》2003,56(4):589-607
Accurate numerical evaluation of integrals arising in the boundary element method is fundamental to achieving useful results via this solution technique. In this paper, a number of techniques are considered to evaluate the weakly singular integrals which arise in the solution of Laplace's equation in three dimensions and Poisson's equation in two dimensions. Both are two‐dimensional weakly singular integrals and are evaluated using (in a product fashion) methods which have recently been used for evaluating one‐dimensional weakly singular integrals arising in the boundary element method. The methods used are based on various polynomial transformations of conventional Gaussian quadrature points where the transformation polynomial has zero Jacobian at the singular point. Methods which split the region of integration into sub‐regions are considered as well as non‐splitting methods. In particular, the newly introduced and highly accurate generalized composite subtraction of singularity and non‐linear transformation approach (GSSNT) is applied to various two‐dimensional weakly singular integrals. A study of the different methods reveals complex relationships between transformation orders, position of the singular point, integration kernel and basis function. It is concluded that the GSSNT method gives the best overall results for the two‐dimensional weakly singular integrals studied. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
3.
A cell vertex finite volume method for the solution of steady compressible turbulent flow problems on unstructured hybrid
meshes of tetrahedra, prisms, pyramids and hexahedra is described. These hybrid meshes are constructed by firstly discretising
the computational domain using tetrahedral elements and then by merging certain tetrahedra. A one equation turbulence model
is employed and the solution of the steady flow equations is obtained by explicit relaxation. The solution process is accelerated
by the addition of a multigrid method, in which the coarse meshes are generated by agglomeration, and by parallelisation.
The approach is shown to be effective for the simulation of a number of 3D flows of current practical interest.
Sponsored by The Research Council of Norway, project number 125676/410
Dedicated to the memory of Prof. Mike Crisfield, a respected colleague 相似文献
4.
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
5.
6.
7.
Paul J. Flory 《Polymer International》1985,17(2):96-102
The earliest investigations on rubber elasticity, commencing in the 19th century, were necessarily limited to phenomenological interpretations. The realisation that polymers consist of very long molecular chains. commencing c. 1930, gave impetus to the molecular theory of rubber elasticity (1932-). according to which the high deformability of an elastomer, and the elastic force generated by deformation, stem from the configurations accessible to long molecular chains. Theories of rubber elasticity put forward from 1934-1946 relied on the assumption that the junctions of the rubber network undergo displacements that are affine in macroscopic strain. The theory of James and Guth (1947) dispensed with this premise, and demonstrated instead that the mean positions of the junctions of a ‘phantom’ network consisting of Gaussian chains devoid of material properties are affine in the strain. The vital significance of the distinction between the actual distribution of chain vectors in a network and their distribution if the junctions would be fixed at their mean positions went unnoticed for nearly 30 years. Experimental investigations, commencing with the incisive work of Gee in 1946. revealed large departures from the relationship of stress to strain predicted by the theories cited. This discrepancy prompted extensive studies, theoretical and experimental, during succeeding years. Inquiry into the fundamentals of polymer networks, formed for example by interlinking very long polymer molecules, exposed the need to take account of network imperfections, typically consisting of chains attached at only one end to a network junction. Various means were advocated to make corrections for these imperfections. The cycle rank ζ of the network has been shown (1976) to be the fundamental measure of its connectivity, regardless of the junction functionality and pattern of imperfections. Often overlooked is the copious interpenetration of the chains comprising typical elastomeric networks. Theories that attempt to represent such networks on a lattice are incompatible with this universal feature. Moreover, the dense interpenetration of chains may limit the ability of junctions in real networks to accommodate the fluctuations envisaged in the theory of phantom networks. It was suggested in 1975 that departures from the form predicted for the elastic equation of state are due to constraints on the fluctuations of junctions whose effect diminishes with deformation and with dilation. Formulation of a self-consistent theory based on this suggestion required recognition of the non-affine connection between the chain vector distribution function and the macroscopic strain in a real network, which may partake of characteristics of a phantom network in some degree. Implementation of the idea was achieved through postulation of domains of constraint affecting the equilibrium distribution of fluctuations of network junctions from their mean positions. This led in due course to a theory that accounts for the relationship of stress to strain virtually throughout the ranges of strain accessible to measurement. The theory establishes connections between structure and elastic properties. This is achieved with utmost frugality in arbitrary parameters. 相似文献
8.
9.
A novel combline filter is proposed for cellular‐radio base stations. The Q‐factor is significantly improved. The eigenvalue equation is expressed with the single‐team approximation in the gap region of the combline resonator. A two‐pole combline filter is designed. The calculation, simulation, and experiment results are presented and are in good agreement. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006. 相似文献
10.
J Schlipf 《Bulletin of Materials Science》1989,12(3-4):185-193
A model for propagating deformation bands is developed, based on a mechanical equation of state and on evolution equations
for the structure parameters. It is shown that, contrary to normal deformation, it is necessary to discriminate between global
parameters which depend solely on time elapsed and local parameters which are functions of the strain history. Correspondingly,
two sets of equations are presented, one describing the development of the global parameters in the course of time, the other
giving the evolution of the local state parameters in the course of deformation, i.e. as a function of strain. Measurable
quantities derived from the first set are the load serrations and the band velocity, while the second set yields the flow
stress and the strain profile of the propagating band. 相似文献