全文获取类型
收费全文 | 180462篇 |
免费 | 18023篇 |
国内免费 | 11238篇 |
专业分类
电工技术 | 13544篇 |
技术理论 | 3篇 |
综合类 | 22415篇 |
化学工业 | 18225篇 |
金属工艺 | 9534篇 |
机械仪表 | 15835篇 |
建筑科学 | 23687篇 |
矿业工程 | 7839篇 |
能源动力 | 5735篇 |
轻工业 | 9002篇 |
水利工程 | 7534篇 |
石油天然气 | 7454篇 |
武器工业 | 2469篇 |
无线电 | 12542篇 |
一般工业技术 | 24935篇 |
冶金工业 | 7048篇 |
原子能技术 | 2762篇 |
自动化技术 | 19160篇 |
出版年
2024年 | 756篇 |
2023年 | 2173篇 |
2022年 | 4132篇 |
2021年 | 4912篇 |
2020年 | 5472篇 |
2019年 | 4644篇 |
2018年 | 4605篇 |
2017年 | 5821篇 |
2016年 | 6497篇 |
2015年 | 6929篇 |
2014年 | 11052篇 |
2013年 | 10608篇 |
2012年 | 13953篇 |
2011年 | 14285篇 |
2010年 | 10941篇 |
2009年 | 11365篇 |
2008年 | 10349篇 |
2007年 | 12808篇 |
2006年 | 11260篇 |
2005年 | 9384篇 |
2004年 | 7686篇 |
2003年 | 6592篇 |
2002年 | 5458篇 |
2001年 | 4508篇 |
2000年 | 4060篇 |
1999年 | 3503篇 |
1998年 | 2688篇 |
1997年 | 2405篇 |
1996年 | 2082篇 |
1995年 | 1839篇 |
1994年 | 1522篇 |
1993年 | 1133篇 |
1992年 | 980篇 |
1991年 | 718篇 |
1990年 | 598篇 |
1989年 | 563篇 |
1988年 | 399篇 |
1987年 | 242篇 |
1986年 | 190篇 |
1985年 | 93篇 |
1984年 | 87篇 |
1983年 | 46篇 |
1982年 | 58篇 |
1981年 | 74篇 |
1980年 | 45篇 |
1979年 | 43篇 |
1978年 | 17篇 |
1976年 | 14篇 |
1975年 | 17篇 |
1959年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
The main purpose of this paper is to find the mixed-mode stress intensity factors of composite materials using the crack opening displacement (COD). First, a series solution of the composite material with a crack was used to evaluate COD values. Then, the least-squares method was used to calculate mixed-mode stress intensity factors. This algorithm can be applied to any method that generates or measures COD values. The major advantage of this method is that COD values very near the crack tip are not necessary. Both finite element simulations and laboratory experiments were applied to validate this least-squares method with acceptable accuracy if the even terms of the series solution are removed. 相似文献
122.
This paper presents a new concept for symmetric boundary element method (SBEM) applicable to 2-D steady-state and transit potential problems. Two kinds of SBEM formulations are derived. Symmetry is obtained simply through matrix manipulation, and no hypersingularity appears. Therefore, SBEM is much easier than the traditional symmetric Galerkin BEM. Compared with the traditional asymmetric BEM, the present SBEM can reduce the computational cost for time domain problems only. However, when applied to BEM/FEM coupling procedure, SBEM can reduce the computational cost for both steady-state and time domain problems. Three numerical examples are included to illustrate the effectiveness and accuracy of the present formulations. 相似文献
123.
A solution method suitable for the multi-threaded simulation ofmechanical systems represented in Cartesian coordinates isproposed and analyzed. In a state-space framework for thesolution of the Differential Algebraic Equations (DAE) ofMultibody Dynamics, the position/velocity stabilization and theacceleration computation are based on iterative solvers applied toequivalent reduced problems. The most in-depth computationalaspect analyzed is the preconditioning, i.e., the direct solutionof the reduced systems. Provided a topology index reduction is first applied to the model, the effort for the direct solution of the reduced systems is shown to be of order O(N
J
), where N
J
is the number of joints in the model. The recurring theme of thepaper is the central role that the topology of the mechanicalsystem plays in the overall performance of the numericalsimulation. Based on the topology of the model, parallelcomputational threads can be established to start in the equationformulation and continue through the iterative numericalalgorithms employed for the numerical solution. Task schedulingthese parallel threads is expected to redeem real-time performancefor certain classes of complex applications. 相似文献
124.
钢铁企业的氧气厂要深入了解本企业的用氧情况及周边市场的需要,据此确定拟新增空分装置的设计参数,选定最适宜的空分流程。探讨了空分流程选择时要考虑的几个方面。介绍了一种对空分装置的投资和长期运行费用之间进行经济性分析的定量计算公式,并得出了四点结论。 相似文献
125.
Michael Fox Richard Hastings Scott Lovald Juan Heinrich 《Journal of Failure Analysis and Prevention》2007,7(3):165-174
A failure analysis case study is presented for a two-piece aerosol containing tetrafluoroethane, commonly referred to as Refrigerant
134a. A gentleman was preparing to recharge the air conditioning system of an automobile when the bottom exploded off the
aerosol container, propelling the body of the aerosol container like a rocket, which hit the man in the eye and blinded him
in that eye. The aerosol was never connected to the air conditioner, therefore backpressure from the air conditioner (AC)
compressor was ruled out as a cause for the explosion. The objective of the study was to determine why the aerosol exploded.
Several recently developed test methods were used, including two types of heat-to-burst tests and a puncture chamber to measure
the pressure-versus-temperature behavior of aerosols. More common test methods were also used, such as water bath pressure
tests, hydro pressure burst tests, pneumatic pressure burst tests, hardness measurements, weight measurements, metallography,
scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and an accident scenario recreation. A semi-empirical
correlation between the hardness and weights of the container bottoms was used to determine the explosion temperature and/or
pressure. This semi-empirical correlation agrees in principle with an analysis of the explosion pressures using finite-element
analysis (FEA). The root cause for the explosion was determined to be a lack of strength of the bottom of the two-piece aerosol
coupled with heating the aerosol to temperatures significantly above room temperature. 相似文献
126.
127.
This paper presents an application of digital signal processing to data acquired by the radio imaging method (RIM) that was adopted to measure moisture distribution inside the human body. RIM was originally developed for the mining industry; we are applying the method to a biomedical measurement because of its simplicity, economy, and safety. When a two‐dimensional image was constructed from the measured data, the method provided insufficient resolution because the wavelength of the measurement medium, a weak electromagnetic wave in a VHF band, was longer than human tissues. We built and measured a phantom, a model simulating the human body, consisting of two water tanks representing large internal organs. A digital equalizer was applied to the measured values as a weight function, and images were reconstructed that corresponded to the original shape of the two water tanks. As a result, a two‐dimensional image containing two individual peaks corresponding to the original two small water tanks was constructed. The result suggests the method was applicable to biomedical measurement by the assistance of digital signal processing. This technique may be applicable to home‐based medical care and other situations in which safety, simplicity, and economy are important. 相似文献
128.
Ashraf Ayoub 《Computers & Structures》2003,81(7):411-421
This paper presents an inelastic element for the analysis of beams on foundations. The element is derived from a two-field mixed formulation with independent approximation of forces and displacements. The state determination algorithm for the implementation of the element in a general purpose nonlinear finite element analysis program is presented and its stability characteristics are discussed. Numerical studies are performed to compare the model with the classical displacement formulation. The studies confirm the superiority of the proposed model in describing the inelastic behavior of beams on foundations. 相似文献
129.
130.
Exact integration in the boundary element method for two-dimensional elastostatic problems 总被引:3,自引:0,他引:3
This paper derives the exact integrations for the integrals in the boundary element analysis of two-dimensional elastostatics. For facilitation, the derivation is based on the simple forms of the fundamental functions by taking constant, discontinuous linear and discontinuous quadratic elements as examples. The efficiency and accuracy of the derived exact integrations are verified against five benchmark problems; the results indicate that the derived exact integrations significantly reduces the CPU time for forming the matrices of the boundary element analysis and solving the internal displacements. 相似文献