全文获取类型
收费全文 | 312423篇 |
免费 | 29912篇 |
国内免费 | 18161篇 |
专业分类
电工技术 | 24831篇 |
技术理论 | 10篇 |
综合类 | 34943篇 |
化学工业 | 32894篇 |
金属工艺 | 13212篇 |
机械仪表 | 25326篇 |
建筑科学 | 36819篇 |
矿业工程 | 12940篇 |
能源动力 | 12328篇 |
轻工业 | 21418篇 |
水利工程 | 13410篇 |
石油天然气 | 14062篇 |
武器工业 | 3842篇 |
无线电 | 19554篇 |
一般工业技术 | 34656篇 |
冶金工业 | 12448篇 |
原子能技术 | 4627篇 |
自动化技术 | 43176篇 |
出版年
2024年 | 1292篇 |
2023年 | 3801篇 |
2022年 | 7585篇 |
2021年 | 8873篇 |
2020年 | 9634篇 |
2019年 | 8130篇 |
2018年 | 7951篇 |
2017年 | 9912篇 |
2016年 | 11440篇 |
2015年 | 11994篇 |
2014年 | 19550篇 |
2013年 | 19290篇 |
2012年 | 23559篇 |
2011年 | 25044篇 |
2010年 | 18569篇 |
2009年 | 19065篇 |
2008年 | 17697篇 |
2007年 | 21559篇 |
2006年 | 18782篇 |
2005年 | 15721篇 |
2004年 | 13154篇 |
2003年 | 11221篇 |
2002年 | 9314篇 |
2001年 | 7686篇 |
2000年 | 6669篇 |
1999年 | 5640篇 |
1998年 | 4623篇 |
1997年 | 3981篇 |
1996年 | 3304篇 |
1995年 | 2853篇 |
1994年 | 2474篇 |
1993年 | 1818篇 |
1992年 | 1656篇 |
1991年 | 1198篇 |
1990年 | 1006篇 |
1989年 | 921篇 |
1988年 | 708篇 |
1987年 | 444篇 |
1986年 | 395篇 |
1985年 | 275篇 |
1984年 | 316篇 |
1983年 | 269篇 |
1982年 | 235篇 |
1981年 | 143篇 |
1980年 | 121篇 |
1979年 | 94篇 |
1978年 | 60篇 |
1977年 | 57篇 |
1976年 | 54篇 |
1959年 | 56篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
LaNiO3 was synthesized by sol-gel method in which lanthanum nitrate and nickel nitrate were used as start materials and citric acid was used as complex for gel formation.The precursor was dried and subsequently heated at elevated temperature to form the desired product.XRD analysis shows that pure LaNiO3 was synthesized.Electrical conductivity and electrochemical performance of the material were tested.The electrical conductivity decreases from 34.5that there are current peaks in the curve, which is the evidence of the electrochemical activity of LaNiO3. 相似文献
53.
讨论了直流法在线测量钯氢化物电极电阻时的电化学效应,计算了电解液的共导、测量电流与电解电流引起的浓差电池效应以及电极作为集流体引起的电阻贡献。结果表明:当电极具有高的长度与半径比值、粗糙的表面、高的溶液电导以及大的电解电流时容易引起显著的附加电阻。 相似文献
54.
Using boundary element based three dimensional modelling for linear fracture mechanics, we present an analysis of cracking in a homogeneous medium subject to contact load. The proposed iterative solution procedure allows a simultaneous treatment of a reasonable number of partially closed cracks. It is shown that the most probable direction of propagation of a vertical internal crack is strongly dependent on its size compared to the contact radius and its location with respect to the axis of maximum normal load. 相似文献
55.
A. Yu. Luchka 《Cybernetics and Systems Analysis》2003,39(6):880-888
A modified variational-gradient method is proposed and substantiated for quasilinear operator equations in a Hilbert space. 相似文献
56.
Chuanju Xu 《Journal of scientific computing》2006,27(1-3):495-505
A stabilization method for the spectral element computation of incompressible flow problems is investigated. It is based on a filtering procedure which consists in filtering the velocity field by a spectral vanishing Helmholtz-type operator at each time step. Relationship between this filtering procedure and SVV-stabilization method, introduced recently in [JCP, 2004, 196(2), p680], is established. A number of numerical examples are presented to show the accuracy and stabilization capability of the method. 相似文献
57.
The dynamic flexibility (DF) and improved dynamic flexibility (IDF) methods can be applied to extract constrained structural modes from free-free modal test data. The residual flexibility method is also good for boundaries of constrained structure with rigid supports. Under elastic support boundary conditions both the DF and residual flexibility methods cannot produce accurate results. This paper expands the previously published IDF method to become a more general approach for structural design engineers. A new method called the general dynamic flexibility (GDF) method has been developed in this paper to extract constrained structural modes from free test data. The GDF method can always be applied as follows: (1) when the boundary support stiffness is very stiff, the GDF method can accurately obtain results from rigid support as by Liu et al. in 2001 and Zhang and Wei in 2003; (2) when the support stiffness is soft, the present method can produce results similar to those free-free modal parameters measured by hanging structures using rubber band; (3) when the support stiffness is zero, the method can reproduce true free-free modal parameters; and (4) when the support stiffness has any finite values, the GDF method can also achieve satisfactory results for engineering use. The algorithm included in the GDF method converges rapidly and is numerically stable in the analysis. This feature is very practical for many engineering applications for using the GDF method. 相似文献
58.
This paper studies a Kansas Department of Transportation welded plate girder bridge that developed fatigue cracks at small web gaps close to the girder top flange. Repair had been previously performed by softening the connection plate end with a slot retrofit, but cracks were recently found to have reinitiated at some of the repaired details and are again propagating. A comprehensive finite-element method study was performed to investigate the cracking behavior observed in the bridge and to recommend appropriate measures for future bridge retrofit. The analytical results show that stresses developed at the top flange web gaps could exceed yielding under the loading of an HS15 fatigue truck. The current slot repair used in the bridge was found to have introduced higher magnitude fatigue stresses in the web gap. To achieve a permanent repair of the bridge, it is recommended that a welded connection plate to flange attachment be used during future bridge retrofit. The web gap details should be able to withstand unlimited number of load cycles once this additional repair is performed. 相似文献
59.
Hong Long Chen 《Canadian Metallurgical Quarterly》2007,23(4):171-181
The difficulty in applying the standard curve (S-curve) and cost-schedule integration (CSI) techniques for company-level cost flow forecasting in a project-based industry is the prerequisite of forecasting future unknown individual projects and contract classifications. By analyzing cost flows at the company level through a pool of macroeconomic and internal financial data, this paper proposes an innovative approach to firm-specific model estimation. First, a series of data transformations introduce linear relationships between cost, macroeconomic, and internal financial variables. Second, multivariate regression analysis is employed for initial model building. Third, for the purposes of model restructuring, a subsequent application of Yule–Walker estimates and incomplete principal component analysis is used. This paper uses a sample of four project-based construction firms to demonstrate model performance. Using this methodology, mean absolute percentage error (MAPE) values of the forecasting models range from 0.27 to 0.60%. As such, the transformed cost, macroeconomic, internal financial data could strongly predict company-level cost flow forecasting. While converting the predicted cumulative cost data to periodic cost flows, the MAPE values were augmented, ranging from 7.04 to 17.55%, thus, requiring future research. 相似文献
60.
This paper presents a semianalytical method for the prediction of interlaminar stresses and displacements near the free edges and ply cracks in general angle-ply laminates subjected to biaxial extensions and/or in plane shear deformation. The method is based on a state space representation of the three-dimensional equations of elasticity. Numerical solutions are obtained by using layer refinement in the through thickness direction and Fourier series expansion in the other directions. By this approach, an angle-ply laminate may be composed of an arbitrary number of monoclinic layers and each layer may have different material property and thickness. This method guarantees continuous fields of all interlaminar stresses across interfaces between material layers. Numerical results are compared with those obtained from other methods. It is found that the theory provides a satisfactory approximation to the stress singularities near the free edges and ply cracks. Numerical solutions for antisymmetric laminates under extension and general laminates under shearing are new in the literature and can be used as benchmarks for validating new models. 相似文献