全文获取类型
收费全文 | 521篇 |
免费 | 30篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 4篇 |
化学工业 | 93篇 |
金属工艺 | 21篇 |
机械仪表 | 14篇 |
建筑科学 | 9篇 |
能源动力 | 20篇 |
轻工业 | 34篇 |
水利工程 | 2篇 |
石油天然气 | 1篇 |
无线电 | 51篇 |
一般工业技术 | 176篇 |
冶金工业 | 73篇 |
原子能技术 | 3篇 |
自动化技术 | 52篇 |
出版年
2023年 | 11篇 |
2022年 | 14篇 |
2021年 | 18篇 |
2020年 | 18篇 |
2019年 | 18篇 |
2018年 | 29篇 |
2017年 | 17篇 |
2016年 | 23篇 |
2015年 | 11篇 |
2014年 | 22篇 |
2013年 | 38篇 |
2012年 | 18篇 |
2011年 | 24篇 |
2010年 | 23篇 |
2009年 | 17篇 |
2008年 | 21篇 |
2007年 | 14篇 |
2006年 | 10篇 |
2005年 | 13篇 |
2004年 | 11篇 |
2003年 | 6篇 |
2002年 | 6篇 |
2001年 | 6篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1998年 | 10篇 |
1997年 | 12篇 |
1996年 | 11篇 |
1995年 | 7篇 |
1994年 | 10篇 |
1993年 | 6篇 |
1992年 | 9篇 |
1991年 | 6篇 |
1990年 | 12篇 |
1989年 | 7篇 |
1988年 | 9篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1977年 | 2篇 |
1976年 | 7篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有553条查询结果,搜索用时 640 毫秒
11.
Uma Batra S. Ray S. R. Prabhakar 《Journal of Materials Engineering and Performance》2003,12(5):597-601
A ductile iron containing 0.6% copper as the main alloying element was austempered at a fixed austempering temperature of
330 °C for a fixed austempering time of 60 min after austenitization at 850 °C for different austenitization periods of 60,
90, and 120 min. The austempering process was repeated after changing austenitization temperature to 900 °C. The effect of
austenitization temperature and time was studied on the carbon content and its distribution in the austenite after austenitization.
The effect of austenitization parameters was also studied on austempered microstructure, structural parameters like volume
fraction of austenite, X
γ
, carbon content C
γ
, and X
γ
C
γ
, and bainitic ferrite needle size, d
α
after austempering. The average carbon content of austenite increases linearly with austenitization time and reaches a saturation
level. Higher austenitization temperature results in higher carbon content of austenite. As regards the austempered structure,
the lowering austenitization temperature causes significant refinement and more uniform distribution of austempered structure,
and a decrease in the volume fraction of retained austenite. 相似文献
12.
In the present investigation, the effect of alloying elements on the austempering process, austempered microstructure, and
structural parameters of two austempered ductile irons (ADI) containing 0.6% Cu and 0.6% Cu/1.0% Ni as the main alloying elements
was investigated. The optical metallography and x-ray diffraction were used to study the changes in the austempered structure.
The effect of alloying additions on the austempering kinetics was studied using the Avrami equation. Significantly more upper
bainite was observed in the austempered Cu-Ni alloyed ADI than in Cu alloyed ADI. The volume fraction of retained austenite
(X
γ), the carbon level in the retained austenite (C
γ), and the product X
γ
C
γ in an austempered structure of Cu-alloyed ADI are higher than in Cu-Ni-alloyed ADI. The austempering Kinetics is slowed down
by the addition of Ni. 相似文献
13.
Ritika Puri Mohit Mahajan Nikhil Shri Sahajpal Harjeet Singh Harmanpreet Singh 《Drug development and industrial pharmacy》2016,42(7):1032-1041
Context: Docosahexanoic acid (DHA) is an essential omega-3 fatty acid for normal brain development and its use has increased considerably in recent years.Objective: The aim of this study is to develop and evaluate self-nanoemulsifying drug delivery systems (SNEDDS) of DHA for improved palatability, dispersibility and bioavailability.Methods: The SNEDDS were prepared and evaluated for miscibility, employing different combinations of olive oil and soyabean oil as oil phase, Span 80, Span 20, soya phosphatidylcholine, Labrafil M 1944 CS as surfactants while Tween 80, PEG 400, Cremophor RH40 and propylene glycol as cosurfactants. Thermodynamically stable SNEDDS were characterized for dispersibility, self-emulsification time, droplet size, zeta potential along with sensory analysis. The optimized formulation was subjected to ex vivo and in vivo evaluation such as intestinal permeability, memory performance test, brain concentration and histopathology studies.Results: The optimized SNEDDS formulation showed emulsification time of 27?±?4.7?s with droplet size of 17.6?±?3.5?nm and zeta potential of??37.6?±?0.5?mV. Intestinal absorption study depicted 18.3%, 21.5%, 41.5%, 98.7% absorption of DHA with SNEDDS-based formulation in comparison to 8.2%, 15.1%, 28.8%, 46.1% absorption of DHA with oil-based marketed formulation after 0.5, 1, 2 and 4?h. DHA concentration in brain homogenate was found to be increased to 2.6-fold in comparison to DHA-marketed formulation. This could be ascribed to enhanced dispersibility and bioavailability of DHA from nanosized formulation.Conclusion: The developed formulation led to enhanced dispersibility and bioavailability of DHA due to the formation of nanodroplets. 相似文献
14.
Almuatasim Alomari Ashok Batra Mohan Aggarwal C. R. Bowen 《Journal of Materials Science: Materials in Electronics》2016,27(10):10020-10030
This paper demonstrates a multi-source energy harvester that is able to utilize simultaneously both piezoelectric and pyroelectric effects in lead magnesium niobate-lead titanate (PMN-PT) single crystal. The paper presents a study of PMN-PT single crystal with a (67:33) composition grown in our laboratory via a vertical gradient freeze method without any flux. The performance of the piezoelectric and pyroelectric energy harvester using unimorph device structure was evaluated via modeling and experiment. The theoretical study was implemented based on a distributed parameter electromechanical model and the modelling procedure was approximated using finite element analysis to predict the electromechanical behavior of the harvester. The maximum power density at a resonance frequency of 50 Hz and optimum resistance of 2 MΩ was 16.7 nW/(g2 cm3) under a 1 g acceleration of vibration. The measured values of electrical output parameters were in good agreement with theoretical and modelling results using MATLAB and COMSOL Multiphysics, respectively. By using the pyroelectric effect along with the piezoelectric effect, the output voltage of the energy harvester was found to be enhanced at the optimum resistance and specific frequency values. It was noticed that the output voltage was increased monotonically with temperature-difference (ΔT) and reaches up to 180 % of its original value under temperature difference of 1.7 °C at a frequency value of 49 Hz. 相似文献
15.
A.J.M. Ferreira R.C. Batra C.M.C. Roque L.F. Qian R.M.N. Jorge 《Composite Structures》2006,75(1-4):593-600
We use the global collocation method, the first and the third-order shear deformation plate theories, the Mori–Tanaka technique to homogenize material properties, and approximate the trial solution with multiquadric radial basis functions to analyze free vibrations of functionally graded plates. Frequencies computed by the present method are found to agree well with those from the analytical solution of Vel and Batra, and the numerical solution of Qian et al. based on the meshless local Petrov–Galerkin formulation. 相似文献
16.
Optimization of process parameters is helpful in efficient working of the process and, hence, in lowering the cost of machining. Optimization of ECM process parameters has been achieved by considering only one objective at a time from metal removal rate, geometrical accuracy, and total process cost. From a practical point of view, a solution of the ecm problem satisfying all three objectives simultaneously is highly desirable.In the proposed model, a multi-objective problem involving the ecm process is formulated producing highly nonlinearized equations. These are then linearized by regression analysis and converted into a goal programming format. Finally, the problem is solved by the partitioning algorithm.It is concluded that the tool, or cathode, remains safe at the optimal values of design variables obtained in the examples discussed. The optimal value of voltage when metal removal rate is the only objective, is found to be higher than the case when the geometrical accuracy requirement is also to be satisfied. 相似文献
17.
18.
Wireless Networks - In this article, we propose a novel routing algorithm for wireless sensor network, which achieves uniform energy depletion across all the nodes and thus leading to prolonged... 相似文献
19.
Polyethersulfone (PES) composites were developed with carbon fabric (CF). Cold remote nitrogen oxygen plasma (CRNOP) treatment
was employed to the CF to incorporate functional groups and promote fiber–matrix adhesion. This study includes the effect
of PES melt flow index (MFI) on the wettability of CF and its influence on fretting wear performance. Evaluations of fretting
wear properties of composites led to the conclusion that the CRNOP treatment proved beneficial to enhance performance properties
significantly. Polymer MFI and treatment to CF proved to be the decisive parameters for controlling performance of composites
apart from operating parameters. Perforations on the treated carbon fiber, evidently observed by FESEM, improved the fiber–matrix
adhesion, and hence the performance properties. Artificial neuron network (ANN) was used for prediction of the wear behavior
of composites. 相似文献
20.
R. C. Batra 《International journal for numerical methods in engineering》1981,17(12):1823-1833
The nonlinear elastic problem involving the indentation of a slightly compressible rubber-like layer bonded to a rigid cylinder and indented by another rigid cylinder is analysed by the finite element method. Both the geometric and material nonlinearities are accounted for. The finite element formulation of the problem is based upon a variational principle recently proposed by Cescotto and Fonder, and is valid for both slightly compressible and incompressible materials. The results computed and presented graphically include the shape of the indented surface, the pressure distribution over the contact surface, and the stress distribution at the bond surface. For the same contact width, the results for the compressible material are found to differ significantly from those for the case when the rubber-like layer is assumed to be incompressible. 相似文献