全文获取类型
收费全文 | 911篇 |
免费 | 54篇 |
国内免费 | 8篇 |
专业分类
电工技术 | 21篇 |
化学工业 | 107篇 |
金属工艺 | 18篇 |
机械仪表 | 27篇 |
建筑科学 | 25篇 |
矿业工程 | 1篇 |
能源动力 | 40篇 |
轻工业 | 107篇 |
水利工程 | 7篇 |
石油天然气 | 3篇 |
无线电 | 112篇 |
一般工业技术 | 228篇 |
冶金工业 | 97篇 |
原子能技术 | 2篇 |
自动化技术 | 178篇 |
出版年
2023年 | 18篇 |
2022年 | 41篇 |
2021年 | 34篇 |
2020年 | 40篇 |
2019年 | 38篇 |
2018年 | 56篇 |
2017年 | 35篇 |
2016年 | 27篇 |
2015年 | 21篇 |
2014年 | 28篇 |
2013年 | 44篇 |
2012年 | 35篇 |
2011年 | 48篇 |
2010年 | 39篇 |
2009年 | 38篇 |
2008年 | 15篇 |
2007年 | 24篇 |
2006年 | 22篇 |
2005年 | 16篇 |
2004年 | 18篇 |
2003年 | 6篇 |
2002年 | 8篇 |
2001年 | 14篇 |
2000年 | 10篇 |
1999年 | 8篇 |
1998年 | 26篇 |
1997年 | 22篇 |
1996年 | 12篇 |
1995年 | 12篇 |
1994年 | 16篇 |
1993年 | 19篇 |
1992年 | 11篇 |
1991年 | 17篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 13篇 |
1986年 | 6篇 |
1985年 | 11篇 |
1984年 | 8篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1981年 | 11篇 |
1980年 | 12篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1977年 | 11篇 |
1976年 | 13篇 |
1975年 | 4篇 |
1972年 | 4篇 |
排序方式: 共有973条查询结果,搜索用时 15 毫秒
71.
P. B. Thanedar J. S. Arora C. H. Tseng O. K. Lim G. J. Park 《International journal for numerical methods in engineering》1986,23(12):2187-2203
This paper describes the basic ideas of sequential quadratic programming (SQP) algorithms for design optimization. There are two fundamental differences between the various algorithms: (i) the difinition of the QP subproblem solved at each iteration, and (ii) the descent function used during step size determination. The performances of the algorithms can change dramatically depending on how the two steps are executed. Numerical implementation details of various computational steps are discussed. Three programs based on SQP algorithms are used to solve 17 structural design problems having 7 to 96 design variables and 10 to 1051 performance constraints besides design variable bounds. Based on the performance of these programs, efficient procedures to execute various steps of the SQP methods are determined. It is concluded that the potential constraint strategy, where only a subset of the constraints is used to define the QP subproblem, is essential for large scale engineering design applications. With this strategy the SQP methods are quite robust and have great potential for routine application in engineering design. 相似文献
72.
Ashok D. Belegundu Jasbir S. Arora 《International journal for numerical methods in engineering》1985,21(9):1583-1599
A comprehensive study of various mathematical programming methods for structural optimization is presented. In recent years, many modern optimization techniques and convergence results have been developed in the field of mathematical programming. The aim of this paper is twofold: (a) to discuss the applicability of modern optimization techniques to structural design problems, and (b) to present mathematical programming methods from a unified and design engineers' viewpoint. Theoretical aspects are considered here, while numerical results of test problems are discussed in a companion paper. Special features possessed by structural optimization problems, together with recent developments in mathematical programming (recursive quadratic programming methods, global convergence theory), have formed a basis for conducting the study. Some improvements of existing methods are noted and areas for future investigation are discussed. 相似文献
73.
Charu Mathur Melissa H Stigler Cheryl L Perry Monika Arora K Srinath Reddy 《Nicotine & tobacco research》2008,10(1):109-116
This study examined whether the distribution of tobacco use and related psychosocial risk factors among youth in urban India vary by socioeconomic status (SES). Data were derived from a cross-sectional survey of students enrolled in the 6th and 8th grades in 32 schools in Delhi and Chennai (N = 11,642). The survey was conducted in 2004, before the implementation of a program designed to prevent and reduce tobacco use (MYTRI). Mixed-effect regression models were used (a) to determine the prevalence of tobacco use among private (higher SES) and government (lower SES) school students, (b) to investigate whether certain psychosocial factors were associated with increased tobacco use, and (c) to determine how these factors varied by school type. Ever-use of multiple forms of tobacco (e.g., gutkha, bidis, and cigarettes) was more prevalent among government school students than private school students. After adjusting for city, gender, grade, and age, we found the prevalence rate for ever-use of any tobacco product to be 18.9% for government school students, compared with 12.2% for private school students (p<.01). Students in government schools scored lower than private school students on most psychosocial risk factors for tobacco use studied here, indicating higher risk. Government school students scored the lowest for refusal skills, self-efficacy, and reasons not to use tobacco. Social susceptibility to chewing tobacco and social susceptibility to smoking were strong correlates of current tobacco use among government school students. Exposure to tobacco advertising was also a strong correlate of current tobacco use for government school students but not private school students. In two large cities of India, students attending government schools are using many forms of tobacco at higher rates than private school students. The psychosocial risk profile of government school students suggests they are more vulnerable to initiation and use and to outside influences that encourage use. 相似文献
74.
A practical approach towards mathematical modeling of deposition rate during twin-wire submerged arc welding 总被引:1,自引:1,他引:0
Abhay Sharma Navneet Arora Bhanu K. Mishra 《The International Journal of Advanced Manufacturing Technology》2008,36(5-6):463-474
The present paper deals with a shop floor applicable mathematical model for deposition rate during twin-wire submerged arc
welding. The salient features of this model are (1) instead of melting rate, as modeled during past investigations, it quantifies
the deposition rate, which is the actual outcome of the process and always remains smaller than the melting rate because of
evaporation or spatters losses and (2) it estimates electrode extension in order to predict the deposition rate which makes
the proposed model more practical than the models constituted with the help of experimental measurement of electrode extension.
The model is more scientific than the simplified models where contact tube to work-piece distance has been considered as the
electrode extension. A critical review of the relevant past investigation is given and a mathematical model is developed for
deposition rate during the twin-wire welding with both the polarities, i.e., direct current electrode positive and direct
current electrode negative. The model is calibrated using the results of 200 experimental runs and it is found to be very
accurate with very high coefficient of regression and admissible standard error. The developed model is further validated
with extra experimental runs. The practicality of the considered approach for prediction of deposition rate can further be
used in future research for other consumable arc welding processes. 相似文献
75.
76.
Rakesh Kumar Soni Harjeet Singh Krishna Dutt Priyanka Arora 《Journal of Polymer Research》2010,17(3):411-427
The mixing torque behavior of ter blends of isotactic-polypropylene (iPP) with ethylene-propylene diene rubber (EPDM)/Nitrile
rubber (NBR) was studied with the help of Rheometer using resole type phenolic resin as a cross-linking agents. Systematic
changes with varying blend composition were observed in stress-strain behavior in the yield region viz., width of yield peak,
work of yield, yield stress and yield strain. Analysis of yield stress data was made on the basis of various mathematical
expressions of first power and two-thirds power laws of blend composition dependence and the porosity model. It led to consistent
result from the expressions about the variation of stress concentration effect in both uncross-linked and cross-linked blend
systems. With the aid of scanning electron microscopy (SEM) shapes and sizes of dispersed elastomer phase (EPDM / NBR) domains
at varying blend compositions were studied. 相似文献
77.
Deepti Mishra Ruma Arora Swati Lahiri Sudhir Sitaram Amritphale Navin Chandra 《Protection of Metals and Physical Chemistry of Surfaces》2014,50(5):628-631
In the present work iron oxide nanoparticles have been synthesized by alkaline solvo thermal method using anhydrous ferric chloride, sodium hydroxide, polyethylene glycol and cetyl trimethyl ammonium bromide and characterized by X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Field Emission Scanning Electron Microscopy (FESEM), Energy-dispersive X-ray Spectroscopy (EDX) and Thermal Gravimetric Analysis (TGA). XRD indicated that the product is a mixture of different phases of iron oxide viz. gamma-Fe2O3 (maghemite, tetragonal), Fe2O3 (maghemite, cubic), Fe3O4 (magnetite, cubic) and ?-Fe2O3(epsilon iron oxide). FESEM studies indicated that size of the particles is observed in the range of about 19.8 nm to 48 nm. EDX spectral analysis reveals the presence of carbon, oxygen, iron in the synthesized nanoparticles. The FTIR spectra indicated absorption bands due to O-H stretching, C-O bending, N-H stretching and bending, C-H stretching and Fe-O stretching vibrations. TGA curve represented weight loss of around 3.0446 % in the sample at temperature of about 180°C due to the elimination of the water molecules absorbed by the nanoparticles from the atmosphere. 相似文献
78.
Ankit Agarwal Kathleen M. Guthrie Charles J. Czuprynski Michael J. Schurr Jonathan F. McAnulty Christopher J. Murphy Nicholas L. Abbott 《Advanced functional materials》2011,21(10):1863-1873
The design of polyelectrolyte multilayers (PEMs) that can be prefabricated on an elastomeric stamp and mechanically transferred onto biomedically‐relevant soft materials, including medical‐grade silicone elastomers (E’~450–1500 kPa; E’‐elastic modulus) and the dermis of cadaver skin (E’~200–600 kPa), is reported. Whereas initial attempts to stamp PEMs formed from poly(allylamine hydrochloride) and poly(acrylic acid) resulted in minimal transfer onto soft materials, we report that integration of micrometer‐sized beads into the PEMs (thicknesses of 6–160 nm) led to their quantitative transfer within 30 seconds of contact at a pressure of ~196 kPa. To demonstrate the utility of this approach, PEMs were impregnated with a range of loadings of silver‐nanoparticles and stamped onto the dermis of human cadaver skin (a wound‐simulant) that was subsequently incubated with bacterial cultures. Skin dermis stamped with PEMs that released 0.25 ± 0.01 μg cm?2 of silver ions caused a 6 log10 reduction in colony forming units of Staphylococcus epidermidis and Pseudomonas aeruginosa within 12 h. Significantly, this level of silver release is below that which is cytotoxic to NIH 3T3 mouse fibroblast cells. Overall, this study describes a general and facile approach for the functionalization of biomaterial surfaces without subjecting them to potentially deleterious processing conditions. 相似文献
79.
Ankit Srivastava Sia Nemat-Nasser 《Mechanics of materials : an international journal》2011,43(12):913-917
In this paper we consider a sample of a linearly elastic heterogeneous composite in elastodynamic equilibrium and present universal theorems which provide lower bounds for the total elastic strain energy plus the kinetic energy, and the total complementary elastic energy plus the kinetic energy. For a general heterogeneous sample which undergoes harmonic motion at a single frequency, we show that, among all consistent boundary data which produce the same average strain, the uniform-stress boundary data render the total elastic strain energy plus the kinetic energy an absolute minimum. We also show that, among all consistent boundary data which produce the same average momentum in the sample, the uniform velocity boundary data render the total complementary elastic energy plus the kinetic energy an absolute minimum. We do not assume statistical homogeneity or material isotropy in our treatment, although they are not excluded. These universal theorems are the dynamic equivalent of the universal theorems already known for the static case
[Nemat-Nasser and Hori, 1993] and [Nemat-Nasser and Hori, 1995]. It is envisaged that the bounds on the total energy presented in this paper will be used to formulate computable bounds on the overall dynamic properties of linearly elastic heterogeneous composites with arbitrary microstructures. 相似文献
80.
Glass-fibre reinforced polymer (GFRP) sandwich structures (1.6 m × 1.3 m) were subject to 30 kg charges of C4 explosive at stand-off distances 8–14 m. Experiments provide detailed data for sandwich panel response, which are often used in civil and military structures, where air-blast loading represents a serious threat. High-speed photography, with digital image correlation (DIC), was employed to monitor the deformation of these structures during the blasts. Failure mechanisms were revealed in the DIC data, confirmed in post-test sectioning. The experimental data provides for the development of analytical and computational models. Moreover, it underlines the importance of support boundary conditions with regards to blast mitigation. These findings were analysed further in finite element simulations, where boundary stiffness was, as expected, shown to strongly influence the panel deformation. In-depth parametric studies are ongoing to establish the hierarchy of the various factors that influence the blast response of sandwich composite structures. 相似文献