全文获取类型
收费全文 | 413993篇 |
免费 | 35604篇 |
国内免费 | 22748篇 |
专业分类
电工技术 | 29214篇 |
技术理论 | 53篇 |
综合类 | 53465篇 |
化学工业 | 44712篇 |
金属工艺 | 17948篇 |
机械仪表 | 25452篇 |
建筑科学 | 55885篇 |
矿业工程 | 20925篇 |
能源动力 | 12621篇 |
轻工业 | 23102篇 |
水利工程 | 19632篇 |
石油天然气 | 18498篇 |
武器工业 | 4597篇 |
无线电 | 28331篇 |
一般工业技术 | 38232篇 |
冶金工业 | 21221篇 |
原子能技术 | 5393篇 |
自动化技术 | 53064篇 |
出版年
2024年 | 1455篇 |
2023年 | 4279篇 |
2022年 | 8148篇 |
2021年 | 9754篇 |
2020年 | 10611篇 |
2019年 | 8990篇 |
2018年 | 8648篇 |
2017年 | 10730篇 |
2016年 | 12495篇 |
2015年 | 13693篇 |
2014年 | 23864篇 |
2013年 | 22293篇 |
2012年 | 28919篇 |
2011年 | 30258篇 |
2010年 | 23848篇 |
2009年 | 24791篇 |
2008年 | 23148篇 |
2007年 | 29611篇 |
2006年 | 27254篇 |
2005年 | 23528篇 |
2004年 | 19825篇 |
2003年 | 17612篇 |
2002年 | 14664篇 |
2001年 | 12342篇 |
2000年 | 10510篇 |
1999年 | 8797篇 |
1998年 | 6740篇 |
1997年 | 5861篇 |
1996年 | 5246篇 |
1995年 | 4524篇 |
1994年 | 3962篇 |
1993年 | 2915篇 |
1992年 | 2581篇 |
1991年 | 1900篇 |
1990年 | 1635篇 |
1989年 | 1470篇 |
1988年 | 1157篇 |
1987年 | 739篇 |
1986年 | 586篇 |
1985年 | 439篇 |
1984年 | 414篇 |
1983年 | 307篇 |
1982年 | 280篇 |
1981年 | 220篇 |
1980年 | 167篇 |
1979年 | 149篇 |
1978年 | 88篇 |
1977年 | 87篇 |
1976年 | 71篇 |
1959年 | 83篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Mehmet Dorduncu Junuthula Narasimha Reddy 《Journal of Adhesion Science and Technology》2019,33(2):156-186
This study presents an improved mathematical model to analyse the stress wave propagation in adhesively bonded functionally graded (FG) circular cylinders (butt joint) under an axial impulsive load. The volume fractions of the material constituents in the upper and lower cylinders were functionally tailored through the thickness of each cylinder using a power-law. The effective material properties of both cylinders, which are made of aluminum (Al) and silicon carbide (SiC), at any point were predicted by using the Mori–Tanaka homogenization scheme. In this improved model, the governing equations of the wave propagation include the spatial derivatives of local mechanical properties and were discretized by means of the finite difference method. The influence of these spatial derivatives and the compositional gradient exponent on the displacement and stress distributions of the joint was investigated. The material composition variations of both cylinders affected the displacement and stress fields whereas the compositional gradient exponent had a minor effect. The stress concentrations were alleviated in time, the displacement and stress distributions/variations around/along the upper and lower cylinder-adhesive interfaces were significantly affected by the adhesive layer. The spatial derivatives also affected the temporal histories of the displacement and stress components evaluated at the selected critical points of the upper cylinder, adhesive layer and lower cylinder. The consideration of the spatial local material derivatives provided a more accurate mathematical model of wave propagations through the graded layered structures. 相似文献
22.
Elli Ntakou Ralph Masiello Farnaz Farzan Shay Bahramirad Aleksi Paaso M.A. Nayeem Maigha Maigha Daniel Kushner 《The Electricity Journal》2019,32(4):45-49
This paper presents part of the work ComEd and Quanta Technology have performed to quantify the locational and temporal value of DER to avoid distribution grid upgrade investments. It focuses on the formulation of a robust and efficient algorithm for DER optimal dispatch on a distribution feeder to mitigate the violation of current and voltage limits using the allocated cost of capacity and locational marginal value of real and reactive DER injection/withdrawal. 相似文献
23.
24.
An electrolyte Equation of State is presented by combining the Cubic Plus Association Equation of State,Mean Spherical Approximation and the Born equation.This new model uses experimental relative static permittivity,intend to predict well the activity coefficients of individual ions (ACI) and liquid densities of aqueous solutions.This new model is applied to model water + NaCl binary system and water + gas +NaCl ternary systems.The cation/anion-water interaction parameters of are obtained by fitting the exper-imental data of ACI,mean ionic activity coefficients (MIAC) and liquid densities of water + NaCl binary system.The cation/anion-gas interaction parameters are obtained by fitting the experimental data of gas solubilities in aqueous NaCl solutions.The modeling results show that this new model can correlate well with the phase equilibrium and volumetric properties.Without gas,predictions for ACI,MIAC,and liquid densities present relative average deviations of 1.3%,3.6% and 1.4% compared to experimental ref-erence values.For most gas-containing systems,predictions for gas solubilities present relative average deviations lower than 7.0%.Further,the contributions of ACI,and salting effects of NaCl on gases are ana-lyzed and discussed. 相似文献
25.
The effect of the emergency perception of bystanders of cyberbullying victims on helping behaviors is often neglected in research on cyberbullying. In this study, we explored the influence of this cognitive factor on cyber-bystanders’ helping tendencies as well as elucidated possible underlying processes. The results of two studies were reported. In Study 1, 150 undergraduates read a true case of a girl experiencing cyberbullying. The results indicated that when the participants perceived the victim’s situation to be more critical (i.e., higher emergency perception), their helping tendencies were stronger, partly through increased state empathy followed by feelings of responsibility to help. In Study 2, we randomly assigned 300 undergraduates to two groups. The low emergency group read the same cyberbullying case as Study 1, whereas the cyberbullying case read by the high emergency group contained additional emergency information of the victim. The results indicated that the high emergency group expressed stronger helping tendencies than did the low emergency group. This effect was caused by a stronger perception that the victim was in an emergency situation, which not only strengthened the participants’ helping tendencies directly but also indirectly through increasing their state empathy and feelings of responsibility to help. 相似文献
26.
Hydrogel-based nanofibers or vice versa are a relatively new class of nanomaterials, in which hydrogels are structured in nanofibrous form. Structure and size of the material directly governs its functionality, therefore, in hydrogel science, the nanofibrous form of hydrogels enables its usage in targeted applications. Hydrogel nanofiber system combines the desirable properties of both hydrogel and nanofiber like flexibility, soft consistency, elasticity, and biocompatibility due to high water content, large surface area to volume ratio, low density, small pore size and interconnected pores, high stiffness, tensile strength, and surface functionality. Swelling behavior is a critical property of hydrogels that is significantly increased in hydrogel nanofibers due to their small size. Electrospinning is the most popular method to fabricate “hydrogel nanofibers,” while other processes like self-assembly, solution blowing and template synthesis also exist. Merging the characteristics of both hydrogels and nanofibers in one system allows applications in drug delivery, tissue engineering, actuation, wound dressing, photoluminescence, light-addressable potentiometric sensor (LAPS), waterproof breathable membranes, and enzymatic immobilization. Treatment of wastewater, detection, and adsorption of metal ions are also emerging applications. In this review paper, we intend to summarize in detail about electrospun “hydrogel nanofiber” in relation to its synthesis, properties, and applications. 相似文献
27.
28.
《International Journal of Hydrogen Energy》2022,47(54):22981-22992
In this study, a three-dimensional model was established using the lattice Boltzmann method (LBM) to study the internal ice melting process of the gas diffusion layer (GDL) of the proton exchange membrane fuel cell (PEMFC). The single-point second-order curved boundary condition was adopted. The effects of GDL carbon fiber number, growth slope of the number of carbon fibers and carbon fiber diameter on ice melting were studied. The results were revealed that the temperature in the middle and lower part of the gradient distribution GDL is significantly higher than that of the no-gradient GDL. With the increase of the growth slope of the number of carbon fiber, the temperature and melting rate gradually increase, and the position of the solid-liquid interface gradually decreases. The decrease in the number of carbon fibers has a similar effect as the increase in the growth slope of the number of carbon fibers. In addition, as the diameter of the carbon fiber increases, the position of the solid-liquid interface gradually decreases first and then increases. 相似文献
29.
Zachary Zander Deirdre Newton Heather Scaglione Averie Reiber Parminder Agarwal 《Polymer Engineering and Science》2021,61(12):3029-3036
The incursion of microbial growth on polymeric products can deteriorate their performance and lead to the development of undesirable staining and odors. A growing trend in the industry has aimed to reduce microbial populations on high-touch surfaces via the use of antimicrobials to protect material aesthetics and durability or to prevent the spread of pathogenic microorganisms. In this study, a variety of plastic substrates (30 unique polymer compounds), including poly(acrylonitrile-co-butadiene-co-styrene), poly(butylene terephthalate), poly(etherimide), various thermoplastic elastomers (TPEs), poly(carbonates), and poly(amides), were screened for susceptibility to microbial attack using American Society for Testing and Materials (ASTM) G21 (fungi susceptibility), Japanese Industrial Standard (JIS) Z2801, and modified ASTM E1428-15a (bacterial susceptibility) test standards. TPEs were determined to be most susceptible to microbial attack under the appropriate environmental conditions. Subsequent studies assessed the use of an antimicrobial additive, zinc pyrithione (ZPT), for potential efficacy in a variety of TPE blends for diverse target market applications. ZPT proved to be very effective in protecting TPEs, reducing Staphylococcus aureus and Escherichia coli populations by 99.9% or more in JIS Z2801 testing and inhibiting fungal growth (rating = 0) according to the ASTM G21 standard. 相似文献