首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   129687篇
  免费   7775篇
  国内免费   3624篇
电工技术   6407篇
技术理论   7篇
综合类   11723篇
化学工业   9604篇
金属工艺   5371篇
机械仪表   14390篇
建筑科学   29071篇
矿业工程   4051篇
能源动力   3048篇
轻工业   5958篇
水利工程   3922篇
石油天然气   4449篇
武器工业   1478篇
无线电   7820篇
一般工业技术   13131篇
冶金工业   2964篇
原子能技术   722篇
自动化技术   16970篇
  2024年   229篇
  2023年   1211篇
  2022年   2017篇
  2021年   2731篇
  2020年   2973篇
  2019年   2280篇
  2018年   2258篇
  2017年   2811篇
  2016年   3293篇
  2015年   3574篇
  2014年   9274篇
  2013年   7356篇
  2012年   9262篇
  2011年   9896篇
  2010年   8361篇
  2009年   8617篇
  2008年   7759篇
  2007年   9319篇
  2006年   7846篇
  2005年   6923篇
  2004年   5544篇
  2003年   5247篇
  2002年   4192篇
  2001年   3497篇
  2000年   2856篇
  1999年   2217篇
  1998年   1825篇
  1997年   1491篇
  1996年   1297篇
  1995年   1065篇
  1994年   847篇
  1993年   599篇
  1992年   460篇
  1991年   407篇
  1990年   260篇
  1989年   265篇
  1988年   202篇
  1987年   144篇
  1986年   84篇
  1985年   95篇
  1984年   124篇
  1983年   85篇
  1982年   92篇
  1981年   32篇
  1980年   39篇
  1979年   30篇
  1978年   15篇
  1977年   11篇
  1959年   12篇
  1951年   7篇
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
81.
The consumption of healthful foods is relevant for the well-being of society. However, understanding healthfulness may be difficult because, in some cultures (i.e., the U.S.), individuals assume that unhealthy equals tasty, an association that does not hold in other contexts (i.e., France). Auditory cues could serve to inform consumers about the expected experience with food and thus could signal the sensory experience of a healthy product. This research contributes to the literature on the use of sound symbolism for analysis of the influence of onomatopoeias as packaging information that influences the expected healthfulness of a bottled drink. The study is a 4 × 4 mixed-model experiment. Grouping was done according to onomatopoeia variables as follows: “Fizz,” “Glup,” “Ahhh,” and control. Beverage color, a within-subject variable, was grouped as green, yellow, red, and control. Results show that the healthful concept is defined in two dimensions: fulfilling and light. Onomatopoeias motivated the experience of a less fulfilling beverage, which had the strongest effect on “Fizz” condition. For the light dimension, “Ahhh” diminishes the perception of light, thus creating the idea that the drink is high in calories. This study reaches out to food industries on the need to find the most consistent and pleasurable sound associated with their products. This will enable food industries to provide information to consumers as well as ascertain how much they enjoy the product.  相似文献   
82.
Asphalt concrete is the prevailing material used for road surface construction. Its adequate characteristics in providing stability, durability and driving safety are controlled by complex interactions between its components. Thus, it is important to estimate the sensitivity of asphalt concrete mechanical properties as a function of its volumetrics. For this study, different combinations between asphalt content (3.5, 5 and 7.5%) and porosity values (above 4%) were used in order to disassociate these properties. The influence of mixing in fiberglass (0.5%) was also analyzed. It was found that porosity is significantly more relevant than the asphalt content in the prediction of tensile strength and resilient modulus of fiber-free asphalt concretes. In fiber-reinforced mixtures, the mechanical properties are improved by increasing the asphalt content, which suggests a better bonding between fibers and aggregates. For both cases, decreasing porosity is beneficial. By grouping both sets of results, it was possible to create a unique theoretical curve for both the tensile strength (qt) and the resilient modulus (RM). The RM/qt ratio was 5800 for the fiber-free group, and 3900 for the fiber-reinforced group - suggesting a better fatigue life indicator for asphalt concretes when fibers are added.  相似文献   
83.
The colour of the background on which products are presented may affect their perceived attractiveness. In order to find out on which type of background various fresh food products look most attractive, we presented five different vegetables (tomato, carrot, yellow bell pepper, eggplant, mushroom) on five different backgrounds with neutral grey colours varying in degree of blackness: 5, 30, 50, 65, and 90%. Forty-six participants provided colour matches for the vegetables and evaluated them on 10 attributes.Overall, the blackness of the backgrounds had little or no effect on the perceived colour of the vegetable. Only for carrots we found a small but significant difference, mainly between the 5% and 90% blackness backgrounds. On the darkest background, the carrot would be perceived as a bit lighter, more saturated, and more yellow rather than red, compared to the lightest background.Differences in perceived attractiveness on the grey backgrounds varied between 0.3 and 1.0 units on a 9-point scale. Attractiveness and expensiveness ratings for most vegetables were highest on the 90% blackness background. In comparison to our previous study where we presented vegetables on hued backgrounds, differences between mean attractiveness ratings were smaller. Because mean attractiveness ratings in the current study were higher, we expect that grey backgrounds are more likely to present vegetable assortments with a variety of hues in an attractive way than hued backgrounds.  相似文献   
84.
Many reservoir formation brines are characterized by high salinity and contain high concentrations of divalent ions such as calcium, magnesium, and potassium. These challenging conditions can render the surfactants ineffective during chemical flooding for enhanced heavy oil recovery. Various brine types can have an impact on the stability of emulsions generated with chemicals as chemicals have various resistant levels toward hard divalent ions and salinities. To investigate the impact of brine hardness on heavy oil-in-water emulsion stability, glass tube experiments, microscopic visualization and sandpack flooding experiments, and Hele-Shaw visualization experiments were conducted in this study under low-salinity/hard-brine, high-salinity/hard-brine conditions using commercial chemicals, which are designed for specific reservoir brine conditions. Recovery results demonstrated that complex colloidal solution introduced in the previous study with silica and Dodecyltrimethylammonium bromide (DTAB) along with screened chemicals from glass tube tests in this study can enhance heavy oil recovery significantly with an addition of low concentration of xanthan gum (Lee and Babadagli 2018). The results confirmed the robustness of the complex colloidal solution formula to enhance oil recovery with low concentration of polymer under any reservoir brine conditions. The study also demonstrates the potential of polymer as an emulsion stabilization additive for enhanced heavy oil recovery by in situ emulsion generation. Polymer effects seemed to be particularly dominant under the low-salinity conditions than high-salinity conditions.  相似文献   
85.
Controlling the electromechanical response of piezoelectric biological structures including tissues, peptides, and amino acids provides new applications for biocompatible, sustainable materials in electronics and medicine. Here, the piezoelectric effect is revealed in another class of biological materials, with robust longitudinal and shear piezoelectricity measured in single crystals of the transmembrane protein ba3 cytochrome c oxidase from Thermus thermophilus. The experimental findings from piezoresponse force microscopy are substantiated using a range of control measurements and molecular models. The observed longitudinal and shear piezoelectric responses of ≈ 2 and 8 pm V−1, respectively, are comparable to or exceed the performance of commonly used inorganic piezoelectric materials including quartz, aluminum nitride, and zinc oxide. This suggests that transmembrane proteins may provide, in addition to physiological energy transduction, technologically useful piezoelectric material derived entirely from nature. Membrane proteins could extend the range of rationally designed biopiezoelectric materials far beyond the minimalistic peptide motifs currently used in miniaturized energy harvesters, and the finding of robust piezoelectric response in a transmembrane protein also raises fundamental questions regarding the molecular evolution, activation, and role of regulatory proteins in the cellular nanomachinery, indicating that piezoelectricity might be important for fundamental physiological processes.  相似文献   
86.
The sintering behavior of WC-Ni nanocomposite powder was evaluated through experimental and statistical approaches to study the contribution of involving parameters of chemical composition (Ni wt. %) and sintering temperature on sinterability of system by assessing the resulted densification and microhardness. The experimental process was designed based on factorial experimental design for independent effective parameters of Ni percentage (12, 18 and 23 wt %), and sintering temperature (8 different values within 1350–1485 °C). The resulted products of experimental testing after compaction and sintering were analyzed by FESEM and EDX to image the microstructure and evaluate the chemical composition and elemental distribution. The density and microhardness were measured as well. An artificial neural network (ANN) was applied to describe the corresponding individual and mutual impacts on sintering. The ANN model was developed by feed-forward back propagation network including topology 2:5:2 and trainlm algorithm to model and predict density and microhardness. A great agreement was observed between the predicted values by the ANN model and the experimental data for density and microhardness (regression coefficients (R2) of 0.9983 and 0.9924 for target functions of relative density and microhardness, respectively). Results showed that the relative importance of operating parameters on target functions (relative density and microhardness) was found to be 62% and 38% for sintering temperature and Ni percentage, respectively. Also, ANN model exhibited relatively high predictive ability and accuracy in describing nonlinear behavior of the sintering of WC-Ni nanocomposite powder. The experimental results confirmed that the appropriate sintering temperature was influenced by Ni content. The optimum parameters were found to be 12 wt % Ni sintered at 1460 °C with the highest microhardness and relative density.  相似文献   
87.
王丽娜 《包装工程》2021,42(2):271-278, 285
目的针对社会文创设计出现的两种典型误区,以敦煌莫高窟第61窟女供养人文创设计为例进行设计研究实践,梳理出传统视觉形象的研究方法和创新设计方法,以此传承和保护中国传统文化。方法采用“图解法”对莫高窟第61窟东壁南侧女供养人的人物身份、妆容、发饰、服饰、色彩、局部等进行深入剖析,并将其作为文创衍生设计的根本来源,总结适用于当今社会的传统文化视觉元素创新设计方法,实现以传统文化为本源、艺术设计为手段、文创设计为载体的传统文化现代设计转译。结论依据“图解法”完成文创衍生设计,实现传统文化与现代设计的深度融合,有助于为不同传统文化题材的文创设计提供借鉴之意。  相似文献   
88.
Heat capacity data for compounds located in the binary CaO–SiO2, CaO–Al2O3 and MgO–Al2O3 systems are fitted by Debye-Einstein integrals. Starting from the fitted heat capacities, the standard values of the thermodynamic functions of these compounds are calculated. In almost all cases investigated, the derived standard entropies are within the uncertainties of the values provided in literature. The Debye-Einstein coefficients obtained in this thermodynamic assessment can be used to approximate the heat capacities, enthalpies and entropies of these compounds in the temperature range from 0 to 298.15 K.  相似文献   
89.
This study proposes a multiperiod mixed integer linear programming model for the management of a single municipal solid waste (MSW) treatment plant with sustainability as the objective. Discrete and continuous variables define the capacity selections for diverse MSW technologies, and the operation of the MSW network, respectively. The economic target is considered to maximize the net present value. The environmental impact is the minimization of a normalized environmental objective function (NEOF). The social target is the maximization of jobs. An interesting feature about the research work is the requirement of biodrying technologies for MSW moisture content control. Due to the conflicted nature among the sustainability components, a multiobjective optimization (MO) is carried out to find the Pareto optimal solutions. The MO results show that the Pareto optimal solutions vary around profit range of $4.9–8.5 billion, NEOF impact range of 3.2–3.6 units, and social benefit range of 2700–4828 jobs.  相似文献   
90.
Based on orthogonal experimental design (OED), the effects of the sintering pressure, sintering temperature and holding time on the mechanical properties of 50 vol% silicon carbide particle (SiCp)/2024Al composites prepared by spark plasma sintering (SPS) were investigated. The sintering pressure had the greatest effect on the density and bending strength of the material among these three factors, followed by sintering temperature and holding time. The optimised process conditions for producing the 50 vol% SiCp/2024Al were sintering at 550 °C for 5 min under 40 MPa, which resulted in a composite material with a density of 99.7% and good interface bonding with a comparatively high bending strength of 766.65 MPa. This work provides a promising method to produce high volume fraction composites that can meet high strength requirements.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号