全文获取类型
收费全文 | 314488篇 |
免费 | 27129篇 |
国内免费 | 18949篇 |
专业分类
电工技术 | 17787篇 |
技术理论 | 51篇 |
综合类 | 42567篇 |
化学工业 | 33311篇 |
金属工艺 | 15450篇 |
机械仪表 | 17690篇 |
建筑科学 | 51102篇 |
矿业工程 | 20958篇 |
能源动力 | 9133篇 |
轻工业 | 16414篇 |
水利工程 | 17296篇 |
石油天然气 | 17028篇 |
武器工业 | 2903篇 |
无线电 | 17774篇 |
一般工业技术 | 25428篇 |
冶金工业 | 18335篇 |
原子能技术 | 2974篇 |
自动化技术 | 34365篇 |
出版年
2024年 | 493篇 |
2023年 | 2900篇 |
2022年 | 5710篇 |
2021年 | 7873篇 |
2020年 | 7796篇 |
2019年 | 6726篇 |
2018年 | 6282篇 |
2017年 | 7616篇 |
2016年 | 9068篇 |
2015年 | 9978篇 |
2014年 | 17852篇 |
2013年 | 16656篇 |
2012年 | 21363篇 |
2011年 | 22910篇 |
2010年 | 17971篇 |
2009年 | 18779篇 |
2008年 | 17479篇 |
2007年 | 22502篇 |
2006年 | 21234篇 |
2005年 | 18685篇 |
2004年 | 15853篇 |
2003年 | 14107篇 |
2002年 | 11686篇 |
2001年 | 9847篇 |
2000年 | 8312篇 |
1999年 | 6812篇 |
1998年 | 5217篇 |
1997年 | 4554篇 |
1996年 | 4195篇 |
1995年 | 3639篇 |
1994年 | 3216篇 |
1993年 | 2407篇 |
1992年 | 2112篇 |
1991年 | 1547篇 |
1990年 | 1355篇 |
1989年 | 1207篇 |
1988年 | 923篇 |
1987年 | 646篇 |
1986年 | 479篇 |
1985年 | 399篇 |
1984年 | 375篇 |
1983年 | 267篇 |
1982年 | 249篇 |
1981年 | 181篇 |
1980年 | 160篇 |
1979年 | 149篇 |
1978年 | 64篇 |
1977年 | 74篇 |
1976年 | 56篇 |
1975年 | 56篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Ali Hojeij Laurent Jossic Philippe Séchet Cyrille Bonamy Albert Magnin Stéphane Hattou 《American Institute of Chemical Engineers》2022,68(2):e17442
Mixing by gas injection is an operation used in industrial processes such as wastewater treatment, metallurgy, or methanization in which pressurized gas is injected into a fluid in order to reduce concentrations and temperatures gradients. This study demonstrates how the CFD toolbox OpenFOAM can be used to simulate such flows. Experimental measurements and observations have been performed on a pilot-scale reactor where pressurized air is injected in a yield stress fluid. The volume of fluid method and an adaptive mesh with refinement at the interface have been used to track the gas inclusions. The numerical model accuracy has been assessed by comparing experimental and numerical results related to the bubble's frequency, dimensions, and rising velocities as well as the fluid recirculation, yielded, and unyielded regions in the tank. The influence of injection parameters such as the injection flow rate and the fluid rheological parameters has been quantified. 相似文献
992.
Target design methodologies (DfX) were developed to cope with specific engineering design issues such as cost-effectiveness, manufacturability, assemblability, maintainability, among others. However, DfX methodologies are undergoing the lack of real integration with 3D CAD systems. Their principles are currently applied downstream of the 3D modelling by following the well-known rules available from the literature and engineers’ know-how (tacit internal knowledge).This paper provides a method to formalize complex DfX engineering knowledge into explicit knowledge that can be reused for Advanced Engineering Informatics to aid designers and engineers in developing mechanical products. This research work wants to define a general method (ontology) able to couple DfX design guidelines (engineering knowledge) with geometrical product features of a product 3D model (engineering parametric data). A common layer for all DfX methods (horizontal) and dedicated layers for each DfX method (vertical) allow creating the suitable ontology for the systematic collection of the DfX rules considering each target. Moreover, the proposed framework is the first step for developing (future work) a software tool to assist engineers and designers during product development (3D CAD modelling).A design for assembly (DfA) case study shows how to collect assembly rules in the given framework. It demonstrates the applicability of the CAD-integrated DfX system in the mechanical design of a jig-crane. Several benefits are recognized: (i) systematic collection of DfA rules for informatics development, (ii) identification of assembly issues in the product development process, and (iii) reduction of effort and time during the design review. 相似文献
993.
994.
《Advanced Powder Technology》2022,33(9):103719
To get more accurate quantitative impact effects of selective parameters of the sand-ejecting fire extinguisher on the scattering results by the CFD-DEM coupling method, orthogonal experimental design, analysis of range and variance, full factorial design and the OFAT design were used in this paper. The single impact effects and mixed impact effects of blade number, blade incidence and sand mass flow on scattering vertical distance and inclination were analysed and concluded, as well as the details of the sand distribution. The results show that only the sand mass flow has the dominating influence on the vertical distance, while all three factors have no significant influence on the scattering inclination. The larger the sand mass flow is, the more obvious influence of air resistance and airflow from the outlet of the scattering unit can be shown, and the scattering bifurcation phenomenon can be displayed more obviously. 相似文献
995.
《International Journal of Hydrogen Energy》2022,47(41):18139-18147
Designing cathode functional layer (CFL) to accelerate oxygen reduction reaction (ORR) is widely studied. However, the relationship between morphology and ORR kinetic of CFL need to be in-depth studied. Here, a highly efficient and robust La0·6Sr0·4CoO3 (LSC) CFL is prepared into Ce0.9Gd0.1O1.95 (GDC) scaffold in a commercial anode supported half-cell by infiltrating method, which exhibits remarkably enhanced ORR activity, compared with the traditional LSC CFL fabricated by mechanical mixing LSC-GDC. As a proof, the infiltrated LSC CFL based single SOFC delivers a maximum power density of 1.2 W cm?2 at 750 °C and an excellent long-term stability with a voltage attention rate of 0.058%/100 h at 0.5 A cm?2 for 550 h. The distribution of relaxation times (DRT) method is introduced to understand improved electrochemical performances. Optimized porosity, extend three phase boundary and shorted charge transfer path change the rate-determining step in the infiltrated CFL cell. 相似文献
996.
《International Journal of Hydrogen Energy》2022,47(56):23772-23786
As the PEMFC is a complex multi-physics device whose reliability and durability depend on the thermal-mechanical-electrical and chemical parameters. In this paper, theoretical and numerical studies is proposed to optimize the fuel cell performance using multiphysics model and design of experiments. 3D finite element analysis including a fully coupling of thermal-electrical-mechanical model is proposed to predict the electrical resistance of fuel cell. As the mechanical parameters (bending radius of the bipolar plate, thickness of the GDL and clamping pressure) remain uncertain, the design of experiments procedure is used to optimize the fuel cell behavior under several conditions. 相似文献
997.
《International Journal of Hydrogen Energy》2022,47(75):32071-32080
Ni-based catalysts have been widely studied in reforming methane with carbon dioxide. However, Ni-based catalysts tends to form carbon deposition at low temperatures (≤600 °C), compared with high temperatures. In this paper, a series of Ni/SiO2-XG catalysts were prepared by the glycine-assisted incipient wetness impregnation method, in which X means the molar ratio of glycine to nitrate. XRD, H2-TPR, TEM and XPS results confirmed that the addition of glycine can increase Ni dispersion and enhance the metal-support interaction. When X ≥ 0.3, these catalysts have strong metal-support interaction and small Ni particle size. The Ni/SiO2-0.7G catalyst has the best catalytic performance in dry reforming of methane (DRM) test at 600 °C, and its CH4 conversion is 3.7 times that of Ni/SiO2-0G catalyst. After 20 h reaction under high GHSV (6 × 105 ml/gcat/h), the carbon deposition of Ni/SiO2-0.7G catalyst is obviously lower than that of Ni/SiO2-0G catalyst. Glycine-assisted impregnation method can enhance the metal-support interaction and decrease the metal particle size,which is a method to prepare highly dispersed and stable Ni-based catalyst. 相似文献
998.
覆岩结构综放开采顶板渗水现象仍然为煤矿生产主要制约因素之一。以斜沟煤矿3号煤层为主要研究对象,通过对覆岩结构综放开采裂隙分布规律研究以及覆岩结构综放开采涌水量数值分析,实现对覆岩结构综放开采顶板涌水量的预测,以期对矿井水害防治研究有所帮助。 相似文献
999.
《Journal of dairy science》2022,105(6):4882-4894
Detection of adulteration of small ruminant milk is very important for health and commercial reasons. New analytical and cost-effective methods need to be developed to detect new adulteration practices. In this work, we aimed to explore the ability of the MALDI-TOF mass spectrometry to detect bovine milk in caprine and ovine milk using samples from 18 dairy farms. Different levels of adulteration (0.5, 1, 5, 10, 20, 40, 60, and 80%) were analyzed during the lactation period of goat and sheep (in May, from 60 to 90 d in milk, and in August, from 150 to 180 d in milk). Two different ranges of peptide-protein spectra (500–4,000 Da; 4–20 kDa) were used to establish a calibration model for predicting the concentration of adulterant using partial least squares and generalized linear model with lasso regularization. The low molecular weight part of the spectra together with the generalized linear model with lasso regularization regression model appeared to have greater potential for our aim of detection of adulteration of small ruminants' milk. The subsequent prediction model was able to predict the concentration of bovine milk in caprine milk with a root mean square error of 11.4 and 17.0% in ovine milk. The results offer compelling evidence that MALDI-TOF can detect the adulteration of small ruminants' milk. However, the method is severely limited by (1) the complexity of the milk proteome resulting from the adulteration technique, (2) the potential degradation of thermolabile proteins, and (3) the genetic variability of tested samples. Additionally, the root mean square error of prediction based only on one individual sample adulteration series can drop down to 6.34% for quantification of adulterated caprine milk and 6.28% for adulterated ovine milk for the full set of concentrations or down to 2.33 and 4.00%, respectively, if we restrict only to low concentrations of adulteration (0, 0.5, 1, 5, 10%). 相似文献
1000.
为探究南水北调中线水源区丹江口水库浮游植物群落结构变化及其生物多样性,于 2014—2015 年对丹江
口水库进行为期 1 年的调查和分析。发现浮游植物共 8 门 76 属 101 种,其中,绿藻门、蓝藻门及硅藻门占总种数
90.10%,绿藻门种类数最多(45 种),其次是蓝藻门(26 种)和硅藻门(20 种)。浮游植物群落结构随季节变化有所
不同:夏秋季节生物量明显高于冬春季节;优势种在冬季以颗粒直链藻、颗粒直链藻极狭变种、铜绿微囊藻和小
环藻为主,春季以球衣藻、薄甲藻属及小环藻为主,夏季以简单颤藻、单胞衣藻原变种和球衣藻为主,秋季以类颤
藻鱼腥藻、简单颤藻、球衣藻和小环藻为主。应用 Shannon-Wiener 多样性指数 H′、Pielou 均匀度指数 J′、Margalef
丰富度指数 Dm评价水质结果表明:丹江口水库夏秋季水体营养化程度更高。典型对应分析表明:水温、透明度、
总氮、总磷等是影响浮游植物群落结构的主要环境因子,夏秋季受温度影响蓝藻、绿藻数量逐渐增多,一定程度
上增加了受水区生态变化风险。本研究可为南水北调中线水源区丹江口水库生态环境变化及生物迁移风险提供
数据支持。 相似文献