全文获取类型
收费全文 | 31986篇 |
免费 | 3274篇 |
国内免费 | 2106篇 |
专业分类
电工技术 | 4035篇 |
技术理论 | 1篇 |
综合类 | 3586篇 |
化学工业 | 2575篇 |
金属工艺 | 1695篇 |
机械仪表 | 2537篇 |
建筑科学 | 3352篇 |
矿业工程 | 1150篇 |
能源动力 | 752篇 |
轻工业 | 461篇 |
水利工程 | 755篇 |
石油天然气 | 1741篇 |
武器工业 | 644篇 |
无线电 | 3774篇 |
一般工业技术 | 3205篇 |
冶金工业 | 1192篇 |
原子能技术 | 230篇 |
自动化技术 | 5681篇 |
出版年
2024年 | 68篇 |
2023年 | 326篇 |
2022年 | 559篇 |
2021年 | 702篇 |
2020年 | 783篇 |
2019年 | 723篇 |
2018年 | 640篇 |
2017年 | 877篇 |
2016年 | 982篇 |
2015年 | 1088篇 |
2014年 | 1917篇 |
2013年 | 1873篇 |
2012年 | 2263篇 |
2011年 | 2502篇 |
2010年 | 1834篇 |
2009年 | 2035篇 |
2008年 | 1928篇 |
2007年 | 2352篇 |
2006年 | 2103篇 |
2005年 | 1767篇 |
2004年 | 1557篇 |
2003年 | 1430篇 |
2002年 | 1163篇 |
2001年 | 998篇 |
2000年 | 884篇 |
1999年 | 694篇 |
1998年 | 589篇 |
1997年 | 475篇 |
1996年 | 369篇 |
1995年 | 354篇 |
1994年 | 327篇 |
1993年 | 212篇 |
1992年 | 190篇 |
1991年 | 111篇 |
1990年 | 131篇 |
1989年 | 98篇 |
1988年 | 99篇 |
1987年 | 64篇 |
1986年 | 30篇 |
1985年 | 41篇 |
1984年 | 41篇 |
1983年 | 32篇 |
1982年 | 19篇 |
1981年 | 19篇 |
1979年 | 10篇 |
1965年 | 9篇 |
1964年 | 11篇 |
1957年 | 10篇 |
1956年 | 9篇 |
1955年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
1.
William M. Pitts Martin Werrel Marco Fernandez Mary A. Long Evan A. Eisenberg James Filliben Cory D. Runyon 《火与材料》2021,45(1):127-154
Fire spread and growth on real‐scale four cushion mock‐ups of residential upholstered furniture (RUF) were investigated with the goal of identifying whether changes in five classes of materials (barrier, flexible polyurethane foam, polyester fiber wrap, upholstery fabric, and sewing thread), referred to as factors, resulted in statistically significant changes in burning behavior. A fractional factorial experimental design plus practical considerations yielded a test matrix with 20 material combinations. Experiments were repeated a minimum of two times. Measurements included fire spread rates derived from video recordings and heat release rates (HRRs). A total of 13 experimental parameters (3 based on the videos and 10 on the HRR results), referred to as responses, characterized the measurements. Statistical analyses based on Main Effects Plots (main effects) and Block Plots (main effects and factor interactions) were used. The results showed that three of the factors resulted in statistically significant effects on varying numbers of the 13 responses. The Barrier and Fabric factors had the strongest main effects with roughly comparable magnitudes. Foam was statistically significant for fewer of the responses and its overall strength was weaker than for Barrier and Fabric. No statistically significant main effects were identified for Wrap or Thread. Multiple two‐term interactions between factors were identified as being statistically significant. The Barrier*Fabric interaction resulted in the highest number of and strongest statistically significant effects. The existence of two‐term interactions means that it will be necessary to consider their effects in approaches designed to predict the burning behavior of RUF. 相似文献
2.
针对某在建矿山深井开拓方案探索需求,通过对胶带运输系统发展应用情况介绍和胶带运输系统运输特性影响因素分析,并结合深井开拓胶带斜井方案与竖井加胶带斜井方案投资经济性比较,以及对胶带运输系统在运行过程中关键问题的分析和讨论,得出随着胶带运输技术的不断发展,在大规模深井开拓中,胶带斜井开拓将大有可为,为冶金矿山深井开拓方案选择提供决策支持。 相似文献
3.
Polymer‐grafted inorganic particles (PGIPs) are attractive building blocks for numerous chemical and material applications. Surface‐initiated controlled radical polymerization (SI‐CRP) is the most feasible method to fabricate PGIPs. However, a conventional in‐batch reaction still suffers from several disadvantages, including time‐consuming purification processes, low grafting efficiency, and possible gelation problems. Herein, a facile method is demonstrated to synthesize block copolymer–grafted inorganic particles, that is, poly(poly(ethylene glycol) methyl ether methacrylate) (PPEGMEMA)‐b‐poly(N‐isopropylacrylamide) (PNIPAM)–grafted silica micro‐particles using continuous flow chemistry in an environmentally friendly aqueous media. Immobilizing the chain transfer agent and subsequent SI‐CRP can be accomplished sequentially in a continuous flow system, avoiding multi‐step purification processes in between. The chain length (MW) of the grafted polymers is tunable by adjusting the flow time or monomer concentration, and the narrower molar mass dispersity (Ð < 1.4) of the grafted polymers reveals the uniform polymer chains on the particles. Moreover, compared with the in‐batch reaction at the same condition, the continuous system also suppresses possible gelation problems. 相似文献
4.
针对异构计算节点组成的大规模多状态计算系统的容错性能分析问题,提出了一种计算系统容错性能的评估方法。该方法采用自定义的两级容错性能形式化描述框架进行系统描述,通过构造多值决策图(Multi-value Decision Diagram,MDD)模型对系统进行容错性能建模,并基于构造的模型高效地计算出部件故障的条件下计算系统在特定性能水平上运行的概率,减少了计算的冗余性。实验结果表明,该方法在模型的大小和构建时间上均优于传统方法。该方法的提出将对系统操作员或程序设计者具有重要意义,使其确保系统适合预期应用。 相似文献
5.
This paper presents a stochastic performance modelling approach that can be used to optimise design and operational reliability of complex chemical engineering processes. The framework can be applied to processes comprising multiple units, including the cases where closed form process performance functions are unavailable or difficult to derive from first principles, which is often the case in practice. An interface that facilitates automated two-way communication between Matlab® and process simulation environment is used to generate large process responses. The resulting constrained optimisation problem is solved using both Monte Carlo Simulation (MCS) and First Order Reliability Method (FORM); providing a wide range of stochastic process performance measures. Adding such capabilities to traditional deterministic process simulators provides a more informed basis for selecting optimum design factors; giving a simple way of enhancing overall process reliability and cost-efficiency. Two case study systems are considered to highlight the applicability and benefits of the approach. 相似文献
6.
7.
8.
《Journal of the European Ceramic Society》2020,40(13):4655-4663
As a figure-of-merit, the rising ratio of crack propagation resistance to fracture initiation resistance indicates a reduction of the brittleness and enhances the thermal shock resistance of ordinary refractory ceramics. The significant nonlinear fracture behaviour is related to the development of a fracture process zone (FPZ). The universal dimensionless load–displacement diagram method is applied as a promising graphical method for the determination of R-curves for magnesia refractories showing different brittleness. By applying digital image correlation (DIC) together with the graphical method, the problems arisen with accurate determination of the fracture initiation resistance and the crack length are overcome. Meanwhile, the R-curve is subdivided with respect to the fracture processes, viz the fracture initiation, the development of FPZ and the onset of traction free macro-crack. With the simultaneous crack lengths evaluated from DIC, the contribution of each fracture process to the crack propagation resistance at certain loading stage is quantitatively presented. 相似文献
9.
Yong Xu Yun Li Songlin Li Francis Balestra Gerard Ghibaudo Wenwu Li Yen‐Fu Lin Huabin Sun Jing Wan Xinran Wang Yufeng Guo Yi Shi Yong‐Young Noh 《Advanced functional materials》2020,30(20)
Unreliable mobility values, and particularly greatly overestimated values and severely distorted temperature dependences, have recently hampered the development of the organic transistor field. Given that organic field‐effect transistors (OFETs) have been routinely used to evaluate mobility, precise parameter extraction using the electrical properties of OFETs is thus of primary importance. This review examines the origins of the various mobilities that must be determined for OFET applications, the relevant extraction methods, and the data selection limitations, which help in avoiding conceptual errors during mobility extraction. For increased precision, the review also discusses device fabrication considerations, calibration of both the specific gate‐dielectric capacitance and the threshold voltage, the contact effects, and the bias and temperature dependences, which must actually be handled with great care but have mostly been overlooked to date. This review serves as a systematic overview of the OFET mobility extraction process to ensure high precision and will also aid in improving future research. 相似文献
10.
针对高可靠度机载多余度EWIS各组成部分寿命服从指数分布但参数未知的情况,提出采用无失效数据可靠度分析方法评估EWIS的可靠度水平。通过Monte-Carlo仿真方法对连接形式为“先并联、后串联”EWIS各组成部分寿命进行抽样,利用“最小最大值”方法获得系统寿命的抽样值,用概率纸检验法初步判断EWIS寿命是否服从威布尔分布,再用Pearson拟合优度检验法判断EWIS寿命是否服从威布尔分布。结合无故障飞行时间的样本值与EWIS寿命服从威布尔分布的假设,采用无失效数据分析方法评估EWIS的可靠度水平。研究方法对机载多余度EWIS无失效数据可靠度分析有一定的贡献。 相似文献