全文获取类型
收费全文 | 61221篇 |
免费 | 6464篇 |
国内免费 | 2232篇 |
专业分类
电工技术 | 3680篇 |
综合类 | 4766篇 |
化学工业 | 10856篇 |
金属工艺 | 5579篇 |
机械仪表 | 3345篇 |
建筑科学 | 6807篇 |
矿业工程 | 1208篇 |
能源动力 | 8854篇 |
轻工业 | 3214篇 |
水利工程 | 984篇 |
石油天然气 | 2765篇 |
武器工业 | 401篇 |
无线电 | 2009篇 |
一般工业技术 | 6321篇 |
冶金工业 | 3850篇 |
原子能技术 | 1233篇 |
自动化技术 | 4045篇 |
出版年
2024年 | 247篇 |
2023年 | 841篇 |
2022年 | 1613篇 |
2021年 | 1838篇 |
2020年 | 1982篇 |
2019年 | 1630篇 |
2018年 | 1447篇 |
2017年 | 1714篇 |
2016年 | 2121篇 |
2015年 | 2132篇 |
2014年 | 3779篇 |
2013年 | 3815篇 |
2012年 | 4384篇 |
2011年 | 4659篇 |
2010年 | 3412篇 |
2009年 | 3579篇 |
2008年 | 2915篇 |
2007年 | 3888篇 |
2006年 | 3523篇 |
2005年 | 3067篇 |
2004年 | 2665篇 |
2003年 | 2358篇 |
2002年 | 2209篇 |
2001年 | 1797篇 |
2000年 | 1468篇 |
1999年 | 1227篇 |
1998年 | 973篇 |
1997年 | 848篇 |
1996年 | 703篇 |
1995年 | 579篇 |
1994年 | 495篇 |
1993年 | 383篇 |
1992年 | 343篇 |
1991年 | 226篇 |
1990年 | 197篇 |
1989年 | 186篇 |
1988年 | 124篇 |
1987年 | 90篇 |
1986年 | 75篇 |
1985年 | 54篇 |
1984年 | 82篇 |
1983年 | 63篇 |
1982年 | 68篇 |
1981年 | 20篇 |
1980年 | 15篇 |
1979年 | 9篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1959年 | 28篇 |
1951年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
本文研究了加法复合布尔函数和乘法复合布尔函数,在平衡性、k次项系数、K次扩散准则(PC)、相关免疫 性(CI)、Walsh谱、代数次数、小项分布等方面得到了一批新结果。 相似文献
82.
83.
Shumin Zhai Jing Kong Xiangshi Ren 《International journal of human-computer studies》2004,61(6):823-856
Pointing tasks in human–computer interaction obey certain speed–accuracy tradeoff rules. In general, the more accurate the task to be accomplished, the longer it takes and vice versa. Fitts’ law models the speed–accuracy tradeoff effect in pointing as imposed by the task parameters, through Fitts’ index of difficulty (Id) based on the ratio of the nominal movement distance and the size of the target. Operating with different speed or accuracy biases, performers may utilize more or less area than the target specifies, introducing another subjective layer of speed–accuracy tradeoff relative to the task specification. A conventional approach to overcome the impact of the subjective layer of speed–accuracy tradeoff is to use the a posteriori “effective” pointing precision We in lieu of the nominal target width W. Such an approach has lacked a theoretical or empirical foundation. This study investigates the nature and the relationship of the two layers of speed–accuracy tradeoff by systematically controlling both Id and the index of target utilization Iu in a set of four experiments. Their results show that the impacts of the two layers of speed–accuracy tradeoff are not fundamentally equivalent. The use of We could indeed compensate for the difference in target utilization, but not completely. More logical Fitts’ law parameter estimates can be obtained by the We adjustment, although its use also lowers the correlation between pointing time and the index of difficulty. The study also shows the complex interaction effect between Id and Iu, suggesting that a simple and complete model accommodating both layers of speed–accuracy tradeoff may not exist. 相似文献
84.
This paper deals with a new boundary element method for analysis of the quasistatic problems in coupled thermoelasticity. Through some mathematical manipulation of the Navier equation in elasticity, the heat conduction equation is transformed into a simpler form, similar to the uncoupled-type equation with the modified thermal conductivity which shows the coupling effects. This procedure enables us to treat the coupled thermoelastic problems as an uncoupled one, A few examples are computed by the proposed BEM, and the results obtained are compared with the analytical ones available in the literature, whereby the accuracy and versatility of the proposed method are demonstrated. 相似文献
85.
Sarrazin Jean-Christophe; Giraudo Marie-Dominique; Pailhous Jean; Bootsma Reinoud J. 《Canadian Metallurgical Quarterly》2004,30(3):411
In 3 experiments, the authors studied the organization of spatiotemporal information in memory. Stimuli consisted of configurations of dots, presented sequentially. The stimuli were either proportional, with interdot distances corresponding to interdot durations, or not proportional, with interdol distances not corresponding to interdot durations. After a learning phase, participants reproduced the spatial (Experiment 1), temporal (Experiment 2), or spatial and temporal (Experiment 3) characteristics of the target 60 times in succession. In the nonproportional conditions, effects of variable interdot durations or distances on the reproduction of, respectively, constant distances (tau effect) or durations (kappa effect) were observed, whereas no such effects were observed when variable distances or durations were to be produced. Tau and kappa effects influenced the accuracy but not the variability of responses. The results are discussed in light of the distinction between properties of the stabilized mental image and the process of stabilization. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
86.
Periklis E. Ergatis Panagiotis G. Massouros Georgia C. Athanasouli George P. Massouros 《国际能源研究杂志》2003,27(9):795-811
A time‐dependent coefficient of heat transfer is proposed for the computation of thermal power required, so that a room temperature reaches a desired value within a given time. A mathematical formulation of the room heating transient phenomenon is constructed in a dimensionless form. Using an integral approximate solution an analytical expression for this coefficient is provided and it is verified by diagrams adopted by DIN 4701. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
87.
HLA-DRB1等位基因主要参与人类的抗原免疫功能,对其进行比较研究,有助于追溯人类的进化迁移史,开发类群特异性药物.本研究以Matlab为平台,用自组织竞争网络(Self-Organizing Competitive Neural Network),对世界54个民族和人群、14个HLA-DRB1等位基因,进行了无监督模式分类.结果表明,各民族之间存在差异性,同民族的各人群之间有相似性.西伯利亚各人群,澳洲各土著人群,黑人各人群,南美印第安各人群,犹太族各人群,日本各人群,及欧美白人各人群有相对独立性:南美印第安人与西伯利亚人有高度相似性;中国民族在南方人群和北方人群间存在较大差异;中国汉族中,广东汉族地位特殊,与少数民族如拉祜族、瑶族关系密切. 相似文献
88.
渗透率是反映储层渗流能力的重要参数,目前对于单一储层的渗透率表征方法,通常是在岩心分析渗透率或测井解释渗透率的基础上进行厚度加权算术平均。这种方法对于均质的储层来说是适用的,但对于非均质严重的储层,不能准确反映该储层的实际渗流能力。本文提出一种应用可动流体体积权衡表征渗透率的方法,经实际资料验证,能较好地反映储层的实际渗透能力。 相似文献
89.
An approximate method is presented for predicting the effect of a louvered blind on the centre‐glass thermal performance of a fenestration. The method combines a one‐dimensional heat transfer model with data from a numerical simulation of the window and blind. Sample results for a blind mounted on the indoor surface of a window show the effect of blind slat angle on heat transmission. Both summer and winter conditions are considered. The results show that a louvered blind can improve the U‐value of a standard double‐glazed window by up to 37%. Also, the radiation heat exchange with the room can be dramatically reduced (by up to 60%), which will improve the level of occupant comfort. However, there was found to be a trade‐off between U‐value and occupant comfort; placing the blind closer to the window improves the U‐value, but increases the radiation heat exchange with the room. The predictions from the present simplified method compare well with results from a full two‐dimensional computational fluid dynamics solution of the conjugate blind/window interaction. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
90.
油井热洗是油田最常用的一种清蜡方法。靖安长6油藏是采油三厂的主力油藏,截至2004年底建成油井1064口,由于长6层原油含蜡量高,油井结蜡严重,通常采用常规热洗方法进行油井清蜡。存在以下两方面问题:一是常规油井热洗方法操作比较复杂,运行动力设施多,热洗费用较高;二是常规洗井油源均来自联合站或接转站,为不同层所采的混合原油,进入地层后,会对地层造成一定程度的伤害。为此,我们认真分析了现有油井热洗工艺的不足,查找了油井热洗费用高的影响因素,结合靖安油田长6油藏丰富的伴生气资源,自主研发了撬装式油井热洗装置,经过现场应用取得了较好的效果。 相似文献