全文获取类型
收费全文 | 12304篇 |
免费 | 1136篇 |
国内免费 | 564篇 |
专业分类
电工技术 | 3155篇 |
技术理论 | 1篇 |
综合类 | 1184篇 |
化学工业 | 769篇 |
金属工艺 | 838篇 |
机械仪表 | 553篇 |
建筑科学 | 959篇 |
矿业工程 | 365篇 |
能源动力 | 549篇 |
轻工业 | 765篇 |
水利工程 | 613篇 |
石油天然气 | 980篇 |
武器工业 | 102篇 |
无线电 | 683篇 |
一般工业技术 | 613篇 |
冶金工业 | 625篇 |
原子能技术 | 84篇 |
自动化技术 | 1166篇 |
出版年
2024年 | 38篇 |
2023年 | 141篇 |
2022年 | 263篇 |
2021年 | 305篇 |
2020年 | 357篇 |
2019年 | 314篇 |
2018年 | 270篇 |
2017年 | 420篇 |
2016年 | 459篇 |
2015年 | 488篇 |
2014年 | 750篇 |
2013年 | 643篇 |
2012年 | 877篇 |
2011年 | 932篇 |
2010年 | 678篇 |
2009年 | 756篇 |
2008年 | 674篇 |
2007年 | 775篇 |
2006年 | 734篇 |
2005年 | 614篇 |
2004年 | 520篇 |
2003年 | 513篇 |
2002年 | 420篇 |
2001年 | 341篇 |
2000年 | 294篇 |
1999年 | 252篇 |
1998年 | 208篇 |
1997年 | 197篇 |
1996年 | 171篇 |
1995年 | 143篇 |
1994年 | 116篇 |
1993年 | 76篇 |
1992年 | 83篇 |
1991年 | 55篇 |
1990年 | 27篇 |
1989年 | 30篇 |
1988年 | 12篇 |
1987年 | 12篇 |
1986年 | 12篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1982年 | 6篇 |
1979年 | 2篇 |
1967年 | 1篇 |
1966年 | 2篇 |
1965年 | 2篇 |
1964年 | 3篇 |
1960年 | 1篇 |
1956年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
A new technique of EDM coring of single crystal silicon carbide (SiC) ingot was proposed in this paper. Currently single crystal SiC devices are still of high cost due to the high cost of bulk crystal SiC material and the difficulty in the fabrication process of SiC. In the manufacturing process of SiC ingot/wafer, localized cracks or defects occasionally occur due to thermal or mechanical causes resulted from fabrication processes which may waste the whole piece of material. To save the part of ingot without defects and maximize the material utilization, the authors proposed EDM coring method to cut out a no defect ingot from a larger diameter ingot which has localized defects. A special experimental setup was developed for EDM coring of SiC ingot in this study and its feasibility and machining performance were investigated. Meanwhile, in order to improve the machining rate, a novel multi-discharge EDM coring method by electrostatic induction feeding was established, which can realize multiple discharges in single pulse duration. Experimental results make it clear that EDM coring of SiC ingot can be carried out stably using the developed experimental setup. Taking advantage of the newly developed multi-discharge EDM method, both the machining speed and surface integrity can be improved. 相似文献
2.
黄浦江为感潮河流,低潮位重现期的确定对黄浦江航道的设计具有重要意义。为了准确估计黄浦江低潮位的重现期,以黄浦江下游吴淞口站年最低潮位序列为例,在对样本进行三性审查的基础上,分别采用传统的数理统计方法和时变矩方法进行水文频率分析。结果表明:吴淞口站年最低潮位序列在1996年发生了变异;还现修正后的序列服从位置参数线性时变的GEV模型,低潮位存在缓慢的上升趋势;一致性条件下百年一遇低潮位约为0.261 m,在非一致性条件下其重现期增大为150 a。非一致性条件下的重现期增大说明黄浦江现有的航道设计标准偏安全,航道通航保证率提高。 相似文献
3.
Eight datasets of 1-h black carbon (BC) concentrations measured in Warsaw agglomeration (Poland), at urban background and sub-urban sites, and in Racibórz, a small town in Upper Silesia district (regional background site) were analyzed to evaluate BC levels, daily profiles and statistical distributions of concentrations in Central-Eastern European region. The observed mean levels ranged from 1483 ng m−3 in suburban site during summer to 3358 ng m−3 in regional background site in winter. Observed diurnal patterns were bimodal in the locations dominated by traffic emissions, but unimodal, with elevated evening peak in individually heated residential area. Three theoretical frequency distributions were applied to fit analyzed datasets separately. The lognormal distribution was the most appropriate to represent the middle-range values, while the high concentrations were satisfactorily predicted by the type I two-parameter exponential distribution which was used to estimate the return periods of extreme concentrations for winter months. 相似文献
4.
The aim of the study was to identify the importance of individual food product attributes (the use of preservatives, processing method, shelf-life period and nutritional value) as well as their relation to the purchase behaviour. To achieve this, consumer preferences were decomposed in conditions of full access to information, and data was compared with actual consumer behaviour related to making purchasing decisions in front of the store shelf. Based on data from 338 respondents, conjoint analysis and repeated ANOVA measurements were carried out, allowing to eliminate individual behavioural patterns. The results showed a dissonance between the consumers attitudes towards the attributes and their shopping behaviour. The processing method was the most important declared attribute for consumers, meanwhile this information was the least searched for during purchase. At the same time, shelf-life period marked as the least important was the main information searched for by consumers when shopping. The results also show a clear dislike towards the use of microwaves as a preservation method, while traditional thermal preservation was marked as the most positive for consumers. In addition, consumers were classified into 3 heterogeneous groups, identifying differences in the preferences of food attributes. The obtained results have practical value relating not only to the preferences of individual attributes, but also to their various variants. The results can be a guide for companies to properly label food products. The indicated dissonance illustrates the educational gap and related insufficient motivation to get to know the product before buying it. This is extremely important in connection with technological development and new food processing methods. 相似文献
5.
Mohamed Becherif 《Asian journal of control》2019,21(4):2137-2154
Induction machines (IM) constitute a theoretically interesting and practically important class of nonlinear systems. They are frequently used as wind generators for their power/cost ratio. They are described by a fifth‐order nonlinear differential equation with two inputs and only three state variables available for measurement. The control task is further complicated by the fact that IM are subject to unknown (load) disturbances and the parameters can be of great uncertainty. One is then faced with the challenging problem of controlling a highly nonlinear system, with unknown time‐varying parameters, where the regulated output, besides being unmeasurable, is perturbed by an unknown additive signal. Passivity‐based control (PBC) is a well‐established structure‐preserving design methodology which has shown to be very powerful to design robust controllers for physical systems described by Euler‐Lagrange equations of motion. PBCs provide a natural procedure to "shape" the potential energy yielding controllers with a clear physical interpretation in terms of interconnection of the system with its environment and are robust vis á vis to unmodeled dissipative effects. One recent approach of PBC is the Interconnection and Damping Assignment Passivity‐Based Control (IDA‐PBC) which is a very useful technique to control nonlinear systems assigning a desired (Port‐Controlled Hamiltonian) structure to the closed‐loop. The aim of this paper is to give a survey on different PBC of IM. The originality of this work is that the author proves that the well known field oriented control of IM is a particular case of the IDA‐PBC with disturbance. 相似文献
6.
用周期波导的方法分析平面阵列波导光栅(AWG)的本征方程及波导模式参数,结果表明波导传播常数是带状分布的,与波导间隔有关。分析结果对器件的优化设计有一定的指导意义。 相似文献
7.
8.
采用类比法确定现役水工钢闸门结构的荷载评估基准期。以静水压力为例,得了其在荷载评估基准期内的统计参数,讨论了闸门主梁受弯碱坏时可靠指标随继续使用期的变化。 相似文献
9.
10.
两相异步电动机变频调速装置 总被引:4,自引:0,他引:4
主要讨论对称两相变频器主电路的结构以及介绍一种简单实用的磁链轨迹控制技术. 相似文献