全文获取类型
收费全文 | 6978篇 |
免费 | 530篇 |
国内免费 | 381篇 |
专业分类
电工技术 | 326篇 |
技术理论 | 1篇 |
综合类 | 769篇 |
化学工业 | 424篇 |
金属工艺 | 142篇 |
机械仪表 | 196篇 |
建筑科学 | 1030篇 |
矿业工程 | 300篇 |
能源动力 | 212篇 |
轻工业 | 547篇 |
水利工程 | 588篇 |
石油天然气 | 1383篇 |
武器工业 | 51篇 |
无线电 | 441篇 |
一般工业技术 | 366篇 |
冶金工业 | 268篇 |
原子能技术 | 53篇 |
自动化技术 | 792篇 |
出版年
2024年 | 21篇 |
2023年 | 81篇 |
2022年 | 165篇 |
2021年 | 195篇 |
2020年 | 215篇 |
2019年 | 192篇 |
2018年 | 146篇 |
2017年 | 220篇 |
2016年 | 195篇 |
2015年 | 222篇 |
2014年 | 453篇 |
2013年 | 368篇 |
2012年 | 510篇 |
2011年 | 530篇 |
2010年 | 361篇 |
2009年 | 427篇 |
2008年 | 367篇 |
2007年 | 443篇 |
2006年 | 409篇 |
2005年 | 328篇 |
2004年 | 312篇 |
2003年 | 314篇 |
2002年 | 250篇 |
2001年 | 207篇 |
2000年 | 170篇 |
1999年 | 146篇 |
1998年 | 124篇 |
1997年 | 120篇 |
1996年 | 100篇 |
1995年 | 62篇 |
1994年 | 72篇 |
1993年 | 34篇 |
1992年 | 41篇 |
1991年 | 25篇 |
1990年 | 14篇 |
1989年 | 13篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1984年 | 5篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1967年 | 1篇 |
1965年 | 1篇 |
1964年 | 2篇 |
1962年 | 2篇 |
1961年 | 1篇 |
1956年 | 4篇 |
1955年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有7889条查询结果,搜索用时 218 毫秒
1.
石油和天然气行业不断关注增材制造技术在航空航天和汽车行业的应用发展。研发了利用增材制造技术的超高膨胀封隔器,该封隔器的支承环系统由增材制造。增材制造设计大幅减少了支承系统的构件数量,同时显著提高了膨胀能力和额定压力。密封元件系统与增材制造支承环安装在一起,提供了极端膨胀比、零挤压间隙和对不规则孔的良好适应性。分析和测试结果表明:直径膨胀比高达111%,与常规封隔器相比,提高50%以上; 至少涵盖5种线重的套管(外径相同); 在148.89 ℃的温度下,密封元件能够保持压力68.95 MPa。介绍了增材制造技术、增材制造支承环概念、增材制造材料力学性能、密封元件系统优化和测试情况,以期给我国的完井作业提供借鉴。 相似文献
2.
We study a two-agent scheduling problem in a two-machine permutation flowshop with learning effects. The objective is to minimize the total completion time of the jobs from one agent, given that the maximum tardiness of the jobs from the other agent cannot exceed a bound. We provide a branch-and-bound algorithm for the problem. In addition, we present several genetic algorithms to obtain near-optimal solutions. Computational results indicate that the algorithms perform well in either solving the problem or efficiently generating near-optimal solutions. 相似文献
3.
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
4.
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
5.
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
6.
7.
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
8.
9.
水力射孔对套管强度的影响研究 总被引:4,自引:2,他引:2
水力射孔技术是一种新型的完井方式,深穿透水力射孔技术辅助定向水力压裂可以实现油气层改造和油气井增产。但是,水力射孔套管会在孔眼处造成应力集中,使得局部应力过大而削弱了套管和水泥环的强度,可能会影响套管的使用寿命。因此,文章利用有限元软件建立了射孔套管的三维有限元模型,分析了水力射孔后套管管体的应力分布,重点研究了水力射孔参数-孔密、孔径、孔深、射孔方位角等对套管强度的影响规律。分析结果表明,沿着最大水平地应力方向深穿透水力射孔,选择合适的孔密、孔径可将射孔对套管的损害降至最小。研究结果为提高水力射孔完井设计水平提供了一定的参数依据。 相似文献
10.