全文获取类型
收费全文 | 10843篇 |
免费 | 1054篇 |
国内免费 | 470篇 |
专业分类
电工技术 | 2576篇 |
技术理论 | 1篇 |
综合类 | 1092篇 |
化学工业 | 538篇 |
金属工艺 | 302篇 |
机械仪表 | 893篇 |
建筑科学 | 928篇 |
矿业工程 | 400篇 |
能源动力 | 378篇 |
轻工业 | 214篇 |
水利工程 | 436篇 |
石油天然气 | 558篇 |
武器工业 | 55篇 |
无线电 | 817篇 |
一般工业技术 | 833篇 |
冶金工业 | 1028篇 |
原子能技术 | 144篇 |
自动化技术 | 1174篇 |
出版年
2024年 | 52篇 |
2023年 | 119篇 |
2022年 | 220篇 |
2021年 | 236篇 |
2020年 | 320篇 |
2019年 | 230篇 |
2018年 | 207篇 |
2017年 | 280篇 |
2016年 | 322篇 |
2015年 | 384篇 |
2014年 | 639篇 |
2013年 | 522篇 |
2012年 | 807篇 |
2011年 | 921篇 |
2010年 | 680篇 |
2009年 | 615篇 |
2008年 | 601篇 |
2007年 | 776篇 |
2006年 | 711篇 |
2005年 | 614篇 |
2004年 | 552篇 |
2003年 | 479篇 |
2002年 | 371篇 |
2001年 | 330篇 |
2000年 | 245篇 |
1999年 | 206篇 |
1998年 | 146篇 |
1997年 | 150篇 |
1996年 | 114篇 |
1995年 | 96篇 |
1994年 | 83篇 |
1993年 | 44篇 |
1992年 | 49篇 |
1991年 | 37篇 |
1990年 | 40篇 |
1989年 | 31篇 |
1988年 | 25篇 |
1987年 | 15篇 |
1986年 | 5篇 |
1985年 | 6篇 |
1984年 | 8篇 |
1981年 | 4篇 |
1965年 | 7篇 |
1964年 | 8篇 |
1962年 | 5篇 |
1960年 | 5篇 |
1959年 | 10篇 |
1958年 | 5篇 |
1956年 | 3篇 |
1955年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Data fitting with B-splines is a challenging problem in reverse engineering for CAD/CAM, virtual reality, data visualization, and many other fields. It is well-known that the fitting improves greatly if knots are considered as free variables. This leads, however, to a very difficult multimodal and multivariate continuous nonlinear optimization problem, the so-called knot adjustment problem. In this context, the present paper introduces an adapted elitist clonal selection algorithm for automatic knot adjustment of B-spline curves. Given a set of noisy data points, our method determines the number and location of knots automatically in order to obtain an extremely accurate fitting of data. In addition, our method minimizes the number of parameters required for this task. Our approach performs very well and in a fully automatic way even for the cases of underlying functions requiring identical multiple knots, such as functions with discontinuities and cusps. To evaluate its performance, it has been applied to three challenging test functions, and results have been compared with those from other alternative methods based on AIS and genetic algorithms. Our experimental results show that our proposal outperforms previous approaches in terms of accuracy and flexibility. Some other issues such as the parameter tuning, the complexity of the algorithm, and the CPU runtime are also discussed. 相似文献
2.
Although previous research has investigated widespread use of social media, especially Facebook, by youth attending college, the conditions under which these media foster adjustment to college remain unclear. This study tested a model illuminating pathways linking social competence to college adjustment via students’ perceptions about the usefulness of Facebook and ways in which they used the medium. Self-report survey data from 321 college students (M age = 20.09; 58% female; 84% Caucasian) attending a major Midwestern university supported the proposed model, indicating that higher social competence could foster or impede college adjustment, depending upon how it was related to beliefs about the usefulness of different Facebook functions and how these perceptions, in turn, were associated with patterns of Facebook use. Findings underscore the importance of considering connections among personal attributes, perception of media effectiveness, and media behaviors in assessing the implications of social media for users’ psychosocial well-being. 相似文献
3.
M1080B无心外圆磨床砂轮及导轮宽度较窄,磨削轴承套圈外圆时,磨削效率低,托板架调整较为繁琐、皮带打滑、磨损较为严重。针对上述问题,提出了相应的解决办法,提高了磨削效率。 相似文献
4.
运用过程中各类相关因子的变化,会使得机车柴油机配气相位出现一定程度变化,采取某种措施调整或是处理可以解决动力不足的问题。 相似文献
5.
In the early design stage, automotive modeling should both meet the requirements of aesthetics and engineering. Therefore, a vehicle CAD (computer aided design) model that can be easily adjusted by feedbacks is necessary. Based on CE-Bézier surface, this paper presents a set of algorithms for parametric segmentation and fairing surface generation in a car model. This model is defined by a simplified automotive template and relevant control points, shape parameters and segmentation parameters, which can be modified to alter the car form efficiently. With this model and the corresponding adjustment method, more than fifty various vehicle models are established in this research according to different parameters. And two methods for calculating similarity index between car models are constructed, which are suitable for brand design trend analysis and modelling design decisionmaking. 相似文献
6.
钻井钢丝绳对于钻井平台安全可靠性有直接影响。采用磁性检测方法对钻井钢丝绳进行检测,并对钻井钢丝绳的励磁方式、聚磁方法及传感器与钢丝绳的配合间隙问题进行分析。在此基础上,研制了钻井钢丝绳检测仪器,能够实现对钻井钢丝绳断丝、磨损等缺陷的定性、定量检测,并能够对缺陷进行定位,为钻井钢丝绳的寿命评估提供了依据,对提高钻井平台的安全性具有重要意义。 相似文献
7.
无刷同步电机的励磁系统对励磁电流的测量是制约该励磁方式发展的一大障碍。设计了一个射频系统可以用来解决同步电机的励磁电流的测量问题。该系统可以方便地检测到同步电机励磁机的整流二极管的工作状态并且可以动态地显示励磁电流,极大地方便了运行人员做出判断,而且结构简单、方便实用。 相似文献
8.
9.
Silverberg Koerner Susan; Wallace Sara; Jacobs Lehman Stephanie; Lee Sun-A; Escalante Kristine A. 《Canadian Metallurgical Quarterly》2004,18(1):46
This study addressed two main questions: (a) Are adolescent sons and daughters exposed to sensitive maternal disclosures after divorce with similar frequency and in similar detail? and (b) Does gender act as a moderator in the association between maternal disclosures and adolescent adjustment difficulties? Forced-choice and open-ended data were collected from 194 adolescents within 2 years after their parents' divorce. Quantitative analyses revealed that although the majority of adolescents experience some level of maternal disclosure, neither frequency nor detail of maternal disclosure differed as a function of adolescent gender. Frequent and detailed maternal disclosures were associated with adolescent adjustment difficulties, primarily psychological distress. Gender did not moderate that significant association. Qualitative analysis shed light on the link between maternal disclosures and adolescent distress, suggested the importance of how disclosures are made, and revealed several gender differences in reactions to maternal disclosures. Implications of the findings are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
10.
测向定位技术是无线电管理的一个重要课题。测向定位过程中的误差的种类和产生的原因很多。选择适当的方法对误差进行校正,可以有效的减小测向误差带来的损失,提高无线电管理的效率。 相似文献