全文获取类型
收费全文 | 13489篇 |
免费 | 1372篇 |
国内免费 | 748篇 |
专业分类
电工技术 | 1060篇 |
技术理论 | 3篇 |
综合类 | 1345篇 |
化学工业 | 843篇 |
金属工艺 | 267篇 |
机械仪表 | 580篇 |
建筑科学 | 1580篇 |
矿业工程 | 486篇 |
能源动力 | 641篇 |
轻工业 | 271篇 |
水利工程 | 4791篇 |
石油天然气 | 811篇 |
武器工业 | 41篇 |
无线电 | 483篇 |
一般工业技术 | 390篇 |
冶金工业 | 956篇 |
原子能技术 | 91篇 |
自动化技术 | 970篇 |
出版年
2024年 | 25篇 |
2023年 | 149篇 |
2022年 | 274篇 |
2021年 | 338篇 |
2020年 | 393篇 |
2019年 | 357篇 |
2018年 | 330篇 |
2017年 | 404篇 |
2016年 | 491篇 |
2015年 | 548篇 |
2014年 | 804篇 |
2013年 | 714篇 |
2012年 | 984篇 |
2011年 | 1074篇 |
2010年 | 814篇 |
2009年 | 755篇 |
2008年 | 706篇 |
2007年 | 928篇 |
2006年 | 898篇 |
2005年 | 780篇 |
2004年 | 660篇 |
2003年 | 573篇 |
2002年 | 496篇 |
2001年 | 425篇 |
2000年 | 301篇 |
1999年 | 262篇 |
1998年 | 203篇 |
1997年 | 164篇 |
1996年 | 133篇 |
1995年 | 102篇 |
1994年 | 99篇 |
1993年 | 71篇 |
1992年 | 73篇 |
1991年 | 41篇 |
1990年 | 37篇 |
1989年 | 45篇 |
1988年 | 31篇 |
1987年 | 19篇 |
1986年 | 8篇 |
1985年 | 14篇 |
1984年 | 8篇 |
1980年 | 4篇 |
1965年 | 7篇 |
1964年 | 6篇 |
1962年 | 5篇 |
1960年 | 5篇 |
1959年 | 11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.
寒区河道凌汛灾害河势“弯道效应”的量化评估十分重要。基于分形理论提出河道横断面-纵剖面-平面多维度河势分形维数计算方法及其物理机制,并探讨黄河内蒙古段不同维度河势演变分形特征及其与凌汛灾害的关联关系。结果表明,黄河内蒙古段不同维度河势均具有多尺度自相似分形特征,且具有多年记忆周期的长程相关性;冰坝(严重性冰塞)发生频次与河道主槽弯曲分形维数呈正相关指数型函数关系,与河相系数、深泓点高程和河段平均底坡分形维数负相关,与水深-面积分形维数正相关,总体表明冰坝灾害更易发生于主槽偏移摆动大、蜿蜒曲折、河湾发育程度高的宽浅型弯曲河道,研究成果可为凌汛期冰塞冰坝灾害易发河段诊断及预测提供重要理论依据。 相似文献
2.
A venturi device is commonly used as an integral part of a multiphase flowmeter (MPFM) in real-time oil-gas production monitoring. Partial flow mixing is required by installing the venturi device vertically downstream of a blind tee pipework that conditions the incoming horizontal gas-liquid flow (for an accurate determination of individual phase fraction and flow rate). To study the flow-mixing effect of the blind tee, high-speed video flow visualization of gas-liquid flows has been performed at blind tee and venturi sections by using a purpose-built transparent test rig over a wide range of superficial liquid velocities (0.3–2.4 m/s) and gas volume fractions (10–95%). There is little ‘homogenization’ effect of the blind tee on the incoming intermittent horizontal flow regimes across the tested flow conditions, with the flow remaining intermittent but becoming more axis-symmetric and predictable in the venturi measurement section. A horizontal (blind tee) to vertical (venturi) flow-pattern transition map is proposed based on gas and liquid mass fluxes (weighted by the Baker parameters). Flow patterns can be identified from the mean and variance of a fast electrical capacitance holdup measured at the venturi throat. 相似文献
3.
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
4.
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
5.
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
6.
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
7.
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
8.
机械压力机的飞轮、支撑套及圆盘类等零件在钻床、龙门铣床进行垂直、斜孔或面精密加工时,需要直立或倾斜固定于机床工作台或地平台基面,人工操作用时长,效率低,工人劳动强度大,零件倾斜角度调整定位精度较低,加工零件质量差,通过本文设计的这种弯板式斜度机械调整卡具装置可有效解决这类问题,达到零件进行垂直、斜孔或面精密加工的特殊要求。 相似文献
9.
The polymer electrolyte based solid-state lithium metal batteries are the promising candidate for the high-energy electrochemical energy storage with high safety and stability. Moreover, the intrinsic properties of polymer electrolytes and interface contact between electrolyte and electrodes have played critical roles for determining the comprehensive performances of solid-state lithium metal batteries. In this review, the development of polymer electrolytes with the design strategies by functional units adjustments are firstly discussed. Then the interfaces between polymer electrolyte and cathode/anode, including the interface issues, remedy strategies for stabilizing the interface contact and reducing resistances, and the in-situ polymerization method for enhancing the compatibilities and assembling the batteries with favorable performances, have been introduced. Lastly, the perspectives on developing polymer electrolytes by functional units adjustment, and improving interface contact and stability by effective strategies for solid-state lithium metal batteries have been provided. 相似文献
10.