全文获取类型
收费全文 | 11824篇 |
免费 | 1579篇 |
国内免费 | 1113篇 |
专业分类
电工技术 | 1429篇 |
综合类 | 1148篇 |
化学工业 | 981篇 |
金属工艺 | 404篇 |
机械仪表 | 855篇 |
建筑科学 | 1018篇 |
矿业工程 | 298篇 |
能源动力 | 487篇 |
轻工业 | 413篇 |
水利工程 | 1193篇 |
石油天然气 | 867篇 |
武器工业 | 440篇 |
无线电 | 1269篇 |
一般工业技术 | 1606篇 |
冶金工业 | 479篇 |
原子能技术 | 295篇 |
自动化技术 | 1334篇 |
出版年
2024年 | 66篇 |
2023年 | 219篇 |
2022年 | 379篇 |
2021年 | 424篇 |
2020年 | 504篇 |
2019年 | 473篇 |
2018年 | 462篇 |
2017年 | 560篇 |
2016年 | 593篇 |
2015年 | 605篇 |
2014年 | 736篇 |
2013年 | 926篇 |
2012年 | 790篇 |
2011年 | 951篇 |
2010年 | 662篇 |
2009年 | 738篇 |
2008年 | 624篇 |
2007年 | 732篇 |
2006年 | 687篇 |
2005年 | 567篇 |
2004年 | 466篇 |
2003年 | 378篇 |
2002年 | 315篇 |
2001年 | 244篇 |
2000年 | 241篇 |
1999年 | 182篇 |
1998年 | 150篇 |
1997年 | 143篇 |
1996年 | 119篇 |
1995年 | 93篇 |
1994年 | 98篇 |
1993年 | 59篇 |
1992年 | 63篇 |
1991年 | 47篇 |
1990年 | 46篇 |
1989年 | 36篇 |
1988年 | 22篇 |
1987年 | 28篇 |
1986年 | 11篇 |
1985年 | 8篇 |
1984年 | 6篇 |
1982年 | 10篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1966年 | 4篇 |
1963年 | 5篇 |
1959年 | 5篇 |
1956年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
A novel approach is presented to calculate the sensitivities of the scattering parameters of microwave filters obtained with the full‐wave mode‐matching (MM) technique. Using only the MM simulation of the original network, the sensitivities of the scattering parameters with respect to all designable parameters are obtained. The adjoint network method (ANM) is applied to the generalized scattering matrices of the different filter components. This guarantees good accuracy of the calculated sensitivities. The implementation details are discussed for N‐resonator ridge waveguide filters. Excellent agreement is obtained between the sensitivities calculated using ANM and those obtained using the expensive central differences. © 2006 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006. 相似文献
32.
A function minimization algorithm that updates solutions based on approximated derivative information is proposed. The algorithm generates sample points with Gaussian white noise, and approximates derivatives based on stochastic sensitivity analysis. Unlike standard trust region methods which calculate gradients with n or more sample points, where n is the number of variables, the proposed algorithm allows the number of sample points M to be less than n. Furthermore, it ignores small amounts of noise within a trust region. This paper addresses the following two questions: how does the derivative approximation become worse when the number of sample points is small? Can the algorithm find good solutions with inexact derivative information when the objective landscape is noisy? Through intensive numerical experiments using quadratic functions, the algorithm is shown to be able to approximate derivatives when M is about n/10 or more. The experiments using a formulation of the traveling salesman problem show that the algorithm can find reasonably good solutions for noisy objective landscapes with inexact derivatives information. 相似文献
33.
一个基于优化的有限元模型修正方法 总被引:10,自引:5,他引:5
本文提供了一个基于一阶搜索优化的有限元模型修正方法。它只需利用结构模态试验的部分固有频率,就能获得较精确的有限元模型。文中附有某无人机上垂尾有限元模型修正的实例。根据上垂尾前二阶试验的固有频率,采用本文方法,对有限元模型进行了修正。修正后有限元模型的前二阶固有频率与试验值的相对误差在2.35%以内,而第三阶固有频率与试验值的相对误差仅为5.81%。它不仅大大地缩小了用修正前有限元模型算得的固有频率与试验值的相对误差,而且还能较精确地预测无试验结果的高阶固有频率值。 相似文献
34.
This study examines the ways in which therapists function as attachment figures for patients. Patients in long-term psychoanalytic therapy answered questionnaires about their feelings about their therapists and their closest personal relationships. Components of attachment prominent in the therapeutic relationships were looking up to the therapist and feeling the therapist was responsive to emotional needs. Stronger attachment to therapists was associated with greater frequency and duration of therapy, a stronger working alliance, and greater security of the patients' attachment style, as well as with the gender of the patient and therapist. Using attachment theory to understand psychoanalytic relationships emphasizes the unique importance of a therapist to a patient and can offer new perspectives on both therapeutic and attachment processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
35.
36.
In this paper an H∞ optimal, robust flight control system design for a supersonic aircraft has been described. Separate controllers are designed for longitudinal and lateral motions. A general two-degrees-of-freedom controller is proposed, where feedback control is designed for robust performance augmentation, while a series compensator is used to ensure that requisite handling qualities. Three alternative methods to achieve performance robustness have been discussed. The results obtained are very encouraging. It is hoped that this will equip the flight control engineers with an alternative to the conventional methods. 相似文献
37.
本文对原始状态和在火力发电厂使用不同时间的高这热器102钢管进行了显微组织和相结构变化规律的探讨和研究。显微组织研究表明,102钢管在高温高压下长期运行过程中,使用温度对显微组织和碳化物相有明显影响,而使用时间对其影响不如温度影响强烈。碳化物颗粒图象分析表明,碳化物随着使用时间缓慢长大,而新的碳化物不沉淀,使颗粒总数不断增加,颗粒,间距逐渐缩小。X射线衍射数据证明,钢管在高温长期使用过程中,MC相 相似文献
38.
39.
40.
三维结构可靠度对随机变量的敏感性研究 总被引:13,自引:2,他引:11
本文基于三维随机有限元提出了结构点可靠度、失效模式的可靠度及整个结构体系的可靠度分别对随机变量的"分布参数"和"极限状态方程参数"的敏感性计算方法,并以一典型重力坝为例进行了计算,得出了若干有益的结论。 相似文献