全文获取类型
收费全文 | 3451篇 |
免费 | 94篇 |
国内免费 | 168篇 |
专业分类
系统科学 | 98篇 |
丛书文集 | 99篇 |
教育与普及 | 130篇 |
理论与方法论 | 21篇 |
现状及发展 | 20篇 |
研究方法 | 6篇 |
综合类 | 3339篇 |
出版年
2024年 | 14篇 |
2023年 | 33篇 |
2022年 | 58篇 |
2021年 | 83篇 |
2020年 | 38篇 |
2019年 | 9篇 |
2018年 | 18篇 |
2017年 | 30篇 |
2016年 | 42篇 |
2015年 | 86篇 |
2014年 | 108篇 |
2013年 | 113篇 |
2012年 | 114篇 |
2011年 | 139篇 |
2010年 | 151篇 |
2009年 | 170篇 |
2008年 | 189篇 |
2007年 | 145篇 |
2006年 | 126篇 |
2005年 | 135篇 |
2004年 | 89篇 |
2003年 | 83篇 |
2002年 | 88篇 |
2001年 | 87篇 |
2000年 | 97篇 |
1999年 | 186篇 |
1998年 | 167篇 |
1997年 | 156篇 |
1996年 | 142篇 |
1995年 | 139篇 |
1994年 | 141篇 |
1993年 | 97篇 |
1992年 | 88篇 |
1991年 | 77篇 |
1990年 | 75篇 |
1989年 | 66篇 |
1988年 | 53篇 |
1987年 | 40篇 |
1986年 | 20篇 |
1985年 | 9篇 |
1984年 | 2篇 |
1981年 | 1篇 |
1979年 | 2篇 |
1975年 | 1篇 |
1969年 | 1篇 |
1968年 | 2篇 |
1966年 | 1篇 |
1965年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有3713条查询结果,搜索用时 15 毫秒
991.
针对目前软件过程领域知识缺乏明确统一的表示、不同组织构造的过程模型缺少互操作性而难以共享和重用的情况,划分并描述了软件过程的顶层本体;在此基础上,对其中包含的任务描述、过程模型和过程实施与改进三个核心本体分别进行了展开和细化,给出了涉及到的关键概念的形式化定义.传统的本体系统并不适宜描述动态过程,因此使用谓词逻辑定义了过程本体中概念间的基本关系,以此来表示和描述软件过程模型的“柔性”和动态知识,使不同的参与者易于交流而达成共识,为构造可共享、易重用的过程模型元模型提供坚实、统一的基础. 相似文献
992.
Gang Du Jianzhong Wang 《系统科学与信息学报》2009,7(3):245-252
After reviewing the literature and methodology-related issues within the field of product family design, a deficiency in the current design and development of product family is pointed out. The concept of hierarchical associated design is proposed in this article, according to the deficiency~ and the methods and models for realizing the notion above are described. A two-dimensional analytical model is constructed based on the composing levels and developing processes of product family. The optimization models to hierarchical associated design problems are grouped into two categories: overall-local and key-subordinate. The algorithms of the models are discussed in this paper 相似文献
993.
This paper proves the error reduction property(saturation property),convergence and optimality of an adaptive mixed finite element method(AMFEM) for the Poisson equation.In each step of AMFEM,the local refinement is performed basing on simple either edge-oriented residuals or edge-oriented data oscillations,depending only on the marking strategy,under some restriction of refinement.The main tools used here are the strict discrete local efficiency property given by Carstensen and Hoppe(2006) and the quasi-orthogonality estimate proved by Chen,Hoist,and Xu (2009).Numerical experiments fully confirm the theoretical analysis. 相似文献
994.
A novel model for the charging station planning problem of plug-in electric vehicles is proposed in this paper considering the users’ daily travel. With the objective of minimizing the total cost, including the charging stations’ cost (including installing cost and management cost) and the users’ cost (including station access cost and charging cost), the proposed model simultaneously handles the problems where to locate the charging stations and how many chargers to be established in each charging station. Considering that different users may have different perception of station access cost and charging cost, two cases (i.e., homogeneous users and heterogeneous users) are typically investigated. The impacts of different discount rates, operating period of the charging stations, number of electric vehicles and number of charging stations on the location of the charging station are also studied. The simulation results not only show that it is very important to locate the charging stations according to the traveling behavior of users, but also verify the validity of the proposed model. 相似文献
995.
探讨了具有非线性测量方程的跟踪系统的计算机仿真方法。给出了一类常见的跟踪系统的数学模型和仿真模型。并以一个实例说明了该仿真方法的可行性。 相似文献
996.
Yu Du Jianlong Wang Sijing Wu Qing Liu Qinghong Zhao Yingxin Zhao Qian Ma Yujie Zhou 《科学通报(英文版)》2021,(24):2431-2433
Coronary artery disease (CAD) is the leading cause of death worldwide.Implantation of traditional cylindrical stents into the stenotic coronary arteries is wide... 相似文献
997.
998.
999.
Xian-hu Liu Fei-hong Wang Cong-ying Shao Gang-feng Du Bing-qing Yao 《矿物冶金与材料学报》2021,28(10):1716-1725
Synthesizing atomically precise Ag nanoclusters (NCs), which is essential for the general development of NCs, is quite challenging. In this study, we report the synthesis of high-purity atomically precise Ag NCs via a kinetically controlled strategy. The Ag NCs were prepared using a mild reducing agent via a one-pot method. The as-prepared Ag NCs were confirmed to be Ag49(D-pen)24 (D-pen: D-penicillamine) on the basis of their matrix-assisted laser desorption ionization time-of-flight mass spectrometric and thermogravimetric characteristics. The interfacial structures of the Ag NCs were illustrated by proton nuclear magnetic resonance and Fourier-transform infrared spectroscopy. The Ag NCs were supported on activated carbon (AC) to form Ag NCs/AC, which displayed excellent activity for the catalytic reduction of 4-nitrophenol with a kinetic reaction rate constant k of 0.21 min?1. Such a high k value indicates that the composite could outperform several previously reported catalysts. Moreover, the catalytic activity of Ag NCs/AC remained nearly constant after six times of recycle, which suggests its excellent stability. 相似文献
1000.
中国很多新一代天气雷达正在或已经进行了双偏振升级改造,双偏振雷达将在未来业务应用中发挥极大的作用,而雷达标定的可靠性直接影响其应用效益。以中国首批业务化双偏振天气雷达(广州、阳江、韶关、梅州、厦门)开展双偏振技术试验的标定数据为研究对象,从机内标定、接收链路标定、全链路标定及旋转关节标定共4方面展开分析。结果表明:机内标定和接收链路标定基本满足技术要求,但部分雷达受到不定期的外界电磁干扰,影响了噪声系数的标定,需进一步净化电磁环境;全链路标定结果表明,5部雷达系统Z_(DR)误差分别为:-0.38、0、0.38、0.44、-1.38 dB,系统误差整体偏大,这与基层雷达台站缺乏实时有效的监测方法有关;旋转关节标定表明,由旋转关节引入的一致性偏差是动态变化的,具有不确定性,对差分反射率和差分传播相移的测量结果会造成一定程度的影响,随着旋转关节的磨损,需要对其影响进行长期跟踪检测。这些结果可为后续双偏振雷达升级改造、运行评估及制定双偏振雷达业务化标定流程提供科学依据。 相似文献