全文获取类型
收费全文 | 54902篇 |
免费 | 6698篇 |
国内免费 | 4831篇 |
专业分类
电工技术 | 4565篇 |
技术理论 | 12篇 |
综合类 | 7616篇 |
化学工业 | 1387篇 |
金属工艺 | 508篇 |
机械仪表 | 2531篇 |
建筑科学 | 3707篇 |
矿业工程 | 2314篇 |
能源动力 | 870篇 |
轻工业 | 825篇 |
水利工程 | 2267篇 |
石油天然气 | 1138篇 |
武器工业 | 1018篇 |
无线电 | 8890篇 |
一般工业技术 | 2738篇 |
冶金工业 | 2203篇 |
原子能技术 | 103篇 |
自动化技术 | 23739篇 |
出版年
2024年 | 110篇 |
2023年 | 660篇 |
2022年 | 1289篇 |
2021年 | 1546篇 |
2020年 | 1703篇 |
2019年 | 1322篇 |
2018年 | 1232篇 |
2017年 | 1610篇 |
2016年 | 1942篇 |
2015年 | 2176篇 |
2014年 | 3964篇 |
2013年 | 3689篇 |
2012年 | 4396篇 |
2011年 | 4405篇 |
2010年 | 3472篇 |
2009年 | 3717篇 |
2008年 | 3994篇 |
2007年 | 4405篇 |
2006年 | 3886篇 |
2005年 | 3487篇 |
2004年 | 2909篇 |
2003年 | 2537篇 |
2002年 | 1818篇 |
2001年 | 1481篇 |
2000年 | 1130篇 |
1999年 | 774篇 |
1998年 | 537篇 |
1997年 | 425篇 |
1996年 | 330篇 |
1995年 | 268篇 |
1994年 | 242篇 |
1993年 | 192篇 |
1992年 | 120篇 |
1991年 | 100篇 |
1990年 | 62篇 |
1989年 | 69篇 |
1988年 | 52篇 |
1987年 | 30篇 |
1986年 | 34篇 |
1985年 | 44篇 |
1984年 | 44篇 |
1983年 | 35篇 |
1982年 | 22篇 |
1981年 | 16篇 |
1980年 | 22篇 |
1979年 | 20篇 |
1978年 | 8篇 |
1977年 | 10篇 |
1965年 | 10篇 |
1964年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
从时代性、行业性及人力资源价值等方面分析了非线性因素对会计信息质量的影响,认为高质量的会计信息应该反映公司价值,并尝试建立了一个非线性模型,据此大体测算公司价值。 相似文献
52.
Lack of constraint-free crane path planning is one of the critical concerns in the dynamic on-site assembly process of prefabrication housing production (PHP). For decades, researchers and practitioners have endeavored to improve both the efficiency and safety of crane path planning from either static environment or re-planning the path when colliding with constraints or periodically updating the path in the dynamic environment. However, there is a lack of approach related to the in-depth exploration of the nature of dynamic constraints so as to assist the crane operators in making adaptive path re-planning decisions by categorizing and prioritizing constraints. To address this issue, this study develops the smart work packaging (SWP)-enabled constraints optimization service. This service embraces the core characteristics of SWP, including adaptivity, sociability, and autonomy to achieve autonomous initial path planning, networked constraints classification, and adaptive decisions on path re-planning. This service is simulated and verified in the BIM environment, and it is found that SWP-enabled constraints optimization service can generate the constraint-free path when it is necessary. 相似文献
53.
摘 要:针对城市地理信息平台构建过程中存在的数据获取困难、研发成本较高等问题,
引入开源技术,对基于开源数据、开源开发平台与开源工具的城市地理信息平台构建技术进行
研究。所提出的城市地理信息平台由数据模块与可视化模块 2 部分组成。为构建数据模块,由
开源地理信息项目(OSM)获取了建筑与区划数据,并设计了建筑合并算法以提升数据质量。建
筑数据随之基于行政区划分级存储,通过由 ASP. NET 构建的数据接口提供给具体应用。可视
化模块则基于开源地理信息系统(GIS)项目 Cesium 实现,并设计了完善的用户界面。以北京市
为例,完成了原型系统的开发与测试,证实了该技术体系的可行性,通过开源技术降低平台研
发成本,推进城市地理信息平台的研究与应用。 相似文献
54.
55.
《International Journal of Hydrogen Energy》2020,45(38):19455-19464
This paper presents a new procedure for optimal allocation and optimal sizing of a battery energy storage system (BESS) for primary frequency support in an isolated power system. For the BESS allocation, a transmission bus system with larger frequency decline is recognized and the BESS sizing is performed by a constrained optimization strategy based on a new modified metaheuristic, called Developed Harris Hawks Optimization (DHHO). The simulation results of the suggested DHHO are compared with Bat Optimization Algorithm (BOA) and Genetic Algorithm (GA) from the literature to show the method efficiency. The final results showed higher precision with lower required iterations for the suggested DHHO method. Also, the proposed DHHO gives lower investment costs for BESS with lower power and energy requirement toward the other compared methods. 相似文献
56.
针对实体产业对科技资源的服务需求,以服务效应作为资源文本分类标准,提出一种基于多元神经网络融合的分布式资源空间文本分类模型。设计了包含词嵌入层、卷积层、双向门控循环单元层、注意力机制层和softmax层的多元神经网络通路;在此基础上采用基于需求—效应—资源分类策略,完成了从定性科技资源需求到定量资源服务效应求解,再到定性科技资源输出的映射变换,重点解决了分布式科技资源局部和全局语义特征形式多样、文本长距离依赖特征显著、重要资源信息难以准确识别的问题,进而从分布式科技资源空间中快速准确地获取效应知识,提升实体产业产品研发效率和创新能力;通过万方专利科技资源数据集验证了所提方法的可行性和有效性,为更加全面地挖掘资源文本特征和按需服务实体产业提供了一种新的思路和手段。 相似文献
57.
58.
Asli Agirbas 《建筑学研究前沿(英文版)》2020,9(4):940-950
This study aims to test two hypotheses: teaching building information modeling (BIM) in relation to construction science provides students with a remarkable understanding of the nature of construction science (Hypothesis 1), and if the student has positive attitude toward the use of the BIM program, then efficiency by which construction science is taught by its means is improved (Hypothesis 2). Results and process of a case study with a novel teaching methodology were discussed in terms of the benefits of the students. A questionnaire study was conducted on the student group with which the case study was performed to test each student's attitude. Results were evaluated statistically. When BIM is integrated with the teaching of basic construction courses within architecture degree programs, the students understood the building system principles simply and effectively. As a result of the statistical analysis, the students find the applied method effective. Moreover, their attitude toward BIM affects the process. 相似文献
59.
Puxian Xiong Chibin Zheng Mingying Peng Zhihao Zhou Feifei Xu Kexin Qin Yiyu Hong Zhijun Ma 《Journal of the American Ceramic Society》2020,103(12):6922-6931
Till now, many doped persistent luminescence (PersL) phosphors have been investigated and found various applications in such as bioimaging, photocatalysis and information storage, but introducing PersL emitters into a proper host is mostly complex. In this research, a self-activated PersL phosphor Ba2Zr2Si3O12 (BZSO) is prepared by solid state reaction. By adding NH4Cl, the self-activated PersL intensity is evidently enhanced. The trap depths and concentrations are examined by thermoluminescence spectra. Meanwhile, Bi3+ ions are introduced into BZSO and show wide band photoluminescence (PL) from 300 to 600 nm. Moreover, the PL of Bi3+ is tunable under excitation by 265-350 nm lights. Furthermore, as a proof-of-concept design, we designed a patterned quick response (QR) code based on the self-activated PersL of BZSO, and the information of “South China University of Technology (SCUT)” can be read out by the code scanning technology. Bi3+-doped BZSO phosphors are suggested to provide potential applications in information storage by its self-activated PersL, and to excite researchers to study the tunable PL in Bi3+-doped phosphor. 相似文献
60.
马晓楠 ' target='_blank'> 吕振福 ' target='_blank'> 武秋杰 ' target='_blank'> 李作敏 ' target='_blank'> 丁国峰 ' target='_blank'> 《中州煤炭》2020,(11):103-106
我国铅锌矿产资源丰富,生产能力、消费量、出口量居世界前列,是我国的优势矿种。以10个铅锌矿能源资源基地为研究对象,对基地分布、矿山数量、产能结构、开发利用指标、矿业固废循环利用指标等进行了分析研究。研究表明,2018年,我国铅锌矿大型资源基地的矿业集中度和铅锌矿的综合利用率均高于全国平均水平。 相似文献