全文获取类型
| 收费全文 | 33748篇 |
| 免费 | 3515篇 |
| 国内免费 | 1450篇 |
学科分类
| 69篇 | |
| 农业科学 | 2850篇 |
| 艺术 | 11篇 |
| 地球科学 | 3738篇 |
| 航空航天 | 253篇 |
| 生物科学 | 4142篇 |
| 文化教育 | 1429篇 |
| 经济 | 364篇 |
| 环境安全 | 292篇 |
| 自然科学 | 3423篇 |
| 社会科学 | 483篇 |
| 历史地理 | 128篇 |
| 工业技术 | 9214篇 |
| 语言文字 | 124篇 |
| 文学 | 13篇 |
| 数理化 | 3874篇 |
| 医药卫生 | 7784篇 |
| 军事 | 78篇 |
| 哲学宗教 | 164篇 |
| 政治法律 | 47篇 |
| 交通运输 | 233篇 |
出版年
| 2025年 | 260篇 |
| 2024年 | 670篇 |
| 2023年 | 694篇 |
| 2022年 | 854篇 |
| 2021年 | 1078篇 |
| 2020年 | 1302篇 |
| 2019年 | 1205篇 |
| 2018年 | 1019篇 |
| 2017年 | 1197篇 |
| 2016年 | 1252篇 |
| 2015年 | 1272篇 |
| 2014年 | 1773篇 |
| 2013年 | 2023篇 |
| 2012年 | 1884篇 |
| 2011年 | 1856篇 |
| 2010年 | 1538篇 |
| 2009年 | 1680篇 |
| 2008年 | 1781篇 |
| 2007年 | 1869篇 |
| 2006年 | 1682篇 |
| 2005年 | 1405篇 |
| 2004年 | 1208篇 |
| 2003年 | 1147篇 |
| 2002年 | 968篇 |
| 2001年 | 892篇 |
| 2000年 | 771篇 |
| 1999年 | 656篇 |
| 1998年 | 655篇 |
| 1997年 | 589篇 |
| 1996年 | 534篇 |
| 1995年 | 425篇 |
| 1994年 | 390篇 |
| 1993年 | 358篇 |
| 1992年 | 304篇 |
| 1991年 | 235篇 |
| 1990年 | 230篇 |
| 1989年 | 163篇 |
| 1988年 | 145篇 |
| 1987年 | 122篇 |
| 1986年 | 106篇 |
| 1985年 | 107篇 |
| 1984年 | 96篇 |
| 1983年 | 59篇 |
| 1982年 | 69篇 |
| 1981年 | 49篇 |
| 1980年 | 42篇 |
| 1979年 | 32篇 |
| 1978年 | 8篇 |
| 1977年 | 10篇 |
| 1976年 | 11篇 |
排序方式： 共有10000条查询结果，搜索用时 31 毫秒
981.
Luis Angel Villegas-Armenta Priti Wanjara Javad Gholipour Isao Nakatsugawa Yasumasa Chino Mihriban Pekguleryuz 《Materials》2021,14(11)
Solid-state welding offers distinct advantages for joining reactive materials, such as magnesium (Mg) and its alloys. This study investigates the effect of linear friction welding (LFW) on the microstructure and mechanical properties of cast AZ91 (Mg–9Al–1Zn) and AZ91–2Ca alloys, which (to the best knowledge of the authors) has not been reported in the literature. Using the same set of LFW process parameters, similar alloy joints—namely, AZ91/AZ91 and AZ91–2Ca/AZ91–2Ca—were manufactured and found to exhibit integral bonding at the interface without defects, such as porosity, inclusions, and/or cracking. Microstructural examination of the AZ91/AZ91 joint revealed dissolution of the Al-rich second phase in the weld zone, while the Mn containing phases remained and were refined. In the AZ91–2Ca/AZ91–2Ca joint, the weld zone retained Ca- and Mn-rich phases, which were also refined due to the LFW process. In both joint types, extensive recrystallization occurred during LFW, as evidenced by the refinement of the grains from ~1000 µm in the base materials to roughly 2–6 µm in the weld zone. These microstructural changes in the AZ91/AZ91 and AZ91–2Ca/AZ91–2Ca joints increased the hardness in the weld zone by 32%. The use of digital image correlation for strain mapping along the sample gage length during tensile testing revealed that the local strains were about 50% lower in the weld zone relative to the AZ91 and AZ91–2Ca base materials. This points to the higher strength of the weld zone in the AZ91/AZ91 and AZ91–2Ca/AZ91–2Ca joints due to the fine grain size, second phase refinement, and strong basal texture. Final fracture during tensile loading of both joints occurred in the base materials. 相似文献
982.
针对生物信息分析中基因短序列比对任务计算耗时长的问题,采用Spark平台、RDD数据集以及分布式文件系统HDFS设计了一种分布式计算模型.采用分而治之的策略将庞大的计算任务分割为多个互不重叠的小任务在分布式集群上并行执行.通过基于位置偏移量等分的数据分区算法实现数据的分发;通过将基因短序列封装入RDD数据集的方法实现了... 相似文献
983.
984.
Modern manufacturing enterprises are shifting toward multi-variety and small-batch production. By optimizing scheduling, both transit and waiting times within the production process can be shortened. This study integrates the advantages of a digital twin and supernetwork to develop an intelligent scheduling method for workshops to rapidly and efficiently generate process plans. By establishing the supernetwork model of a feature-process-machine tool in the digital twin workshop, the centralized and classified management of multiple data types can be realized. A feature similarity matrix is used to cluster similar attribute data in the feature layer subnetwork to realize rapid correspondence of multi-source association information among feature-process-machine tools. Through similarity calculations of decomposed features and the mapping relationships of the supernetwork, production scheduling schemes can be rapidly and efficiently formulated. A virtual workshop is also used to simulate and optimize the scheduling scheme to realize intelligent workshop scheduling. Finally, the efficiency of the proposed intelligent scheduling strategy is verified by using a case study of an aeroengine gear production workshop. 相似文献
985.
Simultaneous Localisation and Mapping (SLAM) is the archetypal chicken and egg problem: Localisation of a robot with respect to a map requires an estimate of the map, while mapping an environment from data acquired by a robot requires an estimate of the robot localisation. The nonlinearity and co-dependence of the SLAM problem has made it an ongoing research problem for more than thirty years. The present paper details recent advances in understanding the SLAM problem, specifically the existence of an underlying geometry and symmetry structure that provides significant insight into the difficulties that have plagued many SLAM algorithms. To demonstrate the power of the geometric insight we derive a constant gain observer for the SLAM problem that; that does not depend on linearisation, has globally asymptotically stable error dynamics, is very robust, and operates in dynamic environments (estimating the landmark velocities as states in the observer). 相似文献
986.
Adam Jacobson Fan Zeng David Smith Nigel Boswell Thierry Peynot Michael Milford 《野外机器人技术杂志》2021,38(1):5-27
Robustly and accurately localizing vehicles in underground mines is particularly challenging due to the unavailability of GPS, variable and often poor lighting conditions, visual aliasing in long tunnels, and airborne dust and water. In this paper, we present a novel, infrastructure‐less, multisensor localization method for robust autonomous operation within underground mines. The proposed method integrates with existing mine site commissioning and operation procedures and includes both an offline map‐building process and an online localization algorithm. The approach combines the strengths of visual‐based place recognition, LIDAR‐based localization, and odometry in a particle filter fusion process. We provide an extensive experimental validation using new large data sets acquired in two operational Australian underground hard‐rock mines (including a 600m‐deep multilevel mine with approximately 33 km of mapping data and 7 km of vehicle localization) by actual mining vehicles during production operations. We demonstrate a significant increase in localization accuracy over prior state‐of‐the‐art SLAM research systems and real‐time operation, with processing times in the order of 10 Hz. We present results showing a mean error of 0.68 m from the Queensland Mine data set and 1.32 m from the New South Wales Mine data set and at least 86% reduction in error compared with prior state of the art. We also analyze the impact of the particle filter parameters with respect to localization accuracy. Together this study represents a new approach to positioning systems for currently deployed autonomous vehicles within underground mine environments. 相似文献
987.
989.
《工程（英文）》2024,42(11)
Crop phenomics has rapidly progressed in recent years due to the growing need for crop functional geno-mics,digital breeding,and smart cultivation.Despite this advancement,the lack of standards for the cre-ation and usage of crop phenomics technology and equipment has become a bottleneck,limiting the industry's high-quality development.This paper begins with an overview of the crop phenotyping indus-try and presents an industrial mapping of technology and equipment for big data in crop phenomics.It analyzes the necessity and current state of constructing a standard framework for crop phenotyping.Furthermore,this paper proposes the intended organizational structure and goals of the standard frame-work.It details the essentials of the standard framework in the research and development of hardware and equipment,data acquisition,and the storage and management of crop phenotyping data.Finally,it discusses promoting the construction and evaluation of the standard framework,aiming to provide ideas for developing a high-quality standard framework for crop phenotyping. 相似文献
990.
Radovan Hynek Iva Michalus Pavel Cejnar Jiří Šantrůček Sabina Seidlová Štěpánka Kučková Petra Sázelová Václav Kašička 《Electrophoresis》2021,42(23):2552-2562
Proteomic characterization of alveolar bones in oral surgery represents an analytical challenge due to their insoluble character. The implementation of a straightforward technique could lead to the routine use of proteomics in this field. This work thus developed a simple technique for the characterization of bone tissue for human maxillary and mandibular bones. It is based on the direct in-bone tryptic digestion of proteins in both healthy and pathological human maxillary and mandibular bone samples. The released peptides were then identified by the LC-MS/MS. Using this approach, a total of 1120 proteins were identified in the maxillary bone and 1151 proteins in the mandibular bone. The subsequent partial least squares–discrimination analysis (PLS-DA) of protein data made it possible to reach 100% discrimination between the samples of healthy alveolar bones and those of the bone tissue surrounding the inflammatory focus. These results indicate that the in-bone protein digestion followed by the LC-MS/MS and subsequent statistical analysis can provide a deeper insight into the field of oral surgery at the molecular level. Furthermore, it could also have a diagnostic potential in the differentiation between the proteomic patterns of healthy and pathological alveolar bone tissue. Data are available via ProteomeXchange with the identifier PXD026775. 相似文献
