全文获取类型
收费全文 | 88303篇 |
免费 | 7418篇 |
国内免费 | 3781篇 |
专业分类
电工技术 | 5012篇 |
技术理论 | 12篇 |
综合类 | 5857篇 |
化学工业 | 14810篇 |
金属工艺 | 4667篇 |
机械仪表 | 5205篇 |
建筑科学 | 7177篇 |
矿业工程 | 2522篇 |
能源动力 | 2466篇 |
轻工业 | 6345篇 |
水利工程 | 1616篇 |
石油天然气 | 5044篇 |
武器工业 | 643篇 |
无线电 | 10289篇 |
一般工业技术 | 10881篇 |
冶金工业 | 4290篇 |
原子能技术 | 936篇 |
自动化技术 | 11730篇 |
出版年
2024年 | 326篇 |
2023年 | 1477篇 |
2022年 | 2499篇 |
2021年 | 3647篇 |
2020年 | 2869篇 |
2019年 | 2299篇 |
2018年 | 2607篇 |
2017年 | 2751篇 |
2016年 | 2610篇 |
2015年 | 3405篇 |
2014年 | 4373篇 |
2013年 | 5052篇 |
2012年 | 5640篇 |
2011年 | 6089篇 |
2010年 | 5135篇 |
2009年 | 4834篇 |
2008年 | 4793篇 |
2007年 | 4519篇 |
2006年 | 4422篇 |
2005年 | 3929篇 |
2004年 | 2774篇 |
2003年 | 2445篇 |
2002年 | 2226篇 |
2001年 | 2011篇 |
2000年 | 2126篇 |
1999年 | 2565篇 |
1998年 | 2139篇 |
1997年 | 1771篇 |
1996年 | 1721篇 |
1995年 | 1445篇 |
1994年 | 1226篇 |
1993年 | 826篇 |
1992年 | 665篇 |
1991年 | 497篇 |
1990年 | 419篇 |
1989年 | 369篇 |
1988年 | 268篇 |
1987年 | 171篇 |
1986年 | 134篇 |
1985年 | 84篇 |
1984年 | 65篇 |
1983年 | 46篇 |
1982年 | 59篇 |
1981年 | 36篇 |
1980年 | 33篇 |
1979年 | 15篇 |
1977年 | 9篇 |
1976年 | 13篇 |
1974年 | 11篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A new type of modified bismaleimide resin was obtained by copolymerization between tris(allylphenoxy)triazine monomer (TAPT) and an aromatic diamine‐chain‐extension bismaleimide [e.g., 4,4′‐diaminodiphenylmethane (DADPM)‐chain‐extension 4,4′‐bismaleimidodiphenylmethane (BMDPM)]. The new three‐component‐polymer system had good processibility and mechanical properties. Better results were obtained when the weight ratio of TAPT to the DADPM‐chain‐extension BMDPM resin was 30%. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 475–480, 2004 相似文献
992.
993.
In Role Based Access Control (RBAC) systems, it is necessary and important to update the role–permission assignments in order to reflect the evolutions of the system transactions. However, role updating is generally complex and challenging, especially for large-scale RBAC systems. This is because the resulting state is usually expected to meet various requirements and constraints. In this paper, we focus on a fundamental problem of role updating in RBAC, which determines whether there exists a valid role–permission assignment, i.e., whether it can satisfy all the requirements of the role updating and without violating any role–capacity or permission–capacity constraint. We formally define such a problem as the Role Updating Feasibility Problem (RUFP), and study the computational complexity of RUFP in different subcases. Our results show that although several subcases are solvable in linear time, this problem is NP-complete in the general case. 相似文献
994.
Huapeng Yu Yongxin Chang Pei Lu Zhiyong Xu Chengyu Fu Yafei Wang 《Computers & Electrical Engineering》2014
In this paper, we make use of biologically inspired selective attention to improve the efficiency and performance of object detection under clutter. At first, we propose a novel bottom-up attention model. We argue that heuristic feature selection based on bottom-up attention can stably select out invariant and discriminative features. With these selected features, performance of object detection can be improved apparently and stably. Then we propose a novel concept of saccade map based on bottom-up attention to simulate the saccade (eye movements) in vision. Sliding within saccade map to detect object can significantly reduce computational complexity and apparently improve performance because of the effective filtering for distracting information. With these ideas, we present a general framework for object detection through integrating bottom-up attention. Through evaluating on UIUC cars and Weizmann–Shotton horses we show state-of-the-art performance of our object detection model. 相似文献
995.
通过对硅溶胶泥浆的流变性实验确定了硅溶胶泥浆的流变模型,验证并分析了加入少量经过低温氧化过的甘油三酸脂(GTO)不改变硅溶胶泥浆的流变模型,但能有效地改善其流变性能。因此,GTO可作为硅溶胶结合浇注料的高效减水剂。 相似文献
996.
本文介绍了一个微机上运行的注塑模CAD系统,此系统主要解决了四个难点,浇注系统设计,冷却系统分析,型腔,型芯的曲面造型设计,装配图和零件工作图的设计绘制,经厂家实际运用证明,该系统使用方便,结果正确,能提高设计效率,降低生产成本。 相似文献
997.
采用新工艺合成克林霉素,流程短,收率高,重量收率比传统工艺提高了21.55个百分点,可达88.0%,产品质量符合中国药典2000版标准. 相似文献
998.
In existing Active Access Control (AAC) models, the scalability and flexibility of security policy specification should be well balanced, especially: (1) authorizations to plenty of tasks should be simplified; (2) team workflows should be enabled; (3) fine-grained constraints should be enforced. To address this issue, a family of Association-Based Active Access Control (ABAAC) models is proposed. In the minimal model ABAAC0, users are assigned to roles while permissions are assigned to task-role associations. In a workflow case, to execute such an association some users assigned to its component role will be allocated. The association's assigned permissions can be performed by them during the task is running in the case. In ABAAC1, a generalized association is employed to extract common authorizations from multiple associations. In ABAAC2, a fine-grained separation of duty (SoD) is enforced among associations. In the maximal model ABAAC3, all these features are integrated, and similar constraints can be specified more concisely. Using a software workflow, case validation is performed. Comparison with a representative association based AAC model and the most scalable AAC model so far indicates that: (1) enough scalability is achieved; (2) without decomposition of a task, different permissions can be authorized to multiple roles in it; (3) separation of more fine-grained duties than roles and tasks can be enforced. 相似文献
999.
Claudia Kuster Jean‐Charles Bazin Cengiz Öztireli Teng Deng Tobias Martin Tiberiu Popa Markus Gross 《Computer Graphics Forum》2014,33(2):1-10
Multi‐view reconstruction aims at computing the geometry of a scene observed by a set of cameras. Accurate 3D reconstruction of dynamic scenes is a key component for a large variety of applications, ranging from special effects to telepresence and medical imaging. In this paper we propose a method based on Moving Least Squares surfaces which robustly and efficiently reconstructs dynamic scenes captured by a calibrated set of hybrid color+depth cameras. Our reconstruction provides spatio‐temporal consistency and seamlessly fuses color and geometric information. We illustrate our approach on a variety of real sequences and demonstrate that it favorably compares to state‐of‐the‐art methods. 相似文献
1000.