全文获取类型
收费全文 | 9534篇 |
免费 | 1072篇 |
国内免费 | 731篇 |
专业分类
电工技术 | 298篇 |
技术理论 | 1篇 |
综合类 | 618篇 |
化学工业 | 699篇 |
金属工艺 | 154篇 |
机械仪表 | 190篇 |
建筑科学 | 592篇 |
矿业工程 | 269篇 |
能源动力 | 152篇 |
轻工业 | 681篇 |
水利工程 | 288篇 |
石油天然气 | 1916篇 |
武器工业 | 26篇 |
无线电 | 1182篇 |
一般工业技术 | 664篇 |
冶金工业 | 382篇 |
原子能技术 | 132篇 |
自动化技术 | 3093篇 |
出版年
2024年 | 35篇 |
2023年 | 166篇 |
2022年 | 258篇 |
2021年 | 394篇 |
2020年 | 378篇 |
2019年 | 308篇 |
2018年 | 289篇 |
2017年 | 297篇 |
2016年 | 398篇 |
2015年 | 370篇 |
2014年 | 595篇 |
2013年 | 750篇 |
2012年 | 626篇 |
2011年 | 657篇 |
2010年 | 540篇 |
2009年 | 498篇 |
2008年 | 668篇 |
2007年 | 639篇 |
2006年 | 593篇 |
2005年 | 523篇 |
2004年 | 471篇 |
2003年 | 355篇 |
2002年 | 248篇 |
2001年 | 207篇 |
2000年 | 198篇 |
1999年 | 152篇 |
1998年 | 100篇 |
1997年 | 115篇 |
1996年 | 88篇 |
1995年 | 67篇 |
1994年 | 62篇 |
1993年 | 44篇 |
1992年 | 42篇 |
1991年 | 28篇 |
1990年 | 29篇 |
1989年 | 23篇 |
1988年 | 11篇 |
1987年 | 6篇 |
1986年 | 12篇 |
1985年 | 8篇 |
1984年 | 14篇 |
1982年 | 9篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1977年 | 5篇 |
1973年 | 4篇 |
1966年 | 5篇 |
1956年 | 6篇 |
1955年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
101.
102.
103.
Cyberattacks are difficult to prevent because the targeted companies and organizations are often relying on new and fundamentally insecure cloud-based technologies, such as the Internet of Things. With increasing industry adoption and migration of traditional computing services to the cloud, one of the main challenges in cybersecurity is to provide mechanisms to secure these technologies. This work proposes a Data Security Framework for cloud computing services (CCS) that evaluates and improves CCS data security from a software engineering perspective by evaluating the levels of security within the cloud computing paradigm using engineering methods and techniques applied to CCS. This framework is developed by means of a methodology based on a heuristic theory that incorporates knowledge generated by existing works as well as the experience of their implementation. The paper presents the design details of the framework, which consists of three stages: identification of data security requirements, management of data security risks and evaluation of data security performance in CCS. 相似文献
104.
文章提出了一种基于虚拟化的服务备份技术,该技术能够以较低的成本投入实现在提供的服务崩溃时迅速恢复服务,提高用户对服务的满意度,同时,文章对就影响该技术实现效果的服务备份速度、服务恢复速度、负载均衡三个因素进行了研究,提出了解决方案。 相似文献
105.
Many P2P applications require security services such as privacy, anonymity, authentication, and non-repudiation. Such services could be provided through a hierarchical Public Key Infrastructure. However, P2P networks are usually Internet-scale distributed systems comprised of nodes with an undetermined trust level, thus making hierarchical solutions unrealistic. In this paper, we propose Chord-PKI, a distributed PKI architecture which is build upon the Chord overlay network, in order to provide security services for P2P applications. Our solution distributes the functionality of a PKI across the peers by using threshold cryptography and proactive updating. We analyze the security of the proposed infrastructure and through simulations we evaluate its performance for various scenarios of untrusted node distributions. 相似文献
106.
Distributed match-making 总被引:1,自引:0,他引:1
In many distributed computing environments, processes are concurrently executed by nodes in a store- and-forward communication network. Distributed control issues as diverse as name server, mutual exclusion, and replicated data management involve making matches between such processes. We propose a formal problem called distributed match-making as the generic paradigm. Algorithms for distributed match-making are developed and the complexity is investigated in terms of messages and in terms of storage needed. Lower bounds on the complexity of distributed match-making are established. Optimal algorithms, or nearly optimal algorithms, are given for particular network topologies.The work of the second author was supported in part by the Office of Naval Research under Contract N00014-85-K-0168, by the Office of Army Research under Contract DAAG29-84-K-0058, by the National Science Foundation under Grant DCR-83-02391, and by the Defence Advanced Research Projects Agency (DARPA) under Contract N00014-83-K-0125. Current address of both authors: CWI, Kruislaan 413, 1098 SJ Amsterdam, The Netherlands. 相似文献
107.
在本文中,以利用适地性服务机制之设计,来建立一个行动导览系统带领用户体验空间和主题维度的古迹导览服务。为了满足此需求,设计了一套后设数据(Metadata)来描述导览内容,并且在适地性服务机制设计上,提供包含适地性内容方法有效取得使用者附近的内容,并藉由适地性内容的暂存与安排方法,减少网络间的讯息传递,提供用户结构化的介绍内容,并在适当的时机触发内容的呈现。最后,以所提供之内容的相关性来比较所提方法与一般适地性服务之差异。邀请用户进行实地系统测试,以了解系统的实用性,取得测试者的建议。结果证实所设计之导览系统可以是导览解说员的多媒体辅助工具,或在没有导览解说员时,为使用者提供景点导览解说的服务。 相似文献
108.
测定沂沭河底泥的有机质(OM)、总氮(TN)、总磷(TP)及有效磷含量,分析了污染物之间的相关性,评价了沂沭河底泥的污染状况。结果表明:沂沭河流域表层沉积物中TN、TP分布特性相似,沂河中OM含量远低于沭河,OM、TN、TP分布的空间差异较大。有效磷含量约占TP含量的17.7%,表明农田及人类活动对流域水环境造成了一定程度的污染。C/N、N/P及OM与氮、磷含量的回归分析表明,碳、氮具有同源性,底质中OM及氮主要源于生物沉降,而磷主要源于外部输入。经评价,沂沭河底质沉积物环境质量整体较好,污染程度属于清洁水平。 相似文献
109.
The voltage-gated proton channel, Hv1, also termed VSOP, was discovered in 2006. It has long been suggested that proton transport through voltage-gated proton channels regulate reactive oxygen species (ROS) production in phagocytes by counteracting the charge imbalance caused by the activation of NADPH oxidase. Discovery of Hv1/VSOP not only confirmed this process in phagocytes, but also led to the elucidation of novel functions in phagocytes. The compensation of charge by Hv1/VSOP sustains ROS production and is also crucial for promoting Ca2+ influx at the plasma membrane. In addition, proton extrusion into neutrophil phagosomes by Hv1/VSOP is necessary to maintain neutral phagosomal pH for the effective killing of bacteria. Contrary to the function of Hv1/VSOP as a positive regulator for ROS generation, it has been revealed that Hv1/VSOP also acts to inhibit ROS production in neutrophils. Hv1/VSOP inhibits hypochlorous acid production by regulating degranulation, leading to reduced inflammation upon fungal infection, and suppresses the activation of extracellular signal-regulated kinase (ERK) signaling by inhibiting ROS production. Thus, Hv1/VSOP is a two-way player regulating ROS production. Here, we review the functions of Hv1/VSOP in neutrophils and discuss future perspectives. 相似文献
110.