全文获取类型
收费全文 | 501篇 |
免费 | 90篇 |
国内免费 | 32篇 |
专业分类
化学 | 74篇 |
晶体学 | 4篇 |
力学 | 32篇 |
综合类 | 19篇 |
数学 | 346篇 |
物理学 | 148篇 |
出版年
2023年 | 4篇 |
2022年 | 27篇 |
2021年 | 30篇 |
2020年 | 9篇 |
2019年 | 12篇 |
2018年 | 12篇 |
2017年 | 23篇 |
2016年 | 28篇 |
2015年 | 17篇 |
2014年 | 38篇 |
2013年 | 36篇 |
2012年 | 24篇 |
2011年 | 38篇 |
2010年 | 28篇 |
2009年 | 32篇 |
2008年 | 26篇 |
2007年 | 43篇 |
2006年 | 30篇 |
2005年 | 25篇 |
2004年 | 17篇 |
2003年 | 22篇 |
2002年 | 11篇 |
2001年 | 16篇 |
2000年 | 10篇 |
1999年 | 10篇 |
1998年 | 10篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 4篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 9篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1980年 | 1篇 |
排序方式: 共有623条查询结果,搜索用时 15 毫秒
601.
Let G be a compact Lie group, and consider the loop group LeG:={?∈C([0,1],G); ?(0)=?(1)=e}. Let ν be the heat kernel measure at the time 1. For any density function F on LeG such that Entν(F)<∞, we shall prove that there exists a unique optimal transportation map which pushes ν forward to Fν. 相似文献
602.
The evolution of acoustic Lichtenberg figure (ALF) in ultrasound fields is studied using high-speed photography. It is observed that bubbles travel along the branch to the aggregation region of an ALF, promoting the possibility of large bubble or small cluster formation. Large bubbles move away from the aggregation region while surrounding bubbles are attracted into this structure, and a bubble transportation cycle arises in the cavitation field. A simplified model consisting of a spherical cluster and a chain of bubbles is developed to explain this phenomenon. The interaction of the two units is analyzed using a modified expression for the secondary Bjerknes force in this system. The model reveals that clusters can attract bubbles on the chain within a distance of 2 mm, leading to a bubble transportation process from the chain to the bubble cluster. Many factors can affect this process, including the acoustic pressure, frequency, bubble density, and separation distance. The larger the bubble in the cluster, the broader the attraction region. Therefore, the presence of large bubbles might enhance the process in this system. Local disturbances in bubble density could destroy the ALF structure. The predictions of the model are in good agreement with the experimental phenomena. 相似文献
603.
Data traffic forwarding and network optimization is essential to effective congestion management in software-defined vehicular networks, and it is necessary for software-defined vehicle networks (SDVN). SDVN is needed to optimize connection performance and network controls in dense and sparse networks to govern data flow between nodes as effectively as possible. Intelligent software-defined internet of vehicles (iSDIoVs) has recently emerged as a potential technology for future vehicular networks. It manages the vehicular ad hoc networks systematically. The link connection of moving vehicles from the central SDN controller may fail. It impacts the efficiency and communication performance because of the lack of connection between vehicles and infrastructure (V2I). The researchers have analyzed the network performance and mobility models in a dense and sparse network to maximize network performance by iSDIoVs. By integrating heterogeneous systems such as IEEE 802.11p and cellular networks into vehicular ad-hoc networks, it is possible to reduce buffer occupancy in iSDIoV and control the mobility and delay bound analysis in V2V communication. The SDN will provide flexibility and reliability to the vehicular networks. An SDN controller manages the data flow in the vehicular network and controls the flow matching rules in the control plane. The iSDIoV and queuing models improve the response time and resource utilization and enhance the network complexity analysis for traffic management services. 相似文献
604.
Container terminals pay more and more attention to the service quality of inland transport modes such as tucks, trains and barges. Truck appointment systems are a common approach to reduce truck turnaround times. This paper provides a tool to use the truck appointment system to increase not only the service quality of trucks, but also of trains, barges and vessels. We propose a mixed integer linear programming model to determine the number of appointments to offer with regard to the overall workload and the available handling capacity. The model is based on a network flow representation of the terminal and aims to minimize overall delays at the terminal. It simultaneously determines the number of truck appointments to offer and allocates straddle carriers to different transport modes. Numerical experiments, conducted on actual data, quantify the benefits of this combined solution approach. Discrete-event simulation validates the results obtained by the optimization model in a stochastic environment. 相似文献
605.
606.
Road freight transportation is a major contributor to carbon dioxide equivalent emissions. Reducing these emissions in transportation route planning requires an understanding of vehicle emission models and their inclusion into the existing optimization methods. This paper provides a review of recent research on green road freight transportation. 相似文献
607.
608.
近年来,我国的内河航运得到了长足发展,其运能大、占地少、能耗低、污染小的独特优势和带动经济社会发展的作用逐步凸显。然而,由于航道分布广泛、错综复杂且通行船舶大小各异,我国的内河航运很难实现对船舶的全面动态监管,不能提供优质的信息服务。随着计算机技术和电子技术的不断发展,GPS、AIS、RFID等技术在内河航运监管与服务系统也逐渐出现,此类技术的应用在一定程度上实现了船舶的动态监管或信息服务。针对现有技术因为岸基建设成本或终端成本高而无法实现推广的状况,将充分利用智能手机定位功能和RFID的身份识别功能,同时结合手机通信网络,提出一种基于智能手机和RFID的内河航运管理与服务系统。该系统借助于现有网络运营商的手机通信网络,只需要增加一个RFID标签和在智能手机上安装一个第三方软件便可实现对船舶的全面动态监管,并能提供丰富的信息服务。极大降低了内河航运监管与服务系统的建设成本,具有较强地实际推广意义。 相似文献
609.
610.
The aim of this study was to investigate the transport behavior and efflux of berberine through the primary culture cortical neurons. High-performance liquid chromatography coupled with an UV-vis detector at 347 nm was applied. The mobile phase was 0.05 m potassium dihydrogen phosphate solution (containing 0.5% triethylamine, pH 3.0)-acetonitrile (73:27, v/v). Neurons were incubated with Coptidis rhizoma extract 6.5 microg/mL (containing 1.91 microg/mL berberine) and verapamil, KCN or cimetidine for 2 h, and then lysed in methanol to extract intracellular berberine. A 20 microL aliquot of sample was injected into the HPLC system to determine berberine concentration. The results showed that metabolic inhibitor KCN and P-glycoprotein inhibitor verapamil could increase berberine concentration within the neurons, indicating that efflux of berberine was energy-dependent and P-glycoprotein was likely to be involved. Moreover, the organic cation transporter inhibitor cimetidine could decrease berberine concentration within the neurons, suggesting that the organic cation transporter might be involved in the berberine transport process. 相似文献