全文获取类型
收费全文 | 2486篇 |
免费 | 337篇 |
国内免费 | 13篇 |
专业分类
化学 | 10篇 |
力学 | 4篇 |
综合类 | 15篇 |
数学 | 624篇 |
物理学 | 156篇 |
无线电 | 2027篇 |
出版年
2024年 | 18篇 |
2023年 | 76篇 |
2022年 | 89篇 |
2021年 | 79篇 |
2020年 | 98篇 |
2019年 | 94篇 |
2018年 | 75篇 |
2017年 | 120篇 |
2016年 | 114篇 |
2015年 | 128篇 |
2014年 | 235篇 |
2013年 | 177篇 |
2012年 | 192篇 |
2011年 | 166篇 |
2010年 | 159篇 |
2009年 | 144篇 |
2008年 | 133篇 |
2007年 | 139篇 |
2006年 | 112篇 |
2005年 | 78篇 |
2004年 | 50篇 |
2003年 | 69篇 |
2002年 | 60篇 |
2001年 | 47篇 |
2000年 | 33篇 |
1999年 | 15篇 |
1998年 | 24篇 |
1997年 | 22篇 |
1996年 | 16篇 |
1995年 | 11篇 |
1994年 | 8篇 |
1993年 | 10篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有2836条查询结果,搜索用时 9 毫秒
91.
Energy harvesting (EH) has been considered as a promising technology to solve the constrained energy problem in the devices of IoT with its advantages of flexible deployment and sustainable energy supply.For multiple access channel with energy harvesting,a hybrid energy storage structure model composed by super capacitor and battery was proposed for the devices of IoT.According to the peculiarities of medium access channel and energy harvesting system,an optimized energy allocation strategy with exponential-type decline (ETD) was presented,the upper and lower bounds of the average throughput were deduced,in particular,the gap of two bounds was derived to be a constant.The channel capacity was further obtained by utilizing the relationship between the average throughput and the channel capacity.In the simulations,the effect of harvested energy,storage capacity and the number of nodes on the channel capacity were analyzed respectively.Experiment results show that compared with the conventional wireless node with single battery storage,the proposed hybrid energy storage structure can improve the harvested energy value and increase the multiple access channel capacity by using adaptive modulation scheme when transmitting the signals. 相似文献
92.
针对全电缆系统与HFC系统两种网络结构对有线电视系统指标的叠加与分配进行了探讨,论述了它们的不同点,提出在HFC系统中应使用HFC的指标计算公式。 相似文献
93.
Kanthen?K?HarikrishnanEmail author Hiroaki?Ishii 《Fuzzy Optimization and Decision Making》2005,4(2):141-147
We consider a batch scheduling problem on a single machine which processes jobs with resource dependent setup and processing time in the presence of fuzzy due-dates given as follows:1. There are n independent non-preemptive and simultaneously available jobs processed on a single machine in batches. Each job j has a processing time and a due-date.2. All jobs in a batch are completed together upon the completion of the last job in the batch. The batch processing time is equal to the sum of the processing times of its jobs. A common machine setup time is required before the processing of each batch.3. Both the job processing times and the setup time can be compressed through allocation of a continuously divisible resource. Each job uses the same amount of the resource. Each setup also uses the same amount of the resource.4. The due-date of each job is flexible. That is, a membership function describing non-decreasing satisfaction degree about completion time of each job is defined.5. Under above setting, we find an optimal batch sequence and resource values such that the total weighted resource consumption is minimized subject to meeting the job due-dates, and minimal satisfaction degree about each due-date of each job is maximized. But usually we cannot optimize two objectives at a time. So we seek non-dominated pairs i.e. the batch sequence and resource value, after defining dominance between solutions.A polynomial algorithm is constructed based on linear programming formulations of the corresponding problems. 相似文献
94.
We prove the following theorem. Let m and n be any positive integers with mn, and let
be a subset of the n-dimensional Euclidean space
n
. For each i=1, . . . , m, there is a class
of subsets M
i
j
of
Tn
. Assume that
for each i=1, . . . , m, that M
i
j
is nonempty and closed for all i, j, and that there exists a real number B(i, j) such that
and its jth component
xjB(i, j)
imply
. Then, there exists a partition
of {1, . . . , n} such that
for all i and
We prove this theorem based upon a generalization of a well-known theorem of Birkhoff and von Neumann. Moreover, we apply this theorem to the fair allocation problem of indivisible objects with money and obtain an existence theorem. 相似文献
95.
Simulation optimization of buffer allocations in production lines with unreliable machines 总被引:3,自引:0,他引:3
Gül Gürkan 《Annals of Operations Research》2000,93(1-4):177-216
We use a recent simulationbased optimization method, sample path optimization, to find optimal buffer allocations in tandem production lines where machines are subject to random breakdowns and repairs, and the product is fluidtype. We explore some of the functional properties of throughput of such systems and exploit these properties to prove the almost sure convergence of our optimization technique, under a regularity condition on the steady state. Utilizing a generalized semiMarkov process (GSMP) representation of the system, we derive recursive expressions to compute onesided directional derivatives of throughput, from a single simulation run. Finally, we give computational results for lines with up to 50 machines. We also compare results for smaller lines with the results from a more conventional method, stochastic approximation, whenever applicable. In these numerical studies, our method performed quite well on problems that are considered difficult by current computational standards. 相似文献
96.
Muhammad Qadeer Sharif Pingzhi Fan 《中国电子科技》2007,5(2):97-101
This paper presents an efficient dynamic spectrum allocation (DSA) scheme in a flexible spectrum licensing environment where multiple networks coexist and interfere with each other. In particular, an extension of virtual boundary concept in DSA is proposed, which is spectrally efficient than the previous virtual boundary concept applied to donor systems only. Here, the same technique is applied to both donor and rental systems so as to further reduce the occurrences where the insertion of guard bands is obligatory and as a result provides better spectral efficiency. The proposed extension improves the spectrum utilization without any compromise on interference and fairness issues. 相似文献
97.
对地面固定辐射源的机载双站无源定位配置 总被引:1,自引:0,他引:1
以机载双站对辐射源进行联合定位为背景,建立了相应的数学模型并分析了定位精度。研究了双站间距和有效定位面积之间的关系,将定位精度和有效定位面积这两项重要指标综合一起从而确定出双站最佳配置模型,最后给出仿真结果。 相似文献
98.
In this paper, we present MPARC (Multi-Priority Admission and Rate Control), a novel joint admission control and rate policing protocol for multi-priority ad hoc networks. MPARC is based on our novel bandwidth allocation model, which captures the bandwidth allocation for saturated, unsaturated and semi-saturated networks. MPARC guarantees that the throughput of admitted realtime flows will not decrease due to later arriving realtime flows with equal or lower priorities or due to best effort flows. MPARC achieves this goal by performing accurate admission control on every newly arriving realtime flow and appropriate rate policing on all best effort traffic. Through simulation, we demonstrate that MPARC has better performance than existing approaches. 相似文献
99.
Dinh Thuy Phan Huy Jonathan Rodriguez Atílio Gameiro Rahim Tafazolli 《Wireless Personal Communications》2007,43(4):1727-1740
The Multicarrier CDMA Transmission Techniques for Integrated Broadband Cellular Systems (MATRICE) project addresses a candidate
solution for a Beyond 3G (B3G) air-interface based on Multi-Carrier Code Division Multiple Access (MC-CDMA). It investigates
dynamic resource allocation strategies at the Medium Access Control (MAC) layer to support the transport of Internet Protocol
(IP) packets over the air-interface in a cost effective manner and maximise the cell capacity with a target QoS. A candidate
Dynamic Resource Allocation (DRA) protocol architecture is proposed that is based on cross-layer signalling to provide reactive
resource allocation according to the fast channel and traffic variations. In-line with B3G expectations, the proposed DRA
handles a very large number of users with inherent flexibility and granularity necessary to support heterogeneous traffic,
and still with limited complexity. Thanks to the modular architecture of the DRA, various scheduling policies are investigated
and compared in terms of capacity and reactivity to the system environment. Simulation results have shown that the MATRICE
system has the potential to deliver broadband heterogenous services in a cost-effective manner, and emerge as a propespective
candidate air-interface for B3G cellular networks. 相似文献
100.
This paper investigates subset antenna transmission (SAT) for multiple-input multiple-output (MIMO) systems in the presence
of strong dominant co-channel interferer. The capacity gain from SAT is investigated in the context of optimal antenna subset
selection and power allocation. The SAT does not require channel state information of the co-channel interference, and achieves
capacity gains by distributing the transmit power equally over a selected subset of the transmit antennas. The capacity gain
of the SAT method is analyzed in terms of transmit power and eigenvalues of channel matrix, and its performance in V-BLAST
MIMO systems with various signal constellations is evaluated by computer simulation. 相似文献