全文获取类型
收费全文 | 50952篇 |
免费 | 7137篇 |
国内免费 | 5512篇 |
专业分类
电工技术 | 4686篇 |
技术理论 | 3篇 |
综合类 | 5789篇 |
化学工业 | 2559篇 |
金属工艺 | 1454篇 |
机械仪表 | 3169篇 |
建筑科学 | 1512篇 |
矿业工程 | 1025篇 |
能源动力 | 1349篇 |
轻工业 | 872篇 |
水利工程 | 876篇 |
石油天然气 | 900篇 |
武器工业 | 538篇 |
无线电 | 8630篇 |
一般工业技术 | 3111篇 |
冶金工业 | 1033篇 |
原子能技术 | 171篇 |
自动化技术 | 25924篇 |
出版年
2024年 | 340篇 |
2023年 | 1315篇 |
2022年 | 2170篇 |
2021年 | 2568篇 |
2020年 | 2556篇 |
2019年 | 1897篇 |
2018年 | 1488篇 |
2017年 | 1661篇 |
2016年 | 1728篇 |
2015年 | 1923篇 |
2014年 | 2680篇 |
2013年 | 2992篇 |
2012年 | 3241篇 |
2011年 | 3630篇 |
2010年 | 2845篇 |
2009年 | 3273篇 |
2008年 | 3586篇 |
2007年 | 3794篇 |
2006年 | 3196篇 |
2005年 | 2867篇 |
2004年 | 2396篇 |
2003年 | 1986篇 |
2002年 | 1694篇 |
2001年 | 1491篇 |
2000年 | 1301篇 |
1999年 | 1095篇 |
1998年 | 888篇 |
1997年 | 733篇 |
1996年 | 601篇 |
1995年 | 452篇 |
1994年 | 329篇 |
1993年 | 243篇 |
1992年 | 169篇 |
1991年 | 92篇 |
1990年 | 67篇 |
1989年 | 42篇 |
1988年 | 30篇 |
1987年 | 21篇 |
1986年 | 31篇 |
1985年 | 43篇 |
1984年 | 37篇 |
1983年 | 35篇 |
1982年 | 40篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1976年 | 2篇 |
1963年 | 3篇 |
1960年 | 2篇 |
1959年 | 4篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Resilient optical networks are predominately designed to protect against single failures of fiber links. But in larger networks, operators also see dual failures. As the capacity was planned for single failures, disconnections can occur by dual failures even if enough topological connectivity is provided. In our approach the design of the network minimizes the average loss caused by dual failures, while single failures are still fully survived. High dual failure restorability is the primary aim, capacity is optimized in a second step. For WDM networks with full wavelength conversion, we formulate mixed integer linear programming models for dedicated path protection, shared (backup) path protection, and path rerouting with and without stub-release. For larger problem instances in path rerouting, we propose two heuristics. Computational results indicate that the connectivity is of much more importance for high restorability values than the overall protection capacity. Shared protection has similar restorability levels as dedicated protection while the capacity is comparable to rerouting. Rerouting surpasses the protection mechanisms in restorability and comes close to 100% dual failure survivability. Compared to single failure planning, both shared path protection and rerouting need significantly more capacity in dual failure planning. 相似文献
82.
83.
采用矿物油、聚α-烯烃、多元醇酯和高压加氢BS光亮油调配半合成发动机油基础油,并测定不同配比下基础油的油膜强度、摩擦系数和粘度指数,通过双隐层BP神经网络对基础油调配进行仿真研究,建立了半合成发动机油基础油调配配方优化模型,经过优化训练后,最终得出综合性能优良的配方组合。按49.9957∶4.3693∶42.4578∶3.1772的配比调配基础油,可以使基础油的油膜强度、摩擦系数和粘度指数分别达到56 kg,0.065和112,经实验后仿真结果与实验结果(56 kg;0.065598;112)极其吻合。 相似文献
84.
In this letter, a new sharing mechanism, SRLG sharing, is proposed, which allows the links of the same shared risk link group (SRLG) in a primary light tree to share protections in WDM optical networks. In previous studies, how to share spare resources with SRLG constraints has not been studied in multicast optical networks. In this letter, considering SRLG sharing, we propose a novel algorithm –multicast with SRLG sharing (MSS)– to establish a protection light tree. Finally, the algorithm MSS and the algorithm multicast with no SRLG sharing (MNSS) are compared through a simulation to show that our new sharing scheme of SRLG sharing is more efficient than that of no SRLG sharing in terms of spare resource utilization and blocking probability. 相似文献
85.
Optical packet assembly is a key function to support inter-working between TCP/IP networks and optical packet-switched networks.
It is characterized by the assembly delay and by the segment aggregation needed to form an optical packet. These counter-balancing
aspects depend on several environment variables, such as the TCP parameters, the access link speed, the optical packet size
whose effects are studied in this paper. Performance evaluations are obtained by extensive simulations in terms of send rate
of TCP flows, fairness, efficiency, and assembly delay. Some guidelines in the design of optical packets that take into account
the results presented are given. 相似文献
86.
The motional transition and heterogeneity of semi‐interpenetrating networks (SIPNs) based on polyurethane (PU) with carboxylic groups and methacrylic copolymer (PM) with tertiary amine groups were studied by the electron spin resonance (ESR) spin probe method. The concentration of functional groups in both prepolymers varied from 0 to 0.45 mmol g?1. Spin‐probed SIPNs show that the temperature‐dependent spectra are sensitive to polymer interactions imposed by functional groups. These interactions determine the free volume distribution in the matrix and temperature at which motional transition takes place. The fraction of free volume increases with functional group concentration and reaches its maximum at 0.25 mmol g?1. Further increases in the functional group concentration reduce the free volume. The results of the networks with strong interactions are discussed in terms of the interference of the plasticizing effect of the PU component and the formation of possible cluster cross‐links, which restricts segmental motions. Copyright © 2003 Society of Chemical Industry 相似文献
87.
Abstract. This paper describes artificial neural network based pure significance tests for the unit root hypothesis against nonlinear alternatives. The theoretical properties of the tests are discussed and a Monte Carlo investigation of their small sample properties is undertaken. 相似文献
88.
89.
一种实现最佳用户检测的非线性优化神经网络 总被引:2,自引:0,他引:2
本文提出并讨论了实现码分多址(CDMA)系统上最佳多用户检测(MUD)的一种神经网络方法。该方法通过将最佳多用户检测视为非线性优化组合问题,利用神经网络能有效求解非线性优化问题的优势,导出了一种非线性优化神经网络来实现最佳多用户检测,理论分析和计算机模拟表明,所提出的神经网络具有可实时应用的动态性能和较传统方法优越得多的误码率性能和抗多址干扰的性能。 相似文献
90.
Boole函数的线性可分性是前向人工神经网络理论中的一个比较困难的问题之一。目前仅对变量数n≤7的某些问题给予讨论。当n≥8时,尚无判别Boole函数线性可分的一般准则,更无线性可分Boole函数的计数公式。基于此,本文详细地研究了与Boole函数线性可分性有关的n-维超立方体的基本理论,包括n-维超立方体的基本性质、超立方体中的平行线、子超立方体的计数等,并给出了构造n-维超立方体图的一种新方法。 相似文献