全文获取类型
收费全文 | 1453491篇 |
免费 | 25598篇 |
国内免费 | 6959篇 |
专业分类
电工技术 | 34061篇 |
综合类 | 6335篇 |
化学工业 | 268180篇 |
金属工艺 | 63495篇 |
机械仪表 | 40596篇 |
建筑科学 | 44943篇 |
矿业工程 | 11311篇 |
能源动力 | 50108篇 |
轻工业 | 105569篇 |
水利工程 | 14489篇 |
石油天然气 | 37380篇 |
武器工业 | 128篇 |
无线电 | 194466篇 |
一般工业技术 | 274492篇 |
冶金工业 | 140317篇 |
原子能技术 | 33843篇 |
自动化技术 | 166335篇 |
出版年
2021年 | 15447篇 |
2020年 | 11736篇 |
2019年 | 14492篇 |
2018年 | 14505篇 |
2017年 | 13729篇 |
2016年 | 20622篇 |
2015年 | 17150篇 |
2014年 | 28506篇 |
2013年 | 87463篇 |
2012年 | 33799篇 |
2011年 | 45274篇 |
2010年 | 41130篇 |
2009年 | 49940篇 |
2008年 | 42651篇 |
2007年 | 39587篇 |
2006年 | 43334篇 |
2005年 | 37856篇 |
2004年 | 40296篇 |
2003年 | 40237篇 |
2002年 | 39541篇 |
2001年 | 35990篇 |
2000年 | 34714篇 |
1999年 | 33361篇 |
1998年 | 37549篇 |
1997年 | 34753篇 |
1996年 | 32466篇 |
1995年 | 29033篇 |
1994年 | 27433篇 |
1993年 | 27316篇 |
1992年 | 25658篇 |
1991年 | 22693篇 |
1990年 | 23098篇 |
1989年 | 22164篇 |
1988年 | 20644篇 |
1987年 | 19030篇 |
1986年 | 18292篇 |
1985年 | 21664篇 |
1984年 | 22052篇 |
1983年 | 20025篇 |
1982年 | 19066篇 |
1981年 | 19177篇 |
1980年 | 17781篇 |
1979年 | 18363篇 |
1978年 | 17609篇 |
1977年 | 17098篇 |
1976年 | 17510篇 |
1975年 | 15903篇 |
1974年 | 15426篇 |
1973年 | 15517篇 |
1972年 | 12994篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
911.
This paper presents a brief overview of recent approaches to two problems in music information retrieval: query by example and automated source separation. It describes the challenges inherent in musical query by example and the systems that take very different approaches to the problem. The paper also explores approaches to source separation in a musical context, focusing on systems that take distinct approaches to the problem. Finally, it comments about the future directions for digital signal processing (DSP) research in the context of music information retrieval. 相似文献
912.
913.
914.
In this paper, we propose a routing algorithm called minimum fusion Steiner tree (MFST) for energy efficient data gathering with aggregation (fusion) in wireless sensor networks. Different from existing schemes, MFST not only optimizes over the data transmission cost, but also incorporates the cost for data fusion, which can be significant for emerging sensor networks with vectorial data and/or security requirements. By employing a randomized algorithm that allows fusion points to be chosen according to the nodes' data amounts, MFST achieves an approximation ratio of 5/4log(k + 1), where k denotes the number of source nodes, to the optimal solution for extremely general system setups, provided that fusion cost and data aggregation are nondecreasing against the total input data. Consequently, in contrast to algorithms that only excel in full or nonaggregation scenarios without considering fusion cost, MFST can thrive in a wide range of applications 相似文献
915.
Pallem C. Chowdhuri P. Demko J.A. Gouge M.J. 《Applied Superconductivity, IEEE Transactions on》2006,16(1):31-37
The objective of this work was to determine the significant parameters of a 3-GW 200-kV dc superconducting cable system which influence the transient voltage distribution in the various parts of the cable. The cable system consists of four coaxial metallic cylinders. It was found that the dielectric constant and the electrical resistivity of the soil significantly affect the severity of the transient voltages; lower dielectric constant and higher resistivity of the soil will increase the magnitudes of the transient voltages by increasing the earth-return impedance. It was also found that the effect of the conductor internal impedances of the cable is insignificant. Shorting the coaxial cylinders of the cryogen flow and the cryostat will lessen the severity of the transient voltages. Grounding the second, third, and fourth cylinders at regular intervals with low-impedance grounding impedance will also improve the transient performance of the cable. More research is needed to evaluate these procedures. 相似文献
916.
Ouzounov S. Hegt H. van Roermund A. 《Circuits and Systems II: Express Briefs, IEEE Transactions on》2006,53(5):399-403
A new type of sigma-delta modulator that operates in a special mode named limit-cycle mode (LCM) is proposed. In this mode, most of the SDM building blocks operate at a frequency that is an integer fraction of the applied sampling frequency. That brings several very attractive advantages: a reduction of the required power consumption per converted bandwidth, an immunity to excessive loop delays and to digital-analog converter waveform asymmetry and a higher tolerance to clock imperfections. The LCMs are studied via a graphical application of the describing function theory. A second-order continuous time SDM with 5 MHz conversion bandwidth, 1 GHz sampling frequency and 125 MHz limit-cycle frequency is used as a test case for the evaluation of the performance of the proposed type of modulators. High level and transistor simulations are presented and compared with the traditional SDM designs. 相似文献
917.
M. J. O’Sullivan C. G. Walker M. L. O’Sullivan T. D. Thompson A. B. Philpott 《Telecommunication Systems》2006,33(4):353-376
The problem of designing fibre-optic networks for local-access telecommunications generates (at least) three non-trivial subproblems.
In the first of these subproblems one must determine how many fibre-optic cables (fibres) are required at either end of a
street. In the next subproblem a minimum-cost network must be designed to support the fibres. The network must also provide
distinct paths from either end of the street to the central exchange(s). Finally, the fibre-optic cables must be placed in
protective covers. These covers are available in a number of different sizes, allowing some flexibility when covering each
section of the network. In this paper we describe a dynamic programming (DP) formulation for finding a minimum-cost (protective)
covering for the network (the third of the subproblems). This problem is a generalised set covering problem with side constraints
and is further complicated by the introduction of fixed and variable welding costs. The DP formulation selects covers along
each arc (in the network), but cannot exactly model the fixed costs and so does not guarantee optimality. We also describe
an integer programming (IP) formulation for assessing the quality of the DP solutions. The cost of the networks constructed
by the IP model is less than those designed using the DP model, but the saving is not significant for the problems examined
(less than 0.1%). This indicates that the DP model will generally give very good solutions. Furthermore, as the problem dimensions
grow, DP gives significantly better solution times than IP. 相似文献
918.
919.
This paper presents an overview of our recent work on the use of soft lithography and two-phase fluid flow to form arrays of droplets. The crucial issues in the formation of stable arrays of droplets and alternating droplets of two sets of aqueous solutions include the geometry of the microchannels, the capillary number, and the water fraction of the system. Glass capillaries could be coupled to the PDMS microchannels and droplets could be transferred into glass capillaries for long-term storage. The arrays of droplets have been applied to screen the conditions for protein crystallization with microbatch and vapor diffusion techniques. 相似文献
920.
Nonlinear dynamics of crack propagation are investigated experimentally and theoretically with the goal of clarifying the nature of limiting crack velocity, the transition from steady state to branching regimes of crack dynamics, and the dynamics of crack arrest. The theoretical explanation of limiting steady-state crack velocity and the transition to a branching regime was proposed due to the study of collective behavior of a microcrack ensemble at the crack tip area. The experimental study of crack dynamics was carried out in a preloaded plate PMMA specimen using the high-speed camera coupled with the photo-elasticity method, the point stress recording with a laser system, and the failure surface roughness measurement. 相似文献