全文获取类型
收费全文 | 19727篇 |
免费 | 1597篇 |
国内免费 | 52篇 |
专业分类
电工技术 | 245篇 |
综合类 | 22篇 |
化学工业 | 4574篇 |
金属工艺 | 628篇 |
机械仪表 | 898篇 |
建筑科学 | 494篇 |
矿业工程 | 14篇 |
能源动力 | 735篇 |
轻工业 | 1798篇 |
水利工程 | 69篇 |
石油天然气 | 25篇 |
无线电 | 3186篇 |
一般工业技术 | 4085篇 |
冶金工业 | 2216篇 |
原子能技术 | 242篇 |
自动化技术 | 2145篇 |
出版年
2023年 | 177篇 |
2022年 | 306篇 |
2021年 | 482篇 |
2020年 | 378篇 |
2019年 | 459篇 |
2018年 | 565篇 |
2017年 | 547篇 |
2016年 | 703篇 |
2015年 | 606篇 |
2014年 | 839篇 |
2013年 | 1357篇 |
2012年 | 1099篇 |
2011年 | 1408篇 |
2010年 | 1046篇 |
2009年 | 1033篇 |
2008年 | 1015篇 |
2007年 | 795篇 |
2006年 | 689篇 |
2005年 | 617篇 |
2004年 | 586篇 |
2003年 | 550篇 |
2002年 | 483篇 |
2001年 | 409篇 |
2000年 | 379篇 |
1999年 | 410篇 |
1998年 | 785篇 |
1997年 | 570篇 |
1996年 | 391篇 |
1995年 | 294篇 |
1994年 | 281篇 |
1993年 | 249篇 |
1992年 | 171篇 |
1991年 | 151篇 |
1990年 | 148篇 |
1989年 | 146篇 |
1988年 | 98篇 |
1987年 | 98篇 |
1986年 | 103篇 |
1985年 | 106篇 |
1984年 | 94篇 |
1983年 | 70篇 |
1982年 | 52篇 |
1981年 | 62篇 |
1980年 | 61篇 |
1979年 | 49篇 |
1978年 | 45篇 |
1977年 | 69篇 |
1976年 | 103篇 |
1975年 | 50篇 |
1973年 | 35篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Coating of 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 (PMN–PT) relaxor ferroelectrics by a sol–gel method is followed by growth of epitaxial SrRuO3 (SRO) metallic oxide electrodes on SrTiO3 (STO) single-crystal substrate by pulsed laser deposition. High-quality PMN–PT films on SRO with preferred growth orientation were successfully fabricated by controlling the operation parameters. Structural properties of relaxor ferroelectric PMN–PT thin films on SRO/STO substrates have been studied by X-ray diffraction (XRD), transmission electron microscopy (TEM) and atomic force microscopy (AFM). In-plane and out-of-plane alignments of the heterostructure are confirmed and the structural twinning of the materials are also revealed. 相似文献
103.
Ho C. Y.-F. Ling B. W.-K. Reiss J. D. 《IEEE transactions on circuits and systems. I, Regular papers》2006,53(12):2729-2738
In this paper, an initial condition of strictly causal rational interpolative sigma-delta modulators (SDMs) is estimated based on quantizer output bit streams and an input signal. A set of initial conditions generating bounded trajectories is characterized. It is found that a set of initial conditions generating bounded trajectories but not necessarily corresponding to quantizer output bit streams is convex. Also, it is found that a set of initial conditions corresponding to quantizer output bit streams but not necessarily generating bounded trajectories is convex too. Moreover, it is found that an initial condition both corresponding to quantizer output bit streams and generating bounded trajectories is uniquely defined if the loop filter is unstable (Here, an unstable loop filter refers to that with at least one of its poles being strictly outside the unit circle). To estimate that unique initial condition, a projection onto convex set approach is employed. Numerical computer simulations show that the employed method can estimate the initial condition effectively 相似文献
104.
105.
Ching‐Nan Chuang Liang Chao Ying‐Jie Huang Tar‐Hwa Hsieh Hung‐Yi Chuang Shu‐Chi Lin Ko‐Shan Ho 《应用聚合物科学杂志》2008,107(6):3917-3924
The synthesis of a p‐toluidine/formaldehyde (PTF) resin was performed, and the effects of the molar ratio of the individual monomers and the polymerization conditions on the structure of the PTF resin were studied. Fourier transform infrared and 13C‐NMR spectra were used to characterize the PTF. Wide‐angle X‐ray diffraction patterns revealed the crystalline structures of various PTFs. Polarized optical microscopy revealed that the molar ratio of the monomers had a strong effect on the crystalline morphologies. A longer polymerization time turned out a polymer with a higher intrinsic viscosity and molecular weight, which led to differences in the proton conductivity. All of the PTFs showed a higher proton conductivity than a commercial Nafion membrane at 90–100°C and 0% relative humidity. The proton conductivity of the PTF series could be improved by sulfonation with sulfuric acid and could be maintained after blending with polyurethane. Pure methanol could be used as a fuel source because of the insolubility and nonwetting properties of PTF in methanol to increase the output current density for a PTF membrane electrode assembly. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008 相似文献
106.
Support for arbitrary topologies has become more popular for system-area networks but very little has been done in trying to characterize their behavior and performance. Traditional parameters like diameter and bisection width are not sufficient for characterizing the irregularities that abound in such networks and fail to give much insight into throughput performance. A clustering approach for partitioning a network into clusters of richly-connected regions is proposed as a means of defining two performance-correlated characterization metrics: intercluster bandwidth index and intercluster link-cost index. The two characterization metrics are shown to have a strong correlation to saturation throughput when link and load distribution of a network is imbalanced. Simulation results also show that the clustering algorithm can be applied to a variety of network configurations and traffic scenarios, particularly irregular ones. With the proposed characterization metrics that correlate more strongly with performance, it is possible to classify networks into categories having similar performance. 相似文献
107.
Sum J. Hong Shen Chi-sing Leung Young G. 《Parallel and Distributed Systems, IEEE Transactions on》2003,14(3):193-202
Ant routing is a method for network routing in agent technology. Although its effectiveness and efficiency have been demonstrated and reported in the literature, its properties have not yet been well studied. This paper presents some preliminary analysis on an ant algorithm in regard to its population growing property and jumping behavior. Results conclude that as long as the value max, {i/spl Omega//sub j/|} is known, the practitioner is able to design the algorithm parameters, such as the number of agents being created for each request, k, and the maximum allowable number of jumps of an agent, in order to meet the network constraint. 相似文献
108.
In this article, the problem of providing a fair bandwidth allocation to the flows sharing a congested link in a router is investigated. Queue management, bandwidth share and congestion control are very important to both the robustness and fairness of the Internet. The buffer at the outgoing link is a simple FIFO, shared by packets belonging to the flows. A new transmission control protocol (TCP)-friendly router-based active queue management scheme, termed WARD, is proposed to approximate the fair queueing policy. WARD is a simple packet-dropping algorithm with a random mechanism which discriminates against flows that submit more packets per second than is allowed as their fair share. By doing this, it not only protects TCP connections from user datagram protocol flows, but also solves the problem of competing bandwidth among different TCP versions, such as TCP Vegas and TCP Reno. In addition, WARD works quite well for TCP flow isolation even with different round trip times. In other words, WARD improves the unfair bandwidth allocation properties. Furthermore, as it is stateless and easy to implement, WARD controls unresponsive or misbehaving flows with only a minimum overhead. 相似文献
109.
110.
Woo Yong Sung Seung Min Lee Wal Jun Kim Jong Girl Ok Ho Young Lee Yong Hyup Kim 《Diamond and Related Materials》2008,17(6):1003-1007
Complementary electroplating combined with electrophoresis enhanced the field emission characteristics of emitters by improving the adhesions between CNT emitters and substrate. The emitting current of the CNT emitters prepared by our combined method increased nine times higher than that of CNT emitters prepared by electrophoresis only, since electroplating improved the adhesion of CNT emitters. During the life-time measurement for 10 h, the emitting current of CNT emitters fabricated by electrophoresis only was drastically decreased to 13% of the initial current, while that prepared by the combination of electrophoresis and successive electroplating decreased to 64% of the initial current. We suggest that our method is a promising approach for the efficient fabrication of reliable CNT emitters. 相似文献