全文获取类型
收费全文 | 8688篇 |
免费 | 883篇 |
国内免费 | 366篇 |
学科分类
工业技术 | 9937篇 |
出版年
2024年 | 23篇 |
2023年 | 115篇 |
2022年 | 241篇 |
2021年 | 340篇 |
2020年 | 271篇 |
2019年 | 272篇 |
2018年 | 258篇 |
2017年 | 283篇 |
2016年 | 307篇 |
2015年 | 325篇 |
2014年 | 508篇 |
2013年 | 559篇 |
2012年 | 594篇 |
2011年 | 689篇 |
2010年 | 612篇 |
2009年 | 520篇 |
2008年 | 519篇 |
2007年 | 471篇 |
2006年 | 399篇 |
2005年 | 415篇 |
2004年 | 278篇 |
2003年 | 281篇 |
2002年 | 298篇 |
2001年 | 280篇 |
2000年 | 197篇 |
1999年 | 167篇 |
1998年 | 131篇 |
1997年 | 108篇 |
1996年 | 69篇 |
1995年 | 84篇 |
1994年 | 64篇 |
1993年 | 52篇 |
1992年 | 43篇 |
1991年 | 24篇 |
1990年 | 25篇 |
1989年 | 23篇 |
1988年 | 12篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1984年 | 10篇 |
1983年 | 9篇 |
1982年 | 7篇 |
1981年 | 12篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1975年 | 3篇 |
1973年 | 3篇 |
1970年 | 2篇 |
排序方式: 共有9937条查询结果,搜索用时 15 毫秒
61.
62.
标准化的目的是“获得最佳秩序和社会效益”,而最佳秩序是企业进行高效率生产和管理的前提条件。能够更及时准确的对企业的生产标准、技术标准、安全标准、管理标准进行监督和管理工作;有助于更好的督促企业在每个环节都建立起互相适应、配套的标准体系,使企业生产活动和经营管理活动井然有序,避免混乱;能够进一步加强对认证及认证咨询工作的质量,提高认证企业质量体系运行的有效性。为此我们提出了建设《哈尔滨市企业产品执行标准数据库管理系统》,对企业的产品执行标准进行登记注册管理,这将有助于组织、监督标准实施工作;有助于组织制订地方标准;推行采用国际标准和国外先进标准;有助于协调指导企业产品标准的制订并管理其备案;组织重要标准的宣传贯彻,监督检查重要标准的实施情况。 相似文献
63.
Jaewoo Choi Nagarajan Balaji Vinh Ai Dao Cheolmin Park Seunghwan Lee Jungmo Kim Minkyu Ju Hoongjoo Lee Youn-Jung Lee Junsin Yi 《Journal of Electronic Materials》2014,43(9):3191-3195
The effect of hydrogen capping of SiN(Si-rich)/SiN(N-rich) stacks for n-type c-Si solar cells was investigated. Use of a passivation layer consisting of Si-rich SiN with a refractive index (n) of 2.7 and N-rich SiN with a refractive index of 2.1 improved the thermal stability. A single SiN passivation layer with a refractive index of 2.05 resulted in an initial lifetime of 200 μs whereas the layer with a refractive index of 2.7 resulted in a high initial lifetime of 2 ms, but the layer degraded rapidly after firing. A stacked passivation layer with refractive indices of 2.1 and 2.7 had a stable lifetime of 1.5 ms with an implied open-circuit voltage (iV oc) of 720 mV after firing. The thermally stable passivation mechanism with changing amounts of Si–N and Si–H bonding was analyzed by Fourier-transform infrared (FTIR) spectroscopy. Incorporation of the SiN x stack layer (2.7 + 2.1) into the passivated rear of n-type Cz silicon screen-printed solar cells resulted in energy conversion efficiency of 19.69%. Improved internal quantum efficiency in the long-wavelength range above 900 nm, with V oc of 630 mV, is mainly because of superior passivation of the rear surface compared with conventional solar cells. 相似文献
64.
Song H.-W. Han W.S. Kim J.-H. Kwon O.-K. Ju Y.-G. Lee J.-H. KoPark S.-H. Kang S.-G. 《Electronics letters》2004,40(14):868-869
A a 1.55 /spl mu/m InAlGaAs/InP vertical-cavity surface-emitting laser grown by metal-organic chemical vapour deposition is presented. Al/sub 2/O/sub 3//a-Si thin-film pairs and InAlGaAs/InAlAs epitaxial layers are used as a top mirror and a bottom-side output coupler, respectively. Direct modulation characteristics through singlemode fibre are reported at a speed of 2.5 Gbit/s. 相似文献
65.
Ju Han Lee Kwanil Lee Young-Geun Han Sang Bae Lee Chul Han Kim 《Lightwave Technology, Journal of》2007,25(10):2891-2897
We propose and experimentally demonstrate a novel bidirectional wavelength-division-multiplexed passive optical network architecture that fully utilizes the superior optical properties of an incoherent continuous-wave (CW) supercontinuum (SC) source. The proposed architecture, which incorporates low-cost Fabry-Perot laser diodes that have been wavelength locked by spectrum-sliced beams from a depolarized 130-nm-bandwidth CW SC source, is based on a unique wavelength band allocation scheme of the C-band for an optical line terminal (OLT), the L-band for optical network units (ONUs), and the U-band for channel monitoring. A cost-effective network that features a single broadband source at the OLT, and no additional wavelength- band-selective monitoring beam reflector at each ONU can be readily achieved. The experimental demonstration presented in this paper is carried out at a data rate of 622 Mb/s over a 25-km standard single-mode fiber. 相似文献
66.
For real‐time interactive multimedia operations, such as video uploading, video play, fast‐forward, and fast‐rewind, solid state disk (SSD)‐based storage systems for video streaming servers are becoming more important. Random access rates in storage systems increase significantly with the number of users; it is thus difficult to simultaneously serve many users with HDD‐based storage systems, which have low random access performance. Because there is no mechanical operation in NAND flash‐based SSDs, they outperform HDDs in terms of flexible random access operation. In addition, due to the multichannel architecture of SSDs, they perform similarly to HDDs in terms of sequential access. In this paper, we propose a new SSD‐based storage system for interactive media servers. Based on the proposed method, it is possible to maximize the channel utilization of the SSD's multichannel architecture. Accordingly, we can improve the performance of SSD‐based storage systems for interactive media operations. 相似文献
67.
Mobile ad hoc networks (MANETs) are spontaneously deployed over a geographically limited area without well-established infrastructure. The networks work well only if the mobile nodes are trusty and behave cooperatively. Due to the openness in network topology and absence of a centralized administration in management, MANETs are very vulnerable to various attacks from malicious nodes. In order to reduce the hazards from such nodes and enhance the security of network, this paper presents a dynamic trust prediction model to evaluate the trustworthiness of nodes, which is based on the nodes’ historical behaviors, as well as the future behaviors via extended fuzzy logic rules prediction. We have also integrated the proposed trust predication model into the Source Routing Mechanism. Our novel on-demand trust-based unicast routing protocol for MANETs, termed as Trust-based Source Routing protocol (TSR), provides a flexible and feasible approach to choose the shortest route that meets the security requirement of data packets transmission. Extensive experiments have been conducted to evaluate the efficiency and effectiveness of the proposed mechanism in malicious node identification and attack resistance. The results show that TSR improves packet delivery ratio and reduces average end-to-end latency. 相似文献
68.
Jyh-Jier Ho Fang Y.K. Lee W.J. Chen F.Y. Hsieh W.T. Ting S.F. Ju M.S. Huang S.B. Kun-Hsien Wu Chen C.Y. 《Electron Devices, IEEE Transactions on》1999,46(12):2289-2294
Both theoretical and experimental studies of the substrate effect on the thermal behavior of a PbTiO3 infrared (IR) sensor have been reported. With active cantilever dimensions of 200×100×5 μm3 formed by etching processes, the pyroelectric micro-electro-mechanical system (pyro/MEMS) structure exhibits a much superior performance to that of a traditional IR-sensing bulk structure under the 800-μW incident optical light with wavelength of 970 nm. Two-order improvement in current responsivity is obtained for the pyro/MEMS structure. This shows the substrate effect on the performance of a pyro/MEMS IR sensor is very significant. A simple model has also been proposed to illustrate the substrate effect more comprehensively 相似文献
69.
70.
The distributions of electric field and induced second‐order nonlinearity are analyzed in the periodic poling of optical fibers. A quasi‐phase matching efficiency for the induced nonlinearity is calculated in terms of both the electrode separation distance between the applied voltage and generalized electrode width for the periodic poling. Our analysis of the quasi‐phase matching efficiency implies that the conversion efficiency can be enhanced through adjusting the separation distance, and the electrode width can be maximized if the electrode width is optimized. 相似文献