全文获取类型
收费全文 | 112603篇 |
免费 | 7871篇 |
国内免费 | 3213篇 |
学科分类
工业技术 | 123687篇 |
出版年
2024年 | 175篇 |
2023年 | 1283篇 |
2022年 | 1719篇 |
2021年 | 3542篇 |
2020年 | 2568篇 |
2019年 | 2392篇 |
2018年 | 2806篇 |
2017年 | 2980篇 |
2016年 | 3328篇 |
2015年 | 3607篇 |
2014年 | 4845篇 |
2013年 | 6903篇 |
2012年 | 6869篇 |
2011年 | 7966篇 |
2010年 | 6676篇 |
2009年 | 6568篇 |
2008年 | 6380篇 |
2007年 | 5679篇 |
2006年 | 5463篇 |
2005年 | 4703篇 |
2004年 | 3880篇 |
2003年 | 3641篇 |
2002年 | 3884篇 |
2001年 | 3146篇 |
2000年 | 2695篇 |
1999年 | 2481篇 |
1998年 | 3216篇 |
1997年 | 2297篇 |
1996年 | 1982篇 |
1995年 | 1643篇 |
1994年 | 1305篇 |
1993年 | 1121篇 |
1992年 | 810篇 |
1991年 | 747篇 |
1990年 | 603篇 |
1989年 | 550篇 |
1988年 | 442篇 |
1987年 | 346篇 |
1986年 | 311篇 |
1985年 | 266篇 |
1984年 | 229篇 |
1983年 | 165篇 |
1982年 | 172篇 |
1981年 | 149篇 |
1980年 | 143篇 |
1979年 | 110篇 |
1978年 | 96篇 |
1977年 | 122篇 |
1976年 | 166篇 |
1975年 | 85篇 |
排序方式: 共有10000条查询结果,搜索用时 24 毫秒
991.
Duan-Shin Lee Benjamin Melamed Amy R. Reibman Bhaskar Sengupta 《Performance Evaluation》1992,16(1-3):21-34
The transport of video images is likely to be a major application of high-speed networks of the future. These applications are capable of utilizing the high bandwidths that will become available with the advent of B-ISDN. In this paper, we propose a new methodology (called TES) for modeling the frame bitrate stream generated by compressed video sources. The main characteristic of this method is that it can model an arbitrary marginal distribution and approximate the autocorrelation structure of the random bitrate process generated by compressed frames. We present a modeling example utilizing this method, based on data from a video coding algorithm employing a layering technique. Using the source model, we develop a simulation model of a multiplexer of video sources. We show that this model can be used to address a number of design issues that arise in this class of problem. In particular, we show that for a layered video coding algorithm, it is possible to have a gain in the number of sources multiplexed at the cost of some loss of low priority packets. 相似文献
992.
A new catalyst loading method, in which catalyst particles are packed in a reactor with a novel internal, has been studied by measuring pressure drop, RTD, liquid holdup and mass transfer. It can be inferred from experimental results that the internal changes the conventional gas and liquid counter-current flow into a new cross-current flow, so the problems of excessive pressure drop and “flooding” are avoided. When pressure drop, liquid holdup, RTD and mass transfer coefficient are similar, the catalyst loading fraction of the new method is much higher than that of conventional methods. Furthermore, the reactive distillation reactor with the novel internal has advantages such as simple structure, low operating cost, and convenience for installation and removal of the catalyst. 相似文献
993.
Jang-Sik Lee Seung-Ki Joo 《Electron Device Letters, IEEE》2002,23(9):517-519
The electrical properties of thin-film ferroelectric capacitors are known to degrade severely when exposed to hydrogen. In this study, we directly measured the effects of the grain boundary on the hydrogen-induced degradation in ferroelectric Pb(Zr, Ti)O3 (PZT) thin films by the location of the top Pt electrode either inside the grains or at the grain boundary. A strong relationship between the grain boundary and the electrical properties of ferroelectric capacitors as a result of hydrogen annealing was found. The degradation of the electrical properties in thin-film ferroelectric capacitors after hydrogen annealing is mainly due to the presence of the grain boundary in the ferroelectric thin film 相似文献
994.
本文提出了以通用阵列逻辑器件 GAL 和只读存贮器 EPROM 为核心器件的频率/待测量变换的设计方法。配以数字式传感器及用最小二乘法编制的曲线自动分段拟合程序生成的 EPROM 中的数据,可用于力、温度、光强等非电量的测量显示和控制。这种装置与采用微处理器的电路相比,有相同的测量精度,电路简单,而且保密性好. 相似文献
995.
Language-level support for object persistence frees programmers from having to confront a broad class of database issues from within their applications. By virtue of its metaobject protocol, CLOS is a language whose semantics can be tailored by individual programmers. We used the metaobject protocol to extend CLOS with support for object persistence. Our goal was to obtain a version of CLOS with persistence to which we could easily port a commercial geometric CAD modeling system. We describe the design and implementation of our persistence extension and highlight the strengths and weaknesses exhibited by the CLOS metaobject protocol during our experiment. For many aspects of the implementation we found that the metaobject protocol was ideal. In other cases we had to choose among paying a large performance penalty, extending the protocol, and bypassing the protocol by modifying the language implementation directly. 相似文献
996.
997.
Sil-Gu Mun Jung-Hyung Moon Ki-Man Choi Jin-Serk Baik Chang-Hee Lee 《Photonics Technology Letters, IEEE》2007,19(21):1729-1731
We propose and demonstrate a wavelength-division-multiplexed passive optical network by employing double-contact Fabry-Perot laser diodes (F-P LDs) without a seed light injection. To avoid the high mode partition noise at low frequency, we use a binary phase-shift keying as a modulation format at a low relative intensity noise window. An error-free transmission is achieved by compensating a lasing envelope shift due to temperature variation with the double-contact F-P LD. 相似文献
998.
This paper addresses the problem of bandwidth allocation under the weighted maximum rate constrained link sharing policy and proves a key theory in the condition of allocation termination. We propose several algorithms with various worst-case and average-case time complexities, and evaluate their computation elapse times. 相似文献
999.
Lee Humphreys 《Journal of Computer-Mediated Communication》2007,13(1):341-360
A mobile social network system (MSNS) allows groups of friends to be accessed and engaged with from one's mobile phone. Dodgeball is a MSNS that seeks to facilitate social connection and coordination among friends in urban public spaces. Based on a year-long qualitative field study, this article reports on the social and behavioral norms of Dodgeball use. A comparison between social network sites and Dodgeball highlights some of the communicative differences of mobile technology and the Internet. The findings of the study suggest that Dodgeball use can influence the way that informants experience public space and social relations therein. At times Dodgeball can facilitate the creation of third spaces, which are dynamic and itinerant forms of "third places." Additionally, exchanging messages through Dodgeball can lead to social molecularization, whereby active Dodgeball members experience and move through the city in a collective manner. 相似文献
1000.
Spherical bulb fibre optic probes, developed and applied for bubble characterization in a bubble column and a slurry bubble column at high temperature, were investigated. The principle of operation of these new optical fibre probes is based on the difference in refractive indices between the gas and the liquid phases. The interaction between the gas bubbles and the fibre optic probes in a bubble column was studied using photographic techniques. The first objective of these experiments was to study the response of the sensors upon contact with gas bubbles of various sizes. The second objective of this study was to establish, under controlled situations, the optical probe bubble detection performance and ability for local quantitative measurements of the bubble rise velocity and the gas hold-up. 相似文献