全文获取类型
收费全文 | 544317篇 |
免费 | 6512篇 |
国内免费 | 2042篇 |
专业分类
电工技术 | 9393篇 |
综合类 | 2847篇 |
化学工业 | 82864篇 |
金属工艺 | 23876篇 |
机械仪表 | 16761篇 |
建筑科学 | 13764篇 |
矿业工程 | 2399篇 |
能源动力 | 12157篇 |
轻工业 | 49057篇 |
水利工程 | 5359篇 |
石油天然气 | 6654篇 |
武器工业 | 36篇 |
无线电 | 61889篇 |
一般工业技术 | 100896篇 |
冶金工业 | 93993篇 |
原子能技术 | 9423篇 |
自动化技术 | 61503篇 |
出版年
2021年 | 3797篇 |
2019年 | 3478篇 |
2018年 | 19599篇 |
2017年 | 18387篇 |
2016年 | 15721篇 |
2015年 | 4726篇 |
2014年 | 7200篇 |
2013年 | 20705篇 |
2012年 | 14344篇 |
2011年 | 24639篇 |
2010年 | 20298篇 |
2009年 | 19149篇 |
2008年 | 21033篇 |
2007年 | 22103篇 |
2006年 | 13494篇 |
2005年 | 13133篇 |
2004年 | 12595篇 |
2003年 | 12441篇 |
2002年 | 11873篇 |
2001年 | 11324篇 |
2000年 | 10751篇 |
1999年 | 11173篇 |
1998年 | 27705篇 |
1997年 | 19446篇 |
1996年 | 15100篇 |
1995年 | 11418篇 |
1994年 | 10128篇 |
1993年 | 9846篇 |
1992年 | 7310篇 |
1991年 | 7021篇 |
1990年 | 6837篇 |
1989年 | 6624篇 |
1988年 | 6421篇 |
1987年 | 5525篇 |
1986年 | 5491篇 |
1985年 | 6453篇 |
1984年 | 5953篇 |
1983年 | 5355篇 |
1982年 | 5011篇 |
1981年 | 5099篇 |
1980年 | 4893篇 |
1979年 | 4642篇 |
1978年 | 4673篇 |
1977年 | 5484篇 |
1976年 | 7633篇 |
1975年 | 4064篇 |
1974年 | 3821篇 |
1973年 | 3950篇 |
1972年 | 3270篇 |
1971年 | 3009篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Two novel configurations for digitally tunable optical filters based on arrayed-waveguide grating (AWG) multiplexers are described in detail with emphasis on the connection of the AWG multiplexer and optical switches. Performance comparisons show that conventional configurations are disadvantaged by the switch size required and loss imbalance among the optical frequency-division-multiplexed (FDM) channels; the proposed configurations require only O(√(N)) switch elements to select one of N FDM channels, and the loss imbalance is lower by up to 75% in decibel 相似文献
72.
Sugawara F. Aoki K. Yamaguchi H. Sasaki K. Sasaki T. Fujisaki H. 《Electron Device Letters, IEEE》1997,18(10):483-485
A new lateral MOS-gated thyristor, called the Base-Current-Controlled Thyristor, is described. This device is designed so that most holes at the on-stage reach the P base through the floating P+ region adjacent to the P base and the on-state MOSFET. At the turn-off stage, the interruption of the hole current to the P base due to switching off the above MOSFET occurs simultaneously with the conventional turn-off operation. The concept of this device is verified experimentally by using the fabricated lateral device with the external MOSFET. This device exhibits a better trade-off relation between the on-state voltage and the turn-off time compared uith the conventional MOS-gated thyristor 相似文献
73.
Watanabe H. Komori J. Higashitani K. Sekine M. Koyama H. 《Semiconductor Manufacturing, IEEE Transactions on》1997,10(2):228-232
A novel monitoring method for plasma-charging damage is proposed. This method performs a quick and accurate evaluation using antenna PMOSFET. It was found that not only hot-carrier (HC) lifetime but transistor parameters such as initial gate current and substrate current were changed according to the degree of plasma-charging damage. However, the present work suggests that monitoring the shift of drain current after a few seconds of HC stress is a more accurate method to indicate plasma-charging damage. The monitoring method using the present test structure is demonstrated to be useful for realizing highly reliable devices 相似文献
74.
The purpose of this paper is to evaluate two methods of assessing the productivity and quality impact of Computer Aided Software Engineering (CASE) and Fourth Generation Language (4GL) technologies: (1) by the retrospective method; and (2) the cross-sectional method. Both methods involve the use of questionnaire surveys. Developers' perceptions depend on the context in which they are expressed and this includes expectations about the effectiveness of a given software product. Consequently, it is generally not reliable to base inferences about the relative merits of CASE and 4GLs on a cross-sectional comparison of two separate samples of users. The retrospective method that requires each respondent to directly compare different products is shown to be more reliable. However, there may be scope to employ cross-sectional comparisons of the findings from different samples where both sets of respondents use the same reference point for their judgements, and where numerical rather than verbal rating scales are used to measure perceptions. 相似文献
75.
A new commercially available diode model is described. This unified model is capable of simulating the widest range of diode technologies of any presently available. The emphasis of this paper is on describing the model's extensive features and flexibility in the different domains of operation and is of particular interest in power applications 相似文献
76.
The capacitive idling converters derived from the Cuk, SEPIC, Zeta, and flyback topologies allow soft commutation of power switches without the need for additional circuitry, making it possible to increase the switching frequency while maintaining high efficiency 相似文献
77.
78.
We present the design of E-kernel, an embedding kernel on the Victor V256 message-passing partitionable multiprocessor, developed for the support of program mapping and network reconfiguration. E-kernel supports the embedding of a new network topology onto Victor's 2D mesh and also the embedding of a task graph onto the 2D mesh network or the reconfigured network. In the current implementation, the reconfigured network can be a line or an even-size ring, and the task graphs meshes or tori of a variety of dimensions and shapes or graphs with similar topologies. For application programs having these task graph topologies and that are designed according to the communication model of E-kernel, they can be run without any change on partitions connected by the 2D mesh, line, or ring. Further, E-kernel attempts the communication optimization of these programs on the different networks automatically, thus making both the network topology and the communication optimization attempt completely transparent to the application programs. Many of the embeddings used in E-kernel are optimal or asymptotically optimal (with respect to minimum dilation cost). The implementation of E-kernel translated some of the many theoretical results in graph embeddings into practical tools for program mapping and network reconfiguration in a parallel system. E-kernel is functional on Victor V256. Measurements of E-kernel's performance on V256 are also included 相似文献
79.
This research was supported under project No. 6.02.02/128-93 as part of the state scientific-technical program on future information
technologies and systems by the Ukrainian State Committee, of Science and Technology. 相似文献
80.