全文获取类型
收费全文 | 567225篇 |
免费 | 6251篇 |
国内免费 | 1005篇 |
专业分类
电工技术 | 10514篇 |
综合类 | 466篇 |
化学工业 | 90154篇 |
金属工艺 | 23367篇 |
机械仪表 | 18520篇 |
建筑科学 | 12538篇 |
矿业工程 | 4312篇 |
能源动力 | 14463篇 |
轻工业 | 45799篇 |
水利工程 | 6947篇 |
石油天然气 | 14963篇 |
武器工业 | 39篇 |
无线电 | 60306篇 |
一般工业技术 | 116310篇 |
冶金工业 | 95600篇 |
原子能技术 | 14685篇 |
自动化技术 | 45498篇 |
出版年
2021年 | 5494篇 |
2019年 | 5279篇 |
2018年 | 9222篇 |
2017年 | 9430篇 |
2016年 | 9859篇 |
2015年 | 6041篇 |
2014年 | 10265篇 |
2013年 | 26139篇 |
2012年 | 15796篇 |
2011年 | 21112篇 |
2010年 | 16995篇 |
2009年 | 18840篇 |
2008年 | 19082篇 |
2007年 | 18778篇 |
2006年 | 16308篇 |
2005年 | 14756篇 |
2004年 | 14011篇 |
2003年 | 13698篇 |
2002年 | 13261篇 |
2001年 | 12857篇 |
2000年 | 12334篇 |
1999年 | 12017篇 |
1998年 | 27663篇 |
1997年 | 20046篇 |
1996年 | 15644篇 |
1995年 | 12007篇 |
1994年 | 10861篇 |
1993年 | 10616篇 |
1992年 | 8337篇 |
1991年 | 8105篇 |
1990年 | 7996篇 |
1989年 | 7764篇 |
1988年 | 7478篇 |
1987年 | 6750篇 |
1986年 | 6535篇 |
1985年 | 7390篇 |
1984年 | 6704篇 |
1983年 | 6437篇 |
1982年 | 5776篇 |
1981年 | 5899篇 |
1980年 | 5631篇 |
1979年 | 5737篇 |
1978年 | 5667篇 |
1977年 | 6180篇 |
1976年 | 7689篇 |
1975年 | 5110篇 |
1974年 | 4903篇 |
1973年 | 4980篇 |
1972年 | 4279篇 |
1971年 | 4038篇 |
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
201.
Tan J.C. Crossley P.A. McLaren P.G. Hall I. Farrell J. Gale P. 《Power Delivery, IEEE Transactions on》2002,17(1):68-74
This paper describes a sequential tripping strategy used in a wide area back-up protection expert system (BPES) to combat situations in which protection relays have maloperated or information is missing. The BPES is an innovative back-up protection scheme designed to prevent the occurrence of widespread blackouts. The BPES evaluates the certainty that transmission lines are likely to be affected by the fault and uses a sequential tripping strategy to isolate the fault if a firm decision is not available due to maloperated relays and/or missing information. The mode of analysis and the sequential tripping strategy ensures that the BPES will clear a fault at minimum risk to the network. An example is included to demonstrate how the certainty factor based sequential tripping strategy is employed by the BPES to clear a fault which occurred on the South Western part of the UK National Grid System 相似文献
202.
203.
204.
205.
206.
207.
Ahn Jaeshin Stromsmoe Keith A. Lawson Ronald P. W. 《Industrial Electronics, IEEE Transactions on》1985,(4):405-409
A microprocessor-based system with 32 A/D, 24 D/A, and 16 ac load controllers, has been designed and built to monitor and control an ion beam thin-film deposition system. The A/D and D/A channels have electrical isolation of 7.5 kV between channels and between input and output. The microprocessor system keeps the ion beam deposition parameters stable for extended periods of operation and it is proposed as a means to greatly simplify switching from one deposition species to another to grow thin multilayer or alloy films. 相似文献
208.
In ray tracing the two most commonly used data structures are the octree and uniform cell division. The octree structure allows efficient adaptive subdivision of space, while taking care of the spatial coherence of the objects in it; however, the tree structure locating the next node in the path of a ray is complex and time consuming. The cell structure, on the other hand, can be stored in a three-dimensional array, and each cell can be efficiently accessed by specifying three indices. However, such a uniform cell division does not take care of object coherence. The proposed data structure combines the positive features of the above data structures while minimising their disadvantages. The entire object space is implicitly assumed to be a three-dimensional grid of cells. Initially, the entire object space is a single voxel which later undergoes “adaptive cell division.” But, unlike in the octree structure, where each voxel is divided exactly at the middle of each dimension, in adaptive cell division, each voxel is divided at the nearest cell boundary. The result is that each voxel contains an integral number of cells along each axis. Corresponding to the implicit cell division we maintain a three-dimensional array, with each array element containing the voxel number which is used to index into the voxel array. The voxel array is used to store information about the structure of each voxel, in particular, the objects in each voxel. While a ray moves from one voxel to another we always keep track of the cell through which the ray is currently passing. Since only arrays are involved in accessing the next voxel in the path of the ray, the operation is very efficient. 相似文献
209.
Poly(vinyl alcohol) is crosslinked in dilute solution (c=0.1 wt%) with glutaraldehyde. The reaction product is characterized by viscometry and gel permeation chromatography (g.p.c.). The intrinsic viscosity decreases with increasing degree of crosslinking and does not depend on temperature. G.p.c. reveals that the reaction product is not homogeneous, but consists of a mixture of particles with different sizes, possibly both intra- and intermolecularly crosslinked molecules. The intramolecularly crosslinked molecules are smaller in size than the initial polymer molecules and their size depends on the degree of crosslinking. They possess a narrow particle size distribution even if the initial polymer sample had a broad molecular weight distribution. 相似文献
210.
A.O. Lebeck 《Tribology International》1985,18(3):188-189