全文获取类型
收费全文 | 228883篇 |
免费 | 71239篇 |
国内免费 | 51167篇 |
专业分类
电工技术 | 31788篇 |
技术理论 | 1篇 |
综合类 | 26067篇 |
化学工业 | 28445篇 |
金属工艺 | 30147篇 |
机械仪表 | 9840篇 |
建筑科学 | 14800篇 |
矿业工程 | 14461篇 |
能源动力 | 9358篇 |
轻工业 | 23061篇 |
水利工程 | 8193篇 |
石油天然气 | 15807篇 |
武器工业 | 4030篇 |
无线电 | 34573篇 |
一般工业技术 | 33545篇 |
冶金工业 | 8460篇 |
原子能技术 | 2957篇 |
自动化技术 | 55756篇 |
出版年
2024年 | 2828篇 |
2023年 | 4736篇 |
2022年 | 5420篇 |
2021年 | 6296篇 |
2020年 | 9225篇 |
2019年 | 18583篇 |
2018年 | 20068篇 |
2017年 | 21432篇 |
2016年 | 21047篇 |
2015年 | 20093篇 |
2014年 | 19197篇 |
2013年 | 18442篇 |
2012年 | 17808篇 |
2011年 | 18057篇 |
2010年 | 14675篇 |
2009年 | 10617篇 |
2008年 | 8443篇 |
2007年 | 7429篇 |
2006年 | 6837篇 |
2005年 | 6599篇 |
2004年 | 11583篇 |
2003年 | 8636篇 |
2002年 | 8303篇 |
2001年 | 6944篇 |
2000年 | 6087篇 |
1999年 | 6544篇 |
1998年 | 5494篇 |
1997年 | 5059篇 |
1996年 | 4415篇 |
1995年 | 4349篇 |
1994年 | 3605篇 |
1993年 | 4582篇 |
1992年 | 4062篇 |
1991年 | 2971篇 |
1990年 | 2434篇 |
1989年 | 2126篇 |
1988年 | 1564篇 |
1987年 | 635篇 |
1986年 | 488篇 |
1985年 | 320篇 |
1984年 | 195篇 |
1983年 | 132篇 |
1982年 | 180篇 |
1981年 | 178篇 |
1980年 | 154篇 |
1976年 | 232篇 |
1975年 | 207篇 |
1972年 | 242篇 |
1971年 | 134篇 |
1960年 | 214篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
A comparison between different PMD compensation techniques 总被引:17,自引:0,他引:17
Sunnerud H. Chongjin Xie Karlsson M. Samuelsson R. Andrekson P.A. 《Lightwave Technology, Journal of》2002,20(3):368-378
We quantify the benefits of using different techniques for compensation of polarization mode dispersion (PMD) in fiber-optic communication systems by means of numerical simulations. This is done both with respect to PMD-induced pulse broadening and in terms of system outage probability for different data formats [nonreturn-to-zero (NRZ) and return-to-zero (RZ)]. Attention is focused on simple and relevant single- and double-stage post-transmission compensators with a few degrees of freedom (DOF). It is generally believed that a PMD compensator with a polarization controller and a variable delay line can only compensate the PMD to the first order. We show, from analytical results, the counterintuitive fact that this scheme can also partially compensate for higher order PMD. We also investigate the benefit of using a polarizer as compensation element where the optical average power can be used as a feedback signal 相似文献
72.
73.
74.
75.
76.
介绍了如何将改造后的全站仪应用于直升机悬停性能测试的方法。经真实飞行试验检验,该方法理论严密,方案合理,改装简单,操作方便,成本低廉。较之原始的摄影测量法有无法替代的优点。 相似文献
77.
78.
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
79.
A new and simple method of finite-element grid improvement is presented. The objective is to improve the accuracy of the analysis. The procedure is based on a minimization of the trace of the stiffness matrix. For a broad class of problems this minimization is seen to be equivalent to minimizing the potential energy. The method is illustrated with the classical tapered bar problem examined earlier by Prager and Masur. Identical results are obtained. 相似文献
80.
测定钠中杂质的手动阻塞计的研究 总被引:1,自引:1,他引:0
文章介绍了测定钠中杂质浓度的手动阻塞计的原理、装置和实验结果。为了减少测量误差,我们研究了影响准确测定阻塞温度的因素,并且找到了减少测量误差的办法。在同样的杂质饱和温度下,该阻塞计测得的高、低阻塞温度所对应的杂质浓度差是很接近的。对氧其差值为1.03ppm;对氢为0.0763ppm。 相似文献