全文获取类型
收费全文 | 7227篇 |
免费 | 960篇 |
国内免费 | 584篇 |
专业分类
电工技术 | 1153篇 |
综合类 | 612篇 |
化学工业 | 377篇 |
金属工艺 | 84篇 |
机械仪表 | 566篇 |
建筑科学 | 359篇 |
矿业工程 | 276篇 |
能源动力 | 94篇 |
轻工业 | 333篇 |
水利工程 | 136篇 |
石油天然气 | 173篇 |
武器工业 | 85篇 |
无线电 | 1337篇 |
一般工业技术 | 669篇 |
冶金工业 | 250篇 |
原子能技术 | 139篇 |
自动化技术 | 2128篇 |
出版年
2024年 | 34篇 |
2023年 | 113篇 |
2022年 | 173篇 |
2021年 | 227篇 |
2020年 | 246篇 |
2019年 | 210篇 |
2018年 | 177篇 |
2017年 | 263篇 |
2016年 | 348篇 |
2015年 | 322篇 |
2014年 | 469篇 |
2013年 | 554篇 |
2012年 | 561篇 |
2011年 | 548篇 |
2010年 | 423篇 |
2009年 | 422篇 |
2008年 | 429篇 |
2007年 | 505篇 |
2006年 | 447篇 |
2005年 | 391篇 |
2004年 | 307篇 |
2003年 | 260篇 |
2002年 | 222篇 |
2001年 | 189篇 |
2000年 | 160篇 |
1999年 | 130篇 |
1998年 | 97篇 |
1997年 | 88篇 |
1996年 | 68篇 |
1995年 | 66篇 |
1994年 | 46篇 |
1993年 | 51篇 |
1992年 | 39篇 |
1991年 | 28篇 |
1990年 | 30篇 |
1989年 | 21篇 |
1988年 | 16篇 |
1987年 | 9篇 |
1986年 | 17篇 |
1985年 | 12篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 8篇 |
1979年 | 3篇 |
1976年 | 3篇 |
1959年 | 5篇 |
1958年 | 2篇 |
1955年 | 2篇 |
排序方式: 共有8771条查询结果,搜索用时 31 毫秒
71.
在线社交网络的UNI64采样方法 总被引:1,自引:0,他引:1
在对社交网络采样方法进行研究时,常以拒绝-接受采样法得到的样本作为对照来评价其他采样方法的优劣.由于各种在线社交网络陆续将其用户ID系统由32位升级为64位,导致拒绝-接受采样法的采样命中率近乎为零.本文根据在线社交网络的特点,以新浪微博为例,对其用户ID分布情况进行分析,提出了一种改进的拒绝-接受采样法UNI64.该方法通过分析网络有效ID样本的分布情况,结合聚类的方法将整个样本空间划分为有效区间和无效区间,并使采样算法避开无效区间,仅在有效区间内生成待测样本,从而有效提高了拒绝-接受采样法在有效样本极为稀疏的样本空间内采样的命中率. 相似文献
72.
一般情况下,以密度函数作为权重的带权测地距离并不满足严格的三角不等式,给诸多几何问题的解决带来了一定的困难.为此,提出一种基于密度函数重构非退化度量的鲁棒算法.该算法将给定密度函数与网格曲面的缺省密度场相结合重设网格曲面的边长,并保证每个三角形的新边长仍然满足三角不等式;然后使用精确的测地线算法计算任意两点之间的带权测地距离.实验结果表明,文中算法以平均曲率作为密度函数重构度量,在自适应采样与重新网格化问题上得到了高质量的结果,展示了该算法的有用性和有效性. 相似文献
73.
In engineering, it is computationally prohibitive to directly employ costly models in optimization. Therefore, surrogate-based optimization is developed to replace the accurate models with cheap surrogates during optimization for efficiency. The two key issues of surrogate-based optimization are how to improve the surrogate accuracy by making the most of the available training samples, and how to sequentially augment the training set with certain infill strategy so as to gradually improve the surrogate accuracy and guarantee the convergence to the real global optimum of the accurate model. To address these two issues, a radial basis function neural network (RBFNN) based optimization method is proposed in this paper. First, a linear interpolation (LI) based RBFNN modelling method, LI-RBFNN, is developed, which can enhance the RBFNN accuracy by enforcing the gradient match between the surrogate and the trend observed from the training samples. Second, a hybrid infill strategy is proposed, which uses the surrogate prediction error based surrogate lower bound as the optimization objective to locate the promising region and meanwhile employs a linear interpolation-based sequential sampling approach to improve the surrogate accuracy globally. Finally, extensive tests are investigated and the effectiveness and efficiency of the proposed methods are demonstrated. 相似文献
74.
介绍了我国尿素合成在线分析的现状及在取样技术上遇到的困难,针对这一难点,研究设计了旋液分离器及成套系统,经实际应用,效果较好。 相似文献
75.
76.
Arnon Shani 《Journal of chemical ecology》1990,16(3):971-980
A cotton wool plug, used as the source for pheromone release, was placed in closed 1-quart Mason jars, either at the mouth or at the rear of the jar. Air sampling of the two components of the sex pheromone (total 2.2 mg at the source) of the almond moth (Ephestia cautella) female showed that the saturation period near the source in still air was 20–22 hr and that far from the source was 40–50 hr, reaching a level of less than 1 ng/ml air. The ratio between the components (Z,E)-9,12-tetradecadienyl acetate, designated D, and (Z)-9-tetradecenyl acetate designated M, in the air was close to the original ratio for both sampling sites, albeit somewhat richer in the more volatile (Z)-9-tetradecenyl acetate (source 77.023.0 DM, air 73.0– 74.327.0–25.7; source 80.119.9, air 77.622.4; source 25.174.9, air 23.976. 1 DM). The total amount of pheromone per milliliter of air was two to three times larger near the source than far from it at the early stages of the evaporation and saturation process. When the amount of pheromone applied to the source was tripled (7 mg), the amount far from the source was almost tripled, or the saturation time was cut by factor of two to three. 相似文献
77.
78.
基于TMS320F2812内部自带ADC模块的优缺点分析,探讨扩展ADS8365的高精度采样系统设计,以求提高整个系统的测量和控制精度,实现数字化变频调速系统中对多路电压、电流、转速等信号的高精度采样.讨论了影响TMS320F2812芯片A/D转换器精度的原因,给出了ADS8365芯片进行电流信号采样的电路设计,并通过仿真和实际电路实验说明了电路设计的有效性.相比于TMS320F2812的单端采样,基于ADS8365的采样电路具有采样精度高、速度快、同步性好、失真小、抗干扰强,同时能够较好的抑制温漂和热噪声等明显优势.将该采样电路应用于本交流调速系统中,不仅可以大大提高系统的采样精度,增加系统的抗干扰性,也便于系统工况的实时分析,进行合理控制及实时保护. 相似文献
79.
80.
Synthetic aperture interferometric technique has wide applications in optics, radio astronomy and microwave remote sensing
areas. With the increasing demands of high resolution imaging observation, a new time-sharing sampling scheme of asynchronous
rotation scan is proposed to meet the technical challenge of achieving a large equivalent aperture and overcome the operating
barriers of space borne application. This configuration is basically composed by two asynchronously and concentrically rotating
antenna groups, whose revolving radii and speeds are different. The synthetic aperture system with asynchronous rotation scanning
scheme can effectively solve the trade-off problem of system complexity, and greatly simplify the system hardware at the cost
of sacrificing a certain time resolution. The basic rules and design methods of asynchronous rotation scan are investigated
The Gridding method is introduced to inverse the spiral sampling data for image reconstruction. The potential applications
of geostationary orbit (GEO) earth observation and solar polar orbit (SPO) plasma cloud observation are explored with numerical
simulations to validate the significance and feasibility of this new imaging configuration.
Supported by the National Natural Science Foundation of China (Grant No. 40574070, 40671121, 40701100 and 40801136) and the
National High-Tech Research Program of China (“863” Program) (Grant No. 2006AA12Z141) 相似文献