全文获取类型
收费全文 | 43100篇 |
免费 | 7284篇 |
国内免费 | 4622篇 |
专业分类
电工技术 | 1563篇 |
综合类 | 3791篇 |
化学工业 | 7311篇 |
金属工艺 | 924篇 |
机械仪表 | 2323篇 |
建筑科学 | 1189篇 |
矿业工程 | 1488篇 |
能源动力 | 448篇 |
轻工业 | 10470篇 |
水利工程 | 346篇 |
石油天然气 | 1697篇 |
武器工业 | 275篇 |
无线电 | 3880篇 |
一般工业技术 | 1923篇 |
冶金工业 | 1640篇 |
原子能技术 | 511篇 |
自动化技术 | 15227篇 |
出版年
2024年 | 322篇 |
2023年 | 948篇 |
2022年 | 1858篇 |
2021年 | 2006篇 |
2020年 | 2063篇 |
2019年 | 1707篇 |
2018年 | 1512篇 |
2017年 | 1687篇 |
2016年 | 1870篇 |
2015年 | 2121篇 |
2014年 | 2798篇 |
2013年 | 3094篇 |
2012年 | 4311篇 |
2011年 | 3881篇 |
2010年 | 2823篇 |
2009年 | 2660篇 |
2008年 | 2551篇 |
2007年 | 3033篇 |
2006年 | 2587篇 |
2005年 | 2074篇 |
2004年 | 1614篇 |
2003年 | 1411篇 |
2002年 | 1098篇 |
2001年 | 894篇 |
2000年 | 805篇 |
1999年 | 640篇 |
1998年 | 507篇 |
1997年 | 428篇 |
1996年 | 345篇 |
1995年 | 268篇 |
1994年 | 200篇 |
1993年 | 150篇 |
1992年 | 158篇 |
1991年 | 102篇 |
1990年 | 100篇 |
1989年 | 70篇 |
1988年 | 42篇 |
1987年 | 43篇 |
1986年 | 40篇 |
1985年 | 38篇 |
1984年 | 31篇 |
1983年 | 29篇 |
1982年 | 15篇 |
1981年 | 13篇 |
1980年 | 14篇 |
1979年 | 9篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1959年 | 6篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
91.
简短评述了大容量和超大容量光通信系统的WDM和OTDM技术,提出了一个在OTDM通信系统中用锁模光纤激光器做时钟提取器的新方法,给出了一个利用设置波分预标时钟脉冲方案构成的新的全光型OTDM通信实验系统结构。 相似文献
92.
93.
本文提出了一种对汉字作任意倍率放缩的算法。该算法先对印刷体汉字作细线化处理,抽取笔划特征点。然后,分割和提取笔划。任意倍率汉字生成是通过变换函数。改变特征点位置,再附加原探察到的笔划修饰来实现的。实验表明本算法是有效的。 相似文献
95.
Extraction of Anthocyanin Pigments from Purple Sunflower Hulls 总被引:2,自引:0,他引:2
The anthocyanin pigments in hulls of purple sunflower seeds were extracted using three solvent systems, 50:1:49 ethanol-acetic acid-water (EAW), 0.01M acetic acid (AAc), or water containing SO2. Solvent, extraction time, size of ground hulls, pH of extracting solvent, hulls/solvent ratio, and concentration of SO2 in water, were investigated. All were significant factors affecting yield of extracted anthocyanins. EAW and SO2 were more effective extractants than AAc. Optimum conditions from response surface optimization for the extraction with sulphurous water were: SO2 at 200 mg/L, hull size 20 mesh, extraction time 5 min at 22°C, and solvent/hulls ratio = 20. 相似文献
96.
A novel successive learning algorithm based on a Test Feature Classifier is proposed for efficient handling of sequentially provided training data. The fundamental characteristics of the successive learning are considered. In the learning, after recognition of a set of unknown data by a classifier, they are fed into the classifier in order to obtain a modified performance. An efficient algorithm is proposed for the incremental definition of prime tests which are irreducible combinations of features and capable of classifying training patterns into correct classes. Four strategies for addition of training patterns are investigated with respect to their precision and performance using real pattern data. A real-world problem of classification of defects on wafer images has been dealt with by the proposed classifier, obtaining excellent performance even through efficient addition strategies. 相似文献
97.
Dynamic web sites commonly return information in the form of lists and tables. Although hand crafting an extraction program for a specific template is time-consuming but straightforward, it is desirable to automatically generate template extraction programs from examples of lists and tables in html documents. Supervised approaches have been shown to achieve high accuracy, but they require manual labelling of training examples, which is also time consuming. Fully unsupervised approaches, which extract rows and columns by detecting regularities in the data, cannot provide sufficient accuracy for practical domains. We describe a novel technique, Post-supervised Learning, which exploits unsupervised learning to avoid the need for training examples, while minimally involving the user to achieve high accuracy. We have developed unsupervised algorithms to extract the number of rows and adopted a dynamic programming algorithm for extracting columns. Our method achieves high performance with minimal user input compared to fully supervised techniques. 相似文献
98.
薄层反射波非零炮检距的属性特征 总被引:1,自引:0,他引:1
本文从薄层顶、底界面反射波的走时入手,研究了薄层反射波在非零炮检距集上出现的干涉现象,导出了薄层反射波在出现干涉时的炮检距计算公式,说明薄层干涉出现的炮检距是多变量函数,即随着埋藏深度h、地层速度v、薄层厚度Δh以及地震波的主频f*的变化而改变。本文重点分析了地层厚度Δh和地震子波主频f*对反射波振幅特性和频率特性的影响。在充分分析薄层反射的振幅、频谱随炮检距变化关系的基础上,指出在应用叠前信息(如AVO分析)进行储层预测等方面的研究时,应充分考虑薄层反射波的干涉和调谐现象带来的振幅和频率特征的变化。 相似文献
99.
Estimation of Width and Depth of the Wetted Soil Volume Under a Surface Emitter,Considering Root Water-Uptake and Evaporation 总被引:1,自引:0,他引:1
A cylindrical flow model that describes local infiltration from a surface point source, by incorporating evaporation and water
extraction by roots, was used to obtain numerical results that were the base for the development and testing of an empirical
method for determining the surface and vertical components of the wetting front. The implementation of the mathematical model
took place against two of the twelve USDA soil classes, using three water application rates for each one. The empirical methodology
consisted of two simple, time dependent empirical relationships: a power law for the stage of the infiltration, which was
applied in both directions and a polynomial for the stage after the end of the irrigation, applied only for the vertical component,
to account for percolation losses. The statistical criteria used for the evaluation of the method showed good agreement between
the numerical results and the values calculated by the empirical relationships. Based on the limited availability of necessary
experimental data for detailed analysis of multidimensional transient infiltration, the introduction of such an empirical
model, as a design tool for trickle irrigation systems, may contribute to the selection of the optimum application rate and
lateral spacing. 相似文献
100.