全文获取类型
收费全文 | 19234篇 |
免费 | 2620篇 |
国内免费 | 1866篇 |
专业分类
电工技术 | 2329篇 |
综合类 | 2037篇 |
化学工业 | 867篇 |
金属工艺 | 538篇 |
机械仪表 | 924篇 |
建筑科学 | 1624篇 |
矿业工程 | 582篇 |
能源动力 | 393篇 |
轻工业 | 482篇 |
水利工程 | 485篇 |
石油天然气 | 708篇 |
武器工业 | 210篇 |
无线电 | 2433篇 |
一般工业技术 | 1632篇 |
冶金工业 | 661篇 |
原子能技术 | 250篇 |
自动化技术 | 7565篇 |
出版年
2024年 | 95篇 |
2023年 | 266篇 |
2022年 | 498篇 |
2021年 | 530篇 |
2020年 | 618篇 |
2019年 | 570篇 |
2018年 | 536篇 |
2017年 | 771篇 |
2016年 | 853篇 |
2015年 | 973篇 |
2014年 | 1272篇 |
2013年 | 1434篇 |
2012年 | 1486篇 |
2011年 | 1709篇 |
2010年 | 1216篇 |
2009年 | 1310篇 |
2008年 | 1346篇 |
2007年 | 1429篇 |
2006年 | 1180篇 |
2005年 | 960篇 |
2004年 | 789篇 |
2003年 | 668篇 |
2002年 | 572篇 |
2001年 | 501篇 |
2000年 | 429篇 |
1999年 | 264篇 |
1998年 | 218篇 |
1997年 | 205篇 |
1996年 | 169篇 |
1995年 | 167篇 |
1994年 | 136篇 |
1993年 | 98篇 |
1992年 | 82篇 |
1991年 | 57篇 |
1990年 | 40篇 |
1989年 | 60篇 |
1988年 | 33篇 |
1987年 | 23篇 |
1986年 | 18篇 |
1985年 | 12篇 |
1984年 | 11篇 |
1983年 | 14篇 |
1982年 | 14篇 |
1981年 | 12篇 |
1980年 | 18篇 |
1979年 | 15篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1976年 | 7篇 |
1975年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Shi Wei Zhao Xuefeng Ma Conghui Management of the National Development Reform Commission 《中国通信》2008,(3)
After the new round of restructuring of Chinese telecom sector,it's pressing to formulate and implement asymmetric regulation policies so as to shape an effectively competitive market structure in a relatively short term.This paper reviewed the asymmetric regulation policies and practices carried out in foreign telecom market,and then according to the specific situations of Chinese telecom market,proposed the principles and corresponding policies for establishing an asymmetric regulation system fit for Chin... 相似文献
42.
In this paper, we consider identifying the minimum effective dose (MED) in a dose-response study when survival data are subject to random right-censorship, where the MED is defined to be the smallest dose level under study that has survival advantage over the zero-dose control. To this end, we suggest single-step-down testing procedures based on three different types of weighted logrank statistics, respectively. The comparative results of a Monte Carlo error rate and power/bias study for a variety of survival and censoring distributions are then presented and discussed. The application of the testing procedures for identifying the MED is finally illustrated by using a numerical example of prostate cancer data. 相似文献
43.
水库淤积初步平衡问题 总被引:2,自引:0,他引:2
水库淤积平衡问题对于确定淤积危害程度、可持续利用标准等都非常重要。本文通过分析大量已建、在建和规划水库淤积情况,对水库淤积初步平衡后淤积变化趋势与设计淤积标准等问题进行了讨论和商榷。研究表明,水库淤积初步平衡后,兴利库容淤积发展仍然很快,库尾河床与水位抬升仍在继续,并未最终稳定。水库淤积平衡应该更加注重兴利库容淤积情况和库尾河床与水位抬升趋势,仅仅关注总淤积量变化情况是不够的。从区域长远利益考虑,大江大河上的水库设计淤积年限还应大大加长。 相似文献
44.
单层开采的圆形定压边界两层油藏压力动态分析 总被引:1,自引:1,他引:0
为更好地分析具有越流的多层油藏的压力动态,采用有效井径的概念,在半透壁模型的基础上建立了圆形定压边界、两层越流油藏单层开采时的渗流数学模型。通过拉氏变换得到了拉氏空间中以Bessel函数表示的精确解。数值反演计算结果表明,单层开采的两层油藏与全部打开的两层油藏的压力动态基本相同,都表现为3个阶段:早期是介于两个渗透层之间的均质流动;中间为过渡段,导数曲线出现下凹特征;晚期表现为整个油藏的均质特征。随着边界距离的增加,压力导数值趋近于0.5。半透率越大过渡段出现得越早。导数曲线下凹程度越小;储容比越大导数曲线峰值越小,导数曲线下凹程度越小;随着两层渗透率比值变小。过渡段变短,导数曲线下凹程度变小。图1参9 相似文献
45.
Across 2 experiments, a new experimental procedure was used to investigate attentional capture by animal fear-relevant stimuli. In Experiment 1 (N = 34), unselected participants were slower to detect a neutral target animal in the presence of a spider than a cockroach distractor and in the presence of a snake than a large lizard distractor. This result confirms that phylogenetically fear-relevant animals capture attention specifically and to a larger extent than do non-fear-relevant animals. In Experiment 2 (N = 86), detection of a neutral target animal was slowed more in the presence of a feared fear-relevant distractor (e.g., a snake for snake-fearful participants) than in presence of a not-feared fear-relevant distractor (e.g., a spider for snake-fearful participants). These results indicate preferential attentional capture that is specific to phylogenetically fear-relevant stimuli and is selectively enhanced in individuals who fear these animals. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
46.
基于单片机控制的无线语音保密通信系统的研究 总被引:2,自引:0,他引:2
本文介绍一种基于单片机控制的无线语音保密通信系统,该系统采用一种新的混沌脉冲宽度调制方式,将数字信息隐藏在脉冲的宽度之中,实现语音信号的无线保密通信。对仿真结果、实验波形进行了分析,详细讨论了该通信系统的同步问题。 相似文献
47.
This study examined whether objects are attended in serial or in parallel during a demanding visual search task. A component of the event-related potential waveform, the N2pc wave, was used as a continuous measure of the allocation of attention to possible targets in the search arrays. Experiment 1 demonstrated that the relative allocation of attention shifts rapidly, favoring one item and then another. In Experiment 2, a paradigm was used that made it possible to track the absolute allocation of attention to individual items. This experiment showed that attention was allocated to one object for 100-150 ms before attention began to be allocated to the next object. These findings support models of attention that posit serial processing in demanding visual search tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
48.
This paper describes an effective analysis of magnetic shielding based on homogenization. The analyses become time‐consuming if the problems include the magnetic substances having fine structure. The homogenization of the structure makes it possible to analyze effectively the magnetic fields. The authors introduce a method to estimate the effective permeability of the homogenized substance. This method can be applied to any periodic structure made of magnetic substance. The magnetic shielding effects by the structures against direct‐current (DC) fields generated by electric railways are analyzed by using the present method. As a result, it is found that the overhead way and the protective fence near the railway work as a magnetic shield, whose effects can be improved by appropriate arrangement of those constructions. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(4): 7–15, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20310 相似文献
49.
The width of the transition layer between the crystalline and amorphous zones in nylon 1010 was determined by SAXS with point collimation and long-slit collimation, respectively. The width of the transition layer, E, was found to be 1.7 nm. The results show that the width of the transition layer is independent of crystallinity. 相似文献
50.
本文将等效介电常数近似分析方法在应用范围和处理方法上进行了一些改进.发展为双等效介电常数近似分析法,然后用它来分析矩形介质波导阵列.推得两个一维周期的耦合特征方程。如果将Macatili方法应用范围扩展用来研究该波导阵列也会得到同样的结果,它们都能在二维平面上较准确地反应出通带和阻带等主要周期特性。 相似文献