全文获取类型
收费全文 | 12263篇 |
免费 | 1869篇 |
国内免费 | 647篇 |
专业分类
电工技术 | 2503篇 |
综合类 | 919篇 |
化学工业 | 1516篇 |
金属工艺 | 235篇 |
机械仪表 | 815篇 |
建筑科学 | 345篇 |
矿业工程 | 261篇 |
能源动力 | 284篇 |
轻工业 | 799篇 |
水利工程 | 96篇 |
石油天然气 | 505篇 |
武器工业 | 129篇 |
无线电 | 2543篇 |
一般工业技术 | 1894篇 |
冶金工业 | 274篇 |
原子能技术 | 346篇 |
自动化技术 | 1315篇 |
出版年
2024年 | 88篇 |
2023年 | 307篇 |
2022年 | 485篇 |
2021年 | 537篇 |
2020年 | 551篇 |
2019年 | 481篇 |
2018年 | 452篇 |
2017年 | 546篇 |
2016年 | 603篇 |
2015年 | 618篇 |
2014年 | 825篇 |
2013年 | 885篇 |
2012年 | 880篇 |
2011年 | 974篇 |
2010年 | 619篇 |
2009年 | 700篇 |
2008年 | 662篇 |
2007年 | 705篇 |
2006年 | 592篇 |
2005年 | 475篇 |
2004年 | 436篇 |
2003年 | 386篇 |
2002年 | 281篇 |
2001年 | 242篇 |
2000年 | 241篇 |
1999年 | 177篇 |
1998年 | 140篇 |
1997年 | 156篇 |
1996年 | 123篇 |
1995年 | 96篇 |
1994年 | 88篇 |
1993年 | 69篇 |
1992年 | 52篇 |
1991年 | 66篇 |
1990年 | 41篇 |
1989年 | 27篇 |
1988年 | 21篇 |
1987年 | 17篇 |
1986年 | 17篇 |
1985年 | 25篇 |
1984年 | 22篇 |
1983年 | 15篇 |
1982年 | 29篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1962年 | 1篇 |
1959年 | 4篇 |
1958年 | 2篇 |
1957年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Oxidation of trans-polyacetylene lowers the activation energy for conduction from 16 kcal mol?1 to 11 kcal mol?1 for oxidation levels of (C2H2On)x, n = 0.144, 0.207 and 0.550. Maximum conductivity levels for 0 < x < 0.144 doped with I2 were almost identical. At long I2 doping times all samples exhibited some loss of conductivity. E.s.r. experiments indicate that: (1) linewidth is directly proportional to oxygen content, and (2) iodine doping is not diffusion controlled. All data are consistent with a molecular picture of PAC consisting of highly reactive localized spin states that are selectively oxidized, and less reactive delocalized states that affect conductivity more strongly via doping. 相似文献
32.
33.
This paper presents some further results on adaptive sliding mode control (ASMC) for a class of nonlinear systems with bounded uncertain parameters. Given a large initial tracking error, current ASMC design generally produces an unnecessarily large switching gain, consequently leading to a serious chattering problem or a large‐amplitude control jump for the continuous counterpart. To solve such an overadaptation problem, the switching gain adaptation mechanism is first analyzed in this paper, and the adaptation induced by the initial tracking error is suggested to be removed. Then, by exploiting the global sliding mode feature of time‐varying sliding mode control and integral sliding mode control, we present two effective methodologies for ASMC design. The proposed ASMC algorithms ensure that there is no overestimation of the switching gain and the system response is not slowed down when a small switching gain is generated. The validity of the proposed methods is verified by both theoretical analysis and simulation results. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
34.
35.
The configurational sequences of 1,2-unit in a series of hydrogenated syndiotactic 1,2-polybutadienes were determined in relation to the sequence distribution of 1,2- and 1,4-units on the basis of the 13C-n.m.r. signal assignment of the methyl carbons. The observed triad distributions of 1,2- and 1,4-units and configurational distributions of the 1,2-unit are in good agreement with the calculated distributions from transition probabilities. The number average sequence lengths of the 1,2-unit and the 1,2-unit in the racemic addition are 5.7 to 8.0 and 4.1 to 5.4, respectively. From the extrapolation of the plot of the number average sequence length against the crystallinity of the starting 1,2-polybutadienes, the minimum sequence length for crystallization is estimated to be 3.7 for the 1,2-unit in the racemic addition. 相似文献
36.
Magnetic‐field probes can be used for electromagnetic interference measurement of high‐speed circuits. The main magnetic probe performance includes sensitivity, spatial resolution, electric‐field suppression ratio (EFSR), and measurement accuracy. In this article, a pair of differential magnetic‐field probes is proposed to improve measurement accuracy without reducing sensitivity. The proposed differential probes consist of two asymmetric loop probes, which are designed in the same plane and separated by a row of periodic vias. The proposed differential probes are fabricated under PCB process. High accuracy can be achieved by measuring difference between outputs of the two probes. In addition, EFSR can be improved by size optimization of the differential magnetic‐field probes. Simulation and measurement results show the operating bandwidth is from 100 MHz to 12 GHz, the measurement error is 3.4% and the EFSR is about 40 dB. The proposed probes have higher measurement accuracy and higher EFSR than the conventional single probe, and larger operation bandwidth than the stacked differential probes. 相似文献
37.
针对脑功能网络的构建受到特定大脑图谱对兴趣点描述准确度及覆盖度的限制,提出了基于认知任务信息和神经影像数据的脑功能网络构建方法。首先计算fMRI体素对于认知任务的敏感度,然后在此基础上选取兼顾分布均衡和去中心化的大脑兴趣点,从而构建任务驱动的脑功能网络。实验通过在人脸情绪识别认知任务相关的梭状回构造任务驱动的脑功能网络,其度中心性、聚类系数、全局效率、局部效率这四个复杂网络指标均优于典型大脑图谱梭状回中兴趣点构成的网络。结果表明,计算得到的大脑兴趣点具有更强的整合性,更适合用于表征特定认知任务下的脑功能网络。 相似文献
38.
Robert B. Heimann 《Surface & coatings technology》2006,201(5):2012-2019
Osteoconductive hydroxyapatite coatings for metallic endoprostheses for hip and knee joint replacement provide a state-of-the-art template for enhanced in-growth of bone cells. However, the high temperature of the plasma jet leads to large scale dehydroxylation and decomposition of the starting powder. A model is being developed to explain the formation of chemically and mechanically inhomogeneous porous calcium phosphate coatings deposited by atmospheric plasma spraying onto titanium alloy substrates. In addition the biofunctionality is being discussed of titania bond coats and their influence on the in vivo performance of hydroxyapatite-titania duplex coating systems. 相似文献
39.
汽轮机油被广泛应用于火力发电厂汽轮机的调节系统,随着使用年限的增加,其润滑性能和电气性能会随之下降。针对汽轮机油老化状态缺少简单有效的实时监测手段这一问题,提出用核磁共振技术进行检测,并设计了一种方便实时监测的微型核磁共振传感器。传感器尺寸为30 mm ×30 mm ×36 mm,重107 g,可以浸泡在汽轮机油中对其进行检测。通过对来自两个发电厂的不同使用年限的汽轮机油进行测量实验发现:汽轮机油的核磁共振参数有效横向弛豫时间T2ef与纵向弛豫时间T1随着其使用年限的增加而减小。该传感器制作成本低,尺寸微小,操作方便,使得实时监测汽轮机油的老化状态成为一种可能。 相似文献
40.