全文获取类型
收费全文 | 695398篇 |
免费 | 73397篇 |
国内免费 | 43137篇 |
专业分类
电工技术 | 68802篇 |
技术理论 | 74篇 |
综合类 | 71212篇 |
化学工业 | 64973篇 |
金属工艺 | 23496篇 |
机械仪表 | 42700篇 |
建筑科学 | 76939篇 |
矿业工程 | 29352篇 |
能源动力 | 20700篇 |
轻工业 | 35905篇 |
水利工程 | 22204篇 |
石油天然气 | 28248篇 |
武器工业 | 8828篇 |
无线电 | 80185篇 |
一般工业技术 | 46871篇 |
冶金工业 | 25664篇 |
原子能技术 | 5635篇 |
自动化技术 | 160144篇 |
出版年
2024年 | 3604篇 |
2023年 | 10373篇 |
2022年 | 20868篇 |
2021年 | 24570篇 |
2020年 | 23096篇 |
2019年 | 17737篇 |
2018年 | 16441篇 |
2017年 | 21374篇 |
2016年 | 25045篇 |
2015年 | 28077篇 |
2014年 | 48360篇 |
2013年 | 41549篇 |
2012年 | 51022篇 |
2011年 | 53723篇 |
2010年 | 40823篇 |
2009年 | 41410篇 |
2008年 | 40393篇 |
2007年 | 49117篇 |
2006年 | 43727篇 |
2005年 | 38370篇 |
2004年 | 31280篇 |
2003年 | 27817篇 |
2002年 | 21647篇 |
2001年 | 17835篇 |
2000年 | 14971篇 |
1999年 | 11885篇 |
1998年 | 8787篇 |
1997年 | 7265篇 |
1996年 | 6129篇 |
1995年 | 5158篇 |
1994年 | 4284篇 |
1993年 | 3045篇 |
1992年 | 2472篇 |
1991年 | 1763篇 |
1990年 | 1524篇 |
1989年 | 1271篇 |
1988年 | 850篇 |
1987年 | 558篇 |
1986年 | 494篇 |
1985年 | 492篇 |
1984年 | 438篇 |
1983年 | 370篇 |
1982年 | 275篇 |
1981年 | 241篇 |
1980年 | 252篇 |
1979年 | 147篇 |
1978年 | 91篇 |
1977年 | 90篇 |
1962年 | 84篇 |
1959年 | 86篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
在干扰条件下,卫星导航抗干扰波束形成算法往往需要卫星信号波达方向(Direction-of-Arrival,DOA)的先验信息。但当存在低信噪比信号或主动干扰源时,常规的DOA估计算法性能急剧下降甚至失效。针对此问题,提出了一种被干扰信号压制的低信噪比“北斗”信号的DOA估计算法。该算法首先通过对接收信号进行子空间投影抑制干扰信号,然后对抑制干扰后的信号进行解扩重构处理,最后通过多重信号分类算法完成对“北斗”信号的DOA估计。仿真结果表明,在干扰信号干信比80 dB条件下,“北斗”信号DOA估计误差在5°以内,为下一步进行波束形成计算提供了高精度的入射角信息。 相似文献
4.
5.
陈彦名 《电信工程技术与标准化》2015,(5)
介绍了目前最炙手可热的REST架构风格,该风格顺应Web2.0的兴起,完美的匹配了云计算时代来临的可扩展要求,在各种应用场景中都得到了充分的表现。根据其技术特点,分析了该风格的API在移动通信网络管理中的应用,从网管系统内部、网管系统之间以及网管系统与上层APP应用之间等多方面对是否适用于REST风格以及如何在合适的位置使用REST API进行了分析。 相似文献
6.
The aim of the research is evaluating the classification performances of eight different machine-learning methods on the antepartum cardiotocography (CTG) data. The classification is necessary to predict newborn health, especially for the critical cases. Cardiotocography is used for assisting the obstetricians’ to obtain detailed information during the pregnancy as a technique of measuring fetal well-being, essentially in pregnant women having potential complications. The obstetricians describe CTG shortly as a continuous electronic record of the baby's heart rate took from the mother's abdomen. The acquired information is necessary to visualize unhealthiness of the embryo and gives an opportunity for early intervention prior to happening a permanent impairment to the embryo. The aim of the machine learning methods is by using attributes of data obtained from the uterine contraction (UC) and fetal heart rate (FHR) signals to classify as pathological or normal. The dataset contains 1831 instances with 21 attributes, examined by applying the methods. In the paper, the highest accuracy displayed as 99.2%. 相似文献
7.
8.
Wenshu Chen Jiajun Gu Yongping Du Fang Song Fanxing Bu Jinghan Li Yang Yuan Ruichun Luo Qinglei Liu Di Zhang 《Advanced functional materials》2020,30(25)
Large‐scale production of hydrogen from water‐alkali electrolyzers is impeded by the sluggish kinetics of hydrogen evolution reaction (HER) electrocatalysts. The hybridization of an acid‐active HER catalyst with a cocatalyst at the nanoscale helps boost HER kinetics in alkaline media. Here, it is demonstrated that 1T–MoS2 nanosheet edges (instead of basal planes) decorated by metal hydroxides form highly active / heterostructures, which significantly enhance HER performance in alkaline media. Featured with rich / sites, the fabricated 1T–MoS2 QS/Ni(OH)2 hybrid (quantum sized 1T–MoS2 sheets decorated with Ni(OH)2 via interface engineering) only requires overpotentials of 57 and 112 mV to drive HER current densities of 10 and 100 mA cm?2, respectively, and has a low Tafel slope of 30 mV dec?1 in 1 m KOH. So far, this is the best performance for MoS2‐based electrocatalysts and the 1T–MoS2 QS/Ni(OH)2 hybrid is among the best‐performing non‐Pt alkaline HER electrocatalysts known. The HER process is durable for 100 h at current densities up to 500 mA cm?2. This work not only provides an active, cost‐effective, and robust alkaline HER electrocatalyst, but also demonstrates a design strategy for preparing high‐performance catalysts based on edge‐rich 2D quantum sheets for other catalytic reactions. 相似文献
9.
《Advanced Powder Technology》2020,31(12):4585-4597
Focussing on visible light active ferrites for high performance removal of noxious pollutants, we report the synthesis of Mg0.5NixZn0.5-xFe2O4 (x = 0.1, 0.2, 0.3, 0.4, & 0.5) ferrite nanoparticle for degradation of reactive blue-19 (RB-19). Lattice parameters calculated using intense X-ray diffraction (XRD) peaks and Nelson-Riley plots (N-R plot) are in well agreement with each other. The sample Mg0.5Ni0.4Zn0.1Fe2O4 (M5N4) exhibits best performance with 99.5% RB-19 degradation in 90 min under visible light. Photoluminescence (PL) results confirm that recombination of charge carriers is highly reduced in the photocatalyst. Scavenging experiments suggest that O2− radicals were the dominant species responsible for photocatalytic performance. The photocatalytic mechanism was explained in terms of dopant driven shifting of conduction bands and valence bands (calculated by Mott-Schottky plots). The thermodynamic probability of radical generation along with role of redox cycles of metal ions has been discussed in the mechanism. The dye degradation was ascertained by detection of intermediates via mass spectrometry analysis and a possible degradation route was also predicted. The findings in this work provide intriguing opportunities to modify the electronic band structure of spinel ferrites for visible and solar light photocatalytic activity for environmental detoxification. 相似文献
10.
In this paper, novel computing approach using three different models of feed-forward artificial neural networks (ANNs) are presented for the solution of initial value problem (IVP) based on first Painlevé equation. These mathematical models of ANNs are developed in an unsupervised manner with capability to satisfy the initial conditions exactly using log-sigmoid, radial basis and tan-sigmoid transfer functions in hidden layers to approximate the solution of the problem. The training of design parameters in each model is performed with sequential quadratic programming technique. The accuracy, convergence and effectiveness of the proposed schemes are evaluated on the basis of the results of statistical analyses through sufficient large number of independent runs with different number of neurons in each model as well. The comparisons of these results of proposed schemes with standard numerical and analytical solutions validate the correctness of the design models. 相似文献