全文获取类型
收费全文 | 329435篇 |
免费 | 28482篇 |
国内免费 | 16401篇 |
专业分类
电工技术 | 22487篇 |
技术理论 | 13篇 |
综合类 | 22585篇 |
化学工业 | 49473篇 |
金属工艺 | 20014篇 |
机械仪表 | 21194篇 |
建筑科学 | 23670篇 |
矿业工程 | 9478篇 |
能源动力 | 8551篇 |
轻工业 | 21754篇 |
水利工程 | 7280篇 |
石油天然气 | 17546篇 |
武器工业 | 3021篇 |
无线电 | 37135篇 |
一般工业技术 | 42526篇 |
冶金工业 | 17534篇 |
原子能技术 | 6662篇 |
自动化技术 | 43395篇 |
出版年
2024年 | 1525篇 |
2023年 | 4871篇 |
2022年 | 9874篇 |
2021年 | 13415篇 |
2020年 | 10074篇 |
2019年 | 8123篇 |
2018年 | 9714篇 |
2017年 | 11119篇 |
2016年 | 9950篇 |
2015年 | 12937篇 |
2014年 | 16556篇 |
2013年 | 19797篇 |
2012年 | 22317篇 |
2011年 | 23491篇 |
2010年 | 21123篇 |
2009年 | 20183篇 |
2008年 | 19915篇 |
2007年 | 18822篇 |
2006年 | 17243篇 |
2005年 | 13985篇 |
2004年 | 10166篇 |
2003年 | 9219篇 |
2002年 | 9096篇 |
2001年 | 8145篇 |
2000年 | 6813篇 |
1999年 | 5742篇 |
1998年 | 4161篇 |
1997年 | 3474篇 |
1996年 | 3141篇 |
1995年 | 2738篇 |
1994年 | 2272篇 |
1993年 | 1746篇 |
1992年 | 1617篇 |
1991年 | 1370篇 |
1990年 | 1329篇 |
1989年 | 1216篇 |
1988年 | 1040篇 |
1987年 | 938篇 |
1986年 | 852篇 |
1985年 | 753篇 |
1984年 | 738篇 |
1981年 | 708篇 |
1979年 | 761篇 |
1978年 | 786篇 |
1977年 | 748篇 |
1976年 | 765篇 |
1975年 | 721篇 |
1974年 | 726篇 |
1973年 | 728篇 |
1972年 | 707篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Hao Li Pengcheng Zhang Shengquan Yu Hongyu Yang Bin Tang Fuhai Li Shuren Zhang 《Ceramics International》2019,45(9):11639-11647
Mg2(Ti1-xSnx)O4 (x?=?0–1) ceramics were prepared through conventional solid-state method. This paper focused on the dependence of microwave dielectric properties on crystal structural characteristics via crystal structure refinement, Raman spectra study and complex chemical bond theory. XRD spectrums delineated the phase information of a spinel structure, and structural characteristic of these compositions were achieved with the help of Rietveld refinements. Raman spectrums were used to depict the correlations between vibrational phonon modes and dielectric properties. The variation of permittivity is ascribed to the Mg2(Ti1-xSnx)O4 average bond covalency. The relationship among the B-site octahedral bond energy, tetrahedral bond energy and temperature coefficient are discussed by defining on the change rate of bond energy and the contribution rate of octahedral bond energy. The quality factor is affected by systematic total lattice energy, and the research of XPS patterns illustrated that oxygen vacancies can be effectively restrained in rich oxygen sintering process. Obviously, the microwave dielectric properties of Mg2(Ti1-xSnx)O4 compounds were obtained (= 12.18, ?=?170,130?GHz, ?=??53.1?ppm/°C, x?=?0.2). 相似文献
3.
In this paper we investigated the BER performance of DS-CDMA using various chip-waveforms, which include three time-limited chip-waveforms and two band-limited chip-waveforms. Closed-form formulae were derived for evaluating the achievable bit-error rate performance with the aid of the standard Gaussian approximation, when communicating over a Nakagami-m channel. The time-limited waveforms impose a low implementational complexity, since they maybe over sampled and read from a look-up table. However, they are outperformed by the frequency-domain raised-cosine waveform as well as the optimum waveform specifically designed by Cho and Lehnert for achieving the lowest possible bit error rate 相似文献
4.
动态评价技术在塔河碳酸盐岩缝洞型油气藏中的应用 总被引:5,自引:2,他引:3
塔河油田奥陶系油气藏是大型碳酸盐岩溶洞型油气藏,其储渗空间主要为大小不同的溶洞、裂缝带、溶蚀孔隙等组成,该油气藏具有极强的非均质性,单纯用静态资料来认识这类油气藏是非常困难。文章提出利用生产动态资料和信息进行该类型油气藏研究的新思路,利用人工神经网络技术在处理非线性相关参数预测方面的优势,并以渗流理论为基础,结合试井成果,选用已知油井的产量、油嘴、油压、含水率、气油比、原油密度等6个开发动态参数作为样品输入数据,推导出影响油气藏开发的重要参数(地层系数)与生产信息的关系,建立了人工神经网络预测储层参数的结构模型。通过塔里木盆地塔河油气田实例研究,说明了利用动态信息评价油气藏技术在碳酸盐岩缝洞型油气藏储层预测和非均质性分析等方面具有较高的实用价值。 相似文献
5.
P. B. Lovyrev A. I. Lavrov V. A. Babkin A. N. Aminov S. M. Melekhin Yu. P. Kazantsev P. M. Korol’kov 《Metallurgist》2006,50(3-4):152-157
Specifications require that all the welds in 12-m-diam. decomposers with a capacity of 3600 m3 be subjected to high-temperature tempering before going into service in order to alleviate the stresses from the welding
operation. Specialists at the organizations VNIIPTkhimnefteapparatury and VNIImontazhspetsstroi have proposed out-of-furnace
volumetric (complete) of the assembled decomposer with the use of special heaters. The use of this heating method has shortened
assembly operations while providing the welds with a highquality heat treatment and reducing the stresses overall (including
welding stresses, stresses from assembly of the decomposer, etc.) The technology ensures uniform heating of the housing of
the decomposer and provides for close control over the process. The experience gained in heat-treating decomposers can also
be used in the construction of other containers that come into contact with corrosive media.
__________
Translated from Metallurg, No. 3, pp. 61–64, March, 2006. 相似文献
6.
N. I. Nikolaikin E. Yu. Barzilovich N. E. Nikolaikina 《Chemical and Petroleum Engineering》2006,42(5-6):332-338
The paper discusses optimal control of ecosystem state for observation of a generalized monotonically varying random parameter.
A model is proposed for the controlled vector random process, whose components are assigned acceptable ranges and the observations
are performed discretely.
__________
Translated from Khimicheskoe i Neftegazovoe Mashinostroenie, No. 6, pp. 40–44, June, 2006. 相似文献
7.
设计并实现了一种DVB—T调制器的外码编码器,着重介绍了码流自适应接口、能量扩散、RS编码器及卷积交织器的设计方法,该设计方案最终在Altera的FPGA上进行验证。 相似文献
8.
Introduction
The IEC central office informed in 7/543/AC that the secretariat of TC 7 would be taken over by the Chinese National Committee on January 10, 2003 and affirmed subsequently in 7/544/AC that the secretariat of TC 7 has been taken over by the Chinese National Committee which appointing secretary in Shanghai Electric Cable Research Institute as no objection has been raised by the Standardization Management Board members. It's the first IEC secretariat that assumed by China, with great significance, just as commented by the media that the commitment indicate undoubtedly China is to play a much more active and important role in the world especially after its entry into world trade organization as well as the trend of global economic integration. 相似文献
9.
The basic methods of verifying continuous automatic belt weighers are described. A comparative analysis of these methods on the basis of experimental studies is made and ways of implementing the results in industry are recommended. 相似文献
10.
Yu. I. Golovin D. V. Lopatin R. K. Nikolaev A. V. Umrikhin 《Technical Physics Letters》2004,30(5):426-428
The effect of crystal orientation on the photogeneration of free charge carriers was studied for C60 single crystals in a weak magnetic field. The photoconductivity sharply depends on the orientation of magnetic field with
respect to the crystallographic directions, showing a 5–8% increase for seven axes of the C60 crystal. 相似文献