全文获取类型
收费全文 | 136294篇 |
免费 | 6317篇 |
国内免费 | 3018篇 |
专业分类
电工技术 | 4254篇 |
技术理论 | 4篇 |
综合类 | 5875篇 |
化学工业 | 19825篇 |
金属工艺 | 7979篇 |
机械仪表 | 6642篇 |
建筑科学 | 6294篇 |
矿业工程 | 2281篇 |
能源动力 | 2759篇 |
轻工业 | 7335篇 |
水利工程 | 2411篇 |
石油天然气 | 3150篇 |
武器工业 | 554篇 |
无线电 | 15233篇 |
一般工业技术 | 22485篇 |
冶金工业 | 5134篇 |
原子能技术 | 1048篇 |
自动化技术 | 32366篇 |
出版年
2024年 | 214篇 |
2023年 | 913篇 |
2022年 | 1611篇 |
2021年 | 2336篇 |
2020年 | 1744篇 |
2019年 | 1535篇 |
2018年 | 15936篇 |
2017年 | 15017篇 |
2016年 | 11529篇 |
2015年 | 2897篇 |
2014年 | 3111篇 |
2013年 | 3545篇 |
2012年 | 6995篇 |
2011年 | 13365篇 |
2010年 | 11732篇 |
2009年 | 8881篇 |
2008年 | 9909篇 |
2007年 | 10717篇 |
2006年 | 2959篇 |
2005年 | 3589篇 |
2004年 | 2903篇 |
2003年 | 2802篇 |
2002年 | 2240篇 |
2001年 | 1592篇 |
2000年 | 1373篇 |
1999年 | 1217篇 |
1998年 | 841篇 |
1997年 | 657篇 |
1996年 | 637篇 |
1995年 | 526篇 |
1994年 | 381篇 |
1993年 | 322篇 |
1992年 | 255篇 |
1991年 | 195篇 |
1990年 | 135篇 |
1989年 | 88篇 |
1988年 | 108篇 |
1987年 | 44篇 |
1986年 | 57篇 |
1968年 | 43篇 |
1967年 | 35篇 |
1966年 | 42篇 |
1965年 | 45篇 |
1960年 | 30篇 |
1959年 | 35篇 |
1958年 | 37篇 |
1957年 | 36篇 |
1956年 | 34篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
71.
Based on the voltage and current fluctuating phenomenon in the arc plasma load under the negative-pulse-bias, usingthe plasma physics theory and analysis of computer simulation expatiates that the nature of plasma load in vacuumarc plasma is a capacitance 相似文献
72.
73.
改性乳化沥青的发展和应用概况 总被引:1,自引:0,他引:1
综述了改性乳化沥青的发展及应用概况,重点讨论了改性乳化沥青的生产、制备工艺、稳定性影响因素,并对国内外改性乳化沥青的应用情况加以概述。 相似文献
74.
A coupled finite-element model, CON2D, has been developed to simulate temperature, stress, and shape development during the
continuous casting of steel, both in and below the mold. The model simulates a transverse section of the strand in generalized
plane strain as it moves down at the casting speed. It includes the effects of heat conduction, solidification, nonuniform
superheat dissipation due to turbulent fluid flow, mutual dependence of the heat transfer and shrinkage on the size of the
interfacial gap, the taper of the mold wall, and the thermal distortion of the mold. The stress model features an elastic-viscoplastic
creep constitutive equation that accounts for the different responses of the liquid, semisolid, delta-ferrite, and austenite
phases. Functions depending on temperature and composition are employed for properties such as thermal linear expansion. A
contact algorithm is used to prevent penetration of the shell into the mold wall due to the internal liquid pressure. An efficient
two-step algorithm is used to integrate these highly nonlinear equations. The model is validated with an analytical solution
for both temperature and stress in a solidifying slab. It is applied to simulate continuous casting of a 120 mm billet and
compares favorably with plant measurements of mold wall temperature, total heat removal, and shell thickness, including thinning
of the corner. The model is ready to investigate issues in continuous casting such as mold taper optimization, minimum shell
thickness to avoid breakouts, and maximum casting speed to avoid hot-tear crack formation due to submold bulging. 相似文献
75.
Atsushi Narumi Kosei Kawasaki Harumi Kaga Toshifumi Satoh Naoya Sugimoto Toyoji Kakuchi 《Polymer Bulletin》2003,49(6):405-410
Summary
The potato phosphorylase-catalyzed polymerization of α-D-glucose-1-phosphate (G-1-P) onto poly[styrene-block-(4-vinylbenzyl maltohexaoside)] (1) was performed at the molar ratios of [G-l-P]0 and [maltohexaose]0 of 35, 80, and 250. The product was found to be soluble in dimethyl sulfoxide, which was a good solvent for amylose, and
showed the complex-formation with iodine, indicating that the product was assignable to poly[styrene-block-(styrene-graft-amylose)] (2). The quantitative analysis of the liberated phosphoric acid gave the average degree of polymerization o f the glucose unit
(n) as 27, 5 1, and 180 for 2-I, 2-II, and 2-III, respectively.
Received: 29 November 2002/Accepted: 22 December 2002
Correspondence to Toyoji Kakuchi 相似文献
76.
From its foundation until 2004, ETRI has registered over 1,000 US patents. This letter analyzes the characteristics of these patents and addresses the explanatory factors affecting their citation counts. For explanatory variables, research team related variables, invention specific variables, and geographical domain related variables are suggested. Zero‐altered count data models are used to test the impact of independent variables. A key finding is that technological cumulativeness, the scale of invention, outputs in the electronic field, and the degree of dependence on the US technology domain positively affect the citation counts of ETRI‐invented US patents. The magnitude of international presence appears to negatively affect the citation counts of ETRI‐invented US patents. 相似文献
77.
提出了一种基于光纤环的光缓存器的结构,对结合半导体光放大器作光开关的此结构的物理模型进行了详细描述,并根据此模型分析了其增益、噪声、信噪比等方面的特性. 相似文献
78.
ZhaoYahong ZhangZhongpei WuWeiling 《电子科学学刊(英文版)》2003,20(3):177-182
Adaptive modulation and power allocation is introduced into the multicarrier DSCDMA system to improve the system performance and bandwidth efficiency.First,the system design appropriate for adaptive modulation and power allocation is given,then the algorithm of adaptive modulation and power allocation is applied.Simulation results demonstrate great performance improvement compared with the fixed modulated one. 相似文献
79.
As an aid towards improving the treatment of exchange and correlation effects in electronic structure calculations, it is
desirable to have a clear picture of the errors introduced by currently popular approximate exchange-correlation functionals.
We have performed ab initio density functional theory and density functional perturbation theory calculations to investigate
the thermal properties of bulk Cu, using both the local density approximation (LDA) and the generalized gradient approximation
(GGA). Thermal effects are treated within the quasiharmonic approximation. We find that the LDA and GGA errors for anharmonic
quantities are an order of magnitude smaller than for harmonic quantities; we argue that this might be a general feature.
We also obtain much closer agreement with experiment than earlier, more approximate calculations. 相似文献
80.
Effect of doping of carbon nanotubes by magnetic transition metal atoms has been considered in this paper. In the case of
semiconducting tubes, it was found that the system has zero magnetization, whereas in metallic tubes the valence electrons
of the tube screen the magnetization of the dopants: the coupling to the tube is usually antiferromagnetic (except for Cr). 相似文献