全文获取类型
收费全文 | 123723篇 |
免费 | 5041篇 |
国内免费 | 2359篇 |
专业分类
电工技术 | 3302篇 |
技术理论 | 3篇 |
综合类 | 5006篇 |
化学工业 | 18033篇 |
金属工艺 | 6996篇 |
机械仪表 | 5452篇 |
建筑科学 | 5165篇 |
矿业工程 | 1747篇 |
能源动力 | 2227篇 |
轻工业 | 6315篇 |
水利工程 | 2049篇 |
石油天然气 | 2938篇 |
武器工业 | 391篇 |
无线电 | 14124篇 |
一般工业技术 | 20934篇 |
冶金工业 | 4409篇 |
原子能技术 | 656篇 |
自动化技术 | 31376篇 |
出版年
2024年 | 246篇 |
2023年 | 849篇 |
2022年 | 1571篇 |
2021年 | 2116篇 |
2020年 | 1562篇 |
2019年 | 1174篇 |
2018年 | 15656篇 |
2017年 | 14717篇 |
2016年 | 11078篇 |
2015年 | 2315篇 |
2014年 | 2425篇 |
2013年 | 2652篇 |
2012年 | 5904篇 |
2011年 | 12340篇 |
2010年 | 10898篇 |
2009年 | 7726篇 |
2008年 | 9106篇 |
2007年 | 9829篇 |
2006年 | 2171篇 |
2005年 | 2991篇 |
2004年 | 2270篇 |
2003年 | 2143篇 |
2002年 | 1476篇 |
2001年 | 919篇 |
2000年 | 976篇 |
1999年 | 1045篇 |
1998年 | 817篇 |
1997年 | 629篇 |
1996年 | 629篇 |
1995年 | 485篇 |
1994年 | 405篇 |
1993年 | 275篇 |
1992年 | 249篇 |
1991年 | 201篇 |
1990年 | 129篇 |
1989年 | 100篇 |
1988年 | 96篇 |
1987年 | 52篇 |
1986年 | 48篇 |
1985年 | 37篇 |
1968年 | 45篇 |
1967年 | 34篇 |
1966年 | 44篇 |
1965年 | 44篇 |
1959年 | 38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 15 毫秒
71.
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
72.
In this paper, we describe a method for increasing the external efficiency of polymer light‐emitting diodes (LEDs) by coupling out waveguided light with Bragg gratings. We numerically model the waveguide modes in a typical LED structure and demonstrate how optimizing layer thicknesses and reducing waveguide absorption can enhance the grating outcoupling. The gratings were created by a soft‐lithography technique that minimizes changes to the conventional LED structure. Using one‐dimensional and two‐dimensional gratings, we were able to increase the forward‐directed emission by 47 % and 70 %, respectively, and the external quantum efficiency by 15 % and 25 %. 相似文献
73.
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
74.
75.
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
76.
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
77.
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
78.
空间数据立方体的物化视图选择方法研究 总被引:1,自引:0,他引:1
针对决策支持系统(DSS)中集成空间分析能力的应用趋势,研究基于空间数据仓库的一种决策分析工具——空间在线分析处理(Spatial OLAP),拟解决影响空间OLAP在线响应的瓶颈难点——空间数据立方体的物化问题。首先系统地提出空间OLAP的模型,然后对现有空间度量物化视图选择方法进行改进,提出了双向空间Greedy算法。实验证明.该算法在降低选择时间和求解质量两方面具有更好的表现。 相似文献
79.
火成岩储层测井评价进展综述 总被引:19,自引:0,他引:19
十多年来,国内外火成岩储层测井评价已从交会图定性分析发展到用岩心分析资料建立裂缝性储层的测井解释模型,半定量、定量评价裂缝。成像测井和核磁测井的纵、横向分辨率高,经过地质刻度,可以较精细地识别岩性和裂缝,在解释火成岩方面有良好的效果。提高岩性识别准确率,识别复杂火成岩储层和孔隙流体,以及综合评价火成岩储层裂缝、饱和度等参数,仍然是火成岩储层测井评价所面临的难题。加强岩石物理基础实验,研究火成岩储层导电机理,系统研究火成岩储层测井评价理论,推广测井新技术在火成岩中的应用,建立统一的测井评价方法,将成为火成岩储层测井评价的发展趋势。 相似文献
80.