全文获取类型
收费全文 | 290048篇 |
免费 | 21514篇 |
国内免费 | 11142篇 |
专业分类
电工技术 | 15416篇 |
技术理论 | 31篇 |
综合类 | 17468篇 |
化学工业 | 50304篇 |
金属工艺 | 16926篇 |
机械仪表 | 18459篇 |
建筑科学 | 22895篇 |
矿业工程 | 9551篇 |
能源动力 | 7964篇 |
轻工业 | 16728篇 |
水利工程 | 4789篇 |
石油天然气 | 20314篇 |
武器工业 | 2234篇 |
无线电 | 31484篇 |
一般工业技术 | 34438篇 |
冶金工业 | 15365篇 |
原子能技术 | 2881篇 |
自动化技术 | 35457篇 |
出版年
2024年 | 1217篇 |
2023年 | 4680篇 |
2022年 | 7937篇 |
2021年 | 11491篇 |
2020年 | 8540篇 |
2019年 | 7279篇 |
2018年 | 8187篇 |
2017年 | 9234篇 |
2016年 | 8033篇 |
2015年 | 11180篇 |
2014年 | 13795篇 |
2013年 | 16466篇 |
2012年 | 17794篇 |
2011年 | 19468篇 |
2010年 | 16794篇 |
2009年 | 15927篇 |
2008年 | 15472篇 |
2007年 | 15113篇 |
2006年 | 16008篇 |
2005年 | 14184篇 |
2004年 | 9064篇 |
2003年 | 7919篇 |
2002年 | 7316篇 |
2001年 | 6490篇 |
2000年 | 7105篇 |
1999年 | 8520篇 |
1998年 | 6862篇 |
1997年 | 5827篇 |
1996年 | 5460篇 |
1995年 | 4521篇 |
1994年 | 3767篇 |
1993年 | 2634篇 |
1992年 | 2145篇 |
1991年 | 1604篇 |
1990年 | 1174篇 |
1989年 | 936篇 |
1988年 | 760篇 |
1987年 | 525篇 |
1986年 | 391篇 |
1985年 | 267篇 |
1984年 | 183篇 |
1983年 | 121篇 |
1982年 | 130篇 |
1981年 | 86篇 |
1980年 | 70篇 |
1979年 | 24篇 |
1978年 | 2篇 |
1965年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Dong Zhang 《Korean Journal of Chemical Engineering》2008,25(5):1205-1207
Ceria-zirconia solid particles have been recognized as a key material of the automotive exhaust catalysts since they can release
and uptake oxygen owing to the rapid reversible oxidation states of cerium between Ce3+ and Ce4+. Several methods have recently been described to prepare the CeO2-ZrO2 solid particles used in the catalysts. In this paper, a new coprecipitation method is used to prepare the CeO2-ZrO2 solid particles. The Ce-Zr alcogel is dried and calcined in flowing N2 not in flowing air under atmospheric pressure. The results show that the ceria-zirconia sample calcined at 650 °C has high
surface area over 90 m2g−1, which drops to 40 m2g−1 following treatment at 900°C. 相似文献
42.
Fan Zhang To-yat Cheung 《IEEE transactions on pattern analysis and machine intelligence》2003,29(1):1-14
The fault-state detection approach for blackbox testing consists of two phases. The first is to bring the system under test (SUT) from its initial state to a targeted state t and the second is to check various specified properties of the SUT at t. This paper investigates the first phase for testing systems specified as observable nondeterministic finite-state machines with probabilistic and weighted transitions. This phase involves two steps. The first step transfers the SUT to some state t' and the second step identifies whether t' is indeed the targeted state t or not. State transfer is achieved by moving the SUT along one of the paths of a transfer tree (TT) and state identification is realized by using diagnosis trees (DT). A theoretical foundation for the existence and characterization of TT and DT with minimum weighted height or minimum average weight is presented. Algorithms for their computation are proposed. 相似文献
43.
44.
Domain-Driven, Actionable Knowledge Discovery 总被引:1,自引:0,他引:1
Data mining increasingly faces complex challenges in the real-life world of business problems and needs. The gap between business expectations and R&D results in this area involves key aspects of the field, such as methodologies, targeted problems, pattern interestingness, and infrastructure support. Both researchers and practitioners are realizing the importance of domain knowledge to close this gap and develop actionable knowledge for real user needs. 相似文献
45.
Nucleation of solidification in liquid droplets 总被引:2,自引:0,他引:2
Analytical and numerical methods have been developed to analyze the solidification kinetics of a mass of liquid droplets dispersed
in a fluid or solid matrix using classical nucleation theory. The resulting analytical expressions and numerical calculations
can be compared directly with calorimetric measurements of the droplet solidification exotherms to obtain information about
the nucleation mechanism. With increasing contact angle at the solid-liquid-matrix triple point, the solidification onset,
peak, and end temperatures and exothermic peak height all decrease sharply and the droplet solidification exotherms become
broader. Decreasing either the droplet radius or the number of potential catalytic nucleation sites produces a similar but
smaller effect. Distributions in droplet radius, contact angle, and nucleation sites have no effect on the solidification
peak temperature, but the droplet solidification exotherms become broader and more symmetric. The solidification onset temperature
is independent of cooling rate in the calorimeter, but the solidification peak and end temperatures decrease and the exothermic
peak height increases with increasing cooling rate. Predicted droplet solidification exotherms are in excellent agreement
with detailed experimental measurements on 10-nm-radius Cd droplets embedded in a solid Al matrix. Analytical predictions
give best-fit values of 43 deg and 430 for the contact angle and the number of potential catalytic nucleation sites per droplet,
respectively; numerical predictions give best-fit values of 43 deg and 750 for the contact angle and the number of potential
catalytic nucleation sites per droplet, respectively. 相似文献
46.
新型超微晶软磁合金FePCCuMoSi微观结构缺陷的正电子湮没研究 总被引:1,自引:0,他引:1
用正电子湮没方法研究了新型超微晶软磁合金的微观结构缺陷,样品选用的是在不同温度下退火的Fe81P12C3Cu1Mo0.5Si2.5合金,结果表明,合金的微观结构构陷大小,密度随退火温度有规律地变化,这种现象可能与非晶的晶化过程有关。 相似文献
47.
论述了无线电引信多普勒信号增速器的实现原理及意义,介绍了采用TMS320C30作为CPU、多片大容量静态RAM芯片构成海量存储体的信号增速器硬件结构和软件设计,并提出了今后的研究方向。 相似文献
48.
49.
50.
Z. -G. Fan Y. -X. Zhuang G. Yang R. Shao G. -F. Zhang 《Journal of Alloys and Compounds》1993,200(1-2):33-36
The oxygen absorption process in highly aligned YBa2Cu3Ox samples in air and in pure oxygen was studied at several constant temperatures. The process can be expressed in two steps, a chemical reaction controlled step and a diffusion controlled step. The kinetic equations are as follows respectively:
(1 − at) ln(1 − at) + at = kDt
The activation energy was calculated using an Arrhenius equation. The technical conditions of heat treatment for oxygen absorption of highly aligned YBa2Cu3Ox crystals are discussed. 相似文献