全文获取类型
收费全文 | 20109篇 |
免费 | 2743篇 |
国内免费 | 1859篇 |
专业分类
电工技术 | 3058篇 |
技术理论 | 3篇 |
综合类 | 2358篇 |
化学工业 | 2858篇 |
金属工艺 | 784篇 |
机械仪表 | 992篇 |
建筑科学 | 1114篇 |
矿业工程 | 525篇 |
能源动力 | 683篇 |
轻工业 | 704篇 |
水利工程 | 352篇 |
石油天然气 | 589篇 |
武器工业 | 243篇 |
无线电 | 2441篇 |
一般工业技术 | 2313篇 |
冶金工业 | 655篇 |
原子能技术 | 326篇 |
自动化技术 | 4713篇 |
出版年
2024年 | 116篇 |
2023年 | 340篇 |
2022年 | 477篇 |
2021年 | 599篇 |
2020年 | 760篇 |
2019年 | 773篇 |
2018年 | 636篇 |
2017年 | 780篇 |
2016年 | 844篇 |
2015年 | 822篇 |
2014年 | 1158篇 |
2013年 | 1320篇 |
2012年 | 1256篇 |
2011年 | 1389篇 |
2010年 | 1017篇 |
2009年 | 1017篇 |
2008年 | 1124篇 |
2007年 | 1215篇 |
2006年 | 1224篇 |
2005年 | 1045篇 |
2004年 | 923篇 |
2003年 | 808篇 |
2002年 | 760篇 |
2001年 | 641篇 |
2000年 | 568篇 |
1999年 | 531篇 |
1998年 | 361篇 |
1997年 | 357篇 |
1996年 | 304篇 |
1995年 | 264篇 |
1994年 | 248篇 |
1993年 | 222篇 |
1992年 | 170篇 |
1991年 | 121篇 |
1990年 | 110篇 |
1989年 | 67篇 |
1988年 | 66篇 |
1987年 | 35篇 |
1986年 | 35篇 |
1985年 | 20篇 |
1984年 | 32篇 |
1983年 | 25篇 |
1982年 | 24篇 |
1981年 | 13篇 |
1980年 | 12篇 |
1979年 | 17篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1960年 | 5篇 |
1959年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
162.
本文讨论静载荷及疲劳载荷作用下 C/Al 正交层压板的力学响应,并考虑损伤过程中的临界现象,以此作为结构设计准则的基础。对静载荷作用的情况:(1)90°铺层的门槛应变ε_(FPF)随着约束程度增加而增加,而且开裂后的行为也受约束程度的影响。(2)经历加载-卸载再重新加载至断裂的过程后,初始试样存在一个剩余永久变形,其损伤状态可以用刚度的变化来表征;而疲劳试样在加载-卸载过程中刚度变化很小,反映其损伤达到一个稳定的状态。对疲劳载荷作用的情况:(1)对于给定的应力比 R,试样会趋于与它所承受的 S_(max)最大值相应的 SDS 状态。循环应力范围的不断增大,会引起基体损伤的增加,从而重新建立新的饱和损伤状态。(2)对于每一损伤状态均有一对应的循环应变范围 Δε。在 SDS 状态下,Δε保持不变。(3)以刚度下降为损伤参数对 C/Al 层压板进行了降级应力分析,并由此来预计在ΔS_(sh)以下,层压板不会发生疲劳损伤累积。 相似文献
163.
乳化炸药的乳化物理模型和理想乳化模态 总被引:3,自引:1,他引:2
文章以平推流模拟了乳化炸药乳胶质的形成过程,并建立了机械强制乳化的物理模型及理想模态。 相似文献
164.
聚合物电解质PEO全固态电致变色窗 总被引:3,自引:0,他引:3
本文用聚合物PEO的锂盐络合物作电解质制作全固态电致变色窗,讨论了器件的特性,以及工艺条件的影响。 相似文献
165.
A prediction method for the thermal conductivity of halocarbon refrigerants in the saturated liquid state in the reduced temperature range 0.3 to well above 0.9 is presented in this paper. The aim of the method is to present a very simple calculation of the transport property useful for engineering purposes. The method determines thermal conductivity as a sole function of the reduced temperature and requires the knowledge of a parameter dependent upon easily available physical constants characteristic of each compound. The method is validated against experimental data available in the literature, giving average absolute deviations which are usually less than 5%, with maximum absolute deviations generally less than 10%. An extension of the method to estimate thermal conductivity of binary mixtures is also presented, along with a comparison with the few experimental data available in the literature.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A. 相似文献
166.
167.
Heat-shock induction of heat-shock protein genes is due to a specific promoter element (the heat-shock element, HSE). This study used lacZ under HSE control (HSE-lacZ) to characterize HSE activity in Saccharomyces cerevisiae cells of different physiological states and differing genetic backgrounds. In batch fermentations HSE-lacZ induction by heat shock was maximal in exponential growth, and showed marked decline with the approach to stationary phase. Expression in the absence of heat shock was unaffected by growth phase, indicating that the growth-dependent expression of many yeast heat-shock genes uses promoter elements in addition to the HSE. Heat-induced expression was strongly influenced by the temperature at which cultures were grown. While basal, uninduced expression was constant during growth at different temperatures to 30 degrees C, induction by transfer to 39 degrees C was reduced by increases in growth temperature as low as 18-24 degrees C. Maximal HSE-lacZ induction (30- to 50-fold) was in cultures grown at low temperatures (18-24 degrees C), then heat shocked at 39 degrees C. Ethanol was a poor inducer. Mutations having little effect on HSE-lacZ expression included a respiratory petite; ubi4 (which inactivates the poly-ubiquitin gene); also ubc4 and ubc5 (which each inactivate one of the ubiquitin ligases involved in degradation of aberrant protein). pep4-3 increased both basal and induced beta-galactosidase about two-fold, probably because of slower turnover of this enzyme in pep4-3 strains. 相似文献
168.
The queue of a single server is considered with independent and identically distributed interarrivai and service times and an infinite (GI/G/1) or finite (GI/G/1/N) waiting room. The queue discipline is non-preemptive and independent of the service times.
A discrete time version of the system is analyzed, using a two-component state model at the arrival and departure instants of customers. The equilibrium equations are solved by a polynomial factorization method. The steady state distribution of the queue size is then represented as a linear combination of geometrical series, whose parameters are evaluated by closed formulae depending on the roots of a characteristic polynomial.
Considering modified boundary constraints, systems with finite waiting room or with an exceptional first service in each busy period are included. 相似文献
169.
Markovian and semi-Markovian random processes are used to analyze the problem of optimal search for signals in a multichannel
communication system with arbitrarily distributed random outputs. The search efficiency factor is found in explicit form based
on state space merging, and a mathematical programming problem is set up to find a numerical suboptimal solution.
__________
Translated from Kibernetika i Sistemnyi Analiz, No. 3, pp. 144–150, May–June 2007. 相似文献
170.
GAOHui LIYan YANGLi-ping DENGHong 《半导体光子学与技术》2005,11(2):85-88,106
Hexagonal microtube ZnO was firstly grown on single crystal p-Si (111) substrates by hydrothermal method, and fabricated Ag/n-ZnO and Au/n-ZnO Schottky junction. Schottky effective barrier heights were calculated by I-V measurement. It is confirmed that the presence of a large amount of surface states related possibly to lattice imperfections existed near the surface leads to the pinning of the surface Fermi level at 0.35 eV below the conduction-band edge. Then the fabricated Schottky barrier junctions are evaluated for their use as UV photodetectors. 相似文献