全文获取类型
收费全文 | 22790篇 |
免费 | 883篇 |
国内免费 | 83篇 |
专业分类
电工技术 | 291篇 |
综合类 | 44篇 |
化学工业 | 5024篇 |
金属工艺 | 478篇 |
机械仪表 | 479篇 |
建筑科学 | 1726篇 |
矿业工程 | 160篇 |
能源动力 | 687篇 |
轻工业 | 2179篇 |
水利工程 | 180篇 |
石油天然气 | 56篇 |
武器工业 | 1篇 |
无线电 | 1492篇 |
一般工业技术 | 4171篇 |
冶金工业 | 2811篇 |
原子能技术 | 139篇 |
自动化技术 | 3838篇 |
出版年
2023年 | 141篇 |
2022年 | 191篇 |
2021年 | 527篇 |
2020年 | 312篇 |
2019年 | 328篇 |
2018年 | 493篇 |
2017年 | 426篇 |
2016年 | 529篇 |
2015年 | 481篇 |
2014年 | 692篇 |
2013年 | 1507篇 |
2012年 | 1084篇 |
2011年 | 1525篇 |
2010年 | 1095篇 |
2009年 | 1051篇 |
2008年 | 1274篇 |
2007年 | 1106篇 |
2006年 | 944篇 |
2005年 | 869篇 |
2004年 | 777篇 |
2003年 | 699篇 |
2002年 | 663篇 |
2001年 | 396篇 |
2000年 | 383篇 |
1999年 | 414篇 |
1998年 | 417篇 |
1997年 | 380篇 |
1996年 | 345篇 |
1995年 | 298篇 |
1994年 | 303篇 |
1993年 | 303篇 |
1992年 | 251篇 |
1991年 | 214篇 |
1990年 | 201篇 |
1989年 | 234篇 |
1988年 | 186篇 |
1987年 | 177篇 |
1986年 | 174篇 |
1985年 | 243篇 |
1984年 | 216篇 |
1983年 | 185篇 |
1982年 | 170篇 |
1981年 | 198篇 |
1980年 | 132篇 |
1979年 | 148篇 |
1978年 | 146篇 |
1977年 | 127篇 |
1976年 | 147篇 |
1975年 | 120篇 |
1974年 | 106篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
Totterdell Peter; Spelten Evelien; Smith Lawrence; Barton Jane; Folkard Simon 《Canadian Metallurgical Quarterly》1995,80(1):43
Although regulations on work hours usually include a minimum weekly rest period, there is little empirical evidence concerning recovery from work. Shift-working nurses (N?=?61) used a handheld computer for 28 days to complete self-ratings, cognitive-performance tasks, and a sleep diary. Many measures were worse on rest days that followed a night shift rather than a day shift and tended to be worse on 1st rest days compared with subsequent rest days. Alertness was lowest on the 1st rest day following a night shift. Social satisfaction was better on workdays that were preceded by 2 rather than 1 rest day. Reaction time (RT) decreased over consecutive night shifts and tended to increase over rest days following night shifts. The results are interpreted as being consistent with the combined adaptive costs of fatigue and adjustment to and from a nocturnal routine. The practical implications for scheduling rest days are considered. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
132.
Peter Rez 《Journal of research of the National Institute of Standards and Technology》2002,107(6):487-495
To calculate the intensity of x-ray emission in electron beam microanalysis requires a knowledge of the energy distribution of the electrons in the solid, the energy variation of the ionization cross section of the relevant subshell, the fraction of ionizations events producing x rays of interest and the absorption coefficient of the x rays on the path to the detector. The theoretical predictions and experimental data available for ionization cross sections are limited mainly to K shells of a few elements. Results of systematic plane wave Born approximation calculations with exchange for K, L, and M shell ionization cross sections over the range of electron energies used in microanalysis are presented. Comparisons are made with experimental measurement for selected K shells and it is shown that the plane wave theory is not appropriate for overvoltages less than 2.5 V. 相似文献
133.
This article describes the development and validation of scales to measure clients' outcome optimism, perceived progress, and self-agency related to change in problems presented in therapy. In Study 1, initial confirmatory and subsequent exploratory factor analyses (N?=?257) identified effort and persistence as an additional unique factor and guided selection of items to measure the 4 constructs. In Study 2, confirmatory factor analysis of the revised scales with a new sample (N?=?93) confirmed the measurement model. Results of convergent and discriminant validity analyses generally were in the predicted directions. The Perceived Progress scale demonstrated criterion validity with changes in dyadic adjustment and family functioning. The Outcome Optimism and Self-Agency scales showed variability in their relationship to the Perceived Progress scale over the first 3 sessions of therapy. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
134.
135.
Peter Brandt 《Journal für Verbraucherschutz und Lebensmittelsicherheit》2007,1(9):393-398
Um Auskunft über die wirtschaftliche Bedeutung von Kaffee, Tee und Kakao zu geben, werden in diesem Mini-Review u.a. aktuelle
Angaben zur weltweiten Produktion dieser drei „Exoten“ gemacht (Menge und Herkunftsl?nder), die jeweiligen Import-Anteile
der Produktionsl?nder nach Deutschland (bzw. in die EU) benannt, der Pro-Kopf-Verbrauch an Kaffee, Tee oder Kakao in Deutschland
mit dem anderer Staaten verglichen und – sofern m?glich – Einblick gegeben in die Entwicklung von weltweitem Angebot und Nachfrage
und die damit verbundene Preisentwicklung in den vergangenen Jahren. 相似文献
136.
137.
138.
We consider a system defined as the product of a finite set of periodic systems on cyclic groups. It is of interest to determine if certain subgroups and unions of subgroups of the state set are reachable from a specified initial state, and in particular to determine the computational complexity of verifying such reachability. These questions are motivated by certain problems that arise in the modelling and control of discrete event systems and certain forms of periodic scheduling. Our main result is that deciding whether or not the union of a certain set of subgroups is reachable or not is NP-complete. 相似文献
139.
Nickel molybdate catalysts used in several different upgrading reactions of coal-derived materials from low-rank Australian coals have been regenerated and their activity assessed using a number of physical and chemical techniques. Regeneration of spent coked catalysts for 20 hours in air at 450°C was sufficient to restore chemical hydrogenation activity to catalyst used for pre-asphaltene, asphaltene and oil upgrading, provided poisoning of the catalyst surface by other impurities, principally chlorine-containing molecules, had not occurred. 相似文献
140.
Experimental studies on phase equilibria in the multicomponent system PbO-ZnO-CaO-SiO2-FeO-Fe2O3 in air have been conducted to characterize the phase relations of a complex slag system used in commercial lead oxidation
smelting. The liquidus in the pseudo-ternary section ZnO-“Fe2O3”-(PbO + CaO + SiO2) with the CaO/SiO2 weight ratio of 0.35 and the PbO/(CaO + SiO2) weight ratio of 5.0 has been constructed using results of over 100 high-temperature equilibration and quenching experiments
followed by electron probe X-ray microanalysis. The liquidus in this pseudoternary section contains primary phase fields of
spinel (zinc ferrite) Zn
x
Fe3−x
O4+y
, zincite Zn
u
Fe1−u
O, melilite Pb
v
Ca2−v
Zn
w
Fe1−w
Si2O7, hematite Fe2O3, magneto-plumbite PbFe10O16, and dicalcium silicate Ca2−t
Pb
t
SiO4. The laboratory results are compared with the slags obtained from an industrial reactor. 相似文献