全文获取类型
收费全文 | 4988篇 |
免费 | 38篇 |
国内免费 | 13篇 |
专业分类
电工技术 | 17篇 |
综合类 | 16篇 |
化学工业 | 162篇 |
金属工艺 | 12篇 |
机械仪表 | 39篇 |
建筑科学 | 59篇 |
矿业工程 | 14篇 |
能源动力 | 17篇 |
轻工业 | 207篇 |
水利工程 | 17篇 |
石油天然气 | 8篇 |
武器工业 | 1篇 |
无线电 | 100篇 |
一般工业技术 | 154篇 |
冶金工业 | 4082篇 |
原子能技术 | 25篇 |
自动化技术 | 109篇 |
出版年
2022年 | 12篇 |
2021年 | 24篇 |
2020年 | 19篇 |
2019年 | 24篇 |
2018年 | 18篇 |
2017年 | 18篇 |
2016年 | 14篇 |
2015年 | 20篇 |
2014年 | 29篇 |
2013年 | 51篇 |
2012年 | 56篇 |
2011年 | 52篇 |
2010年 | 45篇 |
2009年 | 45篇 |
2008年 | 57篇 |
2007年 | 56篇 |
2006年 | 39篇 |
2005年 | 55篇 |
2004年 | 34篇 |
2003年 | 28篇 |
2002年 | 32篇 |
2001年 | 26篇 |
2000年 | 25篇 |
1999年 | 131篇 |
1998年 | 1320篇 |
1997年 | 771篇 |
1996年 | 456篇 |
1995年 | 273篇 |
1994年 | 228篇 |
1993年 | 235篇 |
1992年 | 46篇 |
1991年 | 40篇 |
1990年 | 53篇 |
1989年 | 47篇 |
1988年 | 57篇 |
1987年 | 51篇 |
1986年 | 49篇 |
1985年 | 54篇 |
1984年 | 10篇 |
1983年 | 13篇 |
1982年 | 21篇 |
1981年 | 22篇 |
1980年 | 31篇 |
1979年 | 9篇 |
1978年 | 18篇 |
1977年 | 91篇 |
1976年 | 170篇 |
1975年 | 17篇 |
1974年 | 7篇 |
1970年 | 5篇 |
排序方式: 共有5039条查询结果,搜索用时 0 毫秒
81.
82.
FS Chen PE Di Cesare AA Kale JF Lee VH Frankel SA Stuchin JD Zuckerman 《Canadian Metallurgical Quarterly》1998,13(8):867-873
We have developed a computer program for the rapid assessment of the primary structure differences between a protein of unknown sequence and a homologous known protein. Both proteins are reduced, alkylated, and digested with the same hydrolytic agent. The unfractionated peptide mixtures are submitted to automatic sequence analysis. Based on the knowledge of the reference sequence, the program utilizes the analysis data to identify all the potential peptides present in the two mixtures, determining their primary structure, homology degree, and molecular weight calculated both as integer MH+ and average mass variables. These fingerprints allow the user to easily identify the structural differences between the two proteins and clarify possible doubts by a mass spectrometric analysis of the two mixtures. In order to verify the utility of the program, we provide an application example using the already reported data of two homologous proteins. 相似文献
83.
Crack-detection techniques, developed for room temperature studies, have been applied to the study of magnetite layers growing on mild steel in NaOH solutions at 573 K and 10 MN/m2 pressure, when subjected to varying tensile or compressive strains. It has been found that these films are extremely resistant to failure in compression but that they crack in tension at strains of 0·05–0·08%.Strains, below those necessary to cause cracking, result in changes in the rate of the electrochemical reactions associated with the oxidation process. 相似文献
84.
85.
1. ISA Brown and Shaver 288 pullets were changed from 8 h to 8, 10, 13 or 16 h photoperiods at 42, 63, 84, 105, 126 or 142 d of age. 2. Age at first egg (AFE) was curvilinearly affected by the size and timing of the change in photoperiod. AFE was advanced most by a photoperiod change from 8 to 13 h made at 63 or 84 d. ISA birds were generally more responsive than Shaver to the photoperiod changes. 3. Longer photoperiods significantly increased survivors' egg production, but decreased liveability to 504 d. so that eggs per hen housed were unaffected. Retarding AFE by 10 d reduced survivors' egg numbers by 7.0, but increased mean egg weight by 1.26 g. Egg output by Shaver birds was unaffected by AFE, but that of ISA was curvilinearly affected, with an apogee at an AFE of 135 d. In both breeds, egg weight and egg output were greater following an early or late, rather than a mid-term photostimulation. 4. Photoperiod significantly increased mean daily food intake during lay by 1.26 g/h. A 10 d retardation in AFE resulted in a reduction in food intake of 1 g/d. Efficiency of food conversion deteriorated according to the square of the photoperiod, and changed curvilinearly according to age at photostimulation. Food conversion efficiency improved by 0.05 g/g for each 10 d delay in AFE. 5. Shell quality was unaffected by AFE, but deteriorated with increasing photoperiod and was curvilinearly affected by age at photostimulation with the smallest shell weights associated with photostimulation at 63 d. The incidence of double-yolked (DY) egg production increased with photoperiod and decreased with delayed photostimulation. There was an exponential regression of DY eggs on AFE. 6. Body weight at first egg increased by 75 g/d delay in AFE, but body weight at 504 d of age was unaffected by AFE, photoperiod or age at photostimulation. Body weight gain during lay increased by 15 g/h increase in photoperiod, decreased by 6 g per 10 d delay in photostimulation and by 40 g per 10 d delay in AFE. Fat content at 504 d increased by about 10 g/kg and by 23 g/bird for each 10 d delay in AFE. 7. Mortality in lay increased by 0.8%/h increase in photoperiod, but was unaffected by either age at photostimulation or AFE. 相似文献
86.
JM Ding GF Buchanan SA Tischkau D Chen L Kuriashkina LE Faiman JM Alster PS McPherson KP Campbell MU Gillette 《Canadian Metallurgical Quarterly》1998,394(6691):381-384
Circadian clocks are complex biochemical systems that cycle with a period of approximately 24 hours. They integrate temporal information regarding phasing of the solar cycle, and adjust their phase so as to synchronize an organism's internal state to the local environmental day and night. Nocturnal light is the dominant regulator of this entrainment. In mammals, information about nocturnal light is transmitted by glutamate released from retinal projections to the circadian clock in the suprachiasmatic nucleus of the hypothalamus. Clock resetting requires the activation of ionotropic glutamate receptors, which mediate Ca2+ influx. The response induced by such activation depends on the clock's temporal state: during early night it delays the clock phase, whereas in late night the clock phase is advanced. To investigate this differential response, we sought signalling elements that contribute solely to phase delay. We analysed intracellular calcium-channel ryanodine receptors, which mediate coupled Ca2+ signalling. Depletion of intracellular Ca2+ stores during early night blocked the effects of glutamate. Activators of ryanodine receptors induced phase resetting only in early night; inhibitors selectively blocked delays induced by light and glutamate. These findings implicate the release of intracellular Ca2+ through ryanodine receptors in the light-induced phase delay of the circadian clock restricted to the early night. 相似文献
87.
AG Chiou GJ Florakis RL Copeland VA Williams SA McCormick R Chiesa 《Canadian Metallurgical Quarterly》1998,17(5):566-570
Endoscopic treatment of chronic pancreatitis has drawn benefits from endoscopic procedures previously described for the main bile duct. Endotherapy is developing throughout the world. Cyst drainage procedures certainly represent the largest step forward in that non-surgical approach, whatever it is either direct (through the stomach or the duodenum) or indirect through the papilla in the duodenum. This procedure gives similar results to surgery with a lower morbidity. Pancreatic duct drainage associated with stone clearance is feasible and provides good results which have not yet been compared with those obtained thanks to surgery. Nonetheless, when the duct is not widely dilated it has been proven to be a satisfactory alternative to surgery. By contrast, chronic cholestasis does not appear to be a good indication of endotherapy. 相似文献
88.
89.
Compared to the online interaction behavior of other users, little is known about the difficulties dyslexic Web users encounter online. This paper reviews existing literature at the intersection of dyslexia and accessibility research to determine what useful knowledge exists regarding this important and relatively large group of users. This review uncovers that, although there are few published usability tests with dyslexic users, there is a considerable body of knowledge on dyslexia as well as many design guidelines for authoring dyslexic-accessible interfaces. Through a comparison of existing accessibility guidelines for dyslexic and non-dyslexic users and discussion of the plain language movement, it is argued that dyslexic-accessible practices may redress difficulties encountered by all Internet users. This conclusion suggests that usability testing yielding a clearer profile of the dyslexic user would further inform the practice of universal design, but also that enough knowledge is already available to allow doing more to increase accessibility for dyslexic Internet users. 相似文献
90.
驾驶作业涉及人-汽车-环境,是较复杂的半自动化人机系统,驾驶作业疲劳是由多种因素造成的,对其评价存在不确定性.建立一种多因素多等级的评价模型,对驾驶作业疲劳程度进行总体评价,对致劳因素进行排序,为驾驶疲劳的评价及预防和减轻驾驶疲劳提供一种方法. 相似文献