全文获取类型
收费全文 | 1430篇 |
免费 | 43篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 31篇 |
综合类 | 3篇 |
化学工业 | 250篇 |
金属工艺 | 38篇 |
机械仪表 | 14篇 |
建筑科学 | 48篇 |
矿业工程 | 2篇 |
能源动力 | 36篇 |
轻工业 | 90篇 |
水利工程 | 12篇 |
石油天然气 | 2篇 |
无线电 | 148篇 |
一般工业技术 | 218篇 |
冶金工业 | 407篇 |
原子能技术 | 9篇 |
自动化技术 | 169篇 |
出版年
2023年 | 15篇 |
2022年 | 25篇 |
2021年 | 39篇 |
2020年 | 29篇 |
2019年 | 33篇 |
2018年 | 37篇 |
2017年 | 38篇 |
2016年 | 29篇 |
2015年 | 18篇 |
2014年 | 34篇 |
2013年 | 68篇 |
2012年 | 56篇 |
2011年 | 61篇 |
2010年 | 46篇 |
2009年 | 45篇 |
2008年 | 62篇 |
2007年 | 44篇 |
2006年 | 28篇 |
2005年 | 35篇 |
2004年 | 30篇 |
2003年 | 27篇 |
2002年 | 21篇 |
2001年 | 26篇 |
2000年 | 17篇 |
1999年 | 31篇 |
1998年 | 99篇 |
1997年 | 69篇 |
1996年 | 34篇 |
1995年 | 34篇 |
1994年 | 22篇 |
1993年 | 25篇 |
1992年 | 8篇 |
1991年 | 18篇 |
1990年 | 16篇 |
1989年 | 9篇 |
1988年 | 7篇 |
1987年 | 15篇 |
1986年 | 11篇 |
1984年 | 14篇 |
1983年 | 13篇 |
1982年 | 10篇 |
1981年 | 13篇 |
1980年 | 12篇 |
1979年 | 8篇 |
1978年 | 12篇 |
1977年 | 18篇 |
1976年 | 26篇 |
1975年 | 8篇 |
1974年 | 12篇 |
1973年 | 8篇 |
排序方式: 共有1477条查询结果,搜索用时 15 毫秒
91.
Depth of penetration experiments were conducted with fragment simulating projectiles launched into Celotex® in order to develop an equation for the strike velocity as a function of the FSP mass and the depth of penetration into Celotex® recovery media. A powder gun launched FSPs, designed in accordance with STANAG-2920 [NATO STANAG-2920 Ballistic Test Method for Personal Armour Materials and Combat Clothing, 2nd ed., 1999.] weighing between 0.13 g and 53.78 g at striking velocities between 198 m/s and 1524 m/s. A multiple linear regression analysis was used to determine an empirical relationship for the strike velocity to the impact parameters of depth of penetration, fragment mass, and mean presented area. Sabot launched natural fragments weighing between 2.8 g and 15.8 g at striking velocities between 532 m/s and 1084 m/s were used to validate the equation. 相似文献
92.
Gasification of fuel cane bagasse, the waste residue from fuel cane, a hybrid of wild and commercial clones of sugar cane, was carried out in a novel 50 kWe air-blown autothermal downdraft gasifier. The speciation and distribution of alkali, alkali earth metals and major ash forming elements during gasification were investigated to evaluate the extent of volatilisation of these elements into the syngas and to determine the likely impact on syngas fuelled solid oxide fuel cell systems. Also assessed was the potential for defluidisation of the fuel bed due to agglomerate and deposit formation. Chemical fractionation studies showed that 30% of the potassium was captured by aluminosilicates and was retained in the ash, thereby reducing the alkali loading in the syngas and that more than 50% of the alkali earth metals were released to the syngas. In contrast, although the major ash forming elements were transformed from acid insoluble to acid soluble forms during gasification they remained hard bound in the ash and less than 30% of each one was released into the gas phase. The composition of clinkers and agglomerates produced during gasification was investigated by SEM-EDX and XRD which confirmed the presence of the eutectic systems KAlSi2O6–SiO2, KAlSi2O6–CaMgSi2O6–SiO2 and CaMgSi2O6–NaAlSi3O8. A preliminary model of the distribution behaviour during gasification of the ash forming elements has been developed. 相似文献
93.
Since late 1989, the cycle helmet wearing rate in New Zealand has risen from around 20% for adults and teenagers, and 40% for younger children, to more than 90% in all age groups. Cycle helmet wearing became mandatory under New Zealand law in January 1994. This paper considers the effect of cycle helmet wearing on hospitalised head injuries between 1990 and 1996, using cyclist limb injuries as a measure of exposure to the risk of cycling trauma. Non-motor vehicle crashes were treated separately from those involving a motor vehicle. Non-motor vehicle crashes were further subdivided by age group. Cyclist head injuries decreased with increasing helmet wearing rates for non-motor vehicle crashes in all age groups, and for motor vehicle crashes. For an increase of 5 percentage points in the helmet wearing rate, the corresponding decreases in head injuries in non-motor vehicle accidents were estimated to be 10.2, 5.3 and 3.2% for children of primary school age (5–12 years), secondary school age (13–18 years), and adults respectively. The corresponding decrease in hospitalisations for motor vehicle crashes was 3.6%. All results were significant at the 95% level. The relatively large increase in helmet wearing associated with the passing of a compulsory helmet wearing law in 1994 reduced head injuries by between 24 and 32% in non-motor vehicle crashes, and by 20% in motor vehicle crashes. No increase or decrease in the severity of head injuries for which cyclists were hospitalised over this period could be detected. This may have been due to the small and highly variable number of ‘high severity’ injuries. 相似文献
94.
Jeff D. Gamlin Jordan F. Clark Greg Woodside Roy Herndon 《Canadian Metallurgical Quarterly》2001,127(2):171-174
Sulfur hexafluoride (SF6) was injected into a 9 km reach of the Santa Ana River in Orange County, CA, over a period of two weeks. The entire flow of this river, which averaged 2.8 m3 s?1, percolated into the ground in the field area. The tracer was monitored at wells near the river to determine subsurface flow patterns and flow times with an accuracy much greater than could be achieved using numerical simulations of ground-water flow. During the experiment, SF6 effectively tagged 3.7 × 106 m3 of water. The tracer plume was mapped in the subsurface for 18 months and indicates that linear ground-water velocities averaged about 2 km year?1. The tracer reached two wells adjacent to the river (about 200 m away) within three weeks, giving evidence that SF6 was not retarded significantly relative to the ground-water flow. This is in agreement with previous laboratory experiments. 相似文献
95.
96.
Perri Michael G.; McAdoo W. George; McAllister David A.; Lauer Joan B.; Jordan Randall C.; Yancey Donna Z.; Nezu Arthur M. 《Canadian Metallurgical Quarterly》1987,55(4):615
This study evaluated the effectiveness of two posttreatment programs designed to enhance the maintenance of weight loss. Eighty-five obese clients were randomly assigned to either (a) behavior therapy plus a peer-support maintenance program, (b) behavior therapy plus a therapist-contact maintenance program, or (c) behavior therapy only. At a 7-month follow-up session, the therapist-contact program resulted in significantly greater maintenance of weight loss compared with the peer support and behavior therapy only conditions. However, by the time of an 18-month follow-up assessment, overall relapse rates were equivalent across conditions. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
97.
As a media genre, advertising offers a unique opportunity to study how the beauty ideal is constructed across cultures. This research analyzes the content of advertisements from women's fashion and beauty magazines in Singapore, Taiwan, and the U.S. to compare how beauty is encoded and found a noticeable difference between the portrayals of women from the U.S. and from the two East Asian societies in terms of sexual portrayal. In addition, Asian ads contained a large proportion of cosmetics and facial beauty products whereas the U.S. ads were dominated by clothing. These findings suggest that beauty in the U.S. may be constructed more in terms of "the body," whereas in Singapore and Taiwan the defining factor is more related to a pretty face. The article also discusses how feminist critiques of the sexual objectification of women in advertising may need to be considered within their historical, Western context of origin. 相似文献
98.
K.-A. Frith 《Electrochimica acta》2009,54(13):3600-2631
Selective and sensitive detection of the amino acid tryptophan is of importance in food processing, pharmaceutical formulations and in biological fluids. Electrochemical methods of detection of tryptophan are hampered by sluggish electron transfer kinetics and in complex matrices through overlapping peaks from interferents. This study examines the potential of the cation exchange membrane Nafion® to enhance selectivity and sensitivity of this analyte through a seldom explored feature of this membrane: pH manipulation. A detailed examination of the effect of pH on the selectivity afforded by Nafion® as a function of the analyte charge is presented. Selective detection of tryptophan and significant increases in sensitivity of its detection was observed in the presence of melatonin, dopamine and other interferents present in a pharmaceutical formulation through manipulation of the pH of the solution. At pH 3.0 at a Nafion®-modified electrode, changes in the protonation of melatonin and tryptophan lowered the anodic potential of the analytes in a non-uniform manner increasing the peak resolution and permitting analyses with detection limits of 1.6 ± 0.1 nM and 1.6 ± 0.2 nM, respectively. 相似文献
99.
Lesions to the mesencephalic reticular formation (MRF) in rats severely attenuate the acquisition of long-term habituation of the startle response when the lesions are made prior to habituation training. The present experiments extend the finding of habituation deficits to animals with MRF damage made after the animals have habituated to an auditory stimulus. Following habitation training, some animals received lesions to the MRF. The startle amplitudes of these animals immediately changed from control levels to levels indistinguishable from those of animals that never habituated across days—animals with MRF lesions made prior to habituation training. The mechanism responsible for long-term habituation appears to be a progressive increase in activity within a long-term habituation pathway extrinsic to the reflex circuit for the startle response, but the synaptic mechanisms responsible for this change are unknown. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
100.
Wadden Thomas A.; Stunkard Albert J.; Smoller Jordan W. 《Canadian Metallurgical Quarterly》1986,54(6):869
Examined the effects of 3 variables on reports of psychological functioning in 28 obese women (mean age 42.1 yrs) who lost an average of 19.2 kg in 6 mo. Analysis of the 1st variable, frequency of assessment, showed that although Ss experienced improvements in mood from pre- to posttreatment, more than 50% showed worsening in mood during 1 or more wks. Analysis of the 2nd variable, time of assessment, revealed that retrospective reports of depression and anxiety were greater than were concurrent reports. Analysis of the 3rd variable, method of assessment, showed that Ss reported several symptoms in response to an open-ended interview that were not measured by objective tests. Data indicate that the method of mood assessment determines the answer to the question of whether dieting is associated with adverse psychological consequences. (9 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献