全文获取类型
收费全文 | 18074篇 |
免费 | 523篇 |
国内免费 | 18篇 |
专业分类
电工技术 | 238篇 |
综合类 | 10篇 |
化学工业 | 3574篇 |
金属工艺 | 281篇 |
机械仪表 | 312篇 |
建筑科学 | 1101篇 |
矿业工程 | 109篇 |
能源动力 | 511篇 |
轻工业 | 1383篇 |
水利工程 | 158篇 |
石油天然气 | 194篇 |
武器工业 | 1篇 |
无线电 | 1073篇 |
一般工业技术 | 2887篇 |
冶金工业 | 4183篇 |
原子能技术 | 162篇 |
自动化技术 | 2438篇 |
出版年
2022年 | 139篇 |
2021年 | 214篇 |
2020年 | 170篇 |
2019年 | 223篇 |
2018年 | 265篇 |
2017年 | 259篇 |
2016年 | 321篇 |
2015年 | 238篇 |
2014年 | 382篇 |
2013年 | 1105篇 |
2012年 | 669篇 |
2011年 | 872篇 |
2010年 | 675篇 |
2009年 | 663篇 |
2008年 | 862篇 |
2007年 | 871篇 |
2006年 | 686篇 |
2005年 | 721篇 |
2004年 | 559篇 |
2003年 | 574篇 |
2002年 | 510篇 |
2001年 | 330篇 |
2000年 | 300篇 |
1999年 | 303篇 |
1998年 | 321篇 |
1997年 | 303篇 |
1996年 | 301篇 |
1995年 | 335篇 |
1994年 | 269篇 |
1993年 | 303篇 |
1992年 | 272篇 |
1991年 | 165篇 |
1990年 | 237篇 |
1989年 | 283篇 |
1988年 | 204篇 |
1987年 | 215篇 |
1986年 | 211篇 |
1985年 | 265篇 |
1984年 | 260篇 |
1983年 | 227篇 |
1982年 | 217篇 |
1981年 | 213篇 |
1980年 | 172篇 |
1979年 | 187篇 |
1978年 | 176篇 |
1977年 | 177篇 |
1976年 | 147篇 |
1975年 | 178篇 |
1974年 | 166篇 |
1973年 | 133篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
The objective of this investigation was to determine the chemical and thermal gradients during steel making in a pilot size
basic oxygen furnace. It was postulated that if these gradients could be determined under different conditions, conflicting
theories of operation could be tested and optimum operating conditions would be indicated. New sample probe techniques were
developed in which the probes are inserted through the side of the vessel to desired locations. Shortly after reaching the
desired locations, the tip of an evacuated tube inside the probe opens and delivers metal to the other end of the probe outside
the vessel. Temperatures were determined throughout the bath by specially reinforced but sensitive thermocouple probes. Important
differences in both chemical and thermal gradients were found. The gradients were greatest with shallow penetration of the
jet-for example after 3 min in a heat with about 1 in. penetration, the P content varied from 0.05 to 0.17 pct, silicon from
0.05 to 0.20 pct and the temperature from 2500° to 2900° F. These variations were found in a bath only 6 in. deep and 15 in.
diam. By contrast, with deeper jet penetration to the center of the bath, the gradients were greatly reduced. Regardless of
the operating conditions employed, the data indicate a metal circulation pattern which is upward from the jet cavity and radially
outward at the surface. Even more important, by inserting a spray collector above the bath, it was found that with hard blowing
the jet pumps out a volume of droplets during a heat which is equal to the bath volume. These droplets are rapidly oxidized,e.g. from 3.6 to 0.4 pct C, in their flight above the bath and are an important consideration in refining. 相似文献
992.
Evaluated the short paper presentations at the Rocky Mountain Psychological Association conventions in Salt Lake City and Phoenix to develop a rating form that would provide an assessment of the quality of the presentations for the benefit of the speakers and future convention planners. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
993.
994.
995.
Gregor Gary L.; Smith Richard F.; Simons Lynn S.; Parker Howard B. 《Canadian Metallurgical Quarterly》1972,79(3):488
Hypothesized that, when the degree of crowding is manipulated by varying group size in cages of equal size, it is probable that crowded animals will engage in more contact than uncrowded animals. Home-cage observation of 24 male and 24 female deer mice indicates that crowded Ss do, in fact, engage in more contact behavior. Both home-cage observation and testing in pairs for pain-elicited aggression reveal that (a) crowded Ss display more agonistic behavior than uncrowded Ss, and (b) agonistic behavior increases with prolonged crowding. Support is obtained for the theory that the effect of crowding derives from contact with conspecifics. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
996.
Two comparison groups of 25 Ss each, Fit and Lack of Fit, were generated based on extent of similarity between their ideal and real perceptions of a rehabilitation center on the Community-Oriented Program Environment Scale (an index of person/environment fit). Although Lack of Fit Ss reported more problems in receiving center services, more dissatisfaction with services, and lower life satisfaction in the present, they were no more likely to drop out of their center program. (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
997.
Distortions in received signals in solar occultation measurements made from space arise as a result of the systematic motion of the electro-optical sensor. In a wide range of cases, the motion-related signal distortions caused by the instrument's full modulation transfer function are as important as those from the optics. This paper demonstrates by simulation that existing techniques in the field of digital-image processing can be applied directly to solar occultation experiments to correct for these distortions. The resulting enhanced radiation profile is much closer to the true radiance profile than is the sampled output of the instrument. Use of this enhanced radiance profile in the inversion computation should improve the retrieved atmospheric profiles considerably. It also contains a study of the accuracy of such application from the point of view of instrument noise, uncertainties in the knowledge of the instrument function, and the nature of the power spectrum of the undistorted signal. 相似文献
998.
Richard L. Liboff 《Annals of Nuclear Energy》1981,8(2):87-90
A Bose-atom model is introduced for the molecule DH where H represents a heavy halogen atom. A potential is constructed for this system and corresponding wavefunctions and energies are obtained. In the ground state, the large mass of the deuteron causes large penetration into the ion core. An expression for the probability of deuteron-nuclear overlap is obtained of the form where rN is nuclear radius, a0 is Bohr radius, Z is atomic number and . Thus P is infinitesimally small. Relevance to the exothermic reaction 127I(d,n) 128Xe is discussed. 相似文献
999.
Investigations of biofilms in domestic environments are sparsely represented in the literature. In this study, samples of various household surfaces, including food, laundry and kitchen items, were analyzed for evidence of biofilm presence. Visualization of the surfaces was carried out using cryostage scanning electron microscopy (CSEM) and light microscopy. Qualitative evidence of the presence of biofilm formation was obtained from all of the sample groups analyzed, suggesting the widespread existence of microorganisms in biofilms on domestic surfaces. This suggests that biofilms may be important in household hygiene, and highlights the need for standardized, approved biofilm methods suitable for consumer products testing. 相似文献
1000.
Ruckart PZ Borders J Villanacci J Harris R Samples-Ruiz M 《Journal of hazardous materials》2004,115(1-3):27-31
High winds, flooding, lightning, and other phenomena associated with adverse weather can cause power failures, equipment damage, and process upsets resulting in chemical releases. Of the 5000 events in Texas that were reported to the Hazardous Substances Emergency Events Surveillance (HSEES) system during 2000-2001, adverse weather conditions contributed to 110 (2%) events. Rain was the most frequent adverse weather condition. Most events to which adverse weather conditions contributed occurred during June or September; these months correspond with the high temperature and hurricane season in Texas. Most events occurred in coastal counties with large numbers of industrial facilities. Three industries reported the majority of events: industrial and miscellaneous chemicals manufacturing; petroleum refining; and plastics, synthetics, and resin manufacturing. Power failures were associated more often with adverse weather-related events than with nonweather-related events. Releases occurred most commonly from ancillary process equipment and process vessels. Events associated with adverse weather-related conditions involved nine victims. System and process design improvements, such as improved backup power generation and redesigned secondary containment systems, could be explored to reduce the potential negative effects of severe weather. 相似文献