全文获取类型
收费全文 | 2569篇 |
免费 | 95篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 23篇 |
化学工业 | 591篇 |
金属工艺 | 51篇 |
机械仪表 | 49篇 |
建筑科学 | 71篇 |
矿业工程 | 2篇 |
能源动力 | 30篇 |
轻工业 | 132篇 |
水利工程 | 24篇 |
石油天然气 | 16篇 |
无线电 | 167篇 |
一般工业技术 | 432篇 |
冶金工业 | 780篇 |
原子能技术 | 22篇 |
自动化技术 | 277篇 |
出版年
2022年 | 17篇 |
2021年 | 39篇 |
2020年 | 16篇 |
2019年 | 24篇 |
2018年 | 39篇 |
2017年 | 33篇 |
2016年 | 54篇 |
2015年 | 26篇 |
2014年 | 56篇 |
2013年 | 89篇 |
2012年 | 79篇 |
2011年 | 106篇 |
2010年 | 87篇 |
2009年 | 86篇 |
2008年 | 116篇 |
2007年 | 92篇 |
2006年 | 83篇 |
2005年 | 82篇 |
2004年 | 76篇 |
2003年 | 51篇 |
2002年 | 62篇 |
2001年 | 69篇 |
2000年 | 54篇 |
1999年 | 59篇 |
1998年 | 155篇 |
1997年 | 101篇 |
1996年 | 73篇 |
1995年 | 56篇 |
1994年 | 78篇 |
1993年 | 62篇 |
1992年 | 31篇 |
1991年 | 38篇 |
1990年 | 41篇 |
1989年 | 34篇 |
1988年 | 27篇 |
1987年 | 30篇 |
1986年 | 31篇 |
1985年 | 31篇 |
1984年 | 27篇 |
1983年 | 24篇 |
1982年 | 31篇 |
1981年 | 29篇 |
1980年 | 29篇 |
1979年 | 16篇 |
1978年 | 20篇 |
1977年 | 31篇 |
1976年 | 44篇 |
1975年 | 29篇 |
1974年 | 16篇 |
1972年 | 11篇 |
排序方式: 共有2667条查询结果,搜索用时 0 毫秒
991.
Studies on the mandibular canal in the edentulous mandible have rarely been correlated with mandibular canal position, mandibular body width, mandibular canal width, thickness of bony plates, gender and race. The aim of this investigation was to examine the above parameters by studying the bucco-lingual relationship of the mandibular canal in dry edentulous mandibles of Black and White, males and females (n = 13 in each group), of similar age (mean 58, 17 yrs). The mandibles were radiographed cross-sectionally. The position of the mandibular canal in relation to the buccal and lingual cortical plates, and the widths of the mandibular canal and mandibular body, measured at selected distances, were recorded and the values statistically analysed. Race and gender do not seem to influence the position of the mandibular canal in the bucco-lingual plane. The location of the canal is predominantly closer to the lingual cortex in the bucco-lingual plane. It was found that the widths of the left and right halves of the mandibular body are not statistically significantly different but widths of the left and right mandibular canal are significantly different. 相似文献
992.
Kramer Arthur F.; Wickens Christopher D.; Donchin Emanuel 《Canadian Metallurgical Quarterly》1985,11(4):393
Assessed the conditions under which dual-task integrality can be fostered by manipulating 4 factors likely to influence the integrality between tasks: intertask redundancy (ITD), the spatial proximity of primary and secondary task displays, the degree to which primary and secondary task displays constitute a single object, and the resource demands of the 2 tasks. The resource allocation policy was inferred from changes in the amplitude of the P300 component of the event-related brain potential. 12 university students participated in 3 experimental sessions in which they performed both single and dual tasks. The primary task was a pursuit step tracking task. The secondary tasks required Ss to discriminate between different intensities or different spatial positions of a stimulus. Task pairs that required the processing of different properties of the same object resulted in better performance than task pairs that required the processing of different objects. These same object-task pairs led to a positive relation between primary task difficulty and the resources allocated to secondary task stimuli. ITD and the physical proximity of task displays produced similar effects of reduced magnitude. (54 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
993.
D. J. Arent M. W. Peterson C. Kramer K. A. Bertness J. A. Turner 《Journal of Electronic Materials》1996,25(10):1633-1636
We find a statistically significant correlation between carrier concentration and the Lorentzian linewidth factor determined
from a Voigt lineshape fit to roomtemperature photoluminscence (PL) measurements for partially ordered p-Ga0.52In0.48P epitaxially deposited by organometallic vapor-phase deposition on GaAs. The correlation is independent of the amount of
ordering present in the material. For carrier concentrations over the range of ~1016 to 1019 cm−3, PL provides rapid and nondestructive evaluation, with increasing accuracy above carrier concentration levels of 5 × 1017 cm3. 相似文献
994.
Johnson Katrina W.; Anderson Norman B.; Bastida Elena; Kramer B. Josea; Williams David; Wong Morrison 《Canadian Metallurgical Quarterly》1995,14(7):601
Ethnic minority populations show patterns of health, health care use, and mortality that differ from the overall U.S. population. Each of the broad groups of minorities (Asian. Hispanic, Native, and African Americans) has a unique background of sociocultural factors that influence these patterns. Thus. the larger social environment for ethnic populations, including political, environmental, historical, and economic factors, is a major variable in possible health outcomes. The individual portions in this panel report of the conference seek to identify such factors for each ethnic group and to suggest those macrosocial influences that are most important for observed health effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
995.
W Tao JB Zwischenberger TT Nguyen RA Vertrees LB McDaniel LK Nutt DN Herndon GC Kramer 《Canadian Metallurgical Quarterly》1995,110(3):819-828
Impaired gut mucosal perfusion has been reported during cardiopulmonary bypass. To better define the adequacy of gut blood flow and oxygenation during cardiopulmonary bypass, we measured overall gut blood flow and ileal mucosal flow and their relationship to mucosal pH, mesenteric oxygen delivery and oxygen consumption in immature pigs (n = 8). Normothermic, noncross-clamped, right atrium-to-aorta cardiopulmonary bypass was maintained at 100 ml/kg per minute for 120 minutes. Animals were instrumented with an ultrasonic Doppler flow probe on the superior mesenteric artery, a mucosal laser Doppler flow probe in the ileum, and pH tonometers in the stomach, ileum, and rectum. Radioactive microspheres were injected before and at 5, 60, and 120 minutes of cardiopulmonary bypass for tissue blood flow measurements. Overall gut blood flow significantly increased during cardiopulmonary bypass as evidenced by increases in superior mesenteric arterial flow to 134.1% +/- 8.0%, 137.1% +/- 7.5%, 130.3% +/- 11.2%, and 130.2% +/- 12.7% of baseline values at 30, 60, 90, and 120 minutes of bypass, respectively. Conversely, ileal mucosal blood flow significantly decreased to 53.6% +/- 6.4%, 49.5% +/- 6.8%, 58.9% +/- 11.6%, and 47.8% +/- 10.0% of baseline values, respectively. Blood flow measured with microspheres was significantly increased to proximal portions of the gut, duodenum and jejunum, during cardiopulmonary bypass, whereas blood flow to distal portions, ileum and colon, was unchanged. Gut mucosal pH decreased progressively during cardiopulmonary bypass and paralleled the decrease in ileal mucosal blood flow. Mesenteric oxygen delivery decreased significantly from 67.0 +/- 10.0 ml/min per square meter at baseline to 42.4 +/- 4.6, 44.9 +/- 3.5, 46.0 +/- 3.6, and 42.9 +/- 3.9 ml/min per square meter at 30, 60, 90, and 120 minutes of bypass. Despite the decrease in mesenteric oxygen delivery, mesenteric oxygen consumption increased progressively from 10.8 +/- 1.4 ml/min per square meter at baseline to 13.4 +/- 1.2, 15.9 +/- 1.2, 16.7 +/- 1.4, and 16.6 +/- 1.54 ml/min per square meter, respectively. We conclude that gut mucosal ischemia during normothermic cardiopulmonary bypass results from a combination of redistribution of blood flow away from mucosa and an increased oxygen demand. 相似文献
996.
The microsomal stearoyl-CoA desaturase system was examined in both the Morris hepatoma 7288CTC, maintained in the host Buffalo
strain rat, and the Morris hepatoma 7288C, maintained in tissue culture. In vitro examination shows the stearoyl-CoA desaturase
system to be similar in the 2 tissues. Both show extremely low overall stearoyl-CoA desaturase activity, having 4% and 8%
of normal liver values respectively. Examination of the electron transport system showed both tissues have decreased electron
transport components cytochrome b5 and cytochrome b5 reductase. Particularly noticeable were the extremely low levels of cytochrome b5 (2% compared with normal liver). Microsomes from both tissues showed a decreased ability to reduce an artificial electron
acceptor, cytochrome c. With the low levels of cytochrome b5 observed in these tissues, the low levels of overall desaturase activity may be caused by lack of terminal enzyme, lack of
sufficient cytochrome b5, or both. Analysis of the stearoyl-CoA desaturase system in cultured hepatoma cells suggests that these cells are similar
to the host-grown tumor in this respect and may be used as a model in further examinations of the stearoyl-CoA desaturase
system. 相似文献
997.
The effects of practice on 2 retrievals from a single cue were investigated. In Experiment 1, participants were given extended single-task practice and were then tested on a dual memory retrieval task. Performance was consistent with a sequential retrieval model proposed by T. C. Rickard and H. Pashler (2003). In Experiment 2, participants practiced both single- and dual-retrieval tasks extensively. Initially, data from all participants indicated sequential retrieval. However, participants who grouped the 2 response outputs were eventually able to perform the dual task with a latency that approached the prediction of a parallel race model. Models that assume a transition from sequential to parallel retrieval with practice, along with other models that assume an immutable retrieval bottleneck at all practice levels, are considered. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
998.
Peterson Randall S.; Smith D. Brent; Martorana Paul V.; Owens Pamela D. 《Canadian Metallurgical Quarterly》2003,88(5):795
This article explores 1 mechanism by which leader personality affects organizational performance. The authors hypothesized and tested the effects of leader personality on the group dynamics of the top management team (TMT) and of TMT dynamics on organizational performance. To test their hypotheses, the authors used the group dynamics q-sort method, which is designed to permit rigorous, quantitative comparisons of data derived from qualitative sources. Results from independent observations of chief executive officer (CEO) personality and TMT dynamics for 17 CEOs supported the authors' hypothesized relationships both between CEO personality and TMT group dynamics and between TMT dynamics and organizational performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
999.
Previous individual-level research suggests that positive mood promotes creative problem solving (A. M. Isen, 2000). The current study built on these results to investigate group-level phenomena. Temporary workgroups (N=57) were induced to experience positive, neutral, or negative mood before engaging in a creative production task. The results indicated that positive mood increased creative performance and implementation efficiency, whereas negative mood had no effect. Regarding group process, positive and neutral mood created a stronger task focus, whereas negative mood created a stronger relationship focus within the group, but this effect did not influence group performance. Implications for future research on the role of mood in group creativity and process are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
1000.
A Hlinak T Müller M Kramer RU Mühle H Liebherr K Ziedler 《Canadian Metallurgical Quarterly》1998,34(3):479-486
A cDNA of amine sulfotransferase-RB1 (AST-RB1), which efficiently catalyzes 4-phenyl-1,2,3,6-tetrahydropyridine (PTHP) sulfation, has been isolated by immunoscreening of a rabbit liver cDNA library. The cDNA consisted of 1,117 base pairs and encoded a protein of 301 amino acids with a molecular weight of 35,876. The deduced amino acid sequence matched at six positions those of peptide fragments obtained from purified AST-RB1 protein. The sequence had less than 38% identity at the amino acid level with cytosolic sulfotransferases in mammals, although high degrees of similarity were observed with regions conserved throughout mammalian sulfotransferases. These results indicate that AST-RB1, arbitrarily named sulfotransferase 3A1 (ST3A1), constitutes a new and third gene family of cytosolic sulfotransferases in mammals. ST3A1 expressed in Escherichia coli as a fused protein catalyzed sulfation of amines such as PTHP, aniline, 4-chloroaniline, 2-naphthylamine, and desipramine, but barely O-sulfation of typical aryl and hydroxysteroid sulfotransferase substrates. These data unequivocally demonstrate the existence of a cytosolic sulfotransferase showing a high selectivity for amine substrates, and indicate that multiple forms of sulfotransferase mediate sulfation of xenobiotics in mammalian livers. 相似文献