全文获取类型
收费全文 | 308篇 |
免费 | 2篇 |
专业分类
化学工业 | 19篇 |
金属工艺 | 1篇 |
机械仪表 | 2篇 |
建筑科学 | 3篇 |
轻工业 | 11篇 |
无线电 | 1篇 |
一般工业技术 | 9篇 |
冶金工业 | 258篇 |
自动化技术 | 6篇 |
出版年
2021年 | 2篇 |
2019年 | 2篇 |
2014年 | 3篇 |
2013年 | 1篇 |
2011年 | 3篇 |
2010年 | 1篇 |
2008年 | 2篇 |
2007年 | 2篇 |
2006年 | 1篇 |
2005年 | 2篇 |
2003年 | 6篇 |
2002年 | 1篇 |
2000年 | 6篇 |
1999年 | 8篇 |
1998年 | 56篇 |
1997年 | 55篇 |
1996年 | 38篇 |
1995年 | 17篇 |
1994年 | 19篇 |
1993年 | 14篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 6篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 10篇 |
1976年 | 20篇 |
1974年 | 3篇 |
1972年 | 1篇 |
1967年 | 1篇 |
1966年 | 1篇 |
1928年 | 1篇 |
排序方式: 共有310条查询结果,搜索用时 58 毫秒
51.
Prolonged hypoxia increases vascular endothelial growth factor mRNA and protein in adult mouse brain
NT Kuo D Benhayon RJ Przybylski RJ Martin JC LaManna 《Canadian Metallurgical Quarterly》1999,86(1):260-264
Brain hypoxia induces an increase in brain vascularity, presumably mediated by vascular endothelial growth factor (VEGF), but it is unclear whether VEGF is required to maintain the increase. In these studies, brain VEGF mRNA and protein levels were measured in adult mice kept in hypobaric chambers at 0.5 atm for 0, 0.5, 1, 2, 4, 7, and 21 days. Hypoxia was accompanied by a transient increase of VEGF mRNA expression: twofold by 0.5 day and a maximum of fivefold by 2 days; these were followed by a decrease at 4 days and a return to basal levels by 7-21 days. VEGF protein expression induced by hypoxia was bimodal, initially paralleling VEGF mRNA. There was an initial small increase at 12 h that reached a maximum by day 2, and, after a transient decrease on day 4, the protein expression increased again on day 7 before it returned to normoxic levels after 21 days. Thus, despite continued hypoxia, both VEGF mRNA and protein levels returned to basal after 7 days. These data suggest a metabolic negative-feedback system for VEGF expression during prolonged hypoxia in the brain. 相似文献
52.
Jorn A. Cheney Jonathan P. J. Stevenson Nicholas E. Durston Masateru Maeda Jialei Song David A. Megson-Smith Shane P. Windsor James R. Usherwood Richard J. Bomphrey 《Journal of the Royal Society Interface》2021,18(180)
In gliding flight, birds morph their wings and tails to control their flight trajectory and speed. Using high-resolution videogrammetry, we reconstructed accurate and detailed three-dimensional geometries of gliding flights for three raptors (barn owl, Tyto alba; tawny owl, Strix aluco, and goshawk, Accipiter gentilis). Wing shapes were highly repeatable and shoulder actuation was a key component of reconfiguring the overall planform and controlling angle of attack. The three birds shared common spanwise patterns of wing twist, an inverse relationship between twist and peak camber, and held their wings depressed below their shoulder in an anhedral configuration. With increased speed, all three birds tended to reduce camber throughout the wing, and their wings bent in a saddle-shape pattern. A number of morphing features suggest that the coordinated movements of the wing and tail support efficient flight, and that the tail may act to modulate wing camber through indirect aeroelastic control. 相似文献
53.
Aulacoscelinae beetles have an ancient relationship with cycads (Cycadophyta: Zamiaceae), which contain highly toxic azoxyglycoside
(AZG) compounds. How these “primitive” leaf beetles deal with such host-derived compounds remains largely unknown. Collections
were made of adult Aulacoscelis appendiculata from Zamia cf. elegantissima in Panama, A. vogti from Dioon edule in Mexico, and Janbechynea paradoxa from Zamia boliviana in Bolivia. Total AZG levels were quantified in both cycad leaves and adult beetles by high performance liquid chromatography
(HPLC). On average, cycad leaves contained between 0.5–0.8% AZG (frozen weight, FW), while adult beetles feeding on the same
leaves contained even higher levels of the compounds (average 0.9–1.5% FW). High AZG levels were isolated from reflex bleeding
secreted at the leg joints when beetles were disturbed. Nuclear magnetic resonance and mass spectroscopy identified two AZGs,
cycasin and macrozamin, in the reflex bleeding; this is the first account of potentially plant-derived compounds in secretions
of the Aulacoscelinae. These data as well as the basal phylogenetic position of the Aulacoscelinae suggest that sequestration
of plant secondary metabolites appeared early in leaf beetle evolution. 相似文献
54.
55.
56.
57.
58.
AC Fry WJ Kraemer F Van Borselen JM Lynch NT Triplett LP Koziris SJ Fleck 《Canadian Metallurgical Quarterly》1994,77(2):941-946
Seventeen weight-trained males were divided into an overtraining group [OT; n = 11; age = 22.0 +/- 0.9 (SE) yr] that weight trained their legs daily for 2 wk with 100% 1 repetition maximum relative intensity on a squat machine and a control group (n = 6; age = 23.7 +/- 2.4 yr) that exercised 1 day/wk with low relative intensity (50% 1 repetition maximum). Test batteries including strength assessments and resting and exercise-induced concentrations of epinephrine and norepinephrine were conducted at the beginning, middle, and end (tests 1-3, respectively) of the study. Strength capabilities decreased by test 3 for the OT group (P < 0.05). Resting catecholamine concentrations did not change for either group during the study, whereas exercise-induced concentrations of both epinephrine (test 1 = 3,407.9 +/- 666.6 pmol/l, test 2 = 7,563.7 +/- 1,210.6 pmol/l, test 3 = 6,931.6 +/- 919.3 pmol/l) and norepinephrine (test 1 = 42.9 +/- 7.4 nmol/l, test 2 = 70.0 +/- 8.8 nmol/l, test 3 = 85.2 +/- 14.5 nmol/l) significantly increased by tests 2 and 3 for only the OT group. Correlation coefficients suggested decreased responsitivity of skeletal muscle to sympathetic nervous system activity. It appears that altered exercise-induced sympathetic nervous system activity accompanies high relative intensity resistance exercise overtraining and may be among the initial responses to the onset of the previously theoretical sympathetic overtraining syndrome. 相似文献
59.
60.