全文获取类型
收费全文 | 14182篇 |
免费 | 1469篇 |
国内免费 | 4篇 |
专业分类
15655篇 |
出版年
2022年 | 103篇 |
2021年 | 171篇 |
2020年 | 120篇 |
2019年 | 134篇 |
2018年 | 190篇 |
2017年 | 165篇 |
2016年 | 271篇 |
2015年 | 488篇 |
2014年 | 470篇 |
2013年 | 675篇 |
2012年 | 813篇 |
2011年 | 746篇 |
2010年 | 489篇 |
2009年 | 462篇 |
2008年 | 667篇 |
2007年 | 665篇 |
2006年 | 616篇 |
2005年 | 632篇 |
2004年 | 615篇 |
2003年 | 589篇 |
2002年 | 565篇 |
2001年 | 276篇 |
2000年 | 278篇 |
1999年 | 251篇 |
1998年 | 204篇 |
1997年 | 174篇 |
1996年 | 166篇 |
1995年 | 171篇 |
1994年 | 113篇 |
1993年 | 152篇 |
1992年 | 219篇 |
1991年 | 208篇 |
1990年 | 207篇 |
1989年 | 192篇 |
1988年 | 163篇 |
1987年 | 195篇 |
1986年 | 161篇 |
1985年 | 165篇 |
1984年 | 170篇 |
1983年 | 140篇 |
1982年 | 139篇 |
1981年 | 142篇 |
1980年 | 126篇 |
1979年 | 106篇 |
1978年 | 105篇 |
1977年 | 111篇 |
1976年 | 87篇 |
1975年 | 91篇 |
1974年 | 99篇 |
1973年 | 96篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
62.
63.
64.
65.
66.
67.
Introduction: mucopolysaccharides 总被引:1,自引:0,他引:1
K Meyer 《Federation proceedings》1966,25(3):1032-1034
68.
69.
Curtis E. Meyer 《Applied microbiology》1966,14(4):511-512
The isolation and characterization of antibiotic U-21,963 are discussed. This compound is a highly unsaturated monobasic acid with the molecular formula C(9)H(7)NO(3). The molecular weight is 177. It is dextrorotatory, [alpha](D) = +138 degrees , and has a pK(a) of 5.1. The ultraviolet absorption spectrum, which showed a maximum at 223 mmu (epsilon = 15,115), indicates unsaturation alpha-beta to the carboxyl group, and the infrared spectrum suggests the presence of an acetylenic group. Explosive decomposition of U-21,963 at 97 C conforms with the latter. U-21,963 is relatively insoluble in water, but readily soluble in ethyl alcohol, acetone, and halogenated hydrocarbons. 相似文献
70.
Pulmonary gas exchange in panting dogs 总被引:1,自引:0,他引:1
Pulmonary gas exchange during panting was studied in seven conscious dogs (32 kg mean body wt) provided with a chronic tracheostomy and an exteriorized carotid artery loop. The animals were acutely exposed to moderately elevated ambient temperature (27.5 degrees C, 65% relative humidity) for 2 h. O2 and CO2 in the tracheostomy tube were continuously monitored by mass spectrometry using a special sample-hold phase-locked sampling technique. PO2 and PCO2 were determined in blood samples obtained from the carotid artery. During the exposure to heat, central body temperature remained unchanged (38.6 +/- 0.6 degrees C) while all animals rapidly switched to steady shallow panting at frequencies close to the resonant frequency of the respiratory system. During panting, the following values were measured (means +/- SD): breathing frequency, 313 +/- 19 breaths/min; tidal volume, 167 +/- 21 ml; total ventilation, 52 +/- 9 l/min; effective alveolar ventilation, 5.5 +/- 1.3 l/min; PaO2, 106.2 +/- 5.9 Torr; PaCO2, 27.2 +/- 3.9 Torr; end-tidal-arterial PO2 difference [(PE' - Pa)O2], 26.0 +/- 5.3 Torr; and arterial-end-tidal PCO2 difference, [(Pa - PE')CO2], 14.9 +/- 2.5 Torr. On the basis of the classical ideal alveolar air approach, parallel dead-space ventilation accounted for 54% of alveolar ventilation and 66% of the (PE' - Pa)O2 difference. But the steepness of the CO2 and O2 expirogram plotted against expired volume suggested a contribution of series in homogeneity due to incomplete gas mixing. 相似文献