全文获取类型
收费全文 | 544368篇 |
免费 | 60784篇 |
国内免费 | 354篇 |
专业分类
605506篇 |
出版年
2021年 | 4426篇 |
2018年 | 5550篇 |
2017年 | 5377篇 |
2016年 | 7445篇 |
2015年 | 9527篇 |
2014年 | 11241篇 |
2013年 | 16141篇 |
2012年 | 18050篇 |
2011年 | 18417篇 |
2010年 | 12319篇 |
2009年 | 11265篇 |
2008年 | 15844篇 |
2007年 | 16377篇 |
2006年 | 15343篇 |
2005年 | 14581篇 |
2004年 | 14400篇 |
2003年 | 13707篇 |
2002年 | 13212篇 |
2001年 | 28433篇 |
2000年 | 28258篇 |
1999年 | 22040篇 |
1998年 | 6798篇 |
1997年 | 7341篇 |
1996年 | 6790篇 |
1995年 | 6236篇 |
1994年 | 6020篇 |
1993年 | 5996篇 |
1992年 | 17079篇 |
1991年 | 16314篇 |
1990年 | 15723篇 |
1989年 | 15231篇 |
1988年 | 13924篇 |
1987年 | 12948篇 |
1986年 | 12049篇 |
1985年 | 11832篇 |
1984年 | 9679篇 |
1983年 | 8093篇 |
1982年 | 6002篇 |
1981年 | 5385篇 |
1980年 | 5107篇 |
1979年 | 8953篇 |
1978年 | 6821篇 |
1977年 | 6285篇 |
1976年 | 5649篇 |
1975年 | 6245篇 |
1974年 | 6767篇 |
1973年 | 6554篇 |
1972年 | 5982篇 |
1971年 | 5429篇 |
1970年 | 4683篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
891.
892.
893.
894.
895.
896.
E R Morey-Holton B P Halloran L P Garetto S B Doty 《Journal of applied physiology》2000,88(4):1303-1309
The rat has been used extensively as an animal model to study the effects of spaceflight on bone metabolism. The results of these studies have been inconsistent. On some missions, bone formation at the periosteal bone surface of weight-bearing bones is impaired and on others it is not, suggesting that experimental conditions may be an important determinant of bone responsiveness to spaceflight. To determine whether animal housing can affect the response of bone to spaceflight, we studied young growing (juvenile) rats group housed in the animal enclosure module and singly housed in the research animal holding facility under otherwise identical flight conditions (Spacelab Life Science 1). Spaceflight reduced periosteal bone formation by 30% (P < 0.001) and bone mass by 7% in single-housed animals but had little or no effect on formation (-6%) or mass (-3%) in group-housed animals. Group housing reduced the response of bone to spaceflight by as much as 80%. The data suggest that housing can dramatically affect the skeletal response of juvenile rats to spaceflight. These observations explain many of the discrepancies in previous flight studies and emphasize the need to study more closely the effects of housing (physical-social interaction) on the response of bone to the weightlessness of spaceflight. 相似文献
897.
The mapping of genetic loci within organisms has been accelerated by the advent of Radiation Hybrid (RH) panels. These panels
are available for humans and non-humans including mice, baboon, rat, and canine. This article contains a general protocol
for the use of the Genebridge 4 whole genome RH panel to map a human locus. This protocol may also be adjusted to suit the
other RH panels currently available. 相似文献
898.
899.
900.
By combined application of chemical pretreatments, capillary gas-chromatography and mass spectrometry it was possible to enlighten the structure of atypical fatty acids with hydroxy groups and cyclopropane rings under the use of only a few of reference substances. The direct alkaline saponification of the sample with liberation of fatty acids and following methylation with boron trifluoride/methanol or diazomethane was proved to be the best method regarding to precision and speed of the sample cleanup. 相似文献