全文获取类型
收费全文 | 445443篇 |
免费 | 51504篇 |
国内免费 | 738篇 |
出版年
2018年 | 4163篇 |
2017年 | 4006篇 |
2016年 | 5712篇 |
2015年 | 8252篇 |
2014年 | 9601篇 |
2013年 | 12948篇 |
2012年 | 15335篇 |
2011年 | 15793篇 |
2010年 | 10456篇 |
2009年 | 9493篇 |
2008年 | 13843篇 |
2007年 | 14292篇 |
2006年 | 13429篇 |
2005年 | 12804篇 |
2004年 | 12863篇 |
2003年 | 12007篇 |
2002年 | 11660篇 |
2001年 | 18919篇 |
2000年 | 18849篇 |
1999年 | 15072篇 |
1998年 | 5623篇 |
1997年 | 5633篇 |
1996年 | 5358篇 |
1995年 | 5151篇 |
1994年 | 4851篇 |
1993年 | 4852篇 |
1992年 | 12475篇 |
1991年 | 12434篇 |
1990年 | 12193篇 |
1989年 | 11662篇 |
1988年 | 10833篇 |
1987年 | 10203篇 |
1986年 | 9733篇 |
1985年 | 9500篇 |
1984年 | 7876篇 |
1983年 | 6829篇 |
1982年 | 5135篇 |
1981年 | 4627篇 |
1980年 | 4311篇 |
1979年 | 7349篇 |
1978年 | 5964篇 |
1977年 | 5290篇 |
1976年 | 4959篇 |
1975年 | 5771篇 |
1974年 | 6302篇 |
1973年 | 6120篇 |
1972年 | 5458篇 |
1971年 | 5076篇 |
1970年 | 4274篇 |
1969年 | 4206篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
103.
104.
Samples of marine pleuston were collected from the sea-surface along considerable sections of the track of Eye of the Wind during its 2-year circumnavigational expedition 'Operation Drake' from November 1978 to October 1980. One hundred and eleven of the tow samples contained insects of the genus Halobates . They were assigned to four oceanic species: H. micans, H. sericeus, H. germanus and H. splendens; two coastal species: H. maculatus, H. princeps, and one undescribed species. Various development stages of the oceanic species were found. The locations, time of collection and surface temperatures where sea-skaters were collected are tabulated. Distributional boundaries and population densities of the oceanic species collected are discussed. 相似文献
105.
106.
Rosette and single-element strain gauges were implanted on the tibia in 2 dogs and recordings were made during locomotion on a treadmill. At foot contact and during the swing phase of locomotion, bone strains were low and directions of the principal strains were variable. There was a large shift in the directions of the principal strains at the beginning of the stance phase and bone strains were considerably higher. Peak strain occurred midway through the stance phase. At that time, the maximum principal strain (tension) was directed upwards and anteriorly between 30 and 60 degrees with respect to the long axis of the tibia. These bone strain patterns in the dog are similar to those found in sheep while both differ markedly from those found in humans. 相似文献
107.
Cynthia L. Deitrick Richard E. Katholi David J. Huddleston Kathy Hardiek Lucienne Burrus 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2001,751(2)
Vitamin B6, measured as pyridoxal 5′-phosphate (PLP), is a co-enzyme in the transsulfuration pathway of homocysteine metabolism. Since depletion of PLP has been suggested as an independent risk factor for coronary artery disease, PLP is frequently measured to guide patient care. By a change and utilization of an Aquasil C18 column and the addition of an acetonitrile clean-up gradient to the potassium phosphate, with sodium perchlorate and bisulfite buffer between samples we report the modification of a previously described method for analysis of PLP. The result is a more practical, efficient, reliable and robust method for daily clinical use. We also determined and report that it is critical to protect freshly prepared standard PLP samples from light exposure during assay preparation. 相似文献
108.
109.
110.