全文获取类型
收费全文 | 790篇 |
免费 | 73篇 |
国内免费 | 29篇 |
出版年
2022年 | 6篇 |
2021年 | 9篇 |
2020年 | 7篇 |
2019年 | 10篇 |
2018年 | 17篇 |
2017年 | 10篇 |
2016年 | 18篇 |
2015年 | 24篇 |
2014年 | 28篇 |
2013年 | 40篇 |
2012年 | 34篇 |
2011年 | 51篇 |
2010年 | 33篇 |
2009年 | 28篇 |
2008年 | 25篇 |
2007年 | 22篇 |
2006年 | 31篇 |
2005年 | 32篇 |
2004年 | 24篇 |
2003年 | 24篇 |
2002年 | 25篇 |
2001年 | 25篇 |
2000年 | 15篇 |
1999年 | 15篇 |
1998年 | 15篇 |
1997年 | 14篇 |
1996年 | 9篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1993年 | 6篇 |
1992年 | 15篇 |
1990年 | 9篇 |
1989年 | 8篇 |
1988年 | 13篇 |
1987年 | 14篇 |
1986年 | 6篇 |
1985年 | 14篇 |
1984年 | 15篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1981年 | 11篇 |
1980年 | 7篇 |
1979年 | 8篇 |
1978年 | 9篇 |
1977年 | 12篇 |
1975年 | 6篇 |
1973年 | 8篇 |
1972年 | 10篇 |
1971年 | 8篇 |
1949年 | 6篇 |
排序方式: 共有892条查询结果,搜索用时 15 毫秒
811.
812.
813.
A. D. Pickering 《Journal of fish biology》1986,29(3):335-347
Differential blood cell counts were monitored in three different strains of brown trout through three separate spawning seasons. A consistent elevation in the number of circulating erythrocytes was observed in sexually mature male fish (compared with immature fish of either sex) during October-December of each season. A marked lymphocytopenia also occurred during October in mature fish of both sexes with lymphocyte numbers still being significantly depressed as late as March the following year. It is concluded that the use of haematology as a technique for assessing the state of health of salmonid fish must take into account the sex and state of maturation of the fish. The possible consequences of changes in haematology during sexual maturation are discussed in terms of respiratory function and defence against pathogenic challenge. 相似文献
814.
815.
816.
中国社会经济快速转型背景下土地利用变化所引发的环境问题被广泛关注。以土地利用现状遥感监测数据和统计资料为数据源,借助ArcGIS和SIMCA-P软件平台,基于"三生"空间视角,通过生态环境质量指数测度了1980-2018年甘肃省土地利用转型的生态环境效应,并运用偏最小二乘法揭示生态环境质量演变的驱动机制。研究发现:(1)"三生"空间结构演化和地域分异显著。生产、生活空间集中分布于河西走廊、陇中和陇东黄土高原并呈扩张态势;生态空间主要分布于陇南山地、甘南高原、祁连山地和河西走廊以北地带且整体呈缩减趋势;生产、生活空间的增长源于对生态空间的侵占。(2)生态环境质量改善和恶化趋势并存,整体上经历了先下降后上升的"U"形演化过程;空间上呈"东南高-西北低"的分布特征,空间格局演化具有明显的集聚性。(3)生态建设、科技进步等对生态环境改善具有明显的促进作用;而人口增加、社会消费水平提升在一定程度上加剧了生态环境压力;对外贸易对生态环境的影响具有双面性。 相似文献
817.
N Ergene E C Pickering 《Quarterly journal of experimental physiology and cognate medical sciences》1978,63(1):77-81
Reducing the dietary N intake of sheep resulted in a significant fall in GFR with no change in RPF. Intravenous of urea for 19-46 h had no effect on the high protein diet but on the low protein diet GFR and FF were increased to values approaching those observed on the high protein diet. On the low protein diet GFR was unaffected by infusion of urea for 4 h or of saline alone for 30 h. It is suggested that the observed changes in GFR are associated with changes in the quantity of protein passing to the abomasum and small intestine. 相似文献
818.
Investigations were made of the variation in copper toleranceamong homokaryons and dikaryons originating from one dikaryoticisolate of Polyporus palustris, as shown by their growth onnutrient agar containing copper sulphate, usually at 0.32 Mconcentration (c. 8 per cent of CuSO4.5H2O). Homokaryons obtainedby monobasidiospore isolation were crossed and further homokaryonsobtained in the same way. Selection for copper tolerance gavean increase in the second generation, but no further increasein the third; whilst selection for copper sensitivity gave substantialincreases in both second and third generations. It is concludedthat copper tolerance in this fungus is controlled by a numberof genes. It was found that, in this fungus, the copper toleranceof a dikaryon was substantially greater than that of eitherof its constituent homokaryons. It was also found that differentisolates of P. palustris varied very widely in copper tolerance. 相似文献
819.
820.
R B Pickering D J Conces E M Braunstein F Yurco 《American journal of physical anthropology》1990,83(1):49-55
Computed tomography allows cross-sectional imaging of anthropological as well as clinical subjects. Recently, technical innovations have made three-dimensional reconstruction of these images feasible. We performed two-dimensional and three-dimensional computed tomography of a Late Period Egyptian mummy to reexamine findings seen on previous radiographic studies and to evaluate the usefulness of these techniques in paleopathology. Two-dimensional images provided excellent anatomic detail. There was graphic depiction of the mummification process that corroborated information previously obtained from Egyptological studies. Three-dimensional reconstruction provided images of facial features as if the mummy had been unwrapped. Three-dimensional computed tomography is a useful method of nondestructively evaluating paleopathological remains, and it may yield information not obtainable by any other means. 相似文献