全文获取类型
收费全文 | 2315篇 |
免费 | 156篇 |
国内免费 | 432篇 |
出版年
2024年 | 8篇 |
2023年 | 29篇 |
2022年 | 41篇 |
2021年 | 53篇 |
2020年 | 50篇 |
2019年 | 60篇 |
2018年 | 37篇 |
2017年 | 63篇 |
2016年 | 50篇 |
2015年 | 57篇 |
2014年 | 55篇 |
2013年 | 95篇 |
2012年 | 77篇 |
2011年 | 84篇 |
2010年 | 88篇 |
2009年 | 102篇 |
2008年 | 97篇 |
2007年 | 131篇 |
2006年 | 146篇 |
2005年 | 126篇 |
2004年 | 104篇 |
2003年 | 126篇 |
2002年 | 93篇 |
2001年 | 96篇 |
2000年 | 84篇 |
1999年 | 79篇 |
1998年 | 67篇 |
1997年 | 69篇 |
1996年 | 57篇 |
1995年 | 50篇 |
1994年 | 66篇 |
1993年 | 53篇 |
1992年 | 62篇 |
1991年 | 39篇 |
1990年 | 49篇 |
1989年 | 46篇 |
1988年 | 33篇 |
1987年 | 39篇 |
1986年 | 43篇 |
1985年 | 38篇 |
1984年 | 26篇 |
1983年 | 15篇 |
1982年 | 26篇 |
1981年 | 13篇 |
1980年 | 11篇 |
1979年 | 12篇 |
1978年 | 11篇 |
1977年 | 8篇 |
1976年 | 16篇 |
1972年 | 7篇 |
排序方式: 共有2903条查询结果,搜索用时 875 毫秒
21.
Motility and orientation has been studied in the unicellular photosynthetic flagellate, Euglena gracilis, using real time image analysis capable of tracking up to 200 cells simultaneously in the slow rotating centrifuge microscope (NIZEMI) which allows one to observe the cells' swimming behavior during centrifugation accelerations between 1 g and 5 g. At 1 g the cells show a weak negative gravitaxis, which increases significantly at higher accelerations up to about 3 g. Though most cells were capable of swimming even against an acceleration of 4.5 g, the degree of gravitaxis decreased and some of the cells were passively moved downward by the acceleration force; this is true for most cells at 5 g. The velocity of cells swimming against 1 g is about 10% lower than that of cells swimming in other directions. The velocity decreases even more drastically in cells swimming against higher acceleration forces than those at 1 g. The degree of gravitactic orientation drastically decreases after short exposure to artificial UV radiation which indicates that gravitaxis may be due to an active physiological perception rather than a physical effect such as an asymmetry of the center of gravity within the cell.
Offprint requests to: D.-P. Häder 相似文献
22.
23.
神农香菊干花净油成分的研究 总被引:5,自引:2,他引:3
王国亮;王金凤;张红旗;贾卫疆;袁焱明 《武汉植物学研究》1986,4(1):65-68
神农香菊全草提取的香浸膏香气浓郁独特,可用于调配多种高档化妆用香精,也可直接用于饮料中,在香精香料工业中具有较大的实用价值。本文首次报告了我们用毛细管气相色谱仪和色谱/质谱/计算机联用分析仪,对神农香菊干花净油成分进行分析的初步结果。鉴定出的已知成分包括脂肪族类,含氧或非含氧的单萜及倍半萜类化合物32个。 相似文献
24.
The effect of air-borne ammonium sulphate onPinus nigra var.maritima in the Netherlands 总被引:1,自引:0,他引:1
Summary As a result of air pollution, considerable deposition of ammonium sulphate occurs on vegetation and soil in the vicinity of chicken farms and fields dressed with animal slurry. A clear relation exists between this ammonium sulphate deposition and the distance to certain agricultural activities. Field investigations and ecophysiological experiments both show that the needles ofPinus nigra var.maritima (Ait.) Melville take up ammonium and excrete potassium, magnesium and calcium. This often results in potassium and/or magnesium deficiencies and may lead to premature shedding of needles. The high levels of nitrogen in the needles are strongly correlated to fungal diseases.Whether the observed cation leaching will result in disturbed nutrient budgets depends mainly on soil conditions. Leaching of K, Mg and Ca from the soil, caused by ammonium sulphate, may further inhibit nutrient uptake.Field investigations show a clear correlation between increased ratios of NH4 to K, Mg and Ca in the soil solution and the damage to pine forests. 相似文献
25.
Hector Lozoya-Saldana William O. Dawson T. Murashige 《Plant Cell, Tissue and Organ Culture》1985,(1):41-48
Although both ribavirin (1--ribofuranosyl-1,2,4-triazole-3carboxamide) and adenine arabinoside inhibited the multiplication of tobacco mosaic virus (TMV) in mechanically inoculated leaf tissues, neither chemical inhibited virus multiplication in unorganized tobacco callus after in vitro inoculation. The adenine deaminase inhibitor, pentostatin, did not increase the activity of adenine arabinoside in cultured cells. Several different developmental conditions and media did not increase the ability of either chemical to eradicate the virus from tobacco tissue cultures. However, the virus was eradicated from TMV-infected callus when grown in the presence of combinations of ribavirin and adenine arabinoside in shoot inducing medium. 相似文献
26.
27.
本文以沙田柚为材料,对其染色体组型及带型进行了观察分析。组型分析:染色体数目2n=18,根据染色体的相对长度分成大小染色体两种类型,前者包括1、2、3、4和5对,后者为6、7、8和9对,根据臂比,9对染色体能够被分成中部着丝点和近中着丝点染色体两种类型。即第5、7,9对为亚中部着丝点,其余为中部着丝点,第6对染色体上有随体;Giemsa带型:除第二对染色体只显中间带外,其余都显着丝点带,并在3、4、8对染色体短臂上和2、3、1对染色体长臂上均显端带,第2、3,6对同源染色体之间的C带显示杂合性。 相似文献
28.
29.
30.
毛叶丁香罗勒精油的化学成分分析 总被引:1,自引:0,他引:1
西双版纳引种栽培的毛叶丁香罗勒精油用Finnigan-4510型毛细管色谱/质谱/计算机联用方法进行了化学成分分析,共分离了26个成分,鉴定了其中的16个成分,占全精油含量的98.5%。主要成分是:丁香酚(80.33%);罗勒烯(12.80%);β-毕橙茄烯(4.24%)。 相似文献