全文获取类型
收费全文 | 3238篇 |
免费 | 414篇 |
国内免费 | 178篇 |
出版年
2023年 | 12篇 |
2022年 | 19篇 |
2021年 | 25篇 |
2020年 | 16篇 |
2019年 | 16篇 |
2018年 | 23篇 |
2017年 | 15篇 |
2016年 | 25篇 |
2015年 | 18篇 |
2014年 | 32篇 |
2013年 | 26篇 |
2012年 | 311篇 |
2011年 | 329篇 |
2010年 | 56篇 |
2009年 | 35篇 |
2008年 | 288篇 |
2007年 | 270篇 |
2006年 | 231篇 |
2005年 | 240篇 |
2004年 | 265篇 |
2003年 | 244篇 |
2002年 | 209篇 |
2001年 | 180篇 |
2000年 | 246篇 |
1999年 | 109篇 |
1998年 | 22篇 |
1997年 | 25篇 |
1996年 | 28篇 |
1995年 | 29篇 |
1994年 | 23篇 |
1993年 | 17篇 |
1992年 | 27篇 |
1991年 | 23篇 |
1990年 | 20篇 |
1989年 | 16篇 |
1988年 | 11篇 |
1987年 | 12篇 |
1983年 | 9篇 |
1972年 | 11篇 |
1970年 | 11篇 |
1958年 | 21篇 |
1957年 | 16篇 |
1956年 | 15篇 |
1955年 | 11篇 |
1954年 | 11篇 |
1953年 | 13篇 |
1952年 | 14篇 |
1951年 | 14篇 |
1949年 | 9篇 |
1948年 | 9篇 |
排序方式: 共有3830条查询结果,搜索用时 31 毫秒
41.
胶质细胞源神经营养因子陈哲宇何成王成海(第二军医大学神经生物教研室,上海200433)关键词胶质细胞源神经营养因子多巴胺能神经元运动神经元神经营养因子是指能够促进神经细胞存活、生长和分化的一类蛋白质。胶质细胞源神经营养因子(GDNF),因其最初从大鼠... 相似文献
42.
<正>免疫接种预防传染病是医学科学的突出成就之一。许多危及生命的传染病的流行,之所以逐渐减少,固然是许多因素(例如卫生设备、食品制作、营养状态的改善和抗生素的发展)共同作用的结果,但起主要作用的还是免疫预防。许多在10~20年以前还在增多着的传染病,由于进行了免疫接种,现 相似文献
43.
Movement of Kinetin and Gibberellic Acid in Leaf Petioles during Water Stress-induced Abscission in Cotton
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Movement of [14C]kinetin and [14C]gibberellic acid was examined in cotton (Gossypium hirsutum L.) cotyledonary petiole sections independent of label uptake or exit from the tissue. Sections 20 millimeters in length were taken from well watered, stressed, and poststressed plants. Transport capacity was determined using a pulse-chase technique. Movement of both kinetin and gibberellic acid was found to be nonpolar with a velocity of 1 millimeter per hour or less, suggesting passive diffusion. Neither water stress nor anaerobic conditions during transport of labeled material affected the transport capacity of the petioles. 相似文献
44.
大豆磷脂组成的研究 Ⅰ.磷脂组成的薄层色谱分析 总被引:4,自引:0,他引:4
本文采用一组酸性氯仿甲醇溶剂体系和碱性较强的硅胶薄板,经单向薄层色谱能将制备脂质体用的大豆磷脂多种磷脂组分很好地分开。在同一色谱条件下用标准磷脂进行检测,用薄层扫描进行定量,从而解决了只用微量样品(约30微克)即可直接对多种磷脂组分进行定性和定量分析的问题。 相似文献
45.
46.
Initial organic products of assimilation of [N]ammonium and [N]nitrate by tobacco cells cultured on different sources of nitrogen
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Glutamine is the first major organic product of assimilation of 13NH4+ by tobacco (Nicotiana tabacum L. cv. Xanthi) cells cultured on nitrate, urea, or ammonium succinate as the sole source of nitrogen, and of 13NO3− by tobacco cells cultured on nitrate. The percentage of organic 13N in glutamate, and subsequently, alanine, increases with increasing periods of assimilation. 13NO3−, used for the first time in a study of assimilation of nitrogen, was purified by new preparative techniques. During pulse-chase experiments, there is a decrease in the percentage of 13N in glutamine, and a concomitant increase in the percentage of 13N in glutamate and alanine. Methionine sulfoximine inhibits the incorporation of 13N from 13NH4+ into glutamine more extensively than it inhibits the incorporation of 13N into glutamate, with cells grown on any of the three sources of nitrogen. Azaserine inhibits glutamate synthesis extensively when 13NH4+ is fed to cells cultured on nitrate. These results indicate that the major route for assimilation of 13NH4+ is the glutamine synthetase-glutamate synthase pathway, and that glutamate dehydrogenase also plays a role, but a minor one. Methionine sulfoximine inhibits the incorporation of 13N from 13NO3− into glutamate more strongly than it inhibits the incorporation of 13N into glutamine, suggesting that the assimilation of 13NH4+ derived from 13NO3− may be mediated solely by the glutamine synthetase-glutamate synthase pathway. 相似文献
47.
48.
49.
50.
Enhanced Sensitivity to Ethylene in Nitrogen- or Phosphate-Starved Roots of Zea mays L. during Aerenchyma Formation 总被引:8,自引:5,他引:3
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Adventitious roots of maize (Zea mays L. cv TX 5855), grown in a well-oxygenated nutrient solution, were induced to form cortical gas spaces (aerenchyma) by temporarily omitting nitrate and ammonium (-N), or phosphate (-P), from the solution. Previously this response was shown (MC Drew, CJ He, PW Morgan [1989] Plant Physiology 91: 266-271) to be associated with a slower rate of ethylene biosynthesis, contrasting with the induction of aerenchyma by hypoxia during which ethylene production is strongly stimulated. In the present paper, we show that aerenchyma formation induced by nutrient starvation was blocked, under noninjurious conditions, by addition of low concentrations of Ag+, an inhibitor of ethylene action, or of aminoethoxyvinyl glycine, an inhibitor of ethylene biosynthesis. When extending roots were exposed to low concentrations of ethylene in air sparged through the nutrient solution, N or P starvation enhanced the sensitivity to exogenous ethylene at concentrations as low as 0.05 microliters ethylene per liter air, promoting a more rapid and extensive formation of aerenchyma than in unstarved roots. We conclude that temporary deprivation of N or P enhances the sensitivity of ethylene-responsive cells of the root cortex, leading to cell lysis and aerenchyma. 相似文献