全文获取类型
收费全文 | 51545篇 |
免费 | 2822篇 |
国内免费 | 34篇 |
专业分类
林业 | 1909篇 |
农学 | 1940篇 |
基础科学 | 282篇 |
6431篇 | |
综合类 | 8315篇 |
农作物 | 1744篇 |
水产渔业 | 3005篇 |
畜牧兽医 | 27022篇 |
园艺 | 644篇 |
植物保护 | 3109篇 |
出版年
2020年 | 439篇 |
2019年 | 540篇 |
2018年 | 929篇 |
2017年 | 963篇 |
2016年 | 860篇 |
2015年 | 693篇 |
2014年 | 869篇 |
2013年 | 1970篇 |
2012年 | 1529篇 |
2011年 | 1858篇 |
2010年 | 1292篇 |
2009年 | 1193篇 |
2008年 | 1792篇 |
2007年 | 1696篇 |
2006年 | 1580篇 |
2005年 | 1438篇 |
2004年 | 1444篇 |
2003年 | 1412篇 |
2002年 | 1217篇 |
2001年 | 1950篇 |
2000年 | 2016篇 |
1999年 | 1527篇 |
1998年 | 587篇 |
1997年 | 518篇 |
1996年 | 457篇 |
1995年 | 619篇 |
1994年 | 533篇 |
1993年 | 465篇 |
1992年 | 1167篇 |
1991年 | 1228篇 |
1990年 | 1195篇 |
1989年 | 1107篇 |
1988年 | 1065篇 |
1987年 | 1094篇 |
1986年 | 1040篇 |
1985年 | 970篇 |
1984年 | 812篇 |
1983年 | 693篇 |
1982年 | 426篇 |
1979年 | 649篇 |
1978年 | 504篇 |
1977年 | 444篇 |
1976年 | 413篇 |
1975年 | 454篇 |
1974年 | 531篇 |
1973年 | 515篇 |
1972年 | 532篇 |
1971年 | 456篇 |
1970年 | 427篇 |
1969年 | 470篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
71.
A mathematical model was developed of the dynamics of a plant virus disease within a spatially-referenced lattice of fields of a host crop. The model can be applied to crops in continuous, contiguous cultivation such as tropical irrigated rice. Disease progress in each field of the host crop was assumed to be logistic and determined by incidence within the field itself as well as incidence in neighbouring fields, depending on the gradient of disease spread. The frequency distribution of planting dates (represented by the proportion of the total number of fields planted in successive months) was assumed to follow a normal distribution and the variance of planting date was used as a measure of cropping asynchrony. Analysis of the model revealed that disease incidence within the lattice (i.e. mean incidence over all fields) depended upon the infection efficiency, the slope of the dispersal gradient, and the variance in planting date. Disease endemicity depended mainly on planting date variance and disease persisted in the lattice if this variance exceeded a certain threshold. Above the threshold for persistence, the response of mean disease incidence to planting date variance was non-linear and the region of greatest sensitivity was closest to the threshold. Thus, disease systems that show moderate rather than high cropping asynchrony are more likely to be influenced by changes in the variance of planting date. Implications for the area-wide management of rice tungro virus disease are discussed. 相似文献
72.
Over the last decade, algae have been explored as alternative and sustainable protein sources for a balanced diet and more recently, as a potential source of algal-derived bioactive peptides with potential health benefits. This review will focus on the emerging processes for the generation and isolation of bioactive peptides or cryptides from algae, including: (1) pre-treatments of algae for the extraction of protein by physical and biochemical methods; and (2) methods for the generation of bioactive including enzymatic hydrolysis and other emerging methods. To date, the main biological properties of the peptides identified from algae, including anti-hypertensive, antioxidant and anti-proliferative/cytotoxic effects (for this review, anti-proliferative/cytotoxic will be referred to by the term anti-cancer), assayed in vitro and/or in vivo, will also be summarized emphasizing the structure–function relationship and mechanism of action of these peptides. Moreover, the use of in silico methods, such as quantitative structural activity relationships (QSAR) and molecular docking for the identification of specific peptides of bioactive interest from hydrolysates will be described in detail together with the main challenges and opportunities to exploit algae as a source of bioactive peptides. 相似文献
73.
74.
75.
76.
The oral introduction of 0·5 g histamine as the diphosphate into the rumen of sheep produced no effect on the physiological condition of the animals. The feeding of histamine, as the dihydrochloride, in levels up to 1 g/day to sheep on silage diets did not affect the dry-matter intake. 相似文献
77.
WRIGHT LD CRESSON EL SKEGGS HR PECK RL WOLF DE WOOD TR VALIANT J FOLKERS K 《Science (New York, N.Y.)》1951,114(2972):635-636
78.
79.
80.