全文获取类型
收费全文 | 16914篇 |
免费 | 871篇 |
国内免费 | 3333篇 |
专业分类
林业 | 361篇 |
农学 | 3287篇 |
基础科学 | 925篇 |
3168篇 | |
综合类 | 8663篇 |
农作物 | 1813篇 |
水产渔业 | 236篇 |
畜牧兽医 | 596篇 |
园艺 | 209篇 |
植物保护 | 1860篇 |
出版年
2024年 | 129篇 |
2023年 | 341篇 |
2022年 | 545篇 |
2021年 | 586篇 |
2020年 | 670篇 |
2019年 | 668篇 |
2018年 | 568篇 |
2017年 | 749篇 |
2016年 | 852篇 |
2015年 | 735篇 |
2014年 | 817篇 |
2013年 | 1100篇 |
2012年 | 1262篇 |
2011年 | 1109篇 |
2010年 | 1028篇 |
2009年 | 1000篇 |
2008年 | 879篇 |
2007年 | 1028篇 |
2006年 | 870篇 |
2005年 | 827篇 |
2004年 | 608篇 |
2003年 | 584篇 |
2002年 | 459篇 |
2001年 | 465篇 |
2000年 | 403篇 |
1999年 | 338篇 |
1998年 | 313篇 |
1997年 | 268篇 |
1996年 | 294篇 |
1995年 | 229篇 |
1994年 | 201篇 |
1993年 | 200篇 |
1992年 | 213篇 |
1991年 | 156篇 |
1990年 | 154篇 |
1989年 | 121篇 |
1988年 | 91篇 |
1987年 | 67篇 |
1986年 | 47篇 |
1985年 | 16篇 |
1984年 | 26篇 |
1982年 | 14篇 |
1981年 | 15篇 |
1980年 | 9篇 |
1979年 | 9篇 |
1978年 | 12篇 |
1977年 | 12篇 |
1976年 | 15篇 |
1962年 | 9篇 |
1955年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
101.
利用东北农作区58个气象站点1961—2010年的逐日气象数据,基于Simulation of Evapotranspiration of Applied Water(SIMETAW)模型分析气候变化背景下东北农作区春小麦生育期内作物需水量(Crop evapotranspiration,ETc)和灌溉需要量(Evapotranspiration of applied water,ETaw),以及典型站点春小麦的灌溉需求指数(Irrigation demand index,IDI)的时空变化特征。结果表明:近50年来,东北农作区日平均温度呈显著上升趋势,平均降水量下降趋势不明显,平均太阳辐射及作物蒸散量呈显著下降趋势。春小麦生育期作物需水量和灌溉需要量呈下降趋势,其分布均表现为西多东少。50年来春小麦作物生育期需水量下降主要集中于松辽及兴安岭南部地区,东部地区变化趋势不明显;生育期灌溉需要量下降集中于松辽及兴安岭地区,三江平原地区略有增加,长白山地区多年保持平稳。 相似文献
102.
S. Narayanan P. V. V. Prasad A. K. Fritz D. L. Boyle B. S. Gill 《Journal of Agronomy and Crop Science》2015,201(3):206-218
High temperature is a major environmental factor that limits wheat (Triticum aestivum L.) productivity. Climate models predict greater increases in night‐time temperature than in daytime temperature. The objective of this research was to compare the effects of high daytime and high night‐time temperatures during anthesis on physiological (chlorophyll fluorescence, chlorophyll concentration, leaf level photosynthesis, and membrane damage), biochemical (reactive oxygen species (ROS) concentration and antioxidant capacity in leaves), growth and yield traits of wheat genotypes. Winter wheat genotypes (Ventnor and Karl 92) were grown at optimum temperatures (25/15 °C, maximum/minimum) until the onset of anthesis. Thereafter, plants were exposed to high night‐time (HN, 25/24 °C), high daytime (HD, 35/15 °C), high daytime and night‐time (HDN, 35/24 °C) or optimum temperatures for 7 days. Compared with optimum temperature, HN, HD and HDN increased ROS concentration and membrane damage and decreased antioxidant capacity, photochemical efficiency, leaf level photosynthesis, seed set, grain number and grain yield per spike. Impact of HN and HD was similar on all traits. Greater impact on seed set, grain number and grain yield per spike was observed at HDN compared with HN and HD. These results suggest that HN and HD during anthesis cause damage of a similar magnitude to winter wheat. 相似文献
103.
104.
大白菜花青素含量及色差指标相关性研究 总被引:3,自引:0,他引:3
为了探寻大白菜花青素含量快速测定的方法,本文利用pH差计法和色差仪分别测定了‘城阳青’(普通大白菜)、‘秋宝黄’(黄心白菜)和‘彩凤’3个不同叶色大白菜品种花青素含量以及色差指标,并对6个色泽参数与花青素含量进行了相关和回归分析。结果表明:6个色泽参数均能反映白菜叶片间叶色的细微变化,‘城阳青’和‘秋宝黄’不含花青素,紫色白菜‘彩凤’的花青素主要分布于由外向内的第1~4层叶片。色泽参数L,b,h和C分别与花青素含量呈极显著或显著负相关关系(相关系数分别为-0.85**,-0.58**,-0.49*,-0.58**)。以色泽参数值L、a、h与花青素含量建立了多元回归方程:y=90.24-1.07x1+5.65x2-142.71x3(x1为L值,x2为a值,x3为h值,y为花青素含量),该回归方程相关系数为0.9629。通过色差计依据建立的回归方程可快速测定紫色大白菜花青素的含量。 相似文献
105.
106.
对东京野茉莉花色成分进行了初步的探究。结果表明:通过特征颜色反应和光谱扫描说明了其花瓣细胞内有异黄酮、儿茶精类,还有叶绿素a、b,可能含有胡萝卜素、黄酮类化合物,以及无色花色素,可能不含查耳酮或橙酮。 相似文献
107.
Unpredictable temperatures and rainfall associated with climate change are expected to affect wheat (Triticum aestivum L.) production in various countries. The development of climate-resilient spring wheat cultivars able to maintain grain yield and quality is essential to food security and economic returns. We tested 54 CIMMYT spring bread wheat genotypes, developed and/or released over a span of 50 years, in the field for two years under optimum sowing dates, as well as using two delayed sowing dates to expose crops to medium and severe heat-stress conditions. The grain yield and yield components were severely affected as the heat-stress increased. Two contrasting groups of 10 lines each were identified to determine the effect of heat-stress on bread-making quality. The first set included entries that produced high yields in optimal conditions and maintained higher yields under heat-stress (superior-yielding lines), while the second set included genotypes that did not perform well in the environment with high temperature (inferior-yielding lines). We identified genotypes exhibiting bread-making quality stability, as well as the quality traits that had higher correlation with the loaf volume in the environment without stress and under heat-stress. Of all the quality traits tested, dough extensibility (AlvL) and grain protein content had a significant influence in heat-stress adaptation. Most of the lines from the superior-yielding group were also able to maintain and even improve quality characteristics under heat-stress and therefore, could be used as parents in breeding to develop high-yielding and stable quality wheat varieties. 相似文献
108.
109.
110.