全文获取类型
收费全文 | 14420篇 |
免费 | 834篇 |
国内免费 | 1732篇 |
专业分类
林业 | 1745篇 |
农学 | 2267篇 |
基础科学 | 1367篇 |
2664篇 | |
综合类 | 3986篇 |
农作物 | 767篇 |
水产渔业 | 552篇 |
畜牧兽医 | 2138篇 |
园艺 | 423篇 |
植物保护 | 1077篇 |
出版年
2024年 | 20篇 |
2023年 | 130篇 |
2022年 | 372篇 |
2021年 | 556篇 |
2020年 | 500篇 |
2019年 | 470篇 |
2018年 | 349篇 |
2017年 | 462篇 |
2016年 | 535篇 |
2015年 | 701篇 |
2014年 | 645篇 |
2013年 | 729篇 |
2012年 | 825篇 |
2011年 | 1000篇 |
2010年 | 874篇 |
2009年 | 868篇 |
2008年 | 802篇 |
2007年 | 896篇 |
2006年 | 769篇 |
2005年 | 733篇 |
2004年 | 364篇 |
2003年 | 318篇 |
2002年 | 256篇 |
2001年 | 276篇 |
2000年 | 353篇 |
1999年 | 409篇 |
1998年 | 356篇 |
1997年 | 351篇 |
1996年 | 302篇 |
1995年 | 310篇 |
1994年 | 270篇 |
1993年 | 223篇 |
1992年 | 183篇 |
1991年 | 172篇 |
1990年 | 139篇 |
1989年 | 122篇 |
1988年 | 131篇 |
1987年 | 60篇 |
1986年 | 37篇 |
1985年 | 21篇 |
1984年 | 21篇 |
1983年 | 21篇 |
1982年 | 23篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1979年 | 7篇 |
1965年 | 1篇 |
1964年 | 3篇 |
1956年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
101.
Chenze Zhao Jinyu Zhu Juntao Hu Xiaojing Dong Longsheng Sun Xiaojun Zhang Shuyan Miao 《Aquaculture Nutrition》2019,25(3):712-720
The present study was conducted to investigate the effects of Bacillus pumilus on the growth performance, innate immunity and digestive enzymes of the giant freshwater prawn, Macrobrachium rosenbergii. Prawns (mean weight: 1.81 ± 0.01 g) were fed different levels of B. pumilus at doses of 0, 1 × 107, 1 × 108 and 1 × 109 CFU/g to produce one control group and three experimental groups (G1, G2 and G3), respectively. After a 60‐day experimental feeding period, the results showed that the final weight, weight gain rate (WGR) and specific growth rate (SGR) were significantly higher in experimental groups than in the control (p < 0.05), whereas these improvements did not differ significantly (p > 0.05) among experimental groups. The improvements in phagocytic activity, respiratory burst (RBs) activity and the activity of catalase (CAT), nitric oxide synthase (NOS) and acid phosphatase (ACP) were significantly higher in G2 and G3 than in the control and G1 (p < 0.05). Further, the activity of CAT, NOS and ACP significantly increased with an increase in the dietary level of B. pumilus (p < 0.05). The activity of phenoloxidase (PO) in G3 was significantly higher than that in the control (p < 0.05). The activity of amylase was significantly higher in the groups G2 and G3 than that in the control group. G3 improved the activity of protease compared with the control (p < 0.05). In conclusion, the results of this study indicated that the potential use of B. pumilusat a dose of 1 × 108 CFU/g feed could improve the growth, immunity and digestive enzymes of M. rosenbergii. 相似文献
102.
103.
宁波茶文化历史悠久,人文荟萃,从史籍最早有记载的晋代到当代,茶事凡1900多年,留下了诸多体现人情之美的优美茶事,本文以数位与宁波茶事相关的古今人物为研究对象,论述茶事活动蕴含的人情之美。 相似文献
104.
古语说:“水为茶之母,壶为茶之父”。茶壶是茶具的主角之一,自从文艺界人士参与到造壶活动中后,他们以抽象的艺术语言,展现出了别具一格的艺术之美,赋予茶具以蓬勃的生命。本文以清代至现代五位著名画家为例,浅析他们所作茶壶画的艺术之美。 相似文献
105.
民国时期(1912~1949)报刊中充斥着大量广告,其研究价值已为学界广泛承认。茶叶广告作为一种商品广告,在传播形式上具有图文并茂的特点,此外还有系列广告的运用。在创意理念上,茶叶广告以送礼、国货、卫生、科学、品牌等为主题,力求契合顾客的情感诉求或需要。民国报刊中的茶叶广告不仅具有审美价值,也包含鲜明的时代特征。 相似文献
106.
为优化4层层叠式笼养鸭舍舍内环境,基于计算流体动力学(computational fluid dynamics,CFD)对鸭舍内气流场、温度场及CO_2浓度场进行模拟。将笼架简化,考虑其对气流的阻挡作用,将鸭笼及鸭只视为多孔介质。模拟结果显示,进风口为湿帘时,侧墙湿帘与端墙之间存在通风死区,风速低于0.5 m·s~(-1)。进风口为通风小窗时,鸭舍未安装通风小窗区域风速小,CO_2浓度大。改变纵墙湿帘位置对鸭舍结构进行改进,改进后气流不均匀系数降低了17%。改进通风小窗布置发现,提升通风小窗分布均匀性显著降低舍内温差;提升通风小窗安装高度将显著降低舍内CO_2浓度。该研究可为蛋鸭舍结构设计提供参考。 相似文献
107.
108.
109.
Linfeng Wang Joseph W. McFadden Gaiqing Yang Heshui Zhu Hongxia Lian Tong Fu Yu Sun Tengyun Gao Ming Li 《Journal of animal physiology and animal nutrition》2021,105(4):787-796
Melatonin (MT) influences lipid metabolism in animals; however, the mechanistic effect of melatonin on liver fat and abdominal adipose deposition requires further clarity. In order to study the effects of melatonin on lipid metabolism, and hepatic fat and abdominal adipose deposition in animals, twenty Sprague–Dawley (SD) rats of 6 weeks of age with similar bodyweight were randomly divided into two groups: control (CTL) and MT-treated (10 mg/kg/day). During a 60-day experiment, food intake and bodyweight were measured daily and weekly respectively. At the end of treatment, blood samples were collected to collect plasma to quantify hormones and metabolic indicators of lipid metabolism. In addition, organ and abdominal adipose depots including liver, and omental, perirenal, and epididymal fat were weighed. Liver tissue was sampled for sectioning, long-chain fatty acid (LCFA) quantification, and gene chip and Real-time quantitative PCR (qPCR) analyses. The results showed that liver weight and index (ratio of liver weight to body weight) in MT group reduced by 20.69% and 9.63% respectively; omentum weight and index reduced by 59.88% and 54.93% respectively, and epididymal fat weight reduced by 45.34% (p = 0.049), relative to CTL. Plasma lipid indices, triglyceride (TG), high-density lipoprotein (HDL), low-density lipoprotein (LDL) and total cholesterol (TC) with MT treatment decreased significantly compared with the control. Fat and 8 LCFA content in liver in MT group also decreased. Gene chip and qPCR demonstrated that there were 289 genes up-regulated and 293 genes down-regulated by MT. Further analysis found that the mRNA expression of lipolysis-related genes increased, while the mRNA expression of lipogenesis-related enzymes decreased (p < 0.05) with MT. This study concluded that melatonin greatly affected fat deposition, and hepatic LCFA supply and the expression of genes associated with lipogenesis and lipolysis. 相似文献
110.
冠层光截获能力是反映作物品种间差异的重要功能性状,高通量表型冠层光截获对提高作物改良效率具有重要意义。本研究以小麦为研究目标,利用数字化植物表型平台(D3P)模拟生成了100种冠层结构不同的小麦品种在5个生育期的三维冠层场景,记录了从原始冠层结构中提取的绿色叶面积指数(GAI)、平均倾角(AIA)和散射光截获率(FIPARdif)信息作为真实值,进一步利用上述三维小麦场景开展了虚拟的激光雷达(LiDAR)模拟实验,生成了对应的三维点云数据。基于模拟的点云数据提取了其高度分位数特征(H)和绿色分数特征(GF)。最后,利用人工神经网络(ANN)算法分别构建了从不同LiDAR点云特征(H、GF和H+GF)输入到FIPARdif、GAI和AIA的反演模型。结果表明,对于GAI、AIA和FIPARdif,预测精度从高到低对应的点云特征输入为GF+H > H > GF。由此可见,H特征对提高目标表型特性的估算精度起到了重要作用。输入GF + H特征,在中等测量噪音(10%)情况下,FIPARdif和GAI的估算均获得了满意精度,R2分别为0.95和0.98,而AIA的估算精度(R2=0.20)还有待进一步提升。本研究基于D3P模拟数据开展,算法的实际表现还有待通过田间数据进一步验证。尽管如此,本研究验证了D3P协助表型算法开发的能力,展示了高通量LiDAR数据在估算田间冠层光截获和冠层结构方面的较高潜力。 相似文献