全文获取类型
收费全文 | 47710篇 |
免费 | 5824篇 |
国内免费 | 3920篇 |
专业分类
林业 | 3988篇 |
农学 | 4690篇 |
基础科学 | 3053篇 |
6595篇 | |
综合类 | 16801篇 |
农作物 | 2742篇 |
水产渔业 | 4250篇 |
畜牧兽医 | 9707篇 |
园艺 | 2066篇 |
植物保护 | 3562篇 |
出版年
2024年 | 179篇 |
2023年 | 621篇 |
2022年 | 1530篇 |
2021年 | 1899篇 |
2020年 | 2095篇 |
2019年 | 2549篇 |
2018年 | 1983篇 |
2017年 | 2870篇 |
2016年 | 2357篇 |
2015年 | 2907篇 |
2014年 | 2952篇 |
2013年 | 3445篇 |
2012年 | 3808篇 |
2011年 | 4184篇 |
2010年 | 3926篇 |
2009年 | 3159篇 |
2008年 | 3095篇 |
2007年 | 2656篇 |
2006年 | 2164篇 |
2005年 | 1675篇 |
2004年 | 1034篇 |
2003年 | 843篇 |
2002年 | 906篇 |
2001年 | 833篇 |
2000年 | 766篇 |
1999年 | 539篇 |
1998年 | 376篇 |
1997年 | 312篇 |
1996年 | 257篇 |
1995年 | 238篇 |
1994年 | 209篇 |
1993年 | 210篇 |
1992年 | 144篇 |
1991年 | 148篇 |
1990年 | 141篇 |
1989年 | 137篇 |
1988年 | 71篇 |
1987年 | 50篇 |
1986年 | 28篇 |
1985年 | 23篇 |
1984年 | 16篇 |
1983年 | 12篇 |
1982年 | 8篇 |
1981年 | 13篇 |
1979年 | 9篇 |
1977年 | 8篇 |
1970年 | 6篇 |
1963年 | 8篇 |
1962年 | 6篇 |
1956年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
971.
Liwei Liu Yuliang Luo Xu‐Fang Liang Weimin Wang Junjie Wu Jing Pan 《Journal of the World Aquaculture Society》2013,44(1):56-65
Two 8‐wk studies were conducted to evaluate the effects of neutral phytase supplementation on hemato‐biochemical status, liver biochemical parameter, and intestinal digestive enzyme activity of grass carp, Ctenopharyngodon idellus, and gibel carp, Carassius auratus gibelio, fed with different levels of monocalcium phosphate (MCP). The control diet was prepared with 2% MCP but without phytase (P2.0). The other three experimental diets were prepared with the addition of 1.5, 1.0, and 0.5% MCP, respectively, when supplemented with 500 U/kg neutral phytase in each diet and designated as PP1.5, PP1.0, and PP0.5, respectively. The results indicated that the serum alkaline phosphatase (ALP), alanine transaminase (ALT), and aspartate transaminase (AST) activities, as well as the albumin (ALB) content were increased in grass carp (P < 0.05) and gibel carp (P > 0.05) fed with phytase‐supplemented diets. Meanwhile, the serum cholesterol, high‐density lipoprotein, and total protein contents of the two species of fish were increased in comparison to the control. In addition, dietary phytase inclusion did not significantly affect hepatic ALP, ALT, and AST activities in the two species of carp fed with different levels of MCP. Amylase activity increased in foregut and hindgut of both species when fed with the phytase‐supplemented diets while lipase activity was reduced in the foregut and hindgut in both fish. This study suggests that neutral phytase supplementation increases serum ALP, ALT, and AST activities but does not notably affect these enzyme activities in the liver of the two species of carp when fed different levels of MCP. On the other hand, amylase activity increased while lipase activity was reduced in the intestine of the species of carp fed with phytase‐supplemented diets. 相似文献
972.
973.
Der 1967 in Seehausen auf sandigem Lehm angelegte Düngungs‐Kombinationsversuch dient der Analyse von Langzeitwirkungen gestaffelter Stallmist‐ und Mineral‐N‐Gaben (0,50,100,150 kg N ha?1 a?1) auf Pflanzen, Boden und Umwelt. Anhand von Meß‐, Bilanz‐ und Simulationswerten wird die Nachhaltigkeit dieser Düngungsvarianten bewertet. Organisch‐mineralische Düngung führte zu Maximalerträgen von über 12t TM ha?1 a?1 und N‐Entzügen bis 200 kg ha?1 a?1. Der N‐Entzug der ungedüngten Variante betrug in den letzten Jahren noch etwa 75 kg ha?1a?1 gegenüber 100 kg ha?1a?1 zu Versuchsbeginn. Die Entwicklung der Boden‐Nt‐Gehalte konnte mit e‐Funktionen beschrieben werden. Mineral‐N allein genügte nicht zum Erhalt der Nt‐Ausgangsvorräte, hierfür waren 55 bis 85 kg Stalldung‐N ha?1 a?1 notwendig. Die Nt‐ und Ct‐Gehalte korrelierten mit zahlreichen Bodenparametern. Hohe Humusgehalte forderten die biologische Aktivität. Die N‐Verluste betrugen <10kg ha?1 a?1 (ungedüngt) bis 120 kg ha?1a?1 (höchstgedüngte Variante). Das N‐Verlustpotential lag bei Stallmistanwendung etwas niedriger als bei gleicher N‐Zufuhr in Mineralform. Je nach Stallmist‐Stufe waren 62 bis 104 kg Mineral‐N ha?1 a?1 erforderlich, um den Energieeinsatz je Produkteinheit zu minimieren. Kombinierte Anwendung organischer und mineralischer Dünger (je 100 kg N ha?1 a?1) führte zu höchsten ökonomischen Leistungen, günstigen Bodeneigenschaften und tolerierbaren Umweltwirkungen. Zieht man alle verwendeten Nachhaltigkeitskriterien in Betracht, ist dieses Düngungssystem den anderen überlegen. 相似文献
974.
In this study,the seeds of wild Petunia Juss.were used as explants to investigate the optimal condition for tissue culture.Several different kinds and concentrations of growth regulators were adopted to produce more multiple bud clumps,callus or roots in this study.The experiments may provide experimental foundation for the rapid propagation technology and establishment of tissue culture system for wild Petunia Juss. 相似文献
975.
Md Abdul Wahab Sk Ahmad‐Al‐Nahid Nesar Ahmed Mohammad M Haque Mahmudul Karim 《Aquaculture Research》2012,43(7):970-983
Giant river prawn (Macrobrachium rosenbergii) farming plays an important role in the economy of Bangladesh. Presently, it is cultured in around 50 000 ha area with total annual production of 23 240 t. Traditional extensive prawn farming has been expanding over the last three decades through the introduction and adoption of improved culture systems, such as culture of prawn‐carps, prawn‐shrimp‐fish and prawn‐fish‐rice as concurrent and rotational systems. Efforts for the development of improved techniques on broodstock management, seed production and rearing and grow‐out of prawn have been made over the last decade. The outcomes are low‐cost feed for broodstock, production of post‐larvae in net cages (hapa), all‐male prawn culture, periphyton based prawn‐tilapia culture, C/N based prawn culture, organic prawn farming, prawn‐mola culture and prawn‐carp‐mola polyculture. Despite the development of culture technologies, a number of challenges for sustainable development of prawn farming need to be overcome to realize the potentials of this promising sector. Good aquaculture practises at all levels and application of measures for quality control and food safety would ensure sustainable development of prawn farming in Bangladesh. 相似文献
976.
977.
依据高等院校实验教学管理的应用需求,在分析开源框架体系结构的基础上,通过整合Struts、Spring和Hibernate,利用分层解耦、框架管理层次的思想构建了一个基于开源J2EE的应用架构,并据此架构开发了高校实验教学管理系统。系统可靠性高,安全性好,可扩展性和可维护性强,能有效提高高校实验教学管理和服务效率。 相似文献
978.
在分析我国科技期刊发展的现状的基础上,提出了集团化是科技期刊发展的必然趋势。 相似文献
979.
L. Song D.‐W. Zhang F.‐M. Li X.‐W. Fan Q. Ma N. C. Turner 《Journal of Agronomy and Crop Science》2010,196(5):323-335
Competition for water generates a classic aspect of the tragedy of the commons, the ‘race for fish’, where crops must allocate more resource to acquisition of the limiting resource than is optimal for crop yield allocation. A pot experiment using a simple additive (target–neighbour) design was conducted to examine the above‐ground and below‐ground growth of three spring wheat (Triticum aestivum L.) cultivars when grown alone and in mixtures at three levels of water availability. The effects of competition and water availability were compared by observing patterns of growth, biomass allocation and below‐ground outcomes. Competitive interactions were investigated among cultivars ‘HST’, ‘GY602’ and ‘LC8275’, target plant of each cultivar grown without neighbouring plants are referred to herein as control plant and one target plant of each cultivar sown surrounded either by same or another cultivar as intra‐ or inter‐cultivar competition. Competitive ability was assessed as the response ratio (lnRR) between the target plant surrounded by six other plants and the target plant in isolation. Our results showed that the cultivar ‘HST’, released over a century ago, produced a higher biomass and grain yield than the more recently released cultivars ‘LC8275’ and ‘GY602’ when grown as isolated plants with sufficient water supply. However, competition for resources from neighbours led to target plant biomass and grain yield being significantly reduced relative to controls in all three cultivars, particularly in ‘HST’. When subjected to intra‐cultivar competition, the two recently released cultivars ‘LC8275’ and ‘GY602’ had higher grain yields and water use efficiency for grain than ‘HST’ in all three water regimes. The landrace ‘HST’ had better and significantly linear relationships between biomass and biomass allocation, root length and specific root length, whereas the recent and modern cultivars had much more water‐related species‐specific changes in root morphology and allocation patterns. These results suggest that crop traits that influence competitive ability, such as biomass allocation to roots and root plasticity in response to drought have changed in modern wheat cultivars because of breeding and selection. 相似文献
980.