全文获取类型
收费全文 | 14876篇 |
免费 | 1428篇 |
国内免费 | 2195篇 |
专业分类
林业 | 533篇 |
农学 | 1323篇 |
基础科学 | 1148篇 |
3039篇 | |
综合类 | 4921篇 |
农作物 | 1106篇 |
水产渔业 | 4408篇 |
畜牧兽医 | 1013篇 |
园艺 | 352篇 |
植物保护 | 656篇 |
出版年
2024年 | 105篇 |
2023年 | 316篇 |
2022年 | 528篇 |
2021年 | 613篇 |
2020年 | 741篇 |
2019年 | 928篇 |
2018年 | 717篇 |
2017年 | 938篇 |
2016年 | 1007篇 |
2015年 | 746篇 |
2014年 | 907篇 |
2013年 | 1240篇 |
2012年 | 1114篇 |
2011年 | 1189篇 |
2010年 | 922篇 |
2009年 | 799篇 |
2008年 | 670篇 |
2007年 | 764篇 |
2006年 | 625篇 |
2005年 | 528篇 |
2004年 | 404篇 |
2003年 | 354篇 |
2002年 | 263篇 |
2001年 | 294篇 |
2000年 | 252篇 |
1999年 | 229篇 |
1998年 | 156篇 |
1997年 | 177篇 |
1996年 | 189篇 |
1995年 | 139篇 |
1994年 | 129篇 |
1993年 | 110篇 |
1992年 | 104篇 |
1991年 | 72篇 |
1990年 | 62篇 |
1989年 | 56篇 |
1988年 | 28篇 |
1987年 | 31篇 |
1986年 | 23篇 |
1985年 | 8篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1963年 | 2篇 |
1962年 | 6篇 |
1956年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
61.
Optimising mineral nitrogen (N) use in crop production is inevitable target as mineral fertilisers reflect one of the highest inputs both in terms of economy and energy. The aim of the study was to compare the relationship between the rate of N fertiliser application and different measures of energy parameters exemplary data for spring-wheat in boreal climate condition in Estonia in 2006–2010. The effect of mineral N with rates 0, 40, 80, 120 and 160 kg N ha−1 was studied on the background of composted cow manure and without organic fertilisers. Univalent parameters, energy gain (EG) (energy output − energy input) and energy ratio (ER) (energy output/energy input) were calculated. To aggregate parameters with different units (ER and EG) we proposed two standardisation approaches for combined indices. ER maximisation gave both organic fertilisation background optimum N norms significantly lower than EG (p < 0.05) optimisation. Both the new combined indices gave optimum N norms in between the rate of ER an EG. Composted cow manure background did not affect mineral N optimisation significantly. We suggest optimisation of mineral N according to bi-dimensional parameters as they capture important features of production efficiency and are more objective using as advisory tool for sustainable production systems. 相似文献
62.
63.
Movement patterns of seaward migrating European eel (Anguilla anguilla) at a complex of riverine barriers: implications for conservation
下载免费PDF全文
![点击此处可从《Ecology of Freshwater Fish》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Adam T. Piper Jon C. Svendsen Rosalind M. Wright Paul S. Kemp 《Ecology of Freshwater Fish》2017,26(1):87-98
River infrastructure such as weirs and hydropower stations commonly present migrating fish with multiple potential passage routes. Knowledge of the cues fish use to navigate such environments is required to protect migrants from hazardous areas and guide them towards safe passage; however, this is currently lacking for many species. Employing high‐resolution positioning telemetry, this study examined movements of downstream migrating adult European eel, Anguilla anguilla, as they encountered a complex of water control structures in one location on the River Stour, southern England. The distribution of eels across five potential routes of passage differed from that predicted based on proportion of discharge alone. Certain routes were consistently avoided, even when the majority of flow passed through them. Passage distribution was partially explained by avoidance in the vicinity of a floating debris boom. Movement paths were nonrandomly distributed across the forebay and eels moved predominantly within a zone 2–4 m from the channel walls. Understanding of avoidance and structure oriented movementation exhibited by eels will help advance effective guidance and downstream passage solutions for adults. 相似文献
64.
调亏度及调亏历时对苜蓿生物量分配与水分利用效率的影响 总被引:1,自引:0,他引:1
本研究的目的在于探讨紫花苜蓿营养生长期调亏滴灌对其节水效果的影响,增加其产量的作用。在北京对分枝期苜蓿品种"皇冠"进行调亏程度和调亏历时对其生长的研究。结果发现,秋播苜蓿进行调亏灌溉应把握适当的调亏度,在调亏度达60%FC、调亏历时为14d时,土壤水分对苜蓿形成干旱胁迫;在调亏度达80%FC时,光合同化物更多向苜蓿地上部分配,同时适当增加调亏历时改变苜蓿根系形态可塑性,有利于其根系伸长生长,提高其水分利用效率。适当的将调亏度与调亏持续时间分别维持在80%FC左右和14~21d,更能实现北京地区苜蓿节水促生长的目的。 相似文献
65.
In order to investigate effects of topdressing on grain yield and N use efficiency of mechanically-transplanted hybrid rice,this experiment was conducted with 2-line hybrid rice cultivars,Quanliangyou 1 and Quanliangyou 681 with 3 application levels of N fertilizer,No,N1,N2,respectively.The results showed that there were no significant differences in grain yields of the 2 varieties between treatments N1 and N2.It was indicated that N is not the factor which could limit grain yield within limited application levels of N fertilizer.High N fertilizer treatment could contribute to the formation of effective panicles and spikelets per panicle,but it could also lead to the decline in grain filling rate.It was suggested that lowering the amount of Nfertilizer could facilitate improvement of N-use efficiency. 相似文献
66.
江汉平原棉花合理施氮量研究 总被引:2,自引:0,他引:2
采用田间小区试验研究了江汉平原棉花合理施氮量。结果表明,在施用90 kg/hm~2 P2O5、180 kg/hm~2K2O和3 kg/hm~2持力硼基础上,利用线性+平台模型得到棉花中高产量水平下的合理施氮量为280 kg/hm~2。在不明显减产的条件下,从提高氮肥当季利用率、尽量降低氮肥投入的角度,可以将氮肥用量降低到240kg/hm~2左右,在此施氮水平下仍然可能通过改进田间管理措施获得高产。因此,江汉平原棉花氮肥减量空间为20~60 kg/hm~2。 相似文献
67.
森林消防装备是森林消防工作的基础,是森林防火灭火能力的体现。分析了我国消防装备的现状和存在的问题,探讨了提高我国森林消防装备使用效益的措施。 相似文献
68.
结合工作实际探讨藏书倒架的前期准备工作及倒架时的路线设计、人员组织安排和倒架后的环节完善。以期减轻图书馆人员在倒架工作中的劳动强度和工作量,提高工作效率。 相似文献
69.
70.