全文获取类型
收费全文 | 33862篇 |
免费 | 1973篇 |
国内免费 | 3119篇 |
专业分类
林业 | 4274篇 |
农学 | 2695篇 |
基础科学 | 1930篇 |
6444篇 | |
综合类 | 14625篇 |
农作物 | 1914篇 |
水产渔业 | 1347篇 |
畜牧兽医 | 1945篇 |
园艺 | 928篇 |
植物保护 | 2852篇 |
出版年
2024年 | 195篇 |
2023年 | 666篇 |
2022年 | 1093篇 |
2021年 | 1164篇 |
2020年 | 1164篇 |
2019年 | 1406篇 |
2018年 | 931篇 |
2017年 | 1503篇 |
2016年 | 1804篇 |
2015年 | 1459篇 |
2014年 | 1876篇 |
2013年 | 2188篇 |
2012年 | 2688篇 |
2011年 | 2579篇 |
2010年 | 2136篇 |
2009年 | 2144篇 |
2008年 | 1838篇 |
2007年 | 1960篇 |
2006年 | 1639篇 |
2005年 | 1203篇 |
2004年 | 1016篇 |
2003年 | 769篇 |
2002年 | 683篇 |
2001年 | 625篇 |
2000年 | 578篇 |
1999年 | 461篇 |
1998年 | 390篇 |
1997年 | 372篇 |
1996年 | 314篇 |
1995年 | 363篇 |
1994年 | 277篇 |
1993年 | 275篇 |
1992年 | 238篇 |
1991年 | 222篇 |
1990年 | 190篇 |
1989年 | 184篇 |
1988年 | 114篇 |
1987年 | 89篇 |
1986年 | 42篇 |
1985年 | 21篇 |
1984年 | 20篇 |
1982年 | 11篇 |
1981年 | 8篇 |
1980年 | 12篇 |
1978年 | 11篇 |
1977年 | 5篇 |
1976年 | 8篇 |
1963年 | 3篇 |
1962年 | 4篇 |
1955年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
42.
Two mungbean varieties, Guj-1 and PIMS-1 differing in their productivity potential, were examined to investigate their photosynthetic system at various stages of growth in relation to yield with two different dates of sowing. Vertical leaves were found to be beneficial. On the other hand, excessive leaf area during the later stages of growth may be detrimental to yield. Lower LAD at seedling stage and overall high NAR values may be reflected in higher grain yield. NAR declined as season progressed and this, in turn, may be related with increase in LAI. The grain yield was considerably more at the first date of sowing as compared to second date of sowing, the effect was being more pronounced in var. PIMS-1 . Various environmental factors recorded at two different dates of sowing and at various stages of growth indicated that these factors may have influenced the yield potential at two different dates of sowing. 相似文献
43.
日本落叶松在四川引种栽培的初步研究 总被引:1,自引:0,他引:1
报道了日本落叶松在四川20多年来的引种。栽培试验结果,证明引种是成功的。并进一步探讨了日本落叶松在四川各地的引种效果和树种生态适应性,提出了按四川自然地理分区和森林分区为基础的引种适生区划分标准。综合分析认为日本落叶松应成为四川省中山地带和高山峡谷区低海拔地带主要速生丰产造林树种之一。 相似文献
44.
Frazier和Jawerth系统地研究了分布空间的离散变换,即变换,本文讨论了f~aq,[f_p~[aq]]上的投影算子,得到了‖{sup_〔Q_b〕〔f〕}_Q‖■_p~[aq]与‖{sup_[Q_b]}Q‖■_p_[aq]的等价性以及‖f‖F_p~aq[b]与‖f‖F_p~[aq]的等价性. 相似文献
45.
本文通过光合作用参数的测定,详细的研究了中系8541和8240两种不同产量水平的水稻品种的光合特性.论述了在含等量叶绿素的条件下,中系8541和中系8240之间在对光谱的吸收、叶片的光合作用量子转化效率,叶绿体的PSⅡ(光系统Ⅱ)潜在活性(Fv/F_0)和原初光能转化效率(Fv/Fm等的主要区别.实验结果说明,上述各光合作用参数中系8541都优于中系8240.不仅如此.在Mg~(2+)作用下,Fv/Fo和Fv/Fm比值的提高以及Mg~(2+)对两个光系统激发能分配的调节能力中系8541也强于中系8240. 相似文献
46.
采用TP—801单板机制作作物活体多探头测量仪。该机可在田间对生长状态下的农作物进行多点体内养分积累、运输、分配等测定,且结果可靠。 相似文献
47.
对N×特青示范田中试区与肥料试验田各处理小区稻株分析结果表明:抽穗后,亚种间杂交稻N×特青比常规稻特青干物质生产能力强,灌浆速度快;地上部各器官占植株干重比例,前者叶片比重大于茎,后者茎比重大于叶。亚种间杂交稻对肥料反应敏感,抽穗后,干物质累积,植株高度,每穗总粒数和粒重均随施肥量增加而增加,在高肥区有利于进一步提高产量,但增施氮肥后,灌浆速度明显滞后。 相似文献
48.
2种典型固体表面铺展剂SDS和TX100混合水溶液,无论在其表面层或在混合胶团中两组分之间均存在一定程度的相互作用,使得以廉价的SDS为主的溶液中加入少许TX100组成的复配体系表面活性提高,在植物叶面上的润湿性能改善,并从理论上计算了其相互作用参数,初步解释了实验现象,上述结果不仅对指导优良植物叶面铺展剂配方具有指导意义,也预示了潜在的实用价值. 相似文献
49.
Sugarcane yields have been severely reduced by white leaf and grassy shoot phytoplasma diseases in many parts of Asia. Australian sugarcane crops are not known to be affected by these diseases, but plant pathogenic phytoplasmas found in other introduced and native grasses in northern Australia could pose a serious threat to the Australian sugarcane industry. To further evaluate this threat, leaves from plants of 20 grass species, with and without symptoms, were collected during field surveys in northern Australia and tested to determine whether phytoplasmas were present and whether symptoms were reliable indicators of phytoplasma presence. Molecular tools were used to detect and characterize phytoplasmas. Four different phytoplasmas were found in seven grass species known to grow near healthy sugarcane crops. All the phytoplasmas were closely related to sugarcane white leaf phytoplasma (SCWL), one of the phytoplasmas that causes disease in sugarcane in Asia. Four of the host plant species and two of the phytoplasmas were new records. The relationship between symptoms and phytoplasma presence was poor. Because some plants with symptoms tested negative for phytoplasmas, a series of surveys was carried out in which flowers, leaves, roots and stems of two known host plant species, Whiteochloa cymbiformis and Sorghum stipoideum, were tested separately on nine occasions during two wet seasons. This was done to investigate the distribution of phytoplasmas within plants over time. Results showed that spatial and temporal variation of phytoplasmas occurred in these two host plant species. Hence, evaluation of disease distribution within a region requires repeated testing of all plant parts from plants without symptoms, as well as those with symptoms. To date, there is no report of a vector capable of transmitting to Australian sugarcane the phytoplasmas found in grasses in this study. If one is present, or occurs in the future, then native and introduced grasses could constitute a large reservoir of phytoplasma for vectors to draw on. This work provides an early warning for the sugarcane industry that the potential for infection exists. 相似文献
50.
夏大豆亩产262.1kg生理指标研究 总被引:4,自引:1,他引:3
研究了夏大豆中油-89D亩产262.1kg各项生理指标:叶面积系数,开花期、结荚期、鼓粒期分别为3.98、5.80、4.91;总光合势18.2万m^2·日,平均净光合生产率4.81g/m^2·日,氮磷总积累量分别为22.28kg和3.13kg,每生产100kg籽粒需吸收氮8.50kg,磷1.19kg,总干物质积累876.47kg,粒茎比0.51,经济系数0.30。 相似文献