全文获取类型
收费全文 | 1107篇 |
免费 | 34篇 |
国内免费 | 56篇 |
专业分类
林业 | 132篇 |
农学 | 138篇 |
基础科学 | 3篇 |
44篇 | |
综合类 | 449篇 |
农作物 | 111篇 |
水产渔业 | 70篇 |
畜牧兽医 | 59篇 |
园艺 | 162篇 |
植物保护 | 29篇 |
出版年
2024年 | 3篇 |
2023年 | 13篇 |
2022年 | 15篇 |
2021年 | 17篇 |
2020年 | 22篇 |
2019年 | 27篇 |
2018年 | 15篇 |
2017年 | 27篇 |
2016年 | 33篇 |
2015年 | 37篇 |
2014年 | 36篇 |
2013年 | 56篇 |
2012年 | 65篇 |
2011年 | 75篇 |
2010年 | 78篇 |
2009年 | 87篇 |
2008年 | 76篇 |
2007年 | 82篇 |
2006年 | 50篇 |
2005年 | 53篇 |
2004年 | 26篇 |
2003年 | 40篇 |
2002年 | 24篇 |
2001年 | 25篇 |
2000年 | 25篇 |
1999年 | 21篇 |
1998年 | 11篇 |
1997年 | 18篇 |
1996年 | 18篇 |
1995年 | 14篇 |
1994年 | 22篇 |
1993年 | 10篇 |
1992年 | 19篇 |
1991年 | 10篇 |
1990年 | 16篇 |
1989年 | 13篇 |
1988年 | 4篇 |
1987年 | 7篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有1197条查询结果,搜索用时 343 毫秒
11.
2009~2011年5~8月,在山西芦芽山国家级自然保护区对四声杜鹃的生态习性进行了观察。结果表明,四声杜鹃在本区为夏候鸟,最早5月上旬迁来,最晚8月下旬迁走,居留期为99~111 d。迁来后,该鸟在本区主要在低山疏林地带和村庄附近活动,活动较为敏锐和隐蔽,常能听到叫声,但很少暴露在人前。四声杜鹃在本区的种群密度6、7月最大,每公里遇见数分别为1.17只和1.25只;在8月种群密度最小,每公里遇见数0.47只,种群密度平均为0.89只/km。该鸟为卵寄生性繁殖,自己不营巢,本区发现雌鸟把卵产在山噪鹛的繁殖窝里,让山噪鹛代其孵化和育雏,本窝寄生卵2枚,卵重3.3 g和3.5 g,卵大小为22×17 mm~23×18 mm。卵经山噪鹛义鸟孵化18 d后出壳,雏鸟仍由山噪鹛喂育14 d后离巢。四声杜鹃主要以昆虫为食,昆虫食物量占总食物量的95.5%,其中松毛虫所占比例最大,占昆虫食物重量的24.1%。该鸟为重要的农林益鸟,应予以保护。 相似文献
12.
13.
菜薹(菜心)土壤氮营养诊断指标及合理施氮量 总被引:2,自引:1,他引:2
在不同地点,不同肥力水平的菜园土上进行菜薹(菜心)氮肥田间试验,经过对17个试验点菜心相对产量与土壤碱解氮含量的相关统计分析,并建立回归方程。结果表明:菜心产量与土壤碱解氮含量呈抛物线相关,在质地为中壤土的菜园上种植菜心,土壤碱解氮含量为146~277mg·kg-1时无需施氮,低于此范围应补充氮肥,超过此范围应控制施氮;菜心产量与施氮量呈抛物线相关,在低、中、高肥力水平的菜园土上种植菜心,要求菜心达到6433~6455、6633~6877、6733~7311kg·hm-2的产量水平,推荐氮肥用量分别为67~104、67~89、67~78kg·hm-2。 相似文献
14.
缺镁对菜薹光合作用特性的影响 总被引:10,自引:0,他引:10
研究了缺镁对菜薹光合作用特性的影响, 结果表明, 菜薹叶片净光合速率( Pn) 、气孔导度和蒸腾速率的日变化均呈单峰曲线变化, 且均随缺镁程度的加大而降低, 缺镁还使Pn的高峰提早出现; 缺镁降低了叶片的光补偿点、光饱和点和饱和光强下的Pn max; 缺镁使叶片的CO2 补偿点提高, CO2 饱和点下降(Mg 1 mmol·L - 1 ) 或提高(Mg 0) , 饱和CO2 下的Pn max下降。菜薹叶片细胞间隙CO2 浓度的日变化、对光强和外界CO2 浓度的响应受缺镁处理的影响很小, 表明缺镁菜薹光合作用主要是受非气孔限制。 相似文献
15.
短日照处理天数对一品红开花和观赏品质的影响 总被引:6,自引:0,他引:6
短日照处理不同天数后转到自然长日照下, 研究短日照处理对促成栽培的‘千禧’和‘早生天鹅绒’一品红生长开花的影响。结果表明短日照处理天数对其发育进程、苞片着色和观赏品质有显著影响。苞片转色后结束短日照处理, 节数与连续短日照相似, 但开花显著延迟; 现蕾时结束短日照处理, 开花时间、冠幅与连续短日照相似; 过渡性叶片面积在短日照处理至现蕾后13~14 d才与连续短日照相似。一品红对短日照处理天数的反应存在品种差异。现蕾前结束短日照处理导致一品红过渡性叶片的节间和花梗伸长、苞片着色变差, 出现开花逆转现象。为了保证观赏品质, 短日照处理要持续到现蕾以后。 相似文献
16.
多效唑对八仙花组培苗营养生长及成花的影响 总被引:6,自引:1,他引:6
以八仙花1、2 a生组织培养苗为试验对象,研究了多效唑不同浓度、不同施药时间、不同施药次数对八仙花组培苗促成栽培中其植株营养生长及成花的影响.结果表明:施用浓度和时间是多效唑抑制八仙花组培苗植株营养生长促进其生殖生长的关键,7月中旬以浓度100~150 mg/L的多效唑溶液对八仙花1、2 a生组织培养苗进行叶面喷施,最有利于其花芽分化,成花率高,且从株型、花形花色等各项指标综合考虑,多效唑对促进八仙花2a生组培苗成花效果更显著.施药次数也影响八仙花组培苗营养生长和成花,连续施药3次对抑制其营养生长促进成花效果最佳. 相似文献
17.
S.H. Kim C.E. Niedziela Jr. P.V. Nelson A.A. De Hertogh W.H. Swallow N.C. Mingis 《Scientia Horticulturae》2007
One-year old scale bulblets of Lilium longiflorum Thunb. ‘Nellie White’ (Easter lily) were grown for 107 days during growth period 1 (GP-1) in six growth chambers under constant day/night temperature regimes of 30/26, 26/22, 22/18, 18/14, 14/10 and 10/6 °C. Subsequently, half of the plants in each temperature regime were transferred to 18/14 °C and the other half continued at the six constant temperature regimes. Both groups of plants were grown for an additional 89 days in growth period 2 (GP-2). Continuous temperatures of 26/22, 26/22–22/18 and 26/22–18/14 °C produced the greatest increase in basal bulb fresh weight (the main planted bulb), basal bulb circumference and stem bulb fresh weight, respectively. However, shifting these optimal temperatures to 18/14 °C during GP-2 resulted in a lower increase in basal bulb fresh weight and circumference. The optimum range for stem bulb production was expanded to 30/26–14/10 °C by shifting to 18/14 °C. The greatest increase for basal root growth occurred at 14/10–10/6 °C and for stem root growth at 14/10 °C. The temperature shift did not affect either root type. Maximum increase for stem length was at 26/22 and 22/18 °C and for stem plus leaf weight at 14/10 °C under constant temperature regimes. Transferring the plants from 10/6 to 18/14 °C resulted in the greatest increase in stem length and from 10/6 and 14/10 to 18/14 °C in the greatest increase in stem plus leaf weight. The greatest increase in the number of leaves occurred at 26/22 and 10/6 °C, but this growth parameter was unaffected by shifting to 18/14 °C, indicating that leaf number was determined in GP-1. Bulbils developed only when bulbs at high GP-1 temperature regimes (30/26 and 26/22 °C) were transferred to 18/14 °C during GP-2. Lower temperatures tended to favor an increase in flower bud production under continuous temperature regimes, while shifting to 18/14 °C increased flower bud production after initially high and low temperatures. Meristem abortion was greatest at 30/26 °C followed by 26/22 °C, but was not affected by temperature shifts in GP- 2. Thus, it is concluded that the abortion was induced or initiated during GP-1. 相似文献
18.
Simulation study of the competitive ability of erect, semi-erect and prostrate cowpea (Vigna unguiculata) genotypes 总被引:1,自引:1,他引:1
Ecophysiological simulation models provide a quantitative method to predict the effects of management practices, plant characteristics and environmental factors on crop and weed growth and competition. The INTERCOM interplant competition model was parameterised, calibrated by monoculture data for three cowpea (Vigna unguiculata) genotypes that differed in growth habit, common sunflower (Helianthus annuus) and common purslane (Portulaca oleracea), and used to simulate competition of cowpea cover crops with sunflower or purslane. The simulation results were compared with observations from field competition experiments in 2003 and 2004. INTERCOM more accurately simulated actual field data for the competition of cowpea genotypes and sunflower than companion field experiments for the competition of cowpea and purslane. The validated simulation model of cowpea and sunflower at two densities was used to study the effects of cowpea growth habit on final biomass production of cowpea and sunflower. The model suggested that erect growth habit was more competitive than semi‐erect and prostrate growth habit, when cowpea genotypes were grown with sunflower. Cowpea leaf area distribution was important to higher cowpea biomass production, while cowpea height growth was important to reduce sunflower biomass. Our simulation approach is suggested as a method for crop breeders to gauge the likely success of selection for competitive crops before undertaking expensive long‐term breeding experiments. 相似文献
19.
20.