全文获取类型
收费全文 | 10690篇 |
免费 | 569篇 |
国内免费 | 708篇 |
专业分类
林业 | 1417篇 |
农学 | 1780篇 |
基础科学 | 523篇 |
905篇 | |
综合类 | 4127篇 |
农作物 | 1008篇 |
水产渔业 | 145篇 |
畜牧兽医 | 916篇 |
园艺 | 393篇 |
植物保护 | 753篇 |
出版年
2024年 | 44篇 |
2023年 | 165篇 |
2022年 | 297篇 |
2021年 | 304篇 |
2020年 | 326篇 |
2019年 | 392篇 |
2018年 | 249篇 |
2017年 | 462篇 |
2016年 | 570篇 |
2015年 | 383篇 |
2014年 | 518篇 |
2013年 | 603篇 |
2012年 | 816篇 |
2011年 | 761篇 |
2010年 | 602篇 |
2009年 | 610篇 |
2008年 | 513篇 |
2007年 | 535篇 |
2006年 | 449篇 |
2005年 | 409篇 |
2004年 | 312篇 |
2003年 | 289篇 |
2002年 | 215篇 |
2001年 | 238篇 |
2000年 | 221篇 |
1999年 | 207篇 |
1998年 | 203篇 |
1997年 | 175篇 |
1996年 | 144篇 |
1995年 | 149篇 |
1994年 | 131篇 |
1993年 | 141篇 |
1992年 | 104篇 |
1991年 | 95篇 |
1990年 | 95篇 |
1989年 | 62篇 |
1988年 | 38篇 |
1987年 | 31篇 |
1986年 | 23篇 |
1985年 | 18篇 |
1984年 | 12篇 |
1982年 | 13篇 |
1981年 | 7篇 |
1980年 | 11篇 |
1979年 | 4篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1976年 | 7篇 |
1962年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
131.
132.
籼粳亚种杂交组合的结实率与光合产物供给水平及转运效率间的关系 总被引:6,自引:0,他引:6
通过剪除部分颖花和部分功能叶片以及~(14)CO_2标记光合产物等处理,探讨了亚种组合结实率偏低的生理原因。结果证明:光合产物供给水平是制约亚种组合结实率的一个十分重要的因素。虽然亚种组合的叶面积指数和单株叶面积比常规籼稻大得多,但由于每穗颖花数多。以至每朵颖花占有的叶面积并无明显优势,且其光合速率低于常规籼稻,因而分配给每朵颖花的光合产物量相对减少,限制了部分颖花的发育。~(14)C光合产物分配到穗部的比率不但不低于常规籼稻,而且比其略高,说明亚种组合输导组织的运输能力不是结实率偏低的限制因素。 相似文献
133.
134.
Seed planting equipment with inclined plate seed metering devices is the most commonly used equipment for planting of peanut crop in India. For obtaining the high yield, it is very essential to drop the peanut seeds in rows maintaining accurate seed rate and seed spacing with minimum damage to seeds during metering. This mainly depends on forward speed of the planting equipment, rotary speed of the metering plate and area of cells on the plate. The relationship between these factors and the performance parameters viz., seed rate, seed spacing and percent seed damage can be established using regression analysis. But they may not be very accurate and may pose difficulty in the determination of inputs for a set of desired outputs (reverse mapping). Hence, an attempt has been made in this paper to develop the feed forward artificial neural network (ANN) models for the prediction of the performance parameters of an inclined plate seed metering device. The data were generated in the laboratory by conducting experiments on a sticky belt test stand provided with a seed metering device and an opto-electronic seed counter. The generated data was used to develop both statistical and neural network models. The performance of the developed models was compared among themselves for 4 randomly generated test cases. The results show that the ANN model predicted the performance parameters of the seed metering device better than the statistical models. In order to determine the optimum forward speed of the planting equipment, peripheral speed of the metering plate and the area of cells on the plate to obtain the recommended seed rate of 33.33 seeds/m2, seed spacing of 100 mm and percent seed damage of 0.2% with 100% fill of the cells, a novel technique of reverse mapping using ANN model was followed. It was observed that the optimum forward speed of the planting equipment and optimum area of cells on the metering plate had good correlation with size of seed. Linear regression equations were developed to predict the optimum forward speed of the planting equipment and optimum area of cells on the metering plate using the size of seeds as independent parameter. The peripheral speed of the metering plate of 0.237 m/s was found to be optimum for the size of seeds in the range of 95.42-123.01 mm2. However, the results need to be verified by conducting planting operation under actual field conditions. 相似文献
135.
近年来,由于种子市场竞争激烈,种子质量纠纷案件有所上升,以次充好、假冒伪劣种子案件时有发生,扰乱了种子市场秩序,危害了农业生产安全,增加了社会的不稳定因素。因此,加强农作物种子的监督抽查,防止不合格种子流入市场,确保农业生产安全和社会稳定具有重要意义。 相似文献
136.
干旱区矿区不同立地类型土壤种子库特征 总被引:1,自引:0,他引:1
矿区的自然或人工植被恢复是维持生物多样性及生态系统稳定的重要途径。通过室外萌发法对金昌镍铜矿区7种不同立地生境土壤种子库的研究表明:该区域土壤中物种丰富度较高,包括16科47属,共56种植物,分别为:藜科(Chenopodiaceae)、禾本科(Gramineae)、菊科(Compositae)、柽柳科(Tamaricaceae)、苋科(Amaranthaceae)、马齿苋科(Portulacaceae)、豆科(Leguminosae)、十字花科(Cruciferae)、车前科(Plantaginaceae)、胡颓子科(Elaeagnaceae)、蒺藜科(Zygophyllaceae)、莎草科(Cyperaceae)、大戟科(Euphorbiaceae)、紫草科(Boraginaceae)、蔷薇科(Rosaceae)、茄科(Solanaceae);植物组成以一年生草本植物占绝对优势(89.3%),多年生草本植物次之(7.54%),灌木种最少(2.59%)。土壤种子平均储量412粒·m~(-2),不同立地类型土壤种子库储量差异显著,与其他荒漠地区比较,土壤种子库储量偏低;土壤种子库物种Simpson多样性指数为:新尾矿周边自然植被区龙首矿自然植被区龙首矿开采废弃地供暖公司柽柳林地。 相似文献
137.
138.
《Scandinavian Journal of Forest Research》2012,27(1-4):337-345
Abies lasiocarpa (Hook.) Nutt. seeds germinated and the seedlings grew on under controlled environments (18 h photoperiod and 16/8 h thermoperiods; 10/10oC, 20/20°C, 20/10°C, and 25/10°C). The experiment was concluded after 180 days, and the seedlings were scored for stem diameter and length. Four provenances were included: Colorado “high elevation”; (CO), Oregon 1 600 m a.s.l. (OR), British Columbia 1200 m a.s.l. (BC), and Finland (BCF; originally from British Columbia 1800 m a.s.l.). A cold‐moist pretreatment for 30 days improved germination and seedling growth in the BC and BCF seed lots, while the CO and OR seed lots were less affected. Daily fluctuating temperatures improved germination in the BC and BCF seed lots, the widest fluctuation 25/10°C producing the greatest germination. The average length of the seedlings was 34 mm at 20/20°C, 33 mm at 20/10°C, and 37 mm at 25/10°C; differences in hypocotyl length being most important. There were small but significant differences between the provenances in their reaction to temperature regime. The major part of the seedlings produced 2 or 3 flushes of growth in the 180 days period, the CO provenance having the most stabile buds and the OR provenance being the most labile. 相似文献
139.
140.
GA_3处理对天女木兰种子解除休眠过程中碳水化合物含量的影响 总被引:1,自引:0,他引:1
研究了GA3对天女木兰种子在变温层积条件下解除休眠过程中碳水化合物的影响,以此探讨外源赤霉素(GA3)对层积过程中天女木兰种子解除休眠的作用机理。结果表明,1000mg/LGA3水溶液处理极显著促进天女木兰种子萌发,在整个层积过程中,GA3水溶液处理诱导淀粉含量下降;蔗糖含量变化剧烈,在层积90d降至最低,果糖和葡萄糖含量显著增加;在层积后期(90~120d)果糖和葡萄糖含量下降,蔗糖含量上升,从而说明了碳水化合物参与并调节了天女木兰种子休眠解除这一过程。 相似文献