首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1960篇
  免费   73篇
  国内免费   239篇
林业   80篇
农学   380篇
基础科学   27篇
  184篇
综合类   967篇
农作物   366篇
水产渔业   12篇
畜牧兽医   110篇
园艺   82篇
植物保护   64篇
  2024年   9篇
  2023年   37篇
  2022年   67篇
  2021年   87篇
  2020年   66篇
  2019年   77篇
  2018年   55篇
  2017年   79篇
  2016年   104篇
  2015年   101篇
  2014年   137篇
  2013年   143篇
  2012年   148篇
  2011年   159篇
  2010年   119篇
  2009年   134篇
  2008年   86篇
  2007年   104篇
  2006年   96篇
  2005年   72篇
  2004年   48篇
  2003年   35篇
  2002年   30篇
  2001年   33篇
  2000年   23篇
  1999年   19篇
  1998年   22篇
  1997年   21篇
  1996年   28篇
  1995年   20篇
  1994年   18篇
  1993年   16篇
  1992年   20篇
  1991年   10篇
  1990年   11篇
  1989年   9篇
  1988年   9篇
  1987年   5篇
  1986年   4篇
  1983年   1篇
  1982年   2篇
  1981年   1篇
  1980年   3篇
  1979年   3篇
  1977年   1篇
排序方式: 共有2272条查询结果,搜索用时 15 毫秒
21.
李松克  李克勤  张春林  姜紫勤 《安徽农业科学》2013,41(8):3384-3385,3441
[目的]探究不同播种期对薏苡生长及产量的影响,选出适宜播种期。[方法]采用5个不同播种期、实行田间小区试验的方法。种植方式以窝行距60 cm×60 cm进行种植,每种种植期设3个小区,随机区组排列,小区面积80 m2。苗期以每穴4苗进行定苗。根据生长期进行两次追肥和除草,以及有关生长数据采集,测产验收。[结果]种植期对薏苡产量和生长都有很大的影响。播种期晚,将导致无效分蘖增多,侧枝减少,穗粒数降低,空瘪率高,千粒重减小,大籽粒所占百分率逐渐降低,最终产量降低,质量差。[结论]为了获得高产,播种期应选在清明节之前。  相似文献   
22.
调整玉米播期对玉米粗缩病控制作用研究初报   总被引:1,自引:0,他引:1  
通过罩笼接虫和自然开放式状态下试验 ,对不同播期的玉米粗缩病病情进行了比较 ,明确了玉米敏感叶龄为可见叶 9叶以下 ,展开叶为 6叶以下。研究证实 ,将田间灰飞虱转移迁入高峰期与玉米敏感叶龄期错开 ,可以减轻玉米粗缩病的发病 ,春玉米播期 4月 10~ 15日 ,夏玉米在 6月 10~ 15日 ,能显著控制玉米粗缩病的危害。  相似文献   
23.
播期对油菜"两优586"生育、产量及抗性的影响   总被引:1,自引:1,他引:0  
研究了播期对油菜"两优586"生育、产量及抗性的影响。结果表明:在江西宜春,"两优586"的最佳播期为10月8日,适宜播期为10月1日~10月15日,产量可达1792.50~1929.75kg/hm2,生育期适中(190d左右),单株有效角果数较多,为345个左右,且抗性较强,发病率低于15%,倒伏率低于10%。  相似文献   
24.
25.
通过对不同播种时期(8月15日、8月30日、9月15日、9月30日、10月15日和10月30日)的光叶紫花苕种子生产进行了比较研究,结果表明:不同播期对生育期影响明显,播种越早的其生育期越长。随着播期推迟,其种子产量先增加后减少,在9月15日播种种子产量最高,达1013.55kg/hm^2,10月30日播种种子产量最低,为292.2kg/hm^2。  相似文献   
26.
Two experiments were undertaken in southern Greece during 2000–2002 in which turnip-rooted parsley was tested for its suitability for cultivation in comparison with locally grown curly-leafed and plain-leafed forms. Plants were harvested when the foliage was acceptable for marketing, rather than on completion of the vegetative cycle, hence root size was relatively small. In year 1, the foliage development of plain-leafed parsley was significantly higher than that of the other two forms, irrespective of sowing date. In year 2, both plain-leafed and curly-leafed parsley produced more foliage than turnip-rooted parsley in the early sowing (November), but not in subsequent sowings (December and February). During both years, root development was higher in turnip-rooted parsley than in curly-leafed parsley, although in the November and February sowings of year 1 the root weight of both plain-leafed and turnip-rooted forms were similar. In all three types of parsley, foliage yield fell off significantly in the spring sowing (February), and in year 1 there was a considerable decrease in root production as well. In most cultivars, foliage weight was higher when plants were grown from transplanted seedlings rather than by direct sowing, whereas the effect of sowing method on root weight was sowing date dependent. Cultivar differences in the foliage weight of direct sown and transplanted plants were reflected by differences in plant height and, in some cases, by leaf number. It is concluded that although overall turnip-rooted parsley produced rather less foliage than that plain-leafed parsley, this was compensated for by the satisfactory production of roots and therefore turnip-rooted cultivars may constitute a suitable crop for introduction to the Mediterranean region.  相似文献   
27.
Weed and nutrient management in cropping systems of semi-arid areas is a major constraint to cereal yield. Where the use of herbicides is banned or discouraged, the competitive ability of a crop is crucial to reduce weed growth and diffusion. Genotypic differences in the competitive abilities of crops are an important trait to reduce weeds, especially for plant height. However, there is contrasting information about the interactions of other management practices and genotypic traits on wheat yield and competitive ability against weeds and weed growth. The present study investigated yield and quality of durum wheat (Triticum durum Desf.) and weed growth and composition for two wheat cultivars with contrasting competitive abilities against weeds. Wheat was grown under three spatial arrangements (5-cm, 15-cm, 25-cm inter-row distance) and three sowing densities, and broadleaf weeds were either removed or not. The sowing rate did not affect the yield of these wheat cultivars or the weed growth. Reduced inter-row distance dramatically reduced weed biomass for both wheat cultivars, and increased wheat yield and nitrogen uptake in the low-competitive, high-yielding, semi-dwarf cv. ‘PR22D89’, when both weed free and with weeds. These results have direct implications for weed and nutrient management in low-input and organic cropping systems.  相似文献   
28.
Pearl millet ( Pennisetum glaucum L.R.Br.) hybrid MH 179 was grown under two moisture regimes viz., optimal moisture and rainfed conditions. The field experiment was continued for three consecutive rainy seasons to quantify the pearl millet development with thermal time. The possible influence of variation in natural sowing date on the relationships between crop development and thermal time have been described. At cardinal temperatures of 10°C (base temperature below which pearl millet development ceases), 33°C (optimal temperature for development) and 45°C (maximum temperature at and above which no development takes place), the crop required 1490–1794°Cd thermal time to reach physiological maturity. The thermal time requirement for different developmental stages was influenced by the sowing time and moisture availability during the growing season of the crop.
The leaf tip appearance on the main shoot of pearl millet in relation to thermal time was almost linear under both moisture conditions requiring about 44–50°Cd ± 2.6 °Cd leaf−1, till the appearance of the flag (last) leaf. However, leaf tip appearance on primary tillers was slightly slower and required 53-58°Cd ± 4.7°Cd for each new leaf. Appearance of first primary tiller was later (at 320°Cd after emergence) under the rainfed condition as compared to the crop under the optimal moisture (at 250°Cd).Thereafter, the tiller appearance in relation to thermal time under both moisture conditions was at a linear rate of about 53-56°Cd ± 9.5°Cd tiller−1.
Effect of microclimatic variations, canopy temperature, radiation and photoperiod on the phenology-thermal time relationships have been discussed under both the moisture conditions.  相似文献   
29.
延川县红枣产业发展现状及对策   总被引:1,自引:0,他引:1  
从自然生态环境、生产条件、枣树品种、栽培技术等方面分析了延川县红枣产业发展优势、限制因素及存在问题,提出了红枣产业发展对策与建议。  相似文献   
30.
南方春大豆不同播季主要农艺性状的变化及其遗传研究   总被引:4,自引:0,他引:4  
马继凤  赵政文 《大豆科学》1998,17(4):331-339
本文以12个南方春大豆早熟品种(系)和12个中熟品种(系)为材料,进行春,秋播试验,研究主要农艺性状的秋播变异率,遗传变异系数,遗传力和遗传进度,结果表明:1,两熟期组秋播变异率平均,除分枝起点为负值以外,其它11个性状在2.36%-52.88%之间,说明秋播对为结性状均有一定影响;熟期组之间各性状秋播变异率的大小亦存在较大差异,如秋播对早熟组株高,主茎节数,结荚节数,结荚高度,主茎荚数和百粒重的  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号