全文获取类型
收费全文 | 23042篇 |
免费 | 1567篇 |
国内免费 | 1447篇 |
专业分类
林业 | 1899篇 |
农学 | 1937篇 |
基础科学 | 537篇 |
3058篇 | |
综合类 | 9470篇 |
农作物 | 1534篇 |
水产渔业 | 1748篇 |
畜牧兽医 | 3769篇 |
园艺 | 1060篇 |
植物保护 | 1044篇 |
出版年
2024年 | 70篇 |
2023年 | 292篇 |
2022年 | 574篇 |
2021年 | 749篇 |
2020年 | 777篇 |
2019年 | 860篇 |
2018年 | 647篇 |
2017年 | 956篇 |
2016年 | 1098篇 |
2015年 | 866篇 |
2014年 | 1123篇 |
2013年 | 1401篇 |
2012年 | 1725篇 |
2011年 | 1831篇 |
2010年 | 1403篇 |
2009年 | 1423篇 |
2008年 | 1286篇 |
2007年 | 1508篇 |
2006年 | 1203篇 |
2005年 | 900篇 |
2004年 | 813篇 |
2003年 | 655篇 |
2002年 | 527篇 |
2001年 | 488篇 |
2000年 | 446篇 |
1999年 | 327篇 |
1998年 | 282篇 |
1997年 | 249篇 |
1996年 | 250篇 |
1995年 | 226篇 |
1994年 | 179篇 |
1993年 | 155篇 |
1992年 | 133篇 |
1991年 | 138篇 |
1990年 | 119篇 |
1989年 | 108篇 |
1988年 | 79篇 |
1987年 | 55篇 |
1986年 | 30篇 |
1985年 | 30篇 |
1984年 | 18篇 |
1983年 | 10篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1962年 | 3篇 |
1956年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
对数字图书馆服务环境重塑的必要性进行了阐述,并从四个方面对数字图书馆服务环境重塑进行了探讨与研究,希望能推动我国数字图书馆的发展。 相似文献
993.
《Journal of plant nutrition》2012,35(3):418-428
AbstractAlthough crude oil contamination is a constraint for crop production, some plants can develop under crude oil contaminated conditions by utilizing crude oil as nutrients after decomposition. A greenhouse trial was conducted to investigate growth, nutritional composition and enzymatic response of vetiver grass in confronting with crude-oil contamination as affected by gibberellic acid (GA) and Tween 80. Application of GA or co-application of GA with Tween 80 significantly increased mean shoot dry weight. Application of Twee 80 alone or in combination with GA significantly increased mean root dry weight as compared to control which was attributed to the effectiveness of Tween 80 alone or in combination with GA on the removal of total petroleum hydrocarbons from polluted soil. Application of crude oil diminished shoot phosphorus, iron, zinc and manganese uptakes. Application of GA and Tween 80, however, compensated the decrease in nutrient uptakes in vetiver grass resulted from crude-oil contamination. Application of crude oil at both 2 and 4% (W/W) levels increased catalase (CAT) activity and proline (PRO) content. Superoxide dismutase (SOD) activity increased only following the application of 2% crude oil level, while addition of all amendments decreased CAT activity. Addition of GA decreased activity of SOD. None of the studied amendments had a significant effect on PRO content. Application of a combination of GA and Tween 80 under crude oil contamination are recommendable since such treatments not only inhibited adverse effect of crude oil on nutrients uptake but also caused that vetiver grass tolerated high level of crude oil contamination. 相似文献
994.
针对山区道路的生态环境特性,遵循评价指标选取的原则,采用层次分析法对目标层山区道路生态环境评价指标进行了筛选、优化,最终形成了2大类准则层(自然环境指标、社会环境指标)和17个指标层的山区道路生态环境评价指标体系。 相似文献
995.
996.
997.
998.
《Plant Production Science》2013,16(4):430-441
AbstractThe objectives of this study were to identify the growth parameters involved in determining the number of spikelets on an individual tiller (ST) and to elucidate how ST is determined in rice (Oryza sativa L.). We examined the correlation of ST with the dry weight (DWT), leaf area (LAT), and the amount of nitrogen (NT) at heading for individual tillers grown under different conditions that were expected to affect spikelet production. In 1999, the japonica rice cultivars “Mineasahi” (short-duration), “Hinohikari” (intermediate-duration), and “Akebono” (long-duration) were transplanted in a paddy field on two different dates (EARLY and LATE). In 2000, Hinohikari was grown under three different treatments (gibberellic acid application, nitrogen topdressing, and thinning of hills at panicle initiation) and without treatment (control). Covariance and partial correlation analyses indicated that ST was positively and essentially correlated with DWT rather than with LAT and NT. The regression of ST on DWT was stable within each cultivar regardless of the treatment, year, tiller order, and number of differentiated spikelets. The slope of the regression was the steepest in the short-duration cultivar. These results suggest that the steep slope is desirable for high-yielding cultivars with large panicles. We conclude that ST is mostly determined by dry matter production of an individual tiller regardless of the number of differentiated spikelets. We present a diagram showing the relationship between dry matter production and the number of differentiated, surviving, and degenerated spikelets on an individual tiller. 相似文献
999.
《Plant Production Science》2013,16(3):235-242
AbstractThe objective of this study was to clarify the effects of soil temperature in the stage from late tillering to panicle initiation (SI) and during the grain-filling stage (SII) on grain setting, dry matter production, photosynthesis, non-structural carbohydrate (NSC), xylem exudation and abscisic acid (ABA) levels in rice (Oryza sativa L. cv. Koshihikari). Rice plants were exposed to four different soil temperatures during SI or SII: 17.5, 25, 31.5 and 36.5°C (ST18, ST25, ST32 and ST37, respectively). The yield, yield components, grain filling and quality in SI were negatively influenced by high soil temperature of 37°C. On the other hand, there was no significant difference in those characters among temperature treatments in SII. The root/shoot ratio was smallest in the ST37 plants in both SI and SII, mainly due to their lighter root weight. At 7 days after initiation of treatment (DAT) in both SI and SII, the photosynthetic and xylem exudation rate tended to increase slightly as soil temperature increased up to 32°C. At 21 DAT, however, the photosynthetic rate was lowest in ST37, with concurrent decrease of diffusion conductance and SPAD value. In addition, decrease of NSC concentration in stem and xylem exudation rate, and increase of ABA level in leaves and xylem exudate were observed in ST37 plants at 21 DAT. These results suggested that high soil temperature before heading especially influenced yield, grain quality and plant growth. Possible mechanisms of the effect of soil temperature are discussed. 相似文献
1000.
《Journal of Crop Improvement》2013,27(1-2):227-260
Abstract Pigeonpea (Cajanus cajan [L.] Millsp.), known by several vernacular and trade names such as red gram, tuar, Angola pea, Congo pea, yellow dhal and oil dhal, is one of the major grain legume crops of the tropics and sub-tropics. It is a favorite crop of small holder dryland farmers because it can grow well under subsistence level of agriculture and provides nutritive food, fodder, and fuel wood. It also improves soil by fixing atmospheric nitrogen. India by far is the largest pigeonpea producer where it is consumed as decorticated split peas, popularly called as ‘dhal’ In other countries, its consumption as whole dry seed and green vegetable is popular. Its foliage is used as fodder and milling by-products form an excellent feed for domestic animals. Pigeonpea seeds contain about 20-22% protein and appreciable amounts of essential amino acids and minerals. Dehulling and boiling treatments of seeds get rid of the most antinutritional factors such as tannins and enzyme inhibitors. Seed storage causes considerable losses in the quality of this legume. The seed protein of pigeonpea has been successfully enhanced by breeding from 20-22% to 28-30%. Such lines also agronomically performed well and have acceptable seed size and color. The high-protein lines were found nutritionally superior to the cultivars because they would provide more quantities of utilizable protein and sulfur-containing amino acids. 相似文献