全文获取类型
收费全文 | 14099篇 |
免费 | 885篇 |
国内免费 | 1538篇 |
专业分类
林业 | 1448篇 |
农学 | 1374篇 |
基础科学 | 776篇 |
2840篇 | |
综合类 | 6052篇 |
农作物 | 865篇 |
水产渔业 | 544篇 |
畜牧兽医 | 1409篇 |
园艺 | 422篇 |
植物保护 | 792篇 |
出版年
2024年 | 90篇 |
2023年 | 269篇 |
2022年 | 512篇 |
2021年 | 563篇 |
2020年 | 575篇 |
2019年 | 652篇 |
2018年 | 441篇 |
2017年 | 679篇 |
2016年 | 817篇 |
2015年 | 793篇 |
2014年 | 819篇 |
2013年 | 862篇 |
2012年 | 1083篇 |
2011年 | 1167篇 |
2010年 | 927篇 |
2009年 | 945篇 |
2008年 | 774篇 |
2007年 | 884篇 |
2006年 | 637篇 |
2005年 | 490篇 |
2004年 | 378篇 |
2003年 | 308篇 |
2002年 | 210篇 |
2001年 | 218篇 |
2000年 | 174篇 |
1999年 | 152篇 |
1998年 | 145篇 |
1997年 | 114篇 |
1996年 | 127篇 |
1995年 | 123篇 |
1994年 | 109篇 |
1993年 | 92篇 |
1992年 | 92篇 |
1991年 | 65篇 |
1990年 | 69篇 |
1989年 | 47篇 |
1988年 | 42篇 |
1987年 | 25篇 |
1986年 | 18篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1962年 | 2篇 |
1956年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 22 毫秒
991.
甘薯品种资源抗旱性鉴定研究 总被引:3,自引:0,他引:3
通过对甘薯不同抗旱指标的比较,选用较能客观、准确反映出品种抗旱性的抗旱指数和模糊评判的方法,对50个甘薯品种进行抗旱性评价,初步筛选出17个抗旱性品种,其中有6个品种表现出极强的抗旱性。 相似文献
992.
对冬小麦植被指数(NDVI)变化规律、不同品种冬小麦植被指数差异、农田水肥状况对植被指数的影响以及植被指数与叶面积指数的关系研究结果表明,冬小麦植被指数具有日变化规律,且随冬小麦生长发育而变化,即小麦生长旺盛时植被指数数值较大。不同小麦品种植被指数表现出基本一致的季节变化特点,农田水肥条件交互影响小麦植被指数,水分胁迫时肥料对植被指数的影响明显,而水分满足时肥料对植被指数的影响不明显。 相似文献
993.
994.
张俊斌 《中国水土保持科学》2007,5(1):97-104
对目前台湾地区所使用生态工程施作地点及应用材料等进行调查汇整、研究及分析,并就符合多样性生物栖息环境之生态工程材料进行开发研究,包括现地调查,岛内外资料搜集与资料分类整理,将已汇整的材料表格化。材料组件分为生物材料与非生物材料,而工法组合材料则分为木材工法类、地工材料类、土石材料类、植生工程类和再生材料类。工法所用材料之评估,分别就其功能性、生态栖地特性、经济性和材料再生特性进行综合指数评估。将材料整合评析,如种类、适用范围、使用条件、生命周期及各阶段对环境之兼容性等,进而归纳出生态工程应用材料的规划设计原则。 相似文献
995.
996.
华北地区冬小麦优化灌溉的水分指标与节水性,抗逆性分析 总被引:1,自引:0,他引:1
介绍了冬小麦优化灌溉的水分指标及传统灌溉的区别,并在总结分析试验研究结果的基础上用对比的方法阐述了优化灌溉的节水,节能,抗逆和增产原理。 相似文献
997.
The role of topographic factors in the invasion of hillslopes by Pteronia incana, an unpalatable shrub, was investigated. The study combined field observations with image analysis based on high-resolution infrared imagery. A Digital Elevation Model (DEM) of 20 m spatial resolution was used to derive terrain parameters. The Topographic Wetness Index (WI), a component of the TOPMODEL, was derived from the DEM and its relationship with the spatial distribution of P. incana was explored. The absence/presence of P. incana was noted to be strongly influenced by slope angle and aspect. The probability for P. incana occurrence increased with slope steepness and southerly slope orientation. Abandoned and grazing lands were identified as the main invasion hotspots on hillslopes. The combined influence of slope gradient and aspect, and land use was noted to have promoted the invasion. This is borne out by the concentration of the invasion on abandoned steep slopes with a southerly orientation. 相似文献
998.
Development of Core Subset of Finger Millet Germplasm Using Geographical Origin and Data on 14 Quantitative Traits 总被引:6,自引:0,他引:6
Hari D. Upadhyaya C. L. L. Gowda R. P. S. Pundir V. Gopal Reddy Sube Singh 《Genetic Resources and Crop Evolution》2006,53(4):679-685
Finger millet [Eleusine coracana (L.) Gaertn.] is an important cereal food crop in Africa and South Asia. It is a hardy crop that can be grown in very diverse
environments from almost at sea level to about 2400 m.a.s.l. Finger millet has an excellent food value as its seeds contain
protein ranging from 7 to 14% and are particularly rich in methionine amino acid, iron, and calcium. Despite all these merits,
this crop has been neglected from the main stream of crop improvement research. One of the means to boost its production and
productivity is to enhance utilization of finger millet germplasm to breed superior varieties. Keeping this objective in view,
a core subset of finger millet germplasm (622 accessions) based on origin and data on 14 quantitative traits was developed
from the entire global collection of 5940 accessions held in the genebank at ICRISAT, Patancheru, India. The comparison of
means, variances, frequency distribution, Shannon-Weaver diversity index (H′) and phenotypic correlations indicated that the
core subset represents the entire collection. These tests indicated that sampling was optimal and the diversity has been captured
very well in the core subset. The correlation analysis indicated that panicle exsertion and longest finger length could be
given lower priority in the future germplasm evaluation work of finger millet. 相似文献
999.
Agriculture as a source of phosphorus causing eutrophication in Central and Eastern Europe 总被引:5,自引:0,他引:5
1000.
Nitrate nitrogen losses through subsurface drainage and crop yield are determined by multiple climatic and management variables. The combined and interactive effects of these variables, however, are poorly understood. Our objective is to predict crop yield, nitrate concentration, drainage volume, and nitrate loss in subsurface drainage from a corn (Zea mays L.) and soybean (Glycine max (L.) Merr.) rotation as a function of rainfall amount, soybean yield for the year before the corn-soybean sequence being evaluated, N source, N rate, and timing of N application in northeastern Iowa, U.S.A. Ten years of data (1994-2003) from a long-term study near Nashua, Iowa were used to develop multivariate polynomial regression equations describing these variables. The regression equations described over 87, 85, 94, 76, and 95% of variation in soybean yield, corn yield, subsurface drainage, nitrate concentration, and nitrate loss in subsurface drainage, respectively. A two-year rotation under average soil, average climatic conditions, and 125 kg N/ha application was predicted to loose 29, 37, 36, and 30 kg N/ha in subsurface drainage for early-spring swine manure, fall-applied swine manure, early-spring UAN fertilizer, and late-spring split UAN fertilizer (urea ammonium nitrate), respectively. Predicted corn yields were 10.0 and 9.7 Mg/ha for the swine manure and UAN sources applied at 125 kg N/ha. Timing of application (i.e., fall or spring) did not significantly affect corn yield. These results confirm other research suggesting that manure application can result in less nitrate leaching than UAN (e.g., 29 vs. 36 kg N/ha), and that spring application reduces nitrate leaching compared to fall application (e.g., 29 vs. 37 kg N/ha). The regression equations improve our understanding of nitrate leaching; offer a simple method to quantify potential N losses from Midwestern corn-soybean rotations under the climate, soil, and management conditions of the Nashua field experiment; and are a step toward development of easy to use N management tools. 相似文献