全文获取类型
收费全文 | 153287篇 |
免费 | 8881篇 |
国内免费 | 10001篇 |
专业分类
林业 | 18475篇 |
农学 | 11100篇 |
基础科学 | 9284篇 |
19732篇 | |
综合类 | 74618篇 |
农作物 | 7034篇 |
水产渔业 | 5234篇 |
畜牧兽医 | 15616篇 |
园艺 | 4415篇 |
植物保护 | 6661篇 |
出版年
2024年 | 666篇 |
2023年 | 2460篇 |
2022年 | 3768篇 |
2021年 | 4389篇 |
2020年 | 4362篇 |
2019年 | 4931篇 |
2018年 | 2718篇 |
2017年 | 4879篇 |
2016年 | 6122篇 |
2015年 | 5497篇 |
2014年 | 8040篇 |
2013年 | 8053篇 |
2012年 | 11879篇 |
2011年 | 12127篇 |
2010年 | 9672篇 |
2009年 | 9623篇 |
2008年 | 8753篇 |
2007年 | 10427篇 |
2006年 | 8817篇 |
2005年 | 7262篇 |
2004年 | 5701篇 |
2003年 | 4939篇 |
2002年 | 3679篇 |
2001年 | 3347篇 |
2000年 | 3050篇 |
1999年 | 2336篇 |
1998年 | 1989篇 |
1997年 | 1777篇 |
1996年 | 1629篇 |
1995年 | 1582篇 |
1994年 | 1484篇 |
1993年 | 1217篇 |
1992年 | 1098篇 |
1991年 | 909篇 |
1990年 | 789篇 |
1989年 | 698篇 |
1988年 | 542篇 |
1987年 | 376篇 |
1986年 | 184篇 |
1985年 | 85篇 |
1984年 | 60篇 |
1983年 | 28篇 |
1982年 | 38篇 |
1981年 | 38篇 |
1980年 | 30篇 |
1979年 | 25篇 |
1978年 | 24篇 |
1976年 | 13篇 |
1962年 | 12篇 |
1956年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
82.
83.
Marcus Gumpert 《Growth and change》2019,50(2):775-802
Desmet, Gumpert, and Ort?n have analyzed regional development using the Ricardian model or the Heckscher–Ohlin theorem. However, aspects such as consideration of combined wages, substitution elasticities, marginal costs, fixed costs, and number of companies were completely ignored. This study investigates the underdevelopment of regions in light of Krugman`s core–peripheral model. The extension of the model is intended to analyze the aspects that have so far been ignored and their influence on the benefits of the two regions. The following aspects characterize the model. Two regions with two sectors are considered for the model. The regions are characterized by different technological equipment. The first region is industrial. The second region has an agricultural character. When a new technology is available, both regions can benefit under certain conditions. The financial transfers lead to a convergence of wages. 相似文献
84.
黄瓜病虫害种类多、危害大,传统用药方式严重影响产品质量和口感。为了保证直供上海的黄瓜达到无公害要求,对生产基地采取农业防治、生态控制、生物防治和物理防治相结合的绿色防控措施,化学农药使用量减少30%,综合防治效果在85%以上,有效减少了防治次数,降低了农产品的农药残留,667 m~2增产600 kg,增值600元左右。收到了较好的经济、生态及社会效益。 相似文献
85.
86.
87.
《中国油料作物学报(英文)》2021,6(4):159-163
The International Symposium on Lipid Science and Health (ISLSH), which was organized annually by Oil Crops Research Institute of Chinese Academy of Agricultural Sciences (OCRI-CAAS) since 2016, has gained a strong reputation and attracted hundreds of delegates from around the world for discussion of lipid research trends and advances every year, to promote research and academic exchanges in the fields of lipid science and health. The 5th International Symposium on lipid Science and Health was successfully held in Wuhan, China, from October 23rd to 25th, 2020, to celebrate the 60th anniversary of OCRI-CAAS. The two-day symposium gathered well-known experts specialized in lipid science to share the current state of lipid research with emphasis on aspects covering: (1) lipid profiling and characterization, (2) lipid preparation and modification, (3) lipid improvement and regulation, and (4) lipid nutrition and health. The symposium was conducted by a combination of on-site and network meeting. More than 250 distinguished delegates from academia and industry participated in the on-site multidisciplinary meeting, and thousands of scholars attended the virtual event. This paper is as a record of the symposium proceedings and a brief summary of the advances and trends in 4 aspects of lipid science and health. 相似文献
88.
Four sets of durum samples were used in this study to further understand the interrelationships among hard vitreous kernels (HVK), protein content, and pigment concentration, with a focus on the interaction and synergistic effects of protein content and vitreousness on durum quality. HVK level increases with higher protein content in the range of 9.5–12.5%, but this relationship is less evident in durum samples with high protein content (12.5–14.5%). Both protein content and kernel vitreousness can significantly affect durum milling quality. White starchy kernels (WSK) in low protein durum have a very detrimental impact on milling and pasta processing quality, but high protein content can mitigate the adverse impact of WSK on durum quality. Although protein content plays a dominant role, higher HVK might contribute positively to pasta firmness. There was no significant difference in yellow pigment content between HVK and WSK. However, pigment loss from semolina to dough was higher for WSK than HVK. Despite the difference in protein content, HVK and WSK have little difference in gluten strength. The monomeric protein was preferentially accumulated in HVK. The glutenin proteins of HVK and WSK were similar in the ratios of 1Bx/1By and HMW/LMW-GS. 相似文献
89.
Bertrand C. Y. Collard Joseph C. Beredo Bert Lenaerts Rhulyx Mendoza Ronald Santelices Vitaliano Lopena 《Plant Production Science》2017,20(4):337-352
Rice production needs to increase in the future in order to meet increasing demands. The development of new improved and higher yielding varieties more quickly will be needed to meet this demand. However, most rice breeding programmes in the world have not changed in several decades. In this article, we revisit the evidence in favour of using rapid generation advance (RGA) as a routine breeding method. We describe preliminary activities at the International Rice Research Institute (IRRI) to re-establish RGA on a large scale as the main breeding method for irrigated rice breeding. We also describe experiences from the early adoption at the Bangladesh Rice Research Institute. Evaluation of RGA breeding lines at IRRI for yield, flowering time and plant height indicated transgressive segregation for all traits. Some RGA lines were also higher yielding than the check varieties. The cost advantages of using RGA compared to the pedigree method were also empirically determined by performing an economic analysis. This indicated that RGA is several times more cost effective and advantages will be realized after 1 year even if facilities need to be built. Based on our experience, and previous independent research empirically testing the RGA method in rice, we recommend that this method should be implemented for routine rice breeding in order to improve breeding efficiency. 相似文献
90.
红蓝LED光照强度对茶树生长及生物化学成分的影响 总被引:1,自引:0,他引:1
以‘黔湄601’一年生茶树苗为试材,光量比为1∶3的LED红蓝光作为光源,探讨不同光照强度对茶树幼苗生长特性的影响、光合色素及生物化学成分的变化趋势,探索茶树苗生长发育对光强的响应机制。采用LED精准调节光质和光强,设置50μmol·m-2·s-1、100μmol·m-2·s-1、150μmol·m-2·s-1、200μmol·m-2·s-14个处理。结果表明,不同光强处理15 d后,50μmol·m-2·s-1光照强度有利于茶树叶色素含量的增加及Ca/Cb值的降低;100μmol·m-2·s-1光照强度有利于茶树叶茶多酚含量的降低及氨基酸含量的增加,酚氨比值最低;150μmol·m-2·s-1光照强度对茶树叶重增加有促进作用;200μmol·m-2·s-1光照强度有利于茶树叶茶多酚含量的增加和氨基酸、光合色素含量的减少;酚氨比值最高,光合色素含量最低。红蓝LED光照强度过低、过高都不利于茶叶品质形成,综合考虑,100μmol·m-2·s-1光照强度最有利于茶叶功能成分的积累,是茶叶LED光源设施栽培的理想光照强度。本研究结果对于设施茶树种植具有重要的参考意义。 相似文献