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   817篇
  免费   83篇
  国内免费   46篇
林业   87篇
农学   23篇
基础科学   3篇
  115篇
综合类   226篇
农作物   37篇
水产渔业   70篇
畜牧兽医   125篇
园艺   106篇
植物保护   154篇
  2024年   10篇
  2023年   25篇
  2022年   60篇
  2021年   38篇
  2020年   53篇
  2019年   72篇
  2018年   43篇
  2017年   47篇
  2016年   47篇
  2015年   46篇
  2014年   39篇
  2013年   41篇
  2012年   39篇
  2011年   49篇
  2010年   48篇
  2009年   42篇
  2008年   47篇
  2007年   48篇
  2006年   47篇
  2005年   27篇
  2004年   15篇
  2003年   10篇
  2002年   10篇
  2001年   8篇
  2000年   13篇
  1999年   3篇
  1998年   4篇
  1997年   1篇
  1996年   3篇
  1995年   2篇
  1994年   1篇
  1993年   1篇
  1992年   1篇
  1989年   1篇
  1982年   1篇
  1981年   1篇
  1956年   3篇
排序方式: 共有946条查询结果,搜索用时 0 毫秒
81.
Common ragweed invasion poses serious risks to human health, biodiversity and agricultural production throughout the world. Although ragweed has an enormous potential to expand its range in Turkey, studies on ragweed have only concentrated on the Black Sea region. An exploratory survey was conducted to observe the level of ragweed occurrence on the nodes of predecided 10 × 10 km grids in the Thrace region of Turkey. Ragweed populations were observed in 44 out of 129 sites in a wide range of habitats, including roadsides, pastures, agricultural fields and non‐agricultural areas. The highest levels of ragweed infestation were recorded in the agricultural fields, followed by the roadsides. The most‐invaded crop was sunflower. The sunflower fields had the highest ragweed coverage as well and invasion even resulted in crop failure alongside the field borders. A spatial analysis of the data indicated that ragweed exhibited an aggregated pattern over the Thrace region. Ragweed distribution was not associated with the characteristics of the soils, which had a varying range of pH, electrical conductivity and texture. The results revealed that ragweed invasion can arise as a serious weed problem, interfering with the sustainability of sunflower production in Thrace and other sunflower‐producing regions of the country. A high degree of ragweed infestation also will contribute to the pollen level counts for the most crowded cities in the region, posing a serious danger to human health.  相似文献   
82.
AIM: To investigate the expression of Grb2-associated binding protein 2 (Gab2) in human osteosarcoma cells and its relationship with the invasion and metastases of human osteosarcoma cells. METHODS: The technique of small RNA interference was used to transfect human osteosarcoma U2-OS cell lines. Western blotting and RT-PCR were used to detect the protein and mRNA expression of Gab2 in transfected U2-OS cells. After transfection, through chemotaxis and invasion assays in vitro, the cell migration and invasion abilities were detected. RESULTS: After transfection, the expression of Gab2 at mRNA and protein levels in Gab2 siRNA transfected cells (SiGab2/U2-OS) was lower than that in scrambled siRNA transfected cells (Scr/U2-OS) and U2-OS cells. After stimulation with epidermal growth factor (EGF) at concentration of 10 μg/L, the migration SiGab2/U2-OS cells was significantly less than Scr/U2-OS cells and U2-OS cells (P<0.01). The number of invasion cells of SiGab2/U2-OS group was significantly lower than the other 2 control groups (P<0.01). CONCLUSION: Inhibition of Gab2 expression obviously attenuates the migration and invasion abilities of human osteosarcoma U2-OS cell line.  相似文献   
83.
84.
朱珣之  高婷 《草业科学》2014,8(10):1900-1907
中国入侵植物种类繁多、危害严重,对入侵物种的准确鉴定是开展各项研究的基础。本研究采用植物DNA条形码序列ITS2片段来探讨其在入侵植物中的鉴定能力。结果表明,ITS2序列在入侵物种及其近缘物种间存在明显的遗传差异,种间变异大于种内变异,在17种常见入侵植物与36种近缘物种的300份样品鉴定中成功率达95.5%。构建的NJ树可以很好地显示各不同入侵植物物种的聚类。此外,ITS2的二级结构也具有一定的系统学及分类学意义。因此,ITS2条形码序列能够作为入侵植物分子鉴定的有力工具,具有重要的应用价值。  相似文献   
85.
本文分析了白三叶草十多年生黑麦草混播人工草地上杂草入侵与放牧强度之间的关系,得出如下初步结论:1)杂草入侵的种数主要决定于放牧强度;2)α物种多样性随放牧加重而有增-减-增的趋势;3)入侵的主要杂草种为点腺过路黄等8个种;4)所论人工草地都处在恢复演替的先锋阶段,因而草地退化的进程还是能予以遏制的。  相似文献   
86.
The intestine is the primary organ responsible for digestion and absorption of nutrients and is frequently subjected to external environmental stimulations leading to the development of inflammatory bowel disease (IBD), which can cause serious harm to intestinal health in animals. Dietary amino acids play important roles in promoting intestinal development and maintaining intestinal health and exert diverse effects through multiple signaling pathways on the prevention and treatment of IBD, including affecting the physiological activities of intestinal epithelial cells, improving intestinal barrier function, reducing intestinal oxidative damage, regulating the production of inflammatory cytokines, and promoting the expression of endogenous antimicrobial peptides, and involved in main signaling pathways including AMP-activated kinase (AMPK), mammalian target of rapamycin (mTOR), mitogen-activated protein kinase (MAPK), Toll-like receptors (TLRs), nucleotide binding oligomerization domain (NOD)/nuclear factor kappa-B (NF-κB). In this review, basic characteristics of IBD, effects and involved signaling pathways of the amino acids on IBD, and effects and applications of amino acids in maintaining intestinal health in livestock and poultry production were reviewed, so as to provide effective clues and strategies for dietary nutrients in the prevention and treatment of IBD.  相似文献   
87.
Kiss-1基因编码的Kisspeptins可通过其受体GPR54的介导来调控哺乳动物生殖内分泌。近年来的研究表明,Kiss-1基因具有抑制肿瘤转移、影响滋养细胞浸润、启动动物青春发育、调控能量平衡以及生物节律的功能。因此,本文就Kiss-1基因功能的研究进展做一综述。  相似文献   
88.
Adrenalectomy is the treatment of choice for adrenal tumors that are producing adverse clinical signs. Surgical planning prior to adrenalectomy is aided by identifying tumors with invasion into adjacent vessels or the presence of a tumor thrombus extending into the caudal vena cava. In this paper, we evaluated the sensitivity and specificity of ultrasound in determining if vascular invasion or tumor thrombus is present. Thirty-four dogs with 36 adrenal tumors were reviewed retrospectively. Overall, 36% of tumors had vascular invasion. Abdominal ultrasound was 100% sensitive and 96% specific in identifying the presence of a tumor thrombus in the caudal vena cava. The sensitivity and specificity was 76% and 96%, respectively, when all forms of vascular invasion were evaluated and included patients with vascular wall invasion without concurrent thrombus. Abdominal ultrasound is a good screening tool for identifying vascular invasion or tumor thrombus associated with adrenal tumors in dogs.  相似文献   
89.
黄花刺茄的适应性、繁殖能力、传播能力、侵害力、排挤性极强,是高度危险的检疫性有害植物,被称为"生态杀手"。文章对黄花刺茄的生物学特性、危害特点与防控措施作了简要叙述,以期引起自治区各级政府及相关部门的高度重视,提早防治,不要任其肆意蔓延,破坏我区的生态环境。  相似文献   
90.
研究草履蚧传播扩散规律,主要为预防和控制该虫提供科学依据。通过实地调查获得并分析漯河地区多个草履蚧侵入历史、传播规律,对全市典型发生乡镇的主要参数进行研究,结果表明草履蚧在漯河地区局域扩散速度一般为V=√S/t=63.3 hm2。  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