全文获取类型
收费全文 | 11806篇 |
免费 | 623篇 |
国内免费 | 1225篇 |
专业分类
林业 | 1170篇 |
农学 | 1346篇 |
基础科学 | 1052篇 |
1597篇 | |
综合类 | 4187篇 |
农作物 | 794篇 |
水产渔业 | 483篇 |
畜牧兽医 | 1700篇 |
园艺 | 575篇 |
植物保护 | 750篇 |
出版年
2024年 | 50篇 |
2023年 | 174篇 |
2022年 | 385篇 |
2021年 | 461篇 |
2020年 | 471篇 |
2019年 | 470篇 |
2018年 | 317篇 |
2017年 | 433篇 |
2016年 | 404篇 |
2015年 | 550篇 |
2014年 | 533篇 |
2013年 | 644篇 |
2012年 | 836篇 |
2011年 | 793篇 |
2010年 | 761篇 |
2009年 | 723篇 |
2008年 | 734篇 |
2007年 | 677篇 |
2006年 | 550篇 |
2005年 | 509篇 |
2004年 | 274篇 |
2003年 | 333篇 |
2002年 | 384篇 |
2001年 | 418篇 |
2000年 | 315篇 |
1999年 | 251篇 |
1998年 | 174篇 |
1997年 | 140篇 |
1996年 | 147篇 |
1995年 | 130篇 |
1994年 | 127篇 |
1993年 | 97篇 |
1992年 | 89篇 |
1991年 | 68篇 |
1990年 | 65篇 |
1989年 | 53篇 |
1988年 | 35篇 |
1987年 | 22篇 |
1986年 | 10篇 |
1985年 | 8篇 |
1984年 | 12篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1964年 | 2篇 |
1956年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
81.
改性蒙脱石对黄曲霉毒素B_1和玉米赤霉烯酮的吸附研究 总被引:1,自引:0,他引:1
本试验旨在探究4种不同改性蒙脱石对黄曲霉B1(AFB1)和玉米赤霉烯酮(ZEN)的体外吸附性能。采用体外吸附试验,在霉菌毒素污染的喷浆玉米皮中添加4种改性蒙脱石,检测AFB1和ZEN的浓度变化,以探究不同种类及不同添加比例改性蒙脱石对AFB1和ZEN的吸附作用。结果表明:4种改性蒙脱石对AFB1和ZEN均有显著吸附作用,其中膨润土经十八烷基三甲基氯化铵改性制备的复合改性蒙脱石II型对AFB1和ZEN的吸附效果最好,在添加量为1%时,对AFB1和ZEN的吸附率分别为62.60%和43.38%。在本体外试验条件下,4种改性蒙脱石对喷浆玉米皮中AFB1和ZEN均具有吸附作用,可以降低喷浆玉米皮中的霉菌毒素含量,为改性蒙脱石在饲料脱毒剂的使用提供参考。 相似文献
82.
Boyu LEI Zhenfei ZHENG Jifa CUI Jin ZHAO Chris NEWMAN Youbing ZHOU 《Integrative zoology》2023,18(4):647-660
Ecotourism, by definition, aims to engage peoples’ interest in wildlife and the environment. The use of tourist roads and trails to access sites within protected areas (PAs) can detrimentally affect the behavior and distribution of species. The way mammals respond to anthropogenic pressures may differ across taxonomic, functional, and phylogenetic groups; nevertheless, how ecotourist trail-use affects these different diversity remains under-investigated. Here, we assessed 6 metrics of taxonomic, phylogenetic, and functional diversity for a mammal community in a PA in central China, recording how Trail use (using Trail type as a proxy) and habitat variables affected sightings and signs of mammals across 60 replicate 0.5 km transects. We then examined how Trail use affected the taxonomic, functional, and phylogenetic diversity indices of species (>1 kg). Using generalized liner mixed modeling, we identified that more used trail types had a greater adverse effect on all diversity richness indices than did less used trail types. Consequently, tourist pressure was associated with a general tendency to homogenize the site's mammal community. In contrast, the effects of Trail Types on all diversity evenness indices were non-significant. Furthermore, more developed and more heavily used trail types had a greater, significant negative effect on taxonomic, functional, and phylogenetic richness, whereas these richness indices were unaffected by minor trail types, used less intensively. As a general principle, lower biodiversity indices reduce ecosystem resilience, and so it is vital to better understand these responses to balance public access against biodiversity management in PAs. 相似文献
83.
随着水产养殖产业的高速发展,水产养殖集约化规模扩大,养殖动物密度增大,容易造成氧化应激反应,这迫使水产养殖从业者亟需寻找无毒无害且高效的饲料添加剂以提高水产动物的抗应激能力。硒(Se)是一种人体和动物生长繁育必需的微量元素,其生物学功能主要通过硒蛋白表达,饲料中添加适量的硒能够增强水产动物的抵抗力。本文综述了硒和硒蛋白的种类以及硒对水产动物的生理机制,同时对硒在水产养殖中的应用进行综述,旨在总结不同硒源作为水产饲料添加剂在改善水产动物生长、免疫与肉质等方面的作用,为其在水产养殖中的高效应用提供科学参考。 相似文献
84.
本文针对天祝县岔口驿马产业发展的现状,分析了岔口驿马产业发展的潜在优势,通过政府扶持和政策引导,为岔口驿马产业的健康、快速发展提供了依据。 相似文献
85.
甘肃省草原产草量动态监测模型 总被引:1,自引:0,他引:1
利用MODIS数据和地面实测资料,研究了甘肃省不同草原区的最适草原生物量遥感估算模型,并反演了甘肃省2005-2009年的草原产草量,分析了其空间分布特征。结果表明,不同草原区适合的植被指数和反演模型类型存异,其中河西走廊高平原荒漠草原区适合的植被指数是RVI、模型类型为对数模型,甘南高原草甸草原区适合的植被指数是EVI、模型类型为指数模型,而黄土高原温性草原区适合的植被指数是NDVI、模型类型为二次多项式模型。甘肃省2009年草原总产鲜草3 718.30万t,整体呈现东北低、西南高的空间变化过程,形成3个高产中心,分别是甘南高原、祁连山北麓中东段和陇南南部。与1985年相比,2005年草原明显减产(相对变化率V=19.34%),但2005-2009年间甘肃省草原产草量有总体上升的趋势。 相似文献
86.
Imaging techniques have been introduced to assess the efficacy and toxicity of developing pharmaceuticals. The purpose of this study was to perform a comprehensive characterization of collagen-induced arthritis (CIA) in rats using micro-computed tomography (micro-CT) and to compare the results with data from conventional pathological examination. Arthritis was induced by collagen in 24 female Wistar rats. Micro-CT and pathological analyses were performed to assess arthritis progression. Micro-CT analysis showed marked joint destruction occurring in a time-dependent manner following collagen administration. Bone volume was significantly decreased in the tibia at weeks 3 and 4 compared to week 0 (p < 0.05 and p < 0.01, respectively). Additionally, percent bone volume was significantly reduced in the tibia at week 4 compared to week 0 (p < 0.05). In contrast, bone surface/bone volume and trabecular separation were significantly increased in the tibia of the animals at week 4 compared to week 0 (p < 0.05). Severe joint destruction with extensive inflammation, erosion of cartilage and bone, and infiltration of inflammatory cells were observed in the knee joints of the collagen-treated rats. Taken together, micro-CT made it possible to quantify CIA lesions and should be performed with pathological examination in rats. 相似文献
87.
富硒女贞子粗多糖对小鼠免疫功能的影响 总被引:1,自引:0,他引:1
从富硒女贞子及女贞子中提取粗多糖,探讨其对小鼠免疫功能的影响。将90只小鼠随机均分为3组:对照组、富硒女贞子粗多糖组、普通女贞子粗多糖组。对照组灌服生理盐水,试验组小鼠灌服粗多糖液,灌服2次,每次连续5 d。2次灌胃的第3天注射卵清蛋白,二免后测定胸腺脾脏指数;MTT法检测脾淋巴细胞增殖水平;ELISA试剂盒检测血清中IL-2、IL-4、IFN-γ生成水平及相应抗体生成水平。结果显示:与对照组相比,试验组脾脏和胸腺指数明显升高,脾淋巴细胞增殖作用显著提高;IL-2、IL-4、IFN-γ生成水平明显提高,其中IFN-γ与对照组存在显著差异;而对特异性卵清抗体生成影响不大。这表明富硒女贞子粗多糖较普通女贞子粗多糖能更好地促进机体非特异性免疫及细胞免疫,从而增强机体免疫功能,在特异性体液免疫的作用方面则没有表现出明显的规律性,还需进一步研究。 相似文献
88.
The aim of the present study was to clarify the effect of photoperiod on secretory patterns of growth hormone (GH) in male goats. Adult male goats were kept at 20°C with an 8‐h or 16‐h light photoperiod, and secretory patterns of GH secretion were compared. In addition, plasma profiles of prolactin (PRL), insulin‐like growth factor‐I (IGF‐I) and testosterone (T) were also examined to characterize GH secretion. GH was secreted in a pulsatile manner. There was no significant difference in pulse frequency between the 8‐h and 16‐h photoperiods. However, GH pulse amplitude tended to be greater in the group with the 16‐h photoperiod (P = 0.1), and mean GH concentrations were significantly greater in the 16‐h photoperiod (P < 0.05). The GH‐releasing response to GH releasing hormone was greater in the 16‐h than 8‐h photoperiod (P < 0.05). Plasma PRL and IGF‐I levels were higher in the 16‐h than 8‐h photoperiod (P < 0.05). In contrast, plasma T levels were lower in the 16‐h photoperiod (P < 0.05). These results show that a long light photoperiod enhances the secretion of GH as well as PRL and IGF‐I, but reduces plasma T concentrations in male goats. 相似文献
89.
分析了湖州市1998年迟中秋蚕血液型脓病暴发的原因,并提出了若干控制该病的对策。 相似文献
90.
桑树多倍体育种材料遗传背景的AFLP分析 总被引:5,自引:1,他引:5
利用AFLP(Amplified Fragment Length Polymorphism)分子标记技术,即扩增片段长度多态性,从DNA分子水平对19份人工三倍体桑育种材料进行了遗传背景分析,构建了指纹图谱.19份育种材料可组配70个杂交组合,各材料间AFLP相似系数大于0.750 0的有54个组合,经AFLP分析认为,它们不宜作亲本间杂交组合;AFLP相似系数小于0.750 0的有16个组合,经AFLP分析认为它们适于作亲本间杂交组合.本研究从基因组DNA分子水平上为人工三倍体桑品种选育以及杂交亲本的选择和组配提供了遗传背景依据. 相似文献