全文获取类型
收费全文 | 1702篇 |
免费 | 125篇 |
国内免费 | 240篇 |
专业分类
林业 | 149篇 |
农学 | 88篇 |
基础科学 | 61篇 |
474篇 | |
综合类 | 756篇 |
农作物 | 57篇 |
水产渔业 | 65篇 |
畜牧兽医 | 263篇 |
园艺 | 30篇 |
植物保护 | 124篇 |
出版年
2024年 | 5篇 |
2023年 | 23篇 |
2022年 | 67篇 |
2021年 | 54篇 |
2020年 | 48篇 |
2019年 | 73篇 |
2018年 | 62篇 |
2017年 | 84篇 |
2016年 | 85篇 |
2015年 | 87篇 |
2014年 | 104篇 |
2013年 | 123篇 |
2012年 | 144篇 |
2011年 | 141篇 |
2010年 | 124篇 |
2009年 | 119篇 |
2008年 | 120篇 |
2007年 | 128篇 |
2006年 | 90篇 |
2005年 | 75篇 |
2004年 | 68篇 |
2003年 | 43篇 |
2002年 | 39篇 |
2001年 | 30篇 |
2000年 | 26篇 |
1999年 | 21篇 |
1998年 | 14篇 |
1997年 | 15篇 |
1996年 | 12篇 |
1995年 | 9篇 |
1994年 | 7篇 |
1993年 | 8篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1987年 | 1篇 |
1983年 | 2篇 |
1963年 | 1篇 |
排序方式: 共有2067条查询结果,搜索用时 15 毫秒
21.
为了观察3种治疗方法治疗犬传染性肝炎的疗效并进行对比,选出较好的治疗方案,以提高犬传染性肝炎的治愈率。本研究选宠物医院确诊为犬传染性肝炎的病犬60只,将患犬随机分4组,分别采用茵陈篙汤加味配合西药、单用茵陈篙汤加味、单用西药的治疗方法,并设对照组。结果显示,茵陈篙汤加味配合西药组的治愈率86.67%;茵陈篙汤加味组治愈率73.33%;西药组治愈率66.67%;对照组治愈率为0。试验表明,采用茵陈篙汤加味配合西药治疗犬传染性肝炎的疗效高于其他两种方法,为临床治疗该病提供了确实可行的治疗方法。 相似文献
22.
23.
The extensigraph is particularly useful in characterizing dough viscoelastic properties; however, testing throughput for standard method is low due to the prerequisite for farinograph water absorption, long dough resting and milling to prepare large amounts of flour. Therefore, a rapid extensigraph method was developed that reduced sample size (165 g wheat) for milling and more than tripled throughput. Wheat is milled in Quadrumat Junior mill with a modified sieving system. The resulting flour (100 g) was mixed with a pin mixer at constant water absorption to allow the evaluation of wheat genotypes at the absorption level they are expected to perform. Dough was subsequently stretched by an extensigraph after 15 min of floor time and 30 min resting. Strong correlations for extensigram Rmax (r > 0.93), extensibility (r > 0.64) and area (r > 0.88) were found for the proposed method compared to the standard method. Mixing parameters (time and energy) obtained during dough preparation provided further information about dough strength and mixing requirement. By significantly reducing sample size requirement and increasing testing throughput, this rapid extensigraph method can be widely adopted in milling and baking industry and meets the need for a fast evaluation of dough strength in breeding trials. 相似文献
24.
成都平原不同作物种植模式生产效率及其影响因素研究—以成都市郫都区为例 总被引:1,自引:0,他引:1
为研究成都平原不同种植模式的农田生产效率,基于2017年对成都市郫都区13个乡镇92户农户调查数据,运用DEA-Tobit模型分析了郫都区主要的水旱轮作和旱作种植模式的农田经营效率及影响因素。研究结果表明:不同种植模式平均农田生产效率为0.793,不同模式农田生产效率排序依次为蔬菜连作或轮作(0.957)、水稻-大蒜(0.847)、水稻-油菜(0.782)、韭菜连作(0.759)、水稻-蔬菜(0.722)、水稻-圆根萝卜(0.689),农田生产效率未达到有效值1的原因主要是规模效益较低;同时,各模式均存在资金和劳动力投入冗余,水稻-蔬菜、水稻-油菜模式还存在产出不足问题;影响6种模式生产效率的因素均不相同,政策因素对农田生产效率的影响相对较大。为进一步提高郫都区农田生产效率,建议适度推广农田规模化经营,加强农村富余劳动力转移,完善各类农业政策措施。 相似文献
25.
美国德克萨斯州高地平原区地下水灌溉管理方法研究 总被引:2,自引:2,他引:0
《灌溉排水学报》2019,(1)
德克萨斯州高地平原区是美国灌溉和旱地作物的生产基地,其灌溉水源主要来源于奥加拉拉(Ogallala)地下水含水层。然而,自从1950年灌溉农业发展以来,由于对奥加拉拉含水层地下水的过度开采,使得区域地下水位严重下降,有些地区地下水位下降超过50 m。为了保护地下水资源和实现地下水可持续利用,2000年以来美国德克萨斯州高平原地区在节水压采方面开展了一系列工作,取得了较好的成效。采取的主要措施包括:用德克萨斯州高地平原蒸腾蒸发网络(The Texas High Plains Evapotranspiration Network, TXHPET)进行灌溉及地下水管理,改变作物品种,改进灌溉技术,改变种植结构,保护性耕作方法,加强降雨管理,将小部分灌溉农田转为旱作农田等。该区域1958年的灌溉面积为183万hm~2,1974年灌溉面积达到峰值,为242万hm~2;1989年灌溉面积降为159万hm~2,由于喷灌技术的推广应用,2000年灌溉面积恢复到187万hm~2。1958年大多数灌区为地面灌溉,仅有11%的灌溉面积为喷灌。1974年之后,灌溉总面积在减少,主要灌溉方式转为喷灌,中心支轴式喷灌面积稳步增长。自1989年之后,喷灌在该区域快速发展,2000年喷灌面积已占该区域灌溉面积的72%。早期的喷灌系统在较高压力下运行,自20世纪80年代,低压喷灌系统已全面使用。我国华北地区长期超量开采地下水与美国德克萨斯州高原区地下水超采情况及问题相似。兹系统介绍了美国德克萨斯州高地平原区在地下水超采情况下采取的综合措施拟为我国地下水超采地区的地下水管理工作提供技术与经验参考。 相似文献
26.
Soil organic carbon stock variability in the Northern Gangetic Plains of India: interaction between agro‐ecological characteristics and cropping systems 下载免费PDF全文
V. K. Singh M. Rani B. S. Dwivedi S. K. Singh V. K. Gupta K. Majumdar R. P. Mishra 《Soil Use and Management》2015,31(4):461-473
Soil organic carbon (SOC) content and its spatial distribution in the Northern Gangetic Plain (NGP) Zone of India were determined to establish the cause–effect relationship between agro‐ecological characteristics, prevailing crop management practices and SOC stock. Area Spread Index (ASI) approach was used to collect soil samples from the NGP areas supporting predominant cropping systems. Exponential ordinary kriging was found most suitable geo‐statistical model for developing SOC surface maps of the NGP. Predicted surface maps indicated that 43.7% area of NGP had 0.5–0.6% SOC, while the rest of the area was equally distributed with high (0.61–0.75%) and low (< 0.5%) SOC content levels. Averaged across cropping systems, maximum SOC content was recorded in Bhabar and Tarai Zone (BTZ), followed by Central Plain Zone (CPZ), Mid‐Western Plain Zone (MWPZ), Western Plain Zone (WPZ) and South‐Western Plain Zone (SWPZ) of the NGP. The SOC stock was above the optimum threshold (> 12.5 Mg/ha) in 97.8, 57.6 and 46.4% areas of BTZ, CPZ and MWPZ, respectively. Only 9.8 and 0.4% area of WPZ and SWPZ, respectively, had SOC stock above the threshold value. The variation in SOC stock was attributed largely to carbon addition through recycling of organic sources, cropping systems, tillage intensity, crop or residue cover and land‐use efficiency, nutrient‐use pattern, soil texture and prevailing ecosystem. Adoption of conservation agriculture, balanced use of nutrients, inclusion of legumes in cropping systems and agro‐forestry were suggested for enhancing SOC stock in the region. 相似文献
27.
HUANG Ping ZHANG Jia-bao XIN Xiu-li ZHU An-ning ZHANG Cong-zhi MA Dong-hao ZHU Qiang-gen YANG Shan WU Sheng-jun 《中国农业科学(英文版)》2015,(1)
Cropland productivity has been signiifcantly impacted by soil acidiifcation resulted from nitrogen (N) fertilization, especialy as a result of excess ammoniacal N input. With decades’ intensive agricul... 相似文献
28.
In this paper the results of the first comprehensive study on perception of and satisfaction with urban forests and green space in seven Southeast European cities are presented. The aims of the paper are to analyse 1) citizen perceptions of the current state of urban forests and green space in their cities, 2) to what extent current urban forests and green space meet their needs and how this can be improved. A cross-sectional study was conducted by using a common face-to-face survey questionnaire. Respondents were selected based on census data though a stratified sampling procedure by taking into account age, gender and city district (n = 384 in each city). The results showed that citizens genuinely care for urban forests and green space in their cities, but are not satisfied with their current state. The respondents found issues related to misbehaviour of other users, the presence and quality of facilities, as well as the presence and quality of management or maintenance the most pressing. There were more statistically significant differences than similarities between cities. Socioeconomic variables explained perceptions only to some extent. Citizens were very supportive of educational campaigns about the importance of urban forests and green space as well as of better enforcement of the existing regulations though having more community wardens that were expected to tackle current unsatisfactory situations. Urban planning and urban forest and green space management in these cities are facing many problems characteristic for post-socialist countries. Study findings are expected to contribute to decision making in urban planning and natural resource management. 相似文献
29.
为表达和纯化SP-B蛋白,先对SP-B基因进行稀有密码子优化,PCR反应获得SP-B片段,构建重组质粒pGEX4T-1/SP-B,转化到E.coli BL21(DE3)中诱导表达;用SDS-PAGE与Western blot进行检测;用GSTPrep FF 16/10对融合蛋白进行纯化。经双酶切鉴定证实质粒中插入基因长250bp,测序结果与大鼠SP-B cDNA序列相符;质粒转化后用IPTG进行诱导,在分子质量约34ku处出现1个新条带,与pGEX4T-1/SP-B蛋白预期大小一致,且该融合蛋白能可溶性表达并被纯化。结果表明成功构建了pGEX4T-1/SP-B重组质粒,表达、纯化得到GST/SP-B蛋白,为研究肺表面活性物质替代药物奠定了基础。 相似文献
30.
Eukaryotic translation elongation factor 1A (eEF1A) in plant is a multifunctional protein. In our previous study, we identified a 651-bp EST sequence of eEF-1α from a suppression subtractive hybridization (SSH) library of Chinese jujube (Ziziphus jujuba Mill.), which was established under jujube witches' broom (JWB) phytoplasma stress. Here we isolated the eEF1A gene (ZjeEF-1α, JF488063) from Chinese jujube by single oligonucleotide nested (SON)-PCR and rapid amplification of cDNA ends (RACE). ZjeEF-1α contains an open reading frame (ORF) of 1344 bp, encoding a polypeptide of 447 amino acids with an estimated molecular mass of 49.29 kDa and a theoretical pI of 9.10. ZjeEF-1α shared over 92% similarity with eEF-1α proteins from other 24 eukaryotes including plants and animals. Search Pfam predicted that ZjeEF-1A contains three typical eEF1A functional domains. Moreover, the corresponding genomic sequence of ZjeEF-1α was also sequenced, in which a 115-bp intervening sequence with splicing site GT-AG was found. Real-time quantitative PCR (RT-qPCR) and western blotting assays revealed that the expression of ZjeEF-1α was enhanced in resistant cultivar ‘Xingguang’ and decreased in sensitive cultivar ‘Zanhuangdazao’ at early stages of phytoplasma infection. It is proved that ZjeEF-1A expression is early response to phytoplasma infection and its possible functions in resistant process to JWB phytoplasma are discussed. 相似文献