全文获取类型
收费全文 | 679篇 |
免费 | 42篇 |
国内免费 | 63篇 |
专业分类
林业 | 34篇 |
农学 | 41篇 |
基础科学 | 31篇 |
99篇 | |
综合类 | 328篇 |
农作物 | 34篇 |
水产渔业 | 22篇 |
畜牧兽医 | 105篇 |
园艺 | 59篇 |
植物保护 | 31篇 |
出版年
2024年 | 6篇 |
2023年 | 22篇 |
2022年 | 31篇 |
2021年 | 35篇 |
2020年 | 35篇 |
2019年 | 34篇 |
2018年 | 19篇 |
2017年 | 47篇 |
2016年 | 26篇 |
2015年 | 45篇 |
2014年 | 31篇 |
2013年 | 42篇 |
2012年 | 61篇 |
2011年 | 69篇 |
2010年 | 52篇 |
2009年 | 40篇 |
2008年 | 35篇 |
2007年 | 40篇 |
2006年 | 27篇 |
2005年 | 26篇 |
2004年 | 14篇 |
2003年 | 11篇 |
2002年 | 10篇 |
2001年 | 8篇 |
2000年 | 6篇 |
1999年 | 5篇 |
1995年 | 1篇 |
1993年 | 1篇 |
1991年 | 1篇 |
1989年 | 2篇 |
1981年 | 2篇 |
排序方式: 共有784条查询结果,搜索用时 62 毫秒
21.
为了研究益生菌发酵乳无菌提取物对食源性有害微生物(空肠弯曲杆菌)有毒基因表达的抑制作用,以利用空肠弯曲杆菌的有毒基因flaA σ28启动子和无启动子的质粒pRYluxCDABE联结构建的生物冷光转基因模型为试验材料,通过检测生物发光特性的方法,研究了空肠弯曲杆菌有毒基因flaA表达与益生菌(5种双岐杆菌,6种乳酸杆菌)发酵乳无菌提取物之间的关系。结果表明,益生菌发酵乳无菌提取物对空肠弯曲杆菌flaA σ28启动子的活性有显著的抑制作用(P<0.05),并可显著抑制空肠弯曲杆菌有害基因flaA的表达。 相似文献
22.
AIM:To investigate the effect of ethyl pyruvate (EP) on acute lung injury in dogs with septic shock.METHODS:Twenty dogs with septic shock induced by lipopolysaccharide (LPS) were randomly divided into two groups:dog received placebo (Ringers solution; control group, n=8) or ethyl pyruvate in lactated Ringers solution (0.05 g/kg loading dose over 10 min, thereafter 0.05 g· kg-1·h-1 for 12 h; EP treatment group, n=12).The parameters of respiratory mechanics, including lung dynamic compliance (Cdyn), lung total compliance (Ctot), inspiratory airway resistance (Rawi), peak inspiratory pressure (PIP), work of breathing (WOB), and arterial blood gases were monitored every 4 h after basic measurements (pre-LPS).The contents of TNF-α, IL-6 and IL-10 in serum were also detected by ELISA and compared between two groups.RESULTS:The changes of respiratory mechanics and arterial blood gases were in line with acute lung injury after septic shock induced by LPS.Oxygen index (OI), HCO-3and pH dropped 4 h after septic shock.On the contrary, PCO2 elevated significantly compared with that of septic shock before (P<0.05).Cdyn, Ctot decreased and Rawi, PIP, WOB increased significantly 8 h after septic shock (P<0.05).The changes in parameters of respiratory mechanics and arterial blood gases in control group were more distinguished than those in EP treatment group.There were significantly differences between two groups 8 h after septic shock (P<0.05).Although the significant improvement of respiratory mechanics was not observed, EP did prevent the parameters from worsening further more.Significantly differences between the two groups 12 h after septic shock (P<0.05) were found.Ethyl pyruvate also regulated the network of cytokines:increased the level of TNF-α, IL-6 and reduced the content of IL-10 in serum significantly compared with control group (P<0.05).CONCLUSION:Ethyl pyruvate has protective effects on acute lung injury in dogs with septic shock. 相似文献
23.
寇发荣 《拖拉机与农用运输车》2009,36(2)
将目前航空航天领域先进的EHA(Electro-Hydrostatic Actuator)作动技术引入汽车主动悬架控制结构中。设计了模糊控制以及参数自调整模糊控制算法,并进行了基于EHA主动悬架的参数自调整模糊控制仿真分析,证明了该算法对悬架系统的振动控制具有较好的效果。在所研制开发的两自由度悬架系统试验台架上进行了试验研究,结果表明,与被动悬架系统相比,自调整模糊控制EHA主动悬架系统控制效果显著。 相似文献
24.
为获得高寒草甸根际土中优良溶磷菌资源,本研究从青海省高寒草甸根际土中筛选了4株溶磷菌,结合16S rRNA基因分析法确定其分类地位,并通过钼锑抗比色法和盆栽试验进行了溶磷与促生效果的研究。结果显示:4株溶磷菌均为假单胞菌属(Pseudomonas sp.),均可形成明显的溶磷圈。在无机磷液体培养基中培养7d后,4株菌株的磷增量在156.17~511.33μg·mL-1之间;溶磷过程中4株菌均分泌多种有机酸,总有机酸量在522.36~986.69mg·L-1之间;盆栽试验表明4株菌均能显著增加披碱草(Elymus dahuricus Turcz.)株高和地上部干重;菌株MXSC5,MXSC6和MQC13可使植株全氮、全磷含量增加,且4株菌株对土壤速效氮、速效磷含量也有正向影响。本研究结果将有助于进一步探究溶磷菌对植物的促生作用及微生物菌肥的开发利用。 相似文献
25.
26.
Partial organic substitution weakens the negative effect of chemical fertilizer on soil micro-food webs 下载免费PDF全文
Soil biotic communities play vital roles in enhancing soil nutrient cycling and soil fertility. Long-term excessive nitrogen (N) application is disadvantageous to the stability of soil food webs and affects arable soil health and sustainable utilization. Proper organic substitution is essential to improve soil health and alleviate the disadvantages of excessive chemical fertilization. However, the biological effects of various organic amendments on soil micro-food webs are poorly understood. In order to explore the effects of various organic amendments including stover, biochar and manure on soil micro-food webs (microbial and nematode communities), a field plot experiment with maize having five treatments viz., 100% urea (100% N), 70% urea (70% N), 70% urea plus stover (Stover), 70% urea plus cattle manure (Manure) and 70% urea plus biochar (Biochar) was conducted. Manure treatment increased the carbon (C) to N use efficiency of soil microbes, which contributed to the retention of soil C, while Biochar treatment elevated soil organic C (SOC) and soil pH. Additionally, Biochar treatment mitigated the negative effects of soil acidification on the soil micro-food web and reduced the abundance of plant parasites. Overall, the biological effect of organic amendments was distinguished from chemical fertilization (100% N and 70% N) through principal co-ordinates analysis. Negative relationships among soil properties, microbial and nematode biomass in the 100% N treatment were diminished in treatments where chemical fertilizer was reduced. The bottom-up effects on soil food webs were observed in organic substitution treatments. In conclusion, organic amendments improved soil fertility by regulating soil microbial and nematode communities in the cropland ecosystem, alleviated the negative effects of chemical fertilizer on the micro-food webs and controlled the trophic cascades among soil biota. 相似文献
27.
Detection of Penaeus monodon-type baculovirus (MBV) infection in Penaeus monodon Fabricius by in situ hybridization 总被引:2,自引:0,他引:2
Abstract. A digoxigenin-labelled DNA probe was used for in situ detection of the Penaeus monodon -type baculovirus (MBV) derived from cloned MBV polyhedrin genome in cultured Penaeus monodon Fabricius. First, the specificity of the probe against MBV DNA with dot blot hybridization analysis was verified. This probe indicated that cloned MBV polyhedrin fragment can be used as an MBV-specific probe. This was then used to microscopically examine sections of MBV-infected tissues for a blue-purple precipitate indicative of a positive reaction for MBV. MBV-positive cells were located only in the epithelium of the hepatopancreatic tubules and of the midgut. Furthermore, comparison of the susceptibility to MBV infection among several life-stages of the shrimp showed that the MBV genome was found in the zoea, mysis, post-larva, and adult stages, whereas MBV DNA was not detected in either eggs or nauplii. The results were quantified from in situ hybridization with an image analyser to compare the degree of cell infection among groups of cultured P. monodon collected from various farms in Taiwan. 相似文献
28.
29.
30.
介绍了支持向量机、信息向量机和相关向量机的理论与算法。利用最优化对偶理论,阐述了支持向量机的三种主要算法:硬间隔支持向量机、软间隔线性支持向量机和二次软间隔支持向量机的理论推导过程。对基于高斯过程模型,详细说明了信息向量机和相关向量机算法的实现过程。 相似文献