全文获取类型
收费全文 | 2492篇 |
免费 | 117篇 |
国内免费 | 217篇 |
专业分类
林业 | 235篇 |
农学 | 389篇 |
基础科学 | 194篇 |
530篇 | |
综合类 | 558篇 |
农作物 | 145篇 |
水产渔业 | 96篇 |
畜牧兽医 | 462篇 |
园艺 | 81篇 |
植物保护 | 136篇 |
出版年
2023年 | 46篇 |
2022年 | 120篇 |
2021年 | 99篇 |
2020年 | 100篇 |
2019年 | 104篇 |
2018年 | 76篇 |
2017年 | 106篇 |
2016年 | 84篇 |
2015年 | 92篇 |
2014年 | 70篇 |
2013年 | 146篇 |
2012年 | 144篇 |
2011年 | 161篇 |
2010年 | 123篇 |
2009年 | 119篇 |
2008年 | 114篇 |
2007年 | 104篇 |
2006年 | 98篇 |
2005年 | 96篇 |
2004年 | 35篇 |
2003年 | 45篇 |
2002年 | 44篇 |
2001年 | 54篇 |
2000年 | 48篇 |
1999年 | 52篇 |
1998年 | 43篇 |
1997年 | 48篇 |
1996年 | 35篇 |
1995年 | 18篇 |
1994年 | 21篇 |
1993年 | 15篇 |
1992年 | 18篇 |
1991年 | 19篇 |
1990年 | 22篇 |
1989年 | 16篇 |
1988年 | 18篇 |
1987年 | 18篇 |
1985年 | 13篇 |
1983年 | 12篇 |
1979年 | 23篇 |
1977年 | 9篇 |
1976年 | 11篇 |
1975年 | 8篇 |
1971年 | 21篇 |
1970年 | 14篇 |
1969年 | 14篇 |
1968年 | 8篇 |
1967年 | 20篇 |
1966年 | 21篇 |
1965年 | 10篇 |
排序方式: 共有2826条查询结果,搜索用时 171 毫秒
61.
蒲公英提取物对LPS诱导小鼠乳腺炎的减轻效应及其机制分析 总被引:1,自引:1,他引:0
旨在研究蒲公英提取物对内毒素(LPS)诱导小鼠乳腺炎的减轻效应及其机制分析。将小鼠随机分为空白组、模型组、阳性组和蒲公英提取物高、中、低剂量组。蒲公英提取物高、中、低剂量组分别按10.0、5.0、2.5 g·kg-1灌胃给药,连续灌胃6 d,2次·d-1,空白组灌胃等体积生理盐水。末次给药1 h后,于小鼠乳房基部分别灌注50 μL 0.2 mg·mL-1 LPS,建立LPS诱导的小鼠乳腺炎模型,阳性组在建模后6和12 h腹腔注射5 mg·kg-1地塞米松。24 h后取血,分离血清,剥离乳腺组织。ELISA法测定小鼠血清肿瘤坏死因子α(TNF-α)、白细胞介素-1β(IL-1β)和白细胞介素-6(IL-6)的含量,髓过氧化物酶(MPO)试剂盒测定小鼠血清MPO的含量,HE染色观察病理变化,Western blot法测定小鼠乳腺中TLR4蛋白以及NF-κB信号通路和MAPKs信号通路相关蛋白的表达。结果显示,蒲公英提取物高、中剂量组对LPS诱导的乳腺炎小鼠血清中TNF-α、IL-1β和IL-6的分泌有极显著抑制作用(P<0.01),极显著降低小鼠血清中MPO的含量(P<0.01);蒲公英提取物高、中剂量组能改善LPS诱导的小鼠乳腺组织的病理变化,极显著下调LPS诱导的小鼠乳腺中TLR4、p-IκB、p-p65、p-p38、p-JNK、p-ERK蛋白的表达(P<0.01)。结果表明,蒲公英提取物通过调控NF-κB和MAPKs信号通路对LPS诱导的小鼠乳腺炎有明显减轻作用,为蒲公英的临床开发及应用奠定了基础。 相似文献
62.
63.
64.
【目的】 检验长期保存在国家家畜基因库的湖羊冷冻胚胎和冷冻精液的质量,评价超低温冷冻保存技术保种的效果。【方法】 对保存于国家家畜基因库的冷冻胚胎(保存20年)和冷冻精液(保存20和30年)进行复苏,进行相应鉴定后分别进行胚胎移植和人工授精,同时以0年冷冻精液和新鲜精液为对照,测定其受胎率和后代的羔皮性能、生长性能及繁殖性能,检验保存效果。【结果】 本试验共解冻胚胎36枚,其中,A级胚胎22枚,B级胚胎7枚,C级胚胎5枚,D级胚胎2枚,冷冻胚胎复苏利用率达到94.44%(34/36),A级胚胎率达到61.11%(22/36),移植34枚,产羔17只,冷冻胚胎复苏移植产羔率达50.00%;保存30年的冷冻精液复苏后平均精子活力达35%,受胎率为58.57%,平均产羔1.90只;保存20年冷冻精液复苏后平均精子活力达31%,受胎率为53.66%,平均产羔1.95只;胚胎复苏移植羊、30和20年冷冻精液后代体型外貌鉴定均符合纯种湖羊特征,没有畸形个体;羔羊一级羔皮率分别是31.25%、42.03%和23.81%,保持了当年湖羊的羔皮特性;生长发育及繁殖性能与现有湖羊群体性能基本保持一致。【结论】 利用超低温冷冻技术长期保存湖羊冷冻胚胎和冷冻精液的方法是可行的,对地方品种保种具有重要意义。 相似文献
65.
磷素环境与马褂木种源的生长和干物质积累 总被引:5,自引:0,他引:5
自然土壤中有效磷含量很低,难以满足植物最佳生长的需要。据统计,在全世界13·19亿hm2的耕地中约有43%缺磷,而我国耕地则有2/3缺磷(何绪生等,1998)。我国南方地区高温多雨,富铝化作用明显,多数土壤呈酸性或强酸性,磷素固定强烈,土壤有效磷含量仅在1~2mg·kg-1(邱燕等,2003)。虽然施用磷肥的效果显著,但其利用率一般不超过10%,多为土壤固定并转变成植物较难吸收的Ca-P、Fe-P和Al-P等(熊毅,1997)。鉴于植物具有将土壤难溶态磷转化为有效态磷并加以吸收利用的能力,通过选育磷高效利用的植物品种来开发土壤中难溶态的磷素资源,可减小对施用磷… 相似文献
66.
Investigations on the antinociceptive activity of crude extracts from Croton cajucara leaves in mice
The crude leaf extracts of Croton cajucara Benth. were studied for their antinociceptive property in chemical and thermal models of nociception in mice. All the tested extracts (hexanic, chloroformic and methanolic), at oral doses of 100 and 200 mg/kg demonstrated significant inhibition of acetic acid-induced writhing and the second phase response of formalin, but did not manifest a significant effect in hot-plate test. 相似文献
67.
The potential of hedgerow intecrropping with Leucaena leucocephala was explored on vertic Inceptisols over 4 years at ICRISAT Center, Patancheru, India. The study was conducted using a systematic layout involving different alley widths ranging from 1.35 to 4.95 m and with varying distances between hedge and crops. The alleys were cropped with alternate rows of sorghum and pigeonpea. Hedges composed double Leucaena hedgerows 60 cm apart were periodically harvested for fodder. Sole crops of all components and a sorghum/pigeonpea intercrop were included in all four replications of the study.Starting in the second year, Leucaena was progressively more competitive to annual crops, causing substantial yield reduction. Competition (primarily for moisture) was most severe in narrow alleys and was greatest on pigeonpea.The growth of Leucaena was not sufficient to compensate for reduced crop yields. Land equivalent ratios (LERs) calculated on the basis of grain yield of crops and Leucaena fodder yields showed that hedgerow intercropping (HI) was advantageous over sole crops only during the first two years using wide alleys, but disadvantegeous in the last two years. LERs calculated on the basis of total dry matter indicated only a small advantage for HI (13–17 percent) over sole crops in wider (>4 m) alleys. Average returns per year from HI exceeded those of the most productive annual crop system (sorghum/pigeonpea intercropping) by 8 percent in 4.05 m alleys, and by 16 percent in 4.95 m alleys. Fodder production during the dry season was 40 percent of the annual total in these alley widths. Thus hedgerow intercropping at 4–5 m alley width is not very attractive for farmers in semi-arid India, which has 600–700 mm of annual rainfall. There is a need to examine the potential of HI in wider alleys. The merits and limitations of the systematic design are discussed. 相似文献
68.
P. S. Shanmugam R. Balagurunathan N. Sathiah N. G. V. Rao 《Journal of pest science》2007,80(3):175-181
Cotton bollworm, Helicoverpa armigera Hubner selected for five generations with Bacillus thuringiensis insecticidal crystal protein Cry1Ac in the laboratory developed 12.98-fold resistance. Resistance and susceptible populations
were mass crossed to study the dominance of resistance. The Cry1Ac—selected (BCR) population showed 5.8-fold resistance to
Cry1Aa and 5.04-fold resistance to Cry1Ab. The degree of dominance (D) was 0.34 and 0.40 for the R × S and S × R hybrids, respectively, which indicates incomplete recessive character of Cry1Ac resistance in the population. The estimated
realized heritability (h
2) and response quotient (Q) of resistance for Cry1Ac were 0.52 and 0.15, respectively. This indicated the lower phenotypic variation in the selected
population. The resistance risk assessment based on h
2 indicated that the resistance would increased tenfold after <9 generations for Cry1Ac in the resistant population. The results
show the ability of H. armigera to develop resistance against Cry1Ac and cross-resistance to Cry1Aa and Cry1Ab. 相似文献
69.
70.