全文获取类型
收费全文 | 17088篇 |
免费 | 490篇 |
国内免费 | 1351篇 |
专业分类
林业 | 1021篇 |
农学 | 3040篇 |
基础科学 | 136篇 |
1806篇 | |
综合类 | 8001篇 |
农作物 | 1919篇 |
水产渔业 | 332篇 |
畜牧兽医 | 930篇 |
园艺 | 1149篇 |
植物保护 | 595篇 |
出版年
2024年 | 32篇 |
2023年 | 142篇 |
2022年 | 263篇 |
2021年 | 326篇 |
2020年 | 369篇 |
2019年 | 419篇 |
2018年 | 315篇 |
2017年 | 522篇 |
2016年 | 719篇 |
2015年 | 595篇 |
2014年 | 723篇 |
2013年 | 1101篇 |
2012年 | 1470篇 |
2011年 | 1410篇 |
2010年 | 1092篇 |
2009年 | 1197篇 |
2008年 | 1138篇 |
2007年 | 1157篇 |
2006年 | 914篇 |
2005年 | 792篇 |
2004年 | 596篇 |
2003年 | 462篇 |
2002年 | 373篇 |
2001年 | 333篇 |
2000年 | 286篇 |
1999年 | 265篇 |
1998年 | 212篇 |
1997年 | 204篇 |
1996年 | 226篇 |
1995年 | 162篇 |
1994年 | 188篇 |
1993年 | 149篇 |
1992年 | 166篇 |
1991年 | 138篇 |
1990年 | 135篇 |
1989年 | 106篇 |
1988年 | 72篇 |
1987年 | 49篇 |
1986年 | 30篇 |
1985年 | 9篇 |
1984年 | 10篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 14篇 |
1980年 | 13篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1963年 | 4篇 |
1962年 | 2篇 |
1955年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
为收集优良的草坪种质资源,对北京地区野生早熟禾属(Poa L.)植物资源进行了实地考察。北京共有早熟禾属植物20种1个亚种,其中7个种及1个亚种为新分布,西部和北部山区早熟禾属植物物种分布较为丰富,尤其是东灵山、百花山、海坨山及喇叭沟门。从垂直分布看,草地早熟禾(Poa pratensis L.)为广布种,从平原到高海拔地区均有分布。硬质早熟禾(Poasphondylodes Trin.)在低山区常见,其他物种主要分布在海拔1000 m以上的地区。通过研究23份来自不同居群的草地早熟禾花序特征,发现不同居群的花序性状间存在较大的变异,花序基部最短分枝长的变异最大,花序小穗数次之。 相似文献
102.
对91份不同产地扁穗冰草(Agropyron cristatum(L.)Gaertn)样品的遗传多样性和遗传结构进行研究。采用叶绿体cpDNAtrnT-trnL直接测序的方法和邻接法(NJ)对91份扁穗冰草样品进行遗传多样性和遗传结构分析。结果显示:物种水平上单倍型多样性(Hd)指数为0.608,核苷酸多样性(Pi)指数为0.00295;种群水平上Hd介于0~0.9722,Pi指数介于0~0.00749。分子方差分析表明,扁穗冰草大部分遗传变异(91.63%)发生在居群内,居群间的基因流(Nm=5.474)较高,群体内变异是扁穗冰草的主要变异来源;NJ树表明,受试的6个野生种群可分为4大类群。扁穗冰草的遗传多样性居群内遗传分化较大。 相似文献
103.
用5%、10%、20%复方“蜂产品制品首乌蜜浸泡桑叶4小时,对家蚕(BombyxmoriL.)进行添食试验。结果表明,添食5%、10%、20%首乌蜜溶液分别能使家蚕幼虫寿命较对照组(以蒸馏水代替首乌蜜)延长7.72、7.68、4.82小时,统计学上差异极显著(新复极差检验法;P<0.01)。由此证实,首乌蜜具有抗衰老作用。同时,没有发现家蚕因添食首乌蜜而死亡,说明首乌蜜没有毒性。 相似文献
104.
ZHANG Hai ZHOU Bi-jun YANG Zhong-cheng LIAO Mei WANG Kai-gong WEN Ming CHENG Zhen-tao WANG Wei FENG Xu-fang 《中国畜牧兽医》2016,43(11):2834-2843
In order to study and analyze L1 gene of bovine papillomavirus(BPV)in Guizhou province,the L1 gene of BPV-GZ01 strain was amplified,cloned and sequenced using bioinformatic softwares and methods,and the secondary structure,tertiary structure,B-cell preponderant epitope,conserved domains analysis, transmembrane domain and signal peptide of L1 gene were predicted.The results showed that the length of L1 gene was 1 494 bp,encoding 497 amino acids.The L1 gene of BPV-GZ01 strain shared an amino acid identities of 98.6%,99.4%,98.4%,94.4% and 91.3%,and a nucleotide identities of 99.1%,99.8%,99.4%,87.6% and 82.8% with those of BPV2,BPV2-SW01,BPV2-AKS01,BPV13 and BPV1 strains,respectively.The results of phylogenetic tree analysis indicated that there was a close relationship between BPV-GZ01 and BPV2-SW01 strains.The prediction of secondary structure of L1 protein indicated that the random coil,extended strand and alphahelix took a higher percentage.The L1 protein was supposed contain 6 potential antigen epitopes.And no transmembrane domains and no signal peptide were found.The tertiary structure of L1 protein was curved spiral structure.These results provided a theoretical basis for immunologic diagnosis and further research of nucleic acid vaccine of BPV. 相似文献
105.
106.
为测定陕西、川北地区核桃主栽品种对溃疡病的抗性差异,本文通过和针刺接种法,对11个核桃良种栽培品种1年生枝条进行了抗Botryosphaeria的初步评估;在此基础上,对其中抗性较强的5个品种,采用打孔法接种2年生枝条进一步进行了抗性测定和评估。结果表明“清香”和“香玲”对溃疡病的抗病性强,“鲁光”、“西林3号”和“西洛”对溃疡病的抗病性弱。核桃品种抗病性差异与接种方式和时间有关,但抗病品种清香和香玲抗性表现稳定。该研究结果为核桃引种栽培提供了依据。 相似文献
107.
本文通过用沙棘、白榆、刺槐叶粉加工成的颗粒饲料进行的喂兔试验,探讨了这三种树叶作为林业饲料的开发价值。 相似文献
108.
WANG Leming WANG Yurui ZENG Zixuan RAO Guoshun WU Zhengjiao JIN Weikun WANG Dongying 《中国畜牧兽医》2022,49(2):677-686
【Objective】 This study was intend to obtain cathepsin L1(rFgCat L1) specific monoclonal antibody and construct the double antibody sandwich ELISA.【Method】 Five BALB/c mice were immunized with 1 mg/mL rFgCat L1 protein for four times.Mouse splenocytes were isolated and fused with SP2/0 cells to construct hybridoma cells.Strong positive hybridoma cell lines were screened, 1×106 cells were injected intraperitoneally per mouse to prepare monoclonal antibodies.Antibody titer and antigenic epitope were detected using ELISA method, antibody subtype and specificity were identified using Western blotting method.The double antibody sandwich ELISA was constructed by combining the anti-rFgCat L1 polyclonal antibody, and its sensitivity and specificity were tested.The positive and negative critical value was screened by 20 negative sera with positive control, and the constructed double antibody sandwich ELISA was verified by 47 goat positive sera and 47 dairy cow positive sera.【Result】 After immunization, the antibody titers in serum of 4 mice were all more than 104.After isolated mouse with the highest immune response spleen cells were fused with SP2/0 cells total of 8 of them were positive cell lines were obtained after selective culture.5D5 and 7G6 were identified as strong positive strains with stable antibody secretion.After multiple subcloning screens and subcultures, the antibodies secreted in the cell supernatant were stable, with titers of 29 and 210 respectively, with ascites titers of 107 and 108.Western blotting and antibody subtype identification kits identified that the two antibodies were IgG1 type and the light chain was kappa type, both of which could specifically bind FgESP.According to the same antigen site was recognized by the two kinds of antibodies, the antigen titer of the two monoclonal antibodies were comparied, 7G6 was used as the coating antibody, and anti-rFgCat L1 was used as the enzyme-labeled secondary antibody.The optimized condition of method was that 7G6 was coated at a concentration of 2 μg/mL, the dilution concentration of anti-rFgCat L1 polyclonal antibody was 25 μg/mL, the dilution of Don-HRP-conjugated was 1∶4 000, 5% skimmed milk powder was selected as the blocking solution and the color development time was 25 min.The method was proved that could recognize the lowest antigen concentration of 0.625 μg/mL, also could specifically recognize antigen of Fasciola fasciatus.The constructed sandwich ELISA method was used for antigen detection of 47 dairy cow positive serum and 47 goat positive serum infective samples kept in the laboratory and the positive antigen rate were 72.3% and 78.7%, respectively.【Conclusion】 Anti-rFgCat L1 monoclonal antibody was successfully prepared and the double-sheet sandwich ELISA method for fascioliasis was constructed, which provided a good theoretical basis and material basis for the development of low-cost and rapid diagnostic kits. 相似文献
109.
The molecular mechanism to control the oxidative burst exerted by Mn accumulation in rice (Oryza sativa L.) plants, grown in hydroponics containing 0.5, 2 and 8 mg l–1 Mn and irradiated with a total biological effective UV‐B irradiation of 20.825 kJ m?2, was investigated in the chloroplasts at the 15th and 21st days after germination. In both experimental periods, Mn accumulation kinetics in the leaves and in the chloroplast lamellae displayed overall increases. Coupled to higher membrane selectivity, superoxide production and acyl lipids peroxidation in the thylakoids decreased, prompting upper rates of the Hill and Mehler reactions. Connected to UV‐B irradiation, higher accumulated Mn in thylakoids was found to be chelated in a 36.5 kDa protein, with Mn/protein ratio of about 1 and high content of Gln, Asp, Glu, Leu and Gly, being its EPR spectrum characteristic of high‐spin Mn(II), in a S = 5/2 ground state. As this protein exhibited enzymatic catalysis of superoxide dismutation, it was concluded that, under UV‐B irradiation, the high internal tolerance of Oryza sativa L. to Mn during the vegetative growth also triggers the synthesis of a manganese protein that mimics superoxide dismutase functioning, therefore furnishing an additional intimate protection against oxidative stress. 相似文献
110.
以玉米(Zea mays L.)为材料,研究水分胁迫下玉米叶片中NO与Ca2+和钙调素(CaM)含量之间的关系。结果显示:Ca2+鳌合剂、Ca2+通道阻塞剂和CaM拮抗剂预处理均抑制了水分胁迫诱导的NO产生和一氧化氮合酶(nitric ox-idesynthase,NOS)活性的提高,同时也能抑制水分胁迫诱导的叶片线粒体NO产生,而对叶绿体NO产生并没有影响;NO清除剂羟基2苯基4,4,5,5四咪唑1羟基3氧化物(2-4-carboxypheny l-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide,c-PTIO)能抑制水分胁迫条件下Ca2+和CaM的产生以及CaM1基因表达,但对水分胁迫最初诱导的玉米叶片叶肉细胞原生质体Ca2+和玉米叶片中CaM1基因表达以及CaM含量增加没有影响。上述结果表明:水分胁迫下NO和Ca2+/CaM之间存在相互作用。 相似文献