全文获取类型
收费全文 | 11441篇 |
免费 | 842篇 |
国内免费 | 667篇 |
专业分类
林业 | 938篇 |
农学 | 1321篇 |
基础科学 | 532篇 |
1558篇 | |
综合类 | 3326篇 |
农作物 | 618篇 |
水产渔业 | 664篇 |
畜牧兽医 | 2642篇 |
园艺 | 582篇 |
植物保护 | 769篇 |
出版年
2024年 | 19篇 |
2023年 | 126篇 |
2022年 | 260篇 |
2021年 | 315篇 |
2020年 | 331篇 |
2019年 | 385篇 |
2018年 | 335篇 |
2017年 | 423篇 |
2016年 | 380篇 |
2015年 | 538篇 |
2014年 | 523篇 |
2013年 | 598篇 |
2012年 | 783篇 |
2011年 | 871篇 |
2010年 | 846篇 |
2009年 | 726篇 |
2008年 | 730篇 |
2007年 | 759篇 |
2006年 | 623篇 |
2005年 | 566篇 |
2004年 | 344篇 |
2003年 | 250篇 |
2002年 | 191篇 |
2001年 | 292篇 |
2000年 | 252篇 |
1999年 | 236篇 |
1998年 | 137篇 |
1997年 | 136篇 |
1996年 | 118篇 |
1995年 | 98篇 |
1994年 | 74篇 |
1993年 | 80篇 |
1992年 | 95篇 |
1991年 | 82篇 |
1990年 | 81篇 |
1989年 | 64篇 |
1988年 | 53篇 |
1987年 | 31篇 |
1986年 | 35篇 |
1985年 | 17篇 |
1984年 | 15篇 |
1983年 | 13篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1979年 | 9篇 |
1966年 | 6篇 |
1956年 | 6篇 |
1903年 | 4篇 |
1893年 | 4篇 |
1892年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
为了明确麻地膜覆盖在设施大棚内对樱桃番茄生长及产量的影响,本研究采用‘浙樱粉1号’为实验材料,设置3个处理:麻地膜覆盖、塑料地膜覆盖及对照(不覆盖),比较了不同覆盖措施对‘浙樱粉1号’株高、茎粗、单株鲜重、结果数量及樱桃番茄鲜果重的影响。结果表明,在设施大棚内采用麻地膜覆盖增加了‘浙樱粉1号’株高、茎粗、结果数量及樱桃番茄鲜果重。麻地膜覆盖对设施大棚内种植的樱桃番茄有增产作用,麻地膜的推广应用可以减少塑料地膜对环境污染,利于农业的可持续发展。 相似文献
93.
Dietary α‐linolenic acid affects lipid metabolism and tissue fatty acid profile and induces apoptosis in intraperitoneal adipose tissue of juvenile grass carp (Ctenopharyngodon idella) 下载免费PDF全文
A 56‐day feeding trial was conducted to elucidate the effects and mechanism action of dietary α‐linolenic acid (ALA, 18:3n‐3) on lipid accumulation and fatty acid profile of muscle, hepatopancreas and intraperitoneal fat (IPF) in juvenile grass carp using three isonitrogenous and isoenergetic semi‐purified diets containing 0.0% (control group), 1.0% and 2.0% ALA, respectively. The lowest intraperitoneal fat (IPF) ratio was found in 2.0% group. In the muscle, hepatopancreas and IPF, docosahexaenoic acid (DHA, 22:6n‐3) and eicosapentaenoic acid (EPA, 20:5n‐3) contents increased with the increase in dietary ALA. In the IPF, caspase 3, caspase 8 and caspase 9 showed the highest activities in 2.0% group, while the value of Bcl‐2/Bax (B‐cell leukaemia 2/Bcl‐2‐associated X protein) reached the lowest. Meanwhile, swelling of the IPF mitochondria was observed in 2.0% group. The gene expressions of fatty acid desaturase (FAD) and fatty acid elongase (ELO) in the hepatopancreas and muscle showed significantly higher levels in the treatment groups, whereas an opposite trend was existed in the IPF. Fatty acid synthase (FAS), sterol regulatory element binding protein‐1c (SREBP‐1c) in the IPF and hepatopancreas reached the lowest in 2.0% group. Overall, dietary ALA could promote n‐3 highly unsaturated fatty acids (HUFAs) synthesis and suppress the accumulation of lipid by decreasing the expression of related genes and promoting the apoptosis in IPF. 相似文献
94.
Protoplasts from cell suspension cultures of ‘Bonnaza’ navel orange (Citrus sinensis (L.) Osbeck) were electrically fused with mesophyll protoplasts isolated from seedless ‘Red Blush’ grapefruit (Citrusparadisi). After 6 months of culture, a total of 20 plants were regenerated. Root tip chromosome counting revealed that 4 of them
were tetraploids (2n = 4x = 36)and the rest were diploids (2n = 2x = 18) morphologically resembling the mesophyll parent.
After 6 months of transplantation into the greenhouse, 4 of the diploidmesophyll regenerants unexpectedly flowered, but this
phenomenon disappeared in the next year. This is the first report of precocious flowering in citrus via protoplast fusion.
RAPD analysis further confirmed that the tetraploid regenerants were somatic hybrids while the diploid regenerants were mesophyll
parent type. This somatic hybrid will be utilized as a possible pollen parent for improving the seedy pummelo cultivars in
China by producing triploid seedless pummelo hybrid. The mechanism of early flowering was also discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
95.
Screening crop accessions for allelopathic activity is of paramount importance for crop allelopathy research. Previous bioassays often did not use a mixed culture of donor and target plants, did not use soil and were not conducted under natural conditions. In this study, we designed an inhibitory‐circle method in which a rice accession (donor plant) and Echinochloa crus‐galli (target plant) were cultured together in paddy soil under natural conditions. First, we determined that the highest allelopathic activity of allelopathic rice accession PI312777 was at the 5‐leaf stage, and the suitable distance of rice seedlings and E. crus‐galli was 12 cm apart. This method was then validated by a field test. A further 40 rice accessions were evaluated for allelopathic activity to E. crus‐galli using this method. Two rice accessions, PI312777 and Taichung Native 1, had highly allelopathic activity to E. crus‐galli (inhibitory rate > 50%), while another accession, Lemont, had non‐allelopathic activity. These experimental results were in accordance with previous studies using direct field experiments. The inhibitory‐circle method integrated three necessary conditions, that is donor and target plants grown together, with soil as the medium and under natural conditions for reliable results. The ‘inhibitory‐circle method’, which combined donor and target plants, soil medium and field conditions, can give reliable results in one step, compared with laboratory screening methods. Also, the ‘inhibitory‐circle method’ gave results in 30‐35 days, thereby substantially reducing the requirements for time, labour and cost. 相似文献
96.
对白浆土有机无机复合体进行了测定,阐述了有机无机复合体与土壤肥力的关系。白浆土原土复合量与有机质含量呈正相关,相关系数为0.9999;与全氮量的相关系数为0.9948;90%左右的磷是在有机无机复合体中。因此原土复合量可以做为白浆土的养分指标。原土复合量高的白浆土其结构性好。在三江平原的白浆土上,采用玉米、小麦秸秆还田,种植绿肥,增加土壤有机质,调节 C/N,提高腐殖质的活化度,可做为增加有机无机复合体,培肥土壤的一项根本措施。 相似文献
97.
利用Li-6400光合仪研究了田间自然条件下3种野生匍匐翦股颖(Agrostis stolonifera L.)05GA5、05GA8、05GA11居群和对照品种普特(Putter)的光合作用日变化特征.结果表明,①4个材料净光合速率(Pn)、蒸腾速率(Tr)和气孔导度(Gs)的日变化曲线均呈"双峰"型,都存在明显的光合"午休"现象;且05GA5的Pn、Tr、Gs值都高于其他材料,表明其具有很强的光合能力和对极端高温环境的适应能力.②根据Pn、Ci、气孔限制值(k)的变化方向,推测05GA5、CK的光合"午休"主要受气孔因素限制,05GA8、05GA11主要受气孔和非气孔因素限制.③相关分析结果表明,夏季的光照对05GA5、05GA8、CK都有很大影响,相关系数分别为0.750,0.876,0.756,而对05GA11的影响不大.从总的相关系数大小来看,对Pn影响最大的因子是PAR,其次是Ta、Ca、RH. 相似文献
98.
分别按一次免疫、首免后第15d加强免疫和首免后第60d加强免疫程序,对3组试验牛(每组牛20头)用O型口蹄疫疫苗进行了免疫。免疫后不同时间点用液相阻断ELISA(LPB-ELISA)测定了免疫牛O型口蹄疫抗体效价。结果,首免后第15d加强免疫牛和第60d加强免疫牛抗体水平较高,50%保护牛所占比例分别为56.3%和63.1%,完全受保护的牛所占比例分别为34.3%和29.5%。第60d加强免疫牛的保护率要高于第15d加强免疫牛和一次免疫牛的保护率。结果表明,首免后第60d加强免疫是最理想的免疫程序。 相似文献
99.
100.
Development of peanut varieties with high oil content by in vitro mutagenesis and screening 下载免费PDF全文
WANG Jing-shan SHI Lei LIU Yue ZHAO Ming-xia WANG Xia QIAO Li-xian SUI Jiong-ming LI Guan ZHU Hong YU Shan-lin 《农业科学学报》2020,19(12):2974-2982
Peanut (Arachis hypogaea L.) is an important oil crop globally and high oil content is one of the major targets in peanut breeding programs. Previous studies indicated that the osmotic pressure (OP) of the leaves of peanut plants subjected to drought stress was negatively correlated with kernel oil content. Based on this knowledge, we established a practical and reliable method for creating new peanut varieties with high oil content using in vitro mutagenesis and directional OP-based selection. Using embryonic leaflets of peanut variety Huayu 20 as explants, pingyangmycin (PYM) as the mutagen, and hydroxyproline (HYP) as the OP regulator, we developed 15 HYP-tolerant regenerated plants. For each regenerated plant, we selected offspring with oil content>55% (relative to 49.5% for Huayu 20). We developed and released three new peanut varieties with high yield and high oil content from the offspring of the HYP-tolerant regenerated plants. The three new varieties were named as Yuhua 4, Yuhua 9 and Yuhua 14 and their oil contents were 57.7, 61.1 and 59.3%, respectively. The results indicate that in vitro mutagenesis with PYM followed by directed screening with HYP is a useful approach for breeding peanut varieties with high oil contents. 相似文献