全文获取类型
收费全文 | 22995篇 |
免费 | 1062篇 |
国内免费 | 2672篇 |
专业分类
林业 | 2841篇 |
农学 | 3491篇 |
基础科学 | 1896篇 |
4104篇 | |
综合类 | 6540篇 |
农作物 | 1302篇 |
水产渔业 | 871篇 |
畜牧兽医 | 3281篇 |
园艺 | 708篇 |
植物保护 | 1695篇 |
出版年
2024年 | 46篇 |
2023年 | 211篇 |
2022年 | 524篇 |
2021年 | 860篇 |
2020年 | 785篇 |
2019年 | 753篇 |
2018年 | 538篇 |
2017年 | 763篇 |
2016年 | 744篇 |
2015年 | 999篇 |
2014年 | 913篇 |
2013年 | 1166篇 |
2012年 | 1389篇 |
2011年 | 1439篇 |
2010年 | 1423篇 |
2009年 | 1342篇 |
2008年 | 1254篇 |
2007年 | 1384篇 |
2006年 | 1286篇 |
2005年 | 1098篇 |
2004年 | 537篇 |
2003年 | 494篇 |
2002年 | 407篇 |
2001年 | 434篇 |
2000年 | 545篇 |
1999年 | 688篇 |
1998年 | 615篇 |
1997年 | 532篇 |
1996年 | 516篇 |
1995年 | 508篇 |
1994年 | 465篇 |
1993年 | 414篇 |
1992年 | 388篇 |
1991年 | 302篇 |
1990年 | 248篇 |
1989年 | 207篇 |
1988年 | 164篇 |
1987年 | 91篇 |
1986年 | 63篇 |
1985年 | 32篇 |
1984年 | 16篇 |
1983年 | 34篇 |
1982年 | 18篇 |
1981年 | 23篇 |
1980年 | 11篇 |
1979年 | 7篇 |
1974年 | 9篇 |
1965年 | 6篇 |
1964年 | 6篇 |
1963年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Min Zhang Dan Zheng Zhimei Peng Yuting Zhu Rongrong Li Qiong Wu Yan Li Hongyi Li Weihua Xu Mao Zhang Qichun Hung Yanfa Sun 《The Journal of Poultry Science》2021,58(2):131
In this study, signaling pathways and key differentially expressed genes (DEGs) involved in lipid metabolism in muscle and fat tissues were investigated. Muscle and abdominal fat tissues were obtained from 35-day-old female broilers for RNA sequencing. DEGs between muscle and fat tissues were identified. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses of DEGs were performed. A total of 6130 DEGs were identified to be significantly enriched in 365 GO terms, most of which were involved in biological processes, cellular components, and molecular functions in muscle and fat tissues. Three important lipid signaling pathways (pyruvate metabolism, the insulin signaling pathway, and the adipocytokine signaling pathway) were identified among the fat and muscle tissues of broilers. The key common DEGs in these pathways included phosphoenolpyruvate carboxykinase 2 (PCK2), acetyl-CoA carboxylase 1 alpha and beta (ACACA and ACACB), and the mitogen-activated protein kinase (AMPK) gene family. Hence, our findings revealed the pathways and key genes and gene families involved in the regulation of fat deposition in the muscle and fat tissues of broilers. 相似文献
72.
The role of ectomycorrhizal fungi in alleviating pine decline in semiarid sandy soil of northern China: an experimental approach 总被引:1,自引:0,他引:1
Jiao-jun Zhu Feng-qin Li Mei-ling Xu Hong-zhang Kang Xiang-yun Wu 《Annals of Forest Science》2008,65(3):304-304
The decline of Mongolian pine (Pinus sylvestris var. mongolica) trees on sandy land in northern China has caused serious ecological concerns. Mongolian pine is an ectomycorrhizal fungus (ECM)-dependent species. Three ECM species (Boletus sp., Lactarius deliciosus and L.sp.) were collected from Mongolian pine plantation stands to test their beneficial effects on Mongolian pine seedlings and their responses to environmental factors such as pH, drought stress and temperature. The results indicated that ECM inoculation significantly increased the rate of ECM colonization and the length of seedling shoots. The three ECM could grow in a pH range from 4 to 7, but did not grow under heavy drought stress (?1.53 MPa). High temperatures (over 37 °C) caused death of ECM. When related to soil pH, soil water content and temperature in the Mongolian pine plantations, water conditions and temperature were unfavorable for ECM growth in surface soil, but suitable in deeper soil. Therefore, it was concluded that the failure of natural regeneration in Mongolian pine plantations might be influenced by the lack of ECM in the surface soil because of high temperatures causing ECM death. Moreover, the majority of the root area is distributed in deeper soil, which alleviates the stresses on ECM development and arrests pine decline; this is beneficial for tree growth. 相似文献
73.
中国矮生刺黄瓜品系特性的研究初报 总被引:5,自引:0,他引:5
本文利用由中国蔓生刺黄瓜自然突变产生的矮生型黄瓜为材料,通过多低自交选育及性状观察,初步了解该矮生黄瓜植物学性状除具有自封顶、植株矮化性状外,与蔓生型黄瓜无明显差异。在生物学方面,该矮生黄瓜具有早熟、雌花节率高、结果集中、生长期短等特性。通过对中国矮生刺黄瓜与不同品种蔓生黄瓜杂交后代的观察、分析,初步认为黄瓜植株高度是由单基因体系和多基因体系共同作用决定的。 相似文献
74.
利用废菌渣生产单细胞蛋白饲料研究 总被引:3,自引:0,他引:3
本文以废菌渣为主要原料,利用酿酒酵母(Saccharomyces cerevisiae)和黑曲霉(Aspergillus niger)两菌株进行混合固态发酵生产单细胞蛋白饲料.通过单因素试验和正交试验确定最佳培养条件.结果表明,各因素对粗蛋白质含量的影响为废菌渣与麸皮的比例>培养时间>氮源>水料比;混茵固态发酵的最佳培养条件为废茵渣80%:麸皮20%,硝酸铵2%.尿素1%,KH2PO4 2%,MgSO4·7H2O 1%,水料比为2.5:1,pH为4,接种量为20%,培养时间为120 h时,此时粗蛋白质含量最高,由发酵前的9.61%提高到23.28%. 相似文献
75.
Kosar Gharib-Naseri Sara de Las Heras-Saldana Sarbast Kheravii Lihong Qin Jingxue Wang Shu-Biao Wu 《动物营养(英文)》2021,7(1):239
Necrotic enteritis (NE) is an important enteric disease in poultry and has become a major concern in poultry production in the post-antibiotic era. The infection with NE can damage the intestinal mucosa of the birds leading to impaired health and, thus, productivity. To gain a better understanding of how NE impacts the gut function of infected broilers, global mRNA sequencing (RNA-seq) was performed in the jejunum tissue of NE challenged and non-challenged broilers to identify the pathways and genes affected by this disease. Briefly, to induce NE, birds in the challenge group were inoculated with 1 mL of Eimeria species on day 9 followed by 1 mL of approximately 108 CFU/mL of a NetB producing Clostridium perfringens on days 14 and 15. On day 16, 2 birds in each treatment were randomly selected and euthanized and the whole intestinal tract was evaluated for lesion scores. Duodenum tissue samples from one of the euthanized birds of each replicate (n = 4) was used for histology, and the jejunum tissue for RNA extraction. RNA-seq analysis was performed with an Illumina RNA HiSeq 2000 sequencer. The differentially expressed genes (DEG) were identified and functional analysis was performed in DAVID to find protein–protein interactions (PPI). At a false discovery rate threshold <0.05, a total of 377 DEG (207 upregulated and 170 downregulated) DEG were identified. Pathway enrichment analysis revealed that DEG were considerably enriched in peroxisome proliferator-activated receptors (PPAR) signaling (P < 0.01) and β-oxidation pathways (P < 0.05). The DEG were mostly related to fatty acid metabolism and degradation (cluster of differentiation 36 [CD36], acyl-CoA synthetase bubblegum family member-1 [ACSBG1], fatty acid-binding protein-1 and -2 [FABP1] and [FABP2]; and acyl-coenzyme A synthetase-1 [ACSL1]), bile acid production and transportation (acyl-CoA oxidase-2 [ACOX2], apical sodium–bile acid transporter [ASBT]) and essential genes in the immune system (interferon-, [IFN-γ], LCK proto-oncogene, Src family tyrosine kinase [LCK], zeta chain of T cell receptor associated protein kinase 70 kDa [ZAP70], and aconitate decarboxylase 1 [ACOD1]). Our data revealed that pathways related to fatty acid digestion were significantly compromised which thereby could have affected metabolic and immune responses in NE infected birds. 相似文献
76.
湖北省钟祥市南湖水生态环境评价 总被引:1,自引:0,他引:1
位于湖北省钟祥市城关郢中镇东的南湖,面积800hm^2,集观赏和水产养殖于一体。鱼产量为700t/a。该湖紧靠城市,直接纳人了未经任何处理的大量生活和工业污水,每天流量达40000t,造成水体严重富营养化,鱼类因栖息环境恶化而大量死亡,造成很大经济损失。鉴于此,笔者对南湖水生态环境进行了调查,旨在为南湖的综合治理提供科学依据。 相似文献
77.
78.
Methyl donors dietary supplementation to gestating sows diet improves the growth rate of offspring and is associating with changes in expression and DNA methylation of insulin‐like growth factor‐1 gene 下载免费PDF全文
Yang Zhao Yuedong Xuan Daolin Mou Hong Liu Pan Zhou Zhengfeng Fang Lianqiang Che Shengyu Xu Bin Feng Jian Li Xuemei Jiang Yan Lin De Wu 《Journal of animal physiology and animal nutrition》2018,102(5):1340-1350
The study aimed to investigate the effects of maternal dietary methyl donors on the performance of sows and their offspring, and the associated hepatic insulin‐like growth factor‐1 (IGF‐1) expression of the offspring. A total of 24 multiparous sows were randomly fed the control (CON) or the CON diet supplemented with methyl donors (MD) at 3 g/kg betaine, 15 mg/kg folic acid, 400 mg/kg choline and 150 μg/kg VB12, from mating until delivery. After farrowing, sows were fed a common lactation diet through a 28‐days lactation period and six litters per treatment were selected to be fed until at approximately 110 kg BW. Maternal MD supplementation resulted in greater birthweight (p < 0.05) and increased the piglet weights (p < 0.01) and litter weights (p < 0.05) at the age of day 28, compared with that in CON group. The offspring pigs in the MD group had greater ADG (p < 0.05) and tended to lower F:G ratio (p = 0.07) compared with that of CON group from day 28 to 180 of age. The offspring pigs from MD group had greater serum IGF‐1 concentrations and expressions of hepatic IGF‐1 gene and muscular IGF‐1 receptor (IGF‐1r) protein at birth (p < 0.05), and greater hepatic IGF‐1 protein (p = 0.03) and muscular IGF‐1r gene expressions (p < 0.05) at slaughter, than that from the CON group. Moreover, the methylation at the promoter of IGF‐1 gene in the liver of newborn piglets and finishing pigs was greater in the MD group than that of the CON group (p < 0.05). In conclusion, maternal MD supplementation throughout gestation could enhance the birthweight and postnatal growth rate of offspring, associated with an increased expression of the IGF‐1 gene and IGF‐1r, as well as the altered DNA methylation of IGF‐1 gene promotor. 相似文献
79.
80.