全文获取类型
收费全文 | 19755篇 |
免费 | 1163篇 |
国内免费 | 1808篇 |
专业分类
林业 | 2473篇 |
农学 | 2890篇 |
基础科学 | 1232篇 |
3420篇 | |
综合类 | 5092篇 |
农作物 | 1249篇 |
水产渔业 | 1000篇 |
畜牧兽医 | 3161篇 |
园艺 | 646篇 |
植物保护 | 1563篇 |
出版年
2024年 | 39篇 |
2023年 | 186篇 |
2022年 | 398篇 |
2021年 | 621篇 |
2020年 | 594篇 |
2019年 | 642篇 |
2018年 | 499篇 |
2017年 | 564篇 |
2016年 | 615篇 |
2015年 | 767篇 |
2014年 | 739篇 |
2013年 | 997篇 |
2012年 | 1126篇 |
2011年 | 1283篇 |
2010年 | 1150篇 |
2009年 | 1085篇 |
2008年 | 1130篇 |
2007年 | 1105篇 |
2006年 | 1133篇 |
2005年 | 1005篇 |
2004年 | 572篇 |
2003年 | 448篇 |
2002年 | 337篇 |
2001年 | 402篇 |
2000年 | 474篇 |
1999年 | 607篇 |
1998年 | 557篇 |
1997年 | 478篇 |
1996年 | 399篇 |
1995年 | 398篇 |
1994年 | 329篇 |
1993年 | 351篇 |
1992年 | 296篇 |
1991年 | 279篇 |
1990年 | 219篇 |
1989年 | 165篇 |
1988年 | 154篇 |
1987年 | 108篇 |
1986年 | 63篇 |
1985年 | 40篇 |
1984年 | 37篇 |
1983年 | 24篇 |
1982年 | 23篇 |
1981年 | 24篇 |
1980年 | 17篇 |
1979年 | 15篇 |
1976年 | 17篇 |
1975年 | 12篇 |
1974年 | 12篇 |
1968年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
中国对虾皮下及造血组织坏死杆状病毒(HHNBV)DNA探针的制备及应用 总被引:5,自引:2,他引:5
HHNBV是1993年中国对虾暴发性流行病的主要病原之一。从纯化的病毒中提取DNA,用EcoRl限制性内切酶酶切成DNA片段,与PUC18体外重组,建立HHNBVDNA文库。从中筛选出三个重组质粒(5#、8#、9#),它们所插入的片段大小分别为:2.8Kb、0.8Kb、1.6Kb,它们分别用光敏生物素标记成探针,与感染HHNBV的病虾DNA呈阳性反应,以此利用制备的HHNBVDNA探针的高敏感性和特异性来检测虾病。 相似文献
992.
993.
H.‐H. HUANG L. FENG Y. LIU J. JIANG W.‐D. JIANG K. HU S.‐H. LI X.‐Q. ZHOU 《Aquaculture Nutrition》2011,17(2):e233-e240
A total of 1050 juvenile Jian carp (Cyprinus carpio var. Jian) (8.20 ± 0.02 g) were fed diets containing seven graded levels of thiamin (0.25, 0.48, 0.79, 1.06, 1.37, 1.63 and 2.65 mg kg?1) for 60 days to investigate the effects of thiamin on growth, body composition and digestive enzyme activities. Percent weight gain (PWG), feed intake and feed efficiency (FE) were the lowest in fish fed the basal diet (P < 0.05). Protein productive value and lipid productive value increased with increasing dietary thiamin levels up to 1.06 and 0.79 mg kg?1 diet, respectively (P < 0.05). Body protein and lipid increased with increasing dietary thiamin levels (P < 0.05), while moisture and ash of fish carcasses decreased with the increase in dietary thiamin supplementation (P < 0.05). Intestinal folds height had a similar trend to PWG (P < 0.05). Activities of α‐amylase, lipase, trypsin, Na+, K+‐ATPase, alkaline phosphatase and gamma‐glutamyl transpeptidase in intestine were all affected by the dietary thiamin (P < 0.05). In conclusion, thiamin could improve growth and intestinal enzyme activities of juvenile Jian carp. The dietary thiamin requirement of juvenile Jian carp (8.0–60.2 g) based on PWG was 1.02 mg kg?1 diet. 相似文献
994.
First account of a transient intersex in spotted scat,Scatophagus argus: a marine gonochoristic fish
Mustapha Umar Farouk Zhi Fei Huang Yuang-Qing Assan Daniel Li Guang-Li Jiang Dong-Neng 《Fish physiology and biochemistry》2022,48(4):1011-1023
Fish Physiology and Biochemistry - This study presents the first incidence of intersex associated with testis-ova in spotted scat (Scatophagus argus) reared in a controlled environment. The... 相似文献
995.
In this study, the possible influence of temperature on infectious pancreatic necrosis virus (IPNV)-induced apoptosis in a zebrafish liver epithelium (ZLE) cell line was investigated. At a lower temperature (18 degrees C), there was expression of viral proteins VP2 and VP3 at 4 h post-infection (p.i.). At this time no expression was found in the high temperature group at 28 degrees C. The cell survival ratio was 52 and 18% at 24 and 48 h p.i., respectively, during IPNV infection at 18 degrees C. In addition, we assayed for apoptosis in IPNV-infected cells with terminal deoxynucleotidyl transferase (TdT)-mediated end labelling (TUNEL) of DNA at different dosages of virus. We found a ratio of apoptotic cells of 8 and 25% at 12 and 18 h p.i., respectively, in the multiplicity of infection (MOI) 1 group. The MOI 10 group had 20 and 45% apoptotic cells at 12 and 18 h, respectively. Furthermore, at 18 degrees C IPNV activated the caspase-8 and 3 from 1.5 to 2 times at 12 and 18 h p.i., respectively. Taken together, these findings suggest that successful virus replication occurs at the low temperature (18 degrees C) compared with the non-permissive temperature of 28 degrees C. Thus, IPNV replication is capable of activating caspase-8 and -3 and inducing host apoptosis. 相似文献
996.
Selenium is essential for the normal life processes, and all animals, including fish, need this inorganic element. In order to research the pathology of selenium deficiency in common carp, Cyprinus carpio L., 360 juvenile carp were allocated to three treatments. Each treatment containing 120 fish was randomly divided into four groups, fed with purified diets containing selenium at 0, 0.15, 0.30 and 0.45 mg kg?1. The results indicated that the morbidity and mortality rates of the test groups were negatively correlated with the level of selenium in the diets. The morbidity and mortality rates were, respectively, 46.7%, 33.3%, 13.3%, 0 and 26.7% 16.7%, 6.7%, 0. The affected fish exhibited pathological changes, such as ‘thin back disease’ and lordosis. Histologically, there was no abnormality observed in muscles, liver and pancreas. Ultrastructurally, there was swelling of the mitochondria of the cardiac muscle cells, the liver cells and renal tubular epithelial cells, with disintegration and lysis of the cristae of the mitochondria which vesiculated. Serum glutamic oxaloacetic transaminase and glutamic pyruvic transaminase levels were increased and the activity of the serum glutathione peroxidase and the serum superoxide dismutase was decreased; in contrast, the serum malonaldehyde concentration was increased. 相似文献
997.
国内 LPG 发动机多由汽油机改装而成,第二代电控 LPG 系统的开发和应用水平不高。介绍了一种小功率单缸汽油机的普通电子点火改装成 LPG 发动机微机控制点火与数据采集系统的实验研究。 相似文献
998.
999.
冰雪灾害后南岭常绿阔叶林受损优势种萌条特性 总被引:1,自引:0,他引:1
在南岭冰雪灾害受损常绿阔叶林建立4块样地,分析样地内受损树木的受损类型、径级、树种组成等因子与灾后萌条关系,结果表明:1)灾害后受损优势木72.00%以上均有萌条出现,乔木层优势木萌条率高于灌木层,为南岭地区冰雪灾害后受损森林生态系统快速恢复与重建提供保障;2)不同受损优势木萌条率存在差异,萌条率随着受损程度的增加呈增加的趋势,其中倒伏类型萌条率最高(100%),其他受损类型中灌木层金缕梅科萌条率最低,乔木层樟科萌条率最低;3)冰雪灾害后萌条特性表现出与采伐、刀耕火种后不同的规律,应做为1个特例进行研究;4)建议在我国亚热带地区森林自然干扰频发区,在人工促进恢复时多选用格药柃、小红栲和交让木等,有利于各层次结构与组成的保持. 相似文献
1000.