全文获取类型
收费全文 | 2546篇 |
免费 | 142篇 |
专业分类
林业 | 211篇 |
农学 | 304篇 |
基础科学 | 31篇 |
568篇 | |
综合类 | 119篇 |
农作物 | 204篇 |
水产渔业 | 311篇 |
畜牧兽医 | 662篇 |
园艺 | 70篇 |
植物保护 | 208篇 |
出版年
2023年 | 36篇 |
2022年 | 75篇 |
2021年 | 83篇 |
2020年 | 102篇 |
2019年 | 126篇 |
2018年 | 156篇 |
2017年 | 152篇 |
2016年 | 121篇 |
2015年 | 85篇 |
2014年 | 116篇 |
2013年 | 226篇 |
2012年 | 179篇 |
2011年 | 157篇 |
2010年 | 133篇 |
2009年 | 94篇 |
2008年 | 107篇 |
2007年 | 100篇 |
2006年 | 82篇 |
2005年 | 58篇 |
2004年 | 50篇 |
2003年 | 43篇 |
2002年 | 32篇 |
2001年 | 39篇 |
2000年 | 36篇 |
1999年 | 26篇 |
1998年 | 19篇 |
1997年 | 15篇 |
1996年 | 9篇 |
1995年 | 6篇 |
1994年 | 9篇 |
1993年 | 8篇 |
1992年 | 12篇 |
1991年 | 19篇 |
1990年 | 14篇 |
1989年 | 11篇 |
1988年 | 12篇 |
1987年 | 13篇 |
1986年 | 7篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1983年 | 9篇 |
1982年 | 5篇 |
1981年 | 9篇 |
1980年 | 5篇 |
1979年 | 14篇 |
1974年 | 8篇 |
1973年 | 8篇 |
1971年 | 7篇 |
1969年 | 6篇 |
1967年 | 6篇 |
排序方式: 共有2688条查询结果,搜索用时 15 毫秒
991.
Mahendra Kumar Padhi 《Tropical animal health and production》2010,42(7):1395-1403
To evaluate different crosses and purebreds ducks in respect to various economic traits and to estimate different crossbreeding genetic parameters, a 3?×?3 complete diallel cross involving indigenous duck (DD), Khaki Campbell (KK) and White Pekin (WW) were used to produce three purebreds (DD, KK, WW) three crossbreds (DK, DW, KW) and three reciprocals (KD, WD, WK). A total of 609 ducklings produced were reared on deep litter and the females (316 in number) were evaluated for growing and laying period body weight along with the production performance traits. Different crossbreeding genetic parameters were estimated for different traits. All the traits in respect to body weight gain during growing and laying period and different production traits including laying house mortality rate showed significant (p?≤?0.05) difference between different genetic groups. In general, crossbreds perform better than the purebreds for most of the traits studied. General combining ability (GCA), specific combining ability (SCA) and reciprocal effect (RE) were significant (p?≤?0.01) for body weight and production traits. Egg weight showed significant (p?≤?0.01) difference in respect to GCA, SCA and RE for all the ages of measurement except RE for 30th week egg weight. Laying period mortality rate was only significant (p?≤?0.05) for SCA. Most of the crossbreds recorded heterosis rate in desirable direction for majority of the traits. Overall results revealed that the crossbreds perform well in respect to different traits than the purebreds and may be used to take advantage of heterosis. DW performs well in respect to majority of the traits measured and is of importance for commercial exploitation. Further, pure line selection with development of specialised sire and dam line followed by crossing may be of importance to enhance the performances in the crosses. 相似文献
992.
Polley Shamik De Sachinandan Brahma Biswajit Mukherjee Ayan P.V. Vinesh Batabyal Subhasis Arora Jaspreet Singh Pan Subhransu Samanta Ashis Kumar Datta Tirtha Kumar Goswami Surender Lal 《Tropical animal health and production》2010,42(5):985-993
Tropical Animal Health and Production - Mutation studies in different prolific sheep breeds have shown that the transforming growth factor beta super family ligands viz. the growth differentiation... 相似文献
993.
本文对印度西部5种热带干落叶林中凋落物里生物元素的季节性变化和它们返回到新鲜叶中季节性变化进行研究。对5个树种:阿拉伯金合欢(Acacia nilotica L.)、金合欢(Acacia leucophloea Roxb.)、柚木(Tectonagrandis L.f.)、绒毛野独活(Miliusa tomentosa Roxb.)和紫矿(Butea mono-sperma Lain.)中凋落物的成熟叶、枝和再生部分的N、P、Ca、Mg、K和Na的浓度,以及老叶和幼叶中浓度间的关系进行调查。对这些树种的总干物质进行记录,并分析它们所含的N、P、Ca、Mg、K和Na的含量。其中阿拉伯金合欢叶子中N的含量最高,而金合欢的叶子里Ca和Mg含量最高。叶中含P最多的是阿托伯金合欢、金合欢和紫矿,而含P最少的是柚木和绒毛野独活。K和Na含量在这些树种中没有明显的区别。观察发现,N、P和K的浓度随季节变化大,但Ca和Mg则不然。唯有钾在所有树种中都是最稳定的,吸收N和P可以用于来年新叶的生长。从老叶和凋落物中吸收的营养会支持新叶的生长,并增加土壤的肥力。图1表4参30。 相似文献
994.
利用卫星遥感和GIS技术测定印度切蒂斯格尔地区干旱热带森林的土地利用、生物量和碳贮量 总被引:1,自引:0,他引:1
Arvind Bijalwan S.L.Swamy Chandra Mohan Sharma Neeraj Kumar Sharma A.K.Tiwari 《林业研究》2010,21(2):161-170
2001-2002年间,利用卫星遥感和GIS技术研究印度切蒂斯格尔邦的赖布尔地区干旱热带森林的土地利用、生物量和碳贮量情况。主要森林类型为:柚木森林、混合林、衰退森林和婆罗双树混交林。在这些不同森林类型中,立地的坡度和坡面影响森林植被类型、生物量和碳贮量。不同森林类型中,木材积蓄积量、生物量和碳贮量的变化范围分别为:35.59~64.31 m3·hm-2、45.94~78.31Mg·hm-2和22.97~33.27Mg·hm-2。混合林中每公顷的木材蓄积量、生物量和碳贮量最大,衰退森林中的最低。混合林、柚木森林、衰退森林和婆罗双树混交林的总碳量分别为8170.72 Mg、81656.91 Mg、7833.23 Mg和7470.45 Mg。蒂斯格尔邦地区干旱热带森林处于不成熟的生长阶段,且具有很强的碳回收潜力。图6表7参49。 相似文献
995.
Characterization of a cinnamoyl derivative from broccoli (Brassica oleracea L. var. italica) florets
Nazneen Shaik Survay Brajesh Kumar Chandrama Prakash Upadhyaya EunYoung Ko ChoongHwan Lee Jung Nam Choi Do-Young Yoon Yi-Sook Jung Se Won Park 《Fitoterapia》2010,81(8):1062-1066
A new intact glucosinolate Cinnamoyl derivative [6'-O-trans-(4″- hydroxy cinnamoyl)-4-(methylsulphinyl) butyl glucosinolate] (A) has been isolated from Broccoli (Brassica oleracea L. var. italica) florets. The compound was isolated and characterized by LC, MS-ESI, FTIR, 1H and 13C NMR as well as 1H-1H COSY, DEPT 135° spectrometric experiments. 相似文献
996.
Pravat Manjari Mishra A. Sree Bandita Dash Mallika Panigrahi Susanta Kumar Padhan 《Fitoterapia》2010,81(8):977-981
A deoxy lupane triterpene carboxylic acid, lup-20(29)-en-24-oic acid (1), was isolated from the active chloroform extract of Finlaysonia obovata, a latex exuding mangrove plant. Its structure was evaluated on the basis of different spectroscopic methods, including extensive 1D and 2D NMR spectroscopy. Lup-20(29)-en-24-oic acid (1) has shown moderate antimicrobial activity, against some fish pathogens. 相似文献
997.
A Mukherjee D Kumar KP Singh MS Chauhan SK Singla P Palta RS Manik 《Reproduction in domestic animals》2010,45(6):1118-1121
Comet assay was used in the present study to examine DNA damage to buffalo oocytes and embryos during in vitro culture. Embryos were produced in vitro from oocytes obtained from slaughterhouse ovaries in presence of cysteamine (IVM and IVC media supplemented with 50 and 100 μm , respectively) or in its absence (controls). Compared to controls, cysteamine supplementation increased (p < 0.01) cleavage rate and proportion of oocytes that developed to 8‐ to 16‐cell stage. The incidence of DNA damage was lower (p < 0.01) in cysteamine group than that in controls at 8‐ to 16‐ (19.3 ± 4.24 vs 72.0 ± 5.22%) but not in 2‐cell stage embryos (11.7 ± 5.63 vs 20.8 ± 5.49%) or in mature oocytes (5.3 ± 3.43 vs 10.3 ± 4.73%). The tail length, which indicates magnitude of DNA damage, was shorter (p < 0.01) in cysteamine group than in controls in mature oocytes (25.5 ± 0.5 vs 36.0 ± 0.71 pixels) and 8‐ to 16‐cell stage (49.2 ± 1.64 vs 152.7 ± 1.28 pixels) but not in 2‐cell stage embryos (36.3 ± 1.54 vs 36.4 ± 0.75 pixels). Also, exposure of oocytes/embryos to UV radiation or H2O2 caused extensive DNA damage. In conclusion, these results suggest that oocytes/embryos suffer from DNA damage during progress of in vitro culture, which can be partly ameliorated by cysteamine supplementation of culture media. 相似文献
998.
The present study evaluated the effectiveness of ascorbic acid, catalase, chlorpromazine and their combinations in reducing the cryodamages to crossbred bull (Bos taurus × Bos indicus) spermatozoa. A total of 32 ejaculates (eight each from four bulls) were diluted in Tris–citric acid–fructose–egg yolk–glycerol extender. Each ejaculate was split into six parts (five treatment and one control). Treatment groups included 10 mm ascorbic acid, 0.1 mm chlorpromazine, 200 IU/ml catalase, 10 mm ascorbic acid + 0.1 mm chlorpromazine or 200 IU/ml catalase + 0.1 mm chlorpromazine in the extender. Fluorescent probes (Fluorescein isothiocyanate–Pisum sativum agglutinin + Propidium iodide) were used for the assessment of spermatozoa viability and acrosomal status. The proportion of acrosome intact live (AIL), acrosome intact dead, acrosome reacted live and acrosome reacted dead sperm was assessed in fresh, equilibrated and frozen‐thawed semen. The functional status of the sperm was assessed using hypo‐osmotic sperm swelling test (HOSST). Activities of acrosin and hyaluronidase enzyme were also determined. Lipid peroxidation level was assayed based on the melonaldehyde (MDA) production. In cryopreserved semen, the values of AIL spermatozoa, HOSST response, hyaluronidase and acrosin activity were reduced by 53%, 47%, 34% and 54%, respectively from their initial values in fresh semen. However, MDA level was threefold higher in the frozen‐thawed sperm compared with fresh sperm. Significant (p < 0.05) improvement in motility, viability, HOSST response, retention of hyaluonidase and acrosin and reduction in MDA was recorded in ascorbic acid, catalase, ascorbic acid + chlorpromazine and catalase + chlorpromazine incorporated groups. The percentage of AIL sperm was significantly (p < 0.05) higher in ascorbic acid, catalase and ascorbic acid + chlorpromazine incorporated groups compared with the control. Chlorpromazine alone did not improve the post‐thaw semen quality but when combined with either ascorbic acid or catalse, improvement in semen quality was noticed. It was inferred that incorporation of ascorbic acid, catalase and ascorbic acid + chlorpromazine in semen extender improved the post‐thaw semen quality in crossbred bulls. 相似文献
999.
Seepage through sand bed channels in a downward direction (suction) reduces the stability of particles and initiates the sand movement. Incipient motion of sand bed channel with seepage cannot be designed by using the conventional approach. Metamodeling techniques, which employ a non-linear pattern analysis between input and output parameters and solely based on the experimental observations, can be used to model such phenomena. Traditional approach to find non-dimensional parameters has not been used in the present work. Parameters, which can influence the incipient motion with seepage, have been identified and non-dimensionalized in the present work. Non-dimensional stream power concept has been used to describe the process. By using these non-dimensional parameters; present work describes a radial basis function (RBF) metamodel for prediction of incipient motion condition affected by seepage. The coefficient of determination, R2 of the model is 0.99. Thus, it can be said that model predicts the phenomena very well. With the help of the metamodel, design curves have been presented for designing the sand bed channel when it is affected by seepage. 相似文献
1000.
Senthil Arun Kumar Marie Magnusson Leigh C. Ward Nicholas A. Paul Lindsay Brown 《Marine drugs》2015,13(2):788-805
Increased seaweed consumption may be linked to the lower incidence of metabolic syndrome in eastern Asia. This study investigated the responses to two tropical green seaweeds, Ulva ohnoi (UO) and Derbesia tenuissima (DT), in a rat model of human metabolic syndrome. Male Wistar rats (330–340 g) were fed either a corn starch-rich diet or a high-carbohydrate, high-fat diet with 25% fructose in drinking water, for 16 weeks. High-carbohydrate, high-fat diet-fed rats showed the signs of metabolic syndrome leading to abdominal obesity, cardiovascular remodelling and non-alcoholic fatty liver disease. Food was supplemented with 5% dried UO or DT for the final 8 weeks only. UO lowered total final body fat mass by 24%, systolic blood pressure by 29 mmHg, and improved glucose utilisation and insulin sensitivity. In contrast, DT did not change total body fat mass but decreased plasma triglycerides by 38% and total cholesterol by 17%. UO contained 18.1% soluble fibre as part of 40.9% total fibre, and increased magnesium, while DT contained 23.4% total fibre, essentially as insoluble fibre. UO was more effective in reducing metabolic syndrome than DT, possibly due to the increased intake of soluble fibre and magnesium. 相似文献