全文获取类型
收费全文 | 811篇 |
免费 | 48篇 |
专业分类
林业 | 80篇 |
农学 | 39篇 |
基础科学 | 6篇 |
226篇 | |
综合类 | 50篇 |
农作物 | 48篇 |
水产渔业 | 79篇 |
畜牧兽医 | 200篇 |
园艺 | 21篇 |
植物保护 | 110篇 |
出版年
2023年 | 7篇 |
2022年 | 15篇 |
2021年 | 35篇 |
2020年 | 36篇 |
2019年 | 34篇 |
2018年 | 43篇 |
2017年 | 30篇 |
2016年 | 35篇 |
2015年 | 37篇 |
2014年 | 34篇 |
2013年 | 47篇 |
2012年 | 58篇 |
2011年 | 68篇 |
2010年 | 32篇 |
2009年 | 28篇 |
2008年 | 55篇 |
2007年 | 35篇 |
2006年 | 44篇 |
2005年 | 41篇 |
2004年 | 43篇 |
2003年 | 30篇 |
2002年 | 27篇 |
2001年 | 9篇 |
2000年 | 2篇 |
1999年 | 5篇 |
1998年 | 2篇 |
1997年 | 6篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1976年 | 1篇 |
1972年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有859条查询结果,搜索用时 31 毫秒
91.
92.
Souza Luana Lelis Zorzetto Mariana Furtado Ricci Túlio José Terra Canesin Roberta Carrilho Dias e Silva Nhayandra Christina Negrão João Alberto dos Santos Gonçalves Cyrillo Joslaine Noely Mercadante Maria Eugênia Zerlotti 《Tropical animal health and production》2019,51(7):2045-2055
Tropical Animal Health and Production - Twenty-seven Nellore cow-calf pairs were submitted for feed efficiency testing. The animals were weighed every 21 ± 5 days to... 相似文献
93.
Berta Gonalves Carlos M. Correia Ana Paula Silva Eunice A. Bacelar Alberto Santos Jos M. Moutinho-Pereira 《Scientia Horticulturae》2008,116(4):381-387
Variations in morpho-anatomy, chemical composition, gas exchange and stem water potential (Ψstem) were studied in leaves of Prunus avium L. cultivars with different growth habit: Burlat and Summit (upright, dense canopies), and Van (spreading, open canopy). Light transmittance was highest in Van canopies. Therefore, Van allowed an easier penetration of the visible radiation through the canopy, which improves photosynthetic rates, especially at harvest. Conversely, no differences in Ψstem were found among cultivars. Van showed the highest leaf mass per unit area and variations in this parameter were mainly associated with alterations in leaf thickness than in leaf density. Leaves of Summit and Van were thicker than those of Burlat, mainly due to increased palisade and spongy parenchyma thickness. However, Burlat leaves had the highest palisade/spongy ratio. Total chlorophyll concentration per area and the chlorophyll a/b ratio were always higher in Van leaves than in the other two cultivars. In contrast, Van leaves had the lowest concentrations of soluble carbohydrates and starch. In dense canopies of Summit and Burlat, light reduction caused a notable increase in the relative concentration of total phenols. The above results provide useful information about the biological behaviour of sweet cherry cultivars with open and dense canopies in order to help the agronomical decisions regarding the local environmental conditions and the consumers’ preference. In particular, it is important to manipulate factors such as orchard exposure, row orientation, plant spacing, training system and pruning, which are able to reduce shading in the canopy. 相似文献
94.
An exploratory investigation of echocardiographic parameters and the effects of posture on cardiac structure and function in the Livingstone's fruit bat (Pteropus livingstonii) 下载免费PDF全文
Aimee L. Drane Robert Shave Andrew Routh Alberto Barbon 《Veterinary radiology & ultrasound》2018,59(1):89-97
There is growing evidence that dilated cardiomyopathy may be a major cause of death in captive Livingstone's fruit bats (Pteropus livingstonii). Therefore, the primary aim of this prospective, exploratory study was to examine whether a systematic cardiac ultrasound protocol is feasible in this critically endangered species and to report basic measures of cardiac structure and function from a cohort of apparently healthy bats. A secondary aim was to test the effect posture (dorsal recumbency vs. roosting) has upon cardiac function in this species. Transthoracic echocardiograms, including 2D, Doppler, and tissue Doppler measures of cardiac structure and function were completed as part of routine health examinations for bats at a single center (n = 19). Bats were then grouped by age and disease status and the mean and range data reported for each group. In healthy adult bats, with the exception of a reduction in heart rate (P ≤ 0.05), right atrial systolic area (P ≤ 0.05), and right ventricular velocity during atrial contraction, there were no significant changes in cardiac structure or function in response to the roosting position. However, in the bats presenting with dilated cardiomyopathy the current data suggest that left ventricular ejection fraction is improved while roosting. Further work is required to confirm our initial findings, generate diagnostic reference intervals, and explore the causes of dilated cardiomyopathy in this species. 相似文献
95.
Genetic variation of sweet potatoes (Ipomoea batatas L.) cultivated in Chile determined by RAPDs 总被引:1,自引:0,他引:1
Boris Sagredo Patricio Hinrichsen Horacio López Alberto Cubillos Carlos Muñoz 《Euphytica》1998,101(2):193-198
RAPD (randomly amplified polymorphic DNA) technology was applied to analyze the genetic variability of sweet potato germplasm
existing in Chile and elsewhere. Analysis of 28 cultivars from all over the world showed polymorphic bands with all 18 primers
tested. A total of 124 RAPD bands were scored with an average of 6.9 polymorphic bands per primer. These results confirm that
sweet potato exhibits high genetic variation. Two groups were distinguished: one containing Peruvian cultivars, and another
containing cultivars from the rest of the world. Analysis of 14 accessions from Central Chile and one from Northern Chile
showed polymorphic bands with 24 of 26 primers tested, but almost all of the 140 polymorphic bands merely showed the distinctness
of the Northern accession. The almost complete uniformity of the other 14 accessions shows that sweet potato germplasm collected
in Central Chile has very little genetic variability and may be derived from a single cultivar.
Based on these results and on historical records, some hypotheses are proposed to explain the origin of sweet potatoes cultivated
in Chile.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
96.
David M. Spooner Alberto Salas López Zósimo Huamán Robert J. Hijmans 《American Journal of Potato Research》1999,76(3):103-119
Peru has 103 taxa of wild potatoes (species, subspecies, varieties, and forms) according to Hawkes (1990; modified by us by a reduction of species in theSolanum brevicaule complex) and including taxa described by C. Ochoa since 1989. Sixty-nine of these 103 taxa (67% ) were unavailable from any of the world’s genebanks and 85 of them (83%) had less than three germplasm accessions. We conducted a collaborative Peru (INIA), United States (NRSP-6), and International Potato Center (CIP) wild potato (Solanum sect.Petota) collecting expedition in Peru to collect germplasm and gather taxonomic data. This is the first of a series of planned expeditions from 1998–2002. We collected from February 18 to April 18, 1998, in the southern departments of Apurímac, Arequipa, Cusco, Moquegua, Puno, and Tacna. We made 57 germplasm collections, including 14 taxa that are the first available as germplasm for any country (Solanum aymaraesense, S. chillonanum, S. incasicum, S. megistacrolobum subsp.megistacrolobum f. purpureum, S. longiusculus, S. multiflorum,S. pillahuatense, S. sawyeri, S. sandemanii, S. tacnaense, S. tarapatanum, S. urubambae, S. velardei, S. villuspetalum), and two additional taxa that are the first available for Peru but with germplasm from Bolivia (S. megistacrolobum subsp.toralapanum, S. yungasense). Collections also were made for the rare taxaS. acroscopicum, S. buesii, S. limbaniense, andS. santolallae. Our collections suggest the following minimum synonymy may be needed for Peruvian potatoes:S. sawyeri as a synonym ofS. tuberosum;S. hawkesii andS. incasicum as synonyms ofS. raphanifolium;S. multiflorum andS. villuspetalum as synonyms ofS. urubambae. 相似文献
97.
Maria J. Gil Jos M. Zabalza Javier Navarro Maria A. Maú Alberto Gonzlez Víctor Martínez Merino Arantxa Canal Mercedes Royuela Pedro M. Aparicio-Tejo 《Pest management science》1997,49(2):148-156
Several ethyl 2,3-dihydro-3-oxoisothiazolo[5,4-b]pyridine-2-alkanoate derivatives were synthesized as herbicides. Only 5-methyl derivatives inhibited both hypocotyl and root growth in the lettuce (Lactuca sativa L.) seedling test at 100 mg litre-1. Only ethyl propionate and valerate derivatives showed significant inhibition at 0·1 mg litre-1, whereas ethyl acetate or butyrate derivatives were inactive. Contrary to unoxidized derivatives, the inhibitory effect of 1-oxide and 1,1-dioxide derivatives was strongly dependent on concentration; ethyl 2,3-dihydro-5-methyl-3-oxoisothiazolo[5,4-b]pyridine-2-propionate 1,1-dioxide inhibited 100% of germination at 100 mg litre-1 and 45% of lettuce seedling growth at 0·1 mg litre-1. Quantitative structure–inhibition of growth relationship analysis carried out by adaptive least-squares (ALS) method gave a good correlation with small and hydrophobic 5-substituents as well as with odd carbon-chain ethyl alkanoates in position 2. Active compounds did not show auxin-like activity from 0·1 to 100 mg litre-1. © 1997 SCI. 相似文献
98.
Alberto Pea‐Rodríguez Zo Pelletier‐Morreeuw Jazmín García‐Lujn María del Carmen Rodríguez‐Jaramillo Laura Guzmn‐Villanueva Cristina Escobedo‐Fregoso Dariel Tovar‐Ramírez Ana Gisela Reyes 《Aquaculture Research》2020,51(4):1336-1345
Agave lechuguilla is a succulent plant species, mainly distributed in the northeast of Mexico and south of the United States of America. The main use for this plant is the fibre´s extraction (known as Tampico fibres), resulting in 15% of fibres and 85% of a by‐product waste named guishe. The lechuguilla collectors, normally incinerate the guishe, thus causing environmental contamination. Interestingly, recent studies showed that guishe contains molecules with nutritional properties, such as saponins, flavonoids and sugars. Therefore, in this work, we evaluated the effect of the crude extract of guishe as a feed additive in whiteleg shrimp diets. According to that, MS‐HPLC analysis of the extract showed the presence of saponins such as diosgenin, smilagenin, hecogenin, manogenin, tigogenin hexose, yucagenin, chlorogenin, diosgenin diglucoside and the flavonol, quercetin. After chemical analysis, the crude extract was included into an experimental diet in four levels; 0% (L0%), 0.1% (L0.1%), 0.3% (L0.3%) and 0.6% (L0.6%). Dietary incorporation of the extract was evaluated by zootechnical performance, haemolymph biochemistry, histomorphology and digestive enzyme activity of shrimps. After 5‐week feeding, the L0.3% diet showed significantly higher growth and better feed utilization among treatments. A significant increase in tubule epithelium height and tubule coverage area from hepatopancreas in shrimp under L0.3% diet compared with the control diet suggest an improvement of the health and nutritional status of the shrimp. Inclusion of L0.3% and L0.6% of the crude extract resulted in a reduction in amylase activity, without effect in glucose levels in the haemolymph. Thus, we suggest that lechuguilla guishe crude extract contains nutritional molecules that may be used as a feed additive to promote shrimp productivity. 相似文献
99.
Natalino da Costa Sousa Mrcia Valria Silva do Couto Higo Andrade Abe Peterson Emmanuel Guimares Paixo Carlos Alberto Martins Cordeiro Emilly Monteiro Lopes Jonathan Stuart Ready Gabriel Fernandes Alves Jesus Mauricio Latera Martins Jos Luiz Pereira Mourio Paulo Csar Falanghe Carneiro Alexandre Nizio Maria Rodrigo Yudi Fujimoto 《Aquaculture Research》2019,50(12):3720-3728
Intensive fish farming has resulted in an increased concern for disease outbreaks. Probiotic use is one of the strategies being developed to improve fish health and productivity. Measures of probiotic colonization, growth performance, haematological characteristics and parasite load were used to evaluate the effect of diets supplemented with Enterococcus faecium on growth and health of Arapaima gigas juveniles. A completely randomized design with four treatments (diet with E. faecium at 1 × 106 CFU/g and 1 × 108 CFU/g, control diet and diet with the culture medium MRS) and three replicates was used. Ninety‐six Arapaima juveniles were distributed in 12 cages fed with the specified diet for 68 days. Colonization of the intestinal tract by lactic acid bacteria reduced the total number of heterotrophic bacteria in fish fed with probiotics compared to controls. Fish fed a supplemented diet containing 1 × 108 CFU/g presented higher values of weight gain, survival and fish growth uniformity, and lower values of feed conversion ratio. The prevalence of Trichodina sp. could have affected the survival of fish in the control group. Reduction in parasite load and an increase in haematocrit, the number of erythrocytes, thrombocytes, neutrophils and monocytes were also observed in fish fed the diet containing 1 × 108 CFU/g. Enterococcus faecium presented a probiotic effect in A. gigas juveniles and can be recommended for use at a concentration of 1 × 108 CFU/g to modify the gut microbiota, improve growth performance and haematology and reduce parasitic load. 相似文献
100.