全文获取类型
收费全文 | 2246篇 |
免费 | 129篇 |
专业分类
林业 | 176篇 |
农学 | 109篇 |
基础科学 | 13篇 |
523篇 | |
综合类 | 113篇 |
农作物 | 132篇 |
水产渔业 | 346篇 |
畜牧兽医 | 779篇 |
园艺 | 52篇 |
植物保护 | 132篇 |
出版年
2024年 | 2篇 |
2023年 | 33篇 |
2022年 | 48篇 |
2021年 | 108篇 |
2020年 | 87篇 |
2019年 | 113篇 |
2018年 | 87篇 |
2017年 | 97篇 |
2016年 | 83篇 |
2015年 | 61篇 |
2014年 | 101篇 |
2013年 | 129篇 |
2012年 | 176篇 |
2011年 | 194篇 |
2010年 | 104篇 |
2009年 | 123篇 |
2008年 | 125篇 |
2007年 | 123篇 |
2006年 | 112篇 |
2005年 | 101篇 |
2004年 | 93篇 |
2003年 | 94篇 |
2002年 | 63篇 |
2001年 | 14篇 |
2000年 | 15篇 |
1999年 | 8篇 |
1998年 | 10篇 |
1997年 | 9篇 |
1996年 | 4篇 |
1995年 | 9篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1992年 | 4篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 4篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 3篇 |
1975年 | 1篇 |
1972年 | 1篇 |
1971年 | 3篇 |
1968年 | 1篇 |
1964年 | 1篇 |
排序方式: 共有2375条查询结果,搜索用时 0 毫秒
921.
Carotenoid production by the marine microalgae Nannochloropsis oculata in different low‐cost culture media 下载免费PDF全文
Wladimir Angelino Faé Neto Carlos Rafael Borges Mendes Paulo Cesar Abreu 《Aquaculture Research》2018,49(7):2527-2535
Nannochloropsis oculata (Eustigmatophyceae) is a marine microalga of great biotechnological interest, mainly due to its large production of lipids containing polyunsaturated fatty acids. In addition, this species presents a wide range of commercial interest pigments, such as zeaxanthin, beta‐carotene, and other xanthophylls, with potential for several industrial applications. However, most of the research concerning pigment production by N. oculata has been conducted by employing high‐cost laboratorial growth media, which makes large‐scale pigment production using these microalgae impractical. Considering the high interest and commercial value in microalgae pigments, this study investigates the feasibility of producing pigments by N. oculata using five different low‐cost growth media (fertilizers and aquaculture effluents). Nutrient (ammonia, nitrite and phosphate) concentrations, cell abundance, biomass, and the concentration/composition of pigments were measured. The pigment profile of N. oculata showed chlorophyll‐a as the dominant pigment, along with violaxanthin, vaucheraxanthin, and lower concentrations of antheraxanthin, zeaxanthin and beta‐carotene. Although the highest biomass (516.4 ± 76.71 mg/L) and pigment content (0.98 mg/g) were achieved in the laboratory media (f/2), the low‐cost media (containing ammonium sulfate, calcium superphosphate and urea) revealed a great potential for the production of pigments, specially chlorophyll‐a, violaxanthin and zeaxanthin, due to the high pigment content per unit of biomass. 相似文献
922.
Jos Fernando M. Gonalves Mariana Hinzmann Jorge Machado Sandra Arajo Jos Carlos Oliveira Rodrigo O. A. Ozrio 《International Aquatic Research》2018,10(2):133-143
l-Carnitine plays a key role in the regulation of energy metabolism and growth in fish. The aim of this study was to determine the effects of dietary l-carnitine levels on carnitine homeostasis and energy metabolism in diploid and triploid trout (Oncorhynchus mykiss). Diploid and triploid trout (29.5 ± 0.6 and 31.8 ± 0.5 g, respectively) were fed with three diets supplemented with 15, 200 or 530 mg l-carnitine/kg, respectively, for 56 days. Compared to 15 mg l-carnitine, total carnitine content increased in the liver by 182% in diploid and by 154% in triploid trout fed 530 mg l-carnitine. In muscle, total carnitine content increased by 60 and 73% in diploid and by 34 and 75% in triploid with the increase in dietary l-carnitine levels. l-Carnitine caused no significant change in the plasma concentrations of metabolites like proteins (ammonia, urea and protein), lipid (triglycerides), carbohydrate (glucose, lactate) and enzyme activities (lipase, lactate, alanine transaminase, lactic acid dehydrogenase). Triploid trout had significantly lower plasma ammonia (P = 0.003), lipase (P = 0.005) and triiodothyronine (T3; P = 0.003) levels than diploid trout. In conclusion, ploidy significantly affected the energy metabolism in rainbow trout, dietary l-carnitine levels altered the l-carnitine homeostasis, but not influence nutritional metabolism. 相似文献
923.
924.
Álvaro Cañadas-López Diana Rade-Loor Juan Manuel Domínguez-Andrade J. Jesús Vargas-Hernández Carlos Molina-Hidrovo Carlos Macías-Loor Christian Wehenkel 《New Forests》2017,48(6):785-799
The Ecuadorian Government has, since the end of 2011, promoted an initiative for using pure jatropha oil, derived from the seeds of Jatropha curcas L., to generate electricity to supply Floreana Island (one of the Galapagos Islands). In the present study, nine elite accessions of J. curcas from tropical dry forests in Ecuador were cultivated for the purpose of evaluating seed production in relation to the propagation method used (seed, cutting). A split-plot design with three replicates was applied. Seed production, measured over a period of 7 years (2009–2015) showed a large year-to-year variation. However, seed production varied significantly among accessions and depended on the propagation method (seeds or cuttings). Propagation by stem cuttings stabilized the variability in the vegetative and seed production components measured, increasing the strength of their relationships with seed yield. The three highest yielding accessions produced 0.28–0.30 kg of seeds tree?1 year?1. As seed yield was not correlated with annual precipitation, the year-to-year variation in production of accessions indicates the effect of other factors not considered here, such as agronomic practices. The study findings suggest that agroforestry practices could be developed that would enable J. curcas to play a predominant role in a strategy for tropical dry forests aimed at reducing poverty (also known as pro-poor growth strategy). 相似文献
925.
通过分析哥斯达黎加森林生态服务补偿机制演进历程,总结出其项目类型多样、参加者自主性强、项目合同规范高效、项目资金来源渠道丰富、补偿标准合理、从自愿的补偿向强制性支付转变等对我国有益的启示,并在此基础上提出改进我国森林生态效益补偿机制的建议。 相似文献
926.
Characterization of a novel form of progressive retinal atrophy in Whippet dogs: a clinical,electroretinographic, and breeding study 下载免费PDF全文
927.
Patterns of lymph node metastasis identified following bilateral mandibular and medial retropharyngeal lymphadenectomy in 31 dogs with malignancies of the head 下载免费PDF全文
Owen T. Skinner Sarah E. Boston Carlos H. de M. Souza 《Veterinary and comparative oncology》2017,15(3):881-889
Variable pathways of lymphatic drainage have been described in the dog head and neck. The aim of this study was to retrospectively assess the patterns of lymph node metastasis in dogs with malignancies of the head following bilateral mandibular and medial retropharyngeal lymphadenectomy. Thirty‐one dogs were included. Median age at surgery was 10 years (range: 5 months to 14 years) and mean bodyweight was 21.4 ± 11.9 kg. Lymph node metastasis occurred in 14 dogs (45%), with spread to mandibular lymph nodes in 14 dogs and medial retropharyngeal metastasis in 11 dogs. Eight of 13 dogs (62%) with lymphatic metastasis and a lateralised lesion showed contralateral dissemination, while 12/13 (92%) showed ipsilateral metastasis. Of 13 dogs with oral malignant melanoma, four showed metastasis to all four lymph centres. Contralateral metastasis may occur in dogs with malignancies of the head and should be considered during staging and management. 相似文献
928.
Monizze Vannuci-Silva João M. de Souza Fábio Francisco de Oliveira Marcus A. G. de AraújoJr Eleine Francioni Carlos Eduardo Eismann Chang H. Kiang José S. Govone Maria J. Belzunce-Segarra Amauri Antonio Menegário 《Water, air, and soil pollution》2017,228(6):222
Metals are commonly determined in aquatic organisms, primarily using bivalves to provide important data on their bioavailability. The technique of diffusive gradients in thin films (DGTs) has also been employed to assess the concentration of metals in freshwater and marine environments, determining their lability. The present work evaluated and compared the labile and bioavailable concentrations of Cd, Co, Cu, Mn, Ni and Pb in seawater from Ilha Grande Bay, RJ, using DGT and transplanted bivalves (Nodipecten nodosus), respectively. The scallops and DGTs were immersed in water at three sampling locations within the bay from July to September 2012 (winter campaign) and from December 2012 to February 2013 (summer campaign). The metals were determined by inductively coupled plasma-mass spectrometry (ICP-MS) and optical emission spectrometry (ICP-OES). DGT technique was successfully used to determine the concentrations of metals in waters, except for Pb when short deployment times were used. All metals were determined using transplanted bivalves (N. nodosus), but pre-exposure to Cd was evident, which made the interpretation of the data for this analyte difficult. The data on metal lability in Ilha Grande Bay waters obtained from the DGT technique were correlated with the metal bioavailability determined in the soft tissues of the transplanted N. nodosus for Co, Cu, Mn, Ni and Pb. This is the first evaluation of this type for this area of high environmental concern. Both techniques revealed that Náutico was the location with the highest concentration of metals in the study area. 相似文献
929.
Alcione Miotto Carlos Alberto Ceretta Eduardo Girotto Gustavo Trentin João Kaminski Lessandro De Conti 《Communications in Soil Science and Plant Analysis》2017,48(10):1167-1183
The use of copper (Cu)-based fungicides to control diseases in vineyards can cause excessive Cu accumulation in soils. Greater Cu availability is expected in acid sandy soils with low organic matter (OM), where the risk of toxicity to plants and environment contamination is high. This study aimed to study the evolution of Cu in acid, sandy soils planted with grapevines for a period of time between 2 and 32 years. Two studies were carried out in South Brazil: in the first study, soil samples, from 19 vineyards were collected and analyzed in the first 0.2 m depth-layer for the total and available Cu. In the second study, 3 soils were selected among the previous 19 according to the age of vineyard (5, 11, and 30 year-old), and their 0.60 m-depth profile was analyzed for 5 fractions of Cu (soluble, exchangeable, mineral, organic, and residual). All the soils were classified as Ultisols. The vineyards with more than 25 years under cultivation had a mean total Cu concentration of 90 mg kg?1 in the 0–0.10 m layer. Approximately 80% of it was potentially available to plants. The greatest total and available Cu were found in the soil surface layers (0.2 m depth), where up to 75% of the total Cu is adsorbed in clay minerals and only 20% is complexed in the OM. 相似文献
930.
Chih-Wei Tung Keyan Zhao Mark H. Wright M. Liakat Ali Janelle Jung Jennifer Kimball Wricha Tyagi Michael J. Thomson Kenneth McNally Hei Leung Hyunjung Kim Sang-Nag Ahn Andy Reynolds Brian Scheffler Georgia Eizenga Anna McClung Carlos Bustamante Susan R. McCouch 《Rice》2010,3(4):205-217
We present an overview of a research platform that provides essential germplasm, genotypic and phenotypic data and analytical tools for dissecting phenotype–genotype associations in rice. These resources include a diversity panel of 400 Oryza sativa and 100 Oryza rufipogon accessions that have been purified by single seed descent, a custom-designed Affymetrix array consisting of 44,100 SNPs, an Illumina GoldenGate assay consisting of 1,536 SNPs, and a suite of low-resolution 384-SNP assays for the Illumina BeadXpress Reader that are designed for applications in breeding, genetics and germplasm management. Our long-term goal is to empower basic research discoveries in rice by linking sequence diversity with physiological, morphological, and agronomic variation. This research platform will also help increase breeding efficiency by providing a database of diversity information that will enable researchers to identify useful DNA polymorphisms in genes and germplasm of interest and convert that information into cost-effective tools for applied plant improvement. 相似文献