首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   4628篇
  免费   284篇
  国内免费   2篇
林业   329篇
农学   194篇
基础科学   16篇
  1185篇
综合类   221篇
农作物   359篇
水产渔业   501篇
畜牧兽医   1622篇
园艺   96篇
植物保护   391篇
  2024年   5篇
  2023年   46篇
  2022年   94篇
  2021年   201篇
  2020年   189篇
  2019年   242篇
  2018年   194篇
  2017年   200篇
  2016年   193篇
  2015年   155篇
  2014年   211篇
  2013年   310篇
  2012年   373篇
  2011年   352篇
  2010年   215篇
  2009年   185篇
  2008年   304篇
  2007年   314篇
  2006年   216篇
  2005年   174篇
  2004年   153篇
  2003年   144篇
  2002年   150篇
  2001年   29篇
  2000年   24篇
  1999年   25篇
  1998年   21篇
  1997年   17篇
  1996年   12篇
  1995年   17篇
  1994年   13篇
  1993年   11篇
  1992年   11篇
  1991年   4篇
  1990年   11篇
  1989年   14篇
  1988年   9篇
  1987年   9篇
  1986年   8篇
  1985年   8篇
  1984年   12篇
  1983年   4篇
  1982年   3篇
  1980年   4篇
  1977年   3篇
  1973年   3篇
  1972年   3篇
  1969年   4篇
  1966年   4篇
  1955年   2篇
排序方式: 共有4914条查询结果,搜索用时 15 毫秒
101.
The influence of oil concentration and baking on the properties of low-moisture composites consisting of oil droplets dispersed in a protein-carbohydrate-glycerol matrix was investigated. These composites were produced by blending canola oil, whey protein concentrate (WPC), corn syrup, and glycerol together using a high-speed mixer. The resulting system consisted of oil droplets dispersed in a polar matrix. Some composites were analyzed directly after preparation, while others were analyzed after being heated at 176 degrees C for 10 min to simulate baking. The "lightness" of the composites was greater before baking (higher L value), but the color was more intense after baking (higher a and b values). The lightness and color intensity of the composites decreased as the oil concentration increased, with the effects being more pronounced in the baked samples. The zeta potential of the oil droplets (measured after dilution at pH 6) was highly negative (approximately -40 mV), indicating that whey protein was adsorbed to the droplet surfaces. The mean particle diameter (measured after dilution at pH 6) increased appreciably after baking, which was attributed to droplet flocculation. The rheological properties of the unbaked and baked materials were characterized by squeezing flow viscometry, which showed that the measurements associated with consistency and yield stress increased with increasing oil concentration and with baking.  相似文献   
102.
103.
The paravertebral brachial plexus block (PVB) provides thoracic limb analgesia. The objective was to describe a blind craniocaudal (CC) approach to the PVB and compare its accuracy, time, and difficulty of performance with a blind dorsoventral (DV) approach. The operator was initially trained by experienced clinicians to perform both approaches on 5 cadavers. Next, a CC or DV approach to the PVB was performed on both thoracic limbs of 20 cadavers (20 for each approach). Methylene blue dye was equally divided into 4 aliquots to stain the ventral branches of the sixth to eighth cervical and first thoracic spinal nerves. Successfully stained (stain ≥ 1 cm) spinal nerves were counted. The time to perform each approach was recorded and ease of performance was scored using a numerical scale (1 “easy” to 4 “difficult”). The phrenic nerve was checked for stain. A Wilcoxon signed-rank test was used to compare approaches. The data are presented as median (interquartile range; minimum to maximum range). The number of stained nerves with the CC approach 3 (1; 2 to 4), was higher than the DV approach 2 (2; 0 to 4) (P = 0.002). The time (in seconds) to perform the CC approach 125 (79; 70 to 194), was not different from the DV approach 142 (54; 101 to 232) (P = 0.084). The CC approach 2 (2; 1 to 4) was easier to perform than the DV approach 3 (1; 2 to 4) (P = 0.024). No phrenic nerve staining was observed with either approach. The CC approach is an alternative to the DV approach for performing the PVB in dogs.  相似文献   
104.
Microalgae are known as a producer of proteins and lipids, but also of valuable compounds for human health benefits (e.g., polyunsaturated fatty acids (PUFAs); minerals, vitamins, or other compounds). The overall objective of this research was to prospect novel products, such as nutraceuticals from microalgae, for application in human health, particularly for metabolic diseases. Chlorella vulgaris and Chlorococcum amblystomatis were grown autotrophically, and C. vulgaris was additionally grown heterotrophically. Microalgae biomass was extracted using organic solvents (dichloromethane, ethanol, ethanol with ultrasound-assisted extraction). Those extracts were evaluated for their bioactivities, toxicity, and metabolite profile. Some of the extracts reduced the neutral lipid content using the zebrafish larvae fat metabolism assay, reduced lipid accumulation in fatty-acid-overloaded HepG2 liver cells, or decreased the LPS-induced inflammation reaction in RAW264.7 macrophages. Toxicity was not observed in the MTT assay in vitro or by the appearance of lethality or malformations in zebrafish larvae in vivo. Differences in metabolite profiles of microalgae extracts obtained by UPLC-LC-MS/MS and GNPS analyses revealed unique compounds in the active extracts, whose majority did not have a match in mass spectrometry databases and could be potentially novel compounds. In conclusion, microalgae extracts demonstrated anti-obesity, anti-steatosis, and anti-inflammatory activities and could be valuable resources for developing future nutraceuticals. In particular, the ultrasound-assisted ethanolic extract of the heterotrophic C. vulgaris significantly enhanced the anti-obesity activity and demonstrated that the alteration of culture conditions is a valuable approach to increase the production of high-value compounds.  相似文献   
105.
106.
107.
Plant Foods for Human Nutrition - Grapes contain high contents of phenolics, which are known to possess health promoting properties. Exogenous application of phytoregulators, mainly methyl...  相似文献   
108.
Machado  Rui  Godinho  Sérgio  Guiomar  Nuno  Gil  Artur  Pirnat  Janez 《Landscape Ecology》2020,35(6):1291-1308
Landscape Ecology - The Portuguese montado is an agro-silvopastoral system, similar to the Spanish dehesa, known for its cultural, economic and ecological value. Despite its importance, contrasting...  相似文献   
109.
In this paper, we report molecular investigation of an ectomycorrhizal fungi (EMF) community of European larch (Larix decidua Mill.) seedlings grown in a bare-root nursery. In total, we surveyed 32 nurseries that were each active in supplying planting stocks to restock forests and for afforestation of post-agricultural land. Sequence-based approach was used to identify EMF taxa, quantify EMF richness, and document differences in the relative abundance of individual taxa. We identified seven fungal species that might contribute to the mycorrhizal community structure of 1 to 3-year-old L. decidua seedlings. The species richness in the examined larches varied between one and four fungal taxa, depending on both the nursery stock samples (NSS) and age class of the seedlings. The average was 1.4 for 1-year-old seedlings and 2.3 for 2- and 3-year-old plants. The dominance of Ascomycota over Basidiomycota and the prevalence of two species, Wilcoxina mikolae and Suillus grevillei, as EMF partners were characteristic features of nursery-grown L. decidua seedlings. S. grevillei was the only one basidiomycetes colonized roots of tested seedlings. The rest of the mycorrhizal pool from forest nurseries was typically dominated by pioneer fungal ascomycetes. W. mikolae was the most common mycorrhizal ascomycete present at a high frequency on NSS from both age classes and with very high abundance (average 90%) on 1-year-old seedlings. Some other ascomycetes (Pezizales 1, Pezizales 2 and Pezizales 3) appeared on tested larches at a low frequency, but sometimes in high abundance. Tuber spp. appeared at a low frequency and low abundance. The relative abundance of S. grevillei was positively correlated with the age of seedlings, while W. mikolae was negatively correlated with age. Tuber sp. 1 and 2, Pezizales 2, and W. mikolae were positively associated with the basic soil pH values. However, forward selection of the environmental variables showed that only the age of the larch seedlings contributed significantly (F = 11.45, P = 0.02) to the variance in the ECF community.  相似文献   
110.
Increasingly, economies that have traditionally benefited from offshoring are losing some of their strategical advantages, with a consequent increase in backshoring by developed economies. This paper describes the phenomenon and tries to shed light on the current challenges, trends, and debates in the area, and on the main determinants of backshoring. A new phenomenon known as nearshoring is also analysed—this consists of relocating some previously offshored manufacturing activities so that they are now close to previous core locations, but not so close as to suffer from disagglomeration effects. This combines the advantages of offshoring and backshoring.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号