全文获取类型
收费全文 | 21344篇 |
免费 | 308篇 |
国内免费 | 4篇 |
专业分类
林业 | 3851篇 |
农学 | 1480篇 |
基础科学 | 145篇 |
3696篇 | |
综合类 | 1304篇 |
农作物 | 2563篇 |
水产渔业 | 2161篇 |
畜牧兽医 | 3104篇 |
园艺 | 1174篇 |
植物保护 | 2178篇 |
出版年
2023年 | 28篇 |
2022年 | 89篇 |
2021年 | 116篇 |
2020年 | 97篇 |
2019年 | 107篇 |
2018年 | 2832篇 |
2017年 | 2804篇 |
2016年 | 1330篇 |
2015年 | 225篇 |
2014年 | 213篇 |
2013年 | 289篇 |
2012年 | 1123篇 |
2011年 | 2490篇 |
2010年 | 2280篇 |
2009年 | 1457篇 |
2008年 | 1589篇 |
2007年 | 1842篇 |
2006年 | 296篇 |
2005年 | 343篇 |
2004年 | 332篇 |
2003年 | 337篇 |
2002年 | 260篇 |
2001年 | 148篇 |
2000年 | 159篇 |
1999年 | 77篇 |
1998年 | 32篇 |
1997年 | 18篇 |
1996年 | 20篇 |
1995年 | 22篇 |
1993年 | 33篇 |
1992年 | 35篇 |
1991年 | 27篇 |
1990年 | 34篇 |
1989年 | 42篇 |
1988年 | 42篇 |
1987年 | 41篇 |
1986年 | 18篇 |
1985年 | 32篇 |
1984年 | 23篇 |
1983年 | 27篇 |
1981年 | 19篇 |
1980年 | 15篇 |
1978年 | 21篇 |
1977年 | 23篇 |
1976年 | 28篇 |
1975年 | 14篇 |
1974年 | 20篇 |
1973年 | 22篇 |
1972年 | 23篇 |
1971年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Chun OK Kim DO Moon HY Kang HG Lee CY 《Journal of agricultural and food chemistry》2003,51(25):7240-7245
To study the effect of polyphenolics on antioxidant capacities of plums, the amounts of total phenolics, total flavonoids and individual phenolic compounds, and vitamin C equivalent antioxidant capacity (VCEAC) of eleven plum cultivars was determined. There was a good linear relationship between the amount of total phenolics and total antioxidant capacity (r2 = 0.9887). The amount of total flavonoids and total antioxidant capacity also showed a good correlation (r2 = 0.9653). Although the summation of individual antioxidant capacity was lower than the total antioxidant capacity of plum samples, there was a positive correlation (r2 = 0.9299) of total antioxidant capacity of plum samples with the sum of the VCEACs calculated from individual phenolics. Chlorogenic acids and glycosides of cyanidin, peonidin, and quercetin were major phenolics among eleven plum cultivars. The antioxidant capacity of chlorogenic acids and anthocyanins showed higher correlation (r2) of 0.7751 and 0.6616 to total VCEAC, respectively, than that of quercetin glycosides (r2 = 0.0279). Chlorogenic acids were a major source of antioxidant activity in plums, and the consumption of one serving (100 g) of plums can provide antioxidants equivalent to 144.4-889.6 mg of vitamin C. 相似文献
992.
Biomass and net primary productivity (NPP) are two important parameters in determining ecosystem carbon pool and carbon sequestration. The biomass storage and NPP in desert shrubland of Artemisia ordosica on Ordos Plateau were investigated with method of harvesting standard size shrub in the growing season (June-October) of 2006. Results indicated that above- and belowground biomass of the same size shrubs showed no significant variation in the growing season (p〉0.1), but annual biomass varied significantly (p〈 0.01). In the A. ordosica community, shrub biomass storage was 699.76-1246.40 g.m^-2 and annual aboveground NPP was 224.09 g-m^-2·a^-1. Moreover, shrub biomass and NPP were closely related with shrub dimensions (cover and height) and could be well predicted by shrub volume using power regression. 相似文献
993.
Food quality is an important issue on the global agenda, particularly in high- and middle-income economies, but of little concern in designing Mexico’s food policy. Food policy has focused on quantity and in the case of maize, on satisfying domestic demand by supporting large commercial agriculture and importing from abroad. However, and as argued in this paper, obtaining a food staple (maize-tortilla) of quality is also an important issue for rural households and contributes to motivating continued smallholder production. Based on case studies in the rural district of Atlacomulco, in the state of Mexico, as well as in two regions of the state of Chiapas, this paper analyzes the production and consumption strategies of rural households. We focus on goals of food security and quality and note differential trends among households of varying characteristics and local contexts. We find that the motivation of small-scale producers to grow maize should be supported by Mexico’s food policy. 相似文献
994.
Hong Jie Di Keith C. Cameron Ju-Pei Shen Chris S. Winefield Maureen O’Callaghan Saman Bowatte Ji-Zheng He 《Journal of Soils and Sediments》2011,11(3):432-439
Purpose
Methanotrophs are an important group of methane (CH4)-oxidizing bacteria in the soil, which act as a major sink for the greenhouse gas, CH4. In grazed grassland, one of the ecologically most sensitive areas is the animal urine patch soil, which is a major source of both nitrate (NO3 −) leaching and nitrous oxide (N2O) emissions. Nitrification inhibitors, such as dicyandiamide (DCD), have been used to mitigate NO3 − leaching and N2O emissions in grazed pastures. However, it is not clear if the high nitrogen loading rate in the animal urine patch soil and the use of nitrification inhibitors would have an impact on the abundance of methanotrophs in grazed grassland soils. The purpose of this study was to determine the effect of animal urine and DCD on methanotroph abundance in grazed grassland soils. 相似文献995.
Context
The assessment of land-use impacts on biodiversity is one of the central themes of landscape ecology and conservation biology. However, due to the complexity of biodiversity, it is impossible to obtain complete information about the diversity of all species even for small areas, necessitating the selection of individual species or assemblages thereof as species surrogate. In parts of the world where taxonomic expertise is lacking, species identification has hindered progress in biodiversity conservation, and the only practical, relatively-accurate option, is the use of taxonomic minimalism.Objective
We carried out a rapid biodiversity assessment based on three surrogates—land-use (driver-surrogate), terrestrial arthropods (species-surrogate) and morphospecies (taxonomic-surrogate)—to determine the impacts of land-use on biodiversity of the Western Region (Ghana), an area covering ~4 % of the West African biodiversity hotspot.Method
We used diversity profiles to visualize the distribution of a total of 8848 arthropod individuals over seven land-use types which define the complete heterogeneity of the landscape.Results
Here, we present both sample and asymptotic diversity profiles of arthropod morphospecies for each land-use type and the potential of each land-use type for conserving arthropods.Conclusions
We conclude that (1) the morphospecies approach is useful for detecting differences in species diversity of land-use types; (2) the concept of asymptotic diversity may not be necessary for land-use based biodiversity comparison; and (3) maximum diversity profiles are useful for determining the land-use conservation values in cases where pristine areas are not available.996.
997.
Cloning and characterization of a novel barley gene,HvORG4,induced by Fusarium graminearum infection
Theo Van-Der Lee 《湖南农业大学学报(自然科学版)》2007,(Z1)
Barley Fusarium head blight(FHB),caused by species of the Fusarium fungus,is a devastating disease that is reemerging worldwide in recent years.In this study,a novel gene,HvORG4,was cloned from barley by using cDNA library and suppression subtractive hybridization(SSH) library strategies.The SSH library and cDNA library were constructed from the Chinese barley cultivar Jing02-461(resistance to FHB) infected by Fusarium graminearum isolate Huanggang-1.For the SSH analysis,more than 120 differentially express... 相似文献
998.
Kwang-Ho Cho Hyeung-Sik Lee Sae-Kwang Ku 《Journal of veterinary science (Suw?n-si, Korea)》2008,9(1):9-14
The density of intestinal endocrine cells, in Balb/c mice with colon 26 (CT-26) carcinoma cells, were examined immunohistochemically at 28 days after implantation. After CT-26 cell administration there was a significant decrease in most of the intestinal endocrine cells (p < 0.01) compared with the control group. The significant quantitative changes in the intestinal endocrine cell density might contribute to the development of the gastrointestinal symptoms commonly encountered in cancer patients. 相似文献
999.
1000.
The surface of silk is modified by a cationic reagent, N-(3-chloro-2-hydroxypropyl) trimethylammonium chloride(CHTAC) in order
to enable the fibre to be dyed with superfine pigments by an exhaust process. The effects of cationization pretreatment conditions
such as the amount of cationic reagent, pH, treatment temperature and time on color yield are discussed in detail. The result
shows that the condition suitable for modification treatment is that the concentrationc of cationic reagent is 10 g/l, pH 8, liquor to goods ratio of 100:1 and 60°C for 30 min. The white index decreases with the increase of alkali of cationic
treatment. The crock fastness and wash fastness of silk dyed by pigment exhaust dyeing achieve 3–4 and 4 scale, respectively.
The treated silk fabrics still retain a soft handle because the bending rigidity B and hysteresis 2HB increase slightly after
cationization pretreatment and dyeing procedure. It has been demonstrated that properties of surface modified silk dyed with
superfine pigment by exhaust process are acceptable. 相似文献