全文获取类型
收费全文 | 12471篇 |
免费 | 429篇 |
国内免费 | 122篇 |
专业分类
林业 | 1199篇 |
农学 | 471篇 |
基础科学 | 110篇 |
2276篇 | |
综合类 | 619篇 |
农作物 | 820篇 |
水产渔业 | 1094篇 |
畜牧兽医 | 5160篇 |
园艺 | 308篇 |
植物保护 | 965篇 |
出版年
2023年 | 43篇 |
2022年 | 88篇 |
2021年 | 146篇 |
2020年 | 185篇 |
2019年 | 220篇 |
2018年 | 338篇 |
2017年 | 421篇 |
2016年 | 394篇 |
2015年 | 409篇 |
2014年 | 428篇 |
2013年 | 494篇 |
2012年 | 877篇 |
2011年 | 739篇 |
2010年 | 399篇 |
2009年 | 332篇 |
2008年 | 341篇 |
2007年 | 318篇 |
2006年 | 278篇 |
2005年 | 1012篇 |
2004年 | 837篇 |
2003年 | 626篇 |
2002年 | 256篇 |
2001年 | 206篇 |
2000年 | 117篇 |
1999年 | 204篇 |
1992年 | 126篇 |
1991年 | 152篇 |
1990年 | 178篇 |
1989年 | 156篇 |
1988年 | 178篇 |
1987年 | 118篇 |
1986年 | 147篇 |
1985年 | 120篇 |
1984年 | 96篇 |
1983年 | 83篇 |
1979年 | 136篇 |
1978年 | 97篇 |
1977年 | 93篇 |
1976年 | 79篇 |
1975年 | 138篇 |
1974年 | 129篇 |
1973年 | 116篇 |
1972年 | 139篇 |
1971年 | 120篇 |
1970年 | 88篇 |
1969年 | 105篇 |
1968年 | 113篇 |
1967年 | 126篇 |
1966年 | 103篇 |
1965年 | 70篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Snyder Marcía N. Schumaker Nathan H. Ebersole Joseph L. Dunham Jason B. Comeleo Randy L. Keefer Matthew L. Leinenbach Peter Brookes Allen Cope Ben Wu Jennifer Palmer John Keenan Druscilla 《Landscape Ecology》2019,34(5):1197-1197
Landscape Ecology - In the original publication of the article, the third author name has been misspelt. The correct name is given in this Correction. The original version of this article was revised. 相似文献
102.
1-methylcyclopropene increases storability and shelf life in climacteric and nonclimacteric plums 总被引:2,自引:0,他引:2
Martínez-Romero D Dupille E Guillén F Valverde JM Serrano M Valero D 《Journal of agricultural and food chemistry》2003,51(16):4680-4686
The effect of 1-methylcyclopropene (1-MCP) at three different doses (0.25, 0.50, and 0.75 microL L(-1)) on the ripening processes of a climacteric, cv. Santa Rosa, and a suppressed climacteric type, cv. Golden Japan, plum was studied. For both cultivars, positive effects were observed in terms of inhibition of ethylene production and delays of the physical, chemical, and biochemical changes associated with ripening. 1-MCP-treated plums were firmer with lower weight loss, reduced degrees Brix/titratable acidity ratios, and lower color changes during cold storage and subsequent shelf life at 20 degrees C than controls. For most factors, the effectiveness of 1-MCP was dose-dependent in Santa Rosa but dose-independent for Golden Japan. 相似文献
103.
Piet?C.?N.?GroenewaldEmail author Carin?S.?Viljoen 《Journal of Agricultural, Biological & Environmental Statistics》2003,8(1):75-83
This article aims to determine the effect of certain covariates, such as season of kidding, parity, and time of kidding on
the characteristics of the lactation curve of Saanen dairy goats. Characteristics investigated are peak milk yield, time of
peak milk yield, total milk production, persistency, and the relationship between fat and protein in milk composition, as
well as between lactation curves of the same animal in successive years. The analysis is carried out using a hierarchical
Bayesian approach, together with Wood’s model, to model lactation. Posterior distributions of quantities of interest are obtained
by means of the Markov chain Monte Carlo (MCMC) methods. These clearly illustrate the significant effect of especially parity,
but also season and time of kidding on the characteristics of the lactation curve. Total and peak milk yield increase with
increasing parity up to about the third or fourth parity, while peak yield is later for first than for later parities. The
analysis also enables estimation of lactation characteristics of untested animals, prediction of future characteristics and
identification of exceptional animals. 相似文献
104.
Mathias?FosuEmail author Ronald?F.?Kühne Paul?L.?G.?Vlek 《Biology and Fertility of Soils》2003,39(2):117-122
In order to understand the efficiency of residue-N use and to estimate the minimum input required to obtain a reasonable level of crop response, it is important to quantify the fate of the applied organic-N. The recovery of N from 15N-labelled Crotalaria juncea was followed in the soil and the succeeding maize crop. Apparent N recovery (ANR) by maize from unlabelled Crotalaria juncea, Crotalaria retusa, Calopogonium mucunoides, Mucuna pruriens and mineral fertilizer at three locations were also evaluated. The maize crop recovered 4.7% and 7.3% of the 15N-labelled C. juncea-N at 42 days after sowing (DAS) and at final harvest, respectively. The corresponding 15N recovery from the soil was 92.4% and 58.5%. The highest mean ANR of 57.4% was with mineral fertilizer, whereas the mean ANR of 14.3% from C. retusa was the lowest. A large pool substitution and added-N interaction effect was observed when comparing N recovery from the labelled and unlabelled C. juncea. The amount of residue-N accounted for by the isotope dilution method at 42 DAS was 97.1% and at final harvest 65.8%. The large residue-N recovery in the soil organic-N pool explains the residual effect usually observed with organic residue application. 相似文献
105.
Maria?Teresa?Dell'AbateEmail author Anna?Benedetti Alessandra?Trinchera Daniele?Galluzzo 《Biology and Fertility of Soils》2003,37(2):124-129
Carbon and nitrogen mineralisation of leather meal fertilisers were studied in two soils characterised by different respiration activity. Both C and N mineralisation were highest in the most active soil, and when leather meal was added as a powder rather than as 2- to 4- and 4- to 6-mm particles. Fast and slow soluble N pools were determined after extraction with cold water and with hot buffer, respectively. The N remaining after the second extraction with hot buffer was named slow-release N. The percentage of slow-release N rose as the size of the applied leather meal particles increased, whereas fast soluble N was highest in the coarsest (4-6 mm) fertiliser. 相似文献
106.
J. R. Salinas-García J. de J. Velzquez-García M. Gallardo-Valdez P. Díaz-Mederos F. Caballero-Hernndez L. M. Tapia-Vargas E. Rosales-Robles 《Soil & Tillage Research》2002,66(2):177-152
Quantifying how tillage systems affect soil microbial biomass and nutrient cycling by manipulating crop residue placement is important for understanding how production systems can be managed to sustain long-term soil productivity. Our objective was to characterize soil microbial biomass, potential N mineralization and nutrient distribution in soils (Vertisols, Andisols, and Alfisols) under rain-fed corn (Zea mays L.) production from four mid-term (6 years) tillage experiments located in central-western, Mexico. Treatments were three tillage systems: conventional tillage (CT), minimum tillage (MT) and no tillage (NT). Soil was collected at four locations (Casas Blancas, Morelia, Apatzingán and Tepatitlán) before corn planting, at depths of 0–50, 50–100 and 100–150 mm. Conservation tillage treatments (MT and NT) significantly increased crop residue accumulation on the soil surface. Soil organic C, microbial biomass C and N, potential N mineralization, total N, and extractable P were highest in the surface layer of NT and decreased with depth. Soil organic C, microbial biomass C and N, total N and extractable P of plowed soil were generally more evenly distributed throughout the 0–150 mm depth. Potential N mineralization was closely associated with organic C and microbial biomass. Higher levels of soil organic C, microbial biomass C and N, potential N mineralization, total N, and extractable P were directly related to surface accumulation of crop residues promoted by conservation tillage management. Quality and productivity of soils could be maintained or improved with the use of conservation tillage. 相似文献
107.
Fernández PL Pablos F Martín MJ González AG 《Journal of agricultural and food chemistry》2002,50(7):1833-1839
108.
The influence of a fire retardant (Firesorb, an acrylic–acrylamide copolymer) on the microbial community structure determined by phospholipid fatty acid (PLFA) analysis was examined under laboratory conditions using two different textured soils under pine forest. Firesorb was added to unheated and heated soil samples (350°C for 10 min followed by reinoculation, to mimic a forest fire) at three levels of application (none, usual and three times the usual levels), and measurements were made after 12 weeks of incubation. The relative importance of the three factors considered on the PLFA profiles was as follows: soil heating ≫ soil texture ≈ Firesorb treatment. In the unheated soils, Firesorb had a larger effect than soil texture, while the opposite was found in the heated soils. Soil heating reduced the total PLFAs, while Firesorb tended to increase them in both the unheated and heated soils. Soil heating decreased the PLFAs indicative of gram-positive (G+) bacteria and tended to increase the fatty acids associated with gram-negative (G−) bacteria and, to a lesser extent, the PLFA 18:2ω6, considered to be predominantly of fungal origin. Firesorb treatment decreased the G−/G+ bacteria ratio in the heated soils but tended to increase it in the unheated soils, the effect being dose dependent. 相似文献
109.
Serrano M Valverde JM Guillén F Castillo S Martínez-Romero D Valero D 《Journal of agricultural and food chemistry》2006,54(11):3882-3886
Table grapes (Vitis vinifera L. cv. Crimson Seedless) were coated with Aloe vera gel according to our developed patent (SP Patent P200302937) and then stored for 35 days at 1 degrees C, and the subsequent shelf life (SL) was monitored at 20 degrees C. Uncoated clusters showed a rapid loss of functional compounds, such as total phenolics and ascorbic acid. These changes were accompanied by reduction of the total antioxidant activity (TAA) and increases in total anthocyanins, showing an accelerated ripening process. On the contrary, table grapes coated with Aloe vera gel significantly delayed the above changes, such as the retention of ascorbic acid during cold storage or SL. Consequently, Aloe vera gel coating, a simple and noncontaminating treatment, maintained the functional properties during postharvest storage of table grapes. 相似文献
110.
Ferrer E Alegría A Farré R Clemente G Calvo C 《Journal of agricultural and food chemistry》2005,53(12):4911-4917
Free and total fluorescent compounds, browning index, and color formation were measured in milk-based powdered infant formulas (IF) during 2 years of storage at 20 and 37 degrees C. The excitation spectra from 415 nm emission show three peaks (ex lambda1 = 270 nm, lambda2 = 325/315 nm, lambda3 = 350 nm) and from 347 nm excitation two emission peaks (415 and 520 nm), and no wavelength shifts were observed. Temperature and time of storage exert in general no significant effect on the development of fluorescence emission intensity and browning index. However, an important increase in pentodilysine was recorded-probably because of the iron and ascorbic acid contents of the samples-as well as in browning index in adapted IF. In both IF a color increase (deltaE) throughout storage was observed, this increase being greater in samples stored at 37 degrees C than in those stored at 20 degrees C. The increase in color with time fitted a linear regression model. Color appeared to be an indicator of sufficient sensitivity to measure the effect of temperature or storage time. 相似文献