全文获取类型
收费全文 | 1445篇 |
免费 | 110篇 |
国内免费 | 1篇 |
专业分类
林业 | 268篇 |
农学 | 85篇 |
基础科学 | 9篇 |
345篇 | |
综合类 | 57篇 |
农作物 | 94篇 |
水产渔业 | 122篇 |
畜牧兽医 | 342篇 |
园艺 | 51篇 |
植物保护 | 183篇 |
出版年
2023年 | 10篇 |
2022年 | 10篇 |
2021年 | 32篇 |
2020年 | 25篇 |
2019年 | 36篇 |
2018年 | 94篇 |
2017年 | 89篇 |
2016年 | 107篇 |
2015年 | 66篇 |
2014年 | 81篇 |
2013年 | 117篇 |
2012年 | 110篇 |
2011年 | 106篇 |
2010年 | 65篇 |
2009年 | 64篇 |
2008年 | 43篇 |
2007年 | 55篇 |
2006年 | 51篇 |
2005年 | 54篇 |
2004年 | 32篇 |
2003年 | 39篇 |
2002年 | 27篇 |
2001年 | 26篇 |
2000年 | 29篇 |
1999年 | 22篇 |
1998年 | 16篇 |
1997年 | 9篇 |
1996年 | 8篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 10篇 |
1979年 | 3篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1973年 | 5篇 |
1972年 | 3篇 |
1971年 | 4篇 |
1969年 | 3篇 |
排序方式: 共有1556条查询结果,搜索用时 15 毫秒
81.
Dana Elhottová Václav Krištůfek Jan Tříska Vladislav Chrastný Eva Uhlířová Jiří Kalčík Tomáš Picek 《Water, air, and soil pollution》2006,173(1-4):177-193
In August 2002 extreme floods affected Bohemia a part of the Czech Republic, along Vltava and Labe rivers. After the flood had culminated, soil samples of arable and meadow soil (flooded and control-non-flooded) have been collected in the surroundings of the cities of ?eské Budějovice (CB, South Bohemia, the Vltava river, the upper flood stream) and Ústí nad Labem (UL, the Labe river, the lower flood stream). Different parameters of arable soils have been affected more significantly than those of meadow soils. Soil texture e.g. has been shifted from sandy loam to loam (CB) and clay loam (UL). Organic carbon, total phosphorus and nitrogen contents have been increased as well as the content of some hazardous elements such as arsenic. A shift of soil pH from 6.1 to 4.8 has been noticed in CB and an opposite one from 5.1 to 7.1 was measured in UL. Available phosphorus decreased in CB by 56% while a four-fold increase was measured in UL. Chlorinated organic pesticides level was significantly reduced, but that of polycyclic aromatic hydrocarbons (PAH) increased up to the maximum values of legal limits. The UL arable soil also became heavily contaminated by PAH. The CB arable soil demonstrated high microbial activity, while UL arable soil suffered under stress conditions in this respect. The flooded meadow soils became covered with a layer of drifted soil sediment, which retained enhanced content of the PAH's different hazardous elements, and, in addition, the soil aeration was reduced. 相似文献
82.
Kora EP Souchon I Latrille E Martin N Marin M 《Journal of agricultural and food chemistry》2004,52(10):3048-3056
The influence of thickening agents (modified starch/pectin mixture 0 and 7 g/L) and mechanical treatment (low, medium, and high) on the retention of esters (pentyl acetate and ethyl pentanoate), aldehydes (hexanal and (E)-2-hexenal), and a lactone (gamma-octalactone) in low-fat flavored stirred yogurts were investigated under equilibrium conditions. In the range studied, the thickening agent and mechanical treatment had little influence on aroma compound retention compared to the decreasing effect of increasing dairy protein concentration on aldehyde retention and the "salting out" effect of carbohydrates on esters. Moreover, experiments in dynamic mode (study of the release of hexanal when yogurts were heated) showed, in the conditions studied, that heat and mass transfer coefficients were not influenced by any of the studied factors (thickening agents and mechanical treatment). These results under static and dynamic conditions are not related to the significant decreasing effect of thickening agents on apple sensory scores associated with hexanal, observed in a previous sensory study. Thus, this sensory effect of thickening agents may be due to sensory interactions between perceptions rather than physicochemical interactions. 相似文献
83.
Branimir Urlić Gvozden Dumičić Smiljana Goreta Ban Marija Romić 《Journal of plant nutrition》2016,39(3):389-398
Understanding the mechanisms of phosphorus (P)-use efficiency (PUE) may contribute to enhancing crop P nutrition because species growth variability at low-P is well known. The experiment was carried out to evaluate the response of kale genotypes to different P supply in randomized block design in three replications. Low-P supply led to a decrease in most parameters, whereas an increase was recorded in root growth parameters. Genotypes differed in shoot dry weight (DW), leaf area, root length and area, and shoot and root P content and concentration. Root traits significantly positively correlated with PUE. Genotypes Red Russian (RR) and IJK 17 were superior in terms of shoot DW production at low P supply, and had the highest uptake efficiency. Genotypes IJK 17 and 81 had the highest P utilization efficiency, while Vates blue curled (VBC) showed the lowest PUE. Genotypes had similar shoot P content and concentration at low P supply, but large PUE differences, implying the importance of P utilization efficiency. 相似文献
84.
Nina Petrovna Čuvašina 《Genetic Resources and Crop Evolution》1988,36(1):55-60
Ohne Zusammenfassung 相似文献
85.
Zosima absinthifolia (ZA) extracts and the coumarins (+)-columbianadin and (-)-deltoin were evaluated for their potential hepatoprotective and antiinflamatory effects in a CCl(4)-induced hepatotoxicity assay in rats and by the inhibition of TNF-α production on LPS-stimulated THP-1 macrophages, respectively. Both the ZA extracts and the coumarins showed hepatoprotective activity confirmed by monitoring the ALT/AST levels and by histopathological examination. The antiinflamatory activity, proved by the inhibition of TNF-α production, was found to be higher for the n-hexane root extract than for coumarins, suggesting synergic potential of the extract. The concentration of (-)-deltoin and (+)-columbianadin in extracts was determined by HPLC analysis. 相似文献
86.
• Introduction
The annual development cycle of boreal and temperate trees results from an evolutionary trade-off between two opposing forces. These are namely, the adjustment of leaf phenology to the timing of frost occurrence at the beginning and/or the end of the growth season countered by an effective adjustment to the duration of the growth season to maximise photosynthesis and biomass production during the growing season. 相似文献87.
Alex Beharav Dalia Lewinsohn Aleš Lebeda Eviatar Nevo 《Genetic Resources and Crop Evolution》2006,53(3):467-474
A total of 1027 genotypes of wild Lactuca spp. (L. serriola, L. saligna, and L. aculeata), originating from Israel, Jordan, East Turkey, Armenia, Kazakhstan, China, and various other countries in Europe were screened
for resistance to the lettuce downy mildew (Bremia lactucae Regel). The genotypes of L. serriola (N = 962); L. saligna (N = 43); and L. aculeata (N = 22) were tested at the seedling stage with two isolates of B. lactucae (race Bl-21 and Isr-74) isolated from cultivated lettuce in Italy and Israel, respectively. Altogether, the isolates possess
virulence against 17 out of 20 Dm genes/R-factors composing the established differential set of lettuce lines/varieties. They could therefore be used for preliminary
detection of the presence of new resistance factors. A total of 83 and three genotypes of L. serriola and L. saligna, respectively, were resistant to infection by each of the two isolates alone as well as to the infection by a mix of the
two isolates. These genotypes probably carry previously unknown resistance, and therefore could be suitable for exploitation
by breeders and further detailed research. The wild progenitor of lettuce, L. serriola, and related species harbor significant untapped genetic resources for lettuce improvement. 相似文献
88.
In vitro determination of the indigestible fraction in foods: an alternative to dietary fiber analysis 总被引:3,自引:0,他引:3
Saura-Calixto F García-Alonso A Goñi I Bravo L 《Journal of agricultural and food chemistry》2000,48(8):3342-3347
Dietary fiber (DF) intakes in Western countries only accounts for about one-third of the substrates required for colonic bacterial cell turnover. There is a general trend among nutritionists to extend the DF concept to include all food constituents reaching the colon. In this line, a method to quantify the major nondigestible components in plant foods, namely, the indigestible fraction (IF), is presented. Analytical conditions for IF determination are close to physiological. Samples, analyzed as eaten, were successively incubated with pepsin and alpha-amylase; after centrifugation and dialysis, insoluble and soluble IFs were obtained. IF values include DF, resistant starch, resistant protein, and other associated compounds. IF contents determined in common foods (cereals, legumes, vegetables, and fruits) were higher than DF contents. Calculated IF intakes were close to the estimated amount of substrates reaching the colon. IF data could be more useful than DF data from a nutritional point of view; therefore, IF is proposed as an alternative to DF for food labeling and food composition tables. 相似文献
89.
M. B. Halitligil Ali Akın Nesteren Bilgin Yusuf Deniz Karani Öğretir Bülent Altınel Yusuf Işık 《Biology and Fertility of Soils》2000,31(2):175-182
In order to evaluate the influence of different N rates on percent N derived from fertilizer (%Ndff) at different growth stages, on yields and the percent N use efficiency (%NUE) values of two winter wheat varieties (durum and bread), field experiments on fallow were carried out at four different locations in Central Anatolia, in the 1991–1992 and 1992–1993 growing seasons. At each site the rates of N (0, 40, 80 and 120?kg N/ha) were applied as ammonium sulphate [(NH4)2SO4] using a Latin Square experimental design with four replicates. The total amounts of N fertilizer were applied once after seedling emergence at all experimental sites. Labelled (15NH4)2SO4 fertilizer was applied to sub-plots from which %Ndff values were determined at tillering, booting, grain filling, and harvest stages. Yield sub-plots received unlabelled (NH4)2SO4 from which total dry matter (seed and straw) and N yields were determined. Also the %NUE values were calculated by the 15N and "difference" methods at the harvest stage. Stored soil moisture at 0–90?cm depth, evapotranspiration and water use efficiency values were calculated as well. The results obtained showed that (1) Gerek-79 variety used both the applied N fertilizer and the available soil moisture more efficiently, (2) the percent NUE values obtained overall were generally less than 20 for both varieties and (3) with the 15N method, less variable %NUE values were obtained in comparison to the difference method. 相似文献
90.
Sander Bruun Bo Stenberg Jon Gudmundsson Lars S. Jensen Jesper Luxhøi Anders Pedersen 《Soil biology & biochemistry》2005,37(12):2283-2296
Prediction of carbon (C) and nitrogen (N) mineralization patterns of plant litter is desirable for both agronomic and environmental reasons. Near infrared reflectance (NIR) spectroscopy has recently been introduced in decomposition studies to characterize biochemical composition. The purpose of the current study was to use empirical techniques to predict C and N mineralization patterns of a wide range of plant materials incubated under controlled temperature and moisture conditions. We hypothesized that the richness of information in the NIR spectra would considerably improve predictions compared to traditional stepwise chemical digestion (SCD) or C/N ratios. Initially, we fitted a number of empirical functions to the observed C and N mineralization patterns. The best functions fitted with R2=0.990 and 0.949 to C and N, respectively. The fractions of C and N mineralized at different points in time were then either predicted directly with regression functions or indirectly by prediction of the parameters of the empirical functions fitted to incubation data. In both cases, partial least squares (PLS) regressions were used and predictions were validated by cross-validations. We found that the NIR spectra (best R2=0.925) were able to predict C mineralization patterns marginally better than the SCD fractions (best R2=0.911), but considerably better than the C/N ratios (best R2=0.851). In contrast, N mineralization was better predicted by SCD fractions (best R2=0.533) than the C/N ratio (best R2=0.497), which was better than NIR predictions (best R2=0.446). Although the predictions with the NIR spectra were only slightly better for C and worse for N mineralization compared to SCD fractions, NIR spectroscopy still holds advantages, as it is a much less laborious and cheaper analytical method. Furthermore, exploration of the applications of NIR spectroscopy in decomposition studies has only just begun, and offers new ways to gain insights into the decomposition process. 相似文献