全文获取类型
收费全文 | 296篇 |
免费 | 22篇 |
专业分类
林业 | 38篇 |
农学 | 5篇 |
基础科学 | 4篇 |
89篇 | |
综合类 | 45篇 |
农作物 | 9篇 |
水产渔业 | 18篇 |
畜牧兽医 | 75篇 |
园艺 | 6篇 |
植物保护 | 29篇 |
出版年
2023年 | 5篇 |
2022年 | 3篇 |
2021年 | 4篇 |
2020年 | 8篇 |
2019年 | 4篇 |
2018年 | 9篇 |
2017年 | 6篇 |
2016年 | 5篇 |
2015年 | 9篇 |
2014年 | 11篇 |
2013年 | 18篇 |
2012年 | 17篇 |
2011年 | 19篇 |
2010年 | 19篇 |
2009年 | 12篇 |
2008年 | 16篇 |
2007年 | 18篇 |
2006年 | 15篇 |
2005年 | 19篇 |
2004年 | 16篇 |
2003年 | 18篇 |
2002年 | 10篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1999年 | 4篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1992年 | 1篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 3篇 |
1974年 | 1篇 |
1969年 | 2篇 |
1956年 | 1篇 |
1949年 | 1篇 |
1932年 | 1篇 |
1925年 | 1篇 |
1901年 | 2篇 |
1896年 | 2篇 |
排序方式: 共有318条查询结果,搜索用时 15 毫秒
251.
Zhao X Corrales M Zhang C Hu X Ma Y Tauscher B 《Journal of agricultural and food chemistry》2008,56(22):10761-10766
Chinese purple corn extracts ( Zea mays L., Zhuozhou, Hebei, China) (EZPC) were selected among five Chinese purple corn hybrids due to their higher anthocyanin content, and their thermal stability was evaluated. The total anthocyanin content and total phenolic content of EZPC were 304.5 +/- 16.32 mg of cyanidin-3-glucoside equiv/100 g of dry seeds and 489.8 +/- 24.90 mg of gallic acid equiv/100 g of dry seeds, respectively. Moreover, the individual anthocyanins of EZPC were determined by HPLC-DAD/ESI-MS analysis. Seven main compounds were determined, including cyanidin-3-(malonylglucoside), cyanidin-3-O-glucoside-2-malonylglucoside, cyanidin-3-O-glucoside, peonidin-3-O-glucoside, peonidin-3-(malonylglucoside), pelargonidin-3-(6'-malonylglucoside), and peonidin-3-(dimalonylglucoside). The thermal stability of EZPC was studied by differential scanning calorimetry. Thermodynamic analysis showed that the conversion of EZPC followed an Arrhenius relationship, where the delta enthalpy (H) and activation energy (E(a)) were 97.0 J/g and 204 +/- 2.72 kJ/mol, respectively. Furthermore, the relationships between the degree of conversion of EZPC and time or temperature were reported. This study demonstrated that the evaluated Chinese purple corn hybrids are a natural source of anthocyanins and are stable over a wide range of temperatures and times. 相似文献
252.
Klaus Henle Claudia Andres Detlef Bernhard Annegret Grimm Pavel Stoev Nikolay Tzankov Martin Schlegel 《Landscape Ecology》2017,32(1):131-145
Context
Species show different sensitivity to habitat loss and fragmentation depending on their specialization. Populations of a species at the range margin are generally assumed to be more stenoecious than populations at the core of the distribution and should therefore be more sensitive to habitat fragmentation.Objectives
We evaluated the hypothesis that fragmentation effects species more strongly at the range periphery of their range compared to the core, resulting in lower genetic variability in comparable patch sizes and lower gene flow among populations.Methods
We compared the genetic diversity and structure of five sand lizard (Lacerta agilis) populations at the margin of its range in Bulgaria and of 11 populations at the core of its distribution in Germany. We based the analysis on microsatellites, comprising 15 loci in Bulgaria and 12 in Germany.Results
All diversity indices declined with patch size. For medium-sized patches all diversity indices were lower at the range periphery compared to the core, with two of them being significant. AICc based model selection showed strong support for core/periphery and patch size effects for observed and expected heterozygosity but only a patch size effect for allelic richness. There was no isolation-by-distance and each sampled population was allocated to a separate cluster with high probability for both countries, indicating that all populations are (almost) completely isolated.Conclusion
Our study indicates an increased sensitivity of a species to fragmentation at the periphery compared to the core of its distribution. This differential sensitivity should be accounted for when prioritizing species based on their fragmentation sensitivity in landscape management.253.
In order to investigate the transferability of lysimeter results to the actual field situation, a leaching study with [14C]benazolin and bromide was carried out in a sandy soil. A suction base system, where soil water and solute fluxes through a lateral cross-sectional sampling area could be measured in an undisturbed field environment, was developed as reference system. Using that measuring instrument, possible artefacts of the lysimeter system could be excluded. The outflow of soil water and leaching of benazolin and bromide showed no system-related differences between the lysimeters and the undisturbed field represented by the suction base station. Higher outflow of leachate and bromide in the lysimeters could be attributable to different meteorological conditions at the lysimeter and the field station. © 1999 Society of Chemical Industry 相似文献
254.
Bernhard Schick Pran N Moza Klaus Hustert Antonius Kettrup 《Pest management science》1999,55(11):1116-1122
The photolysis of the fungicide vinclozolin in aqueous and methanol–water (50 + 50 by volume) solution has been examined. Irradiation at λ = 254 nm for 10 minutes resulted in <90% and ≤95% substrate transformation respectively. The dissipation of vinclozolin both in water and methanol + water was linear and the calculated half-lives were 1.01 and 2.0 min respectively. Irradiation (8 h) with UV light (λ ≥ 290 nm) resulted in 10% degradation of the chemical, which is of the same magnitude as that of the control (not irradiated). Irradiation (8 h) under artificial sunlight (Suntest) in the presence of commercially available humic acid (K-salt) resulted in 55% degradation of the chemical. Photolysis leads to the opening of the 2,4-oxazolidine-dione ring, forming 3,5-dichlorophenyl isocyanate and 3,5-dichloroaniline. In addition, dechlorination and elimination of the CHCH2 moiety takes place, and one or both the chlorine atoms are replaced by a methoxy group. © 1999 Society of Chemical Industry 相似文献
255.
Carsten Schulz Steffen Günther Manfred Wirth Bernhard Rennert 《Aquaculture International》2006,14(6):577-586
To assess the effect of dietary composition on growth performance and body composition of pike perch (Sander lucioperca), fingerlings with an initial body weight of 1.36 g (just trained to accept formulated feed) were fed three experimental diets in triplicate for 90 days. Two feeding groups were fed with formulated diets (CD, CD+7) containing varying levels of crude lipid (CL) of 14.65% and 21.94% dry matter (d.m.) with crude protein (CP) levels of 59.73% and 56.56%, and one feeding group was fed a natural diet (chironomids, CP = 65.93% d.m.; CL = 7.20% d.m.). Furthermore, pike perch of the same age caught in different natural habitats were analysed to determine their naturally fluctuations in body composition. Specific growth rate (SGR; CD = 3.36, CD+7 = 3.47) and feed conversion ratio (FCR; CD = 1.02, CD+7 = 0.93) of fish fed formulated diets did not differ significantly with rising dietary lipid content, due to high variability within the individuals of each feeding groups. In contrast, pike perch fed with chironomids showed a significantly lower SGR of 2.49 and higher FCR of 2.37 (on a dry matter basis). Body composition of pike perch fed formulated diets was affected by dietary composition and showed increased lipid contents [CD=6.25% original matter (o.m.), CD+7 = 9.00% o.m.] with rising dietary lipid levels. Pike perch of CD and CD+7 feeding groups showed significant increased hepatosomatic indices (HSIs) of 1.99 and 2.05 in contrast to fish fed chironomids with HSI of 1.11. Fish caught in the different natural habitats were characterised by low body lipid and dry matter contents of 0.64–1.88% o.m. and 21.08–23.75% o.m. Higher lipid incorporation of fish fed with formulated diets accompanied with poor benefit on growth performance at higher dietary lipid content indicated that pike perch ability to utilise lipids is low when dietary crude protein content is higher than 56.56%. 相似文献
256.
Bernhard Wild 《Forstwissenschaftliches Centralblatt》1925,47(11):813-819
Ohne Zusammenfassung 相似文献
257.
Primary minerals of the parent material undergo weathering during the formation of terrestrial soils to varying extent. As a result, secondary minerals develop, which comprise, among many others, hydroxy‐interlayered minerals (HIMs). These minerals have formed by interlayering of hydroxy‐metal complexes (especially of Al3+, also Mg2+, Fe2+/3+) into micas, expansible 2:1 phyllosilicates and forming oligomers, or by weathering of primary chlorite. The degree of interlayer filling and the stability of these fillings affect several physico‐chemical soil properties, for instance the cation exchange capacity. Although many studies have been conducted on formation, occurrence, and properties of HIMs in soil during the last decades, several challenges still exist. These challenges include analytical identification and quantification of HIMs in soil, the nature of the interlayer filling and the identification of favorable conditions in soil for the formation of HIMs. In order to deepen the understanding of formation, properties, and fate of HIMs in soil, we critically reviewed the available literature. Based on the review, we recommend using a new structural model that enables quantification of hydroxy‐interlayered smectite in soil by X‐ray diffractometry, laboratory experiments on the formation and preservation of different types of interlayers and considering the temporal and spatial dimension of the formation of HIMs in soil in more detail. 相似文献
258.
259.
260.
Silke Schaumberger Bernhard Krautzer Wilhelm Graiss Erich M. Pötsch 《Grass and Forage Science》2020,75(3):303-315
We studied the performance of different seed mixtures and the influence of liming on the establishment of a montane pasture under acidic site conditions during a wood-pasture separation process from 1998 to 2001 in Styria, Austria. Two treatments (with and without liming) were established, each with four seeding treatments (without seeding, commercial, site-adapted and site-specific mixtures), and all plots were regularly fertilized from 1998 to 2002. Vegetation surveys and forage analyses regarding development of vegetation cover, seeded species persistence, quality and yield parameters were conducted again in 2014 and 2016; soil samples were taken in 2015. After cessation of regular fertilization, the analysed soil parameters declined to levels that were sufficient or low for grasslands. pH decreased again over time, but still was significantly higher (p = .0034) in the liming treatment. The single liming during experimental set-up also caused better long-term performance for nearly all vegetation, quality and yield parameters. The site-specific seed mixture performed best regarding most analysed parameters, under both liming treatments. Concerning seeded species, the habitat-typical species Agrostis capillaris, Festuca rubra agg. and Trifolium repens persisted best with and without liming. All analysed vegetation and yield parameters stayed far behind their results of 2001 and their potential. The use of site-specific seed mixtures supports the establishment of productive grassland on specific locations. The long-term results also illustrated that even low-input management like liming in multi-annual intervals can help to improve acidic site and growing conditions significantly and thereby increases the sustainability of cost-intensive wood-pasture separation processes under similar conditions. 相似文献