全文获取类型
收费全文 | 377篇 |
免费 | 34篇 |
国内免费 | 1篇 |
专业分类
林业 | 7篇 |
农学 | 8篇 |
基础科学 | 2篇 |
59篇 | |
综合类 | 66篇 |
农作物 | 16篇 |
水产渔业 | 1篇 |
畜牧兽医 | 231篇 |
园艺 | 6篇 |
植物保护 | 16篇 |
出版年
2023年 | 7篇 |
2021年 | 5篇 |
2020年 | 9篇 |
2019年 | 9篇 |
2018年 | 8篇 |
2017年 | 8篇 |
2016年 | 20篇 |
2015年 | 9篇 |
2014年 | 10篇 |
2013年 | 20篇 |
2012年 | 9篇 |
2011年 | 11篇 |
2010年 | 10篇 |
2009年 | 14篇 |
2008年 | 8篇 |
2007年 | 17篇 |
2006年 | 12篇 |
2005年 | 8篇 |
2004年 | 13篇 |
2003年 | 9篇 |
2002年 | 14篇 |
2001年 | 5篇 |
2000年 | 8篇 |
1999年 | 12篇 |
1998年 | 11篇 |
1997年 | 6篇 |
1996年 | 5篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1992年 | 4篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 11篇 |
1988年 | 6篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1983年 | 4篇 |
1980年 | 3篇 |
1977年 | 3篇 |
1975年 | 3篇 |
1973年 | 5篇 |
1972年 | 4篇 |
1971年 | 5篇 |
1970年 | 9篇 |
1969年 | 5篇 |
1968年 | 6篇 |
1966年 | 2篇 |
1924年 | 3篇 |
1901年 | 2篇 |
1897年 | 2篇 |
排序方式: 共有412条查询结果,搜索用时 15 毫秒
61.
G Medeiros-Ribeiro AM Bratkovski TI Kamins DAA Ohlberg RS Williams 《Science (New York, N.Y.)》1998,279(5349):353-355
Chemical vapor deposition of germanium onto the silicon (001) surface at atmospheric pressure and 600 degrees Celsius has previously been shown to produce distinct families of smaller (up to 6 nanometers high) and larger (all approximately 15 nanometers high) nanocrystals. Under ultrahigh-vacuum conditions, physical vapor deposition at approximately the same substrate temperature and growth rate produced a similar bimodal size distribution. In situ scanning tunneling microscopy revealed that the smaller square-based pyramids transform abruptly during growth to significantly larger multifaceted domes, and that few structures with intermediate size and shape remain. Both nanocrystal shapes have size-dependent energy minima that result from the interplay between strain relaxation at the facets and stress concentration at the edges. A thermodynamic model similar to a phase transition accounts for this abrupt morphology change. 相似文献
62.
Inhibition of aflatoxin B(1) biosynthesis in Aspergillus flavus by anthocyanidins and related flavonoids. 总被引:3,自引:0,他引:3
R A Norton 《Journal of agricultural and food chemistry》1999,47(3):1230-1235
Anthocyanidins and precursors or related flavonoids were tested at concentrations from 0.3 to 9.7 mM ( approximately 0.1-3.0 mg/mL) for activity against growth and aflatoxin B(1) biosynthesis by Aspergillus flavus Link:Fr. NRRL 3357. Aflatoxin B(1) production was inhibited by all anthocyanidins tested, and 3-hydroxy compounds were more active than 3-deoxy forms. Monoglycosides of cyanidin were 40% less inhibitory than the aglycon, whereas a monoglucoside and a diglucoside of pelargonidin were 80 and 5%, respectively, as active as the aglycon. Of eight flavonoids tested, only kaempferol was moderately active, whereas luteolin and catechin were weakly inhibitory. Binary combinations of delphinidin and three other aflatoxin inhibitors acted independently of each other. Results with an aflatoxin pathway mutant indicated that anthocyanidin inhibition occurred before norsolorinic acid synthesis. 相似文献
63.
Self-oriented regular arrays of carbon nanotubes and their field emission properties 总被引:4,自引:0,他引:4
S Fan MG Chapline NR Franklin TW Tombler AM Cassell H Dai 《Science (New York, N.Y.)》1999,283(5401):512-514
The synthesis of massive arrays of monodispersed carbon nanotubes that are self-oriented on patterned porous silicon and plain silicon substrates is reported. The approach involves chemical vapor deposition, catalytic particle size control by substrate design, nanotube positioning by patterning, and nanotube self-assembly for orientation. The mechanisms of nanotube growth and self-orientation are elucidated. The well-ordered nanotubes can be used as electron field emission arrays. Scaling up of the synthesis process should be entirely compatible with the existing semiconductor processes, and should allow the development of nanotube devices integrated into silicon technology. 相似文献
64.
Tomas Navratil Jan Rohovec Aria Amirbahman Stephen A. Norton Ivan J. Fernandez 《Water, air, and soil pollution》2009,201(1-4):87-98
We experimentally determined the adsorption characteristics of natural, freshly precipitated Al(OH)3 for SO4 and PO4. The fresh Al precipitate occurred in stream sediment of Jachymov Stream (Czech Republic). The Al-rich sediment strongly adsorbed added PO4 prior to acidification experiment; this sorbed PO4 was released only after substantial dissolution of the sediment, at pH?<?3.67. Sorption of P by Al(OH)3 appears to be an important control on dissolved PO4 concentration in surface waters, unless there is a large excess of PO4. Acidification of the sediment-solution system caused protonation of the sediment surface, thereby increasing the adsorption capacity for SO4. Maximum SO4 adsorption occurred at pH 4.2, below which dissolution of the sediment offset the increasing anion adsorption capacity, and formation of AISO4 + inhibited the increasing SO4 adsorption capacity. This research demonstrates that there are important pH thresholds for anion adsorption in freshwaters below which dissolution of the Al(OH)3 substrate reduces total capacity for anion adsorption. In freshwaters, with sufficient concentrations of suspended Al(OH)3, or in Al(OH)3-rich sediment, PO4 mobility will be severely restricted. Suspended Al(OH)3 in acidified surface waters cannot strongly influence SO4 concentrations because of the considerably higher total SO4 concentrations compared to the available surface area. 相似文献
65.
Soil erosion prediction in the Grande River Basin, Brazil using distributed modeling 总被引:2,自引:0,他引:2
Mapping and assessment of erosion risk is an important tool for planning of natural resources management, allowing researchers to modify land-use properly and implement management strategies more sustainable in the long-term. The Grande River Basin (GRB), located in Minas Gerais State, is one of the Planning Units for Management of Water Resources (UPGRH) and is divided into seven smaller units of UPGRH. GD1 is one of them that is essential for the future development of Minas Gerais State due to its high water yield capacity and potential for electric energy production. The objective of this study is to apply the Universal Soil Loss Equation (USLE) with GIS PCRaster in order to estimate potential soil loss from the Grande River Basin upstream from the Itutinga/Camargos Hydroelectric Plant Reservoir (GD1), allowing identification of the susceptible areas to water erosion and estimate of the sediment delivery ratio for the adoption of land management so that further soil loss can be minimized. For the USLE model, the following factors were used: rainfall–runoff erosivity (R), erodibility (K), topographic (LS), cover-management (C) and support practice (P). The Fournier Index was applied to estimate R for the basin using six pluviometric stations. Maps of the K, C, LS and P factors were derived from the digital elevation model (DEM), and soil and land-use maps, taking into account information available in the literature. In order to validate the simulation process, Sediment Delivery Ratio (SDR) was estimated, which is based on transported sediment (TS) to basin outlet and mean soil loss in the basin (MSL). The SDR calculation included data (total solids in the water and respective discharge) between 1996 and 2003 which were measured at a gauging station located on the Grande River and a daily flow data set was obtained from the Brazilian National Water Agency (ANA). It was possible to validate the erosion process based on the USLE and SDR application for the basin conditions, since absolute errors of estimate were low. The major area of the basin (about 53%) had an average annual soil loss of less than 5 t ha− 1 yr− 1. With the results obtained we were able to conclude that 49% of the overall basin presently has soil loss greater than the tolerable rate, thus indicating that there are zones where the erosion process is critical, meaning that both management and land-use have not been used appropriately in these areas of the basin. The methodology applied showed acceptable precision and allowed identification of the most susceptible areas to water erosion, constituting an important predictive tool for soil and environmental management in this region, which is highly relevant for prediction of varying development scenarios for Minas Gerais State due to its hydroelectric energy potential. This approach can be applied to other areas for simple, reliable identification of critical areas of soil erosion in watersheds. 相似文献
66.
K.A. Hart G.L. Heusner N.A. Norton M.H. Barton 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2009,23(2):344-351
Background: Hypothalamic-pituitary-adrenal (HPA) axis function is dynamic in the neonatal foal. The paired low dose/high dose cosyntropin (ACTH) stimulation test allows comprehensive HPA axis assessment, but has not been evaluated in neonatal foals.
Hypothesis: Foal age will significantly affect cortisol responses to a paired 10 and 100 μg dose cosyntropin stimulation test in healthy neonatal foals.
Animals: Twenty healthy neonatal foals.
Methods: HPA axis function was assessed in 12 foals at birth and at 12–24, 36–48 hours, and 5–7 days of age. At each age, basal cortisol and ACTH concentrations were measured and cortisol responses to 10 and 100 μg cosyntropin were assessed with a paired ACTH stimulation test protocol. Eight additional 36–48-hour-old foals received saline instead of 10 μg cosyntropin in the same-paired ACTH stimulation test design.
Results: At birth, foals had significantly higher basal cortisol and ACTH concentrations and higher basal ACTH : cortisol ratios compared with foals in all other age groups. A significant cortisol response to both the 10 and 100 μg doses of cosyntropin was observed in all foals. The magnitude of the cortisol response to both doses of cosyntropin was significantly different across age groups, with the most marked responses in younger foals. There was no effect of the paired ACTH stimulation test design itself on cortisol responses.
Conclusions and Clinical Importance: A paired 10 and 100 μg cosyntropin stimulation test can be used to evaluate HPA axis function in neonatal foals. Consideration of foal age is important in interpretation of HPA axis assessment. 相似文献
Hypothesis: Foal age will significantly affect cortisol responses to a paired 10 and 100 μg dose cosyntropin stimulation test in healthy neonatal foals.
Animals: Twenty healthy neonatal foals.
Methods: HPA axis function was assessed in 12 foals at birth and at 12–24, 36–48 hours, and 5–7 days of age. At each age, basal cortisol and ACTH concentrations were measured and cortisol responses to 10 and 100 μg cosyntropin were assessed with a paired ACTH stimulation test protocol. Eight additional 36–48-hour-old foals received saline instead of 10 μg cosyntropin in the same-paired ACTH stimulation test design.
Results: At birth, foals had significantly higher basal cortisol and ACTH concentrations and higher basal ACTH : cortisol ratios compared with foals in all other age groups. A significant cortisol response to both the 10 and 100 μg doses of cosyntropin was observed in all foals. The magnitude of the cortisol response to both doses of cosyntropin was significantly different across age groups, with the most marked responses in younger foals. There was no effect of the paired ACTH stimulation test design itself on cortisol responses.
Conclusions and Clinical Importance: A paired 10 and 100 μg cosyntropin stimulation test can be used to evaluate HPA axis function in neonatal foals. Consideration of foal age is important in interpretation of HPA axis assessment. 相似文献
67.
Nimesha Fernando Joe Panozzo Michael Tausz Robert M. Norton Glenn J. Fitzgerald Samuel Myers Cassandra Walker James Stangoulis Saman Seneweera 《Journal of Cereal Science》2012
We investigated wheat (Triticum aestivum) grain quality under Free Air CO2 Enrichment (FACE) of 550 ± 10% CO2 μmol mol−1. In each of two full growing seasons (2008 and 2009), two times of sowing were compared, with late sowing designed to mimic high temperature during grain filling. Grain samples were subjected to a range of physical, nutritional and rheological quality assessments. Elevated CO2 increased thousand grain weight (8%) and grain diameter (5%). Flour protein concentration was reduced by 11% at e[CO2], with the highest reduction being observed at the late time of sowing in 2009, (15%). Most of the grain mineral concentrations decreased under e[CO2] - Ca (11%), Mg (7%), P (11%) and S (7%), Fe (10%), Zn (17%), Na (19%), while total uptake of these nutrients per unit ground area increased. Rheological properties of the flour were altered by e[CO2] and bread volume reduced by 7%. Phytate concentration in grains tended to decrease (17%) at e[CO2] while grain fructan concentration remained unchanged. The data suggest that rising atmospheric [CO2] will reduce the nutritional and rheological quality of wheat grain, but at high temperature, e[CO2] effects may be moderated. Reduced phytate concentrations at e[CO2] may improve bioavailability of Fe and Zn in wheat grain. 相似文献
68.
69.
Joseph A. Araujo Christina de Rivera Jennifer L. Ethier Gary M. Landsberg Sagi Denenberg Stephanie Arnold Norton W. Milgram 《Journal of Veterinary Behavior: Clinical Applications and Research》2010,5(5):268-275
Anxiety and fear are common underlying factors in many canine behavior problems that impair the human–pet bond and often result in abandonment, relinquishment, or euthanasia. A combination of behavioral and pharmacological interventions is used to ameliorate the behavioral signs associated with anxiety-related behaviors in dogs, but there continues to be need for effective interventions. The current study examined the effects of the nutraceutical ANXITANE® (l-Theanine) chewable tablets on fear of unfamiliar human beings. We first characterized dogs as anxious on the basis of the existence of a fear response to human beings in their home-pen. We then demonstrated that dogs characterized as anxious (N = 10) showed reduced interaction with an unknown human being as compared with normal controls (N = 7). The effect of an administration of ANXITANE® tablets (N = 5) on these anxious Beagle dogs was compared with placebo (N = 5). Objective behavioral measures of anxiety were obtained using an open-field test, a human interaction test, and an actiwatch protocol that allowed monitoring of activity over 24-hours. The ANXITANE® tablets-treated dogs showed greater human interaction and approach than the placebo control group, and no side effects related to treatment, including motor stimulant or sedative effects, were seen. The current study suggests that ANXITANE® tablets are effective for reducing fearful behavior toward unfamiliar human beings in dogs and supports their use for treating anxiety-related behaviors. 相似文献
70.
Michael Norton Gert-Jan van Sprundel Calum G. Turvey Miranda P.M. Meuwissen 《国际虫害防治杂志》2016,62(3):195-204
In this paper, we explore the application of weather index insurance to plant pest and disease management strategies using two distinct models: (1) insuring crop loss due to disease incidence (“Crop Insurance”) and (2) insuring the use of pesticides (“Pesticide Insurance”). We find that despite the seeming ease of applying weather-based pest incidence models to an insurance product, insuring plant disease incidence models is presently unsuitable for the insurance market for both scientific and behavioral reasons. However, derivative-like applications of weather index insurance to insure pesticide use offer a means to introduce financial leverage into pesticide usage decisions. Risk management with weather index insurance would thus function as a complement to existing risk management strategies using pesticides, and offer a market-based mechanism for pesticide abatement. We conclude that more interdisciplinary collaboration is needed to develop weather index insurance for remuneration of losses due to plant pests and diseases, but weather index insurance offers a potential mechanism to reduce inefficiencies and negative externalities in agricultural markets if pesticide expenditures are insured instead of crop losses. 相似文献