全文获取类型
收费全文 | 346篇 |
免费 | 5篇 |
国内免费 | 8篇 |
专业分类
林业 | 22篇 |
农学 | 7篇 |
基础科学 | 9篇 |
33篇 | |
综合类 | 146篇 |
农作物 | 14篇 |
水产渔业 | 6篇 |
畜牧兽医 | 79篇 |
园艺 | 30篇 |
植物保护 | 13篇 |
出版年
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 2篇 |
2020年 | 5篇 |
2019年 | 9篇 |
2018年 | 16篇 |
2017年 | 5篇 |
2016年 | 3篇 |
2015年 | 4篇 |
2014年 | 10篇 |
2013年 | 12篇 |
2012年 | 20篇 |
2011年 | 19篇 |
2010年 | 7篇 |
2009年 | 7篇 |
2008年 | 8篇 |
2007年 | 23篇 |
2006年 | 11篇 |
2005年 | 12篇 |
2004年 | 13篇 |
2003年 | 6篇 |
2002年 | 9篇 |
2001年 | 10篇 |
2000年 | 16篇 |
1999年 | 5篇 |
1998年 | 5篇 |
1997年 | 4篇 |
1996年 | 10篇 |
1995年 | 11篇 |
1994年 | 7篇 |
1992年 | 7篇 |
1991年 | 6篇 |
1990年 | 8篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1979年 | 4篇 |
1966年 | 2篇 |
1963年 | 2篇 |
1961年 | 2篇 |
1958年 | 2篇 |
1957年 | 2篇 |
1954年 | 3篇 |
1940年 | 2篇 |
1936年 | 2篇 |
1933年 | 2篇 |
1927年 | 2篇 |
1907年 | 1篇 |
1899年 | 1篇 |
1890年 | 1篇 |
排序方式: 共有359条查询结果,搜索用时 15 毫秒
31.
Characterization of commercial kava-kava herbal drug and herbal drug preparations by means of nuclear magnetic resonance spectroscopy 总被引:1,自引:0,他引:1
Bilia AR Bergonzi MC Lazari D Vincieri FF 《Journal of agricultural and food chemistry》2002,50(18):5016-5025
The efficiency of one- and two-dimensional NMR experiments in characterizing the content of the constituents of both herbal drugs and herbal drug preparations is demonstrated for kava-kava. These experiments directly detect active constituents represented by kavalactones in both a finely powdered herbal drug and a commercial extract. In addition, NMR spectroscopy can detect all other compounds present in the extract. As previously evidenced, NMR experiments can represent a generally applicable technique for rapid screening and are a complement to the classical analytical techniques such as high-performance thin-layer chromatography, high-performance liquid chromatography, capillary gas chromatography, and electrophoresis. These experiments can be considered a very simple and fast analytical method to obtain a fingerprint of the herbal drugs and their preparations, and to quantify the content of the active principles of the extract. 相似文献
32.
The isotopic investigation of vanillin has been extended to the new sources of natural precursors of vanillin recently introduced with a view of obtaining natural vanillin by biotechnological processes. To check the consistency of the isotopic composition of vanillin with that of the corresponding aromatic fragment, a selective degradation reaction into guaiacol was carried out. The reaction was shown to proceed without significant isotopic fractionation at the sites of interest, and an optimized procedure was defined from the results of an experimental design involving the quantity of reagent and the temperature and duration of the experiment. Guaiacol, which can be easily obtained in a reasonable time, is an interesting isotopic probe for carbon- and oxygen-isotope ratio mass spectrometry (IRMS) determinations. It provides (13)C information specific to the aromatic fragment and, combined with delta(13)C values measured on vanillin itself, it improves the authentication potential of carbon-IRMS. Thus, the natural status of ferulic acid may be characterized by significant (13)C depletion at the formyl site. Similarly, the oxygen-18 content of guaiacol is a better authentication tool than delta(18)O of vanillin because it does not suffer the drawback of being altered by chemical exchange of the sp(2) oxygen atom with water in industrial or laboratory procedures. Although collaborative studies are still necessary to improve the interlaboratory reproducibility of the delta(18)O parameters, consistent results can be obtained in an intralaboratory context. It is shown in particular that chemical oxidation of ferulic acid is characterized by a relative enrichment of the aromatic moiety of vanillin. 相似文献
33.
Bergamasco Rde C Zanin GM de Moraes FF 《Journal of agricultural and food chemistry》2005,53(4):1139-1143
Sulfluramid is an expensive active principle of insecticidal baits that is lost by volatilization during the pelletization of baits. To increase the thermal stability of sulfluramid, we tested its molecular encapsulation in beta-cyclodextrin (beta-CD), using molar ratios of 1:1 and 1:2 (sulfluramid:beta-CD), using the complex preparation techniques of coprecipitation and kneading. The physical mixture of sulfluramid and beta-CD was also tested for comparison. The products of complexation were characterized by differential scanning calorimetry, thermogravimetry, and derivative thermogravimetry, indicating the formation of a sulfluramid/beta-CD complex and showing that the release of the complexed sulfluramid occurs in the range of 270-300 degrees C, a temperature range that is well above the temperature at which sulfluramid sublimates (40 degrees C). This result warrants a reduced sulfluramid loss in the preparation of insecticidal baits. The preparation of the complex by kneading with molar ratio of 1:2 gave the highest yield of complex, about 64%, in relation to the theoretical maximum. 相似文献
34.
Mulinacci N Romani A Galardi C Pinelli P Giaccherini C Vincieri FF 《Journal of agricultural and food chemistry》2001,49(8):3509-3514
The production of olive oil yields a considerable amount of waste water, which is a powerful pollutant and is currently discarded. Polyphenols and other natural antioxidants, extracted from olives during oil extraction process, partially end up in the waste waters. Experimental and commercial olive oil waste waters from four Mediterranean countries were analyzed for a possible recovering of these biologically interesting constituents. Identification and quantitation of the main polyphenols were carried out by applying HPLC-DAD and HPLC-MS methods. Representative samples of ripe olives were also analyzed at the same time to correlate, if possible, their polyphenolic profiles with those of the corresponding olive oil waste waters. The results demonstrate that Italian commercial olive oil waste waters were the richest in total polyphenolic compounds with amounts between 150 and 400 mg/100 mL of waste waters. These raw, as yet unused, matrices could represent an interesting and alternative source of biologically active polyphenols. 相似文献
35.
36.
Abraham FF 《Science (New York, N.Y.)》1970,168(3933):833-835
During the growth of embryonic droplets in an imperfect vapor the surface polar molecules pass from a disordered orientation state to an ordered orientation state, the transition size being on the order of 100 molecules. This transition poses an interesting model problem in the study of order-disorder transitions in the thermodynamics of small systems. 相似文献
37.
38.
涪陵榨菜不同器官元素含量分布特征 总被引:2,自引:0,他引:2
对涪陵榨菜(茎瘤芥)叶、膨大茎、缩短茎的必需大量元素(N,K,Ca,Mg,P,S)、必需微量元素(Fe,Mn,Cu,Zn,B,Mo)、有益元素(Si,Co,Se,Ni,Sr)分布特征进行分析,结果表明:叶、膨大茎、缩短茎对各元素的吸收与富集具有明显的规律性,如叶、膨大茎、缩短茎中大量元素含量次序均表现出K>N>Ca>Mg,微量元素含量次序均为Fe>Mn>B>Cu>Mo,有益元素含量次序均有Si>Co>Se的特征。在榨菜各器官中,膨大茎中最富集的元素有必需大量元素K,N,P,S,必需微量元素Zn,Cu,必需有益元素Ni,Co,叶主要富集的元素有大量元素Ca,Mg,必需微量元素Fe,Mn,Mo,必需有益元素Sr,Se等。 相似文献
39.
The source of irregularity in El Ni?o, the large interannual climate variation of the Pacific ocean-atmosphere system, has remained elusive. Results from an El Ni?o model exhibit transition to chaos through a series of frequency-locked steps created by nonlinear resonance with the Earth's annual cycle. The overlapping of these resonances leads to the chaotic behavior. This transition scenario explains a number of climate model results and produces spectral characteristics consistent with currently available data. 相似文献
40.
Frankel RB Blakemore RP DE Araujo FF Esquivel DM Danon J 《Science (New York, N.Y.)》1981,212(4500):1269-1270
Magnetotactic bacteria are present in fresh water and marine sediments of Fortaleza, Brazil, situated close to the geomagnetic equator. Both South-seeking and North-seeking bacteria are present in roughly equal numbers in the same samples. This observation is consistent with the hypothesis that the vertical component of the geomagnetic field selects the predominant polarity type among magnetotactic bacteria in natural environments. 相似文献