全文获取类型
收费全文 | 1545篇 |
免费 | 59篇 |
国内免费 | 1篇 |
专业分类
林业 | 79篇 |
农学 | 44篇 |
基础科学 | 15篇 |
165篇 | |
综合类 | 259篇 |
农作物 | 91篇 |
水产渔业 | 84篇 |
畜牧兽医 | 734篇 |
园艺 | 21篇 |
植物保护 | 113篇 |
出版年
2021年 | 19篇 |
2020年 | 18篇 |
2019年 | 23篇 |
2018年 | 20篇 |
2017年 | 20篇 |
2016年 | 20篇 |
2015年 | 24篇 |
2014年 | 24篇 |
2013年 | 69篇 |
2012年 | 61篇 |
2011年 | 67篇 |
2010年 | 54篇 |
2009年 | 35篇 |
2008年 | 67篇 |
2007年 | 64篇 |
2006年 | 54篇 |
2005年 | 63篇 |
2004年 | 63篇 |
2003年 | 58篇 |
2002年 | 47篇 |
2001年 | 35篇 |
2000年 | 40篇 |
1999年 | 27篇 |
1998年 | 13篇 |
1997年 | 11篇 |
1996年 | 15篇 |
1995年 | 19篇 |
1992年 | 20篇 |
1991年 | 25篇 |
1990年 | 22篇 |
1989年 | 24篇 |
1988年 | 20篇 |
1987年 | 18篇 |
1986年 | 23篇 |
1985年 | 25篇 |
1984年 | 18篇 |
1983年 | 15篇 |
1982年 | 19篇 |
1981年 | 11篇 |
1979年 | 14篇 |
1977年 | 16篇 |
1976年 | 18篇 |
1975年 | 13篇 |
1974年 | 15篇 |
1973年 | 23篇 |
1972年 | 20篇 |
1971年 | 15篇 |
1966年 | 10篇 |
1948年 | 12篇 |
1947年 | 13篇 |
排序方式: 共有1605条查询结果,搜索用时 31 毫秒
61.
J A Hawkins R R Evans T J Newby M H Delivorias T D Tyler 《Veterinary parasitology》1985,17(3):229-238
The efficacy of a morantel sustained release bolus (MSRB) for control of gastrointestinal nematodes in yearling steers was evaluated over a 6-month grazing period commencing on 26 March 1982. Three groups of 15 steers were allotted to the following treatments: Group 1 -- one MSRB at start of trial; Group 2 -- one therapeutic dose of thiabendazole at start of trial; Group 3 -- untreated control. The treatment groups were grazed separately. Parasite egg counts (EPG), herbage larval counts, pepsinogen levels and weight gains were monitored. Every other month, sets of 2 parasite-free tracer calves were placed in the pasture grazed by each treatment group and allowed to graze for 3 weeks before being subsequently necropsied for worm counts. At the end of the trial, 6 animals from each group were also necropsied for worm counts. The MSRB treatment resulted in significantly lower egg counts, fewer infective larvae on pasture, lower pepsinogen levels and lower worm burdens in tracer calves than was the case for the untreated group, but generally the levels were not significantly different from those associated with the thiabendazole treatment. The mean weight gain for the MSRB treated steers showed a significant advantage (70.9 lb) over the untreated animals, but was not significantly different from those which received thiabendazole. Total worm counts at the end of the trial were not different from any treatment group. 相似文献
62.
63.
Effects of zinc sulfate (0 vs 1,142 ppm supplemental zinc from zinc sulfate) and feeding frequency (1 x vs 12x daily) on ruminal protozoa numbers, fermentation patterns and amino acid passage were investigated using four ruminally and abomasally cannulated mature Jersey steers in a 4 x 4 Latin square experiment. Steers (530 kg) were fed a 50:50 roughage:concentrate diet at 1.5 times their NEm requirement. Experimental periods were 14 d in duration; ruminal, abomasal and fecal samples were collected at 6-h intervals during the last 3 d of each period. Protozoa numbers tended to be lowest (1.82 x 10(6)/ml) in steers fed zinc 1 x and tended to be highest (3.83 x 10(6)/ml) in steers fed zinc 12 x daily (P less than .10). Frequent feeding decreased ruminal pH .24 units and increased total VFA 20.7%, ammonia 22.7% and ruminal digestion of dietary amino acids (AA) 61.6% (P less than .05). Zinc supplementation decreased ruminal digestion of dietary AA 35.8% (P less than .05) and the abomasal passage of bacterial OM and AA 21.2% (P less than .05) and increased ruminal output of amino acids as a percentage of intake 15.1% (P less than .05). Although it increased escape of dietary AA, zinc sulfate decreased postruminal passage of bacterial AA and resulted in a net negative effect on total postruminal AA passage as a percentage of intake. The effects of zinc on ruminal AA digestion may be more closely related to an interaction of zinc with dietary CP rather than to an effect of Zn on ruminal microbial populations. 相似文献
64.
Plasma and abomasal fluid concentrations of fenbendazole and its two major metabolites in sheep experimentally infected with Ostertagia circumcincta were compared with those in the same sheep when non-parasitised. Bio-availability of the drug was reduced in the parasitised state. There was also a reduction in the proportion of drug present in the form of metabolites in parasitised as compared with non-parasitised animals. 相似文献
65.
66.
67.
68.
Summary The reaction of ferric chloride with the lignin model guaiacol affords primarily a complex mixture of coupled guaiacol oligomers. Major components were the symmetrical carbon-carbon coupled dimer 3,3-dimethoxy-[1,1-biphenyl]-4,4diol and the trimer 3,3,5-trimethoxy-[1,1:3,1-terphenyl]-4,4,4-triol which were isolated by preparative HPLC and characterized by 1HNMR spectroscopy and mass spectrometry. An unstable component believed to be a 4,4-diphenoquinone derived from the trimer was also prominent. The reaction of chromium trioxide with guaiacol yields the same dimer, trimer and diphenoquinone as well as 2-methoxy-p-benzoquinone. The major product with chromium trioxide, however, is an inert, highly insoluble polymer which was shown by degradation to contain guaiacol oligomers bound or crosslinked by hydroxylated chromium species. Magnetic susceptibility measurements clearly indicated that the valency of chromium in the polymer was + 3. It is postulated that similar complexes formed from phenolic lignin units are responsible for the weather resistance of chromium trioxide treated wood surfaces. In a broader context this study is relevant to the fixation of hexavalent chromium from a range of widely used wood preservative formulations.The authors wish to thank the following: Tom Syers (CSIRO Division of Forest Products) for technical assistance, Mary Reilly (CSIRO Division of Forest Products) for NMR spectral determinations and Ivan Vit (CSIRO Division of Chemicals and Polymers) for mass spectral determinations 相似文献
69.
Makoto Kiguchi Yutaka Kataoka Hiroshi Matsunaga Koichi Yamamoto Philip D. Evans 《Journal of Wood Science》2007,53(3):234-238
The market for wood-fiber plastic composites (WPCs) is expanding rapidly in many countries including Japan, where WPCs are
mainly used for exterior products. In such applications, WPCs undergo undesirable color change, chalking, and shrinkage and
swelling, and accordingly there is a need to better understand the mechanisms responsible for the weathering of WPC and develop
methods of improving their weathering resistance. In this study, weatherability of WPC was assessed by natural and accelerated
weathering trials. Discoloration (whitening) of WPC during exposure was caused by degradation of both wood and plastic. Darker
color pigments as additives improved the color stability of WPC; however, chalking on the surfaces still occurred. The color
stability of WPC was improved by application of exterior coatings. Preweathering of WPC (before coatings were applied) increased
the absorption of coatings by the WPC and had a positive effect on the color stability and prevented chalking of the composites.
Parts of this study were presented at the IUFRO XXII World Congress Meeting, Brisbane, August 2005 and the IAWPS 2005, Yokohama,
November 2005 相似文献
70.
The incidence of damage caused by grey squirrels in the Turinplain was studied to assess the impact this alien species ishaving on the highly fragmented Piedmont environment, in particularon profitable cereals, poplar plantations and semi-natural woodlands.The survey of damage was conducted both by interviews to localfarmers and growers and by direct assessment using the NearestNeighbour Method on plantations and woodlands, studying randomlychosen plots in the Turin plain to gain a general overview ofthe situation. The results show a low incidence of damage causedby grey squirrels in the area: little or none was found in semi-naturalwoodlands and in agricultural crops, apart from maize whereless than 1 per cent of fields showed damage, and poplar plantationswhere 5 per cent had signs of bark stripping. Damage on maizecrops was random across the plain, but debarking damage to poplarswas mostly concentrated on the western side of the plain, andtended to occur only in particular years. Damage was concentratedclose to streams and rivers surrounding fields and plantations.The introduction of the grey squirrel in Italy has already causedecological damage such as the extinction of the red squirrelin some areas. Nevertheless, little or no information is availableon the damage this species is causing on woodlands or agriculturalareas. This study is a preliminary survey in order to fill thisgap. 相似文献