全文获取类型
收费全文 | 1428篇 |
免费 | 91篇 |
国内免费 | 2篇 |
专业分类
林业 | 40篇 |
农学 | 21篇 |
基础科学 | 6篇 |
97篇 | |
综合类 | 502篇 |
农作物 | 37篇 |
水产渔业 | 110篇 |
畜牧兽医 | 642篇 |
园艺 | 25篇 |
植物保护 | 41篇 |
出版年
2021年 | 13篇 |
2020年 | 16篇 |
2019年 | 14篇 |
2018年 | 12篇 |
2017年 | 19篇 |
2016年 | 20篇 |
2015年 | 23篇 |
2014年 | 21篇 |
2013年 | 52篇 |
2012年 | 27篇 |
2011年 | 49篇 |
2010年 | 24篇 |
2009年 | 36篇 |
2008年 | 37篇 |
2007年 | 44篇 |
2006年 | 43篇 |
2005年 | 40篇 |
2004年 | 28篇 |
2003年 | 27篇 |
2002年 | 30篇 |
2001年 | 35篇 |
2000年 | 38篇 |
1999年 | 26篇 |
1998年 | 11篇 |
1995年 | 11篇 |
1992年 | 26篇 |
1991年 | 24篇 |
1990年 | 20篇 |
1989年 | 18篇 |
1988年 | 13篇 |
1987年 | 40篇 |
1986年 | 56篇 |
1985年 | 51篇 |
1984年 | 38篇 |
1983年 | 41篇 |
1982年 | 35篇 |
1981年 | 33篇 |
1980年 | 35篇 |
1979年 | 35篇 |
1978年 | 33篇 |
1977年 | 25篇 |
1976年 | 24篇 |
1975年 | 26篇 |
1974年 | 31篇 |
1973年 | 17篇 |
1972年 | 16篇 |
1971年 | 16篇 |
1970年 | 15篇 |
1969年 | 16篇 |
1966年 | 13篇 |
排序方式: 共有1521条查询结果,搜索用时 15 毫秒
51.
D.J. Robinson M.F.B. Dale D. Todd 《European journal of plant pathology / European Foundation for Plant Pathology》2004,110(9):921-928
Infection of potato plants with Tobacco rattle virus by its nematode vector can have different outcomes, including the development of spraing symptoms in progeny tubers. A novel syndrome described here comprises a generalized mottle in leaves on all stems, together with virtually total failure to produce daughter tubers. The outcome of infection depends partly on the potato genotype, but field trials with 15 varieties showed that the incidence and severity of spraing symptoms at three sites differed. There was no evidence that this was due to differences in virulence among the virus isolates at the sites, but it was probably the result of environmental differences that influenced the numbers and activity of the vector nematodes. At the most severely affected site, spraing symptoms were found in all varieties tested, except Record, including several that were not affected at the other two sites. Taking both severity and incidence of symptoms into account, the ranking of varieties was similar at each site. The incidence of spraing symptoms was greater in larger than in smaller tubers, and increased with later harvest dates, but did not increase when early harvested tubers were stored. Tobacco rattle viruswas detected in the roots of many of the weeds growing at one of the sites and in the roots of a few plants of the subsequent barley crop. 相似文献
52.
Trends in the numbers of infective nematode larvae on pasture plots contaminated by cattle at different seasons of the year were defined in 3 different climatic regions. The main nematodes were Ostertagia ostertagi, Trichostrongylus spp, Haemonchus spp and Cooperia spp.
On the North Coast of New South Wales with a sub-tropical climate, the numbers of infective larvae of all 4 nematodes rose rapidly to peak levels soon after each seasonal period of contamination began, then fell quickly within a few months. On the Central Coast of New South Wales, the trends were similar to those on the North Coast, except that the larvae persisted on the pasture for a much longer time. On the Northern Tablelands of New South Wales, where temperatures were much colder than on the coast, larval development was slower and major peaks of larval availability did not occur until early spring. These different seasonal trends in each region were considered to be related to the climatic differences between the regions.
On pastures which were contaminated continuously, larval numbers reached maximum levels in mid-winter on the Central Coast and in early spring on the Northern Tablelands. It was concluded that the majority of these larvae were derived from the contamination of pastures in autumn and winter. Subsequently in summer, a rapid dying out of larvae was observed in all the regions, probably due to the effect of hotter weather.
The studies suggest that a reduction in the contamination of pasture with nematode eggs in autumn and winter could result in pastures carrying fewer larvae and thus form the basis of effective worm control programs for cattle. 相似文献
On the North Coast of New South Wales with a sub-tropical climate, the numbers of infective larvae of all 4 nematodes rose rapidly to peak levels soon after each seasonal period of contamination began, then fell quickly within a few months. On the Central Coast of New South Wales, the trends were similar to those on the North Coast, except that the larvae persisted on the pasture for a much longer time. On the Northern Tablelands of New South Wales, where temperatures were much colder than on the coast, larval development was slower and major peaks of larval availability did not occur until early spring. These different seasonal trends in each region were considered to be related to the climatic differences between the regions.
On pastures which were contaminated continuously, larval numbers reached maximum levels in mid-winter on the Central Coast and in early spring on the Northern Tablelands. It was concluded that the majority of these larvae were derived from the contamination of pastures in autumn and winter. Subsequently in summer, a rapid dying out of larvae was observed in all the regions, probably due to the effect of hotter weather.
The studies suggest that a reduction in the contamination of pasture with nematode eggs in autumn and winter could result in pastures carrying fewer larvae and thus form the basis of effective worm control programs for cattle. 相似文献
53.
Robinson R Schwendenwein I Wacek S Nell B Mosing M 《Veterinary journal (London, England : 1997)》2011,190(2):268-272
In a prospective cross-over study, the duration and magnitude of effect on the electrolyte and plasma volume changes of intravenous (IV) hypertonic hydroxyethyl starch (hyperHES) (7.5%/6%) and mannitol (20%) were compared. Eight Beagle dogs received an IV infusion of 4mL/kg hyperHES (group H) and 4mL/kg mannitol 20% (group M) on separate occasions. Urine and blood samples were taken in the first (T(60)) and second (T(120)) hour after infusion. Significant increases in plasma volume at each time point in group H and M were noted when compared to baseline (start of infusion=T(0)) level. There was no significant difference between groups. Both fluids resulted in diuresis, although no significant difference between groups was noted. A significant increase in plasma sodium (Na) was demonstrated in group H between T(0) and T(60) with a significant increase in the Na and chloride (Cl) fractional excretion (FE) between T(0), T(60) and T(120). In group M no changes in plasma electrolyte concentrations were detected, although FE of Na, Cl and K was increased significantly between T(0) and T(60). In conclusion, hyperHES and mannitol appear to have a volume expanding effect lasting at least 120 min. The hypernatraemia induced by hyperHES was minimal compared to previous reports of hypertonic saline use, and no clinical side effects were noted. HyperHES showed comparable effects to mannitol in increasing plasma volume and diuresis and could be considered for these applications. 相似文献
54.
55.
56.
Robinson AL 《Science (New York, N.Y.)》1978,200(4343):749-752
57.
REASONS FOR PERFORMING STUDY: Guidelines for administration of oxygen to standing horses are unavailable because previous investigations of the efficacy of oxygen administration to increase arterial oxygenation in standing horses have produced equivocal results. OBJECTIVE: To determine the effect of nasal oxygen supplementation on inspired and arterial blood gas tensions in control horses and those with moderate to severe recurrent airway obstruction (RAO). METHODS: Normal horses (n = 6) and horses during an attack of RAO induced by stabling (n = 6) were studied. Oxygen was administered through either one or 2 cannulae, passed via the nares into the nasopharynx to the level of the medial canthus of each eye. Intratracheal inspired oxygen and carbon dioxide concentration and arterial blood gas tensions were measured at baseline and during delivery of 5, 10, 15, 20 and 30 l/min oxygen. RESULTS: Nasal cannulae and all but the highest oxygen flow rates were well tolerated. Fractional inspired oxygen concentration (F(I)O2) increased with flow but was significantly lower at all flow rates in horses with RAO compared with controls. Arterial oxygen tension (PaO2) was significantly increased (P < 0.001) by all flow rates, but was always lower in RAO-affected animals. At 30 l/min, PaO2 increased to 319 +/- 31 mmHg in control horses and 264 +/- 69 mmHg in horses with RAO. Additionally, a large arterial to end-tidal gradient for CO2 in RAO-affected horses was observed, indicating increased alveolar deadspace ventilation in these animals. CONCLUSIONS: The use of nasal cannulae to deliver oxygen effectively increases both F(I)O2 and PaO2 in horses with moderate to severe RAO. Oxygen flow rates up to 20 l/min are well tolerated, but flow rates of 30 l/min produce occasional coughing or gagging. POTENTIAL RELEVANCE: Oxygen therapy delivered by means of an intranasal cannula is a highly effective means of increasing arterial oxygen tension in horses with respiratory disease. Generally, flows of 10-20 l/min should be effective. If higher flows (20-30 l/min) are necessary, they should be delivered by means of 2 cannulae. 相似文献
58.
Masursky H Batson RM McCauley JF Soderblom LA Wildey RL Carr MH Milton DJ Wilhelms DE Smith BA Kirby TB Robinson JC Leovy CB Briggs GA Duxbury TC Acton CH Murray BC Cutts JA Sharp RP Smith S Leighton RB Sagan C Veverka J Noland M Lederberg J Levinthal E Pollack JB Moore JT Hartmann WK Shipley EN De Vaucouleurs G Davies ME 《Science (New York, N.Y.)》1972,175(4019):294-305
At orbit insertion on 14 November 1971 the Martian surface was largely obscured by a dust haze with an extinction optical depth that ranged from near unity in the south polar region to probably greater than 2 over most of the planet. The only features clearly visible were the south polar cap, one dark, spot in Nix Olympica, and three dark spots in the Tharsis region. During the third week the atmosphere began to clear and surface visibility improved, but contrasts remained a fraction of their normal value. Each of the dark spots that apparently protrude through most of the dust-filled atmosphere has a crater or crater complex in its center. The craters are rimless and have featureless floors that, in the crater complexes, are at different levels. The largest crater within the southernmost spot is approximately 100 kilometers wide. The craters apparently were formed by subsidence and resemble terrestrial calderas. The south polar cap has a regular margin, suggsting very flat topography. Two craters outside the cap have frost on their floors; an apparent crater rim within the cap is frost free, indicating preferentia loss of frost from elevated ground. If this is so then the curvilinear streaks, which were frost covered in 1969 and are now clear of frost, may be low-relief ridges. Closeup pictures of Phobos and Deimos show that Phobos is about 25 +/-5 by 21 +/-1 kilometers and Deimos is about 13.5 +/- 2 by 12.0 +/-0.5 kilometers. Both have irregular shapes and are highly cratered, with some craters showing raised rims. The satellites are dark objects with geometric albedos of 0.05. 相似文献
59.
60.
A stability-indicating liquid chromatographic method is presented for determining sulfamethoxazole in tablets. The method uses a 10 micron silica column, an isooctane-methylene chloride-2-propanol-acetonitrile-glacial acetic acid (70 + 25 + 5 + 5 + 0.5) mobile phase, and photometric detection at 254 nm. Seven laboratories collaboratively studied this method on powdered composite samples prepared from commercial 500 and 1000 mg tablets and on an authentic tablet mixture containing 83.32% added sulfamethoxazole. Mean assay results for the 500 and 1000 mg tablets were 102.2 and 97.9% of declared, respectively (n = 4). The mean recovery value for the synthetic sample was 99.4% (n = 4). The pooled reproducibility standard deviation (SD) (coefficient of variation (CV)) and pooled repeatability SD (CV) were +/- 1.01 (1.01%) and +/- 0.96 (0.96%), respectively. These results were in good agreement with those obtained by the Associate Referee for the titration method of USP XX. The proposed method can also be used for monitoring the presence of sulfanilamide in sulfamethoxazole by increasing the proportions of both acetonitrile and 2-propanol in the mobile phase. The method has been adopted official first action. 相似文献