全文获取类型
收费全文 | 275篇 |
免费 | 6篇 |
出版年
2011年 | 3篇 |
2010年 | 2篇 |
2009年 | 5篇 |
2007年 | 4篇 |
2006年 | 5篇 |
2005年 | 3篇 |
2004年 | 5篇 |
2000年 | 3篇 |
1999年 | 8篇 |
1998年 | 9篇 |
1997年 | 9篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 6篇 |
1993年 | 6篇 |
1992年 | 8篇 |
1991年 | 7篇 |
1990年 | 10篇 |
1989年 | 10篇 |
1988年 | 17篇 |
1987年 | 13篇 |
1986年 | 9篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1975年 | 2篇 |
1973年 | 4篇 |
1972年 | 3篇 |
1971年 | 4篇 |
1966年 | 3篇 |
1965年 | 2篇 |
1959年 | 3篇 |
1958年 | 7篇 |
1957年 | 6篇 |
1956年 | 6篇 |
1955年 | 3篇 |
1954年 | 5篇 |
1953年 | 5篇 |
1952年 | 7篇 |
1951年 | 4篇 |
1950年 | 2篇 |
1948年 | 2篇 |
1946年 | 2篇 |
排序方式: 共有281条查询结果,搜索用时 19 毫秒
51.
52.
P. R. ELLIS B. D. DOWKER G. H. FREEMAN J. A. HARDMAN 《The Annals of applied biology》1985,106(2):349-356
In field trials between 1973 and 1982 families of carrots of cv. Long Chantenay were assessed for their resistance to carrot fly (Psila rosae). In some but not all years, families selected for their observed resistance in earlier trials seemed more resistant than the parent line. In more than half the trials there was an association between carrot fly damage and root density, there being less damage on those families from which more roots were harvested. Thus, family selection within cv. Long Chantenay did not lead to a consistent improvement in resistance to carrot fly. Alternative strategies for achieving plant resistance to this pest are discussed. 相似文献
53.
MILLICENT L. FREAN F.L.S. ELLIS MARKS 《Botanical journal of the Linnean Society. Linnean Society of London》1988,97(3):255-259
FREAN, M. L. & MARKS, E., 1988. Chromosome numbers of C3 and C4 variants within the species Alloteropais semialata (R.Br.) Hitch. (Poaceae). In a study of mid-lamina leaf sections, different variants of A. semialata were found to have C3 or C4 anatomy. The C4 leaf showed a specialized photosynthetic vascular bundle sheath not present in the C3 form. Chromosome counts made from pollen mother cell squashes showed that the C3 form of A. semialata is a fertile diploid 2n = 2x = 18 and the C4 form, a fertile allohexaploid 2n = 6x = 54. The cytological evidence suggests that the two forms should be considered as separate species. 相似文献
54.
Seeds of barley (Hordeum vulgare L.) and mung bean (Vigna radiata(L.) Wilczek), with orthodox seed storage behaviour, were imbibedfor between 8 h and 96 h at 15 °C and 25 °C, respectively,while barley seeds were also maintained in moist aerated storageat 15 °C for 14 d. These seeds and seedlings, together withcontrols, were then dried to various moisture contents between3% and 16% (wet basis) and hermetically stored for six monthsat 20°C, 0°C or 15°C. In both species, neitherdesiccation nor subsequent hermetic storage of the control lotsresulted in loss in viability. The results for barley seedsimbibed for 24 h were similar to the control, but desiccationsensitivity increased progressively with duration of imbibitionbeyond 24 h in barley or 8 h in mung bean; these treatmentsalso reduced the longevity of the surviving seeds in air-drystorage. Loss in viability in barley imbibed for 48 h was mostrapid at the two extreme seed storage moisture contents of 3·6%and 14·3%, and in both these cases was more rapid at15 °C than at cooler temperatures. Similarly, for mung beanimbibed for 8 h, loss in viability was most rapid at the lowest(4·3%) moisture content, but in this case it was morerapid at 20 °C than at warmer temperatures. Thus,these results for the storage of previously imbibed orthodoxseeds conform with the main features of intermediate seed storagebehaviour Key words: Barley, Hordeum vulgare L., mung bean, Vigna radiata (L.) Wilczek, desiccation sensitivity, seed longevity, seed storage behaviour 相似文献
55.
JAYNE E. ELLIS MICHAEL A. WYDER LINDA ZHOU ARUN GUPTA HARRY RUDNEY EDNA S. KANESHIRO 《The Journal of eukaryotic microbiology》1996,43(3):165-170
The lipids of purified preparations of Pneumocystis carinii carinii freshly isolated from infected rats were analyzed and compared with those of whole lungs from normal and methylprednisolone-immunosuppressed uninfected rats. In this study, the neutral lipid fraction was examined in detail; the relative concentrations of individual classes making up this fraction were quantified. Of particular interest was the nature of the organism's ubiquinone (coenzyme Q, CoQ) fraction because atovaquone, a hydroxynaphtho-quinone (566C80) analog of ubiquinone, is efficacious in the treatment of P. carinii pneumonia. The ubiquinone concentration in both P. carinii and lung tissues was relatively low compared to that present in rat heart and liver tissues. Two homologs were identified in the organism: CoQ10 was the predominant homolog with lesser amounts of CoQ9 present. In contrast, the lungs of normal and immunosuppressed uninfected rats had CoQ9 and lesser amounts of CoQ8 , but no detectable CoQ10 . Furthermore, radiolabeled mevalonic acid was incorporated in vitro into the ubiquinone fraction of P. carinii indicating that the organism has the de novo branch of the isoprenoid biosynthetic pathway leading to polyprenyl formation. Hence, it was concluded that CoQ10 (if not both CoQ110 and CoQ9 ) in P. carinii as not scavenged from the host but was synthesized by the organism. Although lung tissues contained substantial free fatty acids, the organism was enriched in these lipids. The high concentration of free fatty acids and relatively low level of triglycerides in P. carinii suggest that fatty acids may represent major carbon sources for ATP production by the organism. 相似文献
56.
Field experiments comparing six spraying programmes and two fungicides for control of coffee berry disease were carried out at three sites during 1968. These established that protection of the crop by sprays applied throughout the long rains (February–July) gave the best control and increased yields threefold. Early season spray programmes, which reduced the sporulating capacity of the pathogen in coffee twigs, but which ceased before the end of the rainy season, gave no disease control in the late crop (harvested October-December) and yields were less than in unsprayed controls. All programmes which gave protection at the onset of the rains gave some disease control in the early crop (harvested June-August). Captafol (‘Ortho-Difolatan’ 80 WP) was better than a 50% copper formulation (‘Perenox’). Conditions suitable for infection, as determined from meteorological records, occurred frequently during both rainy seasons. Estimates of sporulating capacity and data from spore trappings showed that although inoculum from the bark might initiate an epidemic, subsequent disease progress was more dependent upon spores derived from diseased berries; these accounted for most of the inoculum dispersed during the greater part of the season. Removal of the early crop, which was very small, had no detectable effect on disease in the late crop. Although losses were greatest with early season spray programmes, these did nevertheless delay the onset of the epidemic. However, the subsequent rate of disease increase was greatest and ‘scab’ lesion formation least in these treatments. ‘Scab’ lesions were most abundant in those treatments which caused least delay; in unsprayed coffee, it appeared that early exposure to infection resulted in ‘scab’ lesion formation which subsequently retarded the rate of disease progress. Tree height was positively correlated with disease incidence, but there was little effect of tree aspect. Crop density had a small effect on disease incidence within branches. 相似文献
57.
The relationship between seed moisture content and seed longevityin sesame (Sesamum indicum L.) in hermetic storage at 50 °Cis logarithmic. The logarithmic relationship is maintained from15 per cent down to 2 per cent the lowest moisture contenttested but above 15 per cent this air-dryrelationship no longer holds since further increase in seedmoisture content does not reduce longevity. Tentative estimatesof constant values for the improved seed viability equationare provided, and implications for long-term storage are discussed. Sesame, Sesamum indicum L., seed storage, improved viability equation, seed moisture content, seed longevity prediction 相似文献
58.
ABSTRACT. Vairimorpha invictae n. sp. infects the red imported fire ant, Solenopsis invicta Buren, in Brazil. The parasite is dimorphic, producing two morphologically distinct types of spores, which develop sequentially in the same fat cells or oenocytes in the fat body. The binucleate free spores develop from disporous sporonts; the uninucleate octospores develop from multinucleate sporonts within a sporophorous vesicle. Infected cells are transformed into large sacs which contain both types of spores in mature adult hosts. Mature free spores are often present by the time the larvae pupate, but mature octospores are found only in adult hosts. Masses of spores may be seen through the intact cuticle by low power phase-contrast microscopy; there are no other physical signs and no behavioral signs of infection. Attempts to transmit the infection in the laboratory failed. 相似文献
59.
60.
The Development of Desiccation-tolerance and Maximum Seed Quality During Seed Maturation in Six Grain Legumes 总被引:3,自引:0,他引:3
Physiological maturity, i.e. the time when seedsreach their maximum dry weight during development, occurredwhen maturation drying on the parent plant in the field hadreduced seed moisture content to approximately 60 per cent infaba bean (Vicia faba L.), lentil (Lens culinaris Medic.), chickpea(Cicer arietinum L.), white lupin (Lupinus albus L.), soya bean(Glycine max [L.] Merr.) and pea (Pisum sativum L.) The onsetof desiccation-tolerance, i.e. the ability of seeds to germinatefollowing harvest and rapid artificial drying, coincided withphysiological maturity, except in pea where it occurred a littleearlier at about 70 per cent moisture content. Maximum seedquality as determined by maximum viability, minimum seedlingabnormalities and maximum seedling size occurred in pea, chickpeaand lupin when seeds were harvested for rapid drying at physiologicalmaturity; but for maximum seed quality in the other speciesmaturation drying had to proceed further - to about 45 per centmoisture content in soya bean and to about 30 per cent moisturecontent in lentil and faba bean seed crops. Much of this variationamongst the six species, however, was due to differences inthe variation in maturity within each seed crop. Results forindividual pods showed that peak maturity, i.e. maximum seedquality following harvest and rapid artificial drying, was achievedin all six species once maturation drying had reduced the moisturecontent of the seeds to 4550 per cent. In pea, faba beanand soya bean there was a substantial decline in viability andan increase in seedling abnormalities when harvest was delayedbeyond the optimal moisture content for harvest. 相似文献