全文获取类型
收费全文 | 328篇 |
免费 | 14篇 |
专业分类
342篇 |
出版年
2014年 | 4篇 |
2013年 | 4篇 |
2012年 | 7篇 |
2010年 | 8篇 |
2009年 | 12篇 |
2008年 | 7篇 |
2007年 | 9篇 |
2006年 | 9篇 |
2005年 | 9篇 |
2004年 | 6篇 |
2001年 | 7篇 |
2000年 | 6篇 |
1999年 | 4篇 |
1998年 | 10篇 |
1997年 | 8篇 |
1996年 | 13篇 |
1995年 | 8篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1990年 | 7篇 |
1989年 | 7篇 |
1988年 | 5篇 |
1986年 | 9篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1978年 | 3篇 |
1977年 | 6篇 |
1975年 | 3篇 |
1974年 | 5篇 |
1972年 | 5篇 |
1971年 | 5篇 |
1970年 | 3篇 |
1959年 | 6篇 |
1958年 | 6篇 |
1957年 | 6篇 |
1956年 | 6篇 |
1955年 | 3篇 |
1954年 | 9篇 |
1953年 | 14篇 |
1952年 | 3篇 |
1951年 | 5篇 |
1950年 | 4篇 |
1949年 | 4篇 |
1948年 | 4篇 |
排序方式: 共有342条查询结果,搜索用时 0 毫秒
11.
R. O. CLEMENTS B. R. BENTLEY P. J. MURRAY I. F. HENDERSON 《The Annals of applied biology》1991,119(3):513-519
The present two field experiments, involving plots of Italian ryegrass sown in 1976, 1980 and 1984 confirmed results of earlier work in which the yield and persistence of Italian ryegrass was greatly increased by the application of pesticide. A range of pesticide treatments were used. The responses to application of permethrin applied three times per year average 8% for the three years of the first experiment and 5% for the five years of the second experiment. Such responses appeared cost-effective, but the overall environmental impact of such applications is not known. 相似文献
12.
The mouse pink eyed dilution locus, p, located on chromosome 7, mediates coat and eye color. The human correlate of this gene may underlie some forms of tyrosinase-positive oculocutaneous albinism. Mutations at the p locus result in a reduction in pigmentation of the eyes and coat. Although most mutant p alleles (including all spontaneous mutations) affect only pigmentation, several mutant alleles (all radiation induced) are also associated with a variety of other phenotypes. We have focused our attention on the pun mutant allele, a spontaneous mutation, exhibiting one of the highest reversion frequencies reported for a mammalian mutation. Using a new technique, genome scanning, we have cloned fragments of genomic DNA from the p locus that are associated with a DNA duplication in pun DNA. These fragments can now be used to locate the p gene-encoding sequences and aid in the molecular characterization of complex mutant p alleles. 相似文献
13.
VIVIEN K. SIEBER BRIAN G. MURRAY F.L.S. 《Botanical journal of the Linnean Society. Linnean Society of London》1981,83(4):293-310
The meiotic behaviour of plants from mixed populations of Alopecurus pratensis × A. geniculatus and of A. pratensis × A. arundinaceus ( 2n = 4×(= 28) is reported together with observations on some artificially produced hybrids. This meiotic behaviour is correlated with the degree of hybridity as shown by the hybrid index values of the plant. In A. pratensis × A. geniculatus hybrids there are marked differences between populations in the degree of meiotic disturbance and in one population there was an almost complete breakdown of meiosis. Alopecurus pratensis × A. arundinaceus hybrids show fairly regular meiotic pairing but in most plants there are a few univalent chromosomes at metaphase I. Artificially produced hybrids of A. pratensis × A. aequalis gave meiotic configurations that suggest that the genomes of the parent species are very similar. Taken together with the results from artificially produced hybrids of A. pratensis × A. geniculatus , it is suggested that bivalent-promoting mechanisms reduce multivalent formation both in the species and the hybrids. The interaction of different genotypes involved in the control of meiosis may account for the variation in meiotic behaviour in the different populations of hybrids. Pollen fertility is reduced in most populations of hybrids and likely to be an important factor permitting introgressive hybridization. 相似文献
14.
An acid phosphatase (EC 3 1 3 2)isolated from the seed-coatsof developing pea seeds was estimated to have MW 30000 by gelfiltration on Sephadex G-75 It was shown to act on a broad spectrumof physiological substrates, the most preferred being ß-glycerophosphate,3-phosphoglycerate and ADP, wich all showed rates of about halfthe maximum rate shown with p-nitrophenyl phosphate (p-NPP)Another model substrate frequently used in enzyme localizationstudies, -naphthyl acid phosphate, was hydrolysed at about 30% of the rate shown with p-NPP This acid phosphatase was enhancedor stabilized by the chelators EDTA and 1, 10-phenanthrolme,unaffected by Mg2+ and N-ethyl maleimide, but strongly inhibitedby Zn2+ and F Both oxidized and reduced glutathione werewithout effect at low concentration and slightly inhibitoryat high concentration (15 mm) Thiol groups are clearly not involvedin regulating the activity of this acid phosphatase, a featurewhich distinguishes it from acid phosphatases from several otherplant species. Pisum sativum L, pea, acid phosphatase, seed-coats, seed development 相似文献
15.
Functional Significance of Acid Phosphatase Distribution During Embryo Development in Pisum sativum L 总被引:4,自引:0,他引:4
The distribution of P1, ester P and acid-insoluble nucleic acidP has been studied in relation to acid phosphatase activity(EC 3. 1. 3. 2) in the component parts of developing pea seeds(Pisum sativum L.). Despite the favourable pH of the liquidcontents of the embryo sac (pH 5.5), only very low acid phosphataseactivity was detected in this fluid (c. 0.01 units per seed).Potential substrates for phosphatase action were in fact absentfrom the secretion, the only form of P present being Pi, inconcentrations up to 8 mM. The data support the hypothesis thatthe high acid phosphatase activities which develop in the seed-coatsare involved in regulating the supply of P as P1 to the developingembryo. Pisum sativum L., pea, embryo development, acid phosphatase, phosphorus, seed-coats, seed development 相似文献
16.
17.
18.
19.
MICHAEL S.JOHNSON JAMES MURRAY BRYAN CLARKE 《Biological journal of the Linnean Society. Linnean Society of London》2000,69(4):577-598
Partulid land snails of the genus Samoana inhabiting the Marquesas Islands of French Polynesia exist as two distinct types, the 'thick-shelled' and 'thin-shelled' species. The two types differ in size, shell-thickness, pigmentation of the shell and mantle, stickiness of the mucus, and length of the tentacles. A study of variation in allozymes indicates that the species form a monophyletic group, within which the differences between the two types have twice evolved independendy, once in the northern islands and at least once in the south. In the Society Islands the two suites of characters are found in both Partula and Samoana , where there is evidence of at least four other independent derivations of the two types. The thin-shelled species consistendy tend to occur at the higher altitudes (above 200 m). These cases of parallel evolution argue strongly that the complexes of associated characters have arisen through natural selection. 相似文献
20.
Soil samples (0–10 cm depth) taken from plots of continuous winter wheat at intervals between January 1993 and July 1996 were dilution-plated on PCNB agar to identify and enumerate colony-forming units (cfus) of Fusarium spp. Cfus of the main wheat pathogen, F. culmorum, were more numerous in soil from plots that were shallow-cultivated to 10 cm after each harvest than in those that were ploughed. They were also usually more numerous in plots in which straw had been chopped and incorporated (by shallow cultivation or ploughing) than in those in which straw had been burnt. Increasing amounts of straw tended to increase the number of cfus. Deeper sampling (15–25 cm) showed that ploughing resulted in a more even, but diluted, distribution of cfus down the soil profile. Populations of some commonly found species that are not pathogenic on wheat {F. oxysporum, F. equiseti, F. flocciferum and F. merismoides) were sometimes also affected by straw disposal or cultivation treatments. Alternative methods of estimating population densities (baiting soil with wheat kernels or wheat seedlings, or plating-out straw fragments) showed generally similar effects of treatments on populations of F. culmorum; the relative merits of the methods are considered. Large differences in population densities of all species occurred within and between seasons. The smallest populations were found in January 1995 but, in the case of F. culmorum, they increased to relatively large numbers in July 1995. The summer of 1995 was warm and dry and especially favourable for development of fusarium foot rot. Severe disease occurred only in this year and was less frequent after ploughing than after tine-cultivation but more frequent after straw burning than after straw incorporation. The implications of these observations for understanding the role of propagules of F. culmorum in soil as inoculum for foot rot are discussed. 相似文献