全文获取类型
收费全文 | 323篇 |
免费 | 5篇 |
出版年
2018年 | 3篇 |
2014年 | 2篇 |
2013年 | 5篇 |
2012年 | 8篇 |
2011年 | 4篇 |
2010年 | 17篇 |
2009年 | 3篇 |
2008年 | 11篇 |
2007年 | 12篇 |
2006年 | 14篇 |
2005年 | 9篇 |
2004年 | 7篇 |
2003年 | 5篇 |
1999年 | 4篇 |
1998年 | 3篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1992年 | 4篇 |
1991年 | 6篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1974年 | 2篇 |
1973年 | 6篇 |
1972年 | 4篇 |
1971年 | 4篇 |
1970年 | 4篇 |
1968年 | 2篇 |
1959年 | 8篇 |
1958年 | 4篇 |
1957年 | 14篇 |
1956年 | 20篇 |
1955年 | 14篇 |
1954年 | 7篇 |
1953年 | 12篇 |
1952年 | 15篇 |
1951年 | 5篇 |
1950年 | 3篇 |
1924年 | 1篇 |
1922年 | 1篇 |
排序方式: 共有328条查询结果,搜索用时 15 毫秒
71.
RUTH M. HAMILL MOHAMED A. F. NOOR ERIC T. WATSON MICHAEL G. RITCHIE 《Molecular ecology resources》2006,6(2):340-342
Ephippiger ephippiger is a model organism for studies of sexual selection and phylogeography but little is known about fine‐scale population structure. Available microsatellite loci have null allele problems so we used an enrichment technique to isolate 21 new microsatellite loci for E. ephippiger. We present primer pairs for 10 polymorphic loci (3–11 alleles per locus). Observed heterozygosities at polymorphic loci ranged from 0.118 to 0.787, but several were significantly lower than expected. 相似文献
72.
SYNOPSIS. The Spiralia, an assemblage of phyla united by theirstereotypic pattern of early embryonic cell divisions (spiralcleavage), is an interesting group in which to investigate theevolution of development. This paper examines modificationsof developmental mechanisms within the Spiralia with emphasison the basallybranching forms. Although demonstrating a notabledegree of evolutionary conservation, the equal quartet cleavagepattern, which appears to be the ancestral condition, nonethelessexhibits modifications within the various spiralian groups,such as unequal cleavage, changes in cell size and rate of division,formation of two rather than four quadrants (duet spiral cleavage),and in extreme cases the loss of any trace of the spiral pattern.While the cell lineages of spiralians are remarkably conserved,one can discern evolutionary changes, for example in the cellsthat give rise to mesodenn. Studies of blastomere specificationin many spiralian groups and analyses of axis determinationindicate that embryos with equal versus unequal cleavage typicallyuse different determinative mechanisms to establish cell fatesand the dorsoventral axis. These properties are establishedearly in species exhibiting unequal cleavage. While previousexperiments suggested that equal cleavage was associated withlate specification, there is now evidence of precocious specificationof quadrant fates in some equal-cleaving species, such as thenemerteans and the polyclad turbellarians 相似文献
73.
WALTER MAJAK RUTH E. McDIARMID THOMAS W. POWELL ALBERT L. VAN RYSWYK DARRYL G. STOUT RICHARD J. WILLIAMS RICHARD E. TUCKER 《Plant, cell & environment》1979,2(4):335-340
Abstract. The alkaloids of reed canarygrass respond to changes in soil moisture and nitrogen fertility. Gramine and hordenine levels increased under field conditions of moisture deprivation and this effect was enchanced when nitrogen fertilizer was applied. The level of 5-methoxy-N-methyltryptamine was affected mainly by the nitrogen amendment. Exceptional alkaloid levels in reed canarygrass are interpreted in relation to climatic and plant osmotic parameters. Improved TLC fluorescence scanning procedures are presented for quantifying reed canarygrass alkaloids. 相似文献
74.
The fungicide imazalil has potential value for controlling post-harvest diseases caused by Alternaria alternata in pears, apples and persimmons. Imazalil was active in vitro on germination and hyphal growth (ED50) at 1.4 and 0.5 μg/ml, respectively. Protectant action of the fungicide lasted only 1 day after treatment. At 1000 μg/ml the fungicide inhibited development of Alternaria rot in inoculated apples at 0 °C and in naturally infected pears and persimmons at–1 °C. 相似文献
75.
RUTH KIEW F.L.S CHE SU IBRAHIM 《Botanical journal of the Linnean Society. Linnean Society of London》1982,84(2):79-102
The foliar anatomy of 15 Malaysian species of Chionanthus and 3 species of Olea is described and compared with particular reference to sclereids. The anatomy of the two genera is similar except that Chionanthus shows a wider range in sclereid form, eight kinds ofsclereid are recorded. Filiform sclereids are present in all Olea species and most Chionanthus species examined, additional kinds ofsclereid found in these Chionanthus species include astrosclereids, dendrosclereids, osteosclereids and polymorphic sclereids, with brachysclereids of several forms in the petiole. Quantity of sclereids is not related to coriaceousness, which is determined by leaf thickness. Anatomical characters do not support any major grouping of species within Chionanthus and provide further evidence that the sections, Eulinocitra and Ceranthus , are untenable. The distinction between the lepidote scales of Olea and the peltate hairs common to all oleaceous genera is discussed. 相似文献
76.
T. C. E. WELLS P. ROTHERY RUTH COX S. BAMFORD 《Botanical journal of the Linnean Society. Linnean Society of London》1998,126(1-2):39-48
Information taken from two long-term demographic studies on Orchis morio L. and Herminium monorchis (L.) R.Br, is used to explore some of the factors which influence flowering. The proportion of plants which flowered each year varied considerably between species, flowering in O. morio exceeding 40% in all years except one over an 18 year period; over a 30 year period (1966–95), the number of plants of Herminium in flower never exceeded 36% of the population and no inflorescences were produced in 1977 and 1991. The relationship between flowering in Herminium in a given year and the monthly rainfall and temperature for the current and 3 previous years was analysed using logistic regression. Best fits were obtained using data for the summer months in the previous year, with an increasing flowering rate with rainfall and a decline with temperature. It is hypothesized that drought and high temperatures in the summer reduce leaf area and cause premature senescence and the death of leaves, with the result that not enough carbohydrates are stored to enable plants to support or initiate inflorescences the following year. For species such as Orchis morio which produce leaves in the autumn and remain green, summer drought causes no problems as they have no above ground organs. Factors which influence flowering in this species are as yet unknown. 相似文献
77.
78.
79.
80.