全文获取类型
收费全文 | 1920篇 |
免费 | 56篇 |
国内免费 | 115篇 |
出版年
2023年 | 11篇 |
2022年 | 20篇 |
2021年 | 35篇 |
2020年 | 21篇 |
2019年 | 31篇 |
2018年 | 22篇 |
2017年 | 26篇 |
2016年 | 27篇 |
2015年 | 43篇 |
2014年 | 48篇 |
2013年 | 60篇 |
2012年 | 46篇 |
2011年 | 55篇 |
2010年 | 34篇 |
2009年 | 81篇 |
2008年 | 84篇 |
2007年 | 86篇 |
2006年 | 82篇 |
2005年 | 58篇 |
2004年 | 53篇 |
2003年 | 61篇 |
2002年 | 35篇 |
2001年 | 58篇 |
2000年 | 41篇 |
1999年 | 92篇 |
1998年 | 56篇 |
1997年 | 62篇 |
1996年 | 71篇 |
1995年 | 74篇 |
1994年 | 46篇 |
1993年 | 49篇 |
1992年 | 59篇 |
1991年 | 53篇 |
1990年 | 50篇 |
1989年 | 46篇 |
1988年 | 38篇 |
1987年 | 43篇 |
1986年 | 27篇 |
1985年 | 29篇 |
1984年 | 35篇 |
1983年 | 14篇 |
1982年 | 21篇 |
1981年 | 24篇 |
1980年 | 26篇 |
1979年 | 13篇 |
1978年 | 19篇 |
1977年 | 9篇 |
1976年 | 8篇 |
1974年 | 2篇 |
1973年 | 3篇 |
排序方式: 共有2091条查询结果,搜索用时 15 毫秒
1.
Summary A field experiment was conducted using15N-labelled urea on a Reddish Brown Lateritic (Peleustult) soil. Growing two crops on flat land and on soil ridges of 15 cm
height produced similar comparative effects from fertilizer on maize. However, fertilizer applied by broadcasting on maize
with a 50 cm effective band followed by incorporating was more useful to mungbean than that applied by banding below the cereal
seed rows when crops were grown on flat land. The reverse was observed when crops were grown on ridges. It was deduced that
the maize cultivar was not likely to affect comparative efficiencies of fertilizer.
For fertilizer application at sowing, broadcasting in 50 cm maize effective band followed by incorporating was slightly superior
to banding below maize seed rows. Side-dressing of fertilizer to maize at 4 weeks after sowing was superior to application
at sowing. Evenly-split application, at sowing and at 4 weeks after sowing, was either only slightly superior or comparable
to non-split application by banding below maize seed rows at sowing, depending on placement method of the first application.
Soil moisture status as a possible factor rendering discrepancy in the comparative efficiencies obtained by different authors
is discussed. 相似文献
2.
Heat stress reduces maize yield and several lines of evidence suggest that the heat lability of maize endosperm ADP-glucose pyrophosphorylase (AGPase) contributes to this yield loss. AGPase catalyzes a rate-limiting step in starch synthesis. Herein, we present a novel maize endosperm AGPase small subunit variant, termed BT2-TI that harbors a single amino acid change of residue 462 from threonine to isoleucine. The mutant was isolated by random mutagenesis and heterologous expression in a bacterial system. BT2-TI exhibits enhanced heat stability compared to wildtype maize endosperm AGPase.The TI mutation was placed into another heat-stable small subunit variant, MP. MP is composed of sequences from the maize endosperm and the potato tuber small subunit. The MP-TI small subunit variant exhibited greater heat stability than did MP. Characterization of heat stability as well as kinetic and allosteric properties suggests that MP-TI may lead to increased starch yield when expressed in monocot endosperms. 相似文献
3.
Summary. Blood samples from a female sheep-goat hybrid and its back-cross male offspring were tested for electrophoretic variants of plasma albumin, transferrin and esterase, and of red cell carbonic anhydrase, nucleoside phosphorylase, NADH-diaphorase, 'X'-protein, superoxide dismutase, malic enzyme and haemoglobin. Red cells were also tested for blood group antigens. Both animals showed variants that could not be attributed to either sheep or goat alone, thus confirming previous chromosomal data that the female was a genuine sheep-goat hybrid. 相似文献
4.
5.
Mitochondrial DNA (mtDNA) from cell suspension cultures of two intergeneric somatic hybrids of Pennisetum americanum (pearl millet) + Saccharum officinarum (sugarcane) was examined by restriction endonuclease digestion and hybridization with sorghum mtDNA cosmids. The mtDNA of one somatic hybrid was indistinguishable from that of pearl millet, while the second exhibited a combination of parental mtDNAs, suggesting mitochondrial fusion. Several novel, possibly recombinant, mtDNA restriction fragments were detected in this hybrid, which may have resulted from intergenmic recombination.Florida Agriculture Experiment Station Journal Series No: 8090. 相似文献
6.
Paternal inheritance of chloroplast DNA in Larix 总被引:2,自引:0,他引:2
Restriction enzyme analysis was used to determine the inheritance of chloroplast DNA in conifers. The plant material studied included five individual trees of European larch (Larix decidua Mill.) and Japanese larch (Larix leptolepis Sieb. & Zucc.) and six hybrids from controlled crosses between these species. The chloroplast DNA fragment patterns generated by Bam-HI and Bcl-I were species-specific. Paternal inheritance of chloroplast DNA patterns was found in most Larix crosses. One hybrid showed maternal chloroplast DNA patterns. In addition, two other hybrids had mixed Bam-HI patterns suggesting recombination between maternal and paternal chloroplast DNA. The mechanisms favoring paternal inheritance in conifers are not known. Paternal inheritance of chloroplast DNA is suggested it to be a general phenomenon in conifers. 相似文献
7.
8.
B. C. Loughman 《Plant and Soil》1987,99(1):63-74
Summary Little is known about the biochemical basis of the genotypic differences in the capacity for ion absorption and transport
shown by many crop species. If these differences reflect the abundance of a specific membrane component or the activity of
an enzyme we need to have some indication of thein vivo operation of these systems in whole plants. Thein vivo assessment of glycolytic enzymes is illustrated by the effects of mannose on the transport of phosphate in maize varieties.
The application of high resolution31P-NMR to the study of intermediary metabolismin vivo is also helpful in following transport capacity.
The five-fold rise in respiratory rate that occurs when freshly cut potato slices are maintained in aerated water for 24 hours
is accompained by the turning on of a wide range of biochemical systems. Major increases in the capacity for absorption of
phosphate from low concentrations (0.1 μM–10 μM) and in the phosphorylative ability of the tissue are seen, indicating the synthesis of a carrier involved in phosphate transport.
These capacities differ markedly between individual tissues of the tuber,i. e. pith, parenchyma, cortex and buds and large differences have been observed between comparable tissue from different varieties.
Varieties grown under similar conditions have been compared and shown to exhibit different kinetics with respect to the development
of the low concentration absorption site and in their sensitivity to the effects of uncouplers such as 2,4-dinitrophenol. 相似文献
9.
D. A. Laurie M. D. Bennett 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1987,73(3):403-409
Summary Dominant alleles of the Kr1 and Kr2 genes reduce the crossability of hexaploid wheat with many alien species, including rye and Hordeum bulbosum, with Kr1 having the greater effect. However, a cytological study of wheat ovaries fixed 48 h after pollination showed that the wheat genotypes Highbury (kr1, Kr2) and Chinese Spring (Hope 5B) (kr1, kr2) were crossable with Seneca 60 maize, fertilization occurring in 14.4 and 30.7% of embryo sacs respectively. The latter figure was similar to the 29.7% fertilization found in Chinese Spring (kr1, kr2). Most embryo sacs in which fertilization occurred contained an embryo but lacked an endosperm and where an endosperm was formed it was usually highly aberrant. All three wheat x maize combinations were karyotypically unstable and rapidly eliminated maize chromosomes to produce haploid wheat embryos. 相似文献
10.
H.-R. Roth G. Dolf G. Stranzinger 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1987,74(1):42-48
Summary A statistical approach to the interpretation of data from gene assignment with somatic cell hybrids is presented. The observed data are analysed under a variety of hypotheses. The fit to the hypotheses is compared by means of the likelihood obtained under a given hypothesis. Two of these hypotheses are related to fundamental questions: is a gene responsible for the enzyme observation and if so, is that gene located on a specific chromosome or could it change its position and be sometimes on chromosome j and, in another hybrid line, on chromosome k? The other hypotheses concern the assignment of the gene to just one of the chromosomes.To improve the traditional data analysis approach we considered additional information: the uncertainties and possible errors of laboratory methods in all our calculations and the length of the donor chromosomes in connection with one specific hypothesis.This method allows us to account for the reliability of the investigation methods and the nature of the hybrid lines involved. Data can be evaluated at different error probabilities within a realistic range in order to compare and discuss results. 相似文献