全文获取类型
收费全文 | 27901篇 |
免费 | 1969篇 |
国内免费 | 6篇 |
出版年
2023年 | 232篇 |
2022年 | 471篇 |
2021年 | 871篇 |
2020年 | 589篇 |
2019年 | 709篇 |
2018年 | 899篇 |
2017年 | 809篇 |
2016年 | 1163篇 |
2015年 | 1659篇 |
2014年 | 1788篇 |
2013年 | 2156篇 |
2012年 | 2546篇 |
2011年 | 2280篇 |
2010年 | 1409篇 |
2009年 | 1253篇 |
2008年 | 1523篇 |
2007年 | 1490篇 |
2006年 | 1345篇 |
2005年 | 1177篇 |
2004年 | 1129篇 |
2003年 | 970篇 |
2002年 | 852篇 |
2001年 | 250篇 |
2000年 | 200篇 |
1999年 | 217篇 |
1998年 | 199篇 |
1997年 | 148篇 |
1996年 | 143篇 |
1995年 | 118篇 |
1994年 | 109篇 |
1993年 | 67篇 |
1992年 | 88篇 |
1991年 | 86篇 |
1990年 | 93篇 |
1989年 | 60篇 |
1988年 | 54篇 |
1987年 | 70篇 |
1986年 | 51篇 |
1985年 | 44篇 |
1984年 | 59篇 |
1983年 | 53篇 |
1982年 | 33篇 |
1981年 | 43篇 |
1980年 | 28篇 |
1979年 | 32篇 |
1978年 | 32篇 |
1976年 | 20篇 |
1975年 | 27篇 |
1973年 | 23篇 |
1972年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
131.
Paula P. Chee 《Plant cell reports》1996,16(3-4):184-187
Summary Taxusbrevifolia is the source of paclitaxel (Taxol®), an anticancer drug. A method for regeneration ofTaxus brevifolia from immature zygotic embryos via somatic embryogenesis is described. Embryogenic callus tissues were obtained by culturing immature zygotic embryos on Lloyd and McCown medium (MCM) supplemented with 160 M 2,4-dichlorophenoxyacetic acid (2,4-D) + 5 M benzylaminopurine (BA) + 5 M naphthaleneacetic acid (NAA) for 4 weeks. Putative embryoids were obtained following transfer of cultures to MCM medium supplemented with 4 M BA + 5 M kinetin + 1 M NAA for 6 to 8 weeks. Conversion of embryos was obtained on MCM medium supplemented with 40 M abscisic acid (ABA) + 1% activated charcoal. Development of bipolar structures with recognizable shoot and root apices was observed in somatic embryos. Five percent of somatic embryos were regenerated into plantlets on half-strength growth regulator-free MCM medium. 相似文献
132.
Ana Maria Landeira-Fernandez Maricilia S. Costa Leopolde de Meis 《Bioscience reports》1996,16(6):439-451
Vesicles derived from maize roots retain a membrane bound H+-ATPase that is able to pump H+ at the expense of ATP hydrolysis. In this work it is shown that heparin, fucose-branched chondroitin sulfate and dextran sulfate 8000 promote a shift of the H+-ATPase optimum pH from 6.0 to 7.0. This shift is a result of a dual effect of the sulfated polysaccharides, inhibition at pH 6.0 and activation at pH 7.O. At pH 6.0 dextran 8000 promotes an increase of the apparent Km for ATP from 0.28 to 0.95 mM and a decrease of the Vmax from 14.5 to 7.1 mol Pi/mg · 30 min–1. At pH 7.0 dextran 8000 promotes an increase in Vmax from 6.7 to 11.7 mol Pi/mg · 30 min–1. In the presence of lysophosphatidylcholine the inhibitory effect of the sulfated polysaccharides observed at pH 6.0 was not altered but the activation of pH 7.0 decreased. It was found that in the presence of sulfated polysaccharides the ATPase became highly sensitive to K+ and Na+. Both the inhibition at pH 6.0 and the activation promoted by the polysaccharide were antagonized by monovalent cations (K+>Na+Li+).Abbreviations Mops
4-morpholinopropanesulfonic acid
- EDTA
ethylenediaminetetraacetic acid
- ACMA
9-amino-6-chloro-2-methoxyacridine
- FCCP
carbonyl cyanide p(trifluoromethoxy)-phenylhyrazone 相似文献
133.
Results are presented on the phytoplankton species compositionand abundance from bottle samples collected in September 1989near the confluence of the Brazil and Malvinas currents offArgentina. The phytoplankton assemblages were dominated by diatomsand dinoflagellates. A surface diatom bloom was found alongthe west side of the Brazil Current, and was dominated by Thalassiosiradelicatula Ostenfeld emend. Hasle (cell numbers up to 5.5 x105 cells 11) The bloom was associated with strong temperaturegradients separating Brazil and Malvinas waters, and with thepresence of a cyclonic eddy near the confluence of the currents.These features were detected in satellite imagery coincidentwith the in situ sampling dates. 相似文献
134.
David H. Lewis Garry K. Burge David M. Schmierer Paula E. Jameson 《Physiologia plantarum》1996,98(1):179-186
The cytokinin content in fruit tissue of the kiwifruit ( Actinidia deliciosa [A. Chev.] C. F. Liang et A. R. Ferguson var. deliciosa cv. Hayward) was monitored during fruit development to identify which cytokinins were present and if they were linked with specific stages of fruit growth. Cytokinins were isolated and purified by column chromatography and high-performance liquid chromatography and quantified by radioimmunoassay. A novel HPLC step utilising an amine column was successfully introduced as a preparative step in the separation of the O - and 9-glucosides from the free bases and ribosides. The radioimmunoassay results were validated, and the different cytokinins identified, by gas chromatography-mass spectrometry. Cytokinins detected in fruit included the cytokinin free bases, zeatin and isopentenyladenine, their ribosides, nucleotides and both O - and 9-glucosides. Both qualitative and quantitative changes of the cytokinins occurred during fruit development. A decrease in cytokinin concentration occurred after anthesis (from 342 pmol g−1 fresh weight at anthesis to 41 pmol g−1 fresh weight 27 days after anthesis). A large increase in cytokinin concentration and content per fruit occurred as the fruit reached commercial maturity (to 1900 pmol g−1 fresh weight). Individual cytokinins showed quite different patterns. Zeatin, in particular, showed a peak in concentration (13 pmol g−1 fresh weight) 11 days after anthesis that correlated with the beginning of the cell division phase of fruit growth. The accumulation of cytokinin (mostly zeatin riboside or zeatin nucleotide) in mature fruit may be of significance for the postharvest storage of kiwifruit fruit. 相似文献
135.
Markers for selection of the rice Xa21 disease resistance gene 总被引:8,自引:0,他引:8
C. E. Williams B. Wang T. E. Holsten J. Scambray F. de Assis Goes da Silva P. C. Ronald 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1996,93(7):1119-1122
Six molecular markers were mapped to a 7.4-cM region of rice chromosome 11 containing the Xa21 gene, which confers resistance to the pathogen Xanthomonas oryzae pv oryzae. Three markers, RG103, 248 and 818, co-segregated with Xa21 in a population of 1141 plants. Multiple copies of all marker loci were present within the region that was introgressed from Oryza longistaminata into O. sativa. The marker loci were cloned and primers were designed that defined sequence-tagged sites. Physical mapping of the three tightly linked central markers revealed that RG103, the marker that hybridizes to the Xa21 gene, resides on a separate DNA fragment from the other two markers.Disclaimer: Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by USDA implies no approval of the product to the exclusion of others that may also be suitable. 相似文献
136.
Graciela C. Theiler Yanina C. Marcos Edgardo Kolkowski Nancy Lindel Mónica Capucchio Paula Barrionuevo Francisco R. Carnese M. Leonardo Satz 《Immunogenetics》1996,43(6):398-399
The nucleotide sequence data reported in this paper have been submitted to the GenBank nucleotide sequence database and have been assigned the accession number U17107. The nameB*3509 was officially assigned by the WHO Nomenclature Committee in December 1994 相似文献
137.
Ana Cristina Gomes da Cunha Manuel Fernandes Ferreira 《Plant Cell, Tissue and Organ Culture》1996,47(1):1-8
The effects of plant growth regulators (PGR) on calli induction, morphogenesis and somatic embryogenesis of flax were studied. The organogenic and callus formation capacity were assessed for different types of source explants. Root and shoot explants were equally good material for calli production but the former produced calli without shoot regeneration capacity. Under the experimental conditions tested, 2,4-dichlorophenoxyacetic acid (2,4-D) + zeatin was the most efficient PGR combination on calli induction and biomass production. The calli were green but with no rhizogenic capacity. In contrast, and at similar concentrations, indole-3-butyric acid (IBA) + kinetin induced white or pale green friable calli with a good root regeneration capacity (60%). A factorial experiment with different combinations of 2,4-D + zeatin + gibberellic acid (GA3) levels revealed that the direction of explant differentiation was determined by specific PGR interactions and concentrations. The results from these experiments revealed that the morphogenetic pathway (shoot versus root differentiation) can be manipulated on flax explants by raising the 2,4-D level from 0.05 to 3.2 mg l?1 in the induction medium. The induction and development of somatic embryos from flax explants was possible in a range of 2,4-D + zeatin concentrations surrounding 0.4 mg l?1 2,4-D and 1.6 mg l?1 zeatin, the most efficient growth regulator combination. 相似文献
138.
A Familial Factor Independent of CAG Repeat Length Influences Age at Onset of Machado-Joseph Disease 总被引:3,自引:0,他引:3
下载免费PDF全文
![点击此处可从《American journal of human genetics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Anita L. DeStefano L. Adrienne Cupples Patricia Maciel Claudia Gaspar Joao Radvany David M. Dawson Lewis Sudarsky Lee Corwin Paula Coutinho Patrick MacLeod Jorge Sequeiros Guy A. Rouleau Lindsay A. Farrer 《American journal of human genetics》1996,59(1):119-127
Machado-Joseph disease (MJD) is a late-onset, progressive, neurodegenerative disorder caused by the expansion of an unstable trinucleotide (CAG) repeat sequence in a novel gene (MJD1) on chromosome 14. Previous studies showed that age at onset is negatively correlated with the number of CAG repeat units, but only part of the variation in onset age is explained by CAG repeat length. Ages at onset and CAG repeat lengths of 136 MJD patients from 23 kindreds of Portuguese descent were analyzed, to determine whether familial factors independent of CAG repeat length modulate age at onset of MJD. Correlation among sibs for onset age adjusted for CAG repeat length was .43, which indicates that an environmental or genetic factor common to sibs influences onset age. Positive correlations were also observed for avuncular (r = .22) and first-cousin pairs (r = .28), which supports the hypothesis that a genetic factor is influencing age at onset. Commingling analysis of onset ages adjusted for CAG repeat length identified three distributions in this population of affected individuals. Further studies of a much larger sample are needed to determine whether these distributions represent the influence of a genetic or environmental factor. 相似文献
139.
Ana María Planchuelo 《Brittonia》1996,48(2):263-265
Lupinus rubriflorus Planchuelo, from Rio Grande do Sul, Brazil, is described and illustrated. This species is related toL. bracteolaris s.l. differing in pubescence, stipules, and floral characters. 相似文献
140.
Summary Isolated cod brain microtubules from the cold-adapted Atlantic cod (Gadus morhua) have previously been shown to be highly detyrosinated, a post-translational modification of tubulin usually found in stable
subsets of microtubules. In this study we found this was not restricted only to isolated brain microtubules. Microtubules
in primary cultures of brain and skin cells were composed of both tyrosinated (Tyr)- and detyrosinated (Glu)-tubulin seen
by immunocytochemistry. Immunoelectron microscopy of isolated microtubules showed that individual microtubules were composed
of a mixture of Tyr- and Glu-tubulin. Leukocytes with extending lamellopodia contained only microtubules stained with the
antibody against Tyr-tubulin, and isolated heart tubulin lacked both Tyr- and Glu-tubulin, suggesting that a relative high
level of detyrosination is a characteristic of most, but not all, cod microtubules. Brain cell microtubules were more resistant
to mitotic inhibitors than skin cell microtubules, but this was not correlated to a difference in detyrosination. Brain and
skin cell microtubules were only partially disassembled when incubated at 0°C. Upon reassembly of microtubules at 12°C, microtubules
were still made of mixtures of Tyr- and Glu-tubulin, indicating that detyrosination of assembled microtubules is rapid and/or
that in cod cells, in contrast to mammalian cells, Glu-tubulin can reassemble to microtubules. Our data show that most cod
microtubules are highly detyrosinated, but this is not the cause of their cold adaptation or drug stability. 相似文献