全文获取类型
收费全文 | 1902篇 |
免费 | 118篇 |
国内免费 | 1篇 |
专业分类
2021篇 |
出版年
2023年 | 21篇 |
2022年 | 42篇 |
2021年 | 88篇 |
2020年 | 38篇 |
2019年 | 57篇 |
2018年 | 82篇 |
2017年 | 52篇 |
2016年 | 83篇 |
2015年 | 115篇 |
2014年 | 127篇 |
2013年 | 142篇 |
2012年 | 128篇 |
2011年 | 130篇 |
2010年 | 75篇 |
2009年 | 62篇 |
2008年 | 76篇 |
2007年 | 88篇 |
2006年 | 54篇 |
2005年 | 55篇 |
2004年 | 41篇 |
2003年 | 37篇 |
2002年 | 35篇 |
2001年 | 19篇 |
2000年 | 24篇 |
1999年 | 14篇 |
1997年 | 7篇 |
1995年 | 9篇 |
1994年 | 9篇 |
1992年 | 11篇 |
1991年 | 25篇 |
1990年 | 16篇 |
1989年 | 23篇 |
1988年 | 11篇 |
1987年 | 9篇 |
1986年 | 9篇 |
1985年 | 16篇 |
1984年 | 21篇 |
1983年 | 10篇 |
1982年 | 17篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1979年 | 22篇 |
1978年 | 10篇 |
1977年 | 14篇 |
1975年 | 13篇 |
1974年 | 6篇 |
1973年 | 10篇 |
1972年 | 9篇 |
1971年 | 7篇 |
1969年 | 5篇 |
排序方式: 共有2021条查询结果,搜索用时 0 毫秒
1.
A survey of cultivated heirloom tomato varieties identifies four new mutant alleles at the green-flesh locus 总被引:1,自引:0,他引:1
Cornelius S. Barry Priyanka Pandey 《Molecular breeding : new strategies in plant improvement》2009,24(3):269-276
The process of crop domestication occurs through the selection and subsequent propagation of novel alleles that improve traits
of interest. Cultivated tomato (Solanum lycopersicum), particularly heirloom varieties, exhibit a wide range of variation in fruit size, shape and color. The green-flesh mutant of tomato possesses a stay-green phenotype resulting in fruits that ripen to a red-brown color, due to the retention
of chlorophyll and the simultaneous accumulation of lycopene. The recent identification of the GREEN-FLESH gene provides a molecular tool with which to investigate the origin of a subset of cultivated tomato varieties that resemble
the green-flesh mutant. Sequence analysis of the GF locus from 26 varieties revealed the existence of four previously unidentified null alleles. This study illustrates the potential
of cultivated tomato varieties, including heritage cultivars, heirlooms, and land races, for uncovering new alleles in genes
of interest. 相似文献
2.
3.
4.
5.
Migration of O-acetyl groups in N,O-acetylneuraminic acids 总被引:6,自引:0,他引:6
J P Kamerling R Schauer A K Shukla S Stoll H Van Halbeek J F Vliegenthart 《European journal of biochemistry》1987,162(3):601-607
Highly purified N-acetyl-4-O-acetylneuraminic acid (Neu4,5Ac2), N-acetyl-7-O-acetylneuraminic acid (Neu5,7Ac2) and N-acetyl-7,9-di-O-acetylneuraminic acid (Neu5,7,9Ac3) were used to study spontaneous migrations of acetyl groups between hydroxyl groups. The techniques applied involved thin-layer chromatography, gas-liquid chromatography/mass spectrometry, high-performance liquid chromatography and 360-MHz 1H-NMR spectroscopy. It was found that at pH values at which no significant de-O-acetylation is observed: (a) Neu5,7Ac2 can easily be transformed into Neu5,9Ac2, (b) Neu5,7,9Ac3 yields an equilibrium of Neu5,7,9Ac3 and Neu5,8,9Ac3 in a molar ratio of approximately 1:1, and (c) Neu4,5Ac2 does not give rise to O-acetyl migrations. The importance of these findings is discussed in terms of the biosynthesis of O-acetylated sialic acids. 相似文献
6.
7.
D B Buxton S D Shukla D J Hanahan M S Olson 《The Journal of biological chemistry》1984,259(3):1468-1471
1-O-Alkyl-2-acetyl-sn-glyceryl 3-phosphorylcholine or acetylglyceryl ether phosphorylcholine (AGEPC) stimulated glycogenolysis in perfused livers from fed rats at concentrations as low as 10(-11) M. At the lower AGEPC concentrations, e.g. 2 X 10(-10) M, a single transient phase of enhanced hepatic glucose output was elicited upon infusion of this agonist. At higher concentrations, e.g. 2 X 10(-8) M, a sharp transient spike of glucose output was observed, followed by a stable elevated steady state rate of glucose output until the AGEPC infusion was terminated. Increased rates of lactate and acetoacetate output and a diminished hepatic oxygen consumption were characteristic of the response of the livers to AGEPC at 2 X 10(-10) M. Neither alpha- nor beta-adrenergic antagonists blocked the glycogenolytic response of AGEPC. Repeated infusion of AGEPC led to homologous desensitization of the response, but the response of the liver to the alpha-adrenergic agonist, phenylephrine, or to glucagon, subsequent to AGEPC stimulation, was unaffected. Increasing the period of perfusion between successive additions of AGEPC, from 7 to 30 min, resulted in an increased glycogenolytic response to this agonist. When the perfusate calcium concentration was reduced from 1.25 to 0.05 mM, the glycogenolytic response to AGEPC was markedly diminished; calcium efflux from the liver following stimulation with AGEPC was not observed. The data presented in this study illustrate a potent agonist effect of AGEPC on the glycogenolytic system in the rat liver. 相似文献
8.
Two cases of mycotic keratitis caused by the Colletotrichum state of Glomerella cingulata and Acrophialophora fusispora are reported for the first time. Both the isolates produced experimental corneal lesions in rabbit eyes but A. fusispora was more pathogenic. The experimental infection was more severe, with both the fungi, in rabbits pretreated with cortisone as compared with untreated animals. In vitro A. fusispora was most sensitive to miconazole and tolciclate followed by clotrimazole, amphotericin B and lactones while clotrimazole exerted maximum inhibitory effect on Colletotrichum followed by miconazole, lactones, amphotericin B and arnebins. Arnebins and tolciclate were inactive respectively against A. fusispora and Colletotrichum. Of the 3 drugs tested in vivo, against A. fusispora keratitis in rabbit, amphotericin B showed better results than tolciclate and miconazole. 相似文献
9.
Two new compounds, isolated from the rhizomes of Cryptocoryne spiralis, have been characterized as ethyl 14-oxotetracosanoate and 15-oxoeicosanyl 14-oxoheptadecanoate by spectral data and chemical studies. Hentriacontane and sitosterol have also been isolated and identified. 相似文献
10.
A. C. Shukla 《Hydrobiologia》1967,30(2):221-224
Effect of presoaking seeds with different concentrations (0.5, 1 and 5%) of algal extracts on the development of stomata and epidermal cells in rice leaves has been investigated. One percent ether extract of Phormidium foveolarum (Mont.) Gomont suspended in water increases the number of stomata and also the total perimeter of stomatal pores, suggesting that the plants are better adopted for photosynthetic activity. 相似文献