全文获取类型
收费全文 | 6598篇 |
免费 | 442篇 |
国内免费 | 8篇 |
专业分类
7048篇 |
出版年
2023年 | 54篇 |
2022年 | 163篇 |
2021年 | 289篇 |
2020年 | 130篇 |
2019年 | 165篇 |
2018年 | 211篇 |
2017年 | 161篇 |
2016年 | 192篇 |
2015年 | 326篇 |
2014年 | 350篇 |
2013年 | 491篇 |
2012年 | 493篇 |
2011年 | 426篇 |
2010年 | 245篇 |
2009年 | 214篇 |
2008年 | 261篇 |
2007年 | 275篇 |
2006年 | 235篇 |
2005年 | 203篇 |
2004年 | 208篇 |
2003年 | 169篇 |
2002年 | 172篇 |
2001年 | 126篇 |
2000年 | 108篇 |
1999年 | 83篇 |
1998年 | 44篇 |
1997年 | 40篇 |
1996年 | 39篇 |
1995年 | 28篇 |
1994年 | 26篇 |
1992年 | 63篇 |
1991年 | 74篇 |
1990年 | 74篇 |
1989年 | 62篇 |
1988年 | 68篇 |
1987年 | 49篇 |
1986年 | 41篇 |
1985年 | 56篇 |
1984年 | 49篇 |
1983年 | 43篇 |
1982年 | 27篇 |
1980年 | 33篇 |
1979年 | 39篇 |
1978年 | 43篇 |
1977年 | 33篇 |
1976年 | 34篇 |
1974年 | 40篇 |
1973年 | 27篇 |
1971年 | 25篇 |
1970年 | 27篇 |
排序方式: 共有7048条查询结果,搜索用时 15 毫秒
51.
Interactions of Vibrio (formerly Achromobacter) fischeri nitrite reductase were studied by electron paramagnetic resonance spectroscopy. The spectrum of the oxidized enzyme showed a number of features which were attributed to two low-spin ferric hemes. These comprised an unusual derivative peak at g = 3.7 and a spectrum at g = 2.88, 2.26, and 1.51. Neither heme was reactive in the oxidized state with the substrate nitrite and with cyanide and azide. When frozen under turnover conditions (i.e., reduction in the presence of excess nitrite), the enzyme showed the spectrum of a nitrosyl heme derivative. The g = 2.88, 2.26, and 1.51 signals reappeared partially on reoxidation by nitrite, indicating that the nitrosyl species which remained arose from the g = 3.7 heme. The nitrosyl derivative showed a 14N nuclear hyperfine splitting, Az = 1.65 mT. The nitrosyl derivative was produced by treatment of the oxidized nitrite reductase with nitric oxide or hydroxylamine. Exchange of nitric oxide between the nitrosyl derivative and NO gas in solution was observed by using the [15N]nitrosyl compound. A possible reaction cycle for the enzyme is discussed, which involves reduction of the enzyme followed by binding of nitrite to one heme and formation of the nitrosyl intermediate. 相似文献
52.
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
53.
54.
Isotope and thermal effects in chemiosmotic coupling to the flagellar motor of Streptococcus 总被引:14,自引:0,他引:14
The torque generated by the flagellar motor of Streptococcus strain V4051 has been determined from rates of rotation of cells tethered by a single flagellum in media of different isotopic composition and temperature. Starved cells were energized artificially with either a potassium diffusion potential or a pH gradient. The torque increased linearly with protonmotive force. Identical results were obtained in media made with D2O or H2O; there was no solvent isotope effect. At a fixed protonmotive force, the torque was approximately constant over a temperature range of 4 degrees -38 degrees C. In cells chemotactically inert to changes in cytoplasmic pH, the motor turned counterclockwise when protons moved inward and clockwise when they moved outward. We conclude that the motor is a reversible engine driven by simple acid-base dissociation. A detailed model is discussed. 相似文献
55.
M. Islam Khan M. K. Mathew T. Mazumdar D. Pain N. Surolia M. K. Das P. Balaram A. Surolia 《Journal of biosciences》1983,5(1):31-39
The binding ofRicinus communis agglutinin andAbrus agglutinin to 4-methylumbelliferyl β-D-galactopyranoside was studied by equilibrium dialysis, fluo-rescence quenching and fluorescence polarization. The number of binding sites and the association constant value obtained by fluorescence polarization for bothRicinus communis agglutinin andAbrus agglutinin are in close agreement with those obtained by the other methods. This indicates the potential of ligand-fluorescence polarization measurements in the investigation of lectin-sugar interactions. 相似文献
56.
A M Estop J J Garver J Egozcue P Meera Khan P L Pearson 《Cytogenetics and cell genetics》1983,35(1):46-50
The chromosome localization and gene synteny of soluble malate dehydrogenase (MDH1), soluble isocitrate dehydrogenase (IDH1), mitochondrial superoxide dismutase (SOD2), phosphoglucomutase-3 (PGM3), mitochondrial malate dehydrogenase (MDH2), beta-glucuronidase (GUSB), nucleoside phosphorylase (NP), pyruvate kinase M2 (PKM2), hexosaminidase A (HEXA), inosine triphosphatase (ITPA), and N-acetyl-alpha-D-galactosaminidase (NAGA) were determined in the rhesus monkey using somatic cell hybrids. Comparison with the human and Pongidae syntenic groups shows that chromosome banding homologies do not always correlate with gene mapping data. 相似文献
57.
58.
59.
60.