全文获取类型
收费全文 | 2280篇 |
免费 | 195篇 |
国内免费 | 85篇 |
出版年
2024年 | 4篇 |
2023年 | 28篇 |
2022年 | 27篇 |
2021年 | 53篇 |
2020年 | 57篇 |
2019年 | 82篇 |
2018年 | 79篇 |
2017年 | 60篇 |
2016年 | 65篇 |
2015年 | 51篇 |
2014年 | 135篇 |
2013年 | 142篇 |
2012年 | 86篇 |
2011年 | 124篇 |
2010年 | 117篇 |
2009年 | 125篇 |
2008年 | 151篇 |
2007年 | 158篇 |
2006年 | 168篇 |
2005年 | 133篇 |
2004年 | 96篇 |
2003年 | 100篇 |
2002年 | 89篇 |
2001年 | 46篇 |
2000年 | 57篇 |
1999年 | 42篇 |
1998年 | 52篇 |
1997年 | 32篇 |
1996年 | 37篇 |
1995年 | 24篇 |
1994年 | 26篇 |
1993年 | 23篇 |
1992年 | 38篇 |
1991年 | 8篇 |
1990年 | 4篇 |
1989年 | 7篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 1篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 5篇 |
1976年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有2560条查询结果,搜索用时 93 毫秒
1.
Numerous investigations have been carried out on the spectral distribution of the light of different species of fireflies. Here we record the emission spectrum of the Indian species of the firefly Luciola praeusta Kiesenwetter 1874 (Coleoptera : Lampyridae : Luciolinae) on a color film. Green and red color-sectors, with an intense yellow one in between, appear in this spectrum. Intensity profile of this spectrum reveals a hitherto undetected strong narrow yellow line, which lies within the full-width-at-half maximum (FWHM) of the intensity profile. The spectrum recorded in a high-resolution spectrometer confirms the presence of this sharp intense line. This finding lends support to an earlier drawn analogy between the in vivo emission of the firefly and laser light. 相似文献
2.
3.
4.
Phorbol esters are known to alter microfilaments but it is not clear if the changes correspond to modulation of the phosphoinositide turnover/protein kinase C system. The novel technique of laser scanning confocal epifluorescence was used to study fiber orientation in phorbol ester treated cells. We treated endothelial cells with control agents and agents known to stimulate protein kinase C: 4 alpha-phorbol, phorbol 12-myristate 13-acetate (PMA), phorbol dibutyrate (PDB), or lipopolysaccharide. After incubation with the test agents, the endothelial cell microfilaments were stained with rhodamine pholloidin and viewed by conventional epifluorescence and by laser scanning confocal epifluorescence microscopy. The images obtained by the confocal microscopy corresponded to a thin optical section through the cells, 300 nm or more in thickness. The microfilaments extended predominantly in the plane of focus. After exposure of the cells to phorbol esters, the stress fibers became more nearly parallel in arrangement or were shortened, but remained in the plane of focus. The modification of microfilaments in response to phorbol esters was quantitated by a single blind analysis. In order to compare the morphological changes with a biochemical action of the phorbol esters, we measured phosphoinositide turnover. The dose-dependence of morphological changes was compared and contrasted to the dose-dependent effect of phorbol esters on bradykinin-stimulated phosphoinositide turnover. PMA had about the same EC50 (1-5 nM) for both biochemical and morphological processes. PDB was less potent in inducing the disruption of microfilament structure than in inhibiting phosphoinositide turnover. Lipopolysaccharide was ineffective in inducing a morphological change under these conditions. A simple activation of protein kinase C is insufficient to explain the dose-dependent effects of phorbol esters. Thus a morphometric analysis can help distinguish the potency of cytoskeleton modulators. 相似文献
5.
P. J. Skuce C. F. Johnston I. Fairweather D. W. Halton C. Shaw K. D. Buchanan 《Cell and tissue research》1990,261(3):573-581
Summary The presence and distribution of neuropeptides belonging to the pancreatic polypeptide family have been demonstrated by an indirect immunofluorescence technique in the nervous systems of adult male and female Schistosoma mansoni. Seven antisera of differing regional specificity to pancreatic polypeptide (PP), peptide YY (PYY) and neuropeptide Y (NPY) were employed on both whole-mount and cryostat-sectioned material. Positive immunoreactivity (IR) was obtained with all antisera except an N-terminally-directed antiserum to NPY. In the CNS, immunoreactivity was restricted to cell bodies and nerve fibres in the anterior ganglia, central commissure and dorsal and ventral nerve cords of both sexes, whereas, in the PNS, positive-IR was present in the plexuses innervating the subtegumental musculature and the oral and ventral suckers. Intense immunoreactivity was observed in a plexus of nerve fibres and cell bodies in the lining of the gynaecophoric canal and in fine nerve fibres innervating the dorsal tubercles of the male. In contrast, in the female, strong immunoreactivity was evident in nerve plexuses innervating the lining of the ovovitelline duct and in the wall of the ootype, but most notably in a cluster of cells in the region of Mehlis' gland. Results suggest that molecules with C-terminal homology to the PP-family are present in S. mansoni. These peptides would appear to be important regulatory molecules in the parasite's nervous system and may play a role in the control of egg production. 相似文献
6.
S. N. Kovalenko S. G. Stepanian V. P. Chuev M. M. Asimov V. M. Nikitchenko V. P. Chernykh 《Molecular Engineering》1992,2(2):153-163
In order to improve the generating and photochemical properties of coumarin laser dyes, the following active media were synthesized: inclusion complexes of -cyclodextrin (-CD) and 7-amino-4-methylcoumarins (COU1, COU102, COU120). Complex formation processes were studied, and the structure of the inclusion complexes was estimated using the method of MM2 molecular mechanics. The data obtained suggest the reasons underlying the complex structure effects on their spectral, luminescent and generating characteristics. 相似文献
7.
Y. Ishii S. Hitchcock-DeGregori K. Mabuchi S. S. Lehrer 《Protein science : a publication of the Protein Society》1992,1(10):1319-1325
The thermal unfolding of the coiled-coil alpha-helix of recombinant alpha alpha-tropomyosin from rat striated muscle containing an additional 80-residue peptide of influenza virus NS1 protein at the N-terminus (fusion-tropomyosin) was studied with circular dichroism and fluorescence techniques. Fusion-tropomyosin unfolded in four cooperative transitions: (1) a pretransition starting at 35 degrees C involving the middle of the molecule; (2) a major transition at 46 degrees C involving no more than 36% of the helix from the C-terminus; (3) a major transition at 56 degrees C involving about 46% of the helix from the N-terminus; and (4) a transition from the nonhelical fusion domain at about 70 degrees C. Rabbit skeletal muscle tropomyosin, which lacks the fusion peptide but has the same tropomyosin sequence, does not exhibit the 56 degrees C or 70 degrees C transition. The very stable fusion unfolding domain of fusion-tropomyosin, which appears in electron micrographs as a globular structural domain at one end of the tropomyosin rod, acts as a cross-link to stabilize the adjacent N-terminal domain. The least stable middle of the molecule, when unfolded, acts as a boundary to allow the independent unfolding of the C-terminal domain at 46 degrees C from the stabilized N-terminal unfolding domain at 56 degrees C. Thus, strong localized interchain interactions in coiled-coil molecules can increase the stability of neighboring domains. 相似文献
8.
9.
D. Daems M. Van den Zegel N. Boens F. C. De Schryver 《European biophysics journal : EBJ》1985,12(2):97-105
The fluorescence decays of pyrene in small and large unilamellar L,-dipalmitoylphosphatidylcholine vesicles have been investigated as a function of probe concentration and temperature. When the molar ratio of pyrene to phospholipid equals 1:3000, no excimer emission is observed and the fluorescence decays are mono-exponential. When this ratio is equal to or higher than 1:120, excimer formation is observed.Above the phase transition temperature the observed fluorescence decays of monomer and excimer can be adequately described by a bi-exponential function. The monomer decays can be equally well fitted to a decay law which takes into account a time-dependence in the probe diffusion rate constant. The fluorescence decay kinetics are compatible with the excimer formation scheme which is valid in an isotropic medium. The excimer lifetime and the (apparent) rate constant of excimer formation have been determined as a function of probe concentration at different temperatures above the phase transition temperature. The activation energy of excimer formation is found to be 29.4±1.3 kJ/mol. In small unilamellar vesicles the diffusion constant associated with the pyrene excimer formation process varies from 8.0x10-7 cm2/s at 40°C to 2.2x10-6 cm2/s at 70°C.Below the phase transition temperature the monomer decays can be described by a decay law which takes into account a time dependence of the rate constant of excimer formation. The lateral diffusion coefficient of pyrene calculated from the decay fitting parameters of the monomer region varies from 4.0x10-9 cm2/s at 20°C to 7.9x10-8 cm2/s at 35°C. No significant difference could be observed between the pyrene fluorescence decay kinetics in small and large unilamellar vesicles.Abbreviations SUV
small unilamellar vesicles
- LUV
large unilamellar vesicles
- DPPC
dipalmitoylphosphatidylcholine
- DMPC
dimyristoylphosphatidylcholine
- FRAP
fluorescence recovery after photobleaching
Part of this research has been presented at the 5th international symposium on surfactants in solution. Bordeaux, July 9th–13th 1984 相似文献
10.
通过Na_2~(51)CrO_4在肿瘤细胞膜内外的分布比值的测定,观察了激光血卟啉衍生物(简称HPD)对小鼠S-180V肿瘤细胞膜通透性的作用及其影响因素:(1)通过紫外吸收光谱的测定对肿瘤细胞摄取HPD的动态过程作了观察。选择了实验所需的合适HPD浓度和作用时间,并观察到细胞悬液中血清蛋白能阻抑细胞对HPD的摄取。(2)在氦氖激光照射后即可观察到含有HPD的肿瘤细胞膜外~(51)Cr/膜内~(51)Cr的比值明显增加,而单照激光或单加HPD两组的~(51)Cr比值与正常对照组相比无明显变化。(3)上述的~(51)Cr比值变化随着照后保温时间的延长而逐渐加大。与此同时细胞形态也发生相应的变化,细胞死亡率也逐渐增加。说明除了原初的光敏反应外,还有继发的细胞损伤。(4)细胞悬液中血清蛋白的存在虽然对激光血卟啉对肿瘤细胞的杀伤作用有所减弱,但在这样条件下的光敏反应比较接近临床上治疗肿瘤的实际情况。 相似文献