首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1071篇
  免费   22篇
  国内免费   4篇
化学   789篇
晶体学   11篇
力学   17篇
数学   86篇
物理学   194篇
  2023年   4篇
  2022年   4篇
  2021年   16篇
  2020年   12篇
  2019年   13篇
  2018年   13篇
  2017年   7篇
  2016年   21篇
  2015年   18篇
  2014年   22篇
  2013年   38篇
  2012年   59篇
  2011年   63篇
  2010年   41篇
  2009年   27篇
  2008年   87篇
  2007年   74篇
  2006年   77篇
  2005年   78篇
  2004年   80篇
  2003年   45篇
  2002年   50篇
  2001年   17篇
  2000年   15篇
  1999年   14篇
  1998年   10篇
  1997年   11篇
  1996年   14篇
  1995年   14篇
  1994年   20篇
  1993年   10篇
  1992年   6篇
  1991年   10篇
  1990年   9篇
  1989年   7篇
  1988年   4篇
  1987年   6篇
  1986年   5篇
  1985年   7篇
  1984年   5篇
  1983年   8篇
  1982年   4篇
  1981年   6篇
  1980年   11篇
  1979年   2篇
  1978年   7篇
  1977年   3篇
  1976年   11篇
  1974年   6篇
  1972年   4篇
排序方式: 共有1097条查询结果,搜索用时 15 毫秒
171.
172.
173.
2,7-Dialkyl[1]benzothieno[3,2-b]benzothiophenes were tested as solution-processible molecular semiconductors. Thin films of the organic semiconductors deposited on Si/SiO2 substrates by spin coating have well-ordered structures as confirmed by XRD analysis. Evaluations of the devices under ambient conditions showed typical p-channel FET responses with the field-effect mobility higher than 1.0 cm2 V-1 s-1 and Ion/Ioff of approximately 10(7).  相似文献   
174.
The photophysical properties and photoswitching scheme of the reversible photoswitchable green fluorescent protein-like fluorescent proteins Dronpa-2 and Dronpa-3 were investigated by means of ensemble and single-molecule fluorescence spectroscopy and compared to those of the precursor protein Dronpa. The faster response to light and the faster dark recovery of the new mutants observed in bulk also hold at the single-molecule level. Analysis of the single-molecule traces allows us to extract the efficiencies and rate constants of the pathways involved in the forward and backward switching, and we find important differences when comparing the mutants to Dronpa. We rationalize our results in terms of a higher conformational freedom of the chromophore in the protein environment provided by the beta-can. This thorough understanding of the photophysical parameters has allowed us to optimize the acquisition parameters for camera-based sub-diffraction-limit imaging with these photochromic proteins. We show that Dronpa and its mutants are useful for fast photoactivation-localization microscopy (PALM) using common wide-field microscopy equipment, as individual fluorescent proteins can be localized several times. We provide a new approach to achieve fast PALM by introducing simultaneous two-color stroboscopic illumination.  相似文献   
175.
Gastrodin is a bioactive constituent of rhizome in Gastrodia elata Blume (Orchidaceae) The aim of this study is to develop a rapid and sensitive liquid chromatographic method coupled to microdialysis sampling system to measure the unbound of gastrodin in rat blood, brain and bile. Microdialysis probes were simultaneously inserted into the jugular vein, brain striatum and bile duct of each anesthetized rat for sampling after the administration of gastrodin (100 or 300 mg kg−1) through the femoral vein. Separation of unbound gastrodin from various biological fluids was applied to an RP-select B column (250 mm × 4.6 mm i.d., 5 μm). The mobile phase consisted of acetonitrile–50 mM potassium dihydrogen phosphate buffer–triethylamine (5:95:0.1, v/v/v, adjusted to pH 2.5 with orthophosphoric acid) with a flow rate of 1 mL min−1. The UV detector wavelength was set at 221 nm. Fifteen minutes after the administration, the gastrodin reached the peak concentration in brain and bile. In addition, the results indicate that gastrodin penetrates the blood-brain barrier (BBB) and goes through hepatobiliary excretion.  相似文献   
176.
Photoisomerization of encapsulated Z-enecarbamates within the hydrophobic chiral cavities of gamma-CD showed higher diastereoselectivities in the photoproducts than those obtained in solution. The selective encapsulation of the enecarbamates and the following isomerization process are both diastereoselectively controlled by gamma-CD.  相似文献   
177.
A new chemiluminescence biochemical oxygen demand (BODCL) determining method was studied by employing redox reaction between quinone and Baker's yeast. The measurement was carried out by utilizing luminol chemiluminescence (CL) reaction catalyzed by ferricyanide with oxidized quinone of menadione, and Saccharomyces cerevisiae using a batch-type luminometer. In this study, dimethyl sulfoxide was used as a solvent for menadione. After optimization of the measuring conditions, the CL response to hydrogen peroxide in the incubation mixture had a linear response between 0.1 and 100 μM H2O2 (r2 = 0.9999, 8 points, n = 3, average of relative standard deviation; R.S.D.av = 4.22%). Next, a practical relationship between the BODCL response and the glucose glutamic acid concentration was obtained over a range of 11-220 mg O2 L−1 (6 points, n = 3, R.S.D.av 3.71%) with a detection limit of 5.5 mg O2 L−1 when using a reaction mixture and incubating for only 5 min. Subsequently, the characterization of this method was studied. First, the BODCL responses to 16 pure organic substances were examined. Second, the influences of chloride ions, artificial seawater, and heavy metal ions on the BODCL response were investigated. Real sample measurements using river water were performed. Finally, BODCL responses were obtained for at least 8 days when the S. cerevisiae suspension was stored at 4 °C (response reduction, 69.9%; R.S.D. for 5 testing days, 18.7%). BODCL responses after 8 days and 24 days were decreased to 69.9% and 35.8%, respectively, from their original values (R.S.D. for 8 days involving 5 testing days, 18.7%).  相似文献   
178.
Further extensive isolation work on the 1-BuOH-soluble fraction of a MeOH extract of Tricalysia dubia afforded five new ent-kaurane glucosides (4-8) and one new labdane glucoside (9), together with a known megastigmane glucoside, sammangaoside B (1), and monoterpene glucosides (2, 3). The structures of the new compounds were elucidated by analyses of one- and two-dimensional NMR spectroscopic data. The absolute configuration of the 9-position of sammangaoside B was revised to S and its total stereochemistry was established by the modified Mosher's method.  相似文献   
179.
Pharaonis phoborhodopsin (ppR), also called pharaonis sensory rhodopsin II, NpSRII, is a photoreceptor for the photophobic response of Natronomonas pharaonis. Tryptophan 182 (W182) of bacteriorhodopsin (bR) is near the chromophore retinal and has been suggested to interact with retinal during the photoreaction and also to be involved in the hydrogen-bonding network around the retinal. W182 of bR is conserved in ppR as tryptophan 171 (W171). To elucidate whether W171 of ppR interacts with retinal during the photoreaction and/or is involved in the hydrogen-bonding network as in bR, we formed W171-substituted mutants of ppR, W171A and W171T. Our low-temperature spectroscopic study has revealed that the substitution of W171 to Ala or Thr resulted in the stabilization of M- and O-intermediates. The stability of M and absorption spectral changes during the M-decay were different depending on the substituted residue. These findings suggest that W171 in ppR interacts with retinal and the degree of the interaction depends on the substituted residues, which might be rate determining in the M-decay. In addition, the involvement of W171 in the hydrogen-bonding network is suggested by the O-decay. We also found that glycerol slowed the decay of M and not of O.  相似文献   
180.
Activated opioid receptors transmit internal signals through two major pathways: the G-protein-mediated pathway, which exerts analgesia, and the β-arrestin-mediated pathway, which leads to unfavorable side effects. Hence, G-protein-biased opioid agonists are preferable as opioid analgesics. Rubiscolins, the spinach-derived naturally occurring opioid peptides, are selective δ opioid receptor agonists, and their p.o. administration exhibits antinociceptive effects. Although the potency and effect of rubiscolins as G-protein-biased molecules are partially confirmed, their in vitro profiles remain unclear. We, therefore, evaluated the properties of rubiscolins, in detail, through several analyses, including the CellKeyTM assay, cADDis® cAMP assay, and PathHunter® β-arrestin recruitment assay, using cells stably expressing µ, δ, κ, or µ/δ heteromer opioid receptors. In the CellKeyTM assay, rubiscolins showed selective agonistic effects for δ opioid receptor and little agonistic or antagonistic effects for µ and κ opioid receptors. Furthermore, rubiscolins were found to be G-protein-biased δ opioid receptor agonists based on the results obtained in cADDis® cAMP and PathHunter® β-arrestin recruitment assays. Finally, we found, for the first time, that they are also partially agonistic for the µ/δ dimers. In conclusion, rubiscolins could serve as attractive seeds, as δ opioid receptor-specific agonists, for the development of novel opioid analgesics with reduced side effects.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号