全文获取类型
收费全文 | 7432篇 |
免费 | 194篇 |
国内免费 | 13篇 |
专业分类
化学 | 4955篇 |
晶体学 | 55篇 |
力学 | 208篇 |
综合类 | 5篇 |
数学 | 792篇 |
物理学 | 1624篇 |
出版年
2023年 | 59篇 |
2022年 | 238篇 |
2021年 | 228篇 |
2020年 | 176篇 |
2019年 | 196篇 |
2018年 | 196篇 |
2017年 | 136篇 |
2016年 | 288篇 |
2015年 | 227篇 |
2014年 | 287篇 |
2013年 | 457篇 |
2012年 | 493篇 |
2011年 | 559篇 |
2010年 | 372篇 |
2009年 | 377篇 |
2008年 | 465篇 |
2007年 | 416篇 |
2006年 | 346篇 |
2005年 | 285篇 |
2004年 | 253篇 |
2003年 | 200篇 |
2002年 | 171篇 |
2001年 | 134篇 |
2000年 | 122篇 |
1999年 | 74篇 |
1998年 | 66篇 |
1997年 | 63篇 |
1996年 | 52篇 |
1995年 | 46篇 |
1994年 | 67篇 |
1993年 | 64篇 |
1992年 | 63篇 |
1991年 | 35篇 |
1990年 | 31篇 |
1989年 | 26篇 |
1988年 | 28篇 |
1987年 | 20篇 |
1986年 | 23篇 |
1985年 | 25篇 |
1984年 | 26篇 |
1983年 | 27篇 |
1982年 | 18篇 |
1981年 | 26篇 |
1980年 | 18篇 |
1979年 | 24篇 |
1978年 | 21篇 |
1977年 | 14篇 |
1976年 | 12篇 |
1975年 | 12篇 |
1973年 | 12篇 |
排序方式: 共有7639条查询结果,搜索用时 15 毫秒
131.
Lisiani Ritter Eduarda Possa Larissa Bergoza Fabiana Agostini Sidnei M. Silva Leandro Tasso 《Biomedical chromatography : BMC》2020,34(11):e4977
Clindamycin is used for infections caused by Gram-positive and Gram-negative anaerobic pathogens and Gram-positive aerobes. Propionibacterium acnes is an important opportunistic microorganism of the human skin and is related to prostatitis. An LC–electrospray ionization–quadrupole time-of-flight–MS method was validated for determining clindamycin concentrations in plasma and prostate microdialysate. Clindamycin separation was carried out on a C18 column at 0.5 mL/min. The mobile phase employed gradient elution of formic acid and methanol. A mass spectrometer was operated in positive electrospray ionization mode to monitor ion 425.1784 and 253.1152 for clindamycin and cimetidine (internal standard), respectively. Linearity was obtained at 0.5–10.0 μg/mL (plasma) and 0.05–1.0 μg/mL (microdialysate) with coefficients of determination ≥0.999. The intra- and inter-day precision (coefficient of variation - CV%) values were ≤13.83% and 12.51% for plasma, respectively, and ≤10.90% and 9.35% for microdialysate, respectively. The accuracy was between 90.82% and 108.25% for plasma, and 96.97% and 106.98% for microdialysate. The present method was fully validated and applied to investigate clindamycin concentrations in both plasma and prostate by microdialysis in Wistar rats (80 mg/kg, intravenous). Because the penetration of antibiotics into the prostate may be restricted, this method allows us to investigate the prostate concentrations of clindamycin for the first time. 相似文献
132.
Langaro E. A. Costa de Moraes M. Buth I. S. Angulski da Luz C. Pereira Filho J. I. Matoski A. 《Journal of Thermal Analysis and Calorimetry》2020,142(3):1223-1231
Journal of Thermal Analysis and Calorimetry - Alkali-activated cements are low-environmental-impact binders and can be obtained from the alkaline activation of wastes such as slags and fly ashes,... 相似文献
133.
Journal of Solid State Electrochemistry - Controlling the Pt(111)-OHad stability by means of noncovalent interactions with hydrated cations, it was possible to modify natural changes in the... 相似文献
134.
Dr. Giovanny Carvalho dos Santos Juan Carlos Roldao Dr. Junqing Shi Dr. Begoña Milián-Medina Prof. Dr. Luiz Carlos da Silva-Filho Dr. Johannes Gierschner 《Chemphyschem》2020,21(16):1797-1804
A combined spectroscopic and TD-DFT case study was performed, to identify a robust method to calculate the complex near UV/Vis absorption spectra of various amino- vs. nitro-substituted 2,4-diphenylquinolines, which vary strongly under neutral and successively acidic conditions. For this, different DFT functionals were tested for geometry optimization and the TD part to calculate the neutral and different protonated species in a fast screening approach, i. e. using single point calculations in an implicit solvent. Offset-corrected M06HF, hitherto only applied to polymers, was identified as a suitable method to reproduce the absorption spectra in a reasonable fashion for all different substitution pattern and all different protonated species at different pH values; moreover, the method properly predicts the energetic ordering of low-lying n-π* and ππ* transitions, which is decisive for the non-/emissive nature of the different compounds. In all, this might provide a valuable tool for computer-aided design of related classes of compounds. 相似文献
135.
136.
137.
Elionai Cassiana de Lima Gomes Izabella Ercole de Carvalho Silvia Ligório Fialho Jamile Barbosa Maria Irene Yoshida Armando da Silva Cunha Júnior 《Journal of Thermal Analysis and Calorimetry》2018,131(3):2123-2128
Most of the pharmaceutical products are formulated as solid dosage form, which may present drug–excipient interactions that lead to changes in the chemical nature of the drug, such as solubility and bioavailability and may compromise its safety and effectiveness. Differential scanning calorimetry (DSC) is a widely used method for the rapid evaluation of the drug-excipient compatibility and the stability of the mixture formed; however, there is no consensus on the preparation methods of the drug–excipient mixtures. The aim of this study was to investigate the influence of the mixing method on the drug–excipient compatibility studies by means of DSC analysis, using tenofovir disoproxil fumarate as a drug model. Statistical analysis revealed significant differences in the heat of fusion of the drug in the mixtures prepared by several mixing methods. Vortex Mixer with a Pop-Off Cup used for 3 min proved to be very satisfactory for these studies. A polymorphic transition was observed in the mixture prepared with the mortar and pestle. Therefore, this method should be avoided since it may induce errors in the interpretation of DSC results. In this way, the mixing method used to prepare a mixture for studies of interactions between the API and the excipients in a pharmaceutical formulation has a great influence on the results and it must be chosen carefully. 相似文献
138.
J. H. de Araújo J. B. M. da Cunha A. Vasquez L. Amaral J. T. Moro F. C. Montenegro S. M. Rezende M. D. Coutinho Filho 《Hyperfine Interactions》1991,67(1-4):507-511
57Fe Mössbauer effect measurements in the diluted Ising antiferromagnet Fe x Zn1?x F2 withx=0.25 andx=0.57 at temperatures between 4.2 and 55 K, are reported. DC suceptibility measurements show a spin-glass (SG) phase at low temperatures forx≤0.31. Our Mössbauer spectra show a phase transition to a SG state with antiferromagnetic order (AFSG) forx=0.25 and only antiferromagnetic order forx=0.57. 相似文献
139.
R. Serna C. N. Afonso F. Catalina N. Teixeira M. F. da Silva J. C. Soares 《Applied Physics A: Materials Science & Processing》1992,54(6):538-542
Thin films consisting of 3 or 4 Sb and Ge alternating layers are irradiated with single nanosecond laser pulses (12 ns, 193 nm). Real time reflectivity (RTR) measurements are performed during irradiation, and Rutherford backscattering spectrometry (RBS) is used to obtain the concentration depth profiles before and after irradiation. Interdiffusion of the elements takes place at the layer interfaces within the liquid phase. The reflectivity transients allow to determine the laser energy thresholds both to induce and to saturate the process being both thresholds dependent on the multilayer configuration. It is found that the energy threshold to initiate the process is lower when Sb is at the surface while the saturation is reached at lower energy densities in those configurations with thinner layers. 相似文献
140.