全文获取类型
收费全文 | 7753篇 |
免费 | 807篇 |
国内免费 | 525篇 |
专业分类
化学 | 5468篇 |
晶体学 | 96篇 |
力学 | 406篇 |
综合类 | 46篇 |
数学 | 691篇 |
物理学 | 2378篇 |
出版年
2024年 | 7篇 |
2023年 | 109篇 |
2022年 | 133篇 |
2021年 | 273篇 |
2020年 | 271篇 |
2019年 | 265篇 |
2018年 | 193篇 |
2017年 | 208篇 |
2016年 | 307篇 |
2015年 | 279篇 |
2014年 | 360篇 |
2013年 | 552篇 |
2012年 | 698篇 |
2011年 | 696篇 |
2010年 | 491篇 |
2009年 | 433篇 |
2008年 | 545篇 |
2007年 | 459篇 |
2006年 | 433篇 |
2005年 | 371篇 |
2004年 | 319篇 |
2003年 | 263篇 |
2002年 | 261篇 |
2001年 | 166篇 |
2000年 | 126篇 |
1999年 | 121篇 |
1998年 | 102篇 |
1997年 | 83篇 |
1996年 | 85篇 |
1995年 | 74篇 |
1994年 | 48篇 |
1993年 | 54篇 |
1992年 | 50篇 |
1991年 | 53篇 |
1990年 | 27篇 |
1989年 | 24篇 |
1988年 | 23篇 |
1987年 | 20篇 |
1986年 | 15篇 |
1985年 | 16篇 |
1984年 | 13篇 |
1983年 | 9篇 |
1982年 | 11篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1977年 | 3篇 |
1973年 | 3篇 |
1971年 | 6篇 |
1970年 | 6篇 |
排序方式: 共有9085条查询结果,搜索用时 15 毫秒
901.
902.
Kang MJ Lee S Kim BK Eum JY Park SH Kang MH Oh CH Choo J Choi YW 《Chemical & pharmaceutical bulletin》2011,59(1):109-112
A Pep-1 peptide-modified liposomal (Pep1-Lipo) carrier system was investigated to increase the intracellular delivery of gold nanoparticles (Au NPs). Au NPs with a mean diameter of 13 nm were successfully encapsulated into the inner aqueous compartment of the novel carrier using an ethanol injection technique, reserving the distinctive optical characteristics of the surface plasmon resonance peak around 530 nm. The Au NP-loaded liposomal carrier was physically characterized as 150-170 nm in size and 45 mV in zeta potential. Dark field microscopic observation demonstrated that in vitro cellular association and/or translocation of the nanoprobes into the cells was increased by Pep1-Lipo carriers compared to bare Au NPs. In conclusion, this novel liposomal formulation is a promising platform for the intracellular delivery of metallic nanoprobes including Au NPs. 相似文献
903.
Park JS Shim JY Park JS Lee MJ Kang JM Lee SH Kwon MC Choi YW Jeong SH 《Chemical & pharmaceutical bulletin》2011,59(5):529-535
In order to develop a preferable once-a-day oral tablet formulation, various formulations of three-layered tablets containing tamsulosin HCl as a hydrophilic model drug were evaluated and compared with a commercial reference, tamsulosin OCAS?. When the test tablet was exposed to a release medium, the medium quickly permeated to the mid-layer and the two barrier layers swelled surrounding the mid-layer rapidly. Volume expansion showed faster and enough swelling of the three-layered tablet up to 2 h. Larger amount of barrier layers caused reduced release kinetics and a high molecular weight polymer showed more resistance against agitation force. A formulation with water-soluble mid-layer showed fast erosion decreasing its volume significantly. On the pharmacokinetic study, the mean ratio of area under the curve (AUC) and C(max) for the test formulation to the reference was 0.69 and 0.84, respectively, showing that the absorption of the drug was less complete than the reference. Plasma concentration at 24 h of the test formulation was higher than the reference. The Wagner-Nelson method showed that decreased initial dissolution rate might be the cause of the less complete absorption. On considering in vitro-in vivo correlation (IVIVC), level A, the reference (R2=0.981) showed more linear relationship than the test (R2=0.918) due to the decreased dissolution and absorption rate of the formulation. This result suggests that the in vitro dissolution profiles and release kinetics might be useful in correlating absorption kinetics as well as overall plasma drug concentration-time profiles for formulation studies. 相似文献
904.
Porous β-tricalcium phosphate (β-TCP) has been used for bone repair and replacement in clinics due to its excellent biocompatibility, osteoconductivity, and biodegradability. However, the application of β-TCP has been limited by its brittleness. Here, we demonstrated that an interconnected porous β-TCP scaffold infiltrated with a thin layer of poly(lactic-co-glycolic acid) (PLGA) polymer showed improved mechanical performance compared to an uncoated β-TCP scaffold while retaining its excellent interconnectivity and biocompatibility. The infiltration of PLGA significantly increased the compressive strength of β-TCP scaffolds from 2.90 to 4.19 MPa, bending strength from 1.46 to 2.41 MPa, and toughness from 0.17 to 1.44 MPa, while retaining an interconnected porous structure with a porosity of 80.65%. These remarkable improvements in the mechanical properties of PLGA-coated β-TCP scaffolds are due to the combination of the systematic coating of struts, interpenetrating structural characteristics, and crack bridging. The in vitro biological evaluation demonstrated that rat bone marrow stromal cells (rBMSCs) adhered well, proliferated, and expressed alkaline phosphatase (ALP) activity on both the PLGA-coated β-TCP and the β-TCP. These results suggest a new strategy for fabricating interconnected macroporous scaffolds with significantly enhanced mechanical strength for potential load-bearing bone tissue regeneration. 相似文献
905.
He‐Shui Yu Peng Zou Xin‐Bo Song Li‐Ping Kang Yi‐Xun Liu Xu Pang Jie Zhang Jing Fu Yang Zhao Cheng‐Qi Xiong Da‐Wei Tan Li‐Juan Zhang Bai‐Ping Ma 《Helvetica chimica acta》2011,94(7):1351-1358
A new furostanol saponin, sisalasaponin C ( 1 ), and a new spirostanol saponin, sisalasaponin D ( 2 ), were isolated from the fresh leaves of Agave sisalana, along with three other known steroidal saponins and two stilbenes. Their structures were identified as (3β,5α,6α,22α,25R)‐3,26‐bis[(β‐D ‐glucopyrano‐ syl)oxy]‐22‐hydroxyfurostan‐6‐yl β‐D ‐glucopyranoside ( 1 ), (3β,5α,25R)‐12‐oxospirostan‐3‐yl 6‐deoxy‐α‐L ‐mannopyranosyl‐(1→4)‐β‐D ‐glucopyranosyl‐(1→3)‐[β‐D ‐xylopyranosyl‐(1→3)‐β‐D ‐glucopyranosyl‐(1→2)]‐β‐D ‐glucopyranosyl‐(1→4)‐β‐D ‐galactopyranoside ( 2 ), (3β,5α,6α,22α,25R)‐22‐methoxyfurostane‐3,6,26‐triyl tris‐β‐D ‐glucopyranoside, cantalasaponin‐1, polianthoside D, (E)‐ and (Z)‐2,3,4′,5‐tetrahydroxystilbene 2‐O‐β‐D ‐glucopyranosides. The last three known compounds were isolated from the fresh leaves of Agavaceae for the first time. The structures of the new compounds were elucidated by detailed spectroscopic analysis, including 1D‐ and 2D‐NMR experiments, and chemical techniques. 相似文献
906.
907.
He X Liu Y Li H Huang H Liu J Kang Z Lee ST 《Journal of colloid and interface science》2011,356(1):107-110
Fe(3)O(4)/carbon nanocomposite has been prepared by a facile chemical method, and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, fourier transform infrared spectroscopy and scanning electron microscopy. The fluorescent and magnetic properties of the sample were investigated by fluorescence spectroscopy and vibrating-sample magnetometer, respectively. The results indicate that the Fe(3)O(4)/carbon nanocomposite exhibit good photoluminescent (emission ranging from 425 to 550 nm) and strong magnetic (saturation magnetization of 44.2 emu/g) properties. 相似文献
908.
Alata I Broquier M Dedonder-Lardeux C Jouvet C Kim M Sohn WY Kim SS Kang H Schütz M Patzer A Dopfer O 《The Journal of chemical physics》2011,134(7):074307
Vibrational and electronic spectra of protonated naphthalene (NaphH(+)) microsolvated by one and two water molecules were obtained by photofragmentation spectroscopy. The IR spectrum of the monohydrated species is consistent with a structure with the proton located on the aromatic molecule, NaphH(+)-H(2)O. Similar to isolated NaphH(+), the first electronic transition of NaphH(+)-H(2)O (S(1)) occurs in the visible range near 500 nm. The doubly hydrated species lacks any absorption in the visible range (420-600 nm) but absorbs in the UV range, similar to neutral Naph. This observation is consistent with a structure, in which the proton is located on the water moiety, Naph-(H(2)O)(2)H(+). Ab initio calculations for [Naph-(H(2)O)(n)]H(+) confirm that the excess proton transfers from Naph to the solvent cluster upon attachment of the second water molecule. 相似文献
909.
Lee PH Mo J Kang D Eom D Park C Lee CH Jung YM Hwang H 《The Journal of organic chemistry》2011,76(1):312-315
Pd-catalyzed cross-coupling reactions of aryl iodides containing not only an electron-donating group but also an electron-withdrawing group on the aryl ring with organoindium reagents generated in situ from indium and ethyl 4-bromo-2-alkynoates produced selectively ethyl 2-aryl-2,3-alkadienoates in good yield. 相似文献
910.