全文获取类型
收费全文 | 1333篇 |
免费 | 61篇 |
国内免费 | 31篇 |
专业分类
化学 | 1034篇 |
晶体学 | 17篇 |
力学 | 39篇 |
综合类 | 1篇 |
数学 | 109篇 |
物理学 | 225篇 |
出版年
2024年 | 11篇 |
2023年 | 13篇 |
2022年 | 50篇 |
2021年 | 88篇 |
2020年 | 58篇 |
2019年 | 47篇 |
2018年 | 56篇 |
2017年 | 37篇 |
2016年 | 56篇 |
2015年 | 42篇 |
2014年 | 55篇 |
2013年 | 93篇 |
2012年 | 99篇 |
2011年 | 102篇 |
2010年 | 61篇 |
2009年 | 47篇 |
2008年 | 57篇 |
2007年 | 61篇 |
2006年 | 54篇 |
2005年 | 53篇 |
2004年 | 35篇 |
2003年 | 31篇 |
2002年 | 23篇 |
2001年 | 9篇 |
2000年 | 6篇 |
1999年 | 11篇 |
1998年 | 6篇 |
1997年 | 14篇 |
1996年 | 17篇 |
1995年 | 7篇 |
1994年 | 6篇 |
1993年 | 11篇 |
1992年 | 3篇 |
1991年 | 5篇 |
1989年 | 3篇 |
1987年 | 3篇 |
1985年 | 5篇 |
1984年 | 14篇 |
1983年 | 3篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 5篇 |
1975年 | 7篇 |
1974年 | 3篇 |
1973年 | 5篇 |
1972年 | 8篇 |
排序方式: 共有1425条查询结果,搜索用时 15 毫秒
141.
Fatemeh KhaleghiLaily Bin Din Ibrahim JantanWan Ahmad Yaacob Mohammad A. Khalilzadeh 《Tetrahedron letters》2011,52(52):7182-7184
An efficient and simple synthesis of 1,4-benzoxazepin-2-one derivatives has been achieved via the reaction of isoquinoline, activated acetylenes, and 1-(6-hydroxy-2-isopropenyl-1-benzofuran-yl)-1-ethanone in water without using any catalyst. This one-pot reaction occurs in high yields under mild conditions. 相似文献
142.
Syed Qaiser Shah Muhammad Rafiullah Khan 《Journal of Radioanalytical and Nuclear Chemistry》2011,288(2):423-428
In the present study synthesis of the 99mTc?CCNN complex and its efficacy as a prospective Staphylococcus aureus (S. aureus) infection imaging agent was assessed. The 99mTc?CCNN complex was characterized in terms of stability in saline, serum, in vitro binding with S. aureus and in vivo percent absorption in male Wister rats (MWR) infected with live and heat killed S. aureus. Radiochemically the 99mTc?CCNN complex showed stable behavior in saline and serum at different intervals. At 30 min after reconstitution the complex showed maximum radiochemical purity (RCP) yield of 97.55 ± 0.22%. The RCP yield decreased to 90.50 ± 0.18% within 240 min. In serum, 18.15% unwanted side product was appeared within 16 h of the incubation. In vitro saturated binding with S. aureus was observed at different intervals with a 62.00% maximum at 90 min. Normal percent in vivo uptake was observed in MWR artificially infected with live S. aureus with a five times higher in the infected muscle as compared to the inflamed and normal muscles. No difference in the percent uptake of the complex in MWR infected with heat killed S. aureus in the infected, inflamed and normal muscles were observed. Based on the promising in vitro and in vivo radiochemical and biological characteristics, we recommend the 99mTc?CCNN complex for in vivo localization of the S. aureus infectious foci. 相似文献
143.
Syed?Qaiser?ShahEmail author Muhammad?Rafiullah?Khan 《Journal of Radioanalytical and Nuclear Chemistry》2011,288(1):307-312
In the current investigation complexation of the gemifloxacin (GIN) with technetium-99 m (99mTc) and its biological evaluation in artificially Streptococcus pneumoniae (S. pneumoniae) infected rats was assessed as potential S. pneumoniae infection radiotracer. Radiochemically the 99mTc-GIN complex was further analyzed in terms of stability in saline, in vitro stability in serum at 37 °C, in vitro binding with S. pneumoniae and biodistribution in artificially S. pneumoniae (living and heat killed) infected rats. The complex was found 97.25 ± 0.25% radiochemically stable in saline at 30 min after reconstitution. The stability of the 99mTc-GIN complex was decreased to 90.50 ± 0.20% within 240 min after reconstitution. In serum the 99mTc-GIN complex showed stable profile with the appearance of 18.85% free tracer within 16 h of incubation. The 99mTc-GIN complex showed saturated in vitro binding with S. pneumoniae after different intervals. Almost five fold uptake was observed in living S. pneumoniae infected muscle of the rats as compared to the inflamed and normal muscle. No significant difference in the uptake of heat killed S. pneumoniae infected, inflamed and normal muscles of the rats. The high RCP yield in saline, in vitro permanence in serum, in vitro binding with living S. pneumoniae and biodistribution in artificially S. pneumoniae infected rats we recommend the 99mTc-GIN as potential S. pneumoniae infection radiotracer. 相似文献
144.
145.
Prabhakar K Afzal SM Kumar PU Rajanna A Kishan V 《Colloids and surfaces. B, Biointerfaces》2011,86(2):305-313
Indinavir, an antiretroviral protease inhibitor used in treatment of HIV infection has limited penetration into brain due to efflux of P-glycoprotein. The aim of this work was to develop transferrin coupled submicron lipid emulsions (SLEs) containing indinavir for delivery to brain. Stearylamine containing SLEs were prepared, characterized, tested for stability and optimized formulation (SLE-4) was developed. Transferrin was coupled to get SLE-6 by water soluble EDC method and purified by gel filtration. The coupled transferrin was quantified by modified Bradford dye assay method. The fluorescent dye (DiD oil) incorporated SLEs were used to check the brain specific delivery of SLEs. The in vivo pharmacokinetic and tissue distribution were conducted in mice. During pharmacokinetic studies, there was no significant difference in the serum levels of indinavir from SLE-1, SLE-4 and SLE-6 formulations at all time points. In tissue distribution studies the therapeutic availability (TA) of indinavir in brain from SLE-6 was 4.69, 3.1 and 1.7 times higher than drug solution, SLE-1 and SLE-4 respectively whereas, the TA of indinavir from SLE-4 was 2.76 and 1.82 times the drug solution and SLE-1. The brain to serum ratios with SLE-6 were above one indicates the brain specific delivery. The brain delivery of indinavir was improved with transferrin ligand attachment to SLEs by receptor mediated transcytosis. 相似文献
146.
Mujtaba SF Dwivedi A Mudiam MK Ali D Yadav N Ray RS 《Photochemistry and photobiology》2011,87(5):1067-1076
The aim of this study was to analyze the photostability and phototoxicity mechanism of anthracene (ANT) in a human skin epidermal cell line (HaCaT) at ambient environmental intensities of sunlight/UV‐R (UV‐A and UV‐B). Photomodification of ANT under sunlight/UV‐R exposure produced two photoproducts, anthrone and 9,10 anthracenedione. Generation of 1O2, O2?? and ?OH was measured under UV‐R/sunlight exposure. Involvement of reactive oxygen species (ROS) was further substantiated by their quenching with free radical quenchers. Photodegradation of 2‐deoxyguanosine and linoleic acid peroxidation showed that ROS were mainly responsible for ANT phototoxicity. ANT generates significant amount of intracellular ROS in cell line. Maximum cell viability (85%) was reduced under sunlight exposure (30 min). Results of MTT assay accord NRU assay. ANT (0.01 μg mL?1) induced cell‐cycle arrest at G1 phase. RT‐PCR demonstrated constitutive inducible mRNA expression of CYP 1A1 and 1B1 genes. Photosensitive ANT upregulates CYP 1A1 (2.2‐folds) and 1B1 (4.1‐folds) genes. Thus, the study suggests that ROS and DNA damage were mainly responsible for ANT phototoxicity. ANT exposure may be deleterious to human health at ambient environmental intensities reaching the earth’s surface through sunlight. 相似文献
147.
Faraji Hakim Saber-Tehrani Mohamad Mirzaie Afshin Waqif-Husain Syed 《平面色谱法杂志一现代薄层色谱法》2011,24(3):214-217
JPC – Journal of Planar Chromatography – Modern TLC - A novel liquid-phase microextraction method coupled with high-performance thin-layer chromatography (HPTLC) for preconcentration,... 相似文献
148.
The effect of the interior structure of carbon nanomaterials on their electrochemical properties is not well understood. We report here the electron transfer rate (ETR) of ferrocene (Fc) molecules covalently attached to the exposed end of carbon nanofibers (CNFs) in an embedded nanoelectrode array. The ETR in normal DC voltammetry was found to be limited by the conical graphitic stacking structure interior of CNFs. AC voltammetry, however, can cope with this intrinsic materials property and provide over 100 times higher ETR, likely by a new capacitive pathway. This provides a new method for high‐performance electroanalysis using CNF nanoelectrodes. 相似文献
149.
Syed SU Sreekumar J Gibson JR Taylor S 《Journal of the American Society for Mass Spectrometry》2011,22(8):1381-1387
We report here a study using a quadrupole mass spectrometer (QMS) in which a static magnetic field is applied transversely
to the body of the mass filter operating in stability zone 3. Significant improvement in QMS performance was obtained under
certain magnetic field conditions, and these have been explained in terms of our theoretical model. The theoretical approach
assumed in the model is that the QMS contains hyperbolic rods as electrodes and that the magnetic field acts over the full
length of the mass filter assembly. Our latest analysis also predicts for what values of operating parameters an enhancement
of the quadrupole resolution is achieved when a transverse magnetic field is applied. The model predicts instrument resolution
R > 5000 for Ar with a 100 mm long mass filter and R > 3500 for a HT and D2 mixture with a 200 mm long mass filter via application of a transverse magnetic field. 相似文献
150.
A validated spectrophotometric method has been developed for the determination of uranyl ion in soil samples. The method is based on the complexation reaction between uranyl ion and rifampicin in methanol‐water medium at room temperature. The method is followed spectrophotometrically by measuring the absorbance at 375 nm. Under the optimized experimental conditions, Beer's law is obeyed in the concentration range of 1.35–20.25 μg mL‐1 with apparent molar absorptivity and Sandell's sensitivity of 8.0 × 103 L mol‐1cm‐1 and 0.042 μg/cm2/0.001 absorbance unit, respectively. The interference of a large number of anions and cations has been investigated and the optimized conditions developed have been utilized for the determination of uranium(VI) in soil samples. The three sigma detection limit (n = 9) for uranyl ion was found to be 0.20 μg mL‐1. The proposed method was successfully applied to the determination of uranyl ion in soil samples. 相似文献