全文获取类型
收费全文 | 364篇 |
免费 | 19篇 |
国内免费 | 1篇 |
专业分类
化学 | 218篇 |
晶体学 | 6篇 |
力学 | 10篇 |
数学 | 65篇 |
物理学 | 85篇 |
出版年
2023年 | 1篇 |
2022年 | 6篇 |
2021年 | 14篇 |
2020年 | 14篇 |
2019年 | 20篇 |
2018年 | 10篇 |
2017年 | 11篇 |
2016年 | 21篇 |
2015年 | 16篇 |
2014年 | 20篇 |
2013年 | 37篇 |
2012年 | 28篇 |
2011年 | 42篇 |
2010年 | 23篇 |
2009年 | 19篇 |
2008年 | 21篇 |
2007年 | 18篇 |
2006年 | 14篇 |
2005年 | 4篇 |
2004年 | 6篇 |
2003年 | 7篇 |
2002年 | 7篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1998年 | 2篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1987年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1967年 | 1篇 |
1966年 | 1篇 |
1963年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有384条查询结果,搜索用时 797 毫秒
261.
A mixture of bis‐benzimidazole salts ( 1–7 ), Pd(OAc)2 and K2CO3 in DMF ? H2O catalyzes, in high yield, the Suzuki and Heck cross‐coupling reactions assisted by microwave irradiation in a short time. In particular, the yields of the Heck and Suzuki reactions with aryl bromides were found to be nearly quantative. The synthesized bis‐benzimidazole salts ( 1 – 7 ) were identified by 1H? 13C NMR, IR spectroscopic methods and micro analysis. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
262.
A series of rigid and chiral C2-symmetric 18-crown-6 type macrocycles (S,S)-4, (S,S)-5, (S,S)-6 and (R,R)-2 bearing diamide–ester groups were synthesized. The binding properties of these macrocycles were examined for α-(1-naphthyl)ethylammonium perchlorates salts by an 1H NMR titration method. Taking into account the host employed, important differences were observed in the Ka values of (R)- and (S)-enantiomers of guests for macrocycles (S,S)-4 and (S,S)-6, KS/KR = 3.6, and KS/KR = 0.1 (KR/KS = 10.3) ΔΔG = 3.19 and ΔΔG = ?5.77 kJ mol?1, respectively. The results indicated excellent enantioselectivity of macrocyclic (S,S)-6 towards the enantiomers of α-(1-naphthyl)ethylammonium perchlorate salts. 相似文献
263.
Bekkerman A Kolodney E von Helden G Sartakov B van Heijnsbergen D Meijer G 《The Journal of chemical physics》2006,124(18):184312
We address, both experimentally and theoretically, the issue of infrared (IR) resonance enhanced multiphoton ionization (IR-REMPI) and thermally induced redshifts of IR absorption lines in a very large and highly vibrationally excited molecular system. Isolated superhot C60 molecules with well defined and variable average vibrational energy in the range of 9-19 eV, effusing out of a constant flux thermal source, are excited and ionized after the absorption of multiple (500-800) infrared photons in the 450-1800 cm(-1) spectral energy range. Recording the mass-selected ion signal as a function of IR wavelength gives well resolved IR-REMPI spectra, with zero off-resonance background signal. An enhancement of the ion signal of about a factor of 10 is observed when the temperature is increased from 1200 to 1800 K under otherwise identical conditions. A pronounced temperature dependent redshift of some of the IR absorption lines is observed. The observations are found to be in good agreement with a model which is based on the sequential absorption of single photons, always followed by instantaneous vibrational energy redistribution. The mass spectra (C60(+) fragmentation pattern) are found to be strongly excitation wavelength dependent. Extensive fragmentation down to C32(+) is observed following the absorption of 1350-1400 cm(-1) as well as 1500-1530 cm(-1) photons while negligible fragmentation is observed when exciting around 520 cm(-1). 相似文献
264.
Gulsoy M Ozer GH Bozkulak O Tabakoglu HO Aktas E Deniz G Ertan C 《Journal of photochemistry and photobiology. B, Biology》2006,82(3):199-202
The aim of this study was to examine the proliferation of peripheral blood mononuclear cells due to the low energy 632.8-nm He-Ne laser application. The results of previous studies supported the hypothesis that low level laser therapy (LLLT) might have an increasing effect on the proliferation of lymphocytes and production of cytokines. The effect of laser irradiation was investigated by comparing the proliferation of peripheral blood mononuclear cells (PBMC) with a mitogenic stimulator, PHA (phytohemaglutinin) and laser irradiation. PBMCs of control samples, only laser irradiated samples, PHA included samples and both PHA included and laser irradiated samples were quantified and compared. Results of [3H] Thymidine test, 20 s laser irradiated and 40 s laser irradiated samples' proliferation were found statistically higher than control samples. There was no significant difference between control and 60 s laser irradiated samples. PHA also showed its ability to proliferate cells. PHA included samples and both PHA included and laser irradiated samples' proliferation was higher than both control and only laser irradiated samples. Our results showed that He-Ne laser application enhanced the proliferation significantly. Moreover, laser dose was noted as a significant parameter. On the other hand, LLLT by itself was found less effective than PHA. 相似文献
265.
In 2020, the world tried to combat the corona virus (COVID-19) pandemic. A proven treatment method specific to Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) is still not found. In this study, seven new antiviral compounds were designed for COVID-19 treatment. The ability of these compounds to inhibit COVID-19’s RNA processing was calculated by the molecular docking study. It has been observed that the compounds can have high binding affinities especially against NSP12 (between -9.06 and -8.00 kcal/mol). The molecular dynamics simulation of NSP12-ZG 7 complex proved the stability of interaction. The synthesis of two most active molecules was performed by one-pot reaction and characterized by FT-IR, 1H-NMR, 13C-NMR, and mass spectroscopy. The compounds presented with their synthesis are inhibitory core structures against SARS-CoV-2 infection. 相似文献
266.
A wide range of products are produced in the chemical producing industry such as textile dyes, chemicals, printing dyes and chemicals, paper chemicals, electrostatic powder dyes, and optical brighteners. The aim of this study is to investigate the treatability of chemical oxygen demand (COD), aromaticity, and color in the wastewater of this sector, where highly complex chemicals are used. Most of the studies in the literature are related to the treatment of synthetically prepared dyed wastewater. This study is important as it is carried out with real wastewater and gives results of many treatment methods. In the study, COD, UV-vis absorbance, and color values were attempted to be removed from the wastewater of a chemical producing industry that was pretreated by coagulation-flocculation. The COD value of the pretreated wastewater discharged to the central treatment system was restricted as 1000 mg/L. Pretreated wastewater characterization is as follows: COD: 2117 mg/L, UV-vis absorbance values at; 254 nm: 9.91, 280 nm: 8.65, 341 nm: 12.77, 436 nm: 5.01, 525 nm: 2.24, and 620 nm: 1.59. In the study, adsorption, ozonation, and advanced oxidation processes (Fenton and persulfate oxidation) were used to remove COD and UV-vis absorbance values (aromaticity, organics, and color). The method by which the best removal efficiency was obtained for all parameters was the adsorption process using powdered activated carbon (PAC). The equilibrium PAC dose was found as 6 g/L. At this adsorbent dose, the removal efficiencies of UV-vis absorbance values were all around 99% and the efficiency of COD removal was 77%. The Langmuir isotherm constants were found to be qmax= 30.4 mg/g and KL = 487.9 (L/mg). The COD concentration at this adsorbent dose was 486 mg/L and wastewater was suitable for discharge to the central wastewater treatment plant in that region. 相似文献
267.
Photocurrent generation from CdSe/ZnS (core/shell) quantum dots (QDs) in a photoelectrochemical cell was proposed to perform a bioaffinity biosensor in this study. The photocurrent of QDs is reversible and methylene blue as an electron transfer mediator causes a four‐fold increase in the photocurrent. We further present quantitative photoelectrochemical detection of biotin conjugated QDs on the avidin immobilized ITO electrodes. A linear calibration graph was obtained in the range of 4 and 18 nM of biotin conjugated QDs with a coefficient of determination of 0.997. Results imply that QDs can be successfully used as photoelectroactive labels for the photoelectrochemical biosensor systems. 相似文献
268.
Ibrahim H. Mutlu Maharram Z. Zarbaliyev Ferhat Aslan 《Journal of Sol-Gel Science and Technology》2009,50(3):271-274
In this study we describe the preparation of Ga2Se3 semiconductor compound thin films by sol–gel method for different crystal formation temperatures. The films were characterized
by X-ray diffraction analyses (XRD), UV–visible spectrometer, and scanning electron microscope (SEM). The XRD spectrum showed
that the formation of Ga2Se3 crystals were between 743 and 823 K. The thin film crystals that were formed at 773 K corresponded to the β phase and the
preferred crystal structure was monoclinic. The value of band gap from optical absorption spectra for the Ga2Se3 thin films was estimated to be about E
g ~ 2.56 eV. The thickness of the one-coat Ga2Se3 thin films, which was measured by a Spectroscopic Ellipsometer, was about ~200 nm. The average grain sizes of scattered particles
were within the limits between 200 and 500 nm. 相似文献
269.
270.
Başkent D 《The Journal of the Acoustical Society of America》2010,128(4):EL169-EL174
The brain can restore missing speech segments using linguistic knowledge and context. The phonemic restoration effect is commonly quantified by the increase in intelligibility of interrupted speech when the silent gaps are filled with noise bursts. In normal hearing, the restoration effect is negatively correlated with the baseline scores with interrupted speech; listeners with poorer baseline show more benefit from restoration. Reanalyzing data from Bas?kent et al. [(2010). Hear. Res. 260, 54-62], correlations with mild and moderate hearing impairment were observed to differ than with normal hearing. This analysis further shows that hearing impairment may affect top-down restoration of speech. 相似文献