全文获取类型
收费全文 | 1950篇 |
免费 | 118篇 |
国内免费 | 9篇 |
专业分类
化学 | 1542篇 |
晶体学 | 19篇 |
力学 | 41篇 |
数学 | 146篇 |
物理学 | 329篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 27篇 |
2021年 | 43篇 |
2020年 | 36篇 |
2019年 | 43篇 |
2018年 | 32篇 |
2017年 | 35篇 |
2016年 | 94篇 |
2015年 | 65篇 |
2014年 | 97篇 |
2013年 | 187篇 |
2012年 | 171篇 |
2011年 | 163篇 |
2010年 | 115篇 |
2009年 | 89篇 |
2008年 | 111篇 |
2007年 | 111篇 |
2006年 | 117篇 |
2005年 | 97篇 |
2004年 | 79篇 |
2003年 | 75篇 |
2002年 | 97篇 |
2001年 | 31篇 |
2000年 | 25篇 |
1999年 | 20篇 |
1998年 | 14篇 |
1997年 | 13篇 |
1996年 | 13篇 |
1995年 | 10篇 |
1994年 | 11篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 7篇 |
1990年 | 3篇 |
1989年 | 8篇 |
1988年 | 1篇 |
1987年 | 4篇 |
1986年 | 1篇 |
1985年 | 7篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有2077条查询结果,搜索用时 15 毫秒
941.
This infrared (IR) spectroscopic study addresses surfactant effects on cyclopentane (CP) hydrate-water interfaces by observing both ice-like (3100 cm(-1)) and water-like (3400 cm(-1)) bands in the bonded OH region together with free OH bands. IR spectroscopy of hydrates has not been actively employed due to the overwhelming signal saturation of the OH bonding. However, this work is able to utilize this large signal of the OH bonding to understand the water structure changes upon adding sodium dodecyl sulfate (SDS) to CP hydrate-water interfaces. The spectral data suggest a change to more ice like (3100 cm(-1)) features starting from 100 ppm to 750 ppm SDS, indicating favorable nucleation. At the same instance, water like (3400 cm(-1)) features are also shown in this range of SDS concentration, which suggests looser hydrogen bonding that is an indicator for facilitating hydrate growth. Additionally, this ATR-IR study firstly identifies both symmetric and anti-symmetric free OH bands of the hydrogen bond (HB) acceptors in the clathrate hydrate system. Relative area ratios of free and bonded OH bands provide important information about spatial arrangements of adsorbed SDS monomers. 相似文献
942.
Lee JC Francis S Dutta D Gupta V Yang Y Zhu JY Tash JS Schönbrunn E Georg GI 《The Journal of organic chemistry》2012,77(7):3082-3098
Eight- and four-membered analogues of N-butyldeoxynojirimycin (NB-DNJ), a reversible male contraceptive in mice, were prepared and tested. A chiral pool approach was used for the synthesis of the target compounds. Key steps for the synthesis of the eight-membered analogues involve ring-closing metathesis and Sharpless asymmetric dihydroxylation and for the four-membered analogues Sharpless epoxidation, epoxide ring-opening (azide), and Mitsunobu reaction to form the four-membered ring. (3S,4R,5S,6R,7R)-1-Nonylazocane-3,4,5,6,7-pentaol (6) was moderately active against rat-derived ceramide-specific glucosyltransferase, and four of the other eight-membered analogues were weakly active against rat-derived β-glucosidase 2. Among the four-membered analogues, ((2R,3S,4S)-3-hydroxy-1-nonylazetidine-2,4-diyl)dimethanol (25) displayed selective inhibitory activity against mouse-derived ceramide-specific glucosyltransferase and was about half as potent as NB-DNJ against the rat-derived enzyme. ((2S,4S)-3-Hydroxy-1-nonylazetidine-2,4-diyl)dimethanol (27) was found to be a selective inhibitor of β-glucosidase 2, with potency similar to NB-DNJ. Additional glycosidase assays were performed to identify potential other therapeutic applications. The eight-membered iminosugars exhibited specificity for almond-derived β-glucosidase, and the 1-nonylazetidine 25 inhibited α-glucosidase (Saccharomyces cerevisiae) with an IC(50) of 600 nM and β-glucosidase (almond) with an IC(50) of 20 μM. Only N-nonyl derivatives were active, emphasizing the importance of a long lipophilic side chain for inhibitory activity of the analogues studied. 相似文献
943.
Lee SW Kim IJ Jeong BY Choi MH Kim JY Kwon KH Lee JW Yu A Shin MG 《Electrophoresis》2012,33(12):1863-1872
The response criteria for complete remission (CR) in acute myeloid leukemia (AML) are currently based on morphology and blood cell counts. However, these criteria are insufficient to establish a diagnosis in cases with poor quality bone marrow (BM) samples demonstrating a loss of cellular morphology. We investigated whether the sera of patients contained biomarkers that indicate disease response status. First, we performed multidimensional liquid chromatography-differential gel electrophoresis (MDLC-DIGE) to generate protein profiles of two pooled, paired serum samples from patients who had achieved CR; one collected at diagnosis (PreCR) and the other collected after chemotherapy (CR). Then, with the biomarker candidates found, ELISA was carried out for individual PreCR and CR samples, and for other verification sets including nonremission (NR) patients and normal samples. We selected two proteins, complement factor H (CFH) and apolipoprotein H (ApoH), with dye (Cy) ratios showing greater than 2.0-fold differences between the pooled samples. ELISA showed that CFH and ApoH are useful for distinguishing between the recovered (CR and normal) and nonrecovered (PreCR, PreNR, and NR) states in AML (p <0.001). We successfully applied a protein profiling technology of MDLC-DIGE and LC-MS/MS to discover two biomarkers for CR which needs further validation for a clinical setting. 相似文献
944.
Hong YH Jung EY Shin KS Kim TY Yu KW Chang UJ Suh HJ 《Applied biochemistry and biotechnology》2012,166(1):165-175
Ultraviolet B (UVB) irradiation may induce the acceleration of skin aging. The purpose of this study was to develop an effective
formulation containing tannase-converted green tea extract (FTGE) to inhibit UVB-induced oxidative damage. Significant (p < 0.05) prevention of the reduced form of glutathione (GSH) depletion was observed in mice treated with FTGE. The hydrogen
peroxide levels of mice treated with FTGE were similar to those of UVB non-irradiated mice. No significant difference was
observed between No UVB control and FTGE mice. Also, mice treated with FTGE had significant (p < 0.05) decreases in thiobarbituric acid-reactive substance levels by lipid peroxidation compared with No UVB control mice.
Our data suggest that this formulation may be effective in protecting skin from UVB photodamage. 相似文献
945.
Farzana Ahmad Muhammad Jamil Lee Jin Woo Young Jae Jeon 《Colloid and polymer science》2012,290(7):599-606
Acrylic polyethylene glycol(PEG)-based polymer-dispersed liquid crystal (PDLC) films have been fabricated to investigate the
effect of intermolecular interactions on PDLC performance. For this purpose, the amphiphilic liquid crystal and polymers are
selected as PDLC composite materials. The acrylic PEG contents are varied from 0 to 66.66 mol wt.% in order to understand
the effects of different levels of additions on the microstructure and electro-optical properties of the PDLC films. For this
intention, polarized optical microscopy and UV–vis spectroscopy are used. The extent of phase separation and anchoring energy
are also examined using Fourier transform infrared (FTIR) spectroscopy and contact angle measurements in consequence of acrylic
PEG addition. The contrast ratio, threshold voltage, as well as saturation voltage, tended to increase with the addition of
acrylic PEG. The molecular affinity involved in the polymer matrix and LC molecules affected the phase separation which is
responsible for the formation of domain size; this accordingly changed the electro-optical properties of PDLC film. 相似文献
946.
Kwon K Sa YJ Cheon JY Joo SH 《Langmuir : the ACS journal of surfaces and colloids》2012,28(1):991-996
Developments of high-performance cost-effective electrocatalyts that can replace Pt catalysts have been a central theme in polymer electrolyte membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs). In this direction, nitrogen-doped carbon nanostructures free of metallic components have attracted particular attention. Here we show that directing graphitic carbon nitride frameworks into mesoporous architecture can generate a highly promising metal-free electrocatalyst for an oxygen reduction reaction (ORR) in an acidic medium. The ordered mesoporous carbon nitride (OMCN) was synthesized with a nanocasting strategy using ordered mesoporous silica as a template. A variety of characterizations revealed that the OMCN is constructed with graphitic carbon nitride frameworks and ordered arrays of uniform mesopores. The OMCN showed significantly enhanced electrocatalytic activity for ORR compared to bulk carbon nitride and ordered mesoporous carbon in terms of the current density and onset potential. A high surface area and an increased density of catalytically active nitrogen groups in the OMCN appear to contribute concomitantly to the enhanced performance of the OMCN. Furthermore, the OMCN exhibited superior durability and methanol tolerance to a Pt/C catalyst, suggesting its widespread utilization as an electrocatalyst for PEMFCs and DMFCs. 相似文献
947.
Lee DJ Cho KY Jang S Song YS Youn JR 《Langmuir : the ACS journal of surfaces and colloids》2012,28(28):10488-10494
We explored a liquid slip, referred to as the Navier slip, at liquid-solid interface. Such a slip is provoked by the physicochemical features of the liquid-solid system. The goal of this study was to investigate the effect of a nanoengineered surface structure on liquid slip by fabricating the self-assembly structure of nano Zinc oxide (n-ZnO). We have also examined how the liquid-solid surface interaction controlled by hydrophobic chemical treatment affects the liquid slip. The findings showed that liquid slip increases with decreasing the characteristic length scales (e.g., channel height and depth), resulting in drag reduction. It was also found that dewetted (Cassie) state due to the generation of air gap developed by n-ZnO was more critical for the liquid slip than the minimization of interface interaction. The linear and nonlinear Navier slip models showed that liquid slip behavior is more obvious when increasing the nonlinearity. This study will contribute to understanding of the underlying physics behind fluid slip phenomena, such as the Navier slip for Newtonian liquids and Maxwell's slip for Newtonian gases. 相似文献
948.
Lee SJ An HH Han WB Kim HS Yoon CS 《Langmuir : the ACS journal of surfaces and colloids》2012,28(30):10980-10987
Coarsening behavior of the Au nanoparticles produced by thermal evaporation of Au onto a liquid crystalline lipid (1,2-dioleoyl-3-trimethylammonium-propane, DOTAP) membrane was investigated by subjecting the nanoparticle-embedded DOTAP membrane to two different annealing conditions (at 100 °C under no humidity and at 20 °C and 80% relative humidity). Although the coarsening rate was relatively slow because of the low temperature (from 5.6 nm in the as-deposited state to ~7 nm after 30 h), it was identified that at 100 °C without humidity the Au nanoparticles resulted in shape refinement whereas the high humidity at 20 °C induced self-organization of the nanoparticles into a monolayer. It was also found that annealing in both cases tended to segregate the lipid molecules from the nanoparticle array and forced the nanoparticles into a tighter area. In the case of the high-humidity sample, the lipid segregation eventually led to extensive coalescence of the Au nanoparticles. 相似文献
949.
Seung-Chan Baek Ki-Won Jun Yun-Jo Lee Jae Dong Kim Dal Young Park Kwan-Young Lee 《Research on Chemical Intermediates》2012,38(6):1225-1236
The effects of Ru on the self-reducibility of Ru-doped Ni/MgAl2O4 catalysts, which do not need pre-reduction treatment with H2, were investigated in the steam reforming of methane (SRM). The Ru-promoted Ni/MgAl2O4 catalysts with various amounts of Ru (0–0.5 wt%) were prepared by stepwise impregnation and co-impregnation methods using
hydrotalcite-like MgAl2O4 support. For comparison, Ru/MgAl2O4 catalysts with the same amount of Ru were also prepared by the impregnation method. The catalysts were characterized by the
N2-sorption, XRD, H2-TPR, H2-chemisorption, and XPS methods. Ni/MgAl2O4 catalyst in the presence of even the trace amount of Ru (Ru content ≥0.05 wt%) showed higher conversion without pre-reduction
as compared to Ru/MgAl2O4 catalysts in SRM under the same conditions. The self-activation of Ru–Ni/MgAl2O4 catalysts is mainly attributed to the spillover of hydrogen, which is produced on Ru at first and then reduces NiO species
under reaction conditions. Besides, Ru doping makes the reduction of NiO easier. The stepwise impregnated Ru/Ni/MgAl2O4 catalyst produced superior performance as compared to co-impregnated Ru–Ni/MgAl2O4 catalyst for SRM. 相似文献
950.
Jong-il Choi Yong Jae Chung Dai Ill Kang Kyu Shik Lee Ju-Woon Lee 《Radiation Physics and Chemistry》2012,81(8):1051-1054
Fumigants, including methyl bromide and ethylene oxide, are generally used for the preservation of the Korean cultural heritage, especially paper products like letters and books. However, the use of fumigants is banned because of their harmful effects on humans and the environment. Gamma irradiation is being considered as an alternative for the sterilization of insects and fungi in organic products. Therefore, the purpose of this study was to investigate the sterilization effects of radiation and its effect on the mechanical properties of the Korean traditional paper—Hanji. Treatment doses of 9 kGy and 8 kGy of gamma irradiation inactivated 5 log units of Aspergillus niger and Bacillus cereus spores inoculated on Hanji, respectively. The gamma irradiations up to an absorbed dose of 50 kGy resulted in no significant changes in the tensile strength, bursting strength, and appearance of Hanji. These results confirmed that radiation treatment disinfects the Korean traditional paper efficiently without changing its properties and that this treatment could be used to prevent the damage of Korean ancient archives by molds and fungi. 相似文献