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排序方式: 共有350条查询结果,搜索用时 62 毫秒
61.
J. Choi S.‐Y. Kwak S. Kang S.‐S. Lee M. Park S. Lim J. Kim C. R. Choe S. I. Hong 《Journal of polymer science. Part A, Polymer chemistry》2002,40(23):4368-4377
Monodisperse polystyrene particles crosslinked with different concentrations of divinylbenzene were synthesized in the 3.2–9.1 μm size range by dispersion polymerization in an isopropyl alcohol/toluene mixed‐dispersion medium with poly(N‐vinylpyrrolidone) as a steric stabilizer and 2,2′‐azobisisobutyronitrile as a radical initiator. The effects of the reaction parameters such as the crosslinking agent concentration, media solvency (controlled by varying the amount of toluene addition), the initiator concentration, and the stabilizer concentration on the particle size and size distribution were investigated with reference particles with a monodisperse size distribution and crosslinked by 1.5 wt % divinylbenzene. The appropriate increase in media solvency was a prerequisite for preparing crosslinked particles without coagulated and/or odd‐shaped particles. The investigation of the effects of the polymerization parameters also shows that only specific sets of conditions produce particles with a monodisperse size distribution. The glass‐transition temperatures of the particles increased with increasing divinylbenzene concentration. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4368–4377, 2002 相似文献
62.
Cobalt(II) meso-tetraphenylporphyrin (CoTPP)/acrylate hybrid thin films were prepared by CoTPP sublimation and reactive monomer evaporation onto the glass substrate in vacuum conditions. Deposited CoTPP/acrylate thin films were in situ photopolymerized. The oxygen-uptake behaviors of CoTPP/acrylate films were investigated by means of sorption measurements, monitored by gravimetric means, and analyzed using dual mode sorption model. The loading percent of CoTPP in the film was adjusted up to 60% by controlling the CoTPP sublimation rate. The thickness of the CoTPP/acrylate hybrid film was about 200 nm and oxygen-uptake data obtained from the sorption measurements indicated that CoTPP molecules in the CoTPP/acrylate hybrid films were able to bind oxygen molecules reversibly. 相似文献
63.
Myunghun Kim Chang Kook Hong Soona Choe Sang Eun Shim 《Journal of polymer science. Part A, Polymer chemistry》2007,45(19):4413-4420
Multiwalled carbon nanotubes (MWNTs) were effectively functionalized with KMnO4 in the presence of a phase‐transfer catalyst at room temperature. The hydroxyl functionalized MWNTs were reacted with a vinyl‐group carrying silane‐coupling agent and the terminal vinyl groups were used to fabricate polystyrene (PS) brushes by solution polymerization. Finally, PS‐encapsulated MWNTs were obtained. The synthesis results were verified from FT‐Raman, thermal gravimetric analysis, energy dispersive X‐ray analysis, and transmission electron microscope. PS‐encapsulated MWNTs had much improved dispersion stability in hydrophobic medium, toluene since grafted hydrophobic PS interacts with media and has improved compatibility. This functionalization technique would provide a facile route to prepare various polymer brushes on the surface of MWNTs to improve the dispersion of MWNTs for potential applications. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4413–4420, 2007 相似文献
64.
In general, this new equation is significant for designing and operating a pipeline to predict flow discharge. In order to predict the flow discharge, accurate determination of the flow loss due to pipe friction is very important. However, existing pipe friction coefficient equations have difficulties in obtaining key variables or those only applicable to pipes with specific conditions. Thus, this study develops a new equation for predicting pipe friction coefficients using statistically based entropy concepts, which are currently being used in various fields. The parameters in the proposed equation can be easily obtained and are easy to estimate. Existing formulas for calculating pipe friction coefficient requires the friction head loss and Reynolds number. Unlike existing formulas, the proposed equation only requires pipe specifications, entropy value and average velocity. The developed equation can predict the friction coefficient by using the well-known entropy, the mean velocity and the pipe specifications. The comparison results with the Nikuradse’s experimental data show that the R2 and RMSE values were 0.998 and 0.000366 in smooth pipe, and 0.979 to 0.994 or 0.000399 to 0.000436 in rough pipe, and the discrepancy ratio analysis results show that the accuracy of both results in smooth and rough pipes is very close to zero. The proposed equation will enable the easier estimation of flow rates. 相似文献
65.
S. Choe 《The European Physical Journal A - Hadrons and Nuclei》2000,7(3):441-448
In this work we report on a new QCD sum rule analysis to predict masses of the excited baryon states (e.g. Σ (1620) and Λ
(1405)) by using multiquark interpolating fields ((qˉq)(qqq)). For the Σ (1620) we consider the ˉKN, πΣ, and πΛ (I = 1) multiquark
interpolating fields. The calculated mass from those multiquark states is about 1.592 GeV. For the Λ (1405) we first show
the result using the π+Σ−+π0Σ0+π−Σ+ (I = 0) multiquark interpolating field, and compare the calculated mass to that of our previous result using the π0Σ0 multiquark state. We then show that the mass 1.405 GeV is well reproduced when using the ˉKN (I = 0) multiquark state. The
uncertainties in our sum rules are also discussed.
Received: 7 September 1998 / Revised version: 5 January 2000 相似文献
66.
Expression, High Cell Density Culture and Purification of Recombinant EC-SOD in Escherichia coli 总被引:1,自引:0,他引:1
Young-Jin Son Ji-Young Bae Seon-Ha Chong Hui Sun Lee Sang Hyun Mo Tae Yoon Kim Han Choe 《Applied biochemistry and biotechnology》2010,162(6):1585-1598
Superoxide dismutase (SOD) catalyzes the dismutation of the biologically toxic superoxide anion into oxygen and hydrogen peroxide and is deployed by the immune system to kill invading microorganisms. Extracellular SOD (EC-SOD) is a copper- and zinc-containing glycoprotein found predominantly in the soluble extracellular compartment that consists of ~30-kDa subunits. Here, we purified recombinant EC-SOD3 (rEC-SOD) from Escherichia coli BL21(DE3) expressing a pET-SOD3-1 construct. Cells were cultured by high-density fed-batch fermentation to a final OD600 of 51.8, yielding a final dry cell weight of 17.6 g/L. rEC-SOD, which was expressed as an inclusion body, comprised 48.7% of total protein. rEC-SOD was refolded by a simple dilution refolding method and purified by cation-exchange and reverse-phase chromatography. The highly purified rEC-SOD thus obtained was a mixture of monomers and dimers, both of which were active. The molecular weights of monomeric and dimeric rEC-SOD were 25,255 and 50,514 Da, respectively. The purified rEC-SOD had 4.3 EU/mg of endotoxin and the solubility of rEC-SOD was more than 80% between pH 7 and 10. In 2 L of fed-batch fermentation, 60 mg of EC-SOD (99.9% purity) could be produced and total activity was 330.24 U. The process established in this report, involving high-cell-density fermentation, simple dilution refolding, and purification with ion-exchange and reverse-phase chromatography, represents a commercially viable process for producing rEC-SOD. 相似文献
67.
Choi YO Ryu HJ Kim HR Song YS Kim C Lee W Choe H Leem CH Jang YJ 《Experimental & molecular medicine》2006,38(2):180-189
In adipocytes, insulin stimulates glucose transport primarily by promoting the translocation of GLUT4 to the plasma membrane. Requirements for Ca(2+)/calmodulin during insulin-stimulated GLUT4 translocation have been demonstrated; however, the mechanism of action of Ca(2+) in this process is unknown. Recently, myosin II, whose function in non-muscle cells is primarily regulated by phosphorylation of its regulatory light chain by the Ca(2+)/calmodulin-dependent myosin light chain kinase (MLCK), was implicated in insulin-stimulated GLUT4 translocation. The present studies in 3T3-F442A adipocytes demonstrate the novel finding that insulin significantly increases phosphorylation of the myosin II RLC in a Ca(2+)-dependent manner. In addition, ML-7, a selective inhibitor of MLCK, as well as inhibitors of myosin II, such as blebbistatin and 2,3-butanedione monoxime, block insulin-stimulated GLUT4 translocation and subsequent glucose transport. Our studies suggest that MLCK may be a regulatory target of Ca(2+)/calmodulin and may play an important role in insulin-stimulated glucose transport in adipocytes. 相似文献
68.
Rui Nian Duck Sang Kim Thuong Nguyen Lihan Tan Chan-Wha Kim Ik-Keun Yoo Woo-Seok Choe 《Journal of chromatography. A》2010,1217(38):5940-5949
Toxic heavy metal pollution is a global problem occurring in air, soil as well as water. There is a need for a more cost effective, renewable remediation technique, but most importantly, for a recovery method that is selective for one specific metal of concern. Phage display technology has been used as a powerful tool in the discovery of peptides capable of exhibiting specific affinity to various metals or metal ions. However, traditional phage display is mainly conducted in batch mode, resulting in only one equilibrium state hence low-efficiency selection. It is also unable to monitor the selection process in real time mode. In this study, phage display technique was incorporated with chromatography procedure with the use of a monolithic column, facilitating multiple phage-binding equilibrium states and online monitoring of the selection process in search of affinity peptides to Pb2+. In total, 17 candidate peptides were found and their specificity toward Pb2+ was further investigated with bead-based enzyme immunoassay (EIA). A highly specific Pb2+ binding peptide ThrAsnThrLeuSerAsnAsn (TNTLSNN) was obtained. Based on our knowledge, this is the first report on a new chromatographic biopanning method coupled with monolithic column for the selection of metal ion specific binding peptides. It is expected that this monolith-based chromatographic biopanning will provide a promising approach for a high throughput screening of affinity peptides cognitive of a wide range of target species. 相似文献
69.
One critical parameter influencing the structural nature of the phase transitions in magnetocaloric materials Gd5(SixGe(1-x))4 is the Si/Ge ratio (x/1-x), because transition temperatures and structures depend crucially on this value. In this study, single-crystal X-ray diffraction indicates that Si and Ge atoms are neither completely ordered nor randomly mixed among the three crystallographic sites for these elements in these structures. Ge atoms enrich the T sites linking the characteristic slabs in these structures, while Si atoms enrich the T sites within them. Decomposition of the total energy into site and bond energy terms provides a rationale for the observed distribution, which can be explained by symmetry and electronegativity arguments. For any composition in Gd5(SixGe(1-x))4, a structure map is presented that will allow for a rapid assessment of the specific structure type. 相似文献
70.
Dae-Won Park Na-Young Mun Eun-Ha Lee Youngson Choe Sang-Wook Park 《Reaction Kinetics and Catalysis Letters》2006,89(1):149-156
Summary Selective ammoxidation of ethylene over Co-ZSM-5 prepared by aqueous and solid-state ion exchange has been studied. The catalyst
prepared using solid-state exchange showed higher activity and selectivity to acetonitrile. Catalysts tested in the ammoxidation
of ethylene were previously characterized by chemical analysis, XRD, N2-BET measurements and FTIR. TPD of ammonia and FTIR of pyridine used as probe molecule showed that solid-state ion exchange
of H-ZSM-5 with cobalt generates new Lewis acid sites which seem to play a role in the ammoxidation reaction. 相似文献