全文获取类型
收费全文 | 1143篇 |
免费 | 48篇 |
国内免费 | 12篇 |
专业分类
化学 | 823篇 |
晶体学 | 10篇 |
力学 | 40篇 |
数学 | 88篇 |
物理学 | 242篇 |
出版年
2023年 | 7篇 |
2022年 | 20篇 |
2021年 | 22篇 |
2020年 | 19篇 |
2019年 | 26篇 |
2018年 | 10篇 |
2017年 | 9篇 |
2016年 | 24篇 |
2015年 | 30篇 |
2014年 | 50篇 |
2013年 | 45篇 |
2012年 | 82篇 |
2011年 | 92篇 |
2010年 | 58篇 |
2009年 | 74篇 |
2008年 | 88篇 |
2007年 | 69篇 |
2006年 | 72篇 |
2005年 | 50篇 |
2004年 | 32篇 |
2003年 | 28篇 |
2002年 | 27篇 |
2001年 | 19篇 |
2000年 | 16篇 |
1999年 | 16篇 |
1998年 | 12篇 |
1997年 | 19篇 |
1996年 | 13篇 |
1995年 | 10篇 |
1994年 | 16篇 |
1993年 | 11篇 |
1992年 | 14篇 |
1991年 | 7篇 |
1990年 | 8篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 8篇 |
1975年 | 5篇 |
1974年 | 12篇 |
1973年 | 12篇 |
1964年 | 2篇 |
排序方式: 共有1203条查询结果,搜索用时 494 毫秒
101.
Aqueous two-phase flotation (ATPF) is especially applicable to bioseparation. However, there is no previous work reporting on its application in enantioseparation. Using phenylsuccinic acid (H2A) as the model enantiomers, ATPF was first introduced into the field of chiral separation. The contributions of a series of ATPF systems to the enantioseparation were investigated. The results indicated that an appropriate increase in the amount of phase-forming components and a decrease in pH values (from 5.5 to 2) are both beneficial for the enantioseparation. Enantioselective flotation and partitioning behavior are mainly dependent on pH values of the solutions, types, and concentrations of chiral selectors. Furthermore, salt, PEG, flow rates of air, and flotation time also have some effects on the enantioseparation. Under the optimal conditions, the enantioselectivity was calculated in terms of the separation factor (α) and enantiomer excess (e.e. %) as 1.99 and 23.49 %, respectively. Finally, the most reasonable mechanisms for H2A enantioseparation in ATPF system have been proposed. An ATPF system composed of PEG2000/(NH4)2SO4 was proved to have the best ability for the separation of H2A enantiomers. The explorations in our study will further enrich the enantioseparation methods and pave the way for the application of ATPF in the enantioseparation field. 相似文献
102.
B. T. Hsieh Y. J. Chang R. P. Han J. Wu L. L. Hsieh C. J. Chang 《Journal of Radioanalytical and Nuclear Chemistry》2011,290(1):141-148
The newly manufactured N-isopropylacrylamide (NIPAM) polymer gel is composed of four components, i.e., gelatin, monomer (NIPAM), crosslinker (N,N’-methylenebisacrylamide, Bis), and antioxidant (tetrakis hydroxymethyl phosphonium chloride, THPC). In this study, we investigated
the effects of gel composition on the dose response of NIPAM polymer gel. A statistical experiment to analyze the contribution
of each composition to the linearity and sensitivity of NIPAM gel was performed. Results indicate that the amount of gelatin,
NIPAM (15.17%), Bis, and THPC have dominant effects on the sensitivity of the gel, with contributions of 59.73, 15.17, 10.64,
and 14.45%, respectively. The amount of gelatin and Bis mainly affected the linearity of the gel, with contributions of 44.70
and 50.99%, respectively. The linearity of most compositions of the gel was greater than 0.99 when (%C)/(%T) was lower than 8.0. Optimal (%C)/(%T) for higher sensitivity should be in the range of 4−9. The temporal stability experiment showed that the dose response curve
attained stability at about 5 h after irradiation and persisted up to 3 months. 相似文献
103.
Lorenz CD Hsieh CM Dreiss CA Lawrence MJ 《Langmuir : the ACS journal of surfaces and colloids》2011,27(2):546-553
A series of large-scale atomistic molecular dynamics simulations were conducted to study the structural and interfacial properties of nonionic dimethyldodecylamine-N-oxide (DDAO) micelles with an aggregation number of 104 in pure water, which was determined using small-angle neutron scattering (SANS). From these simulations, the micelles were found to be generally ellipsoidal in shape with axial ratios of ~1.3-1.4, which agrees well with that found from small-angle neutron scattering measurements. The resulting micelles have an area per DDAO molecule of 94.8 ?(2) and an average number of hydration water molecules per DDAO molecule of ~8. The effect of the encapsulation of ethyl butyrate (CH(3)(CH(2))(2)COOCH(2)CH(3), C(4)) and ethyl caprylate (CH(3)(CH(2))(6)COOCH(2)CH(3), C(8)) on the structural and interfacial properties of the nonionic DDAO aggregates was also examined. In the presence of the C(4) oil molecules, the aggregates were found to be less ellipsoidal and more spherical than the pure DDAO micelles, while the aggregates in the presence of the C(8) oil molecules were almost perfect spheres. In addition, the C(4) oil molecules move into the core of the aggregates, while the C(8) oil molecules stay in the headgroup region of the aggregates. Finally, the structural properties of two micelles formed from different starting states (a "preassembled" sphere and individual DDAO molecules distributing in water) were found to be nearly identical. 相似文献
104.
Po-Tsung Hsieh Ricky Wen-Kuei Chuang Chao-Qun Chang Chih-Ming Wang Shoou-Jinn Chang 《Journal of Sol-Gel Science and Technology》2011,58(1):42-47
Yttrium-doped ZnO gel was spin-coated on the SiO2/Si substrate. The as-prepared ZnO:Y (YZO) thin films then underwent a rapid thermal annealing (RTA) process conducted at
various temperatures. The structural and photoluminescence characteristics of the YZO films were discussed thereafter. Our
results indicated that the grain size of YZO thin films being treated with various annealing temperatures became smaller as
compared to the ones without being doped with yttrium. Furthermore, unlike other ZnO films, the grains of YZO thin films appeared
to separate from one another rather than aggregating together as both types of the films were annealed under the same environment.
The photoluminescence characteristic measured showed that the UV emission was the only radiation obtained. However, the UV
emission intensity of YZO thin film was much stronger than that of the ZnO thin film after annealing them with the same condition.
It was also found that the intensity increased with an increase in the annealing temperature, which was caused by the exciton
generated and the texture surface of the YZO thin film. 相似文献
105.
Rau CS Yang JC Jeng SF Chen YC Lin CJ Wu CJ Lu TH Hsieh CH 《Photochemistry and photobiology》2011,87(2):441-446
This study was designed to determine the in vitro angiogenic ability of far-infrared (FIR) radiation in the skin-derived cultured human microvascular endothelial cells and to elucidate the role of mitogen-activated protein kinases (MAPKs) in this process. The results revealed that FIR radiation from a WS(TM) TY301 FIR emitter activated p38 and extracellular signal-regulated kinase (ERK), but not Akt or c-Jun N-terminal protein kinases (JNK), and significantly promoted angiogenesis by increasing tube formation in Matrigel and the migration of cells across an eight micron polyester filter. The addition of 50 μM PD98059, a MEK inhibitor, significantly inhibited the activation of ERK and the enhanced angiogenesis; in contrast, the inhibition of p38 phosphorylation did not inhibit the enhanced angiogenesis. After FIR radiation, there was no increase in vascular endothelial growth factor (VEGF) isoforms (VEGF-A, -B, -C and -D) mRNA and VEGF protein, no increase phosphorylation of endothelial nitric oxide synthase (eNOS) detected using Western blotting, and no increase in NO production detected using flow cytometry in cells pre-incubated with the cell-permeable NO-binding dye diluted 4-amino-5-methylamino-2', 7'-difluorofluorescein diacetate (DAF-FM DA). This study revealed that FIR radiation possesses in vitro angiogenic activity via the activation of the MEK/ERK but not the VEGF/Akt/eNOS-dependent signaling pathways. 相似文献
106.
Tsai WC Wang SK He TM Chou LC Hsieh YC Liao KY Chen HC Wen CR 《The Journal of chemical physics》2011,135(16):164704
Continuous-time core-level photon-stimulated desorption (PSD) spectroscopy was used to study the soft x-ray-induced reactions of CF(3)Br molecules adsorbed on Si(111)-7×7 near the Si(2p) edge (98-110 eV). The monochromatic synchrotron radiation was employed as a soft x-ray light source in the photon-induced reactions and also as a probe for investigating the produced fluorination states of the bonding surface Si atom in the positive-ion PSD spectroscopy. Several different surface coverages were investigated. The PSD spectra from the low-CF(3)Br-covered surfaces show the production of surface SiF species, while those from the high-CF(3)Br-covered surfaces depict the formation of surface SiF, SiF(2), and SiF(3) species. The photolysis cross section of the submonolayer CF(3)Br-covered surface is determined as ~4.3×10(-18) cm(2). A comparison with the results on CF(3)Cl/Si(111)-7×7 surface is discussed. 相似文献
107.
This study analyzed variations of tribological behaviors that depend on the injection molding techniques during the blending of short glass fiber (SGF) and polytetrafluoroethylene (PTFE) reinforced polycarbonate (PC) composites. The proposed planning of blending experiments is to use a D‐optimal mixture design (DMD). The tribological behaviors of friction coefficient and wear mass loss were selected for discussion. Nine experimental runs, based on a DMD method, utilized to train the back‐propagation neural network (BPNN) and then the simulated annealing algorithm (SAA) approach is applied to search for an optimal mixture ratio setting. In addition, the result of BPNN integrating SAA was also compared with response surface methodology (RSM) approach. The results of confirmation experiment show that DMD, RSM, and BPNN integrating SAA method are effective tools for the optimization of reinforced process. Furthermore, the scanning electron microscope (SEM) images show that the abundant debris are peeled off from the matrix materials and predominant delamination mechanisms and plastic deformation are shown on the worn surface after tribological behavior tests. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
108.
Hsieh S Thida T Nyamumbo MK Smith KA Naamad N Linck RG 《The journal of physical chemistry. A》2011,115(48):14040-14044
We present laser photoacoustic spectra of ethyl hydroperoxide (EHP) for 3-6 quanta of O-H stretch. Spectra are consistent with ab initio spectral simulations that take into account the influence of torsional motion about the O-O bond on O-H stretch overtone excitation. Experimental and simulated spectra share two trends. First, spectral features due to torsional excitation, including hot bands, become more prominent with increasing O-H stretch excitation, as has been shown previously for similar molecules such as methyl hydroperoxide. Second, contributions from the two different EHP conformers become clearly distinguishable at higher O-H stretch excitation, mainly due to the role of torsional motion. Results are consistent with a higher energy separation (330 cm(-1)) between the lower energy anti and the higher energy gauche conformers than predicted by electronic structure calculations (137 cm(-1)). Calculated absorption intensities are consistently higher than experimental values by ~30% but within the experimental uncertainty. With each additional O-H stretch overtone, the dropoff in calculated integrated absorption intensities at room temperature becomes less extreme, with a 14-fold dropoff from 3ν(OH) to 4ν(OH) and an 8-fold decrease from 5ν(OH) to 6ν(OH). 相似文献
109.
110.