全文获取类型
收费全文 | 239篇 |
免费 | 5篇 |
专业分类
化学 | 169篇 |
晶体学 | 4篇 |
力学 | 6篇 |
数学 | 30篇 |
物理学 | 35篇 |
出版年
2022年 | 5篇 |
2021年 | 7篇 |
2020年 | 2篇 |
2019年 | 2篇 |
2018年 | 5篇 |
2017年 | 2篇 |
2016年 | 4篇 |
2015年 | 6篇 |
2014年 | 8篇 |
2013年 | 11篇 |
2012年 | 11篇 |
2011年 | 19篇 |
2010年 | 14篇 |
2009年 | 13篇 |
2008年 | 18篇 |
2007年 | 12篇 |
2006年 | 13篇 |
2005年 | 14篇 |
2004年 | 15篇 |
2003年 | 9篇 |
2002年 | 9篇 |
2001年 | 5篇 |
2000年 | 2篇 |
1998年 | 3篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 4篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有244条查询结果,搜索用时 31 毫秒
21.
Xinsheng Zhu Kwang-Ho Choo 《Colloids and surfaces. A, Physicochemical and engineering aspects》2008,312(2-3):231-237
The overlapping of charged polymers (e.g., polyelectrolyte) in the liquid phase is one of the key parameters affecting the processing of the macromolecular solutions. This work focused on the development of a novel method for determining the overlap concentration of polyelectrolytes with stirred cell ultrafiltration (UF) techniques. A new, simplified equation that incorporated the resistance-in-series UF model into the osmosis phenomenon caused by polymers was developed, and then applied to estimate the threshold concentration for macromolecular overlap. The overlap concentrations of model polymers, such as poly(dimethylamine-co-epichlorohydrin-co-ethylenediamine) and poly(diallyldimethylammonium chloride), were evaluated with different, initial polymer concentrations and membrane pore sizes. In the correlation between ln Rt/Cr and ln Cr, the concentration where ln Rt/Cr had the minimal value was referred to as the overlap concentration. The gyration radius of polyelectrolytes was calculated using the overlap concentration, which can provide insight into the understanding of the size of polymers and their rejections by membranes. Determining the overlap concentration of polymers with a UF membrane appeared to be viable and practical. 相似文献
22.
A rapid HPLC method was developed and validated for the quantification of oxyresveratrol analog trans‐2,4,3′,5′‐tetramethoxystilbene (oxyresveratrol tetramethyl ether, OTE) in rat plasma. Chromatographic separation was achieved on an RP‐HPLC column, which was protected by a guard column through a 12 min gradient delivery of a mixture of acetonitrile–water at 50°C. The UV absorbance at 325 nm was recorded. The retention time of OTE and trans‐stilbene (internal standard) was about 7.7 and 8.4 min, respectively. The calibration curves were linear (R2 ≥ 0.9986) with a lower limit of quantification of 15 ng/mL. The intra‐ and inter‐day variations, in terms of RSD, were all lower than 9.8% while the intra‐day and inter‐day bias ranged from ?8.3 to +9.2%. The pharmacokinetics of OTE was assessed in rats using 2‐hydroxypropyl‐β‐cyclodextrin as a dosing vehicle. After intravenous administration, OTE possessed a long terminal elimination half‐life (t1/2 λz = 481 ± 137 min) and slow clearance (Cl = 29.1 ± 3.7 mL/min/kg). Upon oral administration, OTE was rapidly absorbed. However, it only displayed minimal plasma exposure and its absolute oral bioavailability (F) was as low as 4.5 ± 3.2%. Fortunately, the levels of OTE after single oral administration were sufficient to inhibit human cytochrome P450 1B1. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
23.
Electronic parameters of a two-dimensional electron gas (2DEG) in modulation-doped highly strained InxGa1−xAs/InyAl1−yAs coupled double quantum wells were investigated by performing Shubnikov-de Haas (S-dH), Van der Pauw Hall-effect, and cyclotron resonance measurements. The S-dH measurements and the fast Fourier transformation results for the S-dH at 1.5 K indicated the electron occupation of two subbands in the quantum well. The electron effective masses of the 2DEG were determined from the cyclotron resonance measurements, and satisfied qualitatively the nonparabolicity effects in the quantum wells. The electronic subband structures were calculated by using a self-consistent method. 相似文献
24.
Fang G Koral N Zhu C Yi Y Glaser MA Maclennan JE Clark NA Korblova ED Walba DM 《Langmuir : the ACS journal of surfaces and colloids》2011,27(7):3336-3342
Self-assembled monolayers (SAMs) were prepared from solutions with different proportions of a photoactive, azobenzene-based, silanized derivative of disperse red one (dDR1), and octyltriethoxysilane (OTE), a shorter, nonphotoactive molecule. The in-plane photoinduced orientational ordering of the resulting two component monolayers was monitored via precision measurement of in-plane birefringence using a dedicated high-extinction polarimeter. Measurements of contact angle, absorption, and birefringence show that introduction of OTE into the dDR1 deposition solution produces a continuous reduction of the surface density of dDR1 in the SAM, enabling the study of photowriting and relaxation dynamics in monolayers ranging from 100% dDR1 to samples where the dDR1 coverage is about 35%. The orientational dynamics depend strongly on the areal density of dDR1. As the fractional area of dDR1 is reduced, the rates of photowriting, photoerasing, and thermal relaxation increase, and the local orientational confinement of the molecules becomes more heterogeneous. 相似文献
25.
Kang T Yoo SM Yoon I Lee S Choo J Lee SY Kim B 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(7):2211-2214
We report an ultrasensitive and selective single nanowire-on-film (SNOF) surface-enhanced resonance Raman scattering (SERRS) sensor for Hg(2+) detection based on structure-switching double stranded DNAs (dsDNAs). Binding of Hg(2+) induces conformational changes of the dsDNAs and let a Raman reporter get close to the SNOF structure, thereby turning on SERRS signal. The well-defined SNOF structure provides a detection limit of 100 pM with improved accuracy in Hg(2+) detection. This sensor is stable over a considerable amount of time and reusable after simple treatment. Since this SNOF sensor is composed of a single Au NW on a film, development of a multiplex sensor would be possible by employing NWs modified by multiple kinds of aptamers. 相似文献
26.
Youngwoo Koh 《Journal of Mathematical Analysis and Applications》2011,373(1):147-160
We study inhomogeneous Strichartz estimates for the Schrödinger equation for dimension n?3. Using a frequency localization, we obtain some improved range of Strichartz estimates for the solution of inhomogeneous Schrödinger equation except dimension n=3. 相似文献
27.
Kang MJ Lee S Kim BK Eum JY Park SH Kang MH Oh CH Choo J Choi YW 《Chemical & pharmaceutical bulletin》2011,59(1):109-112
A Pep-1 peptide-modified liposomal (Pep1-Lipo) carrier system was investigated to increase the intracellular delivery of gold nanoparticles (Au NPs). Au NPs with a mean diameter of 13 nm were successfully encapsulated into the inner aqueous compartment of the novel carrier using an ethanol injection technique, reserving the distinctive optical characteristics of the surface plasmon resonance peak around 530 nm. The Au NP-loaded liposomal carrier was physically characterized as 150-170 nm in size and 45 mV in zeta potential. Dark field microscopic observation demonstrated that in vitro cellular association and/or translocation of the nanoprobes into the cells was increased by Pep1-Lipo carriers compared to bare Au NPs. In conclusion, this novel liposomal formulation is a promising platform for the intracellular delivery of metallic nanoprobes including Au NPs. 相似文献
28.
Choo‐Won Kim Margaret W. Frey Manuel Marquez Yong Lak Joo 《Journal of Polymer Science.Polymer Physics》2005,43(13):1673-1683
Cellulose nonwoven mats of submicron‐sized fibers (150 nm–500 nm in diameter) were obtained by electrospinning cellulose solutions. A solvent system based on lithium chloride (LiCl) and N,N‐dimethylacetamide (DMAc) was used, and the effects of (i) temperature of the collector, (ii) type of collector (aluminum mesh and cellulose filter media), and (iii) postspinning treatment, such as coagulation with water, on the morphology of electrospun fibers were investigated. The scanning electron microscopy (SEM) and X‐ray diffraction studies of as‐spun fibers at room temperature reveal that the morphology of cellulose fibers evolves with time due to moisture absorption and swelling caused by the residual salt and solvent. Although heating the collector greatly enhances the stability of the fiber morphology, the removal of salt by coagulation and DMAc by heating the collector was necessary for the fabrication of dry and stable cellulose fibers with limited moisture absorption and swelling. The presence and removal of the salt before and after coagulation have been identified by electron microprobe and X‐ray diffraction studies. When cellulose filter media is used as a collector, dry and stable fibers were obtained without the coagulation step, and the resulting electrospun fibers exhibit good adhesion to the filter media. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1673–1683, 2005 相似文献
29.
The pressure and laser-power dependence of the product distributions in the TEA CO2 laser induced decomposition of trichloroethylene were studied. At moderate pressures molecular elimination of HCl to give CClCCl via intermolecular energy transfer was found to be the major reaction path. At low pressures a pure laser-induced CCl bond fission to give CHCCl was found to be the primary, reaction step. 相似文献
30.
Pyrolysis of 3,5-dimethyl-1-propynoylpyrazole (1) at 640°C/0.1 torr gives 2-methyl-1-pyrazolo[2,3-a]pyridin-5-one (3) with inversion of the propynoyl chain. 1-Ethynylpyrazole and tricarbon monoxide have been identified in pyrolysates formed at 700–1000°C/0.01–0.1 torr from the parent 1-propynoylpyrazole (4). 相似文献