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191.
Two types of homologues (symmetrical and asymmetrical in rotational symmetry) of novel triphenylene compounds possessing fluoroalkyl and alkyl side chains were synthesized via an alternative method. X-ray diffraction and DSC measurements showed that these homologues are thermotropic liquid crystals with a hexagonal columnar (Colh) mesophase. The phase transition temperatures (Colh-Iso) for both symmetrical and asymmetrical fluoroalkyloxytriphenylenes increase to about 180°C, and are independent of fluoromethylene chain and the rotational symmetry of chemical structure. The Colh phase of symmetrical and asymmetrical fluoroalkyloxytriphenylenes possessing three fluoroalkyl side chains are more stable than fluoroalkyloxytriphenylenes possessing six fluoroalkyl side chains and alkyloxytriphenylenes. The X-ray diffraction patterns for symmetrical and asymmetrical fluoroalkyloxytriphenylenes, fluoroalkyloxytriphenylenes and alkyloxytriphenylenes in the wide-angle region are compared. 相似文献
192.
Kazuki Nakanishi Ryoji Takahashi Tomohiro Nagakane Koji Kitayama Norihito Koheiya Hiroko Shikata Naohiro Soga 《Journal of Sol-Gel Science and Technology》2000,17(3):191-210
By inducing a phase separation parallel to the sol-gel transition of alkoxy-derived silicate systems, gels with well-defined macroporous structure can be prepared. Depending on the post-gelation treatment such as aging and solvent exchange, the final pore structure in the nanometer range of dried and heat-treated gels exhibits a considerable variation. With an aim of completely controlling the hierarchical pore structure in the discrete size ranges of nanometers and micrometers, systematic experimental studies have been performed. The macroporous nature of the wet gels allows an efficient solvent exchange process compared with conventional gels only with mesopores. In addition, the surface chemistry of the wet gel skeleton affects the mesopore formation process by the solvent exchange to a great extent. The median size of mesopores larger than 5 nm can be controlled by adjusting the basic solvent exchange conditions such as pH value, temperature and bath ratio for any kind of macroporous silica gel. On the other hand, the control of pore volume independent of the mesopore size is possible only in the system incorporated with the micelle-forming surfactant. Some examples of the effects of controlled mesopores on the analytical performance of monolithic-type chromatographic columns are also presented. 相似文献
193.
Naohiro Suzuki 《Proceedings of the American Mathematical Society》2000,128(3):819-825
We consider the Dirac operators with electromagnetic fields on 2-dimensional Euclidean space. We offer the sufficient conditions for electromagnetic fields that the associated Dirac operator has only discrete spectrum.
194.
Hiratani K Sakamoto N Kameta N Karikomi M Nagawa Y 《Chemical communications (Cambridge, England)》2004,(13):1474-1475
A 25 membered crownophane with two hydroxy and two amide groups around the cavity has been reported for the first time to be able to include carbonic acid formed from both carbon dioxide and water molecules to give a stable 1:1 complex at room temperature. 相似文献
195.
A broadband light source can be obtained by operating a multimode laser diode with a bias current below threshold. We propose an optical time domain reflectometer for high-resolution with a broadband cw multimode laser. The emission spectrum of the multimode laser diode that affects an interference signal is investigated. With this method, the spatial resolution is measured as 11.5 μm, corresponding to that of 38.3-fs pulses, and a minimum detectable reflectivity < -90 dB is achieved. 相似文献
196.
Persistent polarization in poly(vinylidene fluoride) thermoelectrets prepared under high electric field has been studied by measurements of depolarization and pyroelectricity. Various polarizations are examined in detail; the polarizations related to a characteristic molecular motion near 60°C and the polarizing temperature are not responsible for the major piezoelectric effect in β-form electrets. The piezoelectricity is attributed to a polarization appearing near the melting temperature. The persistent polarization corresponding to d31 of 2 × 10?11 coul/N is about 5 × 10?6 coul/cm2. The pyroelectricity of β-form electrets is linearly correlated with the piezoelectricity. 相似文献
197.
Yoshiro Sato Shin-ichi Ninomiya Feng-Zhi Liu Naohiro Shirai Yutaka Kawazoe 《Tetrahedron letters》1985,26(45):5547-5550
The rate for hydrolysis, chemoselectivitly toward nucleophiles, and partition property of N-neopentyl-, N-trimethylsilylmethyl-, and N-trimethylgermylmethyl-N-nitrosoureas were compared. The latter two compounds are silicon and germanium analogues of the neopentyl derivative. The substitution effect of Ge in place of Si or C are discussed on the chemical and physicochemical properties. 相似文献
198.
Jong Hwa Jung Jeong Ah Rim Soo Jin Lee Naohiro Kameda Toshimi Shimizu 《Tetrahedron》2007,63(31):7449-7456
Asymmetric bolaamphiphilic sugar-based hydrogelators (1-3) were synthesized and their gelation ability with and without alkylammonium ions was investigated by CD, TEM, FTIR and NMR. These compounds acted as versatile gelators for organic solvents and water. The xerogels 1-3 obtained from water showed well-developed structures of fibrils with diameters of 10-38 nm and length of several hundred micrometers. Particularly, the gelation ability of crown-appended gelator 1 was drastically enhanced by addition of alkylammonium ions 4 and 5, suggesting that the bridging effect of alkyldiammonium ions could be the primary driving-force for the stabilization due to the intermolecular hydrogen bonding and electrostatic interactions. The present result is a rare case of a hydrogel being stabilized by a host-guest interaction. In addition, the hydrogel 1 with AgNO3 and KClO4 induced the formation of nanotubular and vesicular structures of silica by sol-gel polymerization of TEOS, respectively. These results indicate that hydrogel 1 acted as a template to produce inorganic nanomaterials. 相似文献
199.
Chavas LM Yamada Y Hiraki M Igarashi N Matsugaki N Wakatsuki S 《Journal of synchrotron radiation》2011,18(1):11-15
A direct outcome of the exponential growth of macromolecular crystallography is the continuously increasing demand for synchrotron beam time, both from academic and industrial users. As more and more projects entail screening a profusion of sample crystals, fully automated procedures at every level of the experiments are being implemented at all synchrotron facilities. One of the major obstacles to achieving such automation lies in the sample recognition and centring in the X-ray beam. The capacity of UV light to specifically react with aromatic residues present in proteins or with DNA base pairs is at the basis of UV-assisted crystal centring. Although very efficient, a well known side effect of illuminating biological samples with strong UV sources is the damage induced on the irradiated samples. In the present study the effectiveness of a softer UV light for crystal centring by taking advantage of low-power light-emitting diode (LED) sources has been investigated. The use of UV LEDs represents a low-cost solution for crystal centring with high specificity. 相似文献
200.
Naohiro Yamazaki Hajime Yuyama Masatoshi Nagai Guang-Hui Ma Shinzo Omi 《Journal of Dispersion Science and Technology》2013,34(1-3):279-292
SPG (Shirasu porous glass) membrane emulsification used to prepare uniform polymeric microspheres is briefly reviewed, and the performance of a hydrophilically treated PTFE [poly(tetrafluoroethylerie)] membrane is described and compared with that of the SPG membrane. A mixture of styrene. divinyl benzene and hexadecane (HD) was extruded through the membranes and dispersed in an aqueous phase containing polyvinylalcohol (PVA) and sodium lauryl sulfate (SLS) as mixed stabilizers. A hvdrophilically treated PTFE membrane was used with a stainless steel mesh support so that the membrane would not expand to affect the pore size during the emulsification. The nominal pore size of the PTFE membrane was replaced with the calculated one using a theoretical expression derived from the force balance between the external pressure and the interfacial tension between oil and water phases. The emulsion droplets prepared with the PTFE membrane revealed a broader size distribution than those obtained with the SPG membrane, and the rate of emulsificaton was nearly same for both membranes. Droplet size control was readily possible. The performance was significantly affected by the adsorption behavior of the stabilizers on the membrane surfaces. The contact angle profile of oil droplets on the PTFE membrane implied that the hydrophilically treated PTFE membrane is still hydrophobic compared to the SPG membrane. This tendency was reflected by the dependence of the average droplet diameter (and coefficient of variation, CV) on the concentration and composition of mixed stabilizers. 相似文献