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991.
992.
Tarek Agag Tsutomu Takeichi 《Journal of polymer science. Part A, Polymer chemistry》2006,44(4):1424-1435
New series of benzoxazine‐based monomers, namely maleimidobenzoxazines, were prepared with hydroxyphenylmaleimide, formalin, and various amines (e.g., aniline, allylamine, and aminophenyl propargyl ether). The structure of the novel monomers was confirmed by IR, 1H NMR, and elemental analysis. The monomers were easily dissolved in many common organic solvents. Differential scanning calorimetry of the novel monomers showed exotherms at different temperature ranges that corresponded to the polymerization regime of benzoxazine and maleimide along with other functionalities such as allyl or propargyl, if any. IR was studied to follow the progress of the curing reaction of maleimidobenzoxazine after various thermal treatments. The thermal cure of the monomers at 250 °C afforded a novel network structure that combined polybenzoxazine and polymaleimide. The dynamic mechanical analyses showed that the storage moduli of the thermosets derived from maleimidobenzoxazine were kept constant up to high temperatures. The glass‐transition temperatures were as high as 241–335 °C. Moreover, thermogravimetric analyses revealed that the thermosets did not show any weight loss up to about 350 °C, with char yields ranging from 62 to 70% at 800 °C. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1424–1435, 2006 相似文献
993.
994.
Masami Sakamoto Mamoru Kato Eishi Oda Shuichiro Kobaru Takashi Mino Tsutomu Fujita 《Tetrahedron》2006,62(13):3028-3032
X-ray crystallographic analysis and the photochemical aspects of N,N-diallylcoumarincarboxamides were investigated. Irradiation of the corresponding amides promoted stereoselective intramolecular cyclobutane formation exclusively. The solid-state photoreaction of the coumarinamide without substituent on the 4-position proceeded in a crystal-to-crystal manner. On the other hand, photolysis of the amide possessing a methyl group at the 4-position also effected 2+2 cycloaddition; however, the reaction proceeded much slower. The difference in the reactivity was explainable on the basis of the molecular conformation in the crystal lattice. 相似文献
995.
Ken‐ichi Iwashita Akihiro Yokoyama Tsutomu Yokozawa 《Journal of polymer science. Part A, Polymer chemistry》2005,43(18):4109-4117
For the synthesis of aromatic polyesters with defined molecular weights and narrow molecular weight distributions (MWDs), we investigated the chain‐growth polycondensation of active amide derivatives of 4‐hydroxybenzoic acid, 1a and 1b , having an octyl or 4,7‐dioxaoctyl side chain, respectively. To suppress the transesterification of the polymer backbone with the monomer, the polymerization of 1 was carried out in tetrahydrofuran (THF) at −30 °C in the presence of initiator 2 and Et3SiH/CsF/18‐crown‐6, which generated a hydride ion as a base in situ. The number‐average molecular weight (Mn) of poly 1a was controlled, and narrow MWDs were maintained, until the [ 1a ]0/[ 2 ]0 feed ratio was 14.3 (Mn ≤ 3500), whereas that of poly 1b was controlled until the feed ratio was 30 (Mn ≤ 7250). The difference stemmed from the higher solubility of poly 1b in THF. This chain‐growth polycondensation was applied to the synthesis of a diblock copolyester of 1a and 1b of a defined architecture. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4109–4117, 2005 相似文献
996.
I. Shigeta Y. Tanaka F. Ichikawa Y. Asano 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(2):141-149
We propose a new approach of smearing origins of a zero-bias
conductance peak (ZBCP) in high-Tc superconductor tunnel
junctions through the analysis based on the circuit theory for a
d-wave pairing symmetry.
The circuit theory has been recently developed from conventional
superconductors to unconventional superconductors.
The ZBCP frequently appears in line shapes for this theory, in which the
total resistance was constructed by taking account of the effects
between a d-wave superconductor and a diffusive normal metal (DN) at a
junction interface, including the midgap Andreev resonant states (MARS),
the coherent Andreev reflection (CAR) and the proximity effect.
Therefore, we have analyzed experimental spectra with the ZBCP of
Ag-SiO-Bi2Sr2CaCu2O8+δ (Bi-2212) planar tunnel
junctions for the {110}-oriented direction by using a simplified
formula of the circuit theory for d-wave superconductors.
The fitting results reveal that the spectral features of the ZBCP are
well explained by the circuit theory not only excluding the Dynes's
broadening factor but also considering only the MARS and the DN
resistance.
Thus, the ZBCP behaviors are understood to be consistent with those of
recent studies on the circuit theory extended to the systems containing
d-wave superconductor tunnel junctions. 相似文献
997.
Shiro Kawabata Satoshi Kashiwaya Yasuhiro Asano Yukio Tanaka 《Physica E: Low-dimensional Systems and Nanostructures》2005,29(3-4):669
We discuss how to make use of high-Tc d-wave Josephson junctions in the construction of a phase qubit. We especially focus on the effect of the quasiparticle dissipation and the zero energy bound state on the macroscopic quantum tunneling which corresponds to the final measurement process of the d-wave phase qubit. 相似文献
998.
Osamu MaidaAkira Asano Masao TakahashiHitoo Iwasa Hikaru Kobayashi 《Surface science》2003,542(3):244-252
Cyanide treatment, which includes the immersion of Si in KCN solutions followed by a rinse, effectively passivates interface states at Si/SiO2 interfaces by the reaction of CN− ions with interface states to form Si-CN bonds. X-ray photoelectron spectroscopy (XPS) measurements show that the concentration of the CN species in the surface region after the cyanide treatment is ∼0.25 at.%. Take-off angle-dependent measurements of the XPS spectra indicate that the concentration of the CN species increases with the depth from the Si/SiO2 interface at least up to ∼2 nm when ultrathin SiO2 layers are formed at 450 °C after the cyanide treatment. When the cyanide treatment is applied to metal-oxide-semiconductor (MOS) solar cells with 〈ITO/SiO2/n-Si〉 structure, the photovoltage greatly increases, leading to a high conversion efficiency of 16.2% in spite of the simple cell structure with no pn-junction. Si-CN bonds are not ruptured by air mass 1.5 100 mW cm−2 irradiation for 1000 h, and consequently the solar cells show no degradation. Neither are Si-CN bonds broken by heat treatment at 800 °C performed after the cyanide treatment. The thermal and irradiation stability of the cyanide treatment is attributable to strong Si-CN bonds, whose bond energy is calculated to be 1 eV higher than that of the Si-H bond energy using a density functional method. 相似文献
999.
A phenomenological model to explain finite time singularity formation in a three-dimensional inviscid vorticity field is given. The thin filament approximation for a vorticity field is used, and the model is based on the three-dimensional interaction of two approximately straight vortex filaments. It is shown that the model has a solution which exhibits finite time singularity formation in a vorticity field. 相似文献
1000.
We study a spin system with both two- and four-spin exchange interactions on the triangular lattice as a possible model for the nuclear magnetism of solid 3He layers adsorbed on grafoil. The ground state is analyzed by the use of the mean-field approximation. It is shown that the four-sublattice state is favored by introduction of the fourspin exchange interaction. A possible phase transition at a finite temperature into a phase with the scalar chirality is predicted. Application of a magnetic field is shown to cause a variety of phase transitions. 相似文献