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71.
Kotaro Shirane Takayuki Tokimoto Osamu Tanimoto 《Zeitschrift für Physik B Condensed Matter》1992,89(2):243-246
Many chemical reactions in vivo are self-controlled by fluxes of chemical energy and matter through biological systems, so the induction of such reactions can be governed by changes in the control parameters of the rate equation. A potential of a system is assumed to be given by Gibbs' functionG(T, P, x), which is continuously differentiable, and the rate equation can be derived from the differential (–G/x) of Taylor's expansion ofG
(T,P)(x) for the order parameterx, which corresponds to the product number, at around the critical pointC(T
C, PC). The equation is described bydx/dt=(x)–k1x–k2x3, andk
2>0. In this equation,k
1 andk
2 are functions of the control parameters, temperatureT and pressureP, andk
1 is allowed to have a positive or negative values as (T, P). Thenk
1 is an important factor that decides the induction conditions of the reactions with a phase transition in the steady statex=0. Because bothk
1 (the transition parameter) andG are the quantity of state, they are given by the total differential, and functions that decideG andk
1 are related to a mutual inverse function. From the above relation, the rate of change ink
1 by G, which corresponds to the reaction energy of the system, is uniquely determined by a function ofk
1, [f(k
1
±
)] andf(k
1
±
) is described approximately by ±1
k
1
±
in the transient process thatk
1 approaches zero, where 1 implies 1/RT. These results indicate that internal driving forces caused by a stimulus in a system are proportional tok
1
±
and that the system is regulated by competition of the forces. an approximate function fork
1 in the transient process is described by tanh (G/RT) and Arrhenius' law is elucidated from this theory.Decreased January 19, 1992 相似文献
72.
We revealed that in ATX-S10.Na(II)(13,17-bis (1-carboxypropionyl) carbamoylethyl-8-etheny-2-hydroxy-3-hydroxyiminoethylidene-2,7,12,18-tetraethyl porphyrin sodium)-mediated photodynamic therapy using 667 nm nanosecond-pulsed light excitation at a peak intensity of 2.0 MW/cm(2), phototoxicity increased with decreasing pulse repetition rate in the range of 5-30 Hz for A549 cell cultures. To examine the relation between the reaction mechanism and measured phototoxicity, we carefully measured the kinetics of photochemical oxygen consumption and photobleaching during irradiation of ATX-S10.Na(II)-sensitized A549 monolayer cultures. Measurements of oxygen consumption with a microelectrode, which was performed just above the cells, showed that there was no significant difference between the magnitudes of decrease in oxygen at the three repetition rates at the same cumulative fluence. Loss of ATX-S10.Na(II) fluorescence intensity also exhibited little repetition rate dependence when compared at the same cumulative fluence. We investigated the correlation between oxygen consumption and photobleaching during irradiation and obtained "fluorescence-oxygen diagrams." The diagrams showed dynamic changes between oxygen-dependent and oxygen-independent photobleaching at the higher repetition rates of 10 and 30 Hz, whereas such change was not clearly seen over the whole irradiation time at 5 Hz. These results suggest that the reduced phototoxicity at high repetition rates might be due to an oxygen-independent reaction. We presumed that the change in the reaction mechanism was associated with the local concentrations of the photosensitizer and oxygen in cells during irradiation. 相似文献
73.
Fluorous reverse-phase silica gel (FRPSG)-supported Lewis acids which have fluorous ligands acted as effective catalysts of Baeyer-Villiger and Diels-Alder reactions in water. Direct esterification of carboxylic acid with alcohol in organic media was also catalyzed. The FRPSG-supported Lewis acids could be recycled by simple filtration after the reaction. 相似文献
74.
The light-emitting principle of the brittle star Ophiopsila californica has been isolated and purified. It was found to be a green-fluorescent photoprotein (molecular weight 45000) which emits green light (λmax 500 nm) when H2 O2 is added, independently of the presence or absence of O2 . The green fluorescence (emission maximum 500 nm, excitation maximum 440 nm) spectrally coincided with the H2 O2 -triggered luminescence, indicating that the green fluorescent chromophore is the light-emitter of the photoprotein luminescence. 相似文献
75.
A dicyano-containing [Fe(bpb)(CN)2]- building block has been employed for the synthesis of cyano-bridged heterometallic Ni(II)-Fe(III) complexes. The presence of steric bpb(2-) ligand around the iron ion results in the formation of low-dimensional species: five are neutral NiFe2 trimers and three are one-dimensional (1D). The structure of the 1D complexes consists of alternating [NiL]2+ and [Fe(bpb)(CN)2]- generating a cyano-bridged cationic polymeric chain and the perchlorate as the counteranion. In all complexes, the coordination geometry of the nickel ions is approximately octahedral with the cyano nitrogen atoms at the trans positions. Magnetic studies of seven complexes show the presence of ferromagnetic interaction between the metal ions through the cyano bridges. Variable temperature magnetic susceptibility investigations of the trimeric complexes yield the following J(NiFe) values (based on the spin exchange Hamiltonian H = -2J(NiFe) S(Ni) (S(Fe(1)) + S(Fe(2))): J(NiFe) = 6.40(5), 7.8(1), 8.9(2), and 6.03(4) cm(-1), respectively. The study of the magneto-structural correlation reveals that the cyanide-bridging bond angle is related to the strength of magnetic exchange coupling: the larger the Ni-N[triple bond]C bond angle, the stronger the Ni- - -Fe magnetic interaction. One 1D complex exhibits long-range antiferromagnetic ordering with T(N) = 3.5 K. Below T(N) (1.82 K), a metamagnetic behavior was observed with the critical field of approximately 6 kOe. The present research shows that the [Fe(bpb)(CN)2]- building block is a good candidate for the construction of low-dimensional magnetic materials. 相似文献
76.
Oike T Kurata T Takimiya K Otsubo T Aso Y Zhang H Araki Y Ito O 《Journal of the American Chemical Society》2005,127(44):15372-15373
The porphyrin-sexithiophene-fullerene triad 2, where the two central thiophene units of the sexithiophene spacer are bridged with a crown-ether-like polyether chain, undergoes efficient intramolecular electron transfer from the photoexcited porphyrin moiety to the fullerene through the sexithiophene. However, complexation with a sodium cation in the crown ether ring causes complete suppression of electron transfer as a result of a drastic conformational change of the sexithiophene backbone. Furthermore, decomplexation resumes the photoinduced electron transfer. This on/off switching phenomenon indicates that the polyether-bridged sexithiophene can function as a complexation-gated molecular wire. 相似文献
77.
To synthesize (3′R,5′S)-3′-hydroxycotinine [(+)-1], the main metabolite of nicotine (2), cycloaddition of C-(3-pyridyl)nitrones 3a, 3c, and 15 with (2R)- and (2S)-N-(acryloyl)bornane-10,2-sultam [(2R)- and (2S)-8] was examined. Among them, l-gulose-derived nitrone 15 underwent stereoselective cycloaddition with (2S)-8 to afford cycloadduct 16, which was elaborated to (+)-1. 相似文献
78.
Yoshikuni Uchida Masao Yoshida Osamu Nishiara Kazunori Matsui 《Journal of Sol-Gel Science and Technology》2003,26(1-3):177-180
Silica gels doped with Cu2+ ions were prepared from the (3-aminopropyl) trimethoxysilane (APTMOS)/tetraethoxysilane (TEOS) systems. Sols showed a broad absorption peak at 640 nm, suggesting 3–5 coordination of the aminopropyl groups to Cu2+. For gels prepared from APTMOS and dried at room temperature, the 640 nm peak decreased and a red-shifted absorption appeared below 400 nm within a few months. The luminescence spectra of the xerogels showed emission bands at 430–470 and 510 nm. The former and latter bands are ascribed to Cu+ monomer and dimer emissions, respectively. These results indicate that Cu2+ ions are reduced to Cu+. When xerogels were prepared from APTMOS/TEOS = 1 (vol/vol), the color of xerogels was blue with an absorption peak at around 670 nm, indicating no reduction of Cu2+ ions. 相似文献
79.
Kanemichi Muraoka Miharu Eguchi Osamu Ishitani Francois Chevire Kazuhiko Maeda 《Journal of Energy Chemistry》2021,(4):176-182
Hybrid materials constructed from a visible-light-absorbing semiconductor and a functional metal complex have attracted attention as efficient photocatalysts for CO2 reduction with high selectivity to a desired product.In this work,defect fluorite-type Ln-Ta oxynitrides LnTaOxNy(Ln=Nd,Sm,Gd,Tb,Dy and Ho)were examined as the semiconductor component in a hybrid photocatalyst system combined with known Ag nanoparticle promoter and binuclear ruthenium(Ⅱ)complex(RuRu’).Among the LnTaOxNy examined,TbTaOxNy gave the highest performance for CO2 reduction under visible light(k>400 nm),with a Ru Ru0-based turnover number of 18 and high selectivity to formate(>99%).Physicochemical analyses indicated that high crystallinity and more negative conduction band potential of Ln Ta OxNywith the absence of Ln-4 f states in the band gap structure contributed to higher activity of the hybrid photocatalyst. 相似文献
80.
Asymmetric synthesis is one of the most important and valuable research fields in modern organic chemistry. Since the use of electricity as a traceless oxidant or reductant under electrochemical conditions, highly reactive intermediates can selectively generate under mild reaction conditions through more environmentally benign conditions compared with the reactions using common chemical oxidants or reductants. Thus, the merging electrochemistry with asymmetric catalysis would provide a unique and powerful approach for the synthesis of optically active compounds under oxidative or reductive conditions. Selected recent (2018–2020) examples of enantioselective electro-organic synthesis using transition metal catalysts or organocatalysts are summarized in this short review. These examples are divided to oxidative and reductive transformations and described together with brief reaction mechanisms. 相似文献