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961.
Miyazaki Y Inaba A Sorai M Taylor PS Lahti PM 《The journal of physical chemistry. B》2008,112(27):8144-8150
The heat capacity of the title organic free radical, PhBABI, was measured over 0.3-300 K by adiabatic calorimetry and relaxation methods in the presence of external magnetic fields up to 9 T. A hump in the magnetic heat capacity was observed with a maximum at about 15 K in zero field, which did not shift at fields up to 9 T. The experimental magnetic entropy was in good agreement with the theoretical value of R ln 2 (= 5.76 J K(-1) mol(-1)) for S = 1/2 systems. The higher temperature, field-insensitive feature was fitted to several antiferromagnetic Heisenberg models. The best fits were obtained using spin ladder and coupled spin bilayer models. 相似文献
962.
The interfacial and aggregation behavior of the nonionic surfactant decanoyl-N-methyl-glucamide (Mega-10) with the cationic surfactant hexadecyltriphenylphosphonium bromide (HTPB) have been studied using
interfacial tension measurements and fluorescence techniques. From interfacial tension measurements, the critical micellar
concentrations (cmc) and various interfacial thermodynamic parameters have been evaluated. The experimental results were analyzed
in the context of the pseudophase separation model, the regular solution theory, and the Maeda’s approach. These approaches
allowed us to determine the interaction parameter and composition in the mixed state. By using the static quenching method,
the mean micellar aggregation numbers of pure and mixed micelles of HTPB+Mega-10 were obtained. It was found that that the
aggregation number decreases with increasing mole fraction of HTPB. This behavior is attributed to the presence of the bulky
head group of HTPB, which creates steric head group incompatibility and/or electrostatic repulsion. The micropolarity of the
micelle was monitored with pyrene fluorescence intensity ratio. It was observed that the increasing participation of HTPB
induces the formation of micelles with a hydrated structure. The polarization of the fluorescent probe Rhodamine B was monitored
in micellar medium and found to increase with the increase of ionic content. This behavior suggests the formation of mixed
micelles with a more ordered or rigid structure. 相似文献
963.
Osamu Kosaka Shunsuke Iida Pankaj Sehgal Hidekazu Doe 《Colloid and polymer science》2008,286(5):545-551
The interaction of endocrine disruptor chemicals (EDCs) such as nonylphenol (NP) and β-estradiol with cationic micelle of
hexadecyltrimethylammonium ion (HTA+) and a monolayer of HTA+ ion adsorbed at the electrode surface has been investigated in the presence of hydrophilic modified (2-hydroxypropyl)-β-cyclodextrin.
NP, which has a similar structure to HTA+, decreased the critical micelle concentration (cmc) of hexadecyltrimethylammonium bromide more effectively. At the low HTA+ concentration, HTA+ inhibited the adsorption of I2. However, as the HTA+ concentration increased, a monolayer of HTA+ was formed at the electrode surface and caused the adsorption of iodine molecule (I2). In the presence of micelle, the I2 was dissolved in the micelle. Both EDCs caused the formation of HTA+ monolayer even at the HTA+ concentration below the cmc. 相似文献
964.
Kuramochi Y Satake A Itou M Ogawa K Araki Y Ito O Kobuke Y 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(9):2827-2841
Trisporphyrinatozinc(II) (1-Zn) with imidazolyl groups at both ends of the porphyrin self-assembles exclusively into a light-harvesting cyclic trimer (N-(1-Zn)(3)) through complementary coordination of imidazolyl to zinc(II). Because only the two terminal porphyrins in 1-Zn are employed in ring formation, macrocycle N-(1-Zn)(3) leaves three uncoordinated porphyrinatozinc(II) groups as a scaffold that can accommodate ligands into the central pore. A pyridyl tripodal ligand with an appended fullerene connected through an amide linkage (C(60)-Tripod) was synthesized by coupling tripodal ligand 3 with pyrrolidine-modified fullerene, and this ligand was incorporated into N-(1-Zn)(3). The binding constant for C(60)-Tripod in benzonitrile reached the order of 10(8) M(-1). This value is ten times larger than those of pyridyl tetrapodal ligand 2 and tripodal ligand 3. This behavior suggests that the fullerene moiety contributes to enhance the binding of C(60)-Tripod in N-(1-Zn)(3). The fluorescence of N-(1-Zn)(3) was almost completely quenched (approximately 97 %) by complexation with C(60)-Tripod, without any indication of the formation of charge-separated species or a triplet excited state of either porphyrin or fullerene in the transient absorption spectra. These observations are explained by the idea that the fullerene moiety of C(60)-Tripod is in direct contact with the porphyrin planes of N-(1-Zn)(3) through fullerene-porphyrin pi-pi interactions. Thus, C(60)-Tripod is accommodated in N-(1-Zn)(3) with a pi-pi interaction and two pyridyl coordinations. The cooperative interaction achieves a sufficiently high affinity for quantitative and specific introduction of one equivalent of tripodal guest into the antenna ring, even under dilute conditions ( approximately 10(-7) M) in polar solvents such as benzonitrile. Additionally, complete fluorescence quenching of N-(1-Zn)(3) when accommodating C(60)-Tripod demonstrates that all of the excitation energy collected by the nine porphyrins migrates rapidly over the macrocycle and then converges efficiently on the fullerene moiety by electron transfer. 相似文献
965.
A liquid nitrogen freezing method was used to collect raindrops for the determination of isotope-size distribution. Water drops that fall onto a surface of liquid nitrogen stay suspended for 10 to 20 s, until their temperature reaches the Leidenfrost point (126 K). As their temperature falls to the freezing point, they release their heat by thermal conduction. At the freezing point, latent heat of fusion is released, along with a significant loss of water. After freezing completely, the ice droplets stay suspended, cooling by thermal conduction until they reach the Leidenfrost point. They then lose buoyancy and start sinking. Consistent isotopic changes of 1.5 +/- 0.4 and 0.33 +/- 0.05 per thousand for hydrogen and oxygen, respectively, were found for droplets with radii between 1.0 and 1.5 mm. Isotope fractionation appeared to occur at the same time as water loss, as the droplets were freezing, in what was probably a kinetic effect. 相似文献
966.
Osamu Onomura Peter G. Kirira Toshimitsu Tanaka Shinsuke Tsukada Yoshihiro Matsumura Yosuke Demizu 《Tetrahedron》2008,64(32):7498-7503
Diastereoselective introduction of nucleophiles into l-proline derivatives at the 5-position was achieved with suitable selection of N-protecting group. N-Methoxycarbonylated or benzyloxycarbonylated l-proline derivatives reacted with arene to give cis-arylated products. On the other hand, N-benzoylated l-proline derivative preferentially gave trans-arylated product, which could be easily transformed into optically active C2-symmetrical pyrrolidine derivative. Such derivative 5 worked well as an organic activator in the asymmetric reduction of aromatic imines by Cl3SiH. 相似文献
967.
Hisatoshi Konishi Takayuki Mita Yusuke Yasukawa Osamu Morikawa Kazuhiro Kobayashi 《Tetrahedron letters》2008,49(48):6831-6834
The thermal isomerization of anti to syn stereoisomers of oxacalix[4]arene bearing two methyl groups at the intra-annular distal positions was investigated by temperature-dependent NMR spectroscopy. The conversion followed a first-order kinetics, and very slowly proceeded at 473 K in nitrobenzene-d5 with a half-life of 7.2 h. The free energy of activation (ΔG≠ 139 kJ mol−1) is much higher than those for the ring inversion of related calix[4]arene derivatives. 相似文献
968.
An atropisomeric lactam which was prepared with high enantioselectivity by catalytic asymmetric intramolecular N-arylation, was efficiently converted to synthetic intermediates for NET inhibitors through highly diastereoselective α-alkylation followed by hydration and trans-tert-butylation. 相似文献
969.
Yuichi Terui Chu Yi-wen Osamu Nozawa Takuya Fukunaga Yoshihisa Toda 《Tetrahedron letters》2008,49(19):3067-3070
In the course of our screening program for novel glycine transporter inhibitors, we obtained a novel cyclic tetrapeptide (WSS2220) from the culture broth of Nonomuraea sp. The structure of WSS2220 was elucidated based on physicochemical data. WSS2220 contained a novel amino acid (4-oxo-3′-sulfoisoleucine), the absolute stereochemistry of which was determined by chemical modifications and the modified Mosher’s method. WSS2220 selectively inhibited glycine transporter type1 with an IC50 of 20 nM. 相似文献
970.
Osamu Muraoka Weijia Xie Mumen F.A. Amer Masayuki Yoshikawa 《Tetrahedron letters》2008,49(51):7315-7317
The reported structure of a potent α-glucosidase inhibitor 7 isolated recently from ayurvedic medicine Salacia reticulata was found incorrect, and the compound was proved to be de-O-sulfated kotalanol 4. Discussion and detailed analysis of the spectral data leading to the revised structure are presented. 相似文献