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991.
Norihiro Tokitoh Keiji Wakita Takeshi Matsumoto Takahiro Sasamori Renji Okazaki Nozomi Takagi Masahiro Kimura Shigeru Nagase 《中国化学会会志》2008,55(3):487-507
Stable silabenzenes ( 1a; R = Tbt, 1b; R = Bbt) were synthesized by taking advantage of extremely bulky and efficient steric protection groups, 2,4,6‐tris[bis(trimethylsilyl)methyl]phenyl (Tbt) and 2,6‐bis‐[bis(trimethylsilyl)methyl]‐4‐[tris(trimethylsilyl)methyl]phenyl (Bbt). The structure of Tbt‐substituted 1a was determined by X‐ray crystallographic analysis, which demonstrated the complete delocalization of the π‐electrons of the silabenzene ring. It was found that silabenzene 1a reacted with C–C and C–O multiple bond compounds to give the corresponding [4+2]‐cycloadducts via 1,4‐addition, while 1a underwent both 1,2‐ and 1,4‐additions by the reaction with methanol. Silabenzene 1a dimerized very gradually to afford its [4+2]‐dimer, although 1b showed no change under the same conditions. Photochemical reaction of 1a gave the corresponding silabenzvalene isomer instead of the Dewar silabenzene isomer. 相似文献
992.
Aoki S Sakurama K Ohshima R Matsuo N Yamada Y Takasawa R Tanuma S Takeda K Kimura E 《Inorganic chemistry》2008,47(7):2747-2754
8-Benzenesulfonyloxy-5- N,N-dimethylaminosulfonylquinolin-2-ylmethyl-pendant cyclen (BS-caged-L(4), BS = benzenesulfonyl) was designed and synthesized as a "caged" derivative of a previously described Zn(2+) fluorophore, 8-hydroxy-5- N,N-dimethylaminosulfonylquinolin-2-ylmethyl-pendant cyclen (L(4)) (cyclen = 1,4,7,10-tetraazacyclododecane). In the absence of metal ions and in the dark, BS-caged-L(4) (10 microM) showed negligible fluorescence emission at pH 7.4 (10 mM HEPES with I = 0.1 (NaNO3)) and 25 degrees C (excitation at 328 nm). Addition of Zn(2+) induced an increase in the UV/vis absorption of BS-caged-L(4) (10 microM) at 258 nm and a significant increase in fluorescence emission at 512 nm. These responses are results from the formation of Zn(H-1L(4)) by the hydrolysis of the sulfonyl ester at the 8-position of the quinoline unit promoted by the Zn(2+)-bound HO(-). Improvement of cell membrane permeation in comparison with L(4) is also described. 相似文献
993.
Time-resolved Raman spectroscopy has been applied to the hydrogen-abstraction reaction of decafluorobenzophenone (DFBP) from 2-propanol in temperatures ranging from room to supercritical temperature (520 K) at 31 MPa. The Raman bands of the intermediate ketyl radical (DFBPK) were identified. The Raman bands assigned to the C=C stretching mode (1639 cm-1) and the C-O stretching modes (1274 cm-1) shift to lower frequencies with increasing temperature. The corresponding Raman bands of stable molecules (reference molecules), benzhydrol, decafluorobenzhydrol, and benzophenone (BP), which all have similar molecular structures to those of DFBP or DFBPK, were also investigated at the same range of temperatures. Assignments of the Raman bands were performed with the help of density functional theoretical calculations and the isotopic exchange method. By comparing the Raman peak shifts of the radical with those of the reference molecules, the shift of the C=C stretching mode with increasing temperature (or decrease in the solvent density) is considered to be primarily due to the decrease in the repulsive interaction between the solute and the solvent. On the other hand, the shift of the C-O stretching mode of the radical reflects the decrease in the solvent Lewis acidity or its hydrogen-bonding donating ability, which is clearly illustrated by the shifts of the C=O stretching mode of BP and the C-O stretching mode of 2-propanol. The frequency of the C-O stretching mode of DFBPK was relatively sensitive to the surrounding environment. It was observed that the bandwidth of the radical was generally large, and this observation supports the previous report by Terazima and Hamaguchi (Terazima, M.; Hamaguchi, H. J. Chem. Phys. 1995, 99, 7891). Additionally, the sensitivity and the deformability of the radical structure due to the change of the solvent temperature and density were revealed in our studies. 相似文献
994.
Sekiguchi A Nishina A Kimura H Fukumoto RH Kanoh K Ishihara H Koketsu M 《Chemical & pharmaceutical bulletin》2005,53(11):1439-1442
We investigated the superoxide anion scavenging effects of thirteen 2-amino-1,3-selenazoles using a highly sensitive quantitative chemiluminescence method. At 166 microM, the 2-amino-1,3-selenazoles scavenged in the range of 14.3 to 96.7% of O2-. 2-Piperidino-1,3-selenazole and 4-phenyl-2-piperidino-1,3-selenazole exhibited the strongest superoxide anion-scavenging activity among the 2-amino-1,3-selenazoles. The 50% inhibitory concentrations (IC50) of 2-piperidino-1,3-selenazole and 4-phenyl-2-piperidino-1,3-selenazole were determined to be 4.03 microM and 92.6 microM, respectively. Thus, these compounds acted in vitro as effective O2- scavengers. 相似文献
995.
A theoretical study has been presented to show that it is possible to align three different diamagnetic susceptibility axes (chi(3) < chi(2) < chi(1) < 0) of a crystallite with respect to the laboratory coordinate system (x, y, z). The time-dependent magnetic field that periodically changes in direction and intensity on the xy plane in an elliptic manner (the intensity stronger in the x direction) at a rate quicker than the intrinsic rate of magnetic response causes the three-dimensional alignment, that is, chi(1) parallel x, chi(2) parallel y, and chi(3) parallel z. The fluctuation of the three susceptibility axes around the corresponding laboratory coordinates is estimated in terms of the fluctuation around the minimum of the time-averaged magnetic potential. This technique enables the three-dimensional alignment of the crystallographic axes. 相似文献
996.
K. Kato K. Tanaka K. Suzuki T. Kimura K. Nishizawa T. Miki 《Applied Physics A: Materials Science & Processing》2005,80(7):1481-1484
In-plane c-axis oriented CaBi4Ti4O15 (CBTi144) films were fabricated on Pt foils using a complex metal alkoxide solution. The a/b-axis orientation of the ferroelectric films was affected by the preferred orientation of Pt foil, which is associated with the thickness. The 500 nm-thick CBTi144 films showed good ferro- and piezoelectric properties on 0.010 mm-thick Pt foils. The Pr and Ec were 26 C/cm2 and 230 kV/cm, respectively, at an applied voltage of 75 V. The d33 was characterized as 25–34 pm/V by piezoresponse force microscopy. The values enhanced compared to those of the CBTi144 thin film with random orientation. The polar-axis oriented CBTi144 films would open for novel devices as Pb-free piezoelectric materials. PACS 77.84.-s; 68.37.-d; 81.15.-z 相似文献
997.
C.?MakochekanwaEmail author H.?Kato M.?Hoshino H.?Cho M.?Kimura O.?Sueoka H.?Tanaka 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2005,35(2):249-255
We have carried out experimental and theoretical
studies on electron scattering from the C3H6 isomers and
C3F6 molecules and we report on total, differential as well
as theoretical integral elastic cross-sections for these
molecules. Vibrational excitation functions are also presented for
the typical vibrational peaks in C3H6 and cyclo-C3H6
for the angle of 90○, impact energy range of 1–16 eV
and loss energies of 0.12 eV and 0.13 eV, respectively. In the
cross-sections, clear differences in peak positions and magnitudes
between the C3H6 isomers can be viewed as the isomer effect.
The same is observed between C3H6 and C3F6 in a clear
manifestation of the fluorination effect. The resemblance of the
π* shape resonance in the cross-sections, observed at about
2.2 eV for C3H6 and 3.5 eV for C3F6, to those in
C2H4 and C2F4 clearly points to the effect of the
double bond in the molecular structures for these molecules.
Theoretical analysis is performed to provide rationales for the
scattering dynamics. 相似文献
998.
The hydration structure around nanometer-size hydrophobic solutes is studied with molecular dynamics simulation by taking aqueous solutions of C60 and C60H60 as examples. In the hydration shell around a single C60 or C60H60, dipoles of simulated water molecules tend to be aligned to form the vortexlike coherent pattern which lasts for 100 ps, while individual water molecules stay within the hydration shell for about 10 ps. This structural pattern organized by fluctuating and diffusively moving molecules should be called a "fluctuating cage". In the narrow region between a pair of C60 molecules or a pair of C60H60 molecules, water density strongly fluctuates and is correlated to the mean force between solutes. The fluctuating caging and drying between solutes affect the hydrophobic interaction and dynamical behaviors of solutes. 相似文献
999.
Asaka T Kimura T Nagai T Yu XZ Kimoto K Tokura Y Matsui Y 《Physical review letters》2005,95(22):227204
We investigated ferromagnetic domain structures on nanometer to micrometer scale for single crystals of a layered ferromagnet, La(2-2x)Sr(1+2x)Mn2O7 (0.32 < or = x < or = 0.40), as functions of x and temperature by means of Lorentz electron microscopy. We have succeeded in observing the evolution of magnetic ripple structure, dynamically, related to a spin reorientation transition where the magnetization direction switches between parallel and perpendicular to the layers. Our high-resolution magnetic domain imaging revealed that the ripple state is characterized by the evolution of magnetic nanowidth domains. 相似文献
1000.
We report the pressure-induced superconductivity in the noncentrosymmetric heavy-fermion CeRhSi3. The superconductivity emerges above about 12 kbar even though the antiferromagnetic ordering persists. Furthermore, another anomaly is observed in the superconducting phase. The anomalous magnetic field-temperature phase diagram with a high upper critical field suggests that an unconventional superconductivity is realized in CeRhSi3. 相似文献