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961.
962.
963.
Hiroyuki Nakamura Makiko Seno Tsuneyuki Sato 《Journal of polymer science. Part A, Polymer chemistry》1997,35(1):153-162
The effect of LiClO4 on the polymerization of di-2-[2-(2-methoxyethoxy)ethoxy]ethyl itaconate (DMEI) with dimethyl 2,2′-azobisisobutyrate (MAIB) was investigated in methyl ethyl ketone (MEK) kinetically and by ESR. The polymerization rate (Rp) at 50°C, where the concentrations of DMEI and MAIB were 1.00 and 5.00 × 10−2 mol/L, increased with increasing [LiClO4]. Marked acceleration was observed at higher [LiClO4]s than 1.0 mol/L. The molecular weight of resulting polymer (ca. 10,000) was relatively insensitive to [LiClO4], indicating occurrence of chain transfer. IR analysis of mixtures of LiClO4/DMEI and LiClO4/poly(DMEI) indicated complexation of LiClO4 with DMEI and its polymer. The rate constants of propagation (kp) and termination (kt) were determined by ESR. kp (1.7–10.5 L/mol s at 50°C) increased with [LiClO4]. kt (5.2–1.0 × 104 L/mol s at 50°C) showed remarkable decrease at higher [LiClO4]s than 1.0 mol/L. Rp of polymerization of equimolar complex of LiClO4/DMEI with MAIB at 50°C in MEK was expressed by Rp = k[MAIB]0.5[DMEI]2.4. kp increased and kt decreased with [DMEI]. The activation energies of overall polymerization, propagation and termination were estimated to be 34.5, 8.0, and 59.4 kJ/mol. Copolymerization of DMEI with styrene was also profoundly affected by the presence of LiClO4. Such large effects of LiClO4 on the homo- and copolymerization of DMEI are explicable in term of association of LiClO4-complexed DMEI monomers. © 1997 John Wiley & Sons, Inc. 相似文献
964.
Two kinds of adsorbents (Si adsorbent and Al adsorbent) for the removal of silicic acid from geothermal water to retard the formation of silica scales were prepared using silicic acid contained in geothermal water. The Si adsorbent was prepared by evaporating geothermal water, and the Al adsorbent was prepared by evaporating geothermal water after the addition of aluminum chloride. The specific surface area of the Si adsorbent was small and it's adsorption capacity of silicic acid was low. Although the specific surface area of the Al adsorbent was also small, it was significantly increased by the adsorption of silicic acid and it's adsorption capacity was high. Based on the change in the local structure of aluminum ion by the adsorption of silicic acid, the Al adsorbent was considered to be silica particles covered with crystalline aluminum hydroxide. Moreover, it was concluded that the increase in the specific surface area of the Al adsorbent and the decrease in the zeta potential were due to the formation of an amorphous aluminosilicate with a large surface area and a negative charge (one 4-coordinated Al) by the reaction between aluminum ions and silicic acids. 相似文献
965.
Takashi Harumoto Javed Iqbal Xiaofang Liu Ji Shi Yoshio Nakamura Ronghai Yu 《Applied Physics A: Materials Science & Processing》2009,97(1):211-215
Co doped SnO2 nanoparticles have been prepared via a wet chemical method with different precipitation processes. The structure and morphology
of Co doped SnO2 nanoparticles demonstrate that the nanoparticles are in a rutile single phase and uniform, respectively. X-ray photoelectron
spectroscopy shows that the Co dopants are in 2+ oxidation valence state and doped ∼2 atm% in SnO2 nanoparticles. Moreover, Raman spectroscopy further confirms that Co doped SnO2 nanoparticles have single phase crystallinity without forming any extra modes related to secondary phases. The magnetic measurements
reveal that all nanoparticles exhibit room temperature ferromagnetism (RTFM) due to the presence of disorders and defects
introduced by hydroxyls in the crystal structure. In addition, it has been clearly observed that the saturated magnetic moments
are strongly affected by the precipitation processes which control the incorporation of hydroxyls into the lattice. 相似文献
966.
Tatsuro Ouchi Tatsuya Nozaki Akira Ishikawa Isao Fujimoto Yuichi Ohya 《Journal of polymer science. Part A, Polymer chemistry》1997,35(2):377-383
Since poly(lactic acid) is the biodegradable polyester having low immunogenicity and good biocompatibility, it is utilized as a medical material. However, poly(lactic acid) is a water-insoluble crystalline polymer having no reactive side-chain group. Thus, the use of poly(lactic acid) is limited. To modify the properties of poly(lactic acid) and to introduce the functionalized pendant groups to poly(lactic acid), we synthesized two kinds of lactic acid-depsipeptide copolymers with reactive pendant groups, namely poly[LA-(Glc-Lys)] and poly[LA-(Glc-Asp)]. This was done through ring-opening copolymerizations of L-lactide with the corresponding protected cyclodepsipeptides, cyclo[Glc-Lys(Z)] and cyclo[Glc-Asp(OBzl)], and subsequent deprotection of benzyloxycarbonyl and benzyl groups, respectively. By changing the mole fraction of the corresponding depsipeptide units, the solubility, thermal transition and degradation behavior of the modified poly(lactic acid) could be varied. © 1997 John Wiley & Sons, Inc. 相似文献
967.
968.
K. Kumagai Y. Nakamichi Y. Nakamura I. Watanabe H. Nakajima T. Fujita 《Hyperfine Interactions》1989,50(1-4):583-591
Nuclear quadrupole resonances (NQR) of139La in La2−xMxCuO4 (M=Ba, Sr) and63Cu in YBa2CU3O7 have been investigated with substitution of Cu by magnetic impurities. For La-system, the strong enhancement of the nuclear
relaxation rate, 1/T
1 atT
c
*≈10 K (suggesting the occurrence of magnetic instability with hole-doping), is suppressed by 3D-antiferromagnetism induced
by magnetic impurities. In the superconducting region, fluctuations of Cu moments at low temperatures remain extremely fast
as at high temperatures. For Y-system, Fe-ions are substituted for both Cu(1) and Cu(2) sites, But Co-ions are preferentially
substituted to Cu1 sites. The peaks in the relaxation rate of Cu indicate the appearance of magnetic ordering without destroying
superconductivity for the 0.5%-Fe doped sample. 相似文献
969.
Five types of non-symmetric calamitic dimers were synthesized to investigate the effect of the core structure and length of the spacer on mesomorphic properties. Two non-symmetric dimers containing a troponoid and benzenoid unit showed smectic A and C phases whereas the corresponding benzenoid dimers showed no mesophase. Non-symmetric dimers with a three-ring system showed smectic A and C phases with higher transition temperatures than the two-ring system. We propose packing models for these non-symmetric dimers by considering the direction of the dipole moments of the ring structures and microsegregation between the polar units and the non-polar chains. 相似文献
970.