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941.
Song HY Joo JM Kang JW Kim DS Jung CK Kwak HS Park JH Lee E Hong CY Jeong S Jeon K Park JH 《The Journal of organic chemistry》2003,68(21):8080-8087
The proposed structure of lasonolide A was synthesized employing radical cyclization reactions of beta-alkoxyacrylates for preparation of the tetrahydropyranyl units A and B, but the spectroscopic data did not match those of the natural product. Both enantiomers of a revised structure featuring 17E,25Z double bonds were synthesized, and the (-)-isomer was found to be the biologically active enantiomer. 相似文献
942.
Blends of poly(4-methylstyrene) (P4MS) with polystyrene (iPS) exhibit an upper critical solution temperature (UCST) at ca. 270 °C. The overall phase behavior and trend of variation in the phase diagrams for the iPS/P4MS blend system with respect to molecular weights of iPS is similar to an earlier studied blend system of atactic PS with P4MS. This suggests that the crystal phase-related tacticity and crystallinity in iPS does not influence the amorphous phase behavior and UCST behavior of the polymer mixtures. A model based on a modified Flory-Huggins expression for binary interactions was constructed to describe the UCST-type behavior of the iPS/P4MS blend and to compare the qualitative effects of molecular weights on iPS/P4MS blend vs. atactic PS/P4MS systems. 相似文献
943.
Cho YS Karupaiyan K Kang HJ Pae AN Cha JH Koh HY Chang MH 《Chemical communications (Cambridge, England)》2003,(18):2346-2347
Synthesis of novel substituted tetrahydropyrans with adjacent exo-methylene groups at the C3 and C4 positions via Prins-type cyclization has been described. 相似文献
944.
The polymers containing ribose rings: poly(5'-acrylamido-5'-deoxy-1',2'-O-isopropylidene-alpha-D-ribose) (11), poly(5'-acrylamido-5'-deoxy-alpha-D-ribose) (12) and poly(5'-acrylamido-5'-deoxy-1'-O-methyl-D-ribose) (13) were prepared as enzyme mimics. Polymers 12 and 13 with free vic-cis-diol groups catalyzed the hydrolysis of phosphodiester (ethyl p-nitrophenyl phosphate and N-methylpyridinium 4-tert-butylcatechol cyclic phosphate) and phosphomonoester substrates with a rate acceleration of 10 approximately equal to 10(3) compared with the uncatalyzed reaction. They also catalyzed the reverse reactions, i.e., the esterification of phosphomonoester to phosphodiester and the phosphorylation of alcohols with phosphate ions. The catalytic activity was attributable to the vic-cis-diols of riboses on polymer chains, which formed hydrogen bonds with two phosphoryl oxygen atoms of phosphates so as to activate the phosphorus atoms to be attacked by nucleophiles. The catalytic activity was negligible for polymer 11 where vic-cis-diol groups were blocked with isopropylidene groups. The catalytic activity was attributable to the vic-cis-diols of riboses on polymer chains, which formed hydrogen bonds with two phosphoryl oxygen atoms of phosphates so as to activate the phosphorus atoms to be attacked by nucleophiles. 相似文献
945.
A simple method for high-pressure combinatorial catalyst discovery with visual (dye-based) assay is described. With this method, the first highly active catalyst, incorporating metals outside the platinum group, has been identified for CO(2) hydrogenation. 相似文献
946.
Huh D Tkaczyk AH Bahng JH Chang Y Wei HH Grotberg JB Kim CJ Kurabayashi K Takayama S 《Journal of the American Chemical Society》2003,125(48):14678-14679
This work is the first demonstration of electrical modulation of surface energy to reversibly switch dynamic high-speed gas-liquid two-phase microfluidic flow patterns. Manipulation of dynamic two-phase systems with continuous high-speed flows is complex and interesting due to the multiple types of forces that need to be considered. Here, distinct stable flow patterns are formed through a multipronged approach: both surface tension forces generated by surface chemistry modulation as well as viscous and inertial forces produced by fluid flows are employed. The novel fluidic actuation mechanism provides insights into better understanding microscale two-phase flow dynamics and offers new opportunities for the development of two-phase biochemical microsystems that are mechanically simple and operational at high speeds. 相似文献
947.
948.
949.
The influence of tyloxapol on the dynamic surface tension response of dipalmitoyl phosphatidylcholine (DPPC) dispersions at pulsating air/liquid interfaces was investigated. For a 1000 ppm DPPC dispersion prepared by sonication with a larger particle size, the dynamic surface activity of DPPC was strongly affected by the addition of 100 ppm tyloxapol. With a longer sonication time or smaller particle size, the DPPC inactivation was still observed but was somewhat less significant, resulting in slightly lower dynamic surface tensions. If a DPPC dispersion was sonicated in the presence of tyloxapol, the particle size of DPPC was greatly reduced by tyloxapol and the inhibitory effect of tyloxapol on the dynamic adsorption of DPPC may be significantly diminished. The results suggest that the competitive adsorption of tyloxapol may have a detrimental effect on the dynamic surface tension lowering ability of a DPPC dispersion with the extent depending on the DPPC dispersion state. Nevertheless, the dynamic surface activity of DPPC may be enhanced through the improved dispersion by tyloxapol if an appropriate preparation protocol is applied, and the inhibitory effect of tyloxapol may be reduced or overcome. Copyright 2001 Academic Press. 相似文献
950.
We prove that there is precisely one normal CM-field of degree 48 with class number one which has a normal CM-subfield of degree 16: the narrow Hilbert class field of with .