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991.
992.
Y. Ohtsuka M. Yamamoto Y. Takaku S. Hisamatsu J. Inaba 《Journal of Radioanalytical and Nuclear Chemistry》2006,268(2):397-403
Summary A
rapid method was developed using ultrafilters with a tangential flow filtering
system for molecular size separation of naturally occurring 210Pb
and 210Po in a freshwater sample. Generally, ultrafiltering of a
large volume water sample for measuring the nuclides was too time consuming and
not practical. The tangential flow filtering system made the filtering time
short enough to adapt for in-situ ultrafiltering the large volume sample. In this
method, a 20 liter water sample was at first passed through the 0.45mm pore size
membrane filter immediately after sample collection to obtain suspended
particle matter [>0.45mm particulate fraction (PRT)]. Two ultrafilters (Millipore
Pellicon 2ò)
were used sequentially. The nuclides in the filtrate were separated into three
fractions: high molecular mass (100 kDa-0.45mm; HMM), low molecular mass (10 k-100 kDa;
LMM) and ionic (<10 kDa; INC) fractions. It took 80 minutes to process the
sample after collection. The cut-off molecular size of each ultrafilter was
confirmed by size exclusion chromatographs (SEC) of the LMN and the HMM
fractions. Adsorption of the nuclides and organic compounds in the sample onto
the ultrafilters was negligibly small. Good reproducibility of the nuclide
concentrations in each fraction was confirmed by repeated experiments. The
method was successfully applied to obtaine the molecular size distributions of 210Pb
and 210Po in an oligotrophic lake, Lake Towada located in the northern
area of Japan.</p>
</p> 相似文献
993.
M. Yamamoto M. Hoshi J. Takada S. Oikawa I. Yoshikawa T. Takatsuji A.Kh. Sekerbaev B.I. Gusev 《Journal of Radioanalytical and Nuclear Chemistry》2002,252(2):373-394
The 137Cs, 238Pu and 239,240Pu activity concentrations were determined together with the atomic ratios of 240Pu/239Pu for the soil samples at 19 sites from the Ust"-Kamenogorsk district, located more than 300 km east of the Semipalatinsk nuclear test site (SNTS). The mean areal deposition of 137Cs ranged from 1,500 to 4,100 Bq/m2. However, some hot spot-like areas showing high concentrations of 5,500–7,700 Bq/m2 were foundat some sites within the city. The 239,240Pu levels ranged from <50 to 510 Bq/m2, however most of them ranged between 120–200 Bq/m2. These levels are nearly the same as those around the Semipalatinsk City. At most of the sites within the city and its adjacent areas, both nuclides were found in the soil layers up to a depth of 30 cm. A fraction of 20–50% of 239,240Pu was not leached by hot digestion with concentrated HNO3 containing a small amount of H2O2. Generally, such tightly bound fraction showed a trend to decrease with increasing distance from the SNTS. The fraction of these radionuclides that were deposited in Ust"-Kamenogorsk district from global and from SNTS fallouts have been determined using the 240Pu/239Pu atomic ratios in both Pu fractions: one which can be leached with hot HNO3 + H2O2 and another that is a non-leacheable for each soil layer of core samples. As a result a fraction of 21–80% (mostly 30–60%) of total 239,240Pu were found to be due to the local fallout of Pu from the SNTS debris. For 137Cs, the contribution (mostly 10–20%) of local fallout from the SNTS were estimated to be far lower as compared to 239,240Pu. 相似文献
994.
NHC-coordinated cyclometalated palladium(II) catalyzed addition of arylboronic acids to methyl 2-hydroxy-2-methoxyacetate gave corresponding various functionalized methyl mandelate derivatives in good yields. 相似文献
995.
996.
Yohsuke Yamamoto Shiro Matsukawa Shin-ya Furuta Kin-ya Akiba 《Phosphorus, sulfur, and silicon and the related elements》2013,188(6-7):1375-1379
Solution and crystal structures of monocyclic pentacoordinate phosphoranes bearing two Martin ligands and two carbon substituents are described. When the two carbon substituents are different, relative apicophilicity of the two monodentate carbon substituents could be determined based on the equilibrium ratio of the pseudorotamers. In some cases, x-ray structural analysis could be carried out and the crystallized structure from CH 3 CN is consistent with the major pseudorotamer in solution (CD 3 CN). Furthermore, when the equilibrium ratio of pseudorotamers is almost unity, novel cocrystallization of two pseudorotamers in a single crystal was observed. 相似文献
997.
Yutaka Kawahara Wataru Takarada Masaki Yamamoto Yasuhito Kondo Kohji Tashiro Takeshi Kikutani 《Journal of Macromolecular Science: Physics》2020,59(7):440-456
AbstractVarious types of bicomponent fibers composed of polylactide (PLA) and poly(butylene terephthalate) (PBT) with different molecular weights, arranging the polymers separately in the skin or core, were produced by high-speed melt-spinning. The bicomponent spinning, arranging the PLA with high molecular weight (melt flow rate =1.9?g/10?min, L-lactide content = 98.7%) in the skin and the PBT with low molecular weight (IV = 0.835–0.865 dL/g) in the core, resulted in orientation-induced crystallization in the PLA component at the spinning speed of 2?km/min. This crystallization effect was ascribed to a chain-extending treatment applied to the original PLA (MFR = 4.0?g/10?min) to increase its molecular weight. By the treatment the PLA could crystallize when spun even at 1?km/min in its single-component spinning. On the other hand, the bicomponent spinning system interfered with the orientation-induced crystallization of PBT in the core. As a result, the critical spinning speed needed to generate the orientation-induced crystallization in the core PBT was elevated to 4?km/min. The inferior tensile behavior of the bicomponent fibers, as compared to the single-component PLA or PBT fibers, suggested poor compatibility between PLA and PBT. Transesterification reactions rarely occurred at the interface of the two polymers. The bicomponent fibers prepared from high molecular weight PLA and low molecular weight PBT, however, showed sufficient antibacterial activity and physical properties to be suitable for designing medical clothing materials. 相似文献
998.
Tatsuya Moriai Dr. Takamasa Tsukamoto Dr. Makoto Tanabe Dr. Tetsuya Kambe Prof. Dr. Kimihisa Yamamoto 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(51):23251-23255
The science of particles on a sub-nanometer (ca. 1 nm) scale has attracted worldwide attention. However, it has remained unexplored because of the technical difficulty in the precise synthesis of sub-nanoparticles (SNPs). We recently developed the “atom-hybridization method (AHM)” for the precise synthesis of SNPs by using a suitably designed macromolecule as a template. We have now investigated the chemical reactivity of alloy SNPs obtained by the AHM. Focusing on the coinage metal elements, we systematically evaluated the oxidation reaction of an olefin catalyzed by these SNPs. The SNPs showed high catalytic performance even under milder conditions than those used with conventional catalysts. Additionally, the hybridization of multiple elements enhanced the turnover frequency and the selectivity for the formation of the hydroperoxide derivative. We discuss the unique quantum-sized catalysts providing generally unstable hydroperoxides from the viewpoint of the miniaturization and hybridization of materials. 相似文献
999.
1000.