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991.
[structure: see text]. Mycapolyols A-F (1-6), six new unusual PKS/NRPS metabolites, were isolated from the marine sponge Mycale izuensis. The gross structures were elucidated by analysis of spectroscopic data, while the stereochemistry was established using chemical method and the universal NMR database. 相似文献
992.
Sasaki S Taniguchi Y Takahashi R Senko Y Kodama K Nagatsugi F Maeda M 《Journal of the American Chemical Society》2004,126(2):516-528
Triplex-forming oligonucleotides (TFOs) are potential DNA-targeting molecules and would become powerful tools for genomic research. As the stabilization of the TFO is partially provided by hydrogen bonds to purine bases, the most stable triplexes form with homopurine/homopyrimidine sequences, and a pyrimidine base in the purine strand of the duplex interrupts triplex formation. If a TFO can recognize sequences including such an interrupting site, the target regions in the genome would be expanded to a greater extent. However, this problem has not been generally solved despite extensive studies. We have previously reported a new base analogue (WNA) constructed of three parts, a benzene ring, a heterocyclic ring, and a bicyclic skeleton to hold these two parts. In this study, we have further investigated modification of WNA systematically and determined two useful WNA analogues, WNA-beta T and WNA-beta C, for selective stabilization of triplexes at a TA and a CG interrupting site, respectively. The triplexes with WNA analogues have exhibited an interesting property in that they are more stable than natural-type triplexes even at low Mg(2+) concentration. From comparison of the results with H-WNA-beta T lacking benzene and those with WNA-H without thymine, it has been suggested that benzene is a major contributor for triplex stability and thymine provides selectivity. Thus, it has been successfully demonstrated that WNA-beta T/TA and WNA-beta C/CG combinations may expand triplex recognition codes in addition to the natural A/AT and G/GC base triplet codes. The results of this study will provide useful information for the design of new WNA analogues to overcome inherent problems for further expansion of triplex recognition codes. 相似文献
993.
Yoshiyuki Sato Hajime HashiguchiKenzo Inohara Shigeki TakishimaHirokatsu Masuoka 《Fluid Phase Equilibria》2007
PVT properties of four polyethylene random copolymers (ethylene-propylene, ethylene-1-butene, ethylene-1-hexene, and ethylene-1-octene) and linear polyethylene were measured at temperatures from 313 to 493 K and pressures up to 200 MPa. Dependence of properties such as specific volume, thermal expansion coefficient, isothermal compressibility, and characteristic parameter of equations of state on the length of the polymer branched chains were examined. It was found that the length of the branched chain did not affect the thermal expansion coefficient and isothermal compressibility. The specific volume of copolymers having longer branched chains were slightly larger than those copolymers with short branched chains. 相似文献
994.
Kodama S Yamamoto A Matsunaga A Soga T Minoura K 《Journal of chromatography. A》2000,875(1-2):371-377
Chiral resolution of native DL-lactic acid was performed by capillary electrophoresis using 2-hydroxypropyl-beta-cyclodextrin as a chiral selector. Various factors affecting chiral resolution, migration time, and peak area of lactic acid were studied. The running conditions for optimum separation of lactic acid were found to be 90 mM phosphate buffer (pH 6.0) containing 240 mM 2-hydroxypropyl-beta-cyclodextrin with an effective voltage of -30 kV at 16 degrees C, using direct detection at 200 nm. In order to enhance the sensitivity, sample injection was done under a pressure of 50 mbar for 200 s. On-line sample concentration was accomplished by sample stacking. With this system, D- and L-lactic acids in food products were analyzed successfully. 相似文献
995.
Takano Hiroyuki Takeyama Haruko Nakamura Noriyuki Sode Koji BURGESS J. Grant Manabe Eichi Hirano Morio Matsunaga Tadashi 《Applied biochemistry and biotechnology》1992,34(1):449-458
A light diffusing optical fiber (LDOF) photobioreactor with an improved gas input system has been used for the high-density culture of a marine cyanobacterium Synechococcus sp. Optimum conditions for CO2 removal and biomass production were investigated. Maximum CO2 removal of 4.44 g/L/d was achieved using an initial cell concentration of 6.8 g/L. The biomass yield was 0.97 g/L for a 12-culture time. Continuous cultures, in which medium was filtered using a ceramic membrane module, showed enhanced growth, with a final cell concentration of 11.2 g/L. These results demonstrate the potential of LDOF photobioreactor units for CO2 removal and biomass production using marine cyanobacteria.
相似文献996.
Shigeki Sasaki Kenji Koga 《Journal of inclusion phenomena and macrocyclic chemistry》1989,7(2):267-276
A novel approach to the enzyme model for the synthesis of peptides has been established by using multi-functionalized chiral crown ethers as hosts. The new strategy consists of three key steps as follows. (1) Guest assembly: the host having one free thiol and one thioester withN-protected-amino acid or peptide proceeds via rapid intra-complex thiolysis of-amino acid ester salts to form the dithioester, and assembles two guests. (2) Amide formation: the intramolecular aminolysis occurs between the bound guests to form the amide bond. (3) Peptide chain elongation: as the thiol reactive group is regenerated, the above two reactions are repeated to elongate the peptide chain. In the present paper, we describe the multiple chiral recognition that could be achieved by the chiral crown ether in both the intra-complex thiolysis and the intramolecular aminolysis. For explanation of the chiral recognition, we propose a likely structure for the intermediate of the aminolysis. 相似文献
997.
A naked-eye detection method for a trace amount of arsenic in aqueous samples has been newly developed. The proposed method is based on the formation of a hetero poly acid in a chelating resin phase. Molybdenum loaded on a chelating resin having β-hydroxypropyl-di(β-hydroxyethyl) amino moiety reacts with arsenic(V) to form the hetero poly acid, which makes the resin beads greenish blue in the presence of a reducing agent under acidic conditions. It was also found that the intensity of the color of the resin depends on the concentration of arsenic(V) in the sample solutions. Since the development of the color occurs in 20 min by heating of the mixture at 40 °C, this system can provide a simple, rapid and low-cost detection method of a trace amount of arsenic(V) in an aqueous media. The detection limit of this method is 1 × 10−6 mol dm−3. A longer preconcentration time with the same resin gave the higher sensitivity of 1 × 10−7 mol dm−3 that is comparable with that of the instrumental analysis. The present method comprises both the concentration and detection step with the same solid material, and hence it gives higher sensitivity and easier handling than the ordinary colorimetric methods using a liquid medium. 相似文献
998.
Toshio Mori Misa Nakane Tsuyoshi Hattori Tsukasa Matsunaga Makoto Ihara Osamu Nikaido 《Photochemistry and photobiology》1991,54(2):225-232
Six new monoclonal antibodies (TDM-2, TDM-3, 64M-2, 64M-3, 64M-4 and 64M-5) specific for ultraviolet (UV) induced DNA damage have been established. In the antibody characterization experiments, two TDM antibodies were found to show a dose-dependent binding to UV-irradiated DNA (UV-DNA), decrease of binding to UV-DNA after cyclobutane pyrimidine dimer photoreactivation, binding to DNA containing cyclobutane thymine dimers, and unchanged binding to UV-DNA after photoisomerization of (6-4)photoproducts to Dewar photoproducts. These results indicated that the epitope of TDM monoclonal antibodies was the cyclobutane pyrimidine dimer in DNA. On the other hand, four 64M antibodies were found to show a dose-dependent binding to UV-DNA, unchanged binding to UV-DNA after cyclobutane pyrimidine dimer photoreactivation, undetectable binding to DNA containing thymine dimers, and decrease of binding to UV-DNA after photoisomerization of (6-4)photoproducts. These results indicated that the epitope of 64M antibodies was the (6-4)photoproduct in DNA. This is the first report of the simultaneous establishment of monoclonal antibodies against the two different types of photolesions from the same mouse. By using these monoclonal antibodies, we have succeeded in measuring both cyclobutane pyrimidine dimers and (6-4)photoproducts in the DNA from human primary cells irradiated with physiological UV doses. 相似文献
999.
(R(S))-1 (85% ee) was prepared by utilizing a porcin pancreatic lipase-promoted hydrolysis of sulfinyldiacetic acid dimethyl ester (8) which was derived from thiodiacetic acid (7). (R(S))-1 (99% ee) and (S(S))-1 (99% ee) were readily obtained by methanolysis of (R(S),S)-12 and (S(S),S)-12 with MeONa in MeOH. (R(S),S)-12 and (S(S),S)-12 were furnished by chromatographic separation of the diastereomeric mixture, obtained by oxidation of thiodiacetic mono-carboxylic acid (11) with 30% H2O2 followed by dehydrative condensation of the resultant sulfinyldiacetic mono-carboxylic acid with 4(S)-isopropyl-1,3-thiazolidine-2-thione. (R(S))-1 (99% ee) was successively treated with (TMS)2NLi, Ac2O, and TMSOTf to give a major chiral-3 product in 75% ee and in a highly chemoselective manner (chiral-3:chiral-2=93:7). 相似文献
1000.
Tadao Ishizuka Tomokazu Katahira Ryushi Seo Hirofumi Matsunaga Takehisa Kunieda 《Tetrahedron letters》2004,45(51):9327-9330
The chiral functionalization of a simple heterocycle, 1,3-dihydro-2-imidazolone, was achieved by the highly enantioselective monodeacylation of meso-1,3-diacetyl-2-imidazolidinones via an oxazaborolidine-catalyzed borane reduction. This kinetically controlled dissymmetrization is sufficiently effective to provide a synthetic route to either enantiomer of (4S, 5S)- or (4R, 5R)-4,5-dimethoxy-2-imidazolidinone derivatives, which serve as chiral synthons for threo-1,2-diamines. 相似文献