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排序方式: 共有362条查询结果,搜索用时 62 毫秒
71.
72.
Tobias Weissenberger Rainer Leonhardt Dr. Benjamin Apeleo Zubiri Dr. Martina Pitínová-Štekrová Dr. Thomas L. Sheppard Bastian Reiprich Dr. Jürgen Bauer Dr. Ralf Dotzel Maik Kahnt Dr. Andreas Schropp Prof. Christian G. Schroer Prof. Jan-Dierk Grunwaldt Dr. John L. Casci Prof. Jiří Čejka Prof. Erdmann Spiecker Prof. Wilhelm Schwieger 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(63):14430-14440
The successful synthesis of hierarchically structured titanium silicalite-1 (TS-1) with large intracrystalline macropores by steam-assisted crystallisation of mesoporous silica particles is reported. The macropore topology was imaged in 3D by using electron tomography and synchrotron radiation-based ptychographic X-ray computed tomography, revealing interconnected macropores within the crystals accounting for about 30 % of the particle volume. The study of the macropore formation mechanism revealed that the mesoporous silica particles act as a sacrificial macropore template during the synthesis. Silicon-to-titanium ratio of the macroporous TS-1 samples was successfully tuned from 100 to 44. The hierarchically structured TS-1 exhibited high activity in the liquid phase epoxidation of 2-octene with hydrogen peroxide. The hierarchically structured TS-1 surpassed a conventional nano-sized TS-1 sample in terms of alkene conversion and showed comparable selectivity to the epoxide. The flexible synthesis route described here can be used to prepare hierarchical zeolites with improved mass transport properties for other selective oxidation reactions. 相似文献
73.
R. Gruß und F. Scheller 《Fresenius' Journal of Analytical Chemistry》1989,333(1):29-32
Summary An electrochemical procedure based on the anodic oxidation of thiocholine iodide for the determination of the activity of cholinesterase both in serum and in the red blood cells is described. Using electronic differentiation of the current time curve the enzyme activity is directly available. The values obtained agree very well with the established method. Furthermore, both reversible and irreversible inhibitors of the cholinesterase have been quantified by using standardized serum samples. 相似文献
74.
75.
The self-diffusion behavior of a triblock copolymer (PEO–b– PPO–b–PEO) in an aqueous solution of 20% (m/m) was investigated
during a temperature-induced phase transition from liquid to gel state using pulsed field gradient NMR and static light scattering.
The measured self-diffusivity shows a strong dependence on the observation time in the gel phase indicating the existence
of diffusion barriers in the size range of about 0.6 μm.
Additional static light-scattering measurements show a structure in the same size range of several hundred nanometers, which
is far above molecular or micellar sizes and thus, has to be caused by larger clusters.
The similarity in the space scales suggests that the restriction of molecular propagation is correlated with the grain boundaries
between the domains of the poly-crystalline structure formed by the arranged micelles.
Received: 28 October 1996 Accepted: 21 March 1997 相似文献
76.
77.
Frank F. Bier Eva Ehrentreich-Förster Christian G. Bauer Frieder W. Scheller 《Analytical and bioanalytical chemistry》1996,354(7-8):861-865
The amplification cycle consisting of NADH independent oligosaccharide dehydrogenase (ODH) and laccase has been recently reported to be highly sensitive to several catecholamines and p-aminophenol. A competitive immunoassay for 2,4-dichlorophenoxyacetic acid has been developed by combining this amplification cycle with β-galactosidase as enzyme label resulting in p-aminophenol as product. The combination of enzymatic amplification cycles with a competitive immunoassay yields a highly sensitive measurement of 2,4-dichlorophenoxyacetic acid. Using a monoclonal antibody the linear range of the assay was between 0.02 and 100 ng/l and the c50 was found at 0.2 ng/l; the detection limit was at 5 pg/l (25 fmol/l) corresponding to 5 amol. 相似文献
78.
Laccase of Coriolus zonatus 总被引:1,自引:0,他引:1
Koroljova OV Stepanova EV Gavrilova VP Biniukov VI Jaropolov AI Varfolomeyev SD Scheller F Makower A Otto A 《Applied biochemistry and biotechnology》1999,76(2):115-127
Laccase is one of the lignolytic enzymes found in liquid cultures of the fungus Coriolus zonatus in defined medium. The enzyme was isolated from culture liquid and characterized. Laccase from C. zonatus is a single-chain protein with a molecular mass of 60 kDa. Carbohydrate moiety of enzyme consisted of mannose, galactose
and N-acetyl-glucosamine in a ratio of 6:2:0,6 respectively, and comprised 10% of the entiremolecule lsoelectric point was detected
at pH 4.6. Laccase was found to have a pH optimum of 4.9 and temperature optimum of 55°C. Substrate specificity studies were
conducted with catechol, K-ferrocyanide, hydroquinone, and sinapinic acid as substrates. The highest efficiency of catalysis
was observed with sinapic acid as the substrate. The kinetic constants k
cat and K28 of this reaction were 624 s−1 and 7 μM, respectively. 相似文献
79.
Anton Gatial Štěpán Sklenák Viktor Milata Peter Klaeboe Stanislav Biskupič Dieter Scheller Jana Jurašková 《Structural chemistry》1996,7(1):17-36
The IR and Raman spectra of aminomethylene propanedinitrile (AM) [H2N-CH=C(CN)2], (methylamino)methylene propanedinitrile (MAM) [CH3NH-CH=C(CN)2] and (dimethylamino)methylene propanedinitrile (DMAM) [(CH3)2N-CH=C(CN)2] as solids and solutes in various solvents have been recorded in the region 4000-50 cm–1. AM and DMAM can exist only as one conformer. From the vibrational and NMR spectra of MAM in solutions, the existence of two conformers with the methyl group orientedanti andsyn toward the double C=C bond were confirmed. The enthalpy difference H
0 between the conformers was measured to be 3.7±1.4 kJ mol–1 from the IR spectra in acetonitrile solution and 3.4±1.1 kJ mol–1 from the NMR spectra in DMSO solution. Semiempirical (AM1, PM3, MNDO, MINDO3) and ab initio SCF calculations using a DZP basis set were carried out for all three compounds. The calculations support the existence of two conformersanti andsyn for MAM, withanti being 7.8 kJ mol–1 more stable thansyn from ab initio and 8.6, 13.4, 11.6, and 10.8 kJ mor–1 from AM1, PM3, MNDO, and MINDO3 calculations, respectively. Finally, complete assignments of the vibrational spectra for all three compounds were made with the aid of normal coordinate calculations employing scaled ab initio force constants. The same scale factors were optimized on the experimental frequencies of all three compounds, and a very good agreement between calculated and experimental frequencies was achieved. 相似文献
80.
Finze M Bernhardt E Willner H Lehmann CW 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(22):6653-6665
The haloacyltris(trifluoromethyl)borate anions [(CF3)3BC(O)Hal]- (Hal=F, Cl, Br, I) have been synthesized by reacting (CF3)3BCO with either MHal (M=K, Cs; Hal=F) in SO2 or MHal (M=[nBu4N]+, [Et4N]+, [Ph4P]+; Hal=Cl, Br, I) in dichloromethane. Metathesis reactions of the fluoroacyl complex with Me3SiHal (Hal=Cl, Br, I) led to the formation of its higher homologues. The thermal stabilities of the haloacyltris(trifluoromethyl)borates decrease from the fluorine to the iodine derivative. The chemical reactivities decrease in the same order as demonstrated by a series of selected reactions. The new [(CF3)3BC(O)Hal]- (Hal=F, Cl, Br) salts are used as starting materials in the syntheses of novel compounds that contain the (CF3)3B-C fragment. All borate anions [(CF3)3BC(O)Hal]- (Hal=F, Cl, Br, I) have been characterized by multinuclear NMR spectroscopy (11B, 13C, 17O, 19F) and vibrational spectroscopy. [PPh4][(CF3)3BC(O)Br] crystallizes in the monoclinic space group P2/c (no. 13) and the bond parameters are compared with those of (CF3)3BCO and K[(CF3)3BC(O)F]. The interpretation of the spectroscopic and structural data are supported by DFT calculations [B3LYP/6-311+G(d)]. 相似文献