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941.
Yoshihisa Kurasawa Kaoru Yamazaki Setsuko Tajima Yoshihisa Okamoto Atsushi Takada 《Journal of heterocyclic chemistry》1986,23(3):957-958
3-Formyl-2-oxo-1,2-dihydroquinoxaline chlorophenylhydrazones 4a-c were synthesized from the reactions of 3-methyl-2-oxo-1,2-dihydroquinoxaline 3 with chlorophenyl diazonium salts, and 4b,c were found to exhibit the tautomeric equilibria between the hydrazone imine and diazenyl enamine forms in the dimethylsulfoxide solutions. 相似文献
942.
943.
Kazuo Yamashita Nobuo Kihara Hiroaki Shimidzu Hitomi Suzuki 《Photochemistry and photobiology》1982,35(1):1-7
Abstract— The photovoltaic properties of meso -tetraphenylporphyrin and its derivatives with various para -substituents, meso-tetrakis(2,4-dimethoxyphenyl)porphyrin and meso -tetrakis (2-fluorenyl)porphyrin have been investigated. The forward dark current-voltage characteristics of Al/porphyrin/Ag cells are attributed to the MIS Schottky barriers consisting of Al/Al2 O3 /porphyrin. The barrier parameters such as the apparent diffusion potential V 0 the barrier width w0 and the density of ionized impurity N are estimated by using the capacitor discharge method. The action spectra of photocurrents closely follow the optical absorption spectra of the porphyrin films. The photocurrents vary as i p α I γ , where I is the incident light intensity, and the Sight exponents y range between 0.83 and 1.0. The sublinear difference from unity could be related to the exponential distribution of hole traps in films of the porphyrins. No obvious correlation between the photocurrent and the fluorescence quantum yields of the sublimed porphyrin films is found. The electron donating substituents such as OCH3 and CH3 strikingly increase the photocurrents. The photocurrent quantum yields correlate exponentially with the first ring oxidation potentials of the porphyrins and also with the substituent constants for the Hammett linear free-energy relationship. The current quantum yields estimated for the porphyrins studied, range in the order of 10-4 –10-2 with power conversion efficiencies 10-7 –10-3 . 相似文献
944.
The reaction of oleanane triterpenoid 1b with a FeIII(PA; picolinate)3/H2O2/MeCN system (reagent system A), a simple model system for mono-oxygenase, gave the 11 alpha-hydroxyl derivative 3 as major product, along with 11-oxo derivative 4 and 12-oxo derivative 6. The reaction of lupane triterpenoid 2b with reagent system A gave only oxidative rearrangement compounds, (20R)-aldehyde 8 and (20S)-aldehyde 9 were epimeric isomers. Then, we have found that iron(III) picolinate complex, FeIII(PA)3 is efficient in effecting the rearrangement of triterpenoid epoxides 5 and 7 into the corresponding carbonyl compounds, 6, 8 and 9 with 1,2-shift of the hydride. 相似文献
945.
Ho Sik Kim Tong Eun Kim Sam Tag Kwag Yong Tae Park Young Seuk Hong Yoshihisa Okamoto Yoshihisa Kurasawa 《Journal of heterocyclic chemistry》1997,34(5):1539-1542
The reaction of the 6-chloro-2-(1-methyl-2-thiocarbamoylhydrazino)quinoxaline 4-oxides 3a-d with trifluoroacetic anhydride gave the 2-(N-aryl)trifluoroacetamido-8-chloro-4-methyl-4H-1,3,4-thiadiazino-[5,6-b]quinoxalines 7a-d , respectively, while the reflux of compounds 3a-c in N,N-dimethylformamide afforded the mesoionic triazolo[4,3-a]quinoxaline 4 . Hydrolysis of compounds 7a-d with triethylamine/water provided the 2-arylamino-8-chloro-4-methyl-4H-1,3,4-thiadiazino[5,6-b)]quinoxalines 8a-d , respectively. 相似文献
946.
Susumu Honda Atsushi Taga Kazuaki Kakehi Shigetaka Koda Yoshihiko Okamoto 《Journal of chromatography. A》1992,590(2):364-368
Cefixime (CX), an oral cephalosporin antibiotic, and its metabolites in human digestive organs were separated by various modes of high-performance capillary electrophoresis. The zone electrophoresis mode in phosphate buffer (pH 6.8) containing 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulphonate gave the best separation, permitting the complete resolution of CX and all of five metabolites. On the other hand, the plain zone electrophoresis mode in phosphate buffer (pH 6.8) offered a simple procedure for the direct determination of urinary CX concentration using intact urine samples. 相似文献
947.
Yasuyuki Takeda Takehiro Iwasaki Yoshihiro Kudo Hiroaki Matsuda 《Journal of inclusion phenomena and macrocyclic chemistry》1992,14(3-4):303-309
Thermodynamic parameters (H
ex
0
and S
ex
0
) for the overall extractions of monovalent metal (Na, K, Rb, and Tl) picrates with benzo-18-crown-6 (B18C6), and those (H
D,L
0
and S
D,L
0
) for the distribution of B18C6 were determined between chloroform and water. All the extracted B18C6 complexes were l:1:1 complexes (B18C6:metal ion: picrate anion). The H
ex
0
and S
ex
0
values for all the metals are negative. Every extraction of the metal picrate with B18C6 is completely enthalpy driven. The H
D,L
0
and S
D,L
0
values of B18C6 are both positive, and the partition of B18C6 is entirely entropy driven. Enthalpy (H
ex,ip
0
) and entropy changes (S
ex,ip
0
) for ion-pair extractions of B18C6-metal ion complexes with picrate anions were calculated. All the H
ex,ip
0
and S
ex,ip
0
values are negative, and the ion-pair extractions are completely enthalpy driven. 相似文献
948.
Seven million times elongation of the lifetime of charge-separated state is attained in the presence of yttrium triflate [Y(OTf)3] in the photoinduced electron-transfer reaction of a ferrocene-anthraquinone dyad (Fc-AQ) with a rigid amide spacer in benzonitrile at 298 K as compared with the lifetime in its absence. Such remarkable elongation of the CS lifetime in the presence of Y(OTf)3 results from the strong binding of Y(OTf)3 with the AQ*- moiety of Fc+-AQ*-. 相似文献
949.
We analyzed the interaction energies between residues (fragments) in an oligopeptide occurring during dynamic simulations by using the fragment molecular orbital-Hamiltonian algorithm (FMO-HA) method, an ab initio MO-molecular dynamics technique. The FMO method enables not only calculation of large molecules based on ab initio MO but also easy evaluation of interfragment interaction energies. The glycine pentamer [(Gly)(5)] and decamer [(Gly)(10)] were divided into five and ten fragments, respectively. alpha-helix structures of (Gly)(5) and (Gly)(10) were stabilized by attractive interaction energies owing to intramolecular hydrogen bonds between fragments n and n+3 (and n+4), and beta-strand structures were characterized by repulsive interaction energies between fragments n and n+2. We analyzed interfragment interaction energies during dynamics simulations as the peptides' geometries changed from alpha helix to beta strand. Intramolecular hydrogen bonds between fragments 2-4 and 2-5 control the geometrical preference of (Gly)(5) for the beta-strand structure. The pitch of one turn of the alpha helix of (Gly)(10) elongated and thus weakened during dynamics due to a shifting of the intramolecular hydrogen bonds, and enabled the beta-strand structure to form. Changes in interaction energies due to the intramolecular hydrogen bonds controlled the tendency toward alpha-helix or beta-strand structure of (Gly)(5) and (Gly)(10). Evaluation of interfragment interaction energies during dynamics simulations thus enabled detailed analysis of the process of the geometrical changes occurring in oligopeptides. 相似文献
950.
Yoshio Okamoto 《Journal of polymer science. Part A, Polymer chemistry》2004,42(18):4480-4491
A chiral diamine alkaloid, (−)-sparteine (Sp), has been found to be very effective as a ligand for Grignard reagents when used for the enantiomer-selective polymerization of racemic RS-1-phenylethyl methacrylate. The enantiomeric excess of the initially polymerized monomer is 93%, and at about a 60% conversion, nearly optically pure R-monomer is recovered. This enantiomer selectivity is today the highest in polymer chemistry. Triphenylmethyl methacrylate (TrMA) is a unique monomer that gives a highly isotactic polymer even during radical polymerization. When TrMA is polymerized with the Sp complex with n-butyllithium in toluene at −78 °C, an optically active, isotactic polymer [poly(triphenylmethyl methacrylate) (PTrMA)] with a one-handed helical conformation is obtained. The helical structure is maintained even at room temperature in solution. Analogous helical polymethacrylates that show various conformational changes have also been found. One-handed helical PTrMA exhibits high chiral recognition to a variety of racemates as a chiral stationary phase (CSP) for high-performance liquid chromatography. This finding has led to the development of very powerful CSPs based on polysaccharides, such as cellulose and amylose. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4480–4491, 2004 相似文献