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71.
Michiya Itoh Kenji Murata Kunihiro Tokumura Koichi Shudo Naoki Miyata Toshihiko Okamoto 《Tetrahedron》1979,35(9):1059-1063
Photorearrangement reactions of K-region arene oxides, 9,10-epoxy-9,10-dihydrophenanthrene (1a), 3-acetyl-9,10-epoxy-9,10-dihydrophenanthrene (1b), and 3,4-epoxy-3,4-dihydropyrene (1c) in dichloroethane (DCE) solution were investigated by steady irradiation and nanosecond transient spectroscopy. Photorearrangements producing substituted oxepins, 2 occur via the singlet excited state of these compounds, while the phenolic products, 9-hydroxyphenanthrene (3a), 3-acetyl-9-hydroxyphenanthrene (3b), and 4-hydroxypyrene (3c) are formed via the triplet state. Phenol 3 formation from the triplet 1 sensitized by the triplet 3 (i.e. product sensitization) is proposed for the photorearrangement reactions of 1a and 1c, and this process is the only way phenol (3a) is formed because of the negligible intersystem crossing probability of 1a. No product sensitization occurs in the photorearrangement reaction of 1b. 相似文献
72.
An efficient synthesis of cyclodextrins (CDs) by using the intramolecular glycosylation is demonstrated. alpha-CD, an alpha(1-->4)linked hexaglucoside, was prepared via a block condensation of three maltose units. A modified key maltose intermediate as a precursor to both glycosyl donor and acceptor components was prepared in 6 steps starting from maltose. All the glycosylation for chain elongation and cyclization of saccharides was carried out after tethering the donor to the acceptor by the phthaloyl bridge to give the desired saccharides in good yields with complete alpha-selectivity. delta-CD composed of 9 glucose units was synthesized by the same manner from three maltotriose units. 相似文献
73.
Tachibana Y Otsuka K Terabe S Arai A Suzuki K Nakamura S 《Journal of chromatography. A》2003,1011(1-2):181-192
A robust and simple interface for microchip electrophoresis-mass spectrometry (MCE-MS) was developed using a spray nozzle connected to the exit of the separation channel of the microchip. The spray nozzle was attached to the microchip using a polyether ether ketone screw without adhesive, thus allowing easy replaced. Sample injection and electrophoretic separation was performed by control of the voltage only. The analysis of a few basic drugs was performed using the optimized MCE-MS system. The separation was improved by using a high-viscosity separation buffer and a spray nozzle with a small bore size. This system was also applied to the separation of peptides and protein-trypsin digests. Sample adsorption was minimized by adding acetonitrile to the separation buffer when using a quartz microchip. 相似文献
74.
Four new iridoid glycosides, named L-phenylalaninosecologanin (1), 7-O-(4-beta-D-glucopyranosyloxy-3-methoxybenzoyl)secologanolic acid (2), 6'-O-(7alpha-hydroxyswerosyloxy)loganin (3) and (Z)-aldosecologanin (5), were isolated, together with a known one, newly named (E)-aldosecologanin (4), from the stems and leaves of Lonicera japonica. Their structures were established on the basis of chemical and spectral data. 相似文献
75.
Belik AA Azuma M Matsuo A Whangbo MH Koo HJ Kikuchi J Kaji T Okubo S Ohta H Kindo K Takano M 《Inorganic chemistry》2005,44(19):6632-6640
SrCu2(PO4)2 was prepared by the solid-state method at 1153 K. Its structure was solved by direct methods in the space group Pccn (No. 56) with Z = 8 from synchrotron X-ray powder diffraction data measured at room temperature. Structure parameters were then refined by the Rietveld method to obtain the lattice parameters, a = 7.94217(8) A, b = 15.36918(14) A, and c = 10.37036(10) A. SrCu2(PO4)2 presents a new structure type and is built up from Sr2O16 and Cu1Cu2O8 units with Cu1...Cu2 = 3.256 A. The magnetic properties of SrCu2(PO4)2 were investigated by magnetic susceptibility, magnetization up to 65 T, Cu nuclear quadrupole resonance (NQR), electron-spin resonance, and specific heat measurements. With spin-dimer analysis, it was shown that the two strongest spin-exchange interactions between Cu sites result from the Cu1-O...O-Cu2 and Cu2-O...O-Cu2 super-superexchange paths with Cu1...Cu2 = 5.861 A and Cu2...Cu2 = 5.251 A, and the superexchange associated with the structural dimer Cu1Cu2O8 is negligible. The magnetic susceptibility data were analyzed in terms of a linear four-spin cluster model, Cu1-Cu2-Cu2-Cu1 with -2J(1)/kB = 82.4 K for Cu1-Cu2 and -2J(2)/k(B) = 59 K for Cu2-Cu2. A spin gap deduced from this model (Delta/kB = 63 K) is in agreement with that obtained from the Cu NQR data (Delta/kB = 65 K). A one-half magnetization plateau was observed between approximately 50 and 63 T at 1.3 K. Specific heat data show that SrCu2(PO4)2 does not undergo a long-range magnetic ordering down to 0.45 K. SrCu2(PO4)2 melts incongruently at 1189 K. We also report its vibrational properties studied with Raman spectroscopy. 相似文献
76.
Takuo Kosuge Kuniro Tsuji Koichi Hirai Kentaro Yamaguchi Toshihiko Okamoto Yoichi Iitaka 《Tetrahedron letters》1981,22(35):3417-3420
A new toxin, named neosurugatoxin, was isolated from the toxic Japanese Ivory Shell and its structure was determined by X-ray crystallographic analysis. 相似文献
77.
Migaku Kawaguchi Norihiro Sakui Noriya Okanouchi Koichi Saito 《Analytica chimica acta》2005,533(1):57-65
A new method, stir bar sorptive extraction (SBSE) with in situ derivatization and thermal desorption (TD)-gas chromatography-mass spectrometry (GC-MS), which is used for the determination of trace amounts of chlorophenols, such as 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TrCP), 2,3,4,6-tetrachlorophenol (2,3,4,6-TeCP) and pentachlorophenol (PCP), in tap water, river water and human urine samples, is described. The derivatization conditions with acetic acid anhydride and the SBSE conditions such as extraction time are investigated. Then, the stir bar is subjected to TD followed by GC-MS. The detection limits of the chlorophenols in tap water, river water and human urine samples are 1-2, 1-2, and 10-20 pg ml−1 (ppt), respectively. The calibration curves for the chlorophenols are linear and have correlation coefficients higher than 0.99. The average recoveries of the chlorophenols in all the samples are higher than 95% (R.S.D. < 10%) with correction using added surrogate standards, 2,4-dichlorophenol-d5, 2,4,6-trichlorophenol-13C6, 2,3,4,6-tetrachlorophenol-13C6 and pentachlorophenol-13C6. This simple, accurate, sensitive and selective analytical method may be applicable to the determination of trace amounts of chlorophenols in liquid samples. 相似文献
78.
Goto K Yano Y Okada E Liu CW Yamamoto K Ueoka R 《The Journal of organic chemistry》2003,68(3):865-870
Specific acid catalysis of p-sulfonatocalix[n]arenes (n = 4, Calix-S4; n = 6, Calix-S6; n = 8, Calix-S8) was observed in the alcoholysis of N-acetyl-l-amino acids in methanol. The methanolysis rates of basic amino acid substrates (His, Lys, and Arg) were markedly enhanced in the presence of Calix-Sn, as compared with rates observed with p-hydroxybenzenesulfonic acid (pHBS), which is a noncyclic analogue of Calix-Sn. This catalytic effect of Calix-Sn was not observed for the methanolysis of Phe, Tyr, and Trp substrates. On the other hand, (1)H NMR experiments following the effect of Calix-Sn on N-acetyl-l-amino acid substrates in CD(3)OD showed that the spectrum of a mixture of the His substrate with Calix-Sn was significantly different from the combined spectra of the respective compounds. These changes in spectra support the formation of an inclusion complex of Calix-Sn with basic amino acids. Furthermore, it was obvious that methanolysis of the His substrate catalyzed by Calix-S4 and Calix-S6 obeyed Michaelis-Menten kinetics. These results indicate that the catalytic activity of Calix-Sn originates from its forming a complex with specific substrates (basic amino acids), similar to enzymatic reactions. 相似文献
79.
[reaction: see text] Indium-mediated allenylation of alpha,beta-unsaturated ketones in the presence of tert-butyldimethylsilyl triflate and dimethyl sulfide gives 6-siloxy-1,2,5-trienes, which undergo W(CO)(5)(L)-catalyzed 5-endo cyclization to give the corresponding cyclopentene derivatives in good yield. Furthermore, this novel W(CO)(5)(L)-catalyzed cyclization of allenyl silyl enol ethers proceeds in a 6-endo manner when 5-siloxy-1,2,5-trienes are employed as a substrate. In these reactions, effective electrophilic activation of allenyl compounds for attack by silyl enol ethers is achieved using a catalytic amount of W(CO)(6). 相似文献
80.
The potential energy surface of benzene (C(6)H(6)) with a He*(2(3)S) atom was obtained by comparison of experimental data in collision-energy-resolved two-dimensional Penning ionization electron spectroscopy with classical trajectory calculations. The ab initio model interaction potentials for C(6)H(6)+He*(2(3)S) were successfully optimized by the overlap expansion method; the model potentials were effectively modified by correction terms proportional to the overlap integrals between orbitals of the interacting system, C(6)H(6) and He*(2(3)S). Classical trajectory calculations with optimized potentials gave excellent agreement with the observed collision-energy dependence of partial ionization cross sections. Important contributions to corrections were found to be due to interactions between unoccupied molecular orbitals and the He*2s orbital. A C(6)H(6) molecule attracts a He*(2(3)S) atom widely at the region where pi electrons distribute, and the interaction of -80 meV (ca. -1.8 kcal/mol) just cover the carbon hexagon. The binding energy of a C(6)H(6) molecule and a He* atom was 107 meV at a distance of 2.40 A on the sixfold axis from the center of a C(6)H(6) molecule, which is similar to that of C(6)H(6)+Li and is much larger than those of the C(6)H(6)+[He,Ne,Ar] systems. 相似文献