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131.
Cyclodextrin-modified monolithic columns for resolving dansyl amino acid enantiomers and positional isomers by capillary electrochromatography 总被引:1,自引:0,他引:1
We describe beta- and gamma-cyclodextrins (beta- and gamma-CD)-modified monolithic columns prepared by sol-gel process and chemical modifications. The monolithic silica column was fabricated inside a fused-silica capillary with 100 microm inner diameter by sol-gel process. The monolithic silica matrix was chemically modified chiral selectors of beta- or gamma-CDs with a spacer of 3-glycidoxypropyltrimethoxysilane by on-column reactions. Gamma-CD-modified monolithic column has successfully been applied for the separation of dansyl amino acid enantiomers. Beta-CD-modified monolithic column has been used for the separation of the positional isomers of o-, m-, and p-cresols and the enantioseparation of racemates of benzoin and several dansyl amino acids by capillary electrochromatography, respectively. For the separation of neutral positional isomers, a positive electric field was applied. However, for the separation of negatively charged analytes, a negative electric field was applied at the inlet of column. The separation efficiency of 5.0 x 10(4) theoretical plates/m for dansyl-L-threonine was obtained at electric field strength of -300 V/cm in the mobile phase of 50 mM 2-(N-morpholino)ethanesulfonic acid (MES)-Tris/methanol (70/30) buffer at pH 7.0. L-enantiomers were eluted as the first peak. Scanning electron micrograph showed that monolithic columns have the morphology of continuous skeleton and large through-pores. 相似文献
132.
We examined low-temperature synthetic route based on the amorphous nature of giant species to succeed to prepare Cs blue bronze (Cs0.3MoO3), which has never obtained by usual high-temperature methods, at ca. 680 K. Solid solutions (K1−xRbx)0.28MoO3 and (Li1−xNax)0.9Mo6O17 were also obtained at lower temperatures (ca. 670 K). For the latter system consisting of non-isostructural end members, Li0.9Mo6O17-structure type solid solution was formed even when 0.25<x<0.70, unlike the case by the usual high-temperature methods. Metastable mixed oxides Ln2Mo3O9 (Ln=La, Gd) were obtained, but not as single phases. 相似文献
133.
The phase diagrams of hexadecyl polyoxyethylene ether (C16POE10)/water/synthetic perfume, and sodium dodecyl sulfate (SDS)/water/synthetic perfume ternary systems were prepared. The synthetic perfumes used are, d-limonene, -hexylcinnamaldehyde, -ionone, benzyl acetate, linalool, and eugenol. In a series of C16POE10/water/synthetic perfume ternary systems, as the hydrophilicity of synthetic perfume increases, the regions of normal and inverse micellar solution phases were found to be extended, while that of the lamellar liquid crystal phase was reduced. Moreover, every region of normal micellar solutions, inverse micellar solutions, and lamellar liquid crystal phases in SDS/water/synthetic perfume ternary systems was found to be smaller than those in C16POE10/water/synthetic perfume systems. 相似文献
134.
Kunihiko Yokoi Toyomi Tomisaki Tsutomu Koide Constant M. G. Berg 《Fresenius' Journal of Analytical Chemistry》1995,352(6):547-549
The effectivity of UV irradiation with low and high pressure mercury (L-Hg and H-Hg) lamps on the decomposition of organic compounds in aqueous solutions, as pretreatment for the voltammetric determination of trace metals, is compared. The photolytic decomposition with the L-Hg lamp was much faster than with the H-Hg lamp. The higher efficiency of the L-Hg lamp is caused by its greater light intensity at short wavelengths. Interferences of organic compounds on the voltammetric determination of nickel and indium were eliminated successfully by 90 min irradiation with the L-Hg lamp. Humic acid and organic interference with the voltammetric determination of nickel in natural river water were successfully eliminated. The decomposition using the L-Hg lamp can be carried out without added oxidizing reagents and at room temperature, thus eliminating loss of water samples by evaporation at higher temperature. 相似文献
135.
136.
A general synthesis of 2?–5? linked oligoribonucleotides has been achieved on the basis of chemoselective formation of the 2?–5? internucleotide linkage using N-unblocked nucleosides. 相似文献
137.
Prof. Dr. Seiichi Uchiyama Kayo Yano Eiko Fukatsu Prof. Dr. A. Prasanna de Silva 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(36):8522-8527
One of the challenges for fluorescent sensors is to reduce their target environment size from a micrometer scale, such as biological cells, to a nanometer scale. Proton maps near membranes are of importance in bioenergetics and are the first goal in nanometer-scale analysis with fluorescent sensors. Thirty-three fluorescent photoinduced-electron-transfer pH sensors bearing an environment-sensitive benzofurazan fluorophore and having different hydrophobicity/hydrophilicity and hydrogen-bonding abilities were prepared. These sensors were scattered in nanospaces associated with anionic and cationic micelles as model membranes to indicate proton availability and polarity in local spaces. Gathering the data from the sensors allowed the successful drawing of proton maps near anionic and cationic micelles, in which electrostatic attraction/repulsion of protons by the charged head groups of micelles and dielectric suppression of protons were clearly observed. 相似文献
138.
139.
Construction of anomalously bent biphenyl structure using conformational properties of calix[4]amide
Masahide Tominaga Terutaka Hatano Masanobu Uchiyama Hyuma Masu Hiroyuki Kagechika Isao Azumaya 《Tetrahedron letters》2006,47(52):9369-9371
C2v-symmetrical cyclic tetramers of aromatic amides were simply synthesized in moderate yield by condensation reaction of N,N′-dimethyl-1,3-phenylenediamine and isophthalic acid derivatives using dichlorotriphenylphosphorane. The calix[4]amides exist in 1,3-alternate structure with cis conformation of tertiary aromatic amides, which were shown to be a versatile scaffold leading to a bowl-shaped macrocyclic compound possessing a anomalously strained structure, a bent hinge angle between two aromatic ring planes of biphenyl moiety, via an intramolecular ligation reaction. 相似文献
140.
Reductive Amination/Cyclization of Keto Acids Using a Hydrosilane for Selective Production of Lactams versus Cyclic Amines by Switching of the Indium Catalyst 下载免费PDF全文
Dr. Yohei Ogiwara Takuya Uchiyama Prof. Dr. Norio Sakai 《Angewandte Chemie (International ed. in English)》2016,55(5):1864-1867
Described herein is that the catalytic construction of N‐substituted five‐ and six‐membered lactams from keto acids with primary amines by reductive amination, using an indium/silane combination. This relatively benign and safe catalyst/reductant system tolerates the use of a variety of functional groups, especially ones that are reduction‐sensitive. A direct switch from synthesizing lactams to synthesizing cyclic amines is achieved by changing the catalyst from In(OAc)3 to InI3. This conversion occurs by further reduction of the lactam using the indium/silane pair. 相似文献