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21.
I. Sugai M. Oyaizu Y. Takeda H. Kawakami K. Kawasaki T. Hattori T. Kadono 《Journal of Radioanalytical and Nuclear Chemistry》2014,299(2):1023-1028
Nitrided carbon stripper (NCS) foils with high nitrogen content were produced by ion beam sputtering of reactive nitrogen gas. Such foils seem to be very useful as strippers in high-intensity heavy ion accelerators. We have conducted comprehensive research, development, and production of such foils with high reproducibility. Krypton, a heavy noble gas, was mixed with the reaction nitrogen gas (IBSRN) in the ion beam sputtering process to produce stripper foils with short sputtering deposition time and long lifetimes in the high intensity ion beam irradiation. With the (N2 + Kr) mixed gas ions we investigated the influence of different sputtering angles (α) on the lifetime of the NCS-foils in case of poly-graphite material. The lifetime measurement of these foils of 20 ± 5 μg/cm2 was performed with a 3.2 MeV Ne+ ion beam as usual. The foils made at a sputtering angle of 15° showed a maximum of 11.0 and 7.5 C/cm2 average charge density, respectively, which corresponded to about 275 and 187 times the lifetime of the best commercially available foils. 相似文献
22.
Prof. Yukishige Ito Prof. Yasuhiro Kajihara Prof. Yoichi Takeda 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(67):15461-15470
The introduction of Asn-linked glycans to nascent polypeptides occurs in the lumen of the endoplasmic reticulum of eukaryotic cells. After the removal of specific sugar residues, glycoproteins acquire signals in the glycoprotein quality control (GPQC) system and enter the folding cycle composed of lectin-chaperones calnexin (CNX) and calreticulin (CRT), glucosidase II (G-II), and UDP-Glc:glycoprotein glucosyltransferase (UGGT). G-II initiates glycoproteins’ entry and exit from the cycle, and UGGT serves as the “folding sensor”. This account summarizes our effort to analyze the properties of enzymes and lectins that play important roles in GPQC, especially those involved in the CNX/CRT cycle. To commence our study, general methods for the synthesis of high-mannose-type glycans and glycoproteins were established. Based on these, various substrates to analyze components of the GPQC were created, and properties of CRT, G-II, and UGGT have been clarified. 相似文献
23.
Yasuda M Nakajima H Takeda R Yoshioka S Yamasaki S Chiba K Baba A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(14):3856-3867
Boron complexes that contain new tridentate ligands, tris(o‐oxyaryl)methanes and ‐silanes, were prepared. These complexes had a cage‐shaped structure around a boron center and showed higher Lewis acidity and catalytic activity than open‐shaped boron compounds. The cage‐shaped ligands determined the properties of the borates by altering the geometry and were consistently bound to the metal center by chelation. The synthesized compounds were L?B(OC6H4)3CH, L?B(OC6H4)3SiMe, and its derivatives (L=THF or pyridine as an external ligand). Theoretical calculations suggested that the cage‐shaped borates had a large dihedral angle (Cipso‐O‐B‐O) compared with open‐shaped borates. The geometric effect due to the dihedral angle means that compared with open‐shaped, the cage‐shaped borates have a greater Lewis acidity. The introduction of electron‐withdrawing groups on the aryl moieties in the cage‐shaped framework increased the Lewis acidity. Substitution of a bridgehead Si for a bridgehead C decreased the Lewis acidity of the boron complexes because the large silicon atom reduces the dihedral angle of Cipso‐O‐B‐O. The ligand‐exchange rates of the para‐fluoro‐substituted compound B(OC6H3F)3CH and the ortho‐phenyl‐substituted compound B(OC6H3Ph)3CH were less than that of the unsubstituted borate B(OC6H4)3CH. The ligand‐exchange rate of B(OC6H4)3SiMe was much faster than that of B(OC6H4)3CH. A hetero Diels–Alder reaction and Mukaiyama‐type aldol reactions were more effectively catalyzed by cage‐shaped borates than by the open‐shaped borate B(OPh)3 or by the strong Lewis acid BF3?OEt2. The cage‐shaped borates with the bulky substituents at the ortho‐positions selectively catalyzed the reaction with less sterically hindered substrates, while the unsubstituted borate showed no selectivity. 相似文献
24.
Diversity oriented synthesis of conjugate dienes and alkenylcyclopropanes by the sequential reactions using silyl group-substituted titanium carbene complexes was studied. Dienylsilanes were obtained by the olefination of carbonyl compounds with γ-silylvinylcarbene complexes. Cyclopropanation of 1-alkenes with the vinylcarbene complexes produced (E)-(β-silylvinyl)cyclopropanes with high stereoselectivity. The reaction of β-(trialkylsilyl)carbene complexes with zinc alkoxides of homopropargyl alcohols produced 6-silyl-3,5-hexadien-1-ols with high regio- and stereoselectivity. The (E)-alkenylsilanes thus obtained were transformed into a range of unsaturated compounds by the palladium-catalyzed or copper(I)-promoted cross-coupling with organic halides with retention of configuration. 相似文献
25.
H Terao T Sugawara Y Kita N Sato E Kaho S Takeda 《Journal of the American Chemical Society》2001,123(43):10468-10474
The crystal structure of a hydrated crystal of bis(squaryl)biphenyl (BSQB*4H2O), in which two squaric acid moieties are connected with a 4,4'-biphenyl unit, was characterized by the presence of a one-dimensional hydrogen-bonded chain composed of BSQB and water molecules. X-ray crystallographic analysis showed that BSQB exists in a dianion form and that, on average, two of the four water molecules are protonated. The enhanced temperature dependence of the thermal parameters of the oxygen atoms of the water molecules suggested dynamic disorder of the water molecules. The solid-state magic angle spinning deuterium NMR spectrum of BSQB*4D2O revealed that deuterons are exchanged between heavy water molecules and oxonium ions with an exchange rate of ca. 700 Hz around 250 K and that deuterons start to migrate in a hydrogen-bonded cluster of water molecules. Ac dielectric measurements were also used to examine the dynamic process in the hydrated crystal. The dielectric permittivity of the crystal dramatically increased above 250 K with a distinct frequency dependence (epsilon' = 4.7 x 10(4) at 340 K and 1 kHz). The frequency dependence of tan delta at 290 K exhibited a maximum at 3.0 kHz, and this maximum shifted to lower frequencies when the temperature of the crystal decreased. These experimental results suggested that in the one-dimensional hydrogen-bonded chain of BSQB*4H2O a proton relay between oxonium ions and water molecules occurred within a cluster of four water molecules and that the relay was transmitted to the adjacent cluster mediated by the modulation of the negative charge distribution of the BSQB dianion. These phenomena were interpreted as the solitonic migration of the charged domain boundaries along the one-dimensional hydrogen-bonded chain. 相似文献
26.
Takeda Y Isai N Masuda T Honda G Takaishi Y Ito M Otsuka H Ashurmetov OA Khodzhimatov OK 《Chemical & pharmaceutical bulletin》2001,49(8):1039-1041
From the aerial parts of Phlomis spinidens, two new flavonol bisglycosides, phlomisflavosides A (1) and B (2), were isolated together with the known compounds, astragalin, isoquercitrin, lamiridoside, phlomoside A, shanzhiside methyl ester, 8-O-acetylshanzhiside methyl ester, phlorigidoside C, rodioloside (=salidroside), forsythoside B, citroside A and lariciresinol-4'-O-beta-D-glucoside. The structures of the new compounds were elucidated based on spectral and chemical evidence. 相似文献
27.
Thin-layer chromatographic behavior of rare earths on silica gel with aqueous alkaline earth metal nitrate solutions as mobile phases 总被引:1,自引:0,他引:1
The TLC behavior of all the rare earths except Pm has been surveyed on silica gel (pH 7.0) pretreated with 0.1 mol L(-1) tris(hydroxymethyl)aminomethane and 0.1 mol L(-1) HCl with aqueous nitrate solutions of alkaline earth metals as mobile phases. The RF values of the lanthanides varied in a regular and characteristic way accompanied by the tetrad effect with increasing atomic number, and when the mobile phases were changed the RF values of each metal decreased in the order Mg2+ > Ca2+ > Sr2+ > Ba2+, as the crystal ionic radii of the alkaline earth metals increased. This adsorption sequence was not observed with alkali metal nitrate and alkali metal chloride mobile phases. A brief discussion concerning the effect on RF values of the solvent cations and the adsorption mechanism is included; also presented are typical chromatograms for the separation of multi-component mixtures containing adjacent lanthanides. 相似文献
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30.
Summary Chiral stationary phases (CSPs) for liquid chromatography were prepared by the way of an activated carbamate intermediate.
The amino group of aminopropylsilyl silica gel was first activated by carbamylation with disuccinimido carbonate (DSC). The
obtained activated carbamate silica gel (ACsil) proved useful as an intermediate for the preparation of urea-type CSPs. The
reaction of ACsil with (S)- of (R)-1-(α-naphthyl)-ethylamine gave naphthylethylurea type CSPs. These CSPs were also obtained
directly from aminopropylsilyl silica gel by its reaction with optically active (S)- or (R)-succinimido 1-(α-naphthyl)ethyl
carbamate (SINEC). Several phenylthiohydantoin amino acid enantiomers and p-bromophenylcarbamyl amino acid enantiomers were
resolved on the CSPs by elution with aqueous mobile phase. 相似文献