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111.
Anaí Duarte Wilson Cunico Claudio M.P. Pereira Alex F.C. Flores Rogério A. Freitag Geonir M. Siqueira 《Ultrasonics sonochemistry》2010,17(2):281-283
An ultrasound-enhanced method has been developed for the synthesis of a variety of thioesters from benzoyl chlorides and 2-mercaptobenzoxa(thia)zoles. Applying this methodology, 14 compounds were synthesized in excellent yields. 相似文献
112.
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114.
Alex G. Harrison 《Journal of the American Society for Mass Spectrometry》2013,24(10):1555-1564
The fragmentation reactions of the MH+ ions as well as the b7, a7, and a7* ions derived therefrom have been studied in detail for the octapeptides MAAAAAAA, AAMAAAAA, AAAAMAAA, and AAAAAAMA. Ionization was by electrospray using a QqToF mass spectrometer, which allowed a study of the evolution of the fragmentation channels as a function of the collision energy. Not surprisingly, the product ion mass spectra for the b7 ions are independent of the original precursor sequence, indicating macrocyclization and reopening to the same mixture of protonated oxazolones prior to fragmentation. The results show that this sequence scrambling results in a distinct preference to place the Met residue in the C-terminal position of the protonated oxazolones. The a7 and a7* ions also produce product ion mass spectra independent of the original peptide sequence. The results for the a7 ions indicate that fragmentation occurs primarily from an amide structure analogous to that observed for a4 ions (Bythell et al. in J Am Chem Soc 132:14766–14779, 2010). Clearly, the rearrangement reaction they have proposed applies equally well to an ions as large as a7. The major fragmentation modes of the MH+ ions at low collision energies produce b7, b6, and b5 ions. As the collision energy is increased further fragmentation of these primary products produces, in part, non-direct sequence ions, which become prominent at lower m/z values, particularly for the peptides with the Met residue near the N-terminus. Figure
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115.
Alex G. Harrison Cagdas Tasoglu Talat Yalcin 《Journal of the American Society for Mass Spectrometry》2013,24(10):1565-1572
The fragmentation reactions of the MH+ ions of Leu-enkephalin amide and a variety of heptapeptide amides have been studied in detail as a function of collision energy using a QqToF beam type mass spectrometer. The initial fragmentation of the protonated amides involves primarily formation of bn ions, including significant loss of NH3 from the MH+ ions. Further fragmentation of these bn ions occurs following macrocyclization/ring opening leading in many cases to bn ions with permuted sequences and, thus, to formation of non-direct sequence ions. The importance of these non-direct sequence ions increases markedly with increasing collision energy, making peptide sequence determination difficult, if not impossible, at higher collision energies. Figure
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116.
Gregory B. Kharas Sonia E. Chavez Alex C. Mast Mark Krzeszowiec Stan Mazo 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(6):451-454
Novel copolymers of trisubstituted ethylene monomers, ring-substituted 1,1-dicyano-2-(1-naphthyl)ethylenes, RC10H6CH?C(CN)2 (where R is H, 2-OCH3, 4-OCH3) and 4-fluorostyrene were prepared by solution copolymerization in the presence of a radical initiator (ABCN) at 70°C. The composition of the copolymers was calculated from nitrogen analysis, and the structures were analyzed by IR, 1H and 13C-NMR. The order of relative reactivity (1/r 1) for the monomers is (5.86) > 2-CH3O (4.28) > 4-CH3O (2.87). Relatively high Tg of the copolymers in comparison with that of poly(4-fluorostyrene) indicates a decrease in chain mobility of the copolymer due to the high dipolar character of the trisubstituted ethylene monomer unit. Decomposition of the copolymers in nitrogen occurred in two steps, first in the 200–500°C range with residue (7.3–7.7% wt.), which then decomposed in the 500–800°C range. 相似文献
117.
Silver electrodes were modified by the adsorption of α-, β-, and γ-cyclodextrin dithiocarbamates (2α–γ) and characterized by reductive desorption experiments. Their molecular recognition properties were studied by cyclic voltammetry using three families of positional isomers of aromatic nitro compounds. Electrodes modified with 2α and 2β were selective for meta and para isomers while 2γ showed little selectivity. These observations are explained in terms of cavity sizes and guest structure. Computational studies suggest that the main reason for the observed selectivity is the different position of the NO2 group in ortho and para isomers with respect to the CD cavity. 相似文献
118.
Pamela Alex Jugal Kishor I. G. Sharma 《Journal of Thermal Analysis and Calorimetry》2013,112(1):45-50
The aim of this work is to evaluate the feasibility of preparation of Nb10Hf1Ti alloy by magnesiothermic reduction of its oxides. DTA studies were conducted to identify the reduction temperature for co reduction of the mixed oxides of Nb2O5, HfO2, and TiO2 by magnesium under reducing atmosphere. Based on DTA analysis, experiments were carried out to prepare Nb10Hf1Ti alloy by magnesiothermic reduction of their oxides at 750 °C. The reduced product was analyzed for its phases by X-ray diffraction. The excess Mg was leached out, the alloy mixture was vacuum dried, pelletized, sintered, and electron beam melted to get a consolidated alloy of the required composition. The alloy was characterized using different techniques such as optical microscopy, scanning electron microscopy, and chemical analysis. Microstructural observations revealed the formation of coarse grain structure in the consolidated alloy. The alloy product was also evaluated for its micro hardness. 相似文献
119.
Satoka Aoyagi John S. Fletcher Sadia Sheraz Tomoko Kawashima Irma Berrueta Razo Alex Henderson Nicholas P. Lockyer John C. Vickerman 《Analytical and bioanalytical chemistry》2013,405(21):6621-6628
A novel application of time-of-flight secondary ion mass spectrometry (ToF-SIMS) with continuous Ar cluster beams to peptide analysis was investigated. In order to evaluate peptide structures, it is necessary to detect fragment ions related to multiple neighbouring amino acid residues. It is, however, difficult to detect these using conventional ToF-SIMS primary ion beams such as Bi cluster beams. Recently, C60 and Ar cluster ion beams have been introduced to ToF-SIMS as primary ion beams and are expected to generate larger secondary ions than conventional ones. In this study, two sets of model peptides have been studied: (des-Tyr)-Leu-enkephalin and (des-Tyr)-Met-enkephalin (molecular weights are approximately 400 Da), and [Asn1 Val5]-angiotensin II and [Val5]-angiotensin I (molecular weights are approximately 1,000 Da) in order to evaluate the usefulness of the large cluster ion beams for peptide structural analysis. As a result, by using the Ar cluster beams, peptide molecular ions and large fragment ions, which are not easily detected using conventional ToF-SIMS primary ion beams such as Bi3 +, are clearly detected. Since the large fragment ions indicating amino acid sequences of the peptides are detected by the large cluster beams, it is suggested that the Ar cluster and C60 ion beams are useful for peptide structural analysis. 相似文献
120.
Robert G. Gilbert Alex C. Wu Mitchell A. Sullivan Gonzalo E. Sumarriva Natascha Ersch Jovin Hasjim 《Analytical and bioanalytical chemistry》2013,405(28):8969-8980
Two highly branched glucose polymers with similar structures—starch and glycogen—have important relations to human health. Slowly digestible and resistant starches have desirable health benefits, including the prevention and alleviation of metabolic diseases and prevention of colon cancer. Glycogen is important in regulating the use of glucose in the body, and diabetic subjects have an anomaly in their glycogen structure compared with that in healthy subjects. This paper reviews the biosynthesis–structure–property relations of these polymers, showing that polymer characterization produces knowledge which can be useful in producing healthier foods and new drug targets aimed at improving glucose storage in diabetic patients. Examples include mathematical modeling to design starch with better nutritional values, the effects of amylose fine structures on starch digestibility, the structure of slowly digested starch collected from in vitro and in vivo digestion, and the mechanism of the formation of glycogen α particles from β particles in healthy subjects. A new method to overcome a current problem in the structural characterization of these polymers using field-flow fractionation is also given, through a technique to calibrate evaporative light scattering detection with starch. Figure
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