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141.
Side chain bromination of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) was carried out by using N-bromosuccinimide followed by phosphorylation of the bromo derivative with triethyl phosphite. Optimum conditions for minimum gel formation have been established. The products have been characterized by 'H-NMR and IR studies. Thermal behavior was investigated by thermogravimetry and differential scanning calorimetry in an air nitrogen atmosphere. Phosphorylated PPO starts to lose weight at 200°C, but the char yield increases with an increase in the phosphorus content of the polymer. 相似文献
142.
D, L-Cis-2-aminocyclobutane-1-carboxylic acid NCA, D, L-cis-and trans-2-aminocyclohexane-1-carboxylic acid N-carboxyanhydride (NCA) and D, L-cis-2-aminocyclohexane-1-carboxylic acid NCA were polymerized under various conditions. The 13C-NMR spectra of the resulting β-polyamides measured in trifluoro-acetic acid show splittings of all signals reflecting diads and triads. Poly-D, L-3-aminobutyric acid obtained by anionic polymerization of D, L-4-methyl acetidinone does not display tacticity effects in its 13C-NMR spectrum. Hence it is concluded that tacticity effects are observable only if both α- and β-carbons have a substituent. Furthermore, it was found that the reaction conditions do not have a strong influence on the stereospecificity of the NCA-polymerization. In all cases nearly random sequences of D and L-units were obtained. 相似文献
143.
Abstract We report a molecular dynamics study on the 1:1 M3+ lanthanide (La3+, Eu3+ and Yb3+) inclusion complexes of an important extractant molecule L: a calix[4]arene-tetraalkyl ether substituted at the wide rim by four NH-C(O)-CH2-P(O)Ph2 arms. The M(NO3)3 and MCl3 complexes of L are compared in methanol solution and at a water / chloroform interface. In the different environments the coordination sphere of M3+ involves the four phosphoryl oxygens and three to four loosely bound carbonyl oxygens of the CMPO-like arms. Based on free energy simulations, we address the question of ion binding selectivity in pure liquid phases and at the liquid-liquid interface where L and the complexes are found to adsorb. According to the simulations, the enhancement of M3+ cation extraction in the presence of the calixarene platform, examined by comparing L to the (CMPO)4 “ligand” at the interface, is related to the fact that (i) the (CMPO)4Eu(NO3)3 complex is more hydrophilic than the LEu(NO3) one and (ii) the free CMPO ligands spread at the interface, and are therefore less organized for cation capture than L. 相似文献
144.
邻位碳硼烷分别与正丁基锂、硫粉和Me4CpCo(CO)I2反应合成得到半夹芯16电子碳硼烷化合物Me4CpCoS2C2B10H10 (1).1与二茂铁炔酮在二氯甲烷中反应得到产物{(Me4CpCoS2C2B10H10)[FcC(O)CHCCHCC(O)Fc]} (2)(Fc=二茂铁基).2是一个1:2的加成产物,2个二茂铁炔酮分子以头-尾的方式加成到分子1中的1个Co-S键上.1和2分别用红外、核磁、元素分析、质谱和单晶X-射线衍射等表征方法进行了结构表征. 相似文献
145.
We present a comparative study on the C-H stretching vibrations at air/DMSO (dimethyl sulfoxide) interface with both the free-induction decay (FID) coherent vibrational dynamics and the sub-wavenumber high resolution sum-frequency generation vibrational spectroscopy measurements. In principle the frequency-domain and time-domain spectroscopic measurements should generate identical information for a given molecular system. However, when the molecular systems are with several coupled or overlapping vibrational modes, obtain- ing detailed spectroscopic and coherent dynamics information is not as straightforward and rather difficult from either the time-domain or the frequency domain measurements. For the case of air/DMSO interface that is with moderately complex vibrational spectra, we show that the frequency-domain measurement with sub-wavenumber high-resolution sum-frequency generation vibrational spectroscopy is probably more advantageous than the time- domain measurement in obtaining quantitative understanding of the structure and coherent dynamics of the molecular interface. 相似文献
146.
Synthesis of nine new benzimidazole derivatives was reported. The products were identified by 1H NMR, mass spectroscopy, and infrared spectroscopy. 相似文献
147.
Abstract Task‐specific ionic liquids possessing two Brönsted acid sites with –COOH, HSO? 4, or H2PO? 4 groups have been designed, synthesized, and characterized. Under mild conditions and without any additional organic solvent, the esterification of isopropanol by chloroacetic acid could be carried out in these new task‐specific ionic liquids. In comparison with most of acidic ionic liquids in current use, these ionic liquids are halogen free and more environmentally benign as media and catalysts. 相似文献
148.
Birgit Hischenhuber Hans Havlicek Jelena Todoric Sonja Höllrigl‐Binder Wolfgang Schreiner Bernhard Knapp 《Journal of computational chemistry》2013,34(21):1862-1879
Antigen presenting cells present processed peptides via their major histocompatibility (MH) complex to the T cell receptors (TRs) of T cells. If a peptide is immunogenic, a signaling cascade can be triggered within the T cell. However, the binding of different peptides and/or different TRs to MH is also known to influence the spatial arrangement of the MH α‐helices which could itself be an additional level of T cell regulation. In this study, we introduce a new methodology based on differential geometric parameters to describe MH deformations in a detailed and comparable way. For this purpose, we represent MH α‐helices by curves. On the basis of these curves, we calculate in a first step the curvature and torsion to describe each α‐helix independently. In a second step, we calculate the distribution parameter and the conical curvature of the ruled surface to describe the relative orientation of the two α‐helices. On the basis of four different test sets, we show how these differential geometric parameters can be used to describe changes in the spatial arrangement of the MH α‐helices for different biological challenges. In the first test set, we illustrate on the basis of all available crystal structures for (TR)/pMH complexes how the binding of TRs influences the MH helices. In the second test set, we show a cross evaluation of different MH alleles with the same peptide and the same MH allele with different peptides. In the third test set, we present the spatial effects of different TRs on the same peptide/MH complex. In the fourth test set, we illustrate how a severe conformational change in an α‐helix can be described quantitatively. Taken together, we provide a novel structural methodology to numerically describe subtle and severe alterations in MH α‐helices for a broad range of applications. © 2013 Wiley Periodicals, Inc. 相似文献
149.
Zhi-Gang Feng 《Journal of Dispersion Science and Technology》2013,34(7):968-974
The hydrodynamics of a sphere with interface slip has been numerically investigated for flows of Reynolds number ranging 0 < Re ≤ 75. A simple correlation of the drag force coefficient in the present of interface slip has been derived based on our numerical simulations. The correlation takes the slip coefficient and Reynolds number as two input parameters. By comparing results found in the literature, we believe that the present correlation is more accurate; it provides a source for future experiment study and for numerical simulations of large multi-particle system where the interface slip is important. 相似文献
150.
Rinki Bhadra Vidya Nand Singh Bodh Raj Mehta Pranayee Datta 《Journal of Dispersion Science and Technology》2013,34(9):1202-1207
ZnO nanocrystals are synthesized using the quenching method. The properties of the grown nanocrystals are studied using ultraviolet-vis spectroscopy, x-ray diffraction, photoluminescence, electron diffraction, energy dispersive x-ray spectroscopy, and high resolution transmission electron microscopy. Current-voltage characteristics of the prepared samples are studied for investigating the possible application of the samples as switch and memristor. 相似文献