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791.
Current approaches to the structural investigations of paramagnetic metal-containing proteins in solution using NMR spectroscopy are surveyed taking iron-sulfur and copper-containing proteins as examples. 相似文献
792.
New, spin-labeled nucleosides, and an efficient synthetic route for a modified uridine amidite, were developed. The spin-labeled part was the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) group, which was linked via an alkynyl chain at the 5 position of uridine. Three typical protecting groups, the t-butyldimethylsilyl (TBDMS) group at 2′, the dimethoxytrityl (DMTr) group at 5′, and the phosphoramidite group at 3′, were introduced to produce an automated nucleic acid synthesizer. The TEMPO group at the 5 position in the uridine structure affected introduction of bulky protecting groups, such as the DMTr group at the 5′ position and the TBDMS group at the 2′ position. The electron paramagnetic resonance (EPR) data revealed a nitroxyl radical in the structure of synthetic nucleoside compounds; however, RNA produced by automated synthesis using a TEMPO-linked uridine phosphoramidite building block was EPR silent. 相似文献
793.
Qing Miao Wei‐Min Liu Thomas Kock Anneloes Blok Monika Timmer Mark Overhand Marcellus Ubbink 《Angewandte Chemie (International ed. in English)》2019,58(37):13093-13100
Synthetic metal complexes can be used as paramagnetic probes for the study of proteins and protein complexes. Herein, two transition metal NMR probes (TraNPs) are reported. TraNPs are attached through two arms to a protein to generate a pseudocontact shift (PCS) using cobalt(II), or paramagnetic relaxation enhancement (PRE) with manganese(II). The PCS analysis of TraNPs attached to three different proteins shows that the size of the anisotropic component of the magnetic susceptibility depends on the probe surroundings at the surface of the protein, contrary to what is observed for lanthanoid‐based probes. The observed PCS are relatively small, making cobalt‐based probes suitable for localized studies, such as of an active site. The obtained PREs are stronger than those obtained with nitroxide spin labels and the possibility to generate both PCS and PRE offers advantages. The properties of TraNPs in comparison with other cobalt‐based probes are discussed. 相似文献
794.
Temperature-Dependent Formation of Redox Sites in Molybdenum Trioxide Studied by Electron Paramagnetic Resonance Spectroscopy 下载免费PDF全文
The formation and qualification of redox sites in transition metal oxides are always the active fields related to electronics, catalysis, sensors, and energy-storage units. In the present study, the temperature dependence of thermal reduction of MoO3 was surveyed at the range of 350 ℃ to 750 ℃. Upon reduction, the formed redox species characterized by EPR spectroscopy are the MoV ion and superoxide anion radical (O2-) when the reduction was induced at the optimal temperature of 300-350 ℃. When heating-up from 350 ℃, the EPR signals started to decline in amplitude. The signals in the range of 400-450 ℃ decreased to half of that at 350 ℃, and then to zero at ~600 ℃. Further treatment at even higher temperature or prolonged heating time at 500 ℃ caused more reduction and more free electrons were released to the MoO3 bulk, which results in a delocalized means similar to the anti-ferromagnetic coupling. These data herein are helpful to prepare and study the metal-oxide catalysts. 相似文献
795.
本文利用热处理还原法,利用三氧化钼诱导形成具有氧化还原活性的中间产物及其温度相关特性. 电子顺磁共振波谱(EPR)实验结果表明,热处理后在MoVI离子被还原成MoV离子并形成了超氧阴离子自由基O2-. 这两种活性中心的最佳热还原温度约300∽350 °C. 自350 °逐渐升温,两种EPR信号强度迅速下降,下降∽50%所对应的温度是400∽450 °C;当温度升至600 °C或更高时,EPR信号降至0. 结果表明,较高温处理或持续长时间处理都使热还原更容易发生,积累了越来越多的电子,在基底中形成类似于反铁磁耦合的电子离域. 随着离域程度增大,EPR信号强度开始下降并直至消失. 相似文献
796.
797.
798.
LIU Hong-Gang WU Xiao-Xuan ZHENG Wen-Chen 《理论物理通讯》2006,46(1):167-170
The EPR 9 factors for cubic, tetragonal and orthorhombic Fe^+ centers in alkali halides MX (M= Li, Na; X = F, CI) are calculated from second-order perturbation formulas of g factors based on cluster approach for 3d^7 ions in three symmetries. From calculations, the g factors of these Fe^+ centers in MX crystals are reasonably explained and the defect structural data for the tetragonal and orthorhombic Fe^+ centers are estimated. The results are discussed. 相似文献
799.
CO2加氢合成甲醇的超细Cu-ZnO-ZrO2催化剂的表征 总被引:6,自引:0,他引:6
采用原位顺磁共振(EPR)、原位X射线光电子能谱(XPS)和程序升温还原(TPR)等手段,对CO2加氢合成甲醇用的不同粒度的超细Cu-ZnO-ZrO2催化剂各组分的相互作用进行了研究。结果表明,ZrO2的加入改变了催化剂的表面结构和配位状态,增加了活性组分的分散度,提高了催化剂的稳定性。实验还发现,催化剂的粒度对各组分的相互作用有着重大的影响,催化剂的粒度较小时,Cu^2+主要以团簇的形式存在,易 相似文献
800.
The local tetragonal distortions (α???α0) (where α is the angle defined as tgα?=?R⊥/R//, R⊥ and R// are the metal–ligand distances parallel with and normal to the C4 axis, α0?=?45° is the same angle in cubic symmetry) of (CrF6)3? and (FeF6)3? octahedral clusters in the tetragonal Rb2KGaF6 crystals are estimated by analyzing their electron paramagnetic resonance (EPR) zero-field splittings D. The results indicate that the two impurity octahedra and hence the host (GaF6)3? octahedra are tetragonally elongated. The distortion (α???α0) in magnitude differs from impurity to impurity because of the different sizes and natures of these impurities. These results are analogous to those in ABX3 and doped ABX3 perovskite crystals where the cubic-to-tetragonal phase transition is due to the rotation of BX6 octahedra associated with the release or elongation of B–X bond along the C4 rotational axis. 相似文献