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101.
Infrared and Raman spectra of cubic magnesium caesium phosphate hexahydrate, MgCsPO4·6H2O (cF100), and its partially deuterated analogues were analyzed and compared to the previously studied spectra of the hexagonal analogue, MgCsPO4·6H2O (hP50). The vibrational spectra of the cubic and hexagonal dimorphic analogues are similar, especially in the regions of HOH stretching and bending vibrations. In the difference IR spectrum of the slightly deuterated analogue (<5% D), one distinctive band appears at 2260 cm−1 with a small shoulder at around 2170 cm−1, but only one band is expected in the region of the OD stretchings of isotopically isolated HDO molecules. The small weak band could possibly result from second-order transitions (a combination of HDO bending and some libration of the same species) rather than statistical disorder of the water molecules. By comparing the IR spectra in the region of external vibrations of water molecules of the protiated compound recorded at RT (room temperature) and at LNT (liquid nitrogen temperature) and those in the series of the partially deuterated analogues, it can be stated with certainty that the bands at 924 and 817 cm−1 result from librations of water molecules, rocking and wagging respectively. And the band at 429 cm−1 can be safely attributed to a stretching Mg–Ow mode. In the ν3(PO4) and ν4(PO4) region in the infrared spectra, one band in each is observed, at 995 and 559 cm−1, respectively. In the region of the ν1 modes, in the Raman spectrum of the protiated compound, one very intense band was observed at 930 cm−1 which is only insignificantly shifted to 929 cm−1 in the spectrum of the perdeuterated compound. The band at 379 cm−1 in the Raman spectrum could be assigned to the ν2(PO4) modes. With respect to the phosphate ion vibrations, the comparison between the two polymorphic forms of MgCsPO4·6H2O and their deuterated compounds shows that ν1(PO4) and ν3(PO4) appear at lower wavenumbers in the cubic phase than in the hexagonal phase. These data are in full agreement with the lower repulsion potential at the cubic lattice sites compared with that for the hexagonal lattice sites. 相似文献
102.
103.
Julia Intemann Dr. Jan Spielmann Dr. Peter Sirsch Prof. Dr. Sjoerd Harder 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(26):8478-8489
A new tetranuclear magnesium hydride cluster, [{ NN ‐(MgH)2}2], which was based on a N? N‐coupled bis‐β‐diketiminate ligand ( NN 2?), was obtained from the reaction of [{ NN ‐(MgnBu)2}2] with PhSiH3. Its crystal structure reveals an almost‐tetrahedral arrangement of Mg atoms and two different sets of hydride ions, which give rise to a coupling in the NMR spectrum (J=8.5 Hz). To shed light on the relationship between the cluster size and H2 release, the thermal decomposition of [{ NN ‐(MgH)2}2] and two closely related systems that were based on similar ligands, that is, an octanuclear magnesium hydride cluster and a dimeric magnesium hydride species, have been investigated in detail. A lowering of the H2‐desorption temperature with decreasing cluster size is observed, in line with previously reported theoretical predictions on (MgH2)n model systems. Deuterium‐labeling studies further demonstrate that the released H2 solely originates from the oxidative coupling of two hydride ligands and not from other hydrogen sources, such as the β‐diketiminate ligands. Analysis of the DFT‐computed electron density in [{ NN ‐(MgH)2}2] reveals a counterintuitive interaction between two formally closed‐shell H? ligands that are separated by 3.106 Å. This weak interaction could play an important role in H2 desorption. Although the molecular product after H2 release could not be characterized experimentally, DFT calculations on the proposed decomposition product, that is, the low‐valence tetranuclear Mg(I) cluster [( NN ‐Mg2)2], predict a structure with two almost‐parallel, localized Mg? Mg bonds. As in a previously reported β‐diketiminate MgI dimer, the Mg? Mg bond is not characterized by a bond critical point, but instead displays a local maximum of electron density midway between the atoms, that is, a non‐nuclear attractor (NNA). Interestingly, both of the NNAs in [( NN ‐Mg2)2] are connected through a bond path that suggests that there is bonding between all four MgI atoms. 相似文献
104.
采用水热法制备了系列富锂尖晶石型正极材料Li2+4xMn0.6+2xNi0.6-6xCr0.8O4(x=1/30,1/20,1/15,1/12),通过X射线衍射(XRD)、电感耦合等离子体-原子发射光谱(ICP-AES)、扫描电子显微镜(SEM)、X射线光电子能谱(XPS)、傅里叶变换红外光谱(FTIR)、拉曼光谱、循环伏安(CV)和充放电测试等手段对其结构及电化学性能进行表征.结果表明,所制备的系列材料为富锂型高电压尖晶石结构正极材料,该系列样品在4.7 V左右有放电平台.x=1/15和x=1/12时,样品中的Cr为+3价,没有观测到Cr6+.随着x值的增大,样品中Li离子与过渡金属离子的混排减小,样品的充放电比容量逐渐增大,且2.7 V处的放电平台容量也增加.当x=1/12时,样品具有较好的充放电比容量和倍率特性,首次放电比容量为107.3 mA·h/g,20次循环后容量保持率为84.9%. 相似文献
105.
106.
Neil R. Judge Dr. Leonie J. Bole Prof. Eva Hevia 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(10):e202104164
Advancing the understanding of using alkali-metal alkoxides as additives to organomagnesium reagents in Mg−Br exchange reactions, a homologous series of mixed-ligand alkyl/alkoxide alkali-metal magnesiates [MMg(CH2SiMe3)2(dmem)]2 [dmem=2-{[2-(dimethylamino)ethyl]methylamino} ethoxide; M=Li, 1 ; Na, 2 ; (THF)K, 3 ] has been prepared. Structural and spectroscopic studies have established the constitutions of these heteroleptic/heterometallic species, which are retained in arene solution. Evaluation of their reactivity towards 2-bromoanisole has uncovered a marked alkali-metal effect with potassium magnesiate 3 being the most efficient of the three ate reagents. Studies probing the constitution of the exchange product from this reaction suggest that the putative [KMgAr2(dmem)]2 (Ar=o-OMe−C6H4) intermediate undergoes redistribution into its single metal components [KAr]n and [MgAr(dmem)]2 ( 5 ). This process can be circumvented by using a different potassium alkoxide containing an aliphatic chain such as KOR’ (R’=2-ethylhexyl) which undergoes co-complexation with Mg(CH2SiMe3) to give [KMg(CH2SiMe3)2(OR’)]2 ( 7 ). This ate, in turn, reacts quantitatively with 2-bromoanisole furnishing [KMgAr2(OR’)]2 ( 9 ) which is stable in solution as a bimetallic compound. Collectively this work highlights the complexity of these alkali-metal mediated Mg−Br exchange reactions, where each reaction component can have a profound effect not only on the success of the reaction; but also the stability of the final metalated intermediates prior to their electrophilic interception. 相似文献
107.
108.
Simon Sengupta Philipp Schüler Dr. Helmar Görls Dr. Phil Liebing Dr. Sven Krieck Prof. Matthias Westerhausen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(50):e202201359
The in situ Grignard Metalation Method (iGMM) is a straightforward one-pot procedure to quickly produce multigram amounts of Hauser bases R2N-MgBr which are valuable and vastly used metalation reagents and novel electrolytes for magnesium batteries. During addition of bromoethane to a suspension of Mg metal and secondary amine at room temperature in an ethereal solvent, a smooth reaction yields R2N-MgBr under evolution of ethane within a few hours. A Schlenk equilibrium is operative, interconverting the Hauser bases into their solvated homoleptic congeners Mg(NR2)2 and MgBr2 depending on the solvent. Scope and preconditions are studied, and side reactions limiting the yield have been investigated. DOSY NMR experiments and X-ray crystal structures of characteristic examples clarify aggregation in solution and the solid state. 相似文献
109.
Jeremy C. Mullins Dr. K. Yuvaraj Yixiao Jiang Dr. Gerard P. Van Trieste III Dr. Asim Maity Prof. David C. Powers Prof. Cameron Jones 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(65):e202202103
UV irradiation of solutions of a guanidinate coordinated dimagnesium(I) compound, [{(Priso)Mg}2] 3 (Priso=[(DipN)2CNPri2]−, Dip=2,6-diisopropylphenyl), in either benzene, toluene, the three isomers of xylene, or mesitylene, leads to facile activation of an aromatic C−H bond of the solvent in all cases, and formation of aryl/hydride bridged magnesium(II) products, [{(Priso)Mg}2(μ-H)(μ-Ar)] 4 – 9 . In contrast to similar reactions reported for β-diketiminate coordinated counterparts of 3 , these C−H activations proceed with little regioselectivity, though they are considerably faster. Reaction of 3 with an excess of the pyridine, p-NC5H4But (pyBut), gave [(Priso)Mg(pyButH)(pyBut)2] 10 , presumably via reduction of the pyridine to yield a radical intermediate, [(Priso)Mg(pyBut⋅)(pyBut)2] 11 , which then abstracts a proton from the reaction solvent or a reactant. DFT calculations suggest two possible pathways to the observed arene C−H activations. One of these involves photochemical cleavage of the Mg−Mg bond of 3 , generating magnesium(I) doublet radicals, (Priso)Mg⋅. These then doubly reduce the arene substrate to give “Birch-like” products, which subsequently rearrange via C−H activation of the arene. Circumstantial evidence for the photochemical generation of transient magnesium radical species includes the fact that irradiation of a cyclohexane solution of 3 leads to an intramolecular aliphatic C−H activation process and formation of an alkyl-bridged magnesium(II) species, [{Mg(μ-Priso−H)}2] 12 . Furthermore, irradiation of a 1 : 1 mixture of 3 and the β-diketiminato dimagnesium(I) compound, [{(DipNacnac)Mg}2] (DipNacnac=[HC(MeCNDip)2]−), effects a “scrambling” reaction, and the near quantitative formation of an unsymmetrical dimagnesium(I) compound, [(Priso)Mg−Mg(DipNacnac)] 13 . Finally, the EPR spectrum (77 K) of a glassed solution of UV irradiated 3 is dominated by a broad featureless signal, indicating the presence of a doublet radical species. 相似文献
110.
Rechargeable Mg batteries (RMBs) are advantageous large-scale energy-storage devices because of the high abundance and high safety, but exploring high-performance cathodes remains the largest difficulty for their development. Compared with oxides and sulfides, selenides show better Mg-storage performance because the weaker interaction with the Mg2+ cation favors fast kinetics. Herein, nanorod-like FeSe2 was synthesized and investigated as a cathode for RMBs. Compared with microspheres and microparticles, nanorods exhibit higher capacity and better rate capability with a smaller particle size. The FeSe2 nanorods show a high capacity of 191 mAh g−1 at 50 mA g−1 and a good rate performance of 39 mAh g−1 at 1000 mA g−1. Ex situ characterizations demonstrate the Mg2+ intercalation mechanism for FeSe2, and a slight conversion reaction occurs on the surface of the particles. The capacity fading is mainly because of the dissolution of Fe2+, which is caused by the reaction between Fe2+ and Cl− of the electrolyte during the charge process on the surface of the particles. The surface of FeSe2 is mainly selenium after long cycling, which may also dissolve in the electrolyte during cycling. The present work develops a new type of Mg2+ intercalation cathode for RMBs. More importantly, the fading mechanism revealed herein has considered the specificity of Mg battery electrolyte and would assist a better understanding of selenide cathodes for RMBs. 相似文献