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91.
《Comptes Rendus Chimie》2017,20(3):261-271
A review of recent advancements in metal-free arylations via photogenerated triplet aryl cations and decatungstate anion ([W10O32]4−) photocatalyzed C–C bond formation is reported herein. These approaches are two examples of the great potentialities of photons as green activants in organic synthesis, allowing the functionalization of different chemical substrates under mild conditions (room temperature, aqueous solvents, absence of aggressive and unstable reactants and of expensive transition metal-based catalysts, and chance to use solar light as the energy source). 相似文献
92.
93.
Antoine Aboukais Elena A. Zhilinskaya Jean-Franois Lamonier Igor N. Filimonov 《Colloids and surfaces. A, Physicochemical and engineering aspects》2005,260(1-3):199-207
Oxygen adsorption experiments were performed on evacuated and prereduced CeO2/SiO2 and CeO2/Al2O3 catalysts with and without platinum. Considerable amounts of the superoxide radical ions were stabilized on all the samples. Signal parameters suggest Ce4+–O2− positioning for all detectable superoxide species. Physisorbed oxygen broadens O2− signal beyond detection for all the alumina-based samples, while the same procedure for all the silica-based samples did not change signal shape of O2− species. Detectable O2− species are localized in the bulk of ceria and the nature of support (silica or alumina) determines the number of oxygen vacancies and the rate of electron transfer. XRD data suggest that for alumina-based samples small and/or thin islands of ceria dominate, while comparatively large ceria particles are stabilized on the surface of silica-based samples with the same ceria content. Average size of ceria crystallites is still not determining factor and cannot account for the observed differences. Higher concentrations of paramagnetic species may be stabilized on alumina-based samples and thus, sensor-like behavior towards gaseous oxygen at room temperature was detected for them—oxygen admission reversibly changes superoxide lineshape. For silica samples, only minor changes of O2− lineshapes were typical upon the change of the partial pressure of oxygen at ambient and low temperatures. Addition of platinum has little effect on parameters of the O2− signal, except an enhancement of the superoxide decay in the reducing media. Possible site for O2− stabilization inside the lattice of CeO2 was proposed and relevance of the observed effects to the redox catalysis discussed. 相似文献
94.
<正>自1999年烯类单体的双光子聚合方法被发现以来[1],其产物在光开关制备[2]、光子晶体[3]、微机械[4]及三维微加工[5]等领域得到了广泛的应用.由此,烯类双光子聚合机理也成为人们研究的焦点[6].到目前为止,研究者们普遍认为烯类单体的双光子聚合反应属于自由基历程,各种利用双光子 相似文献
95.
用密度泛函理论(DFT)研究了过氧亚硝酸与酪氨酸的反应机理. 在B3LYP/6-311G(d,p)水平上对该反应体系的反应物、中间体、过渡态和产物进行了几何构型优化并计算了振动频率和能量. 计算结果表明, 过氧亚硝酸不易直接与酪氨酸反应, 而是先分解产生自由基(·OH和·NO2), 而后再与酪氨酸分步作用. 过氧亚硝酸与酪氨酸的反应生成两种主要产物, 分别为3-羟基酪氨酸和3-硝基酪氨酸, 这一结论与实验所得到的结果一致. 此外在同一计算水平上采用SCRF(PCM)方法计算了溶剂化效应, 结果表明, 极性溶剂可以增加自由基结合的稳定化能, 并降低反应通道的活化能, 有利于反应的进行. 相似文献
96.
Igor V. Kuvychko James B. Whitaker Kristin J. Suhr Olga V. Boltalina 《Journal of fluorine chemistry》2011,132(10):679-685
The first systematic study of heterogeneous fullerene trifluoromethylation using an innovative gradient-temperature gas-solid reactor revealed a significant effect of CF3I pressure on the conversion of C60 and C70 into trifluoromethylated products and on the range of fullerene(CF3)n compositions that were obtained. The design of the reactor allowed us to lower the residence times of fullerene(CF3)n species in the hot zone which resulted in the significant differences in relative isomeric distributions as compared to the earlier methods. For the first time, gram quantities of trifluoromethylated fullerenes were prepared using the new reactor, and the selective synthesis of a single-isomer C60(CF3)2 was developed. The relative reactivity of C70 as a CF3 radical scavenger was found to be much lower than that of C60, especially at an early radical addition stage, which led to the cost-efficient synthesis of C60(CF3)2 from a fullerene extract. 相似文献
97.
A practical, brief and selective synthesis of several pinene oxide derived terpenoids can be achieved from readily available starting materials. The key step is a radical reaction promoted by titanocene chloride. 相似文献
98.
Hydroperoxides, olefins, and arenediazonium salts selectively combine to give azo compounds via an iron(II)-mediated three-component reaction. Starting with a fragmentation liberating acetic acid, the hydroperoxides act as radical source and the diazonium ions as nitrogen-centered radical scavengers. 相似文献
99.
Randolph K. Belter 《Journal of fluorine chemistry》2011,132(11):961-964
At temperatures around 400 °C, nitrogen trifluoride (NF3) readily reacts with alkanes and benzene as well as ethers. In all cases, products were N,N-difluoroamines. This is in contrast to difluoroamination of benzylic substrates where the initial N,N-difluoroamines underwent eliminations or rearrangements and were not isolated. Cyclic and acyclic alkanes generated N,N-difluoroaminoalkanes. Benzene substituted on the ring to form N,N-difluoroaniline. Ethers reacted to generate α-N,N-difluoroamino ethers. Little direct fluorination was observed. 相似文献
100.
Boris A. Trofimov Boris G. Sukhov Svetlana F. Malysheva Natal’ya A. Belogorlova Anatolii P. Tantsirev Lidiya N. Parshina Ludmila A. Oparina Sergey P. Tunik Nina K. Gusarova 《Tetrahedron letters》2004,45(49):9143-9145
Secondary phosphines react readily with a vinyl ether of diacetone-d-glucose under radical initiation conditions to give, in high yield, anti-Markovnikov adducts, diorganyl{2-[3-O-(1,2:5,6-di-O-isopropylidene)-d-glucofuranosyloxy]ethyl}phosphines, which oxidize almost quantitatively upon reacting with air oxygen or elemental sulfur to form the corresponding optically active phosphine oxides or sulfides. 相似文献