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991.
Naoya Morohashi Hiroshi Katagiri Takanori Shimazaki Yuichi Kitamoto Shinya Tanaka Chizuko Kabuto 《Supramolecular chemistry》2013,25(12):812-818
Tetraaminothiacalixarene 3, bearing four amino groups instead of the hydroxy groups of p-tert-butylthiacalix[4]arene 2, exhibits inclusion properties different from those of compound 2 towards small organic molecules upon crystallisation from neat solvents or guest solutions. X-ray crystallographic analyses reveal that nitromethane and acetonitrile are included into the cone-shaped cavity of compound 3, as is often seen in inclusion crystals of compound 2, whereas dichloromethane occupies a space between two distal benzene rings of compound 3, adopting a 1,3-alternate conformation. Acetic acid, which forms a dimer, fills a pore surrounded by four host molecules with a pinched cone conformation. Furthermore, guest-free crystals of compound 3 with a 1,3-alternate conformation absorb acetonitrile to give inclusion crystals with the same crystal structure as that obtained by the crystallisation. Thus, compound 3 flexibly changes its conformation according to the structures of guest compounds. 相似文献
992.
The polymerization of vinyl monomer initiated with poly-2-hydroxyethylmethacrylate (PHEMA) in water was carried out at 85°C. Cu(II) ion was not necessary for this polymerization. Methacrylate monomers were polymerized, while styrene and acrylonitrile were not. The polymerization was found to proceed through a radical mechanism in the interior of PHEMA which was swelled in water. The grafting efficiency of MMA polymer obtained was about 90%. The overall activation energy was estimated to be 32.9 kJ/mol. 相似文献
993.
Here we report total synthesis of enantiomerically pure dysibetaine CPa, isolated from Micronesian marine sponge and expected to serve as a neuroactive agent. Starting from meso-cyclopropane triester, the synthesis was achieved in 12.8% overall yield over 10 steps including organocatalytic enantioselective solvolysis of meso-succinic anhydride as a key step. This work established the absolute configurations of the natural product as (3R,4R). 相似文献
994.
We have developed a versatile method for calculating solvation thermodynamic quantities for molecules, starting from their atomic coordinates. The contribution of each atom to the thermodynamic quantities is estimated as a linear combination of four fundamental geometric measures of the atomic species, which are defined by Hadwiger's theorem, and the coefficients reflecting their solvation properties. This treatment enables us to calculate the solvation free energy with high accuracy despite of the limited computational load. The method can readily be applied to macromolecules in an all‐atom molecular model, allowing the stability of these molecules' structures in solution to be evaluated. © 2013 Wiley Periodicals, Inc. 相似文献
995.
By making full use of heat kernel estimates, we establish the integral tests on the zero-one laws of upper and lower bounds for the sample path ranges of symmetric Markov processes. In particular, these results concerning on upper rate bounds are applicable for local and non-local Dirichlet forms, while lower rate bounds are investigated in both subcritical setting and critical setting. 相似文献
996.
Understanding and Practical Use of Ligand and Metal Exchange Reactions in Thiolate‐Protected Metal Clusters to Synthesize Controlled Metal Clusters 下载免费PDF全文
Yoshiki Niihori Sakiat Hossain Sachil Sharma Bharat Kumar Wataru Kurashige Yuichi Negishi 《Chemical record (New York, N.Y.)》2017,17(5):473-484
It is now possible to accurately synthesize thiolate (SR)‐protected gold clusters (Aun(SR)m) with various chemical compositions with atomic precision. The geometric structure, electronic structure, physical properties, and functions of these clusters are well known. In contrast, the ligand or metal atom exchange reactions between these clusters and other substances have not been studied extensively until recently, even though these phenomena were observed during early studies. Understanding the mechanisms of these reactions could allow desired functional metal clusters to be produced via exchange reactions. Therefore, we have studied the exchange reactions between Aun(SR)m and analogous clusters and other substances for the past four years. The results have enabled us to gain deep understanding of ligand exchange with respect to preferential exchange sites, acceleration means, effect on electronic structure, and intercluster exchange. We have also synthesized several new metal clusters using ligand and metal exchange reactions. In this account, we summarize our research on ligand and metal exchange reactions. 相似文献
997.
Dr. Konstantin V. Purtov Dr. Valentin N. Petushkov Dr. Mikhail S. Baranov Dr. Konstantin S. Mineev Dr. Natalja S. Rodionova Zinaida M. Kaskova Aleksandra S. Tsarkova Dr. Alexei I. Petunin Dr. Vladimir S. Bondar Dr. Emma K. Rodicheva Dr. Svetlana E. Medvedeva Prof. Yuichi Oba Yumiko Oba Prof. Alexander S. Arseniev Prof. Sergey Lukyanov Prof. Josef I. Gitelson Dr. Ilia V. Yampolsky 《Angewandte Chemie (International ed. in English)》2015,54(28):8124-8128
Many species of fungi naturally produce light, a phenomenon known as bioluminescence, however, the fungal substrates used in the chemical reactions that produce light have not been reported. We identified the fungal compound luciferin 3‐hydroxyhispidin, which is biosynthesized by oxidation of the precursor hispidin, a known fungal and plant secondary metabolite. The fungal luciferin does not share structural similarity with the other eight known luciferins. Furthermore, it was shown that 3‐hydroxyhispidin leads to bioluminescence in extracts from four diverse genera of luminous fungi, thus suggesting a common biochemical mechanism for fungal bioluminescence. 相似文献
998.
999.
Osamu Kikuchi Toshio Watanabe Yusuke Satoh Yuichi Inadomi 《Journal of Molecular Structure》2000,507(1-3):53-62
Ab initio MO GB theory which includes the continuum model of solvent effect using generalized Born formula has been applied to the dimerization reaction of HCN in aqueous solution which is the starting step in prebiotic synthesis of purine precursors from aqueous hydrogen cyanide. Three steps considered were: (i) the reaction of HCN and H2O to produce the CN− anion, (ii) the reaction of CN− with HCN to give the NC–CH=N− anion, and (iii) the addition of a proton to the anion to give iminoacetonitrile. The formation of CN− ion from HCN in aqueous solution requires 15.1 kcal/mol (the experimental value estimated from the dissociation constant of HCN in water is 14.8 kcal/mol). The reaction of CN− with HCN requires the activation energy of 32.2 kcal/mol (MP2/6-31++G**//HF/6-31++G**) to give the dimer. This barrier height is reduced to 26.1 kcal/mol when HCN is associated with H3O+. In the presence of NH3 in aqueous solution, CN− is produced easily by the reaction of HCN and NH3 with a low activation energy of 4.3 kcal/mol. It was shown that the formation of CN− becomes easier in ammoniacal solution, and the dimerization occurs efficiently in aqueous solutions which contain NH3. 相似文献
1000.
Shiro Funahashi Yuichi Michiue Takashi Takeda Rong‐Jun Xie Naoto Hirosaki 《Acta Crystallographica. Section C, Structural Chemistry》2014,70(5):452-454
A novel nitride, Sr2−yEuyB2−2xSi2+3xAl2−xN8+x (x≃ 0.12, y≃ 0.10) (distrontium europium diboron disilicon dialuminium octanitride), with the space group P2c, was synthesized from Sr3N2, EuN, Si3N4, AlN and BN under nitrogen gas pressure. The structure consists of a host framework with Sr/Eu atoms accommodated in the cavities. The host framework is constructed by the linkage of MN4 tetrahedra (M = Si, Al) and BN3 triangles, and contains substitutional disorder described by the alternative occupation of B2 or Si2N on the (0, 0, z) axis. The B2:Si2N ratio contained in an entire crystal is about 9:1. 相似文献