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991.
A protein-cleaving catalyst specific for a disease-related protein can be used as a catalytic drug. As the first protein-cleaving catalyst selective for a protein substrate, a catalyst for myoglobin was designed by attaching Cu(II) or Co(III) complex of cyclen to a binding site searched by a combinatorial method using peptide nucleic acid monomers as building units. [reaction: see text] 相似文献
992.
Yoo J Yamaguchi A Nakano M Krzystek J Streib WE Brunel LC Ishimoto H Christou G Hendrickson DN 《Inorganic chemistry》2001,40(18):4604-4616
The preparations, X-ray structures, and detailed physical characterizations are presented for two new mixed-valence tetranuclear manganese complexes that function as single-molecule magnets (SMM's): [Mn4(hmp)6Br2(H2O)2]Br2-4H2O (2) and [Mn4(6-me-hmp)6Cl4]-4H2O (3), where hmp(-) is the anion of 2-hydroxymethylpyridine and 6-me-hmp(-) is the anion of 6-methyl-2-hydroxymethylpyridine. Complex 2-4H2O crystallizes in the space group P2(1)/c, with cell dimensions at -160 degrees C of a = 10.907(0) A, b = 15.788(0) A, c = 13.941(0) A, beta = 101.21(0) degrees, and Z = 2. The cation lies on an inversion center and consists of a planar Mn4 rhombus that is mixed-valence, Mn2(III)Mn2(II). The hmp(-) ligands function as bidentate ligands and as the only bridging ligands in 2-4H2O. Complex 3-4H2O crystallizes in the monoclinic space group C2/c, with cell dimensions at -160 degrees C of a = 17.0852(4) A, b = 20.8781(5) A, c = 14.835(3) A, beta = 90.5485(8) degrees, and Z = 4. This neutral complex also has a mixed-valence Mn2(III)Mn2(II) composition and is best described as having four manganese ions arranged in a bent chain. A mu2-oxygen atom of the 6-me-hmp(-) anion bridges between the manganese ions; the Cl(-) ligands are terminal. Variable-field magnetization and high-frequency and -field EPR (HFEPR) data indicate that complex 2-4H2O has a S = 9 ground state whereas complex 3.4H(2)O has S = 0 ground state. Fine structure patterns are seen in the HFEPR spectra, and in the case of 2.4H(2)O it was possible to simulate the fine structure assuming S = 9 with the parameters g = 1.999, axial zero-field splitting of D/k(B) = -0.498 K, quartic longitudinal zero-field splitting of B4(omicron)/k(B) = 1.72 x 10(-5) K, and rhombic zero-field splitting of E/k(B) = 0.124 K. Complex 2-4H2O exhibits a frequency-dependent out-of-phase AC magnetic susceptibility signal, clearly indicating that this complex functions as a SMM. The AC susceptibility data for complex 2-4H2O were measured in the 0.05-4.0 K range and when fit to the Arrhenius law, gave an activation energy of DeltaE = 15.8 K for the reversal of magnetization. This DeltaE value is to be compared to the potential-energy barrier height of U/k(B) = absolute value DSz(2) = 40.3 K calculated for 2-4H2O. 相似文献
993.
A highly sensitive silver staining method for detecting proteins in sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was developed. It is based on the silver nitrate staining method but also employs an azo dye, calconcarboxylic acid (NN), as a silver-ion sensitizer. It increases silver binding on protein bands or spots by the formation of a silver-dye complex and also increases the reducing power of silver ions to metallic silver by NN itself with formaldehyde. After a 2 h gel fixing step, the protocol including sensitization, silver-ion impregnation, and reduction steps can be completed in 1 h. The sensitivity is superior to that of silver stain with glutardialdehyde as a silver-ion sensitizer. The detection limit of NN-silver stain is 0.05-0.2 ng protein. Considering the high sensitivity without using glutardialdehyde, the NN-silver stain would be useful for routine silver staining of proteins. 相似文献
994.
995.
996.
Ramesh Manda Srinivas Pagidi MinSu Kim Chul Ho Park Hye Sun Yoo Kaur Sandeep 《Liquid crystals》2018,45(5):736-745
Optically isotropic nature can open a new type of high-performance liquid crystal (LC) displays. The main features emerge from the interaction between LC and polymer network at the interface. At this point, we investigated the influence of cross-linking monomer concentration and functionality on electro-optic properties of optically isotropic liquid crystal (OILC) obtained by polymerisation-induced phase separation method. Interestingly, we obtained a pore-like network structure constructed by highly interlinked polymer beads in acrylate monomers and achieved fast decay response time (0.6 ms). We found that the voltage-dependent hysteresis was mostly eliminated (~0.25%), and the contrast ratio was enhanced (1:1550) for high functional monomers. The result inspires a simple way to optimise the materials to fabricate a high-performance OILC device and it shows high-transparency, low-driving voltage, hysteresis-free and sub-millisecond response time. 相似文献
997.
Byeongil Lee Moonyong Shin Youngran Seo Myeong Hak Kim Hye Ryoung Lee Jin Seok Kim Kyu-hyun Chung Dongwon Yoo Young Gyu Kim 《Tetrahedron》2018,74(1):130-134
Azapropellanes are of great interest in many disciplines, including materials science and medicinal chemistry. Various synthetic approaches for azapropellanes have been explored; however, the synthetic study of the polyazapropellane skeleton containing five or more nitrogen atoms is rare. Here, we report a simple yet highly efficient protocol for the synthesis of the hexaaza[3.3.3]propellane skeleton as a building block for high energy materials for the first time. The key reactions include the Boc2O-assisted cyclization of glycoluril diamine without a column purification step and the first full reduction of all the three carbonyl groups to the methylene groups through a combination of LiAlH4 and DIBAL-H. All the structures were confirmed by spectroscopic and X-ray analyses. 相似文献
998.
Xiaochen Liu Dongsub Hong Zhigang She William H. Hersh Barney Yoo Yu Chen 《Tetrahedron》2018,74(45):6593-6606
Two regioselective synthetic routes towards 3,5-disubstituted isoxazoles from ynones are reported. One route takes place via first converting the ynones to ynone O-methyl oximes, followed by a palladium-catalyzed intramolecular cyclization. The other involves the formation of 5-hydroxy-4,5-dihydroisoxazoles by a cyclocondensation between ynones and hydroxylamine, and subsequent acid mediated dehydration. The two routes are not only both highly regioselective, but also complementary to each other as a pair of regioisomeric 3,5-disubstituted isoxazoles are readily prepared from one single ynone substrate. The efficiency of the two routes are further evaluated and demonstrated in the synthesis of three representative 3,5-disubstituted isoxazoles. 相似文献
999.
We have performed an unbiased search for the lowest-energy geometric structures of medium-sized silicon clusters SiN (27 < or = N < or = 39) using a genetic algorithm and nonorthogonal-tight-binding method, followed by a refining and biased search using basin-hopping method coupled with density-functional theory. We show that the carbon fullerene cages are most likely generic cage motifs ("magic cages") to form low-lying stuffed-cage silicon clusters (beyond the size N > 27). An empirical rule that provides optimal "stuffing/cage" combinations for constructing low-energy endohedral silicon fullerenes is suggested, with a hope that it can provide guidance to future synthesis of "bucky" silicon. 相似文献
1000.
A general method is reported for the parallel solid-phase synthesis of 5-amino-1-(substituted thiocarbamoyl)pyrazole and 1,2,4-triazole derivatives based on the cyclization of polymer-bound dithiocarbazate 3 with various electrophiles, such as 3-ethoxyacrylonitriles 8 and cyanocarboimidates 9. The polymer-bound dithiocarbazate 3, produced by nucleophilic reaction with carbon disulfide and Fmoc-hydrazine on the Merrifield resin, served as the key intermediate for subsequent heterocycle diversification. Further nucleophilic substitution on these polymer-bound 5-amino-1-dithiocarboxypyrazoles 4 and 1,2,4-triazoles 6 with various amines under thermal cleavage condition produced the desired 5-amino-1-(substituted thiocarbamoyl)pyrazoles 5 and 1,2,4-triazoles 7. The progress of reactions could be monitored as polymer-bound intermediates by ATR-FTIR spectroscopy on single bead. The final compounds, obtained in good four-step overall yields and high purities upon cleavage from the resins, were characterized by LC/MS, 1H NMR, and 13C NMR spectroscopy. 相似文献