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91.
Akira Takahashi Ryu Yuzaki Yoshihito Ishida Atsushi Kameyama 《Journal of polymer science. Part A, Polymer chemistry》2019,57(24):2442-2449
Ring‐expansion polymerization (REP) of thiiranes was investigated using 3H‐benzothiazol‐2‐one (BT) as the cyclic aromatic thiourethane initiator in the presence of tetrabutylammonium chloride (TBAC) catalyst. The polymerization proceeded in a well‐controlled manner to afford cyclic polysulfides with one BT moiety per macrocycle, as confirmed by MALDI‐TOF MS spectroscopy. Differential scanning calorimetry (DSC) measurement of the obtained cyclic polysulfides revealed slight decrease in the glass‐transition temperature as the increase in the molecular weight, supporting the cyclic topology of the products. Postpolymerization of thiiranes using the BT‐initiated cyclic polysulfide as the macroinitiator afforded the ring‐expanded product while maintaining the narrow polydispersity and well‐defined cyclic structure, which enabled precise synthesis of cyclic block copolymer with different thiirane combination. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2442–2449 相似文献
92.
Inside Cover: Inhibition of Heme Uptake in Pseudomonas aeruginosa by its Hemophore (HasAp) Bound to Synthetic Metal Complexes (Angew. Chem. Int. Ed. 11/2014) 下载免费PDF全文
93.
94.
Electronic circular dichroism (CD) spectra as well as transitions from ground to excited states were predicted for a helical nonapeptide based on alternative sequence--[Z-alpha,beta-dehydrophenylalanine (Delta(Z)Phe)-X]--through semiempirical molecular orbital computation combined with time-dependent (TD) method. The simulation was performed for its various conformers that differ in helix type, helix sense, and Delta(Z)Phe side-chain orientation. These conformational variations have been shown to depend largely on its CD spectra. Comparison between simulated and observed CD profiles reveals that peptide 1 in solution favors a right-handed 3(10)-helix that adopts phenyl (Delta(Z)Phe) planes basically in a vertical orientation with respect to the helix axis. These predictions were essentially supported from CD simulation of a shorter helical analogue at ab inito or density functional TD levels. The theoretical CD-conformation relationship should provide us useful guideline for determination of helix sense in the dehydropeptide, and for estimation of its conformations statistically averaged in solution. 相似文献
95.
96.
Maeda Y Miyashita J Hasegawa T Wakahara T Tsuchiya T Nakahodo T Akasaka T Mizorogi N Kobayashi K Nagase S Kato T Ban N Nakajima H Watanabe Y 《Journal of the American Chemical Society》2005,127(35):12190-12191
The reversible and regioselective reaction of La@C82 with cyclopentadiene was carried out. The activation and thermodynamic parameter of the retro-reaction was estimated from the Arrhenius plots of the rate constants. 相似文献
97.
Minakawa N Kojima N Hikishima S Sasaki T Kiyosue A Atsumi N Ueno Y Matsuda A 《Journal of the American Chemical Society》2003,125(33):9970-9982
The synthesis and thermal stability of oligodeoxynucleotides (ODNs) containing imidazo[5',4':4,5]pyrido[2,3-d]pyrimidine nucleosides 1-4 (N(N), O(O), N(O), and O(N), respectively) with the aim of developing two sets of new base pairing motifs consisting of four hydrogen bonds (H-bonds) is described. The proposed four tricyclic nucleosides 1-4 were synthesized through the Stille coupling reaction of a 5-iodoimidazole nucleoside with an appropriate 5-stannylpyrimidine derivative, followed by an intramolecular cyclization. These nucleosides were incorporated into ODNs to investigate the H-bonding ability. When one molecule of the tricyclic nucleosides was incorporated into the center of each ODN (ODN I and II, each 17mer), no apparent specificity of base pairing was observed, and all duplexes were less stable than the duplexes containing natural G:C and A:T pairs. On the other hand, when three molecules of the tricyclic nucleosides were consecutively incorporated into the center of each ODN (ODN III and IV, each 17mer), thermal and thermodynamic stabilization of the duplexes due to the specific base pairings was observed. The melting temperature (T(m)) of the duplex containing the N(O):O(N) pairs showed the highest T(m) of 84.0 degrees C, which was 18.2 and 23.5 degrees C higher than that of the duplexes containing G:C and A:T pairs, respectively. This result implies that N(O)and O(N) form base pairs with four H-bonds when they are incorporated into ODNs. The duplex containing N(O):O(N) pairs was markedly stabilized by the assistance of the stacking ability of the imidazopyridopyrimidine bases. Thus, we developed a thermally stable new base pairing motif, which should be useful for the stabilization and regulation of a variety of DNA structures. 相似文献
98.
Yoshihito Osada 《Journal of polymer science. Part A, Polymer chemistry》1979,17(11):3485-3498
The degree of linkage, θ, defined as the ratio of the binding groups to the total of potentially interacting groups and the stability constant K of the polymer–polymer complexes in the systems poly(methacrylic acid)–poly(ethylene glycol), poly(acrylic acid)–poly(ethylene glycol), and poly-(methacrylic acid)–poly(vinyl pyrrolidone) in aqueous and aqueous alcohol media were determined as a function of temperature by potentiometric titration. It was found that θ and K are strongly dependent on chain length, temperature, and medium and that hydrophobic interaction is a significant factor in the stabilization of the complexes. The enthalpy and entropy changes and the cooperativeness parameter of the systems were calculated. A mechanism for the complexation in terms of cooperative interaction was proposed. 相似文献
99.
Takimiya K Kunugi Y Toyoshima Y Otsubo T 《Journal of the American Chemical Society》2005,127(10):3605-3612
A series of 2,6-diaryl-substituted naphtho[1,8-bc:5,4-b'c']dithiophene derivatives 2-6, whose aryl groups include 5-hexyl-2-thienyl, 2,2'-bithiophen-5-yl, phenyl, 2-naphthyl, and 4-biphenylyl, was synthesized by the palladium-catalyzed Suzuki-Miyaura coupling and utilized as active layers of organic field-effect transistors (OFETs). All devices fabricated using vapor-deposited thin films of these compounds showed typical p-type FET characteristics. The mobilities are relatively good and widely range from 10(-4) to 10(-1) cm2 V(-1) s(-1), depending on the substituent groups. Among them, the mobilities of the devices using films of 3-5 tend to increase with the increasing temperature of the Si/SiO2 substrate during film deposition. In particular, the device based on the naphthyl derivative 5, when fabricated at 140 degrees C, marked a high mobility of 0.11 cm2 V(-1) s(-1) with an on/off ratio of 10(5), which is a top class of performance among organic thin-film transistors. Studies of X-ray diffractograms (XRDs) have revealed that the film of 4 and 5 is composed of two kinds of crystal grains with different phases, so-called "single-crystal phase" and "thin film phase", and that the proportion of the thin film phase increases with an increase of the substrate temperature. In the thin film phase the assembled molecules stand nearly upright on the substrate in such a way as to be favorable to carrier migration. 相似文献
100.
Benzoins are simply oxidized to benzils in excellent yields with a catalytic amount of triarylstibanes under an aerobic condition. This catalytic oxidation is heteroatom-specific in the antimony compound and no reaction take place with other group 15 reagents such as triphenylphosphane, -arsane and -bismuthane. The reaction should involve an oxidation-reduction cycle between stibane Sb(III) and stiborane Sb(V) under air. 相似文献