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991.
A new stilbene, 4-[(2"E)-7"-hydroxy-3",7"-dimethyloct-2"-enyl]-2',3,4',5-tetrahydroxy-trans-stilbene (1), and the known compound chlorophorin (2) were isolated from the heartwood of Chlorophora excelsa. Both 1 and 2 showed tyrosinase inhibitory activity with IC(50) values of 96 and 1.3 microM, respectively. 相似文献
992.
Okamoto H Yamaji M Satake K Tobita S Kimura M 《The Journal of organic chemistry》2004,69(23):7860-7868
The triplet-sensitized photoreactions of the title biplanophane system 6, the photoisomer of a 2,11-diaza[3,3](9,10)anthracenoparacyclophane derivative 5, were investigated by stationary and laser-flash photolyses using xanthone (XT) and benzophenone (BP) as triplet sensitizers. When photoisomer 6 underwent XT-sensitized irradiation, a triplet cyclophane 5 and a novel polycyclic product 7 were obtained via an adiabatic cycloreversion and a formal [2pia + 2pia + 2sigmas] rearrangement, respectively. The maximum quantum yield for the formation of cyclophane 5 (0.69) and the upper-limit efficiency for the formation of polycycle 7 (0.31) were determined by laser photolysis techniques. For BP-sensitized photolysis of photoisomer 6, oxetane 8, in addition to triplet cyclophane 5 and polycycle 7, was formed by a Paterno-Buchi reaction. The quenching rate constant (k(q)) of triplet BP by photoisomer 6 (3.4 x 10(8) dm(3) mol(-)(1) s(-)(1)) was found to be 1 order of magnitude smaller than that for XT (5.0 x 10(9) dm(3) mol(-)(1) s(-)(1)). On the basis of the relationship between k(q) and the triplet donor-acceptor energy gap, the triplet energy level of photoisomer 6 was estimated to be approximately 71 kcal mol(-)(1). The photochemical and the photophysical processes involved in the sensitized photolyses are summarized in an energetic reaction diagram and discussed in detail. 相似文献
993.
Ogo S Yamahara R Roach M Suenobu T Aki M Ogura T Kitagawa T Masuda H Fukuzumi S Watanabe Y 《Inorganic chemistry》2002,41(21):5513-5520
In our preliminary communication (Ogo, S.; Wada, S.; Watanabe, Y.; Iwase, M.; Wada, A.; Harata, M.; Jitsukawa, K.; Masuda, H.; Einaga, H. Angew. Chem., Int. Ed. 1998, 37, 2102-2104), we reported the first example of X-ray analysis of a mononuclear six-coordinate (hydroxo)iron(III) non-heme complex, [Fe(III)(tnpa)(OH)(RCO(2))]ClO(4) [tnpa = tris(6-neopentylamino-2-pyridylmethyl)amine; for 1, R = C(6)H(5)], which has a characteristic cis (hydroxo)-Fe(III)-(carboxylato) configuration that models the cis (hydroxo)-Fe(III)-(carboxylato) moiety of the proposed (hydroxo)iron(III) species of lipoxygenases. In this full account, we report structural and spectroscopic characterization of the cis (hydroxo)-Fe(III)-(carboxylato) configuration by extending the model complexes from 1 to [Fe(III)(tnpa)(OH)(RCO(2))]ClO(4) (2, R = CH(3); 3, R = H) whose cis (hydroxo)-Fe(III)-(carboxylato) moieties are isotopically labeled by (18)OH(-), (16)OD(-), (18)OD(-), (12)CH(3)(12)C(18)O(2)(-), (12)CH(3)(13)C(16)O(2)(-), (13)CH(3)(12)C(16)O(2)(-), (13)CH(3)(13)C(16)O(2)(-), and H(13)C(16)O(2)(-). Complexes 1-3 are characterized by X-ray analysis, IR, EPR, and UV-vis spectroscopy, and electrospray ionization mass spectrometry (ESI-MS). 相似文献
994.
Explicita priorierror bounds for the approximation by theH10-projection into piecewise polynomial spaces are given. In particular, for the quadratic approximation, the optimal constant is derived, and a nearly optimal value for the cubic is obtained. These constants play an important role in the numerical verification method of finite element solutions for nonlinear elliptic equations. 相似文献
995.
Satoru Inoue Toshiki Higashino Shunto Arai Reiji Kumai Hiroyuki Matsui Seiji Tsuzuki Sachio Horiuchi Tatsuo Hasegawa 《Chemical science》2020,11(46):12493
The construction and control of 2D layered molecular packing motifs with functionally substituted π-electron cores are crucial for developing organic electronic materials and devices. We investigated a regioisomeric structure–property relationship in high-performance and solution-processable layered organic semiconductors based on mono-octyl-substituted benzothieno[3,2-b]naphtho[2,3-b]thiophene (mono-C8-BTNT). We demonstrated that an isomorphous bilayer-type layered herringbone packing motif is obtainable in a series of four positional isomers of mono-C8-BTNTs whose π-electron core is substituted by an octyl chain at one of the four most peripheral positions with roughly keeping the rod-like molecular shape. These regioisomeric compounds exhibited systematic variations in the solvent solubility and liquid-crystalline phase transitions at elevated temperatures. The analysis of intermolecular interaction energies in the crystals based on dispersion-corrected DFT calculations revealed that the crystals of 2- and 8-mono-C8-BTNTs are more stable than those of 3- and 9-mono-C8-BTNTs owing to the higher ordering of alkyl chain layers in the crystals. Such differences of the stability in their crystal formation are closely correlated with TFT performances, where the single-crystal devices of the 2- and 8-mono-C8-BTNTs substituted at the most peripheral positions exhibit high-performance TFT characteristics with a mobility of approximately 10 cm2 V−1 s−1.An isomorphous bilayer-type layered herringbone crystal packing is reported for a series of four positional isomers of mono-C8-BTNTs, where the single-crystal devices with the isomers exhibit high-performance TFT characteristics. 相似文献
996.
997.
Shuichi Haraguchi Youichi Tsuchiya Dr. Tomohiro Shiraki Dr. Kouta Sugikawa Kazuki Sada Prof. Seiji Shinkai Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(42):11221-11228
π‐Conjugated polymers can finely tune their electrical and optical properties in response to their conformational changes. We believe that a deeper understanding of their higher‐order structures will stimulate further development of their applications. We had revealed that one helix‐forming natural polysaccharide (SPG) and one polythiophene derivative (PT‐1) formed a stable one‐dimensional complex and in the polythiophene main chain a helical conformation was induced through the dynamic conformational changes. The objective of our present research is to obtain a better mechanistic understanding on the interaction between SPG and polythiophenes. Here we have used particular left‐ and right‐handed helix‐forming polythiophene derivatives (D ‐ and L ‐POWTs, respectively) and studied their influence on the helical motif of the complexes. We observed that SPG interacts with both D ‐ and L ‐POWTs through their dynamic conformational changes and both D ‐ and L ‐POWTs form the right‐handed co‐helical complexes with SPG according to the inherent helical motif of SPG. In addition, it was confirmed that 1) the complexes do not coagulate in aqueous solution, and 2) the exchange in the helical motif can occur only when the polymers experience the denature–renature process. We believe, therefore, that the mechanism of the helical induction of the SPG/POWT complexes is very unique, being different from conventional equilibrium reactions. 相似文献
998.
999.
Naohiko Shimada Tadashi Okobira Yoichi Takeda Seiji Shinkai Kazuo Sakurai 《Journal of polymer science. Part A, Polymer chemistry》2008,46(4):1440-1448
Schizophyllan (SPG) is a natural β‐1,3‐glucan that forms a triple helix (t‐SPG) in neutral aqueous solutions and t‐SPG can be denatured to single chains (s‐SPGs) in DMSO or alkaline solutions. Exchanging the denatured solutions for neutral water leads the renaturation of the triple helix. We have reported that hydrophobic molecules can form a complex with s‐SPG when they are present in the renaturation process. Some of these, for example poly(dA) and polyaniline, were found to have aromatic amino moieties. This report demonstrates whether s‐SPG can interact with other aromatic amino compounds such as anilinonaphthalene sulfonic acid (ANS) derivatives. Enhanced fluorescence intensity and red‐shifted UV absorption spectra were observed in the mixture of s‐SPG and 2,6‐ANS or 2,6‐TNS. In the circular dichroism measurement, the positive Cotton effects appeared after mixing 2, 6‐ANS with s‐SPG. When the amino proton was replaced by the methyl group or used in intramolecular hydrogen bonds, any spectral changes were not observed. These results indicate that amino proton in the ANS derivatives plays a key role in the complexation. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1440–1448, 2008 相似文献
1000.
Taro Ueda Takayuki Nagano Hajime Okawa Seiji Takahashi 《Electrochemistry communications》2009,11(8):1654-1656
An amperometric zirconia-based sensor attached with perovskite-type oxide sensing electrode was examined for monitoring NO2 in automobile exhaust. The sensor using La0.6Sr0.4Co0.98Mn0.02O3 showed high response to NO2. The response was almost linear to NO2 concentration in the range between 50 and 800 ppm, and a 90% reaction time to 400 ppm NO2 was less than 20 s. Though the NO2 response of the sensor was slightly affected by the changes in O2 concentrations, it showed still high response in the examined range of 5–21 vol%. 相似文献