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排序方式: 共有404条查询结果,搜索用时 15 毫秒
1.
Roberto Martínez Corte C. Eduardo Salazar E. Olivia Linzaga E. Irma 《Journal of heterocyclic chemistry》1994,31(4):1061-1063
Catalytic hydrogenation of o-nitrophenylbenz[a], benz[c], dibenz[a,h] and dibenz[a,g]acridinones using Pd/C as catalyst, at 60 psi of pressure, gave the hiterto unknown benzoquinoacridine N-oxides and benzo-pyranonaphthyridine N-oxides. The structure of all products was corroborated by ir, 1H- and 13C-nmr and mass spectra data. 相似文献
2.
Mathiazhagan C Molzon WR Cousins RD Konigsberg J Kubic J Melese P Rubin P Slater WE Wagner D Hart GW Kinnison WW Lee DM McKee RJ Milner EC Sanders GH Ziock HJ Arisaka K Knibbe P Urheim J Axelrod S Biery KA Irwin GM Lang K Margulies J Ouimette DA Ritchie JL Trang QH Wojcicki SG Auerbach LB Buchholz P Highland VL McFarlane WK Sivertz M Chapman MD Eckhause M Ginkel JF Hancock AD Joyce D Kane JR Kenney CJ Vulcan WF Welsh RE Whyley RJ Winter RG 《Physical review letters》1989,63(20):2181-2184
3.
The association of a C3v-symmetrical calix[6]tris-amine with different concave tris-carboxylic acids of various degrees of flexibility has been explored by 1H NMR spectroscopy. In all cases, self-assembled structures directed by the selective inclusion of a neutral guest molecule were obtained, the more preorganized being stable in protic solvents. With a rigid C3-symmetrical cap, chiral guest recognition in the calixarene cavity resulted. A large tris-acidic partner gave a unique molecular ditopic receptor that is able to simultaneously accommodate two neutral molecules in two distinct hydrophobic cavities with different binding processes. 相似文献
4.
Darbost U Rager MN Petit S Jabin I Reinaud O 《Journal of the American Chemical Society》2005,127(23):8517-8525
The host-guest properties of calix[6]tren 1 have been evaluated. The receptor is based on a calix[6]arene that is covalently capped at the narrow rim by a tren unit. As a result, the system presents a concave hydrophobic cavity with, at its bottom, a grid-like nitrogenous core. Despite its well-defined cavity and opening to the outside at the large rim, 1 did not behave as a good receptor for neutral molecules in chloroform. However, it exhibited efficient endo-complexation of ammonium guests. By contrast, the per-protonated host, 1.4H(+), behaved as a remarkable receptor for small organic molecules. The complexation is driven by a strong charge-dipole interaction and hydrogen bonds between the polar guest and the tetracationic cap of the calixarene. Finally, coordination of Zn(2+) to the tren core led to the asymmetrization of calixarene cavity and to the strong but selective endo-binding of neutral ligands. This study emphasizes the efficiency of a receptor presenting a concave hydrophobic cavity that is polarized at its bottom. The resulting combination of charge-dipole, hydrogen bonding, CH-pi, and van der Waals interactions highly stabilizes the supramolecular architectures. Also, importantly, the tren cap allows the tuning of the polarization, offering either a basic (1), a highly charged and acidic (1.4H(+)), or a coordination (1.Zn(2+)) site. As a result, the system proved to be highly versatile, tunable, and interconvertible in solution by simple addition of protons, bases, or metal ions. 相似文献
5.
Sénèque O Rager MN Giorgi M Prangé T Tomas A Reinaud O 《Journal of the American Chemical Society》2005,127(42):14833-14840
The coordination chemistry of Zn in an N(3)ArOH environment has been explored. The ligands are based on calix[6]arenes that present two imidazole arms and an amino phenol moiety at the narrow rim. Three different types of complexes have been characterized. One is dicationic with Zn(2+) coordinated to the three nitrogen atoms and to the oxygen of the phenol group of the calix[6]ligand. This complex is very sensitive to exogenous coordinating molecules and exists as a 5-coordinate species due to the endo-complexation of a guest. The second species is a monocationic complex for which the phenol group has been deprotonated. The resulting N(3)ArOZn complex can also bind a guest ligand albeit with a lower affinity than the dicationic complex. The third species is neutral. It can be obtained upon reaction with a base to yield a hydroxo complex or with an anion such as a chloride that coordinates the metal center from the outside of the calixarene cavity. The simultaneous binding of two anionic donors decreases the Zn Lewis acidity, allowing an impressive conformational reorganization of the system. One imidazole arm is released by the metal center. The other one undergoes self-inclusion into the pi-basic calixarene cavity because the low affinity of the metal center for neutral ligand does not allow the endo-coordination of an exogenous guest. Hence, the calix[6]N(3)ArOH-based Zn complexes act as an acid-base switch for guest binding. Several aspects of this system appear reminiscent of Zn-peptidases of the astacin and serralisin families. 相似文献
6.
Olivia Vidoni Stefan Neumeier Nathalie Bardou Jean-Luc Pelouard Günter Schmid 《Journal of Cluster Science》2003,14(3):325-336
The elaboration of closed-packed monolayers of Au55(PPh3)12Cl6 clusters on oxidized and non-oxidized GaAs surfaces is reported. The first part of this work describes the use of silanethiol modified GaAs oxide surfaces to trap 18 nm gold colloids and Au55(PPh3)12Cl6 clusters. The surfaces characterized by AFM measurements present high-quality coverage on a quite long range for both metallic species. The second part is devoted to the elaboration of Au55(PPh3)12Cl6 cluster monolayers on non-oxidized p-type GaAs substrates, functionalized with dithiol molecules. AFM measurements demonstrate the presence of closed-packed two-dimensional arrangements of Au55 clusters. 相似文献
7.
Rondelez Y Rager MN Duprat A Reinaud O 《Journal of the American Chemical Society》2002,124(7):1334-1340
Two calixarene-based model systems (a and b) for monocopper enzymes are compared. Both present a tris(pyridine) coordination site for Cu that mimics the imidazole-rich neutral binding site in enzymes. Upon reaction with 1 equiv of copper(I), the tridentate ligands gave rise to ill-defined unsymmetrical complexes. However, in the presence of an organonitrile RCN (R = Me, Et, Ph), tetrahedral species were obtained, with the nitrilo ligand included in the calixarene hydrophobic cone. System b presents a larger cavity than system a, with a wider opening thanks to the removal of three tBu groups from the calixarene structure. As a result, the recognition pattern for MeCN vs PhCN is inverted, and the relative affinity constants differ by 3 orders of magnitude. The mechanism of the acetonitrile exchange at the cuprous centers was studied by (1)H NMR spectroscopy. Thermodynamic and kinetic data show that it follows a dissociative pathway in both cases. The main differences between systems a and b stem from the presence of a door that entraps the guest in case a. In system b indeed, the removal of three calixarene tBu groups led to a 100-fold acceleration of the MeCN exchange rate. Hence, these supramolecular systems provide a rare and interesting model for the hydrophobic substrate channel giving access to a metalloenzyme active site. 相似文献
8.
9.
Belz J Cousins RD Diwan MV Eckhause M Ecklund KM Hancock AD Highland VL Hoff C Hoffmann GW Irwin GM Kane JR Kettell SH Klein JR Kuang Y Lang K Martin R May M McDonough J Molzon WR Riley PJ Ritchie JL Schwartz AJ Trandafir A Ware B Welsh RE White SN Witkowski MT Wojcicki SG Worm S 《Physical review letters》1996,76(18):3277-3280
10.
Arisaka K Auerbach LB Axelrod S Belz J Biery KA Buchholz P Chapman MD Cousins RD Diwan MV Eckhause M Ginkel JF Guss C Hancock AD Heinson AP Highland VL Hoffmann GW Horvath J Irwin GM Joyce D Kaarsberg T Kane JR Kenney CJ Kettell SH Kinnison WW Knibbe P Konigsberg J Kuang Y Lang K Lee DM Margulies J Mathiazhagan C McFarlane WK McKee RJ Melese P Milner EC Molzon WR Ouimette DA Riley PJ Ritchie JL Rubin P Sanders GH Schwartz AJ Sivertz M Slater WE Urheim J Vulcan WF Wagner DL Welsh RE Whyley RJ 《Physical review letters》1993,71(24):3910-3913