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991.
Michael J. Hudson Enrique Rodríguez-Castellón 《Journal of inclusion phenomena and macrocyclic chemistry》1989,7(3):301-308
Monomers which contain unsaturated linkages and amine groups have been intercalated to form either mono- or bi-layers. The monomertrans-N,N-diethyl-2-butene-1,4-diamine (NNBD) has been intercalated into -tin(IV) hydrogen phosphate. The guest molecule, NNBD, forms a monolayer (d
001 = 1.35 nm) in which the amine groups are paired to protons on opposite faces of the phosphate layers. The resultant compound has the formula Sn(C8H18N2)0.73(HPO4)2·H2O indicating that NNBD does not cover a large proportion of the available protons. 4-vinylpyridine slowly forms an intercalate in which the host molecule forms a bilayer (d
001 = 1.56 nn). However, with 4-vinylpyridine there is surface modification in preference to intercalation. 相似文献
992.
Ieda Rottava Priscila F. Cortina Camila E. Grando André R. S. Colla Eduarda Martello Rogério L. Cansian Geciane Toniazzo Helen Treichel Octávio A. C. Antunes Enrique G. Oestreicher Débora de Oliveira 《Applied biochemistry and biotechnology》2010,162(3):719-732
This work is focused on the biotransformation of R-(+)-limonene and (?)-β-pinene to bioflavor production. To carry out the present study, 405 microorganisms were tested for their ability to bioconvert the substrates. From the isolated microorganisms, 193 were selected in the prescreening using mineral medium for limonene degradation. At the screening step, eight strains were able to convert R-(+)-limonene and 15 to transform (?)-β-pinene, both in α-terpineol. The highest concentration in α-terpineol from R-(+)-limonene was about 3,450 mg/L for Penicillium sp. isolated from eucalyptus steam. From (?)-β-pinene, the highest product concentration of 675.5 mg/L was achieved using an Aspergillus sp. strain isolated from orange tree stem. 相似文献
993.
Manuel Algarra Iulius Bobos José Jiménez-Jiménez Ramón Moreno-Tost Enrique Rodríguez-Castellón Joaquim C. G. Esteves da Silva 《Journal of inclusion phenomena and macrocyclic chemistry》2010,67(1-2):225-232
The synthesis and characterization of cadmium sulphide (CdS) quantum dots, conjugated in a porous phosphate heterostructure functionalized with aminopropyl groups is described. The resulting material has fluorescence properties with maximum emission intensity at 575 nm. The fluorescent materials are not soluble in water and exhibit high stability in aqueous solution in the pH ranges from 2 to 9. Energy dispersive X-ray spectroscopy confirmed the qualitative elemental composition of the synthesized materials and X-ray photoelectron spectra showed a surface S/Cd atomic ratio of 1.09. SEM images show that the materials are amorphous, possessing porous with sizes of several tens nanometres, homogeneous and exhibit a layered morphology. The adsorption–desorption analysis by N2 at 77 K showed the accessibility of the CdS quantum dots onto the pores of the structure. The CdS quantum dots were stabilized by mercaptopropionic acid and bounded to the host materials by amine groups. 相似文献
994.
Liam P. Spencer Ping Yang Brian L. Scott Enrique R. Batista James M. Boncella 《Comptes Rendus Chimie》2010,13(6-7):758-766
Novel cis- and trans-bis(imido) uranium disulfonamide derivatives have been prepared from iodide metathesis reactions between two equivalents of K[N(Me)(SO2Ar’)] (Ar’ = 4-Me-C6H4) and U(NtBu)2(I)2(L)x (L = OPPh3, x = 2; Me2bpy, x = 1; Me2bpy = 4,4’-dimethyl-2,2’-bipyridyl). These bis(amide) derivatives serve as useful precursors for the synthesis of the trans-diphenolate complex U(NtBu)2(O-2-tBuC6H4)2(OPPh3)2 (5), cis- and trans-dithiolate complexes U(NtBu)2(SPh)2(L)x (L = OPPh3 (6); Me2bpy (7)), and cis- and trans-dihalide complexes with the general formulas U(NtBu)2(X)2(L)x (X = Cl, L = OPPh3 (8), L = Me2bpy (10); X = Br, L = OPPh3 (9), L = Me2bpy (11)). DFT calculations performed on the trans-dihalide series U(NtBu)2(X)2(L)2 and the UO22+ analogues UO2X2(OPPh3)2 suggest that the uranium centers in the [U(NtBu)2]2+ ions possess more covalent character than analogous UO22+ derivatives but that the U-X bonds in the U(NtBu)2X2L2 complexes possess a more ionic nature. 相似文献
995.
Dr. Sergei V. Chapyshev Dr. Enrique Mendez-Vega Prof. Dr. Wolfram Sander 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(4):1258-1269
Among all C-, N-, and O-centered polyradicals, high-spin nitrenes possess the largest magnetic anisotropy and are of considerable interest as multi-level molecular spin systems for exploration of organic molecular magnetism and quantum information processing. Although the first representatives of quintet and septet nitrenes were obtained almost 50 years ago, the experimental and theoretical studies of these highly reactive species became possible only recently, owing to new achievements in molecular spectroscopy and computational chemistry. Meanwhile, dozens of various quintet dinitrenes and septet trinitrenes were successfully characterized by IR, UV/Vis, and EPR spectroscopy, thus providing important information about the electronic structure, magnetic properties and reactivity of these compounds. 相似文献
996.
Alejandra Catalina Moller Carol Parra Bastian Said Enrique Werner Susana Flores Joan Villena Alessandra Russo Nelson Caro Ivn Montenegro Alejandro Madrid 《Molecules (Basel, Switzerland)》2021,26(1)
The aim of this study was to determine, first, the chemical composition of Aloysia polystachya (Griseb) Moldenke essential oil, from leaves harvested in central Chile; and second, its antioxidant and cytotoxic activity. Eight compounds were identified via gas chromatography–mass spectrometry (GC–MS) analyses, with the most representative being R-carvone (91.03%), R-limonene (4.10%), and dihydrocarvone (1.07%). For Aloysia polystachya essential oil, antioxidant assays (2,2-diphenyl-1-picrylhydrazyl (DPPH), H2O2, ferric reducing antioxidant power (FRAP), and total reactive antioxidant potential (TRAP)) showed good antioxidant activity compared to commercial antioxidant controls; and anti-proliferative assays against three human cancer cell lines (colon, HT-29; prostate, PC-3; and breast, MCF-7) determined an IC50 of 5.85, 6.74, and 9.53 µg/mL, and selectivity indices of 4.75, 4.12, and 2.92 for HT-29, PC-3, and MCF-7, respectively. We also report on assays with CCD 841 CoN (colon epithelial). Overall, results from this study may represent, in the near future, developments for natural-based cancer treatments. 相似文献
997.
Mario Palacios-Corella Javier Ramos-Soriano Manuel Souto Duarte Ananias Joaquín Calbo Enrique Ortí Beatriz M. Illescas Miguel Clemente-Len Nazario Martín Eugenio Coronado 《Chemical science》2021,12(2):757
A family of hexakis-substituted [60]fullerene adducts endowed with the well-known tridentate 2,6-bis(pyrazol-1-yl)pyridine (bpp) ligand for spin-crossover (SCO) systems has been designed and synthesized. It has been experimentally and theoretically demonstrated that these molecular scaffolds are able to form polynuclear SCO complexes in solution. UV-vis and fluorescence spectroscopy studies have allowed monitoring of the formation of up to six Fe(ii)–bpp SCO complexes. In addition, DFT calculations have been performed to model the different complexation environments and simulate their electronic properties. The complexes retain SCO properties in the solid state exhibiting both thermal- and photoinduced spin transitions, as confirmed by temperature-dependent magnetic susceptibility and Raman spectroscopy measurements. The synthesis of these complexes demonstrates that [60]fullerene hexakis-adducts are excellent and versatile platforms to develop polynuclear SCO systems in which a fullerene core is surrounded by a SCO molecular shell.Polynuclear spin-crossover molecules showing both thermal and photoinduced spin transitions have been prepared using a [60]fullerene hexakis-adduct endowed with Fe(ii) complexes of tridentate 2,6-bis(pyrazol-1-yl)pyridine (bpp) ligand. 相似文献
998.
Jorge F. Espeso Enrique Ferrero Jos G. De La Campa Angel E. Lozano Javier De Abajo 《Journal of polymer science. Part A, Polymer chemistry》2001,39(4):475-485
Aromatic polyamides based on a novel bis(ether‐carboxylic acid) were synthesized by the direct phosphorylation condensation method. 1,4‐Bis(4‐carboxyphenoxy)‐2,5‐di‐tert‐butylbenzene was combined with various diamines containing flexible linkages and side substituents to render a set of eight novel aromatic polyamides. The polymers were produced with high yields and moderate to high inherent viscosities (0.49–1.32 dL/g) that corresponded to weight‐average and number‐average molecular weights (by gel permeation chromatography) of 31,000–80,000 and 19,000–50,000, respectively. Except for a single example, the polyamides were essentially amorphous and soluble in a variety of common solvents such as cyclohexanone, dioxane, and tetrahydrofuran. They showed glass‐transition temperatures of 250–295 °C (by differential scanning calorimetry) and 10% weight loss temperatures above 460 °C, as revealed by thermogravimetric analysis in nitrogen. Polymer films, obtained by casting from N,N‐dimethylacetamide solutions, exhibited good mechanical properties, with tensile strengths of 83–111 MPa and tensile moduli of 2.0–2.2 GPa. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 475–485, 2001 相似文献
999.
Enrique Castillo Roberto Mínguez Carmen Castillo Antonio S. Cofiño 《European Journal of Operational Research》2008
It is well known that the least absolute value (?∞) and the least sum of absolute deviations (?1) algorithms produce estimators that are not necessarily unique. In this paper it is shown how the set of all solutions of the ?1 and ?∞ regression problems for moderately large sample sizes can be obtained. In addition, if the multiplicity of solutions wants to be avoided, two new methods giving the same optimal ?1 and ?∞ values, but supplying unique solutions, are proposed. The idea consists of using two steps: in the first step the optimal values of the ?1 and ?∞ errors are calculated, and in the second step, in case of non-uniqueness of solutions, one of the multiple solutions is selected according to a different criterion. For the ?∞ the procedure is used sequentially but removing, in each iteration, the data points with maximum absolute residual and adding the corresponding constraints for keeping these residuals, and this process is repeated until no change in the solution is obtained. In this way not only the maximum absolute residual values are minimized in the modified method, but also the maximum absolute residual values of the remaining points sequentially, until no further improvement is possible. In the ?1 case a least squares criterion is used but restricted to the ?1 residual condition. Thus, in the modified ?1 method not only the ?1 residual is minimized, but also the sum of squared residuals subject to the ?1 residual. The methods are illustrated by their application to some well known examples and their performances are tested by some simulations, which show that the lack of uniqueness problem cannot be corrected for some experimental designs by increasing the sample size. 相似文献
1000.
Jaime Gonzlez‐Villa Enrique Saldívar‐Guerra Ramn Enrique Díaz de Len‐Gmez Hctor Ricardo Lpez Gonzlez Jos Ramiro Infante‐Martínez 《Journal of polymer science. Part A, Polymer chemistry》2019,57(21):2157-2165
The kinetics of isothermal anionic homopolymerization of ß–myrcene (MYR) and 4–methylstyrene (4MS) in cyclohexane, initiated by n–butyllithium was studied at different temperatures (55, 63, and 71 ° C). The kinetic information obtained from the homopolymerizations was used to estimate the parameters of the Eyring equation, ΔH?= 84080 J/mol and ΔS?= ?21.9 J/mol·K for the MYR, and ΔH?= 51250 J/mol and ΔS?= ?116.8 J/mol·K for the 4MS, to calculate the apparent propagation coefficients as a function of temperature. Finally, the parameters obtained for the Eyring equation were validated by applying them in a mathematical model representing the kinetics of nonisothermal (quasi‐adiabatic) polymerization experiments of MYR and 4MS. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2157–2165 相似文献