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941.
Crystallinity and crystalline phase orientation of poly(1,4‐cis‐isoprene) from Hevea brasiliensis and Taraxacum kok‐saghyz 下载免费PDF全文
Sara Musto Vincenzina Barbera Mario Maggio Marco Mauro Gaetano Guerra Maurizio Galimberti 《先进技术聚合物》2016,27(8):1082-1090
Crystallization is studied for poly(isoprene‐1,4‐cis) from Hevea brasiliensis (natural rubber [NR]) and from taraxacum kok‐saghyz, mainly by collecting wide‐angle X‐ray diffraction patterns after processing and stretching. Although rubber samples before stretching are generally fully amorphous, crystallization can be induced in NR samples by processing at room temperature under moderate pressure. This phenomenon is possibly associated with nucleation by saturated fatty acid components. For rubber samples being fully amorphous in the undeformed state, strain‐induced crystallization occurs only at high strain ratios (α > 4), leading to high degrees of crystalline phase orientation (fc > 0.9 for α = 5). Rubber samples presenting some crystallinity already in the unstretched state, on the contrary, reach much lower degrees of axial orientation, even for high strain ratios (fc < 0.7 for α = 5). These differences in crystallinity and in crystalline phase orientations produce large differences in stress–strain behavior of the rubber. By room temperature processing, the considered NR samples can also develop an unreported disordered crystalline modification, with low intensity of 120 and 121 reflections. This disordered crystalline modification, which is also maintained after axial stretching procedures, can rationalized by a structural disorder along the b axis, possibly associated with statistical sequences of A+TA? or A?T A+ conformations for poly(isoprene‐1,4‐cis) chains. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
942.
Pedro Linares Sara Lumbreras Alberto Santamaría Andrea Veiga 《Annals of Operations Research》2016,246(1-2):227-251
We consider the 1-median problem with euclidean distances with uncertainty in the weights, expressed as possible changes within given bounds and a single budget constraint on the total cost of change. The upgrading (resp. downgrading) problem consists of minimizing (resp. maximizing) the optimal 1-median objective value over these weight changes. The upgrading problem is shown to belong to the family of continuous single facility location-allocation problems, whereas the downgrading problem reduces to a convex but highly non-differentiable optimization problem. Several structural properties of the optimal solution are proven for both problems, using novel planar partitions, the knapsack Voronoi diagrams, and lead to polynomial time solution algorithms. 相似文献
943.
Evans WJ Schmiege BM Lorenz SE Miller KA Champagne TM Ziller JW DiPasquale AG Rheingold AL 《Journal of the American Chemical Society》2008,130(26):8555-8563
The reductive reactivity of lanthanide hydride ligands in the [(C5Me5)2LnH]x complexes (Ln = Sm, La, Y) was examined to see if these hydride ligands would react like the actinide hydrides in [(C5Me5)2AnH2]2 (An = U, Th) and [(C5Me5)2UH]2. Each lanthanide hydride complex reduces PhSSPh to make [(C5Me5)2Ln(mu-SPh)]2 in approximately 90% yield. [(C5Me5)2SmH]2 reduces phenazine and anthracene to make [(C5Me5)2Sm]2(mu-eta(3):eta(3)-C12H8N2) and [(C5Me5)2Sm]2(mu-eta(3):eta(3)-C10H14), respectively, but the analogous [(C5Me5)2LaH]x and [(C5Me5)2YH]2 reactions are more complicated. All three lanthanide hydrides reduce C8H8 to make (C5Me5)Ln(C8H8) and (C5Me5)3Ln, a reaction that constitutes another synthetic route to (C5Me5)3Ln complexes. In the reaction of [(C5Me5)2YH]2 with C8H8, two unusual byproducts are obtained. In benzene, a (C5Me5)Y[(eta(5)-C5Me4CH2-C5Me4CH2-eta(3))] complex forms in which two (C5Me5)(1-) rings are linked to make a new type of ansa-allyl-cyclopentadienyl dianion that binds as a pentahapto-trihapto chelate. In cyclohexane, a (C5Me5)2Y(mu-eta(8):eta(1)-C8H7)Y(C5Me5) complex forms in which a (C8H8)(2-) ring is metalated to form a bridging (C8H7)(3-) trianion. 相似文献
944.
Sara Atailia Dr. Abdoullatif Baraket Selma Rabai Messaoud Benounis Nicole Jaffrezic Hala Araar Abdelyamine Naït-Bouda Abdecharif Boumaza Abdelhamid Errachid Moussa Houhamdi 《Electroanalysis》2023,35(9):e202200502
In this study, a novel, sensitive electrochemical enzyme-based biosensor for urea detection was presented. This biosensor combines a three-electrode system consisting of a classic Glassy Carbon Electrode (GCE) as the working electrode, a platinum counter electrode, and Ag/AgCl as the reference electrode. To construct this urea platform, a GCE was modified with a polyaniline (PANi) film. Then, bacterial urease from Proteus mirabilis was immobilized on the modified GCE (Pm-Urease-PANi-GCE). For the characterization of surface modification, Cyclic Voltammetry (CV) and Scanning Electron Microscope (SEM) were applied, while the Square Wave Voltammetry (SWV) technique was performed for urea detection. The main analytical characteristics of the Pm-Urease-PANi-GCE biosensor showed a good linear range from 0.1 to 10 mM of urea, a limit of detection (LOD) of 0.1 mM, a Michaelis-Menten Km of 0.23 mM, and a sensitivity value 46 μA/mM/cm2. This biosensor allows the detection of urea in solutions, and it could be improved for further medical, environmental, or engineering applications. 相似文献
945.
Jiamin Sun Dr. Himanshu Sekhar Jena Dr. Chidharth Krishnaraj Dr. Kuber Singh Rawat Dr. Sara Abednatanzi Dr. Jeet Chakraborty Andreas Laemont Wanlu Liu Hui Chen Prof. Ying-Ya Liu Dr. Karen Leus Prof. Henk Vrielinck Prof. Veronique Van Speybroeck Prof. Pascal Van Der Voort 《Angewandte Chemie (International ed. in English)》2023,62(19):e202216719
Four highly porous covalent organic frameworks (COFs) containing pyrene units were prepared and explored for photocatalytic H2O2 production. The experimental studies are complemented by density functional theory calculations, proving that the pyrene unit is more active for H2O2 production than the bipyridine and (diarylamino)benzene units reported previously. H2O2 decomposition experiments verified that the distribution of pyrene units over a large surface area of COFs plays an important role in catalytic performance. The Py-Py-COF though contains more pyrene units than other COFs which induces a high H2O2 decomposition due to a dense concentration of pyrene in close proximity over a limited surface area. Therefore, a two-phase reaction system (water-benzyl alcohol) was employed to inhibit H2O2 decomposition. This is the first report on applying pyrene-based COFs in a two-phase system for photocatalytic H2O2 generation. 相似文献
946.
Myriam Mikhael Sara N. Alektiar Charles S. Yeung Zachary K. Wickens 《Angewandte Chemie (International ed. in English)》2023,62(30):e202303264
The rapid preparation of complex three-dimensional (3D) heterocyclic scaffolds is a key challenge in modern medicinal chemistry. Despite the increased probability of clinical success for small molecule therapeutic candidates with increased 3D complexity, new drug targets remain dominated by flat molecules due to the abundance of coupling reactions available for their construction. In principle, heteroarene hydrofunctionalization reactions offer an opportunity to transform readily accessible planar molecules into more three-dimensionally complex analogs through the introduction of a single molecular vector. Unfortunately, dearomative hydrofunctionalization reactions remain limited. Herein, we report a new strategy to enable the dearomative hydrocarboxylation of indoles and related heterocycles. This reaction represents a rare example of a heteroarene hydrofunctionalization that meets the numerous requirements for broad implementation in drug discovery. The transformation is highly chemoselective, broad in scope, operationally simple, and readily amenable to high-throughput experimentation (HTE). Accordingly, this process will allow existing libraries of heteroaromatic compounds to be translated into diverse 3D analogs and enable exploration of new classes of medicinally relevant molecules. 相似文献
947.
Dr. Giorgio Facchetti Dr. Jaime Gracia Vitoria Martina Moraschi Dr. Raffaella Bucci Dr. Anne Catherine Abel Prof. Stefano Pieraccini Prof. Sara Pellegrino Prof. Isabella Rimoldi 《European journal of organic chemistry》2023,26(19):e202300240
A dimeric cyclic cysteine analogue, i.e. (1R,1′R,2R,2′R)-2,2′-disulfanediylbis (aminocyclohexane-1-carboxylic acid), was used as a constrained unnatural amino acid and as a folding inducer in ultra-short Leu-Val-containing peptide. Our results showed that both free dimer amino acid L1 and its peptide derivative L2 are able to chelate Cu(II). The obtained complexes resulted to be catalytically active in Michael addition reaction of nitromethane on different types of chalcones. L1-Cu(II) was shown more reactive in terms of conversion, while, in neat conditions, L2-Cu(II) allows to obtain an interesting 60 % e.e. on pyridine chalcone. 相似文献
948.
Two new sensors for the detection of reactive oxygen species have been synthesized and characterized; they contain the 4-amino-7-nitrobenzofurazan (ABF) moiety covalently tethered to a phenol. Comparison of sensors ABFhd and dABFhd (the latter containing two ortho-methyl groups) shows that introduction of steric bulk leads to an improvement of fluorescent sensor performance, thus confirming our previous predictions based on computational chemistry. ABFhd and dABFhd are new tools for biological applications involving reactive oxygen species, in particular oxygen-centered radicals. 相似文献
949.
A new cyclophane featuring two opposite anthracene units linked in 9,10-positions has been synthesized thanks to the template effect of the Me4N(+) ion. It forms pseudorotaxane complexes with alkylviologen ions and undergoes a fast and reversible reaction with tetracyanoethylene. A quantitative analysis has been carried out of the formation of Diels-Alder adducts, whose distribution can be controlled by host-guest complexation. These findings open interesting perspectives in the field of Dynamic Covalent Chemistry. 相似文献
950.
Irena Lasiecka Sara Maad Amol Sasane 《NoDEA : Nonlinear Differential Equations and Applications》2008,15(6):689-715
We consider a quasilinear PDE system which models nonlinear vibrations of a thermoelastic plate defined on a bounded domain
in , n ≤ 3. Existence of finite energy solutions describing the dynamics of a nonlinear thermoelastic plate is established. In addition
asymptotic long time behavior of weak solutions is discussed. It is shown that finite energy solutions decay exponentially
to zero with the rate depending only on the (finite energy) size of initial conditions. The proofs are based on methods of
weak compactness along with nonlocal partial differential operator multipliers which supply the sought after “recovery” inequalities.
Regularity of solutions is also discussed by exploiting the underlying analyticity of the linearized semigroup along with
a related maximal parabolic regularity [1, 16, 44].
The research of I. Lasiecka has been partially supported by DMS-NSF Grant Nr 0606882.
S. Maad was supported by the Swedish Research Council and by the European Union under the Marie Curie Fellowship MEIF-CT-2005-024191. 相似文献