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351.
Shubhendu S. Karandikar Avik Bhattacharjee Bryan E. Metze Nicole Javaly Edward J. Valente Theresa M. McCormick David R. Stuart 《Chemical science》2022,13(22):6532
Diarylhalonium compounds provide new opportunities as reagents and catalysts in the field of organic synthesis. The three center, four electron (3c–4e) bond is a center piece of their reactivity, but structural variation among the diarylhaloniums, and in comparison with other λ3-iodanes, indicates that the model needs refinement for broader applicability. We use a combination of Density Functional Theory (DFT), Natural Bond Orbital (NBO) Theory, and X-ray structure data to correlate bonding and structure for a λ3-iodane and a series of diarylchloronium, bromonium, and iodonium salts, and their isoelectronic diarylchalcogen counterparts. This analysis reveals that the s-orbital on the central halogen atom plays a greater role in the 3c–4e bond than previously considered. Finally, we show that our revised bonding model and associated structures account for both kinetic and thermodynamic reactivity for both acyclic phenyl(mesityl)halonium and cyclic dibenzohalolium salts.A revised bonding model for diarylhalonium salts, that involves partial s-orbital contribution, provides new insight into periodic trends in structure and reactivity. 相似文献
352.
I. K. Daftari D. K. Bhattacharjee S. C. Naha D. C. Ghosh T. Roy 《Fortschritte der Physik》1978,26(9):501-508
The systematics of the number of heavy prongs in proton-nucleus interactions in emulsion in the energy range from a few GeV to few hundred GeV have been studied. The results disfavour the secondary processes in the target nucleus in general and intranuclear cascading of hadrons in particular. 相似文献
353.
Tirtha Bhattacharjee Prasanta Gogoi Vedavati G. Puranik Rupesh L. Gawade Pranjit Barman 《Acta Crystallographica. Section C, Structural Chemistry》2012,68(12):o485-o487
In the title compound, C21H18N2OS2, a strong intramolecular N—H...O hydrogen bond [N...O = 2.642 (3) Å] between the amide N atom and the benzoyl O atom forms an almost planar six‐membered ring in the central part of the molecule. In the crystal, molecules are packed through weak N—H...S interactions. Intra‐ and intermolecular hydrogen bonds and van der Waals interactions are the stabilizing forces for the crystal structure. 相似文献
354.
Vasanthi Palanisamy Palash Sanphui Muthuramalingam Prakash Vladimir Chernyshev 《Acta Crystallographica. Section C, Structural Chemistry》2019,75(8):1102-1117
Lesinurad (systematic name: 2‐{[5‐bromo‐4‐(4‐cyclopropylnaphthalen‐1‐yl)‐4H‐1,2,4‐triazol‐3‐yl]sulfanyl}acetic acid, C17H14BrN3O2S) is a selective uric acid reabsorption inhibitor related to gout, which exhibits poor aqueous solubility. High‐throughput solid‐form screening was performed to screen for new solid forms with improved pharmaceutically relevant properties. During polymorph screening, we obtained two solvates with methanol (CH3OH) and ethanol (C2H5OH). Binary systems with caffeine (systematic name: 3,7‐dihydro‐1,3,7‐trimethyl‐1H‐purine‐2,6‐dione, C8H10N4O2) and nicotinamide (C6H6N2O), polymorphs with urea (CH4N2O) and eutectics with similar drugs, like allopurinol and febuxostat, were prepared using the crystal engineering approach. All these novel solid forms were confirmed by XRD, DSC and FT–IR. The crystal structures were solved by single‐crystal and powder X‐ray diffraction. The crystal structures indicate that the lesinurad molecule is highly flexible and the triazole moiety, along with the rotatable thioacetic acid (side chain) and cyclopropane ring, is almost perpendicular to the planar naphthalene moiety. The carboxylic acid–triazole heterosynthon in the drug is interrupted by the presence of methanol and ethanol molecules in their crystal structures and forms intermolecular macrocyclic rings. The caffeine cocrystal maintains the consistency of the acid–triazole heterosynthons as in the drug and, in addition, they are bound by several auxiliary interactions. In the binary system of nicotinamide and urea, the acid–triazole heterosynthon is replaced by an acid–amide synthon. Among the urea cocrystal polymorphs, Form I (P, 1:1) consists of an acid–amide (urea) heterodimer, whereas in Form II (P21/c, 2:2), both acid–amide heterosynthons and urea–urea dimers co‐exist. Density functional theory (DFT) calculations further support the experimentally observed synthon hierarchies in the cocrystals. Aqueous solubility experiments of lesinurad and its binary solids in pH 5 acetate buffer medium indicate the apparent solubility order lesinurad–urea Form I (43‐fold) > lesinurad–caffeine (20‐fold) > lesinurad–allopurinol (12‐fold) ? lesinurad–nicotinamide (11‐fold) > lesinurad, and this order is correlated with the crystal structures. 相似文献
355.
Palash M. Saikia 《Journal of Dispersion Science and Technology》2013,34(1):33-37
The acid base equilibria of the sulfonephthalein dye bromophenol blue (BPB) in aqueous nonionic micellar solutions of Tween 20, Tween 40, Tween 60, and Tween 80 have been investigated spectroscopically using a partition equilibrium method. A visible red shift in the absorbance of the basic form of the dye with increase in surfactant concentration was observed at and above pH 6.98. This has been attributed to the stabilization of the acid form of the dye by the POE groups on the head of the surfactant monomers. Such stabilization effect was found to decreases with decrease in the number of carbon atom in the hydrophobic tail and with the increase in the hydrophile-lipophile balance (HLB) of the surfactant molecule. The equilibrium constant of the partition of the dyes between micellar and aqueous pseudophases (Kass) was found to increase with the surfactants in the order Tween 80 < Tween 60 < Tween 40 < Tween 20. The pKa2 of the dyes were predicted and found to be in good agreement with the experimental values. 相似文献
356.
Imidazole type ionic liquid, 1‐hexadecyl‐3‐methylimidazolium chloride, was used to template the synthesis of high‐surface‐area mesoporous silica under acidic conditions and crystalline titanium dioxide (TiO2) nanoparticles of anatase phase were inserted utilizing a solvent evaporation‐induced method. The surface area of more than 700 m2 g?1 was obtained after TiO2 impregnation. Further, the polyoxometalate, 12‐tungstophosphoric acid (PW12) was dispersed on the surface of TiO2 to form PW12–TiO2–silica hybrid catalytic materials. The catalytic activity of this hybrid material was tested for solvent‐free, aerobic oxidation of n‐hexadecane. The experimental investigation shows that PW12–TiO2 nanocrystals did not block the pore channels and gave good conversion. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
357.
Precise measurements on electrical conductances of tetraalkylammonium iodides, R(4)NI (R = n-butyl to n-heptyl), in different mass% (0-100) of dichloromethane (DCM) + N,N-dimethylformamide (DMF) at 298.15 K have been performed. Limiting molar conductances (Λ(0)), association constants (K(A)) and co-sphere diameter (R) for ion-pair formation in the mixed solvent mixtures have been evaluated using the Fuoss conductance-concentration equation. However, the deviation of the conductometric curves (Λ versus √c) from linearity for the electrolytes in 100 mass% of DCM indicated triple ion formation, and therefore corresponding conductance data have been analyzed by the Fuoss-Kraus theory of triple ions. Limiting ionic molar conductances λ have been calculated by the reference electrolyte method along with a numerical evaluation of ion pair and triple ion formation constants (K(P)≈K(A) and K(T)). The results have been interpreted in terms of ion-solvent interactions and structural changes in the mixed solvents. 相似文献
358.
Let {Z u = ((εu, i, j))p×n} be random matrices where {εu, i, j} are independently distributed. Suppose {A i }, {B i } are non-random matrices of order p × p and n × n respectively. Consider all p × p random matrix polynomials \(P = \prod\nolimits_{i = 1}^{k_l } {\left( {n^{ - 1} A_{t_i } Z_{j_i } B_{s_i } Z_{j_i }^* } \right)A_{t_{k_l + 1} } }\). We show that under appropriate conditions on the above matrices, the elements of the non-commutative *-probability space Span {P} with state p?1ETr converge. As a by-product, we also show that the limiting spectral distribution of any self-adjoint polynomial in Span{P} exists almost surely. 相似文献
359.
A soft set theory is a new general mathematical tool to dealing with imprecision. The theory differs from traditional mathematical tools to dealing with uncertainties in which many mathematical theories failed. In this paper, we proposed the concept of Bell shaped fuzzy soft set and its application in medical diagnosis using arithmetic operations of discrete- Gaussian fuzzy number, triangular-Cauchy fuzzy number and Gaussian-Cauchy fuzzy number. As an integral part of this paper, we discuss the parametric form of Gaussian membership function is discussed with some important properties. 相似文献
360.
Focused ion beams (FIB) are widely used for research and applications in nanoscience and technology. We have developed a compact microwave plasma based multi element FIB (MEFIB) system in order to widen the applications and overcome the limitations faced by conventional Liquid Metal Ion Source (LMIS) based FIB systems, that provide primarily Ga ions. The MEFIB source provides high density plasmas (∼1.5 × 1011 cm−3) in a compact cross section. Recently the ion energy spread in the plasma meniscus from where the beams are extracted is found to be small (∼5 eV) [1–3]. The beam extraction and focusing are carried out using electrostatic multi electrode assembly. AXCEL INP and SIMION simulation codes are employed for the design of electrostatic Einzel lenses for beam focusing. The beam focal point is measured using a specially designed three slit Faraday cup and the spot size is measured by the micrography of craters formed by the focused ion beams impinging on copper and aluminium substrates. The initial experimental results show a focused beam spot size of ∼ 25 micron which is in good agreement with the simulations. By further reduction of electrode apertures and operating the second Einzel lens at higher potentials, submicron focused ion beams can be expected. 相似文献