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111.
112.
We discuss a new applied probability model: there is a system whose evolution is described by a Markov chain (MC) with known transition matrix on a discrete state space and at each moment of a discrete time a decision maker can apply one of three possible actions: continue, quit, and restart MC in one of a finite number of fixed “restarting” points. Such a model is a generalization of a model due to Katehakis and Veinott (Math. Oper. Res. 12:262, 1987), where a restart to a unique point was allowed without any fee and quit action was absent. Both models are related to Gittins index and to another index defined in a Whittle family of stopping retirement problems. We propose a transparent recursive finite algorithm to solve our model by performing O(n3) operations. 相似文献
113.
Gómez L Garcia-Bosch I Company A Sala X Fontrodona X Ribas X Costas M 《Dalton transactions (Cambridge, England : 2003)》2007,(47):5539-5545
A novel family of chiral manganese complexes Lambda-1(CF(3)SO(3)) and Delta-2(CF(3)SO(3)), have been stereoselectively prepared, characterized and studied as epoxidation catalysts. The complexes are structurally related to [Mn(II)(CF(3)SO(3))(2)(alpha-MCP)] (MCP=N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)cyclohexane-trans-1,2-diamine), recently reported as a very efficient epoxidation catalyst in combination with peracetic acid. Pinene rings have been fused to the 4 and 5 positions of the two pyridine groups of the ligand, giving rise to complexes where the two labile binding sites of the manganese ion are confined in a better-defined chiral pocket than in the parent [Mn(II)(CF(3)SO(3))(2)(alpha-MCP)]. Chirality in these complexes arises from the stereochemistry of the trans-diaminocyclohexane ring, from the pinene ring and also from the topological chirality adopted by the ligand upon binding to the manganese ion. While previous studies have demonstrated that small modifications in the structure of the MCP ligand result in a dramatic loss of efficiency, Lambda-1(CF(3)SO(3)) and Delta-2(CF(3)SO(3)) exhibit comparable catalytic activity to [Mn(II)(CF(3)SO(3))(2)(alpha-MCP)]. In addition, the complexes exhibit a remarkable stereoselectivity (up to 46% ee) in the epoxidation of selected substrates. The results reported in this work point towards modification of the 4 and 5 positions of the pyridine groups as a new strategy towards the design of stereoselective versions of this family of highly active and environmentally benign epoxidation catalysts. 相似文献
114.
We examine the morphological structures of asymmetric poly(ethylene oxide)-b-poly(1,1'-dihydroperflurooctyl methacrylate) (PEO-b-PFOMA) thin films upon annealing in a compressible fluid, supercritical CO2 (Sc-CO2). The strong affinity between PFOMA and CO2 is found to induce phase segregation when annealing PEO-b-PFOMA films at the same temperature as compared with vacuum. In vacuum, PEO-b-PFOMA films remain disordered from 80 to 180 degrees C, whereas, in Sc-CO2 at 13.9 MPa, an upper order-disorder transition (UODT) between 116 and 145 degrees C is found. In Sc-CO2, the observed ordered structure is layers of PEO spheres embedded in the matrix of PFOMA, followed by a brush layer, in which PEO wets the substrate. The swelling isotherms of PFOMA and PEO in CO2 are correlated with the Sanchez-Lacombe equation of state (SLEOS) to estimate the interaction parameters, XPFOMA-CO2 and XPEO-CO2. The phase segregation (order) induced by CO2 relative to vacuum at a given temperature is explained in terms of two factors: (1) copolymer volume fraction upon dilution with CO2, phi, and (2) the relative interaction parameter, DeltaX= XPEO-CO2 - XPFOMA-CO2. The latter factor favors order and is dominant at low temperatures over the phi factor, which always favors disorder. At high temperatures (above the T(ODT)), the preferential swelling of PFOMA by CO2 is less pronounced ( DeltaX decreases), and the copolymer is disordered. 相似文献
115.
Isaac Abrahams Michael Lazell Majid Motevalli Charlotte K. Simon Alice C. Sullivan 《Chemistry of Heterocyclic Compounds》1999,35(8):954-964
Three structurally different metallasiloxanes were formed from reactions between in situ generated suspensions of Ph2Si(OH)2/BuLi (1∶2) in tetrahydrofuran (THF) with, metal dichlorides MgCl2·2THF, CrCl2, or CoCl2 followed by toluene/Py (Py=pyridine) work-up. The X-ray structures are reported for: [Mg{O(Ph2SiO)2}2]-μ-(LiPy)-μ-{(LiPy)3(OH)(Cl)] (1) incorporating two six-membered magnesiasiloxane rings and an MgLi3O3Cl cubane fragment, [{O(Ph2SiO)2}Co{O(Ph2SiO)3}-μ-(LiPy2)2] (2) with both six-and eight-membered cobaltasiloxane rings and [Cr{O(Ph2SiO)2}2-μ-(LiPy2)2] (3) with two six-membered chromiasiloxane rings. Structure assembly in these cases is apparently dictated by the metal dichloride. The compound [{O(Ph2SiO)2}Mg{O(Ph2SiO)3}-μ-(CoClPy)2]·Py (4) is formed from [{O(Ph2SiO)2}Mg{O(Ph2SiO)3}-μ-(LiPy2)2] and CoCl2 (1∶2). 相似文献
116.
Isaac Sonin 《Mathematical Methods of Operations Research》1999,49(1):111-123
We present a new algorithm for solving the optimal stopping problem. The algorithm is based on the idea of elimination of states where stopping is nonoptimal and the corresponding correction of transition probabilities. The formal justification of this method is given by one of two presented theorems. The other theorem describes the situation when an aggregation of states is possible in the optimal stopping problem. 相似文献
117.
Francisco W. M. Ribeiro Isaac Omari Gilian T. Thomas Mathias Paul Peter J. H. Williams J. Scott McIndoe Thiago C. Correra 《Macromolecular rapid communications》2024,45(2):2300470
Herein, an evaluation of the initial step of benzoxazine polymerization is presented by mass spectrometry, with a focus on differentiating the phenoxy and phenolic products formed by distinct pathways of the cationic ring opening polymerization (ROP) mechanism of polybenzoxazine formation. The use of infrared multiple photon dissociation (IRMPD) and ion mobility spectrometry (IMS) techniques allows for differentiation of the two pathways and provides valuable insights into the ROP mechanism. The results suggest that type I pathway is favored in the initial stages of the reaction yielding the phenoxy product, while type II product should be observed at later stages when the phenoxy product would interconvert to the most stable type II phenolic product. Overall, the findings presented here provide important information on the initial step of the benzoxazine polymerization, allowing the development of optimal polymerization conditions and represents a way to evaluate other multifunctional polymerization processes. 相似文献
118.
This review describes recent developments and applications of near-infrared (NIR) spectroscopy for characterization of articular cartilage integrity. It summarizes the research findings in this area and presents some spectral ranges and peaks associated with the different properties and components of articular cartilage. We further describe recent adaptations of NIR spectroscopy for clinical evaluation of articular cartilage injury and degeneration. Critical to accurate decision-making during repair surgery is having clear knowledge of lesion severity and spread, and how to grade the quality of surrounding cartilage. Thus, in this review, we detail efforts aimed at quantification and classification of cartilage pathology using NIR spectroscopy. Finally, we present open questions and challenges with a view to guiding future directions in NIR spectroscopy research on articular cartilage. 相似文献
119.
The syntheses, spectroscopic and electrochemical properties of manganese (3), nickel (4) and iron (5) phthalocyanine complexes, octa-substituted at the peripheral positions with diethlyaminoethanethiol substituent, are reported. The electrochemistry of these complexes and the corresponding cobalt complex (6) are reported. Complex 3 showed two reversible reduction couples attributed to the MnIIIPc−2/MnIIPc−2 (E½ = −0.12 V versus Ag|AgCl) and MnIIPc−2/MnIIPc−3 (E½ = −0.82 V versus Ag|AgCl) species. Two ring-based reduction couples were also observed for complex 4. Two reduction couples, assigned to the FeIIPc−2/FeIPc−2 (E½ = −0.35 V versus Ag|AgCl) and FeIPc−2/FeIPc−3 (E½ = −0.96 V versus Ag|AgCl) species, and an oxidation couple, attributed to FeIIIPc−2/FeIIPc−2 (E½ = 0.26 V versus Ag|AgCl) species, were observed. For complex 6, two reductions and one oxidation were also observed with the potential range of 1.2 to −1.8 V versus Ag|AgCl Spectroelectrochemical studies were used to confirm some of the assigned processes. 相似文献
120.
Pavlína Pelcová Vlastimil Kubáň Isaac K. Kiplagat Petr Kubáň 《Journal of chromatography. A》2009,1216(51):9022-9026
Polyelectrolyte multilayers deposited on the wall of fused silica capillaries were used as stationary phases in open tubular ion chromatography. The multilayers were formed by flushing the capillaries with solutions of polyanions and polycations such as polydiallyldimethylammonium chloride and dextran sulphate. Columns with several bi-layers were constructed and used in low pressure non-suppressed open tubular ion chromatography of common inorganic anions (F−, Cl−, NO3−) and cations (Li+, Na+, NH4+, K+, Cs+) with contactless conductometric detection. Using sodium benzoate and tartaric acid eluents the separations were typically achieved in less than 35 min with separation efficiencies between 2000 and 9000 theoretical plates. A bi-functional column was prepared that contains both anionic and cationic functional groups and was used for simultaneous separation of anions and cations. 相似文献