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991.
Andreas Sofetis Fotini Fotopoulou Catherine P. Raptopoulou Theodoros F. Zafiropoulos Spyros P. Perlepes Nikolaos Klouras 《Polyhedron》2009
The reaction of [TiIV(Cp)2Cl2] (Cp− = η5-C5H5−) and 2,6-bis(3,5-dimethylpyrazolyl-1-yl)pyridine (bdmpp) in Me2CO has afforded complex [TiIVCl2(O2)(bdmpp)] (1). The complex can also be prepared from the 1:1:1 [Ti(Cp)2Cl2]/bdmpp/H2O2 reaction mixture in various solvents. Single-crystal, X-ray crystallography has revealed that the TiIV center is in a distorted pentagonal bipyramidal environment in both of the two, crystallographically independent molecules that are present in the asymmetric unit; the equatorial positions are occupied by the two O atoms of the side-on (η2) O22− group and the three N-atoms of the tridentate chelate, while the two chloro ligands are on the axial positions. IR, Raman, electronic and 1H NMR data are discussed in terms of the known structure and the coordination modes of the peroxo and bdmpp ligands. 相似文献
992.
Konstantis F. Konidaris Michalis Kaplanis Catherine P. Raptopoulou Spyros P. Perlepes Evy Manessi-Zoupa Eugenia Katsoulakou 《Polyhedron》2009
The initial employment of pyridine-3-carbaldehyde oxime, (3-py)C(H)NOH, and pyridine-4-carbaldehyde oxime, (4-py)C(H)NOH, in zinc(II) carboxylate chemistry is reported. The syntheses, crystal structures and IR characterization are described for [Zn3(O2CPh)6{(3-py)C(H)NOH}2] (1) and [Zn2(O2CPh)4{(4-py)C(H)NOH}2] (2). The trinuclear molecule of 1 has a linear structure, with one monoatomically bridging η1:η2:μ and two syn, syn-η1:η1:μ benzoate groups spanning each pair of ZnII ions; the terminal metal ions are each capped by one (3-py)C(H)NOH ligand coordinating through its pyridyl nitrogen. Complex 2 exhibits a dinuclear paddle–wheel structure with a Zn···Zn distance of 2.990(2) Å; each ZnII ion has a square pyramidal geometry with four carboxylate oxygens in the basal plane and the pyridyl nitrogen of one monodentate (4-py)C(H)NOH ligand at the apex. Both complexes form 1D architectures by virtue of hydrogen bonding interactions involving the free oxime group as donor and the oxime nitrogen (1) or carboxylate oxygens (2) as acceptors. IR data are discussed in terms of the known structures and coordination modes of the ligands. 相似文献
993.
Constantinos G. Efthymiou Constantina Papatriantafyllopoulou Nadia I. Alexopoulou Catherine P. Raptopoulou Roman Boča Jerzy Mrozinski Evangelos G. Bakalbassis Spyros P. Perlepes 《Polyhedron》2009
The reactions of 2-(hydromethyl)pyridine, hmpH, with Ni(O2CMe)2·4H2O in H2O, in the absence of counterions, have been investigated. The synthetic study has led to the two new complexes [Ni(O2CMe)2(hmpH)2] (1) and [Ni4(O2CMe)4(hmp)4(H2O)2] (2). Complex 1 can also be transformed into 2 by reacting with an excess of NaOH in H2O. The structures of 1 and 2·2.25H2O·0.5(1,4-dioxane) have been solved by single-crystal, X-ray crystallography. The octahedral NiII center in centrosymmetric 1 is coordinated by two 1.10 (Harris notation) MeCO2− groups and two N,O-chelating (1.11) hpmH ligands. The tetranuclear cluster molecule of 2·2.25H2O·0.5(1,4-dioxane) possesses a distorted cubane {Ni4(μ3-OR′)4}4+ core [R′ = (2-pyridyl)CH2–] with the NiII ions and the oxygen atoms from the 3.31 hmp− ligands occupying alternate vertices of the cube. Two 2.11 MeCO2− groups cap two opposite faces of the cube, while two 1.10 MeCO2− ions and two aqua ligands complete the octahedral coordination sphere of the metal centers. Characteristic IR bands for the two complexes are discussed in terms of the nature of bonding and the structures of the two complexes. The variable-temperature magnetic properties of 2 have been modeled with two J values, and reveal antiferromagnetic exchange interactions between the four NiII ions to give a diamagnetic ground state. 相似文献
994.
Catherine Tessini Claudia Mardones Lorena Rivas Dietrich von Baer 《Accreditation and quality assurance》2009,14(7):381-387
High-performance liquid chromatography (HPLC) to determine shikimic acid is used as a complementary tool to differentiate
wine varieties. In order to correctly classify, measurement uncertainty of shikimic acid by HPLC in red wine was estimated
considering the following components: uncertainty associated with the preparation of shikimic acid stock solution, uncertainty
associated with quantification using a calibration curve, and uncertainty associated with precision. The most important contribution
to total uncertainty was the method precision. The expanded uncertainty (U) for different wine varieties was between 2.6 and
8.5%. The method was applied to determine the concentration of shikimic acid in different emerging wine varieties cultivated
in Chile, such as Carmenère, Shiraz, and Pinot Noir, comparing them with classical varieties, such as Cabernet Sauvignon and
Merlot. Shiraz wines presented lower shikimic acid concentrations (between 27 and 86 mg L−1 with U
(k=2) = 2.6%) than Cabernet Sauvignon wines (between 41 and 142 mg L−1 with U
(k=2) = 8.1%), but their concentrations were higher than found in Merlot (from 9 to 41 mg L−1 with U
(k=2) = 4.3%) and Carmenère wines (between 7 and 49 mg L−1 with U
(k=2) = 5.8%). Pinot Noir was the variety with the lowest concentration of this acid (7–14 mg L−1 with U
(k=2) = 8.5%).
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
995.
Hireche O Weisman C Baltean-Carlès D Le Quéré P Bauwens L 《The Journal of the Acoustical Society of America》2010,128(6):3438-3448
A model of an idealized thermoacoustic engine is formulated, coupling nonlinear flow and heat exchange in the heat exchangers and stack with a simple linear acoustic model of the resonator and load. Correct coupling results in an asymptotically consistent global model, in the small Mach number approximation. A well-resolved numerical solution is obtained for two-dimensional heat exchangers and stack. The model assumes that the heat exchangers and stack are shorter than the overall length by a factor of the order of a representative Mach number. The model is well-suited for simulation of the entire startup process, whereby as a result of some excitation, an initially specified temperature profile in the stack evolves toward a near-steady profile, eventually reaching stationary operation. A validation analysis is presented, together with results showing the early amplitude growth and approach of a stationary regime. Two types of initial excitation are used: Random noise and a small periodic wave. The set of assumptions made leads to a heat-exchanger section that acts as a source of volume but is transparent to pressure and to a local heat-exchanger model characterized by a dynamically incompressible flow to which a locally spatially uniform acoustic pressure fluctuation is superimposed. 相似文献
996.
We present an experimental and numerical study of electron emission from a sharp tungsten tip triggered by sub-8-fs low-power laser pulses. This process is nonlinear in the laser electric field, and the nonlinearity can be tuned via the dc voltage applied to the tip. Numerical simulations of this system show that electron emission takes place within less than one optical period of the exciting laser pulse, so that an 8 fs 800 nm laser pulse is capable of producing a single electron pulse of less than 1 fs duration. Furthermore, we find that the carrier-envelope phase dependence of the emission process is smaller than 0.1% for an 8 fs pulse but is steeply increasing with decreasing laser pulse duration. 相似文献
997.
The spectroscopic properties of 2-[4′-(dimethylamino)phenyl]-benzothiazole (BTA-2) in solution and in the presence of amyloid fibrils were investigated using absorption and fluorescence spectroscopy. Solution studies show that BTA-2 forms micelles in aqueous solutions, but that the dye can be solvated upon the addition of acetonitrile (CH3CN). BTA-2 binds to amyloid fibrils in solution leading to a characteristic blue-shift in the emission spectrum and an increase in fluorescence intensity. However, in solutions with increasing CH3CN concentration, there was a marked decrease in binding of the BTA-2 to fibrils. Studies demonstrating the effect of BTA-2 concentration on binding were performed. A comparison with the standard amyloid fluorescent marker, thioflavin T (ThT), showed that BTA-2 is more fluorescent, making it an excellent dye to label amyloid samples. 相似文献
998.
Matthieu Virot Valérie Tomao Carine Le Bourvellec Catherine M.C.G. Renard Farid Chemat 《Ultrasonics sonochemistry》2010,17(6):1066-1074
Apple pomace, a by-product of the cider production, has been studied as a potential source of polyphenols, compounds of great interest for the industry. Ultrasound has been used to improve extraction efficiency in terms of time needed and total polyphenol content. A preliminary study has been first investigated to optimize ethanol proportion of aqueous extractant (50%, v/v) and solid/liquid ratio (<15%, w/v). A response surface methodology has then been used to maximize total polyphenol content of extracts and investigate influence of parameters involved in extraction procedures for both total polyphenols content and composition of extracts. Optimal settings reached from a central composite design were applied for ultrasound-assisted extraction and were compared to conventional procedure: yields were increased by more than 20%. Ultrasound-assisted polyphenols extraction from apple pomace appears to be a relevant, rapid, sustainable alternative to conventional procedure, and that scale up of the process is possible. 相似文献
999.
Serdar Durdagi Manthos G. Papadopoulos Panagiotis G. Zoumpoulakis Catherine Koukoulitsa Thomas Mavromoustakos 《Molecular diversity》2010,14(2):257-276
When X-ray structure of a ligand-bound receptor is not available, homology models of the protein of interest can be used to
obtain the ligand-binding cavities. The steroelectronic properties of these cavities are directly related to the performed
molecular model coordinates. Thus, the use of different template structures for homology may result in variation of ligand-binding
modes. We have recently reported the MD simulations of a potent CB ligand at bovine rhodopsin-based CB1 and CB2 receptors
(Durdagi et al., Bioorg Med Chem 16:7377–7387, 2008). In this present study, a homology modeling study based on the β2-adrenergic receptor for both CB1 and CB2 receptors was performed, and the results were compared with rhodopsin-based models.
In addition, the role of membrane bilayers to the adopted conformations of potent AMG3 CB ligand has been analyzed for receptor-free
and membrane-associated receptor systems. The performed MD trajectory analysis results have shown that gauche conformations at the terminal segment of the alkyl side chain of AMG3 are not favored in solution. Different adopting dihedral
angles defined between aromatic and dithiolane rings at the active sites of the CB1 and CB2 receptors, which are adapted lead
to different alkyl side chain orientations and thus, may give clues to the medicinal chemists to synthesize more selective
CB ligands. The binding sites of receptors derived by rhodopsin-based models have been regenerated using the β2-adrenergic based template receptors. The re-obtained models confirmed the ligand-binding pockets that were derived based
on rhodopsin. 相似文献
1000.
We organized and led a European study course for American undergraduate university students to explore the early history of relativity and quantum theory. We were inspired by The Physical Tourist articles published in this journal on Munich, Bern, Berlin, Copenhagen, and Göttingen. We describe this adventure both for others wishing to teach such a course and for anyone wishing to walk in the footsteps of the physicists who revolutionized physics in the early decades of the twentieth century. 相似文献