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271.
Non-suppressed ion chromatography (NSIC) has been optimized to permit the determination of chloride, nitrate and sulfate in the low mg/l concentration range within 3 min. Using conductometric detection the extraneous (positive) injection peak was found to adversely affect the early eluting chloride signal when samples with high amounts of total cations are analyzed. The serial arrangement of a downstream potentiometric detector with a chloride ion selective electrode, which does not respond to other alterations of the composition of the eluent than the change in chloride concentrations, is shown to be suitable for interference-free, sensitive and reliable chloride evaluation. Application of the proposed system to the determination of chloride in extracts of filter collected airborne particulates revealed (for those samples that could be evaluated by both detection methods) high precision and no systematic deviations between conductometric and potentiometric detection.Dedicated to Professor Dr. Peter Brätter on the occasion of his 60th birthday  相似文献   
272.
Hydroboration of aliphatic 1-alkynes with freshly prepared dicyclohexylborane (1 mol-equiv., hexane), treatment of the resulting [(E)-1-alkenyl]boranes 5 with Et2Zn or Me2Zn (1.05 mol-equiv.) followed by addition of (?)-3-exo-(dimethylamino)isoborneol (DAIB, 8 ; 0.01 mol-equiv.), subsequent addition of a solution of an aromatic or aliphatic aldehyde (1 mol-equiv., hexane), and quenching with aq. NH4Cl provided (E)-allyl alcohols 6 usually in 70–95% yield with 79–98% enantiomeric excess (Scheme 3 and Table).  相似文献   
273.
Diphenylphosphorylazide N3P(O)(OPh)2 reacts with Pt(PPh3)3, Pt(PPh3)2(C2H4), trans-RhCl(CO)(PPh3)2, Ru(CO)3(PPh3)2, CoCl2(PPh3)2 and CuCl(PPh3)2 to give the azido complexes Pt(PPh3)2(N3)R, Pt(PPh3)2(N3)2R2, the urylene complex RhCl(PPh3)2(RNCONR) and the phosphine imine complexes Ru(CO)3(RPPh3)2, CoCl2(RNPPh3)2, CuCl(RNPPh3)2, respectively, (RP(O)(OPh)2). The oxidative addition of n-C6F13SO2N3 to Pt(PPh3)4 and Pt(PPh3)2(C2H4) affords the complexes Pt(PPh3)2(N3)R and Pt(PPh3)2(N3)2R2, respectively, (RSO2C6F13. The compounds are characterized by elemental analysis and by their IR spectra.  相似文献   
274.
The reaction of diphenyltrichlorophosphorane with amides leads to (C6H5)2P(Cl)?N-acyl compounds, whereas with amines salt-like compounds, [(C6H5)2P(Cl)? NHR]Cl, are formed.  相似文献   
275.
The annelated tetrahydrofuran derivatives 14 and 15, resp., are formed in moderate yield by intramolecular trapping reaction of the carbonyl ylide intermediates 9, which are generated either by thermal ring opening of the trans-stilbene oxides 7t/8t or by photolysis of the cis-isomers 7c/8c.  相似文献   
276.
The nonlinear optical properties of self-assembled monolayers obtained from bonding two different alpha-functionalized terthiophenes (alpha-T3) to (111) silver electrode surfaces have been investigated using second harmonic generation (SHG). The two (alpha-T3) compounds used were functionalized with alkane chains of different lengths (C8 and C4), and each was terminated with a thiol anchoring group. A nitrile group was attached to the terminal thiophene ring of the (alpha-T3) compound with the C4 chain. The orientation of the polarization of the incident beam was changed systematically and gradually between "p" and "s" orientation and the SH signal (isotropic and anisotropic contributions) analyzed in both directions ("P" and "S"). The symmetry of the system was reduced by the presence of the adlayers from C3v to C3. The dependence on the applied potential and the incident wavelength has also been studied. The relative magnitudes and phases of the various second-order tensor elements have been estimated and compared with the values for a bare surface. A resonance process in the (alpha-T3) pi moiety has been investigated, and from this, the effective "band-gap" energies of the organic semiconductor SAMs (i.e., the energy difference between the pi-pi bands) have been estimated.  相似文献   
277.
The reactivity of a Cr‐Te multilayer film consisting of 326 Cr/Te double‐layers with about 88(3) at% Te was investigated with in‐situ X‐ray diffraction. The occurrence of a superstructure reflection caused by the multilayer system is observed. During the annealing procedure between 80 and 90 °C the layer‐by‐layer arrangement is destroyed and elemental Te crystallizes. After 6 h isothermal annealing at 140 °C CrTe3 starts to crystallize. The amount and the crystal size of CrTe3 increase with raising temperature and Te is consumed during the growth process. At 220 °C the formation of crystalline Cr2Te3 is observed and between 220 and 260 °C CrTe3 is completely decomposed into Cr2Te3. The two Cr tellurides grow as highly textured materials. The size of CrTe3 crystals is significantly larger than that of Cr2Te3. For a co‐deposited Cr‐Te film with composition 77(3) at% Te the tri‐telluride and elemental Te crystallize simultaneously. The texture of CrTe3 is less pronounced and different reflections of the tri‐telluride occur besides the (h00)‐reflections. Up to 160 °C a pronounced increase of the crystallite size is observed and the crystals are significantly larger than those obtained with the multifilm sample. At 130 °C the crystallization kinetics seem to be controlled by nucleation.  相似文献   
278.
The copper-tellurolate cluster [(Cu(6)(TePh)(6)(PPh(2)Et)(5)] has been loaded into the pores of MCM-41 by solid-state impregnation techniques. It was found that the best loading conditions are 110 degrees C and 10(-)(3) Torr static vacuum. The resulting material was analyzed by powder X-ray diffraction (PXRD), nitrogen adsorption isotherms, thermogravimetric analysis (TGA), (31)P CP MAS NMR spectroscopy, and TEM. It was observed that loading is accompanied by loss of the phosphine shell, with retention of the copper-tellurium core. Condensation of the impregnated material may proceed thermally or photochemically. Thermal condensation results in the formation of Cu(2)Te nanoparticles as demonstrated by PXRD, and TEM data suggests that the process has taken place inside the pores of MCM-41. Photochemical condensation yields larger metal-chalcogen clusters in the pores as suggested by the result of UV-vis diffuse reflectance spectroscopy and TEM measurements.  相似文献   
279.
Chiral resolution of arginine (Arg) and Arg derivatives is demonstrated using electrospray ionization-tandem mass spectrometry (ESI-MS). Calcium ion (Ca(II))-mediated trimeric clusters are generated, which incorporate the analyte of interest and an enantiomerically pure reference molecule of similar metal ion affinity. Two methods, one based on the measurement of a competitive-dissociation-based branching ratio (R(chir)) by the kinetic method (KM) and one based on the measurement of a chiral recognition ratio (CR) by a similar method, are compared. Incorporating N-blocked Arg derivatives (Z-Arg and Boc-Arg) as chiral references provides chiral resolution greater than that previously reported for Arg enantiomers. In a reciprocal manner, pure Arg enantiomers can be used as references for discriminating enantiomers of these N-blocked Arg derivatives. Condensed-phase and gas-phase Ca(II) ion affinity relative to Arg is also addressed qualitatively for other acidic, basic, and neutral amino acids. In some cases, when only one offspring ion is observed (insufficient for KM analysis), the CR method can be applied as an alternative to obtain a measurable stereoselectivity value for the system. The results of these experiments demonstrate the applicability of, and the difference between, the KM and the CR method for improved quantitative analysis of enantiomeric excess for Arg.  相似文献   
280.
2,3-Dihydropyrazolo[5,1-b]thiazoles 3 are the first representatives of a heterocyclic system, which are conveniently prepared by heating 3-aminorhodanines 1 with ethyl 2-bromo-3,3-diethoxypropionate ( 2 ), via a tandem condensation-sulfur extrusion reaction.  相似文献   
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