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61.
Bis (2,4,6,8-cyclononatetraen-1-yl)methanes Bis (2,4,6,8-cyclononatetraen-1-yl)methanes ( 2a–c ) have been prepared by reaction of all-cis-cyclononatetraenide with 1,1-dichlorodimethyl ether as well as with carbenium ion precursors 9b and 9c . The title compounds 2 are attractive precursors of highly delocalised nonafulvenes of type 3 ; however, elimination experiments 2→3 failed so far. 相似文献
62.
Stefanov A Stibor A Dominguez-Clarimon A Arndt M 《The Journal of chemical physics》2004,121(14):6935-6940
We present an in-flight fluorescence detection scheme for molecular beams which is applied to determine the enthalpy of sublimation of dye molecules. We investigate tetraphenylporphyrin (TPP), porphine, and nile red, which are believed to be suitable candidates for molecular de Broglie wave interferometry. The measured values are H(sub)(TPP)=142+/-3 kJ/mol, H(sub)(porphine)=87+/-3 kJ/mol, and H(sub)(nile red)=66+/-2 kJ/mol. For TPP, sublimation enthalpies differ in the literature by more than a factor of 2. Our measurements confirm a value at the lower end of this scale. We discuss changes in the character of the molecular flow with the source temperature as a prime reason for discrepancies in the published data. 相似文献
63.
64.
Encinas S Flamigni L Barigelletti F Constable EC Housecroft CE Schofield ER Figgemeier E Fenske D Neuburger M Vos JG Zehnder M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(1):137-150
The electronic absorption spectra, luminescence spectra and lifetimes (in MeCN at room temperature and in frozen n-C3H7CN at 77 K), and electrochemical potentials (in MeCN) of the novel dinuclear [(tpy)Ru(3)Os(tpy)]4+ and trinuclear [(tpy)Ru(3)Os(3)Ru(tpy)]6- complexes (3 = 2,5-bis(2,2':6',2'-terpyridin-4-yl)thiophene) have been obtained and are compared with those of model mononuclear complexes and homometallic [(tpy)Ru(3)Ru(tpy)]4+, [(tpy)Os(3)Os(tpy)]4+ and [(tpy)Ru(3)Ru(3)Ru(tpy)]6+ Complexes. The bridging ligand 3 is nearly planar in the complexes, as seen from a preliminary X-ray determination of [(tpy)Ru(3)Ru(tpy)][PF6]4, and confers a high degree of rigidity upon the polynuclear species. The trinuclear species are rod-shaped with a distance of about 3 nm between the terminal metal centres. For the polynuclear complexes, the spectroscopic and electrochemical data are in accord with a significant intermetal interaction. All of the complexes are luminescent (phi in the range 10(-4)-10(-2) and tau in the range 6-340 ns, at room temperature), and ruthenium- or osmium-based luminescence properties can be identified. Due to the excited state properties of the various components and to the geometric and electronic properties of the bridge, Ru --> Os directional transfer of excitation energy takes place in the complexes [(tpy)Ru(3)Os(tpy)]4+ (end-to-end) and [(tpy)Ru(3)Os(3)Ru(tpy)]6+ (periphery-to-centre). With respect to the homometallic case, for [(tpy)Ru(3)Os(3)Ru(tpy)]6+ excitation trapping at the central position is accompanied by a fivefold enhancement of luminescence intensity. 相似文献
65.
Silvia Schaffner Ludwig Macko Markus Neubufger Margareta Zehnder 《Helvetica chimica acta》1997,80(2):463-471
Crystal and solution structures of the enantiomerically pure and the racemic pairs of (η3-allyl) {2-[2′-(diphenylphosphino)phenyl]-4,5-dihydro-4-phenyloxazole}palladium(II) hexafluorophosphates ( 1 , and rac- 1 , resp.) and tetraphenylborates ( 2 , and rac- 2 , resp.) as well as (η3-allyl){2-[2′-(diphenylphosphino)phenyl]-4,5-dihydro-4-isopropyloxazole}palladium(II) tetraphenylborate ( 3 ) were characterized by X-ray crystallography and 1H-NMR spectroscopy. In the solid state, rac- 1 and rac- 2 proved to be disordered with both diastereoisomeric complexes in the crystal. The complexes 2 and 3 exist only in the ‘exo’ form. The X-ray structures show that the [PdII(η3-allyl)] moiety may adopt different configurations between a nearly symmetrical three-electron PdII(π3-allyl) system and an asymmetrical allyl group with a η1- and a η2-bonding to the metal center. The [PdII(η3-allyl)] system of rac- 1 and of ‘endo’ rac- 2 is closer to the former, and that of 2 , ‘exo’-rac- 2 , and 3 closer to the later geometry. The 1H-NMR spectra of the hexafluorophosphates 1 and rac- 1 show two sets of signals of the allylic protons in an ‘exo’/‘endo’ ratio of 2:3. The tetraphenylborates 2, rac- 2 , and 3 give only one set of broad signals of the allylic protons. 相似文献
66.
Syntheses and Crystal Structures of New Selenido-bridged Ruthenium Clusters The reaction of Se(SiMe3)2 with [RuCl2(PPh3)3], or a mixture of [RuCl2(PPh3)3] and alkylphosphines leads to the formation of selenido-bridged ruthenium clusters. In this publication the compounds [Ru6Se8(PPh3)6] ( 1 ), [Ru6Se8(PEt3)6] ( 2 ) und[Ru6Se8(PnPr3)6] ( 3 ) are described.The compounds 1-3 contain Ru616+ cluster cores with Ru2+ and Ru3+ centers. The structures of these compounds were elucidated by single crystal X-ray structural analyses. 相似文献
67.
Small-angle neutron scattering study of structural changes in temperature sensitive microgel colloids 总被引:3,自引:0,他引:3
Stieger M Richtering W Pedersen JS Lindner P 《The Journal of chemical physics》2004,120(13):6197-6206
The structure of temperature-sensitive poly(N-isopropylacrylamide) microgels in dilute suspension was investigated by means of small-angle neutron scattering. A direct modeling expression for the scattering intensity distribution was derived which describes very well the experimental data at all temperatures over an extensive q range. The overall particle form as well as the internal structure of the microgel network is described by the model. The influence of temperature, cross-linking density, and particle size on the structure was revealed by radial density profiles and clearly showed that the segment density in the swollen state is not homogeneous, but gradually decays at the surface. The density profile reveals a box profile only when the particles are collapsed at elevated temperatures. An increase of the cross-linking density resulted in both an increase of the polymer volume fraction in the inner region of the particle and a reduction of the smearing of the surface. The polymer volume fraction inside the colloid decreased with increasing particle size. The structural changes are in good agreement with the kinetics of the emulsion copolymerization used to prepare the microgel colloids. 相似文献
68.
Hans Bock Claudia Arad Christian Nther Zdenek Havlas Ilka Gbel Andreas John Markus Kleine 《Helvetica chimica acta》1995,78(4):866-878
Electron Transfer and Ion Pair Formation Single Crystal Structure of Bis(sodium 1,1′-biphenyl-2-thiolate-diglyme): An Intermediate in the Reductive Ring Opening of Dibenzothiophene On Na-metal reduction of dibenzothiophene, the five-membered sulfur ring opens to form a colorless 1,1′-biphenyl-2-thiolate sodium salt, which, according to its single-crystal structure determination, is a dimer containing a four-membered, twice diglyme-solvated ring (diglyme···Na⊕?SR)2. Additional measurements provide the following information: cyclic voltammetry in aprotic MeCN solution shows one quasi-reversible electron transfer at E = ?2.58 V. The dibenzothiophene radical anion can be generated in aprotic THF solution at a K mirror and characterized by an 81-line ESR spectrum and its simulation. This blue species is also the first UV/VIS detectable one before the solution changes via green (due to blue + yellow color mixing) to yellow, yielding across an isosbestic point a second and diamagnetic compound. All of the above results suggest a consecutive two-electron reduction followed by an intersystem protonation, M + (e?) → M.? (blue) + (e?) → (M??, yellow?) + (H⊕) → MH? (colorless), to yield the crystallized and structurally characterized reaction intermediate. The diglyme-solvated sodium-salt dimer provides a basis for a quantum-chemical discussion of some facets of the most likely microscopic reduction pathway. 相似文献
69.
Lutz Behle Markus Neuburger Margaretha Zehnder Thomas A. Kaden 《Helvetica chimica acta》1995,78(3):693-702
The new bis-macrocycle 1, 1′-[(1H-pyrazol-3], 5-diyl)bis(methylene)bis[1, 4, 7-triazacyclononane] ( 1 ) was synthesized and its complexation with Cu2+ studied. Potentiometric and spectrophotometric titrations indicate that, in addition to the mononuclear species [Cu(LH2)]4+, [Cu(LH)]3+, [CuL]2+, and [Cu(LH?1)]+, binuclear complexes such as [Cu2L]4+, [Cu2(LH?1)]3+, and [Cu2(LH-2)]2+ are also formed in solution. The stability constants and spectral properties of these are reported. The binuclear species [Cu2(LH?1)]3+ specifically reacts with an azide ion to give a ternary complex [Cu2(LH?1)(N3)]2+, the stability and structure of which were determined spectrophotometrically and by X-ray diffraction, respectively. The two Cu2+ ions are in a square-pyramidal coordination geometry. The axial ligand is one of the N-atoms of the 1, 4, 7-triazacyclononane ring, whereas at the base of the square pyramid, one finds the other two N-atoms of the macrocycle, one N-atom of the pyrazolide and one of the azide, both of which are bridging the two metal centres. In [Cu2(LH?1)(N3)]2+, a strong antiferromagnetic coupling is present, thus resulting in a species with a low magnetic moment of 1.36 B.M. at room temperature. 相似文献
70.
Sm(II)-modified periodic mesoporous silica (PMS), Sm[N(SiHMe2)2]2(THF)x@MCM-41, was used for the synthesis of Sm(II) alkyl, alkoxide, and indenyl surface species via secondary ligand exchange. The performance of the novel Sm(II)-based organometallic–inorganic hybrid materials as initiators for the graft polymerization of methyl methacrylate (MMA) is reported. All of the Sm(II) hybrid materials including the new PMMA–PMS composites were characterized via N2 physisorption, elemental analysis, FTIR spectroscopy, and scanning electron microscopy (SEM). The organic–inorganic composites revealed complete pore blockage as well as enrichment and strong adhesion of the polymer at the exterior of the porous silica material. 相似文献