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941.
Sami H. Mahmood Maen A. Gharaibeh Hassan Abu-Safia Ahmad S. Saleh 《Hyperfine Interactions》1993,77(1):255-264
We report the results of a Mössbauer study of the alloy sytem FeAl1?x Co x forx ≥ 0.3 at temperatures down to 83 K. Magnetic splitting is observed forx ≥ 0.35 at all temperatures. However, forx=0.3, no splitting is observed at room temperature, and superparamagnetic behavior occurs at LN2 temperature. The magnetically split spectra are fitted each with a distribution of hyperfine fields and the average hyperfine field \(\bar B_{hf} \) as a function of temperature is obtained. The variation of \(\bar B_{hf} \) withT is explained using the model of magnetic clusters with collective magnetic excitations from which the saturation hyperfine field and the magnetic anisotropy energy for these clusters are obtained. Also, the results are discussed using the model of random atomic distributions, and the agreement between the calculated and the experimentally obtained distributions of hyperfine fields is found improve asx increases. 相似文献
942.
943.
C. Marhag D. Ben Hassen-Chehimi H. Said 《Journal of Thermal Analysis and Calorimetry》2006,86(1):249-254
The thermodynamic
exploitation of the solid–liquid equilibria in the MIPO3–Pb(PO3)2, MIPO3–Cu(PO3)2
and MIPO3–Ce(PO3)3
systems (with M
I=Li,
Na, K, Rb, Cs, Ag, Tl) is carried out using a semi-empirical equation of the
liquidus curves already used with success for similar binary systems.
The enthalpy of fusion is calculated for each pure polyphosphate on
the assumption that the liquid solution is ideal and only formed by MIPO3
and M(PO3)q entities (q=2 for Pb and Cu, q=3
for M=Ce). In the most binary systems,
a wide difference between the calculated values of the melting enthalpies
of these polyphosphates and the measured ones determined from the DTA curves,
was observed. This difference is probably due to the existence of some molecular
associations in the liquid phase. 相似文献
944.
A. Ben Taleb O. Dessaux D. Djebabra P. Goudmand 《Journal of photochemistry and photobiology. A, Chemistry》1987,40(2-3):233-243
The behaviour of the biacetyl molecule (BA) in a cold plasma, obtained by extraction of reactive species from a nitrogen plasma generated in a microwave discharge, is discussed. When the partial pressures of nitrogen and biacetyl are approximately equal (pN2 ≈ 0.60 Torr, pBA ≈ 0.55 Torr), the emission of the 3Au---1Ag transition of biacetyl is observed with a vibrational structure. On reaction of biacetyl with nitrogen cold plasma preferentially enriched in N2(A3Σ+u), an enhancement of the emission intensity of the phosphorescence of biacetyl is observed. The initiator of this transition is the triplet state BA(3Bu) which originates from an isoenergetic transfer from N2(A3Σ+u) according to the overall mechanism 相似文献
945.
Electrophilic palladium-catalyzed cycloisomerization of brominated aryl propiolates produces brominated coumarins. The brominated coumarins can be diversified by reduction of the Pd(II) catalyst to Pd(0) followed by Suzuki, Sonogashira, Heck, or Hartwig-Buchwald coupling. Thus, a single loading of precatalyst can be used to conduct sequential reactions, allowing the synthesis of functionalized coumarins. Extension of this methodology toward the synthesis of coumarin libraries is discussed. 相似文献
946.
947.
A quantitative study by means of a glass pH electrode was made of the successive protonation of triethylenetramine(trien), in the pH range 2.0–12.0 at 25°C for unit ionic strength (KNO3). The successive acidity constants of fully protonated H4 trien4+ were found to be 10?3.97, 10?7.12, 10?9.49 and 10?10.14. 相似文献
948.
Luo K Kuittu MP Tong C Majaniemi S Ala-Nissila T 《The Journal of chemical physics》2005,123(19):194702
We study the dynamics and equilibrium profile shapes of contact lines for wetting in the case of a spatially inhomogeneous solid wall with stripe defects. Using a phase-field model with conserved dynamics, we first numerically determine the contact line behavior in the case of a stripe defect of varying widths. For narrow defects, we find that the maximum distortion of the contact line and the healing length is related to the defect width, while for wide defects, it saturates to constant values. This behavior is in quantitative agreement with the experimental data. In addition, we examine the shape of the contact line between two stripe defects as a function of their separation. Using the phase-field model, we also analytically estimate the contact line configuration and find good qualitative agreement with the numerical results. 相似文献
949.
Schilardi PL Dip P dos Santos Claro PC Benítez GA Fonticelli MH Azzaroni O Salvarezza RC 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,12(1):38-49
Pattern transfer with high resolution is a frontier topic in the emerging field of nanotechnologies. Electrochemical molding is a possible route for nanopatterning metal, alloys and oxide surfaces with high resolution in a simple and inexpensive way. This method involves electrodeposition onto a conducting master covered by a self-assembled alkanethiolate monolayer (SAMs). This molecular film enables direct surface-relief pattern transfer from the conducting master to the inner face of the electrodeposit, and also allows an easy release of the electrodeposited film due their excellent anti-adherent properties. Replicas of the original conductive master can be also obtained by a simple two-step procedure. SAM quality and stability under electrodeposition conditions combined with the formation of smooth electrodeposits are crucial to obtain high-quality pattern transfer with sub-50 nm resolution. 相似文献
950.
Batten SR Bjernemose J Jensen P Leita BA Murray KS Moubaraki B Smith JP Toftlund H 《Dalton transactions (Cambridge, England : 2003)》2004,(20):3370-3375
In order to expand the few known examples of dinuclear iron(II) compounds displaying (weak) intradinuclear exchange coupling and spin-crossover on one or both of the iron(II) centres, various dinuclear compounds have been synthesised and assessed for their spin-crossover and exchange coupling behaviour. The key aim of the work was to prepare and structurally characterise 'weakly linked' and 'covalently bridged' systems incorporating bridging ligands such as alkyldinitriles (e.g.NC(CH(2))(4)CN), bipyrimidine (bpym), dicyanamide (dca(-)), tricyanomethanide (tcm(-)), 3,6-bis(2-pyridyl)tetrazine (bptz) and 3,6-bis(2-pyridyl)2,5-dihydrotetrazine (H(2)bptz). The 'end groups', which complete the Fe(ii)N(6) chromophores, include tris(2-pyridylmethyl)amine (tpa), di(2-pyridylethyl)(2-pyridylmethyl)amine (tpa'), 3-(2-pyridyl)pyrazole (pypzH), 1,10-phenanthroline (1,10-phen), tris(pyrazolyl)methane (tpm) and NCX(-)(X = S, Se). It was quite difficult to achieve the spin-crossover condition, many ligand combinations yielding high-spin/high-spin (HS-HS) Fe(II)Fe(II) spin states at all temperatures (300-2 K) with very weak antiferromagnetic coupling (J < -1 cm(-1)), two such being the crystallographically characterised [(dca)(tpm)Fe(mu(1,5)-dca)(2)Fe(tpm)(dca)], 5, and [(tpa')Fe(mu(1,5)-tcm)(2)Fe(tpa')](tcm)(2)(H(2)O)(2), 6. In contrast, a strong field was created around the Fe(II) centres in [(tpa)Fe(mu-(NC(CH(2))(4)CN))(2)Fe(tpa)](ClO(4))(4).NC(CH(2))(4)CN, 1, and the Fe-N bond distances, at 173 K, reflected this. This weakly-linked dinitrile example showed a spin-crossover beginning above 300 K. 'Half crossover' examples, yielding HS-LS states below the spin transition, similar to those noted by Real and coworkers in some mu-bpym systems, were noted for [(1,10-phen)(NCS)(2)Fe(mu-bpym)Fe(NCS)(2)(1,10-phen)], 2, [(pypzH)(NCSe)(2)Fe(mu-bpym)Fe(NCSe)(2)(pypzH)], 4, and [(tpa)Fe(mu-H(2)bptz)Fe(tpa)](ClO(4))(4), 8. Interestingly, the mu-bptz analogue, 7, remained LS-LS at all temperatures with the start of a broad spin crossover evident above 300 K. No thermal hysteresis was evident in the spin transitions of these new dinuclear crossover species indicating a lack of intra- or interdinuclear cooperativity. 相似文献