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971.
972.
J. W. Hewage F. G. Amar M.-F. de Feraudy G. Torchet 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):249-252
Using realistic pair potentials, we investigate the
structures of mixed clusters of argon and nitrogen in order to
interpret the experimental electron diffraction patterns
reported by the Torchet group. Simulations of small clusters
indicate that argon tends to segregate at the center of the
clusters. For larger clusters, in the range of 50 to 200
molecules, MC methods have been used to simulate structures that
are likely to be generated in the molecular beam. By comparing
predicted electron diffraction patterns with those recorded in
the experiments, our models allow us to estimate the average
size and composition of the mixed clusters for a given set of
experimental conditions (nozzle stagnation pressure and Ar
partial pressure). 相似文献
973.
A. C. Reber S. N. Khanna J. S. Hunjan M. R. Beltran 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):221-224
Theoretical electronic structure studies on (ZnO)n (n= 2–18, 21) have
been carried out to show that the transition from an elementary ZnO molecule
to the bulk wurtzite ZnO proceeds via hollow rings, towers, and cages. Our
first principles electronic structure calculations carried out within a
gradient corrected density functional framework show that small
ZnnOn (n=2–7) clusters form single, highly stable rings.
Zn3O3 and the symmetric cage Zn12O12 are shown to be
particularly stable clusters. Among larger clusters, the most stable are
oblong cages, Zn15O15, Zn18O18, and Zn21O21,
which are reminiscent of nanotubes. 相似文献
974.
G. Ballentine M. Heßler M. Kinza K. Fauth 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(3):535-537
Fe clusters of 105±2 atoms/cluster were mass selectively deposited onto Cu(111) at cryogenic temperatures.
XMCD was used to measure temperature and direction dependent magnetization curves.
The clusters are superparamagnetic at the lowest temperature measured (10 K). Their magnetization curves are consistent with
magnetic moments of ≈2.5μB per atom which are thus enhanced over the bulk values.
Within experimental accuracy, the clusters do not present magnetocrystalline anisotropy in the temperature range
of 10 K to 60 K. 相似文献
975.
Y. Ren R. Moro V. V. Kresin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):109-112
Individual amino acid molecules embedded in helium
nanodroplets fragment extensively when the beam is ionized by electron
bombardment. However, we find that when glycine and tryptophan are picked up
right after, or right before, a small amount of water, the mass spectra
become significantly altered. For glycine, the detected ions consist almost
entirely of intact protonated amino acids, with or without a few water
molecules attached. In other words, the presence of water exerts a striking
“buffering” effect on the ionization-induced fragmentation. For tryptophan
the effect is weaker but also present. In both cases, the hydroxyl group
lost upon ionization overwhelmingly comes from the water partner (in strong
contrast to the situation observed when amino acids are picked up by neat
water clusters). A complementary experiment involving DCl molecules
co-embedded with water shows that in this case Cl and/or DCl invariably
leave the droplet upon ionization. The observed patterns may be steered by
the analytes' dipole moments or by solvation effects. 相似文献
976.
T. Kodaira S. Inoue Y. Murakami 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):267-270
Arrayed cationic K clusters including one 4s-electron in each cluster, i.e., Km+1
m+, were incorporated into α-cages of zeolite LTA with Si/Al=1.5. Although no magnetic phase transition was observed regarding
the temperature (T) dependence of magnetic susceptibilities originating from the 4s-electron spins (χspin) between 2 and 300 K, the χspin-T curve could be fitted by the sum of magnetic susceptibilities based on the Curie-Weiss law and Pauli paramagnetism. A possible
explanation of this behavior is the existence of a narrow energy band formed out of 1s-cluster orbitals of arrayed K clusters,
and the existence of a finite density of state at the Fermi energy. 相似文献
977.
F. Zappa S. Denifl I. Mähr J. Lecointre F. Rondino Olof Echt T. D. Märk P. Scheier 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):117-120
Embedding molecules in helium clusters has become a
powerful technique for the preparation of cold targets for spectroscopy
experiments, as well as for the assembly of complex, fragile molecular
species. We have recently developed a helium cluster source and a pick-up cell
to produce neutral beams of doped helium droplets, to be used as targets in
studies on electron collisions with molecules of biological relevance. In
the present work we present the results of a series of experiments on
electron-impact ionization of helium clusters doped with thymine and
1-methylthymine, where several interesting phenomena were observed, i.e.,
(i) electron impact ionization of molecular clusters inside the helium
droplets leads predominantly to protonated clusters; (ii) the appearance
energies are close to the ionization threshold of the helium atom but
ionization efficiency curves in addition extend down by several eV; (iii)
ionized molecular clusters can undergo metastable decay via the loss of one
neutral monomer. 相似文献
978.
Sergey V. Petrov 《Journal of Molecular Spectroscopy》2007,243(2):245-252
We report and substantiate a method for constructing the rotational energy surface (RES) of a molecule as a pure classical object. For an arbitrary molecule we start from the potential energy surface rather than from a conventional “effective Hamiltonian”. The method is used for constructing the RES of the PH3 molecule in its ground vibrational state. We have used an ab initio potential energy surface [D. Wang, Q. Shi, Q.-S. Zhu, J. Chem. Phys. 112 (2000) 9624-9631; S.N. Yurchenko, M. Carvajal, P. Jensen, F. Herregodts, T.R. Huet, Chem. Phys. 290 (2003) 59-67.]. The shape of the RES is shown not to change for J from 0 to 120. The procedure of quasiclassical quantization of the RES was also undertaken, yielding a set of quasiclassical critical values of the angular momentum. The results explain the structure of quantum rotational energy levels obtained by variational calculations [S.N. Yurchenko, W. Thiel, S. Patchkovskii, P. Jensen, Phys. Chem. Chem. Phys. 7 (2005) 573-582]. 相似文献
979.
W?odzimierz Buchowicz Antoni Pietrzykowski Lucjan B. Jerzykiewicz 《Journal of organometallic chemistry》2005,690(5):1192-1197
Thermolysis of the cyclopentadienylnickelmethyl complex [NiCp(CH3)(η2CH2CHC4H9)] in various solvents was studied. Separation of products by means of column chromatography allowed to isolate and crystallographically characterise (μ3-methylidyne)tris(cyclopentadienylnickel) cluster (NiCp)3(μ3-CH) (1). Cluster 1 crystallised from a hexane/THF mixture in hexagonal crystal system and P63 space group. Ni-Ni and Ni-C(methylidyne) distances were 2.3558(10) and 1.823(4) Å, respectively. Detailed studies showed that cluster (NiCp)3(μ3-CH) (1) was produced during the chromatography on alumina. The plausible precursor to 1 is described as (NiCp)6C. 相似文献
980.
M.P. Machado P. Piquini R. Mota 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(1):91-93
The geometric structures, energetics and electronic properties of the recently discovered BN nanocones are investigated using
first-principles calculations based on the density-functional theory. We have proposed one particular structure for BN nanocones
associated with the 240° disclination, derived by the extraction of four 60° segments, presenting as characteristic four pentagons at the apex and termination in two atoms. The cones are simulated by
three clusters containing 58 B plus N atoms and additional 12 H atoms to saturate the dangling bonds at the edge. The most
stable configuration is obtained when the two terminating atoms are one B and one N. For the cases where the two terminating
atoms are of the same kind, the tip with B atoms is determined to have lower binding energy than with N atoms. The local densities
of states of these BN nanocones are investigated and sharp states are found in the regions close (below and above) to the
Fermi energy.
Received 14 October 2002 / Received in final form 6 December 2002 Published online 11 February 2003
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ID="a"e-mail: ppiquini@smail.ufsm.br 相似文献