全文获取类型
收费全文 | 1885篇 |
免费 | 53篇 |
国内免费 | 11篇 |
专业分类
化学 | 1173篇 |
晶体学 | 10篇 |
力学 | 63篇 |
综合类 | 1篇 |
数学 | 194篇 |
物理学 | 508篇 |
出版年
2020年 | 13篇 |
2019年 | 16篇 |
2017年 | 22篇 |
2016年 | 34篇 |
2015年 | 22篇 |
2014年 | 27篇 |
2013年 | 84篇 |
2012年 | 82篇 |
2011年 | 103篇 |
2010年 | 45篇 |
2009年 | 54篇 |
2008年 | 87篇 |
2007年 | 94篇 |
2006年 | 89篇 |
2005年 | 79篇 |
2004年 | 80篇 |
2003年 | 60篇 |
2002年 | 49篇 |
2001年 | 39篇 |
2000年 | 40篇 |
1999年 | 43篇 |
1998年 | 21篇 |
1997年 | 20篇 |
1996年 | 24篇 |
1995年 | 40篇 |
1994年 | 35篇 |
1993年 | 35篇 |
1992年 | 45篇 |
1991年 | 21篇 |
1990年 | 19篇 |
1989年 | 17篇 |
1988年 | 20篇 |
1987年 | 19篇 |
1986年 | 15篇 |
1985年 | 33篇 |
1984年 | 14篇 |
1983年 | 19篇 |
1982年 | 26篇 |
1981年 | 23篇 |
1980年 | 17篇 |
1979年 | 26篇 |
1978年 | 25篇 |
1977年 | 25篇 |
1976年 | 20篇 |
1975年 | 21篇 |
1974年 | 29篇 |
1973年 | 23篇 |
1972年 | 12篇 |
1971年 | 13篇 |
1934年 | 16篇 |
排序方式: 共有1949条查询结果,搜索用时 359 毫秒
81.
Schumm BA Koetke DS Adolphsen CE Alexander JP Averill D Barish BC Barklow T Barnett BA Blockus D Boyarski A Brabson B Breakstone A Bulos F Burchat PR Burke DL Cence RJ Chapman J Chmeissani M Cords D Coupal DP Dauncey P DeStaebler HC Dorfan JM Drell PS Drewer DC Durrett D Elia R Feldman GJ Field RC Ford WT Fordham C Frey R Fujino D Gan KK Gero E Gidal G Glanzman T Goldhaber G Gomez Cadenas JJ Gratta G Hanson G Harr R Harral B Harris FA Hayes K Hearty C Heusch CA Hildreth MD Himel T Hinshaw DA 《Physical review D: Particles and fields》1992,46(1):453-456
82.
83.
84.
Irreducible covariant tensor modules for the Lie supergroups GL(m/n) and the Lie superalgebras gl(m/n) and sl(m/n) are obtained through the use of Young tableaux techniques. The starting point is the graded permutation action, first introduced by Dondi and Jarvis, on V
l
. The isomorphism between this group of actions and the symmetric group S
l enables the graded generalization of the Young symmetrizers, and hence of the column relations and Garnir relations, to be made. Consequently, corresponding to each partition of l an irreducible GL(m/n) module may be obtained as a submodule of V
l
. A basis for the module labeled by the partition is provided by GL(m/n)–standard tableaux of shape defined by Berele and Regev. The reduction of an arbitrary tableau to standard form is accomplished through the use of graded column relations and graded Garnir relations. The standardization procedure is algorithmic and allows matrix representations of the Lie superalgebras gl(m/n) and sl(m/n) to be constructed explicitly over the field of rational numbers. All the various steps of the standardization algorithm are exemplified, as well as the explicit construction of matrices representing particular elements of gl(m/n) and sl(m/n). 相似文献
85.
Mishra SR Leung WC Arroyo C Bachmann KT Blair RE Foudas C King BJ Lefmann WC Oltman E Quintas PZ Rabinowitz SA Sciulli FJ Seligman WG Shaevitz MH Merritt FS Oreglia MJ Schumm BA Bernstein RH Borcherding F Fisk HE Lamm MJ Marsh W Merritt KW Schellman H Yovanovitch DD Bodek A Budd HS de Barbaro P Sakumoto WK Sandler PH Smith WH 《Physical review letters》1992,69(24):3499-3502
86.
87.
R.B. King 《Journal of mathematical chemistry》1998,23(1-2):197-227
Elemental carbon has recently been shown to form molecular polyhedral allotropes known as fullerenes in addition to the familiar
graphite and diamond known since antiquity. Such fullerenes contain polyhedral carbon cages in which all vertices have degree
3 and all faces are either pentagons or hexagons. All known fullerenes are found to satisfy the isolated pentagon rule (IPR)
in which all pentagonal faces are completely surrounded by hexagons so that no two pentagonal faces share an edge. The smallest
fullerene structures satisfying the IPR are the known truncated icosahedral C60 of I
h
symmetry and ellipsoidal C70 of D
5h
symmetry. The multiple IPR isomers of families of larger fullerenes such as C76, C78, C82 and C84 can be classified into families related by the so-called pyracylene transformation based on the motion of two carbon atoms
in a pyracylene unit containing two linked pentagons separated by two hexagons. Larger fullerenes with 3ν vertices can be
generated from smaller fullerenes with ν vertices through a so‐called leapfrog transformation consisting of omnicapping followed
by dualization. The energy levels of the bonding molecular orbitals of fullerenes having icosahedral symmetry and 60n
2 carbon atoms can be approximated by spherical harmonics. If fullerenes are regarded as constructed from carbon networks of
positive curvature, the corresponding carbon allotropes constructed from carbon networks of negative curvature are the polymeric
schwarzites. The negative curvature in schwarzites is introduced through heptagons or octagons of carbon atoms and the schwarzites
are constructed by placing such carbon networks on minimal surfaces with negative Gaussian curvature, particularly the so-called
P and D surfaces with local cubic symmetry. The smallest unit cell of a viable schwarzite structure having only hexagons and
heptagons contains 168 carbon atoms and is constructed by applying a leapfrog transformation to a genus 3 figure containing
24 heptagons and 56 vertices described by the German mathematician Klein in the 19th century analogous to the construction
of the C60 fullerene truncated icosahedron by applying a leapfrog transformation to the regular dodecahedron. Although this C168 schwarzite unit cell has local O
h
point group symmetry based on the cubic lattice of the D or P surface, its larger permutational symmetry group is the PSL(2,7)
group of order 168 analogous to the icosahedral pure rotation group, I, of order 60 of the C60 fullerene considered as the isomorphous PSL(2,5) group. The schwarzites, which are still unknown experimentally, are predicted
to be unusually low density forms of elemental carbon because of the pores generated by the infinite periodicity in three
dimensions of the underlying minimal surfaces.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
88.
13C NMR studies on benzophenonetricarbonylchromium and its p-F, p-Cl and p-OCH3 derivatives, with the substitutents on the uncomplexed rings, show a small substituent effect on the complexed ring and on the carbons of the Cr(CO)3 group. The SCCCMO calculations show π-electron donation from the ring to the metal but greater σ-electron back-donation which leaves the ring more negatively charged than before complexation. The chromium atom is more positively charged than it is in benzenetricarbonylchromium. The trends is calculated CO bond orders are in agreement with the trends in CO infrared stretching frequencies. 相似文献
89.
A recently proposed perturbational approach to the electron correlation cusp problem 1 is tested in the context of three spherically symmetrical two‐electron systems: helium atom, hydride anion, and a solvable model system. The interelectronic interaction is partitioned into long‐ and short‐range components. The long‐range interaction, lacking the singularities responsible for the electron correlation cusp, is included in the reference Hamiltonian. Accelerated convergence of orbital‐based methods for this smooth reference Hamiltonian is shown by a detailed partial wave analysis. Contracted orbital basis sets constructed from atomic natural orbitals are shown to be significantly better for the new Hamiltonian than standard basis sets of the same size. The short‐range component becomes the perturbation. The low‐order perturbation equations are solved variationally using basis sets of correlated Gaussian geminals. Variational energies and low‐order perturbation wave functions for the model system are shown to be in excellent agreement with highly accurate numerical solutions for that system. Approximations of the reference wave functions, described by fewer basis functions, are tested for use in the perturbation equations and shown to provide significant computational advantages with tolerable loss of accuracy. Lower bounds for the radius of convergence of the resulting perturbation expansions are estimated. The proposed method is capable of achieving sub‐μHartree accuracy for all systems considered here. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003 相似文献
90.
Pan J Song Q Shi H King M Junga H Zhou S Naidong W 《Rapid communications in mass spectrometry : RCM》2004,18(21):2549-2557
A highly sensitive bioanalytical method based on a simple liquid/liquid extraction and hydrophilic interaction liquid chromatography with tandem mass spectrometry (HILIC/MS/MS) analysis has been developed, validated and transferred for the determination of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), a tobacco-specific nitrosamine metabolite. Deuterated NNAL (NNAL-d(4)) was synthesized and used as the internal standard. This method can be used for the analysis of free and total NNAL (free NNAL plus NNAL-gluc) in K(3)-EDTA human plasma. Free NNAL and NNAL-d(4) are extracted from human plasma by liquid/liquid extraction. To analyze for total NNAL and the internal standard, a separate aliquot of the K(3)-EDTA human plasma is treated with beta-glucuronidase to deconjugate the NNAL-gluc; the total NNAL and internal standard are then extracted using liquid/liquid extraction. After drying down under nitrogen, the residue is reconstituted with acetonitrile and analyzed using positive ion electrospray and HILIC/MS/MS at a flow rate of 1.0 mL/min. The chromatographic run time is 1.0 min per injection, with retention time for both NNAL and NNAL-d(4) of 0.75 min with a capacity factor (k') of 2. The standard curve range for this assay is from 5.00-1000 pg/mL for both free and total NNAL, using a total plasma sample volume of 1.0 mL. The interday precision and accuracy of the quality control (QC) samples demonstrated <7.6% relative standard deviation (RSD) and <3.3% relative error (RE) for free NNAL. For total NNAL, the interday precision and accuracy of the QC samples demonstrated <11.7% RSD and <2.8% RE. Optimization of enzyme hydrolysis of NNAL-gluc is discussed in detail. The overall recoveries for free and total NNAL and IS were 68.2 and 71.5% (free) and 70.7 and 65.5% (total). No adverse matrix effects were noticed for this assay. 相似文献