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31.
Über die synthese von in position 5 halogenierten,im aromatischen Kern substituierten Valerophenonen
The preparation of 5-chloro-2-methoxy-valerophenone and 5-iodo-2-methoxy-valerophenone proceeding from the -lactone of the corresponding 2-(o-methoxybenzoyl)-5-hydroxy-valeric acid is described. 相似文献
32.
A lattice model of a symmetrical binary (AB) polymer mixture is studied, modelling the polymer chains by self-avoiding walks withN
A
=N
B
=N steps on a simple cubic lattice. If a pair of nearest neighbour sites is taken by different monomersAB orBA, an energy
ab
is won; if the pair of sites is taken by anAA or aBB pair, an energy is won, while the energy is reduced to zero if at least one of the sites of the pair is vacant. To allow enough chain mobility, 20% of the lattice sites are vacancies. In addition to local motions of the chain segments we use a novel grand-canonical simulation technique:A chains are transformed intoB chains and vice versa, keeping the chemical potential difference fixed. The phase diagram is obtained forN=4, 8,16 and 32; the critical behaviour is analysed by finite-size scaling methods. It is shown that the critical exponents are those of the Ising model (=0.32,=0.63) rather than those of the Flory-Huggins meanfield theory (==1/2). Implications of these results for real polymers are briefly discussed.Paper presented at the Frühjahrstagung 1986, Polymerphysik, der Deutschen Physikalischen Gesellschaft, Kaiserslautern, March 12–14, 1986. 相似文献
33.
The growth of ordered domains in lattice gas models, which occurs after the system is quenched from infinite temperature to a state below the critical temperatureT
c, is studied by Monte Carlo simulation. For a square lattice with repulsion between nearest and next-nearest neighbors, which in equilibrium exhibits fourfold degenerate (2×1) superstructures, the time-dependent energy E(t), domain size L(t), and structure functionS(q, t) are obtained, both for Glauber dynamics (no conservation law) and the case with conserved density (Kawasaki dynamics). At late times the energy excess and halfwidth of the structure factor decrease proportional tot
–x, whileL(t) t
x, where the exponent x=1/2 for Glauber dynamics and x1/3 for Kawasaki dynamics. In addition, the structure factor satisfies a scaling lawS(k,t)=t
2xS(ktx). The smaller exponent for the conserved density case is traced back to the excess density contained in the walls between ordered domains which must be redistributed during growth. Quenches toT>T
c, T=Tc (where we estimate dynamic critical exponents) andT=0 are also considered. In the latter case, the system becomes frozen in a glasslike domain pattern far from equilibrium when using Kawasaki dynamics. The generalization of our results to other lattices and structures also is briefly discussed. 相似文献
34.
Synthesis of the Stannatetraphospholanes (tBuP)4SnR2 (R = tBu, nBu, C6H5) and (tBuP)4Sn(Cl)nBu Molecular and Crystal Structure of (tBuP)4Sn(tBu)2 The reaction of the diphosphide K2[tBuP-(tBuP)2-PtBu] 4 with the halogenostannanes (tBu)2SnCl2, (nBu)2SnCl2, (C6H5)2SnCl2 or nBuSnCl3 in a molar ratio of 1 : 1 leads via a [4 + 1]-cyclocondensation reaction to the stannatetraphospholanes (tBuP)4SnR2 3 b–3 d and (tBuP)4Sn(Cl)nBu 3 e , respectively, with the binary 5-membered P4Sn ring system. 3 b was characterized by a single crystal structure analysis; the 5-membered ring exists in a planar conformation. The compounds 3 b–3 e were identified by NMR and also by mass spectroscopy; the 31P{1H}-NMR spectra of 3 b–3 d showed an AA′MM′ (AA′MM′X), 3 e on the other hand an ABCD (ABCDX) spin system. 相似文献
35.
The hydration of the lipid 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) and of the cationic detergent dodecyltrimethylammonium bromide (DTAB) has been studied by means of isothermal titration calorimetry (ITC), gravimetry, and infrared (IR) spectroscopy. During the experiments films of the amphiphiles are perfused by an inert gas of variable relative humidity. The measurement of adsorption heats using ITC represents a new adaptation of adsorption calorimetry which has been called the humidity titration technique. This method yields the partial molar enthalpy of water upon adsorption. It is found to be endothermic with respect to the molar enthalpy of water on condensation for the water molecules which interact directly with the headgroups of POPC and DTAB. Consequently, the spontaneous hydration of the amphiphiles is entropy driven in an aqueous environment. IR spectroscopy shows that hydration is accompanied by the increase in the conformational and/or motional freedom of the amphiphilic molecules upon water binding. In particular, a lyotropic chain melting transition is induced at a certain characteristic relative humidity. This event is paralleled by the adsorption of water. The corresponding exothermic adsorption heat is consumed completely (POPC) or partially (DTAB) by the hydrocarbon chains upon melting. Differential scanning calorimetry was used as an independent method to determine transition enthalpies of the amphiphiles at a definite hydration degree. Water binding onto the headgroups is discussed in terms of hydrogen bonding and polar interactions. The adsorption isotherms yield a number of 2.6 tightly bound water molecules per POPC and DTAB molecule. 相似文献
36.
Transition Metal Phosphido Complexes. VIII. X-Ray Diffraction Studies of Transition Metal Phosphorus Four- and Six-Membered Ring Complexes. Structures of [(CO)4MnPH2]2, [(CO)4MnPH2]3, and [cpNiPH2]3 [(CO)4MnPH2]2 1 crystallizes triclinic in the space group P1 with a = 680.4 pm, b = 706.4 pm, c = 919.1 pm, α 110.5°, β = 91.92°, γ 115.65°, and Z = 1 formula unit. The molecule exhibits a centrosymmetrical structure. The bond angles within the planar four-membered (Mn? P)2-ring are 76.1° at the Mn atoms and 103.9° at the P atoms, respectively. The average Mn? P bond distance is found to be 235.1 pm. [(CO)4MnPH2]3 2 crystallizes monoclinic in the space group P2/n with a = 905.2 pm, b = 974.8 pm, c = 1264.2 pm, β = 109.1°, and Z = 2 formula units. The framework of the six-membered (Mn? P)3-ring can be described as having a twist boat conformation. The average endocyclic bond angles are with 89.1° at the Mn atoms and 130.1° at the P atoms, respectively, largely widened compared to 1 . The average Mn? P bond distance, which is found to be 238.5 pm, is also slightly increased compared to 1 . [cpNiPH2]3 3 crystallizes rhombohedral in the space group R3. The cell constants (hexagonal setting) are a = b = 1686.1 pm, c = 561.1 pm and Z = 3 formula units. The six-membered (Ni? P)3-ring exhibits a chair conformation. The endocyclic bond angles are with 92.3° at the Ni atoms and 124.3° at the P atoms, respectively, comparable with those of the six-membered ring compound 2 . The Ni? P bond distance is found to be 215.2 pm. The eyclopentadienyl ligands are disordered and have been refined as rigid groups. 相似文献
37.
Phosphorus pentachloride reacts with BF3 · NH3 to give [Cl3P?N? PCl3][BCl4](Va). Mechanism of formation and chemical behaviour to SO2 and H2S are described, followed by a presentation and discussion of the 31P, 19F, and 11B NMR spectra of the adducts formed by P2NOCl5 and BF3, BCl3, and PF5, respectively. 相似文献
38.
Prof. Dr. O. Hromatka D. Binder K. Eichinger 《Monatshefte für Chemie / Chemical Monthly》1974,105(1):123-126
The synthesis of 5-(o-trifluoromethylphenyl)-1H-thieno-[3,4-e]1,4-diazepin-2(3H)-one (7) and its nitration and chlorination in pos. 8 are described. 相似文献
39.
K. Binder 《Zeitschrift für Physik B Condensed Matter》1981,43(2):119-140
The distribution functionP
L
(s) of the local order parameters in finite blocks of linear dimensionL is studied for Ising lattices of dimensionalityd=2, 3 and 4. Apart from the case where the block is a subsystem of an infinite lattice, also the distribution in finite systems with free [P
L
(f)
(s)] and periodic [P
L
(p)(s)
] boundary conditions is treated. Above the critical pointT
c
, these distributions tend for largeL towards the same gaussian distribution centered around zero block magnetization, while belowT
c
these distributions tend towards two gaussians centered at ±M, whereM is the spontaneous magnetization appearing in the infinite systems. However, belowT
c
the wings of the distribution at small |s| are distinctly nongaussian, reflecting two-phase coexistence. Hence the distribution functions can be used to obtain the interface tension between ordered phases.At criticality, the distribution functions tend for largeL towards scaled universal forms, though dependent on the boundary conditions. These scaling functions are estimated from Monte Carlo simulations. For subsystem-blocks, good agreement with previous renormalization group work of Bruce is obtained.As an application, it is shown that Monte Carlo studies of critical phenomena can be improved in several ways using these distribution functions:(i) standard estimates of order parameter, susceptibility, interface tension are improved(ii) T
c
can be estimated independent of critical exponent estimates(iii) A Monte Carlo renormalization group similar to Nightingale's phenomenological renormalization is proposed, which yields fairly accurate exponent estimates with rather moderate effort(iv) Information on coarse-grained hamiltonians can be gained, which is particularly interesting if the method is extended to more general Hamiltonians. 相似文献
40.
A renormalization group for polymer chains with hard-core interaction is considered, where a chain ofN
0 links of lengthl
0 and hard-core diameterh
0 is mapped onto a chain ofN
1=N
0/s links of lengthl
1 and hard-core diameterh
1. The lengthl
1 is defined in terms of suitable interior distances of the original chain, andh
1 is found from the condition that the end-to-end distance is left invariant. This renormalization group procedure is carried through by various Monte-Carlo methods (simple sampling is found advantageous for short enough chains or high dimensionalities, while dynamic methods involving kinkjumps or reptation are used else). Particular attention is paid to investigate systematic errors of the method by checking the dependence of the results on bothN
0 ands. It is found that for dimensionalitiesd=2, 3 only the nontrivial fixed-point is stable, where upon iteration the ratio
k
=h
k
/l
k
tends to nonzero fixed-point value *, while ford=4,5 the method converges to the gaussian fixed point with *=0. Taking both statistical and systematic errors into account, we estimate the exponentv asv=0.74±0.01 (d=2) andv =0.59±0.01 (d=3). The results are consistent with the expected crossover exponents =1/2 (d=3) and =1 (d=2), respectively. 相似文献