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91.
Steady state analysis of a combined hybrid process consisting of a reactive distillation column, pervaporation unit, and a
distillation column is presented. This process configuration was first presented by Steinigeweg and Gmehling (2004) for the
transesterification of methyl acetate and butanol to butyl acetate and methanol. This system is characteristic for its low
reaction rate and complex phase equilibrium. Steinigeweg and Gmehling (2004) have shown that the combination of reactive distillation
and pervaporation is favourable since conversions close to 100 % can be reached with a reasonable size of the reactive section
in the reactive distillation column. The aim of this paper is to show that although high conversion can be achieved, very
complicated steady state behaviour must be expected. The presented analysis is based on mathematical modelling of a process
unit, where the steady-state analysis, including continuation and bifurcation analyses, was used. Multiple steady states were
predicted for the studied system; three steady states with conversions higher than 98 %. However, not all predicted steady
states met the maximal allowed temperature condition in the reactive section (catalyst maximal operation temperature of 393
K). The presence of multiple steady states reduces the operability and controllability of the reactive distillation column
during its start-up and during the occurrence of any variation of operating parameters because the system can be shifted from
one steady state to another one (concurrent exceeding the maximal allowed temperature) with unwanted consequences, e.g. production
loss. Therefore, design and subsequent operation of such a complicated system is an ambitious task requiring knowledge of
any possible system behaviour. 相似文献
92.
The combination of deprotonation (via ion/molecule and ion/ion reactions) and low-energy collision-induced dissociation (CID) has been explored for the enhanced characterisation of tryptic peptides via access to different precursor charge states. This approach allows instant access to fragmentation properties of singly and doubly protonated precursors (arising from the availability of mobile protons) in a single experiment. Considering both charge states extended our base of structurally informative data (in comparison with considering just a single charge state) due to generation of additional sequence ions and by obtaining supplementary structural information derived from selective cleavages. Roughly 37% of combined data sets (CID spectra of doubly and singly charged precursor) showed a greater database identification confidence than each set alone. Moreover, comparison between a number of sequence ions of the singly charged precursor and the doubly charged precursor provided a mean of distinguishing the two classes of tryptic peptides (arginine or lysine containing). 相似文献
93.
Gröger K Baretić D Piantanida I Marjanović M Kralj M Grabar M Tomić S Schmuck C 《Organic & biomolecular chemistry》2011,9(1):198-209
Two novel guanidiniocarbonyl pyrrole-pyrene conjugates 3 and 4 as spectroscopic probes for ds-polynucleotides were synthesized and their interaction with different ds-DNAs/RNAs studied. Compared to a previously reported first set of conjugates (1 and 2) the significant extension and increased rigidity of the central part of the structure resulted in a switch of DNA binding mode from intercalative (previously studied derivatives 1 and 2 with a nonbinding and flexible linker) to minor groove binding of the two novel guanidiniocarbonyl-pyrrole-pyrene conjugates 3 and 4. These two compounds interact strongly with ds-DNAs, but only weakly with ds-RNA. The newly incorporated heterocyclic moieties within the central part of the structure of 3 and 4 were able to control by steric and hydrogen-bonding effects the alignment of the molecules within various, structurally different forms of DNA minor grooves, whereby even small differences in the position of the attached pyrene within the groove were reflected in different fluorimetric responses. In addition, 3 and 4 revealed intriguing in vitro selectivity among various human tumour cell lines. 相似文献
94.
Marko Tadi? 《manuscripta mathematica》2011,135(3-4):417-435
To an irreducible square integrable representation ?? of a classical p-adic group, M?glin has attached invariants Jord(??), ?? cusp and ${\epsilon_\pi}$ . These triples classify square integrable representations modulo cuspidal data (assuming a natural hypothesis). The definition of these invariants in M?glin (J Eur Math Soc 4(2):143?C200, 2002) is rather simple??in terms of induced representations, except at one case when a coherent normalization of standard intertwining operators is required. In this paper we show how one can define this case also in terms of induced representations. 相似文献
95.
Marko D. Petkovi? Milan B. Tasi? Predrag S. Stanimirovi? 《Applied mathematics and computation》2011,217(19):7588-7598
We extend the algorithm for computing {1}, {1, 3}, {1, 4} inverses and their gradients from [11] to the set of multiple-variable rational and polynomial matrices. An improvement of this extension, appropriate to sparse polynomial matrices with relatively small number of nonzero coefficient matrices as well as in the case when the nonzero coefficient matrices are sparse, is introduced. For that purpose, we exploit two effective structures form [6], which make use of only nonzero addends in polynomial matrices, and define their partial derivatives. Symbolic computational package MATHEMATICA is used in the implementation. Several randomly generated test matrices are tested and the CPU times required by two used effective structures are compared and discussed. 相似文献
96.
Some dynamical properties present in a problem concerning the acceleration of particles in a wave packet are studied. The dynamics of the model is described in terms of a two-dimensional area preserving map. We show that the phase space is mixed in the sense that there are regular and chaotic regions coexisting. We use a connection with the standard map in order to find the position of the first invariant spanning curve which borders the chaotic sea. We find that the position of the first invariant spanning curve increases as a power of the control parameter with the exponent 2/3. The standard deviation of the kinetic energy of an ensemble of initial conditions obeys a power law as a function of time, and saturates after some crossover. Scaling formalism is used in order to characterise the chaotic region close to the transition from integrability to nonintegrability and a relationship between the power law exponents is derived. The formalism can be applied in many different systems with mixed phase space. Then, dissipation is introduced into the model and therefore the property of area preservation is broken, and consequently attractors are observed. We show that after a small change of the dissipation, the chaotic attractor as well as its basin of attraction are destroyed, thus leading the system to experience a boundary crisis. The transient after the crisis follows a power law with exponent −2. 相似文献
97.
Arion T Mucke M Förstel M Bradshaw AM Hergenhahn U 《The Journal of chemical physics》2011,134(7):074306
We report the occurrence of interatomic Coulombic decay (ICD) in mixed NeKr clusters. A well-defined feature ranging from 9 to 12 eV in kinetic energy is observed in coincidence with the Ne 2s photoelectrons. It derives from an ICD process, in which an initial Ne 2s vacancy is filled by a Ne 2p electron and an electron is emitted from a 4p level on a neighboring Kr atom. We have studied the dependence of the effect on photon energy, cluster composition, and cluster size. Interestingly, the ICD electron energy increases slightly and grows a shoulder on going from 2% to 5% Kr in the coexpansion process, which we interpret in terms of surface versus bulk effects. 相似文献
98.
A highly facile, straightforward synthesis of 1-(3-indolyl)-tetrahydroisoquinolines was developed using either simple copper or iron catalysts. N-protected and unprotected tetrahydroisoquinolines (THIQ) could be used as starting materials. Extension of the substrate scope of the pronucleophile from indoles to pyrroles and electron-rich arenes was realized. Additionally, methoxyphenylation is not limited to THIQ but can be carried out on isochroman as well, again employing iron and copper catalysis. 相似文献
99.
Hamilton SM Hopkins WS Harding DJ Walsh TR Haertelt M Kerpal C Gruene P Meijer G Fielicke A Mackenzie SR 《The journal of physical chemistry. A》2011,115(12):2489-2497
Far- and mid-infrared multiple photon dissociation spectroscopy has been employed to study both the structure and surface reactivity of isolated cationic rhodium clusters with surface-adsorbed nitrous oxide, Rh(n)N(2)O(+) (n = 4-8). Comparison of experimental spectra recorded using the argon atom tagging method with those calculated using density functional theory (DFT) reveals that the nitrous oxide is molecularly bound on the rhodium cluster via the terminal N-atom. Binding is thought to occur exclusively on atop sites with the rhodium clusters adopting close-packed structures. In related, but conceptually different experiments, infrared pumping of the vibrational modes corresponding with the normal modes of the adsorbed N(2)O has been observed to result in the decomposition of the N(2)O moiety and the production of oxide clusters. This cluster surface chemistry is observed for all cluster sizes studied except for n = 5. Plausible N(2)O decomposition mechanisms are given based on DFT calculations using exchange-correlation functionals. Similar experiments pumping the Rh-O stretch in Rh(n)ON(2)O(+) complexes, on which the same chemistry is observed, confirm the thermal nature of this reaction. 相似文献
100.
The macroscopic thermodynamic stability of a system of 108 diatomic molecules undergoing planar Couette flow far from equilibrium is reported. The system is perturbed from the steady state using a nondissipative variable colour field which induces a polarization in the system. It is found that the steady state for the system corresponds to an extremum in the generalized free energy and entropy production. However, while the free energy is always a minimum, the entropy production may be either a minimum or a maximum depending upon the direction of the colour field. These results, for a molecular system, are fundamentally different from those for an equivalent atomic system. 相似文献