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61.
Ideal conditions for the determination of phosphorus by graphite-furnace atomic absorption spectrometry are investigated by the use of high-temperature equilibrium calculations. All reasonable reaction products resulting from the reaction between P, C, O, H, N, Ca and Ar are considered. The calculations show that phosphorus forms the volatile monoxide and dioxide molecules below 1800 K (Po2? 10-13 atm.). At higher temperatures the relative amount of atomic phosphorus is mainly controlled by the equilibrium between monatomic and diatomic phosphorus. The significance of the theoretical ' study was investigated experimentally. The relative amounts of P2 and PO were monitored by molecular absorption using vaporization under isothermal conditions; the interfering effects of Ca, N2, H2, and O2 on the atomic absorption signal for phosphorus were also studied. The sensitivity was greatly dependent on graphite tube conditions as well as the heating rate of the furnace. For CaHPO4 the sensitivity for phosphorus was 4.5 × lO-8 g. If samples were introduced into a preheated tube, this value was improved to 2 × 10-9 g. 相似文献
62.
63.
Catalytic Water Oxidation by Ruthenium Complexes Containing Negatively Charged Ligand Frameworks 下载免费PDF全文
Artificial photosynthesis represents an attractive way of converting solar energy into storable chemical energy. The H2O oxidation half‐reaction, which is essential for producing the necessary reduction equivalents, is an energy‐demanding transformation associated with a high kinetic barrier. Herein we present a couple of efficient Ru‐based catalysts capable of mediating this four‐proton‐four‐electron oxidation. We have focused on the incorporation of negatively charged ligands, such as carboxylate, phenol, and imidazole, into the catalysts to decrease the redox potentials. This account describes our work in designing Ru catalysts based on this idea. The presence of the negatively charged ligands is crucial for stabilizing the metal centers, allowing for light‐driven H2O oxidation. Mechanistic details associated with the designed catalysts are also presented.
64.
65.
High-temperature equilibrium calculations are used to study potential interferences in the determination of aluminium by flameless a.a.s. The conditions for the formation of interfering aluminium compounds like AlO(g), Al2O(g), Al2O3(s), AlOH(g), AlH(g), AlHO2(g), AlS(g), AlN(g), AlN(s) and AlCl(g) have been calculated. The influence of kinetic parameters on the equilibrium calculations for the reactions involving carbon—oxygen and carbon—sulphur has been established by varying the input amount of carbon. The results indicate that even in the nanomole range the presence of elements like H, O, N, Cl and S may cause severe interferences during the atomization step (2300–2900 K) 相似文献
66.
We introduce a new approach to the model theory of metric structures by defining the notion of a metric abstract elementary class (MAEC) closely resembling the notion of an abstract elementary class. Further we define the framework of a homogeneous MAEC were we additionally assume the existence of arbitrarily large models, joint embedding, amalgamation, homogeneity and a property which we call the perturbation property. We also assume that the Löwenheim-Skolem number, which in this setting refers to the density character of the set instead of the cardinality, is ${\aleph_0}$ . In these settings we prove an analogue of Morley’s categoricity transfer theorem. We also give concrete examples of homogeneous MAECs. 相似文献
67.
ABSTRACTCore–valence double-electron ionisation spectra of a few small molecules – carbon monoxide, ammonia, methyl fluoride and thiophene – are presented and analysed using the self-consistent field algorithm introduced by Hans Jørgen Jensen 30 years ago. It confirms the utility of this algorithm, frequently employed to obtain stable and sharp convergence of wave functions for the benefit of calculations of a great variety of molecular properties, thus also for optimisation of core–valence states and for the interpretation of the corresponding spectra. 相似文献
68.
A new and general procedure is described for a detailed analysis of time-resolved fluorescence depolarisation data in the presence of electronic energy migration. An isotropic ensemble of bifluorophoric molecules (D(1)-R-D(2)) has been studied to demonstrate its utility. Intramolecular donor-donor energy migration occurs between the two donor groups (D), which are covalently connected to a rigid linker group (R). These groups undergo restricted reorientational motions with respect to the R group. The analysis of depolarisation data basically involves the search for best-fit parameters which describe the local reorientational motions, the intermolecular D(1)-D(2) distance, as well as the mutual orientations of the donors. For this, the analysis is partly performed on the Fourier domain and the best-fit parameters are determined by using an approach based on a Genetic Algorithm. The energy migration process has been described by using Monte Carlo simulations and an extended F?rster theory (EFT). It is found that the EFT provides the least time-consuming computational method. Since one-photon and two-photon excited fluorescence experiments can be applied for energy migration studies, a general and unified theoretical formulation is given. 相似文献
69.
Oscar Verho Marléne D. V. Dilenstam Markus D. Kärkäs Dr. Eric V. Johnston Dr. Torbjörn Åkermark Prof. Jan‐E. Bäckvall Prof. Björn Åkermark 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(52):16947-16954
By using a dimeric ruthenium complex in combination with tert‐butyl hydrogen peroxide (TBHP) as stoichiometric oxidant, a mild and efficient protocol for the oxidation of secondary benzylic alcohols was obtained, thereby giving the corresponding ketones in high yields within 4 h. However, in the oxidation of aliphatic alcohols, the TBHP protocol suffered from low conversions owing to a competing Ru‐catalyzed disproportionation of the oxidant. Gratifyingly, by switching to Oxone (2 KHSO5 ? KHSO4 ? K2SO4 triple salt) as stoichiometric oxidant, a more efficient and robust system was obtained that allowed for the oxidation of a wide range of aliphatic and benzylic secondary alcohols, giving the corresponding ketones in excellent yields. The mechanism for these reactions is believed to involve a high‐valent RuV–oxo species. We provide support for such an intermediate by means of mechanistic studies. 相似文献
70.
Beatrix C. Hiesmayr Antonio Di Domenico Catalina Curceanu Andreas Gabriel Marcus Huber Jan-Åke Larsson Pawel Moskal 《The European Physical Journal C - Particles and Fields》2012,72(1):1856
Entanglement and its consequences—in particular the violation of Bell inequalities, which defies our concepts of realism and
locality—have been proven to play key roles in Nature by many experiments for various quantum systems. Entanglement can also
be found in systems not consisting of ordinary matter and light, i.e. in massive meson–antimeson systems. Bell inequalities
have been discussed for these systems, but up to date no direct experimental test to conclusively exclude local realism was
found. This mainly stems from the fact that one only has access to a restricted class of observables and that these systems
are also decaying. In this Letter we put forward a Bell inequality for unstable systems which can be tested at accelerator
facilities with current technology. Herewith, the long awaited proof that such systems at different energy scales can reveal
the sophisticated “dynamical” nonlocal feature of Nature in a direct experiment gets feasible. Moreover, the role of entanglement and CP\mathcal{CP} violation, an asymmetry between matter and antimatter, is explored, a special feature offered only by these meson–antimeson
systems. 相似文献