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排序方式: 共有745条查询结果,搜索用时 15 毫秒
631.
Monica Paravidino Dr. Menno J. Sorgedrager Dr. Romano V. A. Orru Prof. Dr. Ulf Hanefeld Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(25):7596-7604
Water concentration affects both the enantioselectivity and activity of enzymes in dry organic media. Its influence has been investigated using the hydrocyanation of benzaldehyde catalyzed by hydroxynitrile lyase cross‐linked enzyme aggregate (MeHNL‐CLEA) as a model reaction. The enzyme displayed higher enantioselectivity at higher water concentration, thus suggesting a positive effect of enzyme flexibility on selectivity. The activity increased on reducing the solvent water content, but drastic dehydration of the enzyme resulted in a reversible loss of activity. 相似文献
632.
Cornelius T. Martha Anton Heemskerk Jan‐Carel Hoogendoorn Niels Elders Wilfried M. A. Niessen Prof. Dr. Romano V. A. Orru Prof. Dr. Hubertus Irth Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(30):7368-7375
Optimising synthetic conversions and assessing catalyst performance is a tedious and laborious endeavour. Herein, we present an automated alternative to the commonly applied sequential approaches that are used to increase catalyst discovery process efficiencies by increasing the number of entities that can be tested. This new approach combines conversion of the reactants and determination of product formation into a single comprehensive reaction detection system that can be operated with minimal catalyst and reactant consumption. With this approach, rudimentary reaction conditions can be quickly optimised and the same system can then be used to screen for the optimal homogenous catalyst in a selected solution‐phase synthetic conversion. The system, which is composed of standard HPLC components, can be used to screen catalyst libraries at a repetition rate of five minutes and can be run unsupervised. The sensitive mass spectrometric detection that is implemented in the reaction detection methodology can be used for the simultaneous monitoring of reactants, catalysts and product ions. In the experiments, the three‐component reaction that gives a substituted 2‐imidazoline was optimised. Afterwards, the same method was used to assess a library of ferrocene‐based Lewis acid catalysts for performance in the aforementioned conversion in six different solvents. We demonstrate the feasibility of using this methodology to directly compare the performance results obtained in different solvents by calibrating the solvent‐specific MS responses. 相似文献
633.
Niels Elders Eelco Ruijter Dr. Frans J. J. de Kanter Dr. Elwin Janssen Martin Lutz Dr. Anthony L. Spek Prof. Dr. Romano V. A. Orru Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(25):6096-6099
Diversity‐oriented synthesis : The multicomponent reaction of α‐isocyano amides, aldehydes or ketones, and amines affords N‐(cyanomethyl)amides, presenting the fourth class of products from this combination of reagents (see scheme). The scope of the reaction is very broad and various functional groups are tolerated. The outcome of the reaction can also be directed to the formation of 2H‐2‐imidazolines by AgI catalysis.
634.
The development, verification, and comparison study between LC-MS libraries for two manufacturers’ instruments and a verified protocol are discussed. Compounds in the libraries are among those considered by the U.S. EPA Office of Water as threats to drinking water including pesticides, drugs of abuse, and pharmaceuticals. The LC-MS library protocol was verified through an inter-laboratory study that involved Federal, State, and private laboratories. The results demonstrated that the libraries are transferable between the same manufacturer's product line, and have applicability between manufacturers. Although ion abundance ratios within mass spectra were shown to be different between the manufacturers’ instruments, the NIST search engine match probability was at 96% or greater for 64 out of 67 compounds evaluated. 相似文献
635.
Ramos LA Ulic SE Romano RM Tong S Ge M Vishnevskiy YV Berger RJ Mitzel NW Beckers H Willner H Della Védova CO 《Inorganic chemistry》2011,50(19):9650-9659
The novel molecule difluorochloroacetyl cyanide, ClF(2)CC(O)CN, has been characterized by IR (gas phase, Ar matrix), Raman (liquid), (19)F and (13)C NMR, and photoelectron (PES) spectroscopies; photoionization mass spectrometry (PIMS); and gas electron diffraction (GED). The conformational properties of ClF(2)CC(O)CN have been studied by joint application of vibrational spectroscopy, GED, and quantum chemical calculations. The existence of two conformers is detected in the gas and liquid phases, in which the C-Cl bond adopts gauche and syn orientations with respect to the C═O group. The computed enthalpy difference is in harmony with the experimental results of the gauche being more stable than the syn conformer by ΔH° = 1.3 kcal mol(-1) (MP2/cc-pVTZ). The valence electronic properties and the possible ionization and dissociation processes of the title compound are studied using the PES and PIMS. The experimental first vertical ionization energy of 12.0 eV corresponds to the ejection of an electron of the oxygen lone pairs. Taking into account the properties and broad applications of acyl cyanides, ClF(2)CC(O)CN is a promising new precursor in preparative chemistry. 相似文献
636.
We investigate the competition between glass formation and crystallization of open tetrahedral structures for particles with tetrahedral patchy interactions. We analyze the outcome of such competition as a function of the potential parameters. Specifically, we focus on the separate roles played by the interaction range and the angular width of the patches, and show that open crystal structures (cubic and hexagonal diamond and their stacking hybrids) spontaneously form when the angular width is smaller than about 30°. Evaluating the temperature and density dependence of the chemical potential of the fluid and of the crystal phases, we find that adjusting the patch width affects the fluid and crystal in different ways. As a result of the different scaling, the driving force for spontaneous self-assembly rapidly grows as the fluid is undercooled for small-width patches, while it only grows slowly for large-width patches, in which case crystallization is pre-empted by dynamic arrest into a network glass. 相似文献
637.
Escudero R Gómez-Gallego M Romano S Fernández I Gutiérrez-Alonso Á Sierra MA López-Rayo S Nadal P Lucena JJ 《Organic & biomolecular chemistry》2012,10(11):2272-2281
In this study we have obtained experimental evidence that confirms the high activity of aquo complexes III and IV towards the enzyme FCR, responsible for the reduction of Fe(III) to Fe(II) in the process of iron acquisition by plants. The in vivo FCR assays in roots of stressed cucumber plants have shown a higher efficiency of the family of complexes III and a striking structure-activity relationship with the nature of the substituent placed in a phenyl group far away from the metal center. The results obtained in this work demonstrate that all the aquo compounds tested interact efficiently with the enzyme FCR and hence constitute a new concept of iron chelates that could be of great use in agronomy. 相似文献
638.
Ciro Chiappini Ennio Tasciotti Dr. Jean R. Fakhoury Daniel Fine Dr. Lee Pullan Dr. Young‐Chung Wang Lianfeng Fu Xuewu Liu Dr. Mauro Ferrari Dr. 《Chemphyschem》2010,11(5):1029-1035
The use of mesoporous silicon particles for drug delivery has been widely explored thanks to their biodegradability and biocompatibility. The ability to tailor the physicochemical properties of porous silicon at the micro‐ and nanoscale confers versatility to this material. A method for the fabrication of highly reproducible, monodisperse, mesoporous silicon particles with controlled physical characteristics through electrochemical etching of patterned silicon trenches is presented. The particle size is tailored in the micrometer range and pore size in the nanometer range, the shape from tubular to discoidal to hemispherical, and the porosity from 46 to over 80 %. In addition, the properties of the porous matrix are correlated with the loading of model nanoparticles (quantum dots) and their three‐dimensional arrangement within the matrix is observed by transmission electron microscopy tomography. The methods developed in this study provide effective means to fabricate mesoporous silicon particles according to the principles of rational design for therapeutic vectors and to characterize the distribution of nanoparticles within the porous matrix. 相似文献
639.
A. Tumino C. Spitaleri S. Cherubini M. Gulino M. La Cognata L. Lamia R. G. Pizzone S. M. R. Puglia G. G. Rapisarda S. Romano M. L. Sergi R. Spartà 《Few-Body Systems》2013,54(5-6):745-753
With the introduction of the Trojan Horse Method, nuclear cross sections between charged particles at astrophysical energies can now be measured. Here the basic features of the method are recalled together with recent results relevant for Nuclear Astrophysics. New applications in connection with plasma physics and industrial energy production are discussed. 相似文献
640.
H. Chamati S. Romano 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(2):249-254
Generalized xy lattice spin models consist of
three-component unit vectors, associated with a D-dimensional
lattice (say
), parameterized by usual spherical
angles (θk,φk), and interacting via a ferromagnetic
potential restricted to nearest neighbours, of the form
here epsilon is a positive quantity setting energy and
temperature scales. The models were recently introduced,
and proven to support an ordering transition taking place
at finite temperature when D=3; in turn, this transition had been
investigated by different techniques for p=2,3,4, and found to
belong to the same universality class as the xy model (i.e. p=1).
More recently, it was rigorously proven that for
sufficiently large p the transition becomes first order. Here we present
a detailed analysis of the transitional properties of this
class of models for selected values of p.
For p=8 simulation results showed a second order phase
transition belonging to the xy class of universality;
they suggested tricritical behaviour for p=12,
and gave evidence of first-order transitions for both p=16 and p=20. 相似文献