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951.
Biscarini F Cavallini M Leigh DA León S Teat SJ Wong JK Zerbetto F 《Journal of the American Chemical Society》2002,124(2):225-233
The first statistical analyses of the X-ray crystal structures of mechanically interlocked molecular architectures, the first molecular mechanics-based solid-state calculations on such structures and atomic force microscopy (AFM) experiments are used in combination to predict and test which types of benzylic amide macrocycle-containing rotaxanes possess mobile components in the crystalline phase and thus could form the basis of solid-state devices that function through mechanical motion at the molecular level. The statistical studies and calculations show that crystals formed by rotaxanes possess similarities and unanticipated differences with respect to the crystal packing of noninterlocked molecules. Trends in the rotaxane series correlate quantities related to crystal packing, molecular size, stoichiometry, and H-bonding. In accordance with the findings of Gavezzotti et al. for conventional molecular architectures, a principal component analysis (PCA) showed that three vectors related to the size, packing parameters, and stoichiometry are sufficient to describe the crystal properties of benzylic amide macrocycle-containing rotaxanes. When hydrogen bond-related quantities are included in a second PCA, they combine with the size and the stoichiometry vectors but not with packing-related parameters, indicating that the intramolecular "saturation" of the H-bonds (between the interlocked components) takes precedence over crystal assembly (i.e., intermolecular packing) in these systems. However, cluster analyses also suggest a major role for the energy of interaction between the macrocycle and its crystal environment. The identification of such a "privileged" interaction is of fundamental importance to the development of rotaxanes with in-crystal mobility of one or more of their interlocked components, a prerequisite for the exploitation of molecular level mechanical motion in the solid state. The set of trends found, together with the calculated energies, was used to propose guidelines for which benzylic amide macrocycle-containing rotaxanes are best suited to become building blocks for systems with mobile submolecular units in the crystalline phase. An experimental test of the predictive power of such guidelines was carried out using AFM on a rotaxane and its thread, identified by the study as a promising candidate for solid-state mobility. Intuitively, the rotaxane should be less mobile in the solid state since it has multiple sets of both hydrogen bond donors and acceptors that can form strong inter- and intramolecular H-bonds. Conversely, the thread has no hydrogen bond donors and cannot form such bonds. The AFM experiments, however, confirm the statistical analysis prediction that the rotaxane is considerably more mobile in the solid than the thread. 相似文献
952.
This paper is concerned with the dynamics of water around a small globular protein. Dipolar second-rank relaxation time and diffusion properties of surface water were computed by extensive molecular dynamics simulations of lysozyme in water which lasted a total of 28 ns. Our results indicate that the rotational relaxation of water in the vicinity of lysozyme is 3-7 times slower than that in the bulk depending on how the hydration shell is defined in the calculation. We have also verified that the dynamics of water translational diffusion in the vicinity of lysozyme have retardations similar to rotational relaxation. This is a common assumption in nuclear magnetic relaxation dispersion (NMRD) studies to derive residence times. In contrast to bulk water dynamics, surface water is in a dispersive diffusion regime or subdiffusion. Very good agreement of dipolar second-rank relaxation time with NMRD estimates is obtained by using appropriate dimensions of the hydration shell. Although our computed second-rank dipolar retardations are independent of the water model, SPC/E describes more realistically the time scale of the water dynamics around lysozyme than does TIP3P. 相似文献
953.
Fabio de S. Dias Walter N. L. dos Santos Antônio C. S. Costa Bernhard Welz Maria Goreti R. Vale Sérgio L. C. Ferreira 《Mikrochimica acta》2007,158(3-4):321-326
A direct method is proposed for the determination of lead in naphtha and petroleum condensate by electrothermal atomic absorption
spectrometry (ET AAS) using palladium as a permanent modifier. The procedure includes the dilution of 3 mL of sample (naphtha
or petroleum condensate) to a final volume of 10 mL with xylene, and direct injection of 30 μL of this solution into the graphite
furnace. The optimization of the instrumental conditions was performed using multivariate techniques. Firstly, a 23 full factorial design was performed for preliminary evaluation of the factors: pyrolysis time, pyrolysis temperature and
atomization temperature. This experiment showed that in the studied levels only the factors pyrolysis time and atomization
temperature were significant. Then, a 32 full factorial design was performed for the determination of the critical conditions of these variables. The method allows
the determination of lead using the standard calibration technique with a calibration curve from 2.6 to 30 μg L−1 (correlation coefficient higher than 0.998). A limit of detection (3σ) of 0.8 μg L−1 and a characteristic mass of 35 pg were obtained in the presence of palladium as modifier. The precision expressed as relative
standard deviation (RSD) was 1.5 and 0.8% for lead concentrations of 3.0 and 30 μg L−1 (n = 10). Recovery studies demonstrate that lead can be determined in naphtha and petroleum condensate using calibration with
organic standard solutions. This method was applied for the determination of lead in three petroleum condensate and two naphtha
samples. The concentrations found for the petroleum condensate was between 2.7 and 5.7 μg L−1, while the naphtha samples did not contain any detectable lead. 相似文献
954.
We propose a model to investigate the dynamics of fashion traits purely driven by social interactions. We assume that people adapt their style to maximize social success, and we describe the interaction as a repeated group game in which the payoffs reflect the social norms dictated by fashion. On one hand, the tendency to imitate the trendy stereotypes opposed to the tendency to diverge from them to proclaim identity; on the other hand, the exploitation of sex appeal for dating success opposed to the moral principles of the society. These opposing forces promote diversity in fashion traits, as predicted by the modeling framework of adaptive dynamics. Our results link the so-called horizontal dynamics—the primary driver of fashion evolution, compared with the vertical dynamics accounting for interclass and economic drivers—to style variety. 相似文献
955.
M. R. da Silva L. V. A. Scalvi V. S. L. Neto L. H. Dall’Antonia 《Journal of Solid State Electrochemistry》2016,20(6):1527-1538
Resistive monoclinic bismuth vanadate (BiVO4) nanocrystals in the form of thin films were obtained by the solution combustion synthesis coupled with the dip-coating deposition process. The structure, morphology, and optical properties of BiVO4 nanocrystals were characterized by means of x-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-Vis spectroscopy. The photoelectrochemical properties were obtained by cyclic voltammetry and chronoamperometry techniques in potassium chloride (KCl) electrolyte solution under distinct visible light sources irradiation condition. Under blue InGaN light emitting diode (LED) irradiation, the electrode has a better efficiency, faster response time (260 ms), and faster decay time (65 ms), when compared with the irradiation by dichroic lamp. Besides, the photocurrent density (j ph) is approximately 39 times higher than j ph obtained under dichroic lamp. The performance analysis based on the methylene blue degradation reaction has shown that the BiVO4 material has higher electroactivity under InGaN LED irradiation condition, with estimated k obs value of 200 × 10?4 min?1, which is a little higher than the value obtained with dichroic lamp illumination. In the dark condition, the BiVO4 presented much lower photocatalytic activity. 相似文献
956.
Fabio Comin 《Synchrotron Radiation News》2016,29(6)
In 2004, the aim of the X-Tip European Project was to pursue the integration of scanning probe microscopy techniques into synchrotron radiation beamlines to provide new opportunities to both fields of microscopy and spectroscopy. Given the limited X-ray focusing capabilities at that time and the difficulty of alignment, the first emphasis was given to the possibility of exploring the morphology of the sample surface within the area illuminated by the X-rays, selecting an area of interest and, using the scanning tip, aligning it into the X-ray beam and extract by total electron yield spectroscopic information, with lateral resolutions ideally defined by tip dimensions. 相似文献
957.
958.
Filippo Maggi Fabrizio Papa Stefano Dall’Acqua Marcello Nicoletti 《Natural product research》2016,30(7):806-813
Ferula communis is a showy herbaceous plant typical of the Mediterranean area where it is used as a traditional medicine. The plant is a source of bioactive compounds such as daucane sesquiterpenes and prenylated coumarins. In Italy, most of phytochemical studies focused on Sardinian populations where poisonous and nonpoisonous chemotypes were found, while investigations on peninsular populations are scarce. In this work, we report the chemical characterisation of the essential oils obtained from different parts of F. communis growing in central Italy. The chemical profiles of the plant parts, as detected by GC-FID and GC-MS, were different from each other and from those reported in insular populations. Notably, α-pinene (10.5%), γ-terpinene (7.6%) and hedycariol (8.4%) were the major volatile constituents in flowers; α-pinene (55.9%), β-pinene (16.8%) and myrcene (5.9%) in fruits; β-eudesmol (12.1%), α-eudesmol (12.1%) and hedycariol (10.3%) in leaves; (E)-β-farnesene (9.5%), β-cubebene (8.2%) and (E)-caryophyllene (7.2%) in roots. The volatile profiles detected did not allow to classify the investigated central Italy population into the poisonous and nonpoisonous chemotypes previously described in Sardinia. 相似文献
959.
Characterization of crude oil biomarkers using comprehensive two‐dimensional gas chromatography coupled to tandem mass spectrometry 下载免费PDF全文
Noroska Gabriela Salazar Mogollón Paloma Santana Prata Jadson Zeni dos Reis Eugênio Vaz dos Santos Neto Fabio Augusto 《Journal of separation science》2016,39(17):3384-3391
Oil samples from Recôncavo basin (NE Brazil), previously analyzed by traditional techniques such as gas chromatography coupled to tandem mass spectrometry, were evaluated using comprehensive two‐dimensional gas chromatography coupled to quadrupole mass spectrometry and comprehensive two‐dimensional gas chromatography coupled to tandem mass spectrometry along with simplified methods of samples preparation to evaluate the differences and advantages of these analytical techniques to better understand the development of the organic matter in this basin without altering the normal distribution of the compounds in the samples. As a result, the geochemical parameters calculated by comprehensive two‐dimensional gas chromatography coupled to tandem mass spectrometry described better the origin, maturity, and biodegradation of both samples probably by increased selectivity, resolution, and sensitivity inherent of the multidimensional technique. Additionally, the detection of the compounds such as, the C(14α‐) homo‐26‐nor‐17α‐hopane series, diamoretanes, nor‐spergulanes, C19–C26 A‐nor‐steranes and 4α‐methylsteranes resolved and detected by comprehensive two‐dimensional gas chromatography coupled to tandem mass spectrometry were key to classify and differentiate these lacustrine samples according to their maturity and deposition conditions. 相似文献
960.
In Fragnelli et al. (TOP 22:892–933, 2014), we considered a bankruptcy problem with the additional constraint that the estate has to be assigned in integer unities, allowing for non-integer claims. We dealt with the question of existence and uniqueness of a solution and proposed the “box method” that is strongly oriented towards the constrained equal losses solution; uniqueness may be guaranteed by introducing a ranking on the claimants. Here, we introduce a solution oriented towards the constrained equal awards solution and give three characterizations and a simple method for determining the solution. 相似文献