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121.
Adriana CambónSilvia Barbosa Ana Rey-RicoEdgar B. Figueroa-Ochoa José F.A. SolteroSteven G. Yeates Carmen Alvarez-LorenzoAngel Concheiro Pablo Taboada Víctor Mosquera 《Journal of colloid and interface science》2012,387(1):275-284
Two new poly(ethylene oxide)-poly(styrene oxide) triblock copolymers (PEO-PSO-PEO) with optimized block lengths selected on the basis of previous studies were synthesized with the aim of achieving a maximal solubilization ability and a suitable sustained release, while keeping very low material expense and excellent aqueous copolymer solubility. The self-assembling and gelling properties of these copolymers were characterized by means of light scattering, fluorescence spectroscopy, transmission electron microscopy, and rheometry. Both copolymers formed spherical micelles (12-14 nm) at very low concentrations. At larger concentration (>25 wt%), copolymer solutions showed a rich phase behavior, with the appearance of two types of rheologically active (more viscous) fluids and of physical gels depending on solution temperature and concentration. The copolymer behaved notably different despite their relatively similar block lengths. The ability of the polymeric micellar solutions to solubilize the antifungal drug griseofulvin was evaluated and compared to that reported for other structurally-related block copolymers. Drug solubilization values up to 55 mg g−1 were achieved, which are greater than those obtained by previously analyzed poly(ethylene oxide)-poly(styrene oxide), poly(ethylene oxide)-poly(butylene oxide), and poly(ethylene oxide)-poly(propylene oxide) block copolymers. The results indicate that the selected SO/EO ratio and copolymer block lengths were optimal for simultaneously achieving low critical micelle concentrations (cmc) values and large drug encapsulation ability. The amount of drug released from the polymeric micelles was larger at pH 7.4 than at acidic conditions, although still sustained over 1 day. 相似文献
122.
Reinaldo Y. Morita Fábio S. Richart Ronilson V. Barbosa Marilda Munaro Juliana R. Kloss 《Macromolecular Symposia》2012,319(1):108-113
Summary: Disposal of petroleum-derived polymers is a growing global environmental problem of alarming proportions, which has increased interest in the use and production of biodegradable materials. In addition to biodegradation, investment in research and development in the nanotechnology area is also significant. This study evaluated the effect of incorporation of an organophilic nanoclay ammonium-free salt (Novaclay™) on the mechanical properties and biodegradation of a biodegradable polyester (Ecoflex®), according to ASTM G 160. Ecoflex with and without incorporated Novaclay was characterized before and after biodegradation in organically enriched soil for up to 180 days, by visual analysis, optical microscopy, weight loss, differential scanning calorimetry, dynamic mechanical analysis, mechanical testing, and scanning electron microscopy. The pure Ecoflex and the Ecoflex/Novaclay nanocomposite were partially biodegraded by the method used, and showed changes in their morphological and mechanical properties. 相似文献
123.
Anderson N. Mendes Isabela Hubber Mônica Siqueira Gleyce Moreno Barbosa Davyson de Lima Moreira Carla Holandino José Carlos Pinto Marcio Nele 《Macromolecular Symposia》2012,319(1):34-40
Summary: This work aimed to produce poly(methyl methacrylate) nanoparticles for use in drug encapsulation. The polymer nanoparticles were produced using miniemulsion polymerization technique. Monomer miniemulsion showed moderate stability and polymer average particle size was about 90 nm. PMMA nanoparticles were tested for toxicity in human leukemic cell strain K562 and they did not show any adverse effect on cell viability. Therefore, poly(methyl methacrylate) nanoparticles are suitable to encapsulate antitumor agents. 相似文献
124.
Grazziela P. Figueredo Nelson F. F. Ebecken Douglas A. Augusto Helio J. C. Barbosa 《Memetic Computing》2012,4(2):135-147
One issue in data classification problems is to find an optimal subset of instances to train a classifier. Training sets that
represent well the characteristics of each class have better chances to build a successful predictor. There are cases where
data are redundant or take large amounts of computing time in the learning process. To overcome this issue, instance selection
techniques have been proposed. These techniques remove examples from the data set so that classifiers are built faster and,
in some cases, with better accuracy. Some of these techniques are based on nearest neighbors, ordered removal, random sampling
and evolutionary methods. The weaknesses of these methods generally involve lack of accuracy, overfitting, lack of robustness
when the data set size increases and high complexity. This work proposes a simple and fast immune-inspired suppressive algorithm
for instance selection, called SeleSup. According to self-regulation mechanisms, those cells unable to neutralize danger tend
to disappear from the organism. Therefore, by analogy, data not relevant to the learning of a classifier are eliminated from
the training process. The proposed method was compared with three important instance selection algorithms on a number of data
sets. The experiments showed that our mechanism substantially reduces the data set size and is accurate and robust, specially
on larger data sets. 相似文献
125.
We report the measurement of the diffusion length, the Debye screening length and the quantum efficiency of photoelectron
generation in strongly light absorbing photorefractive Bi12TiO20 crystals, using fringe-locked running hologram experiments. The effective applied electric field inside the sample is also
computed and self-diffraction is considered. The novelty here, as compared to formerly reported experiments, is that the diffraction
efficiency is now measured simultaneously with the hologram speed v. From these data the above referred to photorefractive
and experimental parameters are obtained without the need for additional experiments. The method is used to analyze two photorefractive
Bi12TiO20 crystal samples, in different experimental conditions, using the 514.5 nm wavelength. The computed parameters are in good
agreement with the available information about these samples.
Received: 23 November 2000 / Published online: 21 March 2001 相似文献
126.
V Sanz-Nebot I Toro R Bergés R Ventura J Segura J Barbosa 《Journal of mass spectrometry : JMS》2001,36(6):652-657
The aim of this work was to develop a method for the characterization and determination of diuretics in human urine samples by liquid chromatography (LC) coupled to pneumatically assisted electrospray ionization (ES) mass spectrometry (MS). The diuretics studied were substances forbidden by the IOC such as trichlormethiazide, furosemide, canrenoic acid, benzthiazide, bendroflumethiazide, bumetanide, etacrynic acid and spironolactone. For this purpose, the operational parameters of electrospray, such as counter electrode voltage, capillary voltage, sample cone voltage and source temperature, were optimized in order to obtain the best signal stability and the highest sensitivity for the greatest number of diuretic agents. The optimized separation method was successfully coupled with the MS system to analyze the above-mentioned diuretics extracted from spiked urine samples by a liquid extraction and clean-up procedure at basic pH, using ethyl acetate as solvent and the salting-out effect (NaCl). The mass spectra obtained provide adequate information for identification purposes. Positive urine samples obtained from athletes were also analyzed. The presence of these substances in human urine was confirmed by this method, making LC/ES-MS an analytical tool to be considered in the area of antidoping control. 相似文献
127.
Éder C. Lima Francisco J. Krug Fernando Barbosa Jr Carlos E. C. Magalhães 《Mikrochimica acta》2000,134(1-2):113-121
A tungsten-rhodium coating on the integrated platform of a transversely heated graphite atomiser (THGA) was used as a permanent
chemical modifier for the determination of Cd in sediment slurries by electrothermal atomic absorption spectrometry. Slurries
were ultrasonicated during 20 s before being delivered to the previously W-Rh treated platform. The permanent W-Rh modifier
remains stable by approximately 250 measurements when 20 μl of slurries containing up to 1.0% m/v are delivered into the atomiser.
In addition, the permanent modifier increases the tube lifetime up to 720 analytical firings. Also, when the W-Rh permanent
modifier was employed, there was less variation of the slope of the analytical curves during the total atomiser lifetime,
resulting in a decreased need of re-calibration during routine analysis, increasing the sample throughput.
The atomiser lifetime was limited to the THGA wall durability, because the W-Rh treated platform was intact after more than
720 analytical firings.
Detection limits based on integrated absorbance for 1.0% m/v slurries were 1.5 ng g−1 Cd for 250 μg W +200 μg Rh permanent modifier and 11.5 ng−1 Cd for 5 μg Pd +3 μg Mg(NO3)2.
Results for the determination of cadmium in sediment slurries using the W-Rh permanent modifier were in agreement with those
obtained with dissolved sample solutions by using Pd + Mg(NO3)2, since no statistical differences were found by the paired t-test at the 99% level.
Received September 6, 1999. Revision December 1, 1999. 相似文献
128.
Direct in vivo measurements of neurometabolic markers in the brain with high spatio-temporal resolution, sensitivity, and selectivity is highly important to understand neurometabolism. Electrochemical biosensors based on microelectrodes are very attractive analytical tools for continuous monitoring of neurometabolic markers, such as lactate and glucose in the brain extracellular space at resting and following neuronal activation. Here, we assess the merits of a platinized carbon fiber microelectrode (CFM/Pt) as a sensing platform for developing enzyme oxidase-based microbiosensors to measure extracellular lactate in the brain. Lactate oxidase was immobilized on the CFM/Pt surface by crosslinking with glutaraldehyde. The CFM/Pt-based lactate microbiosensor exhibited high sensitivity and selectivity, good operational stability, and low dependence on oxygen, temperature, and pH. An array consisting of a glucose and lactate microbiosensors, including a null sensor, was used for concurrent measurement of both neurometabolic substrates in vivo in the anesthetized rat brain. Rapid changes of lactate and glucose were observed in the cortex and hippocampus in response to local glucose and lactate application and upon insulin-induced fluctuations of systemic glucose. Overall, these results indicate that microbiosensors are a valuable tool to investigate neurometabolism and to better understand the role of major neurometabolic markers, such as lactate and glucose. 相似文献
129.
R. Aldrovandi V. C. de Andrade A. L. Barbosa J. G. Pereira 《International Journal of Theoretical Physics》2003,42(12):2955-2970
Applied to the electroweak interactions, the theory of Lie algebra extensions suggests a mechanism by which the boson masses are generated without resource to spontaneous symmetry breaking. It starts from a gauge theory without any additional scalar field. All the couplings predicted by the Weinberg–Salam theory are present, and a few others which are nevertheless consistent within the model. 相似文献
130.
A series of commercial indicators in N,N-dimethylformamide has been established. Their chromaticity coordinates, transition pH ranges, pH of maximum colour change, optimum concentration for titration, quality of colour change and the effect of ionic strength have been determined. A variety of acids and their mixtures have been titrated to test the indicators. 相似文献