全文获取类型
收费全文 | 1173篇 |
免费 | 46篇 |
国内免费 | 4篇 |
专业分类
化学 | 722篇 |
晶体学 | 9篇 |
力学 | 22篇 |
数学 | 166篇 |
物理学 | 304篇 |
出版年
2023年 | 10篇 |
2022年 | 45篇 |
2021年 | 37篇 |
2020年 | 27篇 |
2019年 | 36篇 |
2018年 | 26篇 |
2017年 | 24篇 |
2016年 | 50篇 |
2015年 | 30篇 |
2014年 | 39篇 |
2013年 | 64篇 |
2012年 | 78篇 |
2011年 | 79篇 |
2010年 | 65篇 |
2009年 | 46篇 |
2008年 | 63篇 |
2007年 | 63篇 |
2006年 | 56篇 |
2005年 | 56篇 |
2004年 | 36篇 |
2003年 | 34篇 |
2002年 | 24篇 |
2001年 | 25篇 |
2000年 | 25篇 |
1999年 | 9篇 |
1998年 | 12篇 |
1997年 | 7篇 |
1996年 | 18篇 |
1995年 | 11篇 |
1994年 | 12篇 |
1993年 | 15篇 |
1992年 | 15篇 |
1991年 | 11篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1984年 | 4篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1973年 | 2篇 |
1971年 | 3篇 |
1965年 | 2篇 |
排序方式: 共有1223条查询结果,搜索用时 31 毫秒
91.
Rocio Díez Azofra Luis A. Sarabia Maria Cruz Ortiz 《Analytical and bioanalytical chemistry》2010,396(2):923-935
The objective of this work is to optimize a solid-phase extraction procedure for the simultaneous determination of sulfadiazine,
sulfamerazine, and sulfamethazine in milk by fluorimetric detection. For this task, an alternative strategy is employed, which
allows one to reduce noticeably the number of experiments without losing the quality of the estimations. It consists of the
use of a D-optimal design together with PARAFAC decomposition for the calculation of the response in the experimental design.
Effects of amount of cartridge sorbent, kind of milk, volume of conditioning solutions, kind of wash and elution, and kind
of mixture of sulfonamides have been evaluated, for maximizing sulfonamide mean recovery and minimizing its standard deviation.
Since milk without sulfonamides may give some matrix effect over the fluorescence signal, its behavior has also been studied.
Optimal conditions have been selected where the ratio between sulfonamide recovery and milk without sulfonamides was the highest,
which are 500 mg of cartridge sorbent, acid wash, and elution and 3 mL of conditioning solutions. The type of milk and mixture
of sulfonamides not significant. This makes the procedure suitable for the combined determination of sulfadiazine, sulfamerazine,
and sulfamethazine in any kind of milk. Finally, an experimental procedure is proposed, obtaining a sulfonamide mean recovery
equal to 68.5% with values of standard deviation between 7 and 8 μg kg−1. 相似文献
92.
Sonia Herranz Markéta Bocková María Dolores Marazuela Ji?í Homola María Cruz Moreno-Bondi 《Analytical and bioanalytical chemistry》2010,398(6):2625-2634
A surface plasmon resonance (SPR) biosensor for the detection of microcystins (MCs) in drinking water has been developed.
Several assay formats have been evaluated. The selected format is based on a competitive inhibition assay, in which microcystin-LR
(MCLR) has been covalently immobilized onto the surface of an SPR chip functionalized with a self-assembled monolayer. The
influence of several factors affecting sensor performance, such as the nature and concentration of the antibody, the composition
of the carrier buffer, and the blocking and regeneration solutions, has been evaluated. The optimized SPR biosensor provides
an IC50 0.67 ± 0.09 μg L−1, a detection limit of 73 ± 8 ng L−1, and a dynamic range from 0.2 to 2.0 μg L−1 for MCLR. Cross-reactivity to other related MCs, such as microcystin-RR (88%) and microcystin-YR (94%), has also been measured.
The SPR biosensor can perform four simultaneous determinations in 60 min, and each SPR chip can be reused for at least 40
assay–regeneration cycles without significant binding capacity loss. The biosensor has been successfully applied to the direct
analysis of MCLR in drinking water samples, below the provisional guideline value of 1 μg L−1 established by the World Health Organization for drinking water. 相似文献
93.
WO3 nanoparticles were synthesized by the precipitation method varying the time employed in the formation of their precursor in aqueous media and the calcination temperature. The WO3 crystallization process and morphology of the synthesized samples were followed by the XRD, TEM and SEM techniques. The effects of the calcination temperature on the surface area and optical properties of the WO3 nanoparticles were also investigated. Nanoparticles with morphologies such as square and rectangular plates and ovoid forms were observed for the different experimental conditions. WO3 nanoparticles with different morphologies were tested for the photocatalytic degradation of organic dyes. In general, the photocatalysts showed a capacity to bleach the dye solution in the following sequence: indigo carmine (IC) > rhodamine B (rhB) > congo red (CR). The extent of mineralization was determined by means of total organic carbon (TOC) measurements, which showed a satisfactory TOC reduction (93%, within 75 h) only for IC. This value was even better than the one concerning the P-25 Degussa reference. 相似文献
94.
Ladie Kimberly De La Cruz Xiaoxiao Yang Anna Menshikh Maya Brewer Wen Lu Minjia Wang Siming Wang Xingyue Ji Alyssa Cachuela Haichun Yang David Gallo Chalet Tan Leo Otterbein Mark de Caestecker Binghe Wang 《Chemical science》2021,12(31):10649
Carbon monoxide as an endogenous signaling molecule exhibits pharmacological efficacy in various animal models of organ injury. To address the difficulty in using CO gas as a therapeutic agent for widespread applications, we are interested in developing CO prodrugs through bioreversible caging of CO in an organic compound. Specifically, we have explored the decarboxylation–decarbonylation chemistry of 1,2-dicarbonyl compounds. Examination and optimization of factors favorable for maximal CO release under physiological conditions led to organic CO prodrugs using non-calorific sweeteners as leaving groups attached to the 1,2-dicarbonyl core. Attaching a leaving group with appropriate properties promotes the desired hydrolysis–decarboxylation–decarbonylation sequence of reactions that leads to CO generation. One such CO prodrug was selected to recapitulate the anti-inflammatory effects of CO against LPS-induced TNF-α production in cell culture studies. Oral administration in mice elevated COHb levels to the safe and efficacious levels established in various preclinical and clinical studies. Furthermore, its pharmacological efficacy was demonstrated in mouse models of acute kidney injury. These studies demonstrate the potential of these prodrugs with benign carriers as orally active CO-based therapeutics. This represents the very first example of orally active organic CO prodrugs with a benign carrier that is an FDA-approved sweetener with demonstrated safety profiles in vivo.1,2-Dicarbonyl compounds with FDA-approved sweeteners as leaving groups deliver CO for protection against acute kidney injury in mice. 相似文献
95.
Villegas I. L. Cuadrado-Laborde C. Díez A. Cruz J. L. Martínez-Gámez M. A. Andrés M. V. 《Laser Physics》2011,21(9):1650-1655
We show an actively Q-switched ytterbium-doped strictly all-fiber laser. Cavity loss modulation is achieved in a tapered optical
fiber by core-to-cladding mode-coupling induced by travelling flexural acoustic waves. When the acoustical signal is switched-off,
the optical power losses within the cavity are reduced, and then a laser pulse is emitted. Trains of Q-switched pulses were
successfully obtained at repetition rates in the range 1–10 kHz, with pump powers between 59 and 88 mW, at the optical wavelength
of 1064.1 nm. Best results were for laser pulses of 118 mW peak power, 1.8 μs of time width, with a pump power of 79 mW, at
7 kHz repetition rate. 相似文献
96.
W. T. Cruz A. R. Gomes C. A. S. Almeida 《The European Physical Journal C - Particles and Fields》2011,71(11):1790
In this work we investigate the issue of fermion localization and resonances in (4,1)-deformed branes constructed with one
scalar field coupled with gravity. Such models provide us branes with internal structures that turns the gravitational interaction
more effective for fermions aside the brane, increasing their lifetime. The coupling between the scalar field and spinors
is a necessary condition for fermions to be localized on such branes. After performing a chiral decomposition of the five-dimensional
spinor we found resonances with both chiralities. The correspondence between the spectra for left and right chirality is guaranteed
and Dirac fermions are realized on the brane. 相似文献
97.
Francisco Eduardo de Sousa Filho João Hermínio da Silva Antônio Álamo Feitosa Saraiva Deyvid Dennys S. Brito Bartolomeu Cruz Viana Bruno Tavares de Oliveira Abagaro Paulo de Tarso Cavalcante Freire 《Brazilian Journal of Physics》2011,41(4-6):275-280
X-ray diffraction was combined with X-ray energy-dispersion, Fourier-transform infrared, and Raman spectroscopies to study the fossilization of a Cretaceous specimen of the plant Brachyphyllum castilhoi, a fossil from the Ipubi Formation, in the Araripe Sedimentary Basin, Northeastern Brazil. Among the possible fossilization processes, which could involve pyrite, silicon oxide, calcium oxide, or other minerals, we were able to single out pyritization as the central mechanism producing the fossil, more than 100 million years ago. In addition to expanding the knowledge of the Ipubi Formation, this study shows that, when combined with other experimental techniques, Raman spectroscopy is a valuable tool at the paleontologist’s disposal. 相似文献
98.
A. Ruiz De la Cruz A. Ferrer J. del Hoyo J. Siegel J. Solis 《Applied Physics A: Materials Science & Processing》2011,104(2):687-693
In this work, we report a model for accurately calculating the focal volumes corresponding to astigmatic elliptical beams
used in fs-laser waveguide writing. The model is based on the use of the ABCD matrix formalism for the propagation of a Gaussian beam. The code includes the effects of propagation on the astigmatic elliptical
beam, and the effects of beam truncation and diffraction at the entrance pupil of the focusing objective due to beam clipping
when overfilling the pupil. The results predict that for a given astigmatism value and propagation distance it is possible
to efficiently suppress the astigmatic focus closer to the surface. This explains previous experimental results where single
structure waveguides with controllable aspect-ratio were fabricated using astigmatic-elliptical beams. Furthermore, we investigate
the respective roles of astigmatism and beam propagation, as well as the strong impact of truncation and diffraction effects
caused by clipping the beam at the pupil of the focusing optics. Finally, based on the results from our model, we present
some practical considerations in terms of beam propagation and phase wrapping constraints. 相似文献
99.
Carla Cruz Maria Irene Falcão Helmuth R. Malonek 《Mathematical Methods in the Applied Sciences》2014,37(12):1723-1735
The use of a non‐commutative algebra in hypercomplex function theory requires a large variety of different representations of polynomials suitably adapted to the solution of different concrete problems. Naturally arises the question of their relationships and the advantages or disadvantages of different types of polynomials. In this sense, the present paper investigates the intrinsic relationship between two different types of monogenic Appell polynomials. Several authors payed attention to the construction of complete sets of monogenic Appell polynomials, orthogonal with respect to a certain inner product, and used them advantageously for the study of problems in 3D‐elasticity and other problems. Our goal is to show that, as consequence of the binomial nature of those generalized Appell polynomials, their inner structure is determined by interesting combinatorial relations in which the central binomial coefficients play a special role. As a byproduct of own interest, a Riordan–Sofo type binomial identity is also proved. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
100.
J. Y. Bello Cruz R. Díaz Millán 《Journal of Optimization Theory and Applications》2014,161(3):728-737
We propose a direct splitting method for solving a nonsmooth variational inequality in Hilbert spaces. The weak convergence is established when the operator is the sum of two point-to-set and monotone operators. The proposed method is a natural extension of the incremental subgradient method for nondifferentiable optimization, which strongly explores the structure of the operator using projected subgradient-like techniques. The advantage of our method is that any nontrivial subproblem must be solved, like the evaluation of the resolvent operator. The necessity to compute proximal iterations is the main difficulty of other schemes for solving this kind of problem. 相似文献