全文获取类型
收费全文 | 336篇 |
免费 | 23篇 |
国内免费 | 2篇 |
专业分类
化学 | 266篇 |
晶体学 | 1篇 |
力学 | 10篇 |
数学 | 33篇 |
物理学 | 51篇 |
出版年
2024年 | 2篇 |
2023年 | 6篇 |
2022年 | 17篇 |
2021年 | 15篇 |
2020年 | 18篇 |
2019年 | 18篇 |
2018年 | 9篇 |
2017年 | 13篇 |
2016年 | 27篇 |
2015年 | 23篇 |
2014年 | 30篇 |
2013年 | 31篇 |
2012年 | 19篇 |
2011年 | 25篇 |
2010年 | 18篇 |
2009年 | 8篇 |
2008年 | 22篇 |
2007年 | 13篇 |
2006年 | 16篇 |
2005年 | 17篇 |
2004年 | 8篇 |
2003年 | 2篇 |
2002年 | 2篇 |
1982年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有361条查询结果,搜索用时 15 毫秒
81.
Omar Clo Neves Pereira Tiago Peres da Silva Suguiura Anaih Pastana Pereira Altair Bertonha Isolde Previdelli 《Natural Resource Modeling》2019,32(2)
In this study, we evaluated the lettuce accumulated evapotranspiration (ET) across four levels of irrigation, using a nonlinear mixed‐effects model. The plants were grown in protected environments and monitored over 23 consecutive days. When the moisture of the substrate in the vessels reached 50% of their maximum retention capacity, the water levels were elevated according to four treatments: , , , and . The model appeared to provide a good fit to the data and showed that the estimates of the maximum amount of accumulated ET were similar for the three treatments with soil water deficit and lower for . The results of the study supported the idea that optimization of the ET of lettuce plants could be achieved through irrigation with deficit, also indicating that the economical use of water was the most efficient way to boost agricultural production. Recommendations for resource managers
- The continued growth of the world population will result in a decrease of quality and availability of water and also an increase in demand for food. Therefore, sustainability will depend on high agricultural productivity with rational use of water.
- Considered the most efficient technology for boosting agricultural productivity, irrigation is also the largest water consumer in the world. With any kind of irrigation in the vegetable production area, the water intake for the plants must be treated with great caution.
- Both a lack or excess in water can decrease plant productivity. The amount of water available in the soil should be enough to maximize production. It is shown that high levels of irrigation are not necessary for this.
- It is important to balance the amount of irrigated water for an optimal level, in order that the production has its the production is maximized and valuable water resources are not wasted.
82.
Tiago C. Adorno Alexander I. Breev Antonio J. D. Farias Jr. Dmitri M. Gitman 《Annalen der Physik》2023,535(7):2300118
The problem of the electromagnetic radiation produced by charge distributions in the framework of a semiclassical approach proposed in the work by Bagrov, Gitman, Shishmarev, and Farias Jr. [J. Synchrotron Rad. 27 , 902–911 (2020)] is addressed here. In this approach, currents, generating the radiation are considered classically, while the quantum nature of the radiation is kept exactly. Quantum states of the electromagnetic field are solutions of Schrödinger's equation, and relevant quantities to the problem are evaluated with the aid of transition probabilities. This construction allows us to introduce the quantum transition time in physical quantities and assess its role in radiation problems by classical currents. Radiated electromagnetic energies are studied in detail and a definition for the rate at which radiation is emitted from sources is presented. In calculating the total energy and rate radiated by a pointlike charged particle accelerated by a constant and uniform electric field, it is discovered that these results are compatible with results obtained by other authors in the framework of the classical radiation theory under an appropriate limit. Numerical and asymptotic analyses of the results are also performed. 相似文献
83.
Kirby AJ Davies JE Brandão TA da Silva PF Rocha WR Nome F 《Journal of the American Chemical Society》2006,128(38):12374-12375
Ammonia oxide is revealed as a stable molecule in a crystal structure and as a likely reactive species in many reactions of hydroxylamine. 相似文献
84.
The characterization and control of the phase of broadband femtosecond pulses in nonlinear microscopy are successfully demonstrated with a collinear configuration of spectral shear interferometry for direct electric field reconstruction (SPIDER). A femtosecond-pulse shaper is used as a dispersionless interferometer for the measurement of the spectral phase and to actively compress a broadband supercontinuum from a photonic crystal fiber. This allows in situ online phase management and enables the application of quantum control spectroscopy in microenvironments. 相似文献
85.
Rodrigues T dos Santos CG Riposati A Barbosa LR Di Mascio P Itri R Baptista MS Nascimento OR Nantes IL 《The journal of physical chemistry. B》2006,110(25):12257-12265
This work characterizes, for the first time, the photochemical behavior of the antipsychotic drugs thioridazine (TR), trifluoperazine (TFP), and fluphenazine (FP) influenced by the aggregation state of the molecules. Samples of monomeric and aggregated forms of phenothiazines were submitted to 20 min of irradiation at 254 nm for intervals of 1, 5, 10, 15, 20, or 25 days. In high phenothiazine concentrations, the irradiation led to the appearance of absorbance bands in the visible region peaking at 633 nm for TR and 509 nm for FP and TFP. In the dark, at room temperature and at 4 degrees C, these bands disappeared, after approximately 15 and approximately 60 min, respectively, but reappeared after a new irradiation session. These visible bands were assigned to stable cation radicals that were characterized by direct EPR measurements and by flash photolysis. Photogenerated stable cation radicals in the phenothiazine aggregates at room temperature are formed probably due to the stacking of the thiazine phenyl moieties. For the monomeric forms of phenothiazines, the spectral changes observed during the irradiation suggested the formation of sulfoxide and hydroxylated derivates. Oxidized derivates were detected by mass spectrometry of the aggregated forms of phenothiazines (>100 microM) only in the samples irradiated for more than 20 days. In contrast, monomeric phenothiazines were totally converted to the oxidized forms after 20 min of irradiation. Surface tension measurements of phenothiazines revealed that, in concentrations above 100 microM, the drugs formed aggregates. In the case of TR, small-angle X-ray scattering measurements indicated that this compound forms large lamellar-like aggregates in aqueous solutions. 相似文献
86.
Rafaela Osuna-Gómez Tiago Mendonca da Costa Beatriz Hernández-Jiménez Gabriel Ruiz-Garzón 《Mathematical Methods in the Applied Sciences》2023,46(2):2319-2333
This paper presents necessary and sufficient conditions for generalized Hukuhara differentiability of interval-valued functions and counterexamples of some equivalences previously presented in the literature, for which important results are based on. Moreover, applications of interval generalized Hukuhara differentiability are presented. 相似文献
87.
Nonlinear Dynamics - A “circular orbital forcing” makes a chosen point on a rigid body follow a circular motion while the body spins freely around that point. We investigate this... 相似文献
88.
Natalia Canhete de Moraes Eiva Natiele Tiago da Silva Jacqueline Marques Petroni Valdir Souza Ferreira Bruno Gabriel Lucca 《Electrophoresis》2020,41(5-6):278-286
This paper describes the development of a novel, simple, and inexpensive electrochemical device containing an integrated and disposable three-electrode system for detection. The base of this platform consists on a PDMS structure containing microchannels which were prototyped using 3D-printed molds. Pencil graphite leads were inserted into these microchannels and utilized as working, counter and reference electrodes in a novel design. Morphological analysis and electrochemical experiments with benchmark redox probes were carried out in order to evaluate the performance and characterize the miniaturized device proposed. Even using inexpensive materials and a simple fabrication protocol, the electrochemical platform developed provided good repeatability and reproducibility over a low cost (ca. $2 per device), acceptable lifetime (ca. 250 voltammetric runs) and extremely reduced consumption of samples and reagents (order of µL). As proof of concept, the analytical feasibility of the platform was investigated through the simultaneous determination of dopamine (DOPA) and acetaminophen (AC). The two analytes showed linear dependence on the concentration range from 1 to 15 µM and the LODs achieved were 0.21 µM for DOPA and 0.29 µM for AC. Moreover, the platform was successfully applied on the determination of DOPA and AC in spiked blood serum and urine samples. The results obtained with the device described here were better than some reports in literature that use more costly electrodic materials and complex modification steps for the detection of the same analytes. 相似文献
89.
Nonlinear Dynamics - This paper presents an adaptive smooth controller for a class of nonlinear dynamical systems in the presence of bounded uncertainties with unknown bounds. Motivated by the... 相似文献
90.