全文获取类型
收费全文 | 1973篇 |
免费 | 79篇 |
国内免费 | 62篇 |
专业分类
化学 | 332篇 |
晶体学 | 14篇 |
力学 | 345篇 |
综合类 | 2篇 |
数学 | 77篇 |
物理学 | 1344篇 |
出版年
2024年 | 4篇 |
2023年 | 29篇 |
2022年 | 20篇 |
2021年 | 45篇 |
2020年 | 36篇 |
2019年 | 23篇 |
2018年 | 29篇 |
2017年 | 30篇 |
2016年 | 37篇 |
2015年 | 50篇 |
2014年 | 46篇 |
2013年 | 267篇 |
2012年 | 86篇 |
2011年 | 136篇 |
2010年 | 73篇 |
2009年 | 113篇 |
2008年 | 116篇 |
2007年 | 99篇 |
2006年 | 92篇 |
2005年 | 74篇 |
2004年 | 55篇 |
2003年 | 58篇 |
2002年 | 57篇 |
2001年 | 54篇 |
2000年 | 61篇 |
1999年 | 39篇 |
1998年 | 53篇 |
1997年 | 15篇 |
1996年 | 21篇 |
1995年 | 21篇 |
1994年 | 29篇 |
1993年 | 21篇 |
1992年 | 21篇 |
1991年 | 15篇 |
1990年 | 16篇 |
1989年 | 22篇 |
1988年 | 27篇 |
1987年 | 21篇 |
1986年 | 12篇 |
1985年 | 14篇 |
1984年 | 16篇 |
1982年 | 7篇 |
1981年 | 15篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1978年 | 9篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1975年 | 3篇 |
1973年 | 4篇 |
排序方式: 共有2114条查询结果,搜索用时 31 毫秒
51.
Wentian Li 《Journal of statistical physics》1992,68(5-6):829-882
Dynamical systems with nonlocal connections have potential applications to economic and biological systems. This paper studies the dynamics of nonlocal cellular automata. In particular, all two-state, three-input nonlocal cellular automata are classified according to the dynamical behavior starting from random initial configurations and random wirings, although it is observed that sometimes a rule can have different dynamical behaviors with different wirings. The nonlocal cellular automata rule space is studied using a mean-field parametrization which is ideal for the situation of random wiring. Nonlocal cellular automata can be considered as computers carrying out computation at the level of each component. Their computational abilities are studied from the point of view of whether they contain many basic logical gates. In particular, I ask the question of whether a three-input cellular automaton rule contains the three fundamental logical gates: two-input rules AND and OR, and one-input rule NOT. A particularly interesting edge-of-chaos nonlocal cellular automaton, the rule 184, is studied in detail. It is a system of coupled selectors or multiplexers. It is also part of the Fredkin's gate—a proposed fundamental gate for conservative computations. This rule exhibits irregular fluctuations of density, large coherent structures, and long transient times. 相似文献
52.
《Arabian Journal of Chemistry》2020,13(1):1198-1228
Vanadate and vanadium compounds exist in many environmental, biological and clinical matrices, and despite the need only limited progress has been made on the analysis of vanadium compounds. The vanadium coordination chemistry of different oxidation states is known, and the result of the characterization and speciation analysis depends on the subsequent chemistry and the methods of analysis. Many studies have used a range of methods for the characterization and determination of metal ions in a variety of materials. One successful technique is high performance liquid chromatography (HPLC) that has been used mainly for measuring total vanadium level and metal speciation. Some cases have been reported where complexes of different oxidation states of vanadium have been separated by HPLC. Specifically reversed phase (RP) HPLC has frequently been used for the measurement of vanadium. Other HPLC methods such as normal phase, anion-exchange, cation-exchange, size exclusion and other RP-HPLC modes such as, ion-pair and micellar have been used to separate selected vanadium compounds. We will present a review that summarizes and critically analyzes the reported methods for analysis of vanadium salts and vanadium compounds in different sample matrices. We will compare various HPLC methods and modes including sample preparation, chelating reagents, mobile phase and detection methods. The comparison will allow us to identify the best analytical HPLC method and mode for measuring vanadium levels and what information such methods provide with regard to speciation and quantitation of the vanadium compounds. 相似文献
53.
《Arabian Journal of Chemistry》2022,15(12):104330
The present study was carried out to design and synthesize a number of novel aromatic carboxamide derivatives of dehydroabietylamine. The preliminary antifungal assay indicated that most of title compounds displayed moderate to good antifungal activity toward the six fungal strains in vitro. Compounds 3i, 3q, 4b and 4d showed significant antifungal activity against Sclerotinia sclerotiorum, with EC50 values ranging from 0.067 ~ 0.393 mg/L. Compounds 3i, 4b and 4d also showed pronounced mycelial growth inhibition activities against B. cinerea and A. solani. Furthermore, in the in vivo assay, compound 4b exhibited brilliant protective activity against S. sclerotiorum-infected rape leaves. Meanwhile, the in vivo bioassay on tomato plants infected by B. cinerea showed that compound 3i and 4d displayed excellent protective activity at 200 mg/L, which were near to boscalid. Primary mechanistic study revealed that 4b could inhibit sclerotia formation as well as reduce the exopolysaccharide level. SEM and TEM analysis indicated that 4b possessed a strong ability to destroy the surface morphology of mycelia, cell structure and seriously interfere with the growth of the fungal pathogen. In addition, 4b exhibited good inhibitory activity (IC50 = 23.3 ± 1.6 μM) toward succinate dehydrogenase (SDH). Molecular modeling study confirmed the binding modes between compound 4b and SDH. The above antifungal results and fungicidal mechanism study revealed that this class of dehydroabietylamine derivatives could be potential SDH inhibitors and lead compounds for novel fungicides development. 相似文献
54.
ZENG ChunHua WANG Hua & HU JianHang Faculty of Science Kunming University of Science Technology Kunming China Province Engineering Research Center of Industrial Energy Conservation New Technology 《中国科学:物理学 力学 天文学(英文版)》2011,(8)
In this paper, we investigate the escape of Brownian particles and stochastic resonance (SR) with low-temperatures quantum fluctuations by using the quantum Smoluchowski equations at low-temperature. Two specific examples have been considered: one is the example of bistable system, and the other is the example of metastable system. The explicit expressions of the mean-first passage time (MFPT) and signal-to-noise ratio (SNR) for both specific examples are obtained, respectively. Based on the numerical compu... 相似文献
55.
Internal pressurization testing at room temperature was performed to evaluate the effect of flame-spraying aluminum-12silicon on the leakage behavior of fibre-reinforced composite tubes fabricated by filament winding, and covered with garnet sand. A group of specimens were completely coated with flame-sprayed metal particles and another set remained uncoated. t-tests were conducted at a significance level of α = 0.05 to analyze the effect of the coating on the leakage behavior of the specimens. Ultraviolet imaging was used to illustrate a characteristic leakage pattern of the composite tubes. Coated specimens exhibited slightly higher mean leakage and burst pressures than the uncoated specimens. The t-test results provided strong statistical evidence that the flame spraying process employed did not damage the filament wound tubes covered with garnet sand. 相似文献
56.
57.
H. DagistanliR.H. Mutlu 《Radiation Physics and Chemistry》2012,81(3):240-241
The occupation numbers of the 3d transition metals are calculated as a function of pressure by means of the linear muffin-tin-orbital method. This data is used with the multiconfiguration Dirac-Fock (MCDF) X-ray intensity ratios (R) to estimate the variation of the intensity ratios of 3d metals with pressure. It is found that R decreases with pressure for the early 3d metals whereas it increases for the heavier 3d transition metals. 相似文献
58.
An investigation into the bulk properties, elastic properties and Debye temperature under pressure, and deformation mode under tension of Al8Cu4Y and Al8Cr4Y compounds was investigated by using first principles calculations based on density functional theory. The calculated lattice constants for the ternary compounds (Al8Cu4Y and Al8Cr4Y) are in good agreement with the experimental data. It can be seen from interatomic distances that the bonding between Al1 atom and Cr, Y, and Al2 atoms in Al8Cr4Y are stronger than Al8Cu4Y. The results of cohesive energy show that Al8Cr4Y should be easier to be formed and much stronger chemical bonds than Al8Cu4Y. The bulk modulus B, shear modulus G, Young's modulus E and Poisson's ratio ν can be obtained by using the Voigt–Reuss–Hill averaging scheme. From the results of elastic properties, Al8Cr4Y has the stronger mechanical behavior than Al8Cu4Y. Our calculations also show that pressure has a greater effect on mechanical behavior for both compounds. The ideal tensile strength are obtained by stress-strain relationships under [001](001) uniaxial tensile deformation, which are 15.4 and 23.4 GPa for Al8Cu4Y and Al8Cr4Y, respectively. The total and partial density of states and electron charge density under uniaxial tensile deformations for Al8Cu4Y and Al8Cr4Y compounds are also calculated and discussed in this work. 相似文献
59.
《Comptes Rendus Chimie》2014,17(3):261-267
Solvent extraction processes have been largely used in various industries. They recently were improved through new physical concepts such as CO2 Supercritical Fluid Extraction, Ultrasound assisted process, Microwave-assisted extraction, Instant Controlled Pressure Drop DIC-assisted extraction… Systematically, a pretreatment stage of grinding takes place in order to improve the exchange surface increasing the starting accessibility. Swelling of the material structure implies an increase of the porosity thus leading to higher solvent diffusivity within the solid matrix. A new concept of expanded granule powder has recently been defined using Instant Controlled Pressure Drop DIC technology. Whatever the type of solvent is (even CO2-SFE), such a swelled structure dramatically intensifies the kinetics through a higher specific exchange surface thanks to the open pores, while improving the solution solvent–solute diffusivity within the solid. Coupled to ultrasound, the internal transfer of solute within the pore solvent can likewise be intensified by replacing molecular diffusion within the pores by an effective convection transfer. In this work, we carried out a first approach of modeling of solvent extraction kinetics of expanded granules involving higher exchange surface and greater internal diffusion process. 相似文献
60.
Experiments were carried out to observe the effect of a magnetic field and grid biasing voltage in presence of a plasma bubble in a magnetized, filamentary discharge plasma system. A spherical mesh grid of 80% optical transparency was negatively biased and introduced into the plasma for creating a plasma bubble. Diagnostics via an electrical Langmuir probe and a hot emissive probe were extensively used for scanning the plasma bubble. Plasma floating potential fluctuations were measured at three different positions of the plasma bubble. The instability in the pattern showed the dynamic transition from periodic to chaotic for increasing magnetic fields. Time scale analysis using continuous wavelet transform was carried out to identify the presence of non‐linearity from the contour plots. The mechanisms of the low‐frequency instabilities along with the transition to chaos could be qualitatively explained. Non‐linear techniques such as fast Fourier transform, phase space plot, and recurrence plot were used to explore the dynamics of the system appearing during plasma fluctuations. In order to demonstrate the observed chaotic phenomena in this study, characteristics of chaos such as the Lyapunov exponent were obtained from experimental time series data. The experimentally observed potential structure is confirmed with numerical analysis based on fluid hydrodynamics. 相似文献