全文获取类型
收费全文 | 1847篇 |
免费 | 82篇 |
国内免费 | 3篇 |
专业分类
化学 | 1114篇 |
晶体学 | 44篇 |
力学 | 66篇 |
数学 | 358篇 |
物理学 | 350篇 |
出版年
2024年 | 4篇 |
2023年 | 10篇 |
2022年 | 36篇 |
2021年 | 50篇 |
2020年 | 60篇 |
2019年 | 52篇 |
2018年 | 56篇 |
2017年 | 73篇 |
2016年 | 83篇 |
2015年 | 73篇 |
2014年 | 86篇 |
2013年 | 247篇 |
2012年 | 138篇 |
2011年 | 145篇 |
2010年 | 118篇 |
2009年 | 90篇 |
2008年 | 97篇 |
2007年 | 87篇 |
2006年 | 61篇 |
2005年 | 47篇 |
2004年 | 62篇 |
2003年 | 32篇 |
2002年 | 35篇 |
2001年 | 15篇 |
2000年 | 18篇 |
1999年 | 14篇 |
1998年 | 15篇 |
1997年 | 7篇 |
1996年 | 16篇 |
1995年 | 9篇 |
1994年 | 11篇 |
1993年 | 3篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1980年 | 4篇 |
1979年 | 8篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1972年 | 6篇 |
1937年 | 1篇 |
1907年 | 1篇 |
排序方式: 共有1932条查询结果,搜索用时 31 毫秒
141.
O. Çakır İ. T. Çakır H. Duran Yıldız R. Mehdiyev 《The European Physical Journal C - Particles and Fields》2008,56(4):537-543
We study the single production of fourth-family quarks through the process pp→Q′jX at the Large Hadron Collider (LHC). We have calculated the decay widths and branching ratios of the fourth-family quarks
(b′ and t′) in the mass range 300–800 GeV. The cross sections for the signal and background processes have been calculated in a Monte
Carlo framework. It is shown that the LHC can discover single t′ and b′ quarks if the CKM matrix elements |V
t′q
|,|V
qb′|≳0.01. 相似文献
142.
Yavuz Surme Ibrahim Narin Mustafa Soylak Huseyin Yuruk Mehmet Dogan 《Mikrochimica acta》2007,157(3-4):193-199
The conditions for cloud point extraction of lead(II) from aqueous solutions were investigated and optimized. The procedure
is based on the separation of Pb(II) – brillant cresyl blue (BCB) complexes into the micellar media by adding the surfactant
Triton X-114. After phase separation, the surfactant-rich phase was dissolved with 1 mol L−1 HNO3 in ethanol and diluted with 1 mol L−1 HNO3 solution before lead was determined by flame atomic absorption spectrometry. Optimization of the pH, ligand and surfactant
quantities, incubation time, temperature, viscosity, sample volume, and interfering ions was performed. The effects of the
matrix ions were also examined. The detection limits for three times the standard deviations of the blank for lead were 7.5 μg L−1 for water samples and 0.33 μg g−1 for sediment samples. The validity of cloud point extraction was checked by employing certified reference samples of Lake
Sediment IAEA-SL-1 and Sewage Sludge BCR-CRM 144R. The procedure was applied to natural waters and sediment samples with satisfactory
results (recoveries >95%, relative standard deviations <6.4%). 相似文献
143.
Prof. Jean-FranÇois Mertens 《Probability Theory and Related Fields》1972,22(1):45-68
Sans résuméCe nous est un très agréable devoir d'adresser ici nos plus vifs remerciements à Monsieur J. Paris qui a bien voulu, avec une bienveillance toute particulière, veiller au meilleur déroulement de ce travail, partie de notre thèse de doctorat défendue à l'Université Catholique de Louvain.Nous sommes également très reconnaissants à Monsieur P.A. Meyer, qui nous a signalé la seconde partie du théorème 12. 相似文献
144.
The paper derives the relevant non-linear integro-differential evolution equation by the method due to Collins expanding on a procedure by Keller. The quadratically non-linear case is not a trivial variation over the cubically non-linear case that was presented in preceding papers. As expected a different scaling and ordering of terms is needed and the first order perturbation solution provides no information on resonance. Nevertheless, although obtained by much longer calculations, the final equation for the present case is of identical form, with differences only in numerical coefficients, with the cubic case that was presented and solved earlier. 相似文献
145.
We retrospectively reviewed MR studies on 10 patients with renal-related perinephric fluid collections who underwent MRI in three institutions between January 2001 and August 2004. All patients underwent MRI of the abdomen and T1-weighted, T2-weighted and serial contrast-enhanced images, including delayed-phase contrast-enhanced images 10-12 min after contrast injection, were obtained. Perinephric fluid collections in 5 patients revealed MRI findings of simple fluid content (i.e., hypointense on T1-weighted images and hyperintense on T2-weighted images). In another 5 patients, a complex perinephric fluid content (i.e., mixed hyper/hypointense on T1-weighted images and mixed hypo/hyperintense on T2-weighted images compatible with blood breakdown products and pus) was observed. In 5 patients, contrast extravasation on late-phase images that was compatible with urine leak was demonstrated. Our results suggest that MRI may determine the content of perinephric fluid collections on noncontrast T1-weighted and T2-weighted images and that contrast extravasation on late-phase images is associated with urine extravasation from renal collecting systems. 相似文献
146.
O?uz??elikelEmail author ?zcan?Bazkir Mehmet?Kü?üko?lu Farhad?Samedov 《Optical and Quantum Electronics》2005,37(6):529-543
This paper covers the absolute spectral power responsivity calibration of spectralon-coated Integrating Sphere Radiometer (ISR) equipped with 3 mm diameter InGaAs photodiode to be used as a transfer standard in fiber optic power measurements against Electrical Substitution Cryogenic Radiometer (ESCR) in Optics Laboratory of National Metrology Institute (TUBITAK UME) of Turkey. The initial uncertainty arising from the use of the Electrically Calibrated Pyroelectric Radiometer (ECPR) as a transfer standard in radiometric scale is 0.5% (k=2), which particularly comes from irregularity in the surface homogeneity of ECPR. In order to eliminate the ECPR step as well as its initial uncertainty contribution in fiber optic power measurements, the calibration application herein was carried out. Moreover power stabilization measurements of DFB laser sources at both 1309.1 nm and 1549.0 nm, the beam size determinations, and spectral analyses of these laser sources as well as spatial and angular dependence of spectral responsivities of the ISR were presented in this paper. The total expanded uncertainties were calculated as 0.283% and 0.315% in the determination of absolute spectral power responsivities of the ISR for 1309.1 nm and 1549.0 nm wavelengths respectively (k=2). 相似文献
147.
148.
Akçay M 《Journal of colloid and interface science》2004,280(2):1-304
The characterization of tetraethylammonium bentonite and the adsorption of p-chlorophenol (p-CP) onto organophilic bentonite (tetraethylammonium bentonite) was studied as a function of the solution concentration and temperature. The observed adsorption rates were found to fit first-order kinetics. The rate constants were calculated for temperatures ranging between 15.0 and 35.0 degrees C at constant concentration. The adsorption energy E and adsorption capacity q(m) for the phenolic compound adsorbing on organophilic bentonite were estimated using the Dubinin-Radushkevic equation. Thermodynamic parameters (Deltag(a), Deltah(a), Deltas(a)) were calculated by a new approximation from the isotherms of p-CP adsorption on organophilic bentonite. These isotherms were modeled according to Freundlich and Dubinin-Radushkevic adsorption isotherms. The amount of adsorption of p-chlorophenol on organophilic bentonite was found to be dependent on the relative energies of adsorbent-adsorbate, adsorbate-solvent, and adsorbate-adsorbate interactions. 相似文献
149.
All-optical transistor action with bistable switching in a photonic crystal cross-waveguide geometry
We demonstrate all-optical switching action in a nonlinear photonic crystal cross-waveguide geometry with instantaneous Kerr nonlinearity, in which the transmission of a signal can be reversibly switched on and off by a control input. Our geometry accomplishes both spatial and spectral separation between the signal and the control in the nonlinear regime. The device occupies a small footprint of a few micrometers squared and requires only a few milliwatts of power at a 10-Gbit/s switching rate by use of Kerr nonlinearity in AlGaAs below half the electronic bandgap. We also show that the switching dynamics, as revealed by both coupled-mode theory and finite-difference time domain simulations, exhibits collective behavior that can be exploited to generate high-contrast logic levels and all-optical memory. 相似文献
150.
E
N
T values were determined for 8 1-methyl-2-pyrrolidinone--solvent mixturesover the whole mole fraction range at 20, 30, and 50°C. The solvents used wereacetone, dimethyl sulfoxide, 2-propanol, 1,2-dichloroethane, water, 1,4-dioxane,benzyl alcohol, and hexamethylphosphoric triamide. The E
N
T values werepositive for the NMP + solvent systems, except for the NMP + water system. 相似文献