全文获取类型
收费全文 | 1083篇 |
免费 | 56篇 |
国内免费 | 7篇 |
专业分类
化学 | 703篇 |
晶体学 | 30篇 |
力学 | 57篇 |
综合类 | 2篇 |
数学 | 153篇 |
物理学 | 201篇 |
出版年
2023年 | 7篇 |
2022年 | 35篇 |
2021年 | 44篇 |
2020年 | 36篇 |
2019年 | 32篇 |
2018年 | 40篇 |
2017年 | 27篇 |
2016年 | 58篇 |
2015年 | 40篇 |
2014年 | 57篇 |
2013年 | 105篇 |
2012年 | 83篇 |
2011年 | 91篇 |
2010年 | 57篇 |
2009年 | 49篇 |
2008年 | 41篇 |
2007年 | 56篇 |
2006年 | 43篇 |
2005年 | 36篇 |
2004年 | 20篇 |
2003年 | 23篇 |
2002年 | 24篇 |
2001年 | 9篇 |
1999年 | 8篇 |
1998年 | 9篇 |
1997年 | 6篇 |
1996年 | 13篇 |
1995年 | 9篇 |
1994年 | 5篇 |
1993年 | 11篇 |
1992年 | 6篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 9篇 |
1982年 | 9篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 4篇 |
1973年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1964年 | 2篇 |
1962年 | 1篇 |
排序方式: 共有1146条查询结果,搜索用时 15 毫秒
921.
For Rayleigh‐Bénard‐Poiseuille flows, thermal stratification resulting from a wall‐normal temperature gradient together with an opposing gravitational field can lead to buoyancy‐driven instability. Moreover, for sufficiently large Reynolds numbers, viscosity‐driven instability can occur. Two higher‐order‐accurate methods based on the full and linearized Navier‐Stokes equations were developed for investigating the temporal stability of such flows. The new methods employ a spectral discretization in the homogeneous directions. In the wall‐normal direction, the convective and viscous terms are discretized with fifth‐order‐accurate biased and fourth‐order‐accurate central compact finite differences. A fourth‐order‐accurate explicit Runge‐Kutta method is employed for time integration. To validate the methods, the primary instability was investigated for different combinations of the Reynolds and Rayleigh number. The results from these primary stability investigations are consistent with linear stability theory results from the literature with respect to both the onset of the instability and the dependence of the temporal growth rate on the wave angle. For the cases with buoyancy‐driven instability, strong linear growth is observed for a broad range of spanwise wavenumbers. The largest growth rates are obtained for a wave angle of 90°. For the cases with viscosity‐driven instability, the linear growth rates are lower and the first mode to experience nonlinear growth is a higher harmonic with half the wavelength of the fundamental. 相似文献
922.
Effect of Central Metal Ions of Analogous Metal–Organic Frameworks on Adsorption of Organoarsenic Compounds from Water: Plausible Mechanism of Adsorption and Water Purification 下载免费PDF全文
Jong Won Jun Minman Tong Beom K. Jung Dr. Zubair Hasan Prof. Chongli Zhong Prof. Sung Hwa Jhung 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(1):347-354
The adsorptive removal of organoarsenic compounds such as p‐arsanilic acid (ASA) and roxarsone (ROX) from water using metal–organic frameworks (MOFs) has been investigated for the first time. A MOF, iron benzenetricarboxylate (also called MIL‐100‐Fe) exhibits a much higher adsorption capacity for ASA and ROX than activated carbon, zeolite (HY), goethite, and other MOFs. The adsorption of ASA and ROX over MIL‐100‐Fe is also much more rapid than that over activated carbon. Moreover, the used MIL‐100‐Fe can be recycled by simply washing with acidic ethanol. Therefore, it is determined that a MOF such as MIL‐100‐Fe can be used to remove organoarsenic compounds from contaminated water because of its high adsorption capacity, rapid adsorption, and ready regeneration. Moreover, only one of three analogous MIL‐100 species (MIL‐100‐Fe, rather than MIL‐100‐Al or MIL‐100‐Cr) can effectively remove the organoarsenic compounds. This selective and high adsorption over MIL‐100‐Fe, different from other analogous MIL‐100 species, can be explained (through calculations) by the facile desorption of water from MIL‐100‐Fe as well as the large (absolute value) replacement energy (difference between the adsorption energies of the organoarsenic compounds and water) exhibited by MIL‐100‐Fe. A plausible adsorption/desorption mechanism is proposed based on the surface charge of the MOFs, FTIR results, calculations, and the reactivation results with respect to the solvents used in the experiments. 相似文献
923.
Kumar Rajnish Zambrano Franklin Peszlen Ilona Venditti Richard Pawlak Joel Jameel Hasan Gonzalez Ronalds 《Cellulose (London, England)》2022,29(12):6907-6924
Cellulose - Global sustainability megatrends are promoting the utilization of sustainably perceived fibers such as recycled and agricultural residue fibers in hygiene tissue applications. Tissue... 相似文献
924.
Ahmad Nazrul Rosli Noriza Ahmad Zabidi Hasan A. Kassim Keshav N. Shrivastava 《Journal of Cluster Science》2010,21(2):197-210
We have performed the calculation of structures of clusters containing carbon and nitrogen atoms. We determine the bond lengths
in each case. We also calculate the vibrational frequencies of all of the clusters. We compare the calculated values of the
vibrational frequencies with those measured by the Raman spectra of amorphous carbon nitrides. Some of the calculated frequencies
are in agreement with those measured. We identity that linear structures and hence “back bones” are present in the glassy
state. 相似文献
925.
Parviz Norouzi Mohammad Reza Ganjali Rassoul Dinarvand Mohammad Hasan Eshraghi Hassan Ali Zamani 《Russian Journal of Electrochemistry》2010,46(9):999-1006
The determination of prilocain, used to manage tonic-clonic seizures, has been carried out at micro gold electrode (Au UME)
using continuous fast Fourier transform square wave voltammetry. The Au UME electrode exhibited an effective response towards
prilocaine adsorption. The peak current was also found to be significantly increased. The determination was carried out in
phosphate containing electrolyte in the pH of 2.0 and a well-defined change on the peak current were noticed. The peak current
was found to be linearly dependent on concentration of prilocain in the concentration range 5.0 × 10−7–1.0 × 10−11 M with a detection limit of 5.0 × 10−12 M. This paper describes development of a new analysis system to determine of prilocain by a novel square wave voltammetry
method to perform a very sensitive method. The method used for determination of prilocain by measuring the changes in admittance
voltammogram of a gold ultramicroelectrode (in 0.05 M H3PO4 solution) caused by adsorption of the prilocain on the electrode surface. Variation of admittance in the detection process
is created by inhibition of oxidation reaction of the electrode surface, by adsorbed of prilocain. Furthermore, signal-to-noise
ratio has significantly increased by application of discrete Fast Fourier Transform (FFT) method, background subtraction and
two-dimensional integration of the electrode response over a selected potential range and time window. Also in this work some
parameters such as SW frequency, eluent pH, and accumulation time were optimized. The relative standard deviation at concentration
5.0 × 10−8 M is 5.8% for 5 reported measurements. 相似文献
926.
Base hydrolysis of [Cr(ox)2(quin)]3− (where quin2− is N,O-bonded 2,3-pyridinedicarboxylic acid dianion) causes successive ligand dissociation and leads to a formation of a
mixture of oligomeric chromium(III) species, known as chromates(III). The reaction proceeds through [Cr(ox)(quin)(OH)2]3− and [Cr(quin)(OH)4]3− formation. Dissociation of oxalato ligands is preceded by the opening of the Cr-quin chelate-ring at the Cr–N bond. The kinetics
of the chelate-ring opening and the first oxalate dissociation were studied spectrophotometrically, within the lower energy
d–d band region at 0.4–1.0 M NaOH. The pseudo-first-order rate constants (k
obs0 and k
obs1) were calculated using SPECFIT software for an A → B → C reaction pattern. Additionally, kinetics of base hydrolysis of [Cr(ox)(quin)(OH)2]3− and cis-[Cr(ox)2(OH)2]3− were studied. The determined pseudo-first-order rate constants were independent of [OH−]. A mechanism is postulated that the reactive intermediate with the one-end bonded quin ligand, [Cr(ox)2(O-quin)(OH)]4−, formed in the first reaction stage, subsequently undergoes oxalates substitution. Kinetic parameters for the chelate-ring
opening and the first oxalate dissociation were determined. 相似文献
927.
The optical and electrical properties of compressively strained GaInSb/GaInAlSb mid-infrared quantum well lasers are numerically studied solving one-dimensional Schrödinger equation using finite difference method. The simulation results demonstrate that band-mixing effects and effective mass of hole are reduced when the well is compressively strained. The strain-dependent optical and differential gains are evaluated for 0.6, 0.9, 1.21, and 1.52% compressively strained quantum well and found maximum when well is strained by 1.52%. The emission wavelength for the proposed laser can be tuned from 2.40 to 2.26 μm due to change in compressive strain from 0.60 to 1.52% at temperature 300 K. For the range of strain, the shift in wavelength is found from 2.38 to 2.24 μm at temperature 275 K. The results obtained from PSPICE simulation indicate that, the optical output power and threshold current are strongly depend on the number of wells and found to be almost constant for the number of wells three and above. 相似文献
928.
Husein Mor H Weihe H Bendix J 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2010,207(2):283-286
Utilizing a standard spin Hamiltonian for an S=32 spin system, we fit complete X-band powder EPR spectra of the Cr(oxalate)(3)(3-) anion diluted into K(3)[Co(oxalate)(3)]·3H(2)O. By using models for the bandshape and bandwidths of varying degree of flexibility, we show that the successful outcome of such a fitting endeavour very much depends on the used bandshape-bandwidth model. The best results are obtained when the bandwidth model incorporates anisotropic intrinsic bandwidths in addition to being able to account for inhomogeneous line broadening caused by distributions of the spin Hamiltonian parameters. 相似文献
929.
On some new analytical solutionsforthe (2+1)-dimensional burgers equation and the special type of dodd_bullough_Mikhailov equation 下载免费PDF全文
Some new travelling wave transform methods are very importantfor obtaining analytical solutions of special type of nonlinear partial differentialequations (NLPDEs). Some of these solutions of NLPDEs may be inthe different forms such as rational function solutions, trigonometric functionsolutions, hyperbolic function solutions, exponential function solutions andJacobi elliptic function solutions. These forms tell us the various propertiesof the NLPDEs from scientifical applications to engineering.In this research, we have studied to obtain the analytical solution ofthe nonlinear (2+1)-dimensional Burgers equation which is named from JohannesMartinus Burgers and the nonlinear special type of the Dodd-Bullough-Mikhailov equation introduced to the literature by Roger Dodd, Robin Bullough,and Alexander Mikhailov. 相似文献
930.
Sarkar M. Abe Kawsar Imtiaj Hasan Sultana Rajia Yasuhiro Koide Yuki Fujii Ryuhei Hayashi Masao Yamada Yasuhiro Ozeki 《Molecules (Basel, Switzerland)》2021,26(16)
Lectins facilitate cell–cell contact and are critical in many cellular processes. Studying lectins may help us understand the mechanisms underlying tissue regeneration. We investigated the localization of an R-type lectin in a marine annelid (Perinereis sp.) with remarkable tissue regeneration abilities. Perinereis nuntia lectin (PnL), a galactose-binding lectin with repeating Gln-X-Trp motifs, is derived from the ricin B-chain. An antiserum was raised against PnL to specifically detect a 32-kDa lectin in the crude extracts from homogenized lugworms. The antiserum detected PnL in the epidermis, setae, oblique muscle, acicula, nerve cord, and nephridium of the annelid. Some of these tissues and organs also produced Galactose (Gal) or N-acetylgalactosamine (GalNAc), which was detected by fluorescent-labeled plant lectin. These results indicated that the PnL was produced in the tissues originating from the endoderm, mesoderm, and ectoderm. Besides, the localizing pattern of PnL partially merged with the binding pattern of a fluorescent-labeled mushroom lectin that binds to Gal and GalNAc. It suggested that PnL co-localized with galactose-containing glycans in Annelid tissue; this might be the reason PnL needed to be extracted with haptenic sugar, such as d-galactose, in the buffer. Furthermore, we found that a fluorescein isothiocyanate-labeled Gal/GalNAc-binding mushroom lectin binding pattern in the annelid tissue overlapped with the localizing pattern of PnL. These findings suggest that lectin functions by interacting with Gal-containing glycoconjugates in the tissues. 相似文献