全文获取类型
收费全文 | 1077篇 |
免费 | 55篇 |
国内免费 | 17篇 |
专业分类
化学 | 704篇 |
晶体学 | 4篇 |
力学 | 91篇 |
数学 | 145篇 |
物理学 | 205篇 |
出版年
2023年 | 10篇 |
2022年 | 13篇 |
2021年 | 30篇 |
2020年 | 55篇 |
2019年 | 56篇 |
2018年 | 58篇 |
2017年 | 61篇 |
2016年 | 79篇 |
2015年 | 47篇 |
2014年 | 67篇 |
2013年 | 123篇 |
2012年 | 101篇 |
2011年 | 93篇 |
2010年 | 62篇 |
2009年 | 43篇 |
2008年 | 51篇 |
2007年 | 46篇 |
2006年 | 33篇 |
2005年 | 24篇 |
2004年 | 12篇 |
2003年 | 20篇 |
2002年 | 13篇 |
2001年 | 6篇 |
2000年 | 5篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有1149条查询结果,搜索用时 77 毫秒
1.
Goudarzy Forough Zolgharnein Javad Alizadeh Vahid 《Journal of Analytical Chemistry》2022,77(6):711-716
Journal of Analytical Chemistry - In this article, a new spectrofluorometric method was developed for the determination of methamphetamine based on a turn-on luminescence response of captopril... 相似文献
2.
Jeon Min-Kyung Kim Seunghee Hosseini Zadeh Amin Kwon Tae-Hyuk 《Transport in Porous Media》2020,133(2):207-227
Transport in Porous Media - We investigate viscous fluid flows and concurrent fluid-driven deformations in porous media. The hydro-mechanically (H-M) coupled pore-network model (PNM) is developed,... 相似文献
3.
4.
O.G. Kosareva N.A. Panov N. Akozbek V.P. Kandidov Q. Luo S.A. Hosseini W. Liu J.-F. Gravel G. Roy S.L. Chin 《Applied physics. B, Lasers and optics》2006,82(1):111-122
We demonstrate a three orders of magnitude increase and stability in the backscattered fluorescence signal from nitrogen molecules
by terawatt femtosecond laser pulse induced air filaments using a new method. The method is based on squeezing the initial
beam diameter using a telescope. The effect of laser shot-to-shot fluctuations was included in numerical simulations by a
random distribution of the initial intensity in both squeezed and non-squeezed beams. Statistical processing of the simulation
results shows that the average diameter of plasma channels as well as the total amount of free electrons generated in a bunch
of multiple filaments in air is larger in the squeezed beam. Shot-to-shot stability of the simulated plasma density increases
in the squeezed beam. The change of this plasma density with propagation distance is in good qualitative agreement with the
change of the range-corrected nitrogen fluorescence signal with distance.
PACS 42.65.Jx; 42.60.Jf; 42.68.Ay; 42.68.Wt 相似文献
5.
Vahid Karimipour 《Letters in Mathematical Physics》1994,30(2):87-98
Quantum de Rham complexes on the quantum plane and the quantum group itself are constructed for the nonstandard deformation of Fun(SL(2)). It is shown that in contrast to the standardq-deformation of SL(2), the above complexes are unique for SL
h
(2). Also, as a byproduct, a new deformation of the two-dimensional Heisenberg algebra is obtained which can be used to construct models ofh-deformed quantum mechanics. 相似文献
6.
Several planar waveguides have been fabricated. The waveguides have been polished for determination of their refractiveindex profiles (RIP) by wedge method. The RIP determined by inserting the sample in a Mach-Zehnder interferometer andapplying fringe analysis methods. 相似文献
7.
Headspace solvent microextraction (HSME) into a single drop is developed for the determination of six trihalomethanes, CH2Cl2, CHCl3, C4H9Cl, CCl4, C2HCl3, and C2Cl4, in aqueous solution. A drop of benzyl alcohol containing bromoform, as an internal standard, is used for extraction. The analytes are extracted by suspending a 3-microL drop directly from the needle of a microsyringe. The needle passes through the septum of a vessel, and the needle tip appears above the surface of the solution. After the prescribed extraction time, the drop is drawn back into the syringe. The syringe is then removed, and its content is injected directly into a gas chromatography column for analysis. The main parameters affecting the HSME process, such as stirring speed, microdrop volume, sample solution temperature, microsyringe needle temperature, sample volume, solution pH, extracting solvent, and ionic strength of the solution, are studied. Also, the linear range and precision of the method are examined. 相似文献
8.
In this work a modified form of the Ghotbi–Vera Mean Spherical Approximation model (MGV-MSA) has been used to correlate the mean ionic activity coefficients (MIAC) for a number of symmetric and asymmetric aqueous electrolyte solutions at 25 °C. In the proposed model the hard sphere as well as the electrostatic contributions to the MIAC and the osmotic coefficient of the previously GV-MSA model has been modified. The results of the proposed model for the MIAC of the electrolyte solutions studied in this work are used to directly calculate the values of the osmotic coefficients without introducing any new adjustable parameter. In the MGV-MSA model the cation diameter as well as the relative permittivity of water depends on the electrolyte concentration. Having considered such dependency for both cation and relative permittivity for water in an electrolyte solution the modification of the GV-MSA has been made. It should be stated that in the MGV-MSA model the anion diameter in the solution similar to that in the GV-MSA model remains constant and independent of the electrolyte concentration. The results obtained from the proposed model have been favorably compared with those of the GV-MSA model. The results showed that the MGV-MSA model can more accurately correlate the MIAC of the single electrolyte solutions than those of the GV-MSA model. The same comparison has been observed in case of the osmotic coefficients for the electrolyte solutions studied in this work. It should be noted that in order to do an unequivocal comparison between the results obtained from the models used in this work the same minimization procedure and the same experimental data for the MIAC and the osmotic coefficients have been used. Also it should be mentioned that in the MGV-MSA model the conversion from the McMillan–Mayer (MM) framework to that of the Lewis–Randall (LR) has been performed. It has been concluded that such transformation can affect the results in particular at higher electrolyte concentrations. 相似文献
9.
Potentiometric determination of ultratrace amounts of fluoride enriched by zirconia in a flow system
A satisfactory method was described for separation and preconcentration of ultratrace amounts of fluoride ions enriched by
zirconia (ZrO2) as an inorganic ion exchanger. Fluoride ions can be adsorbed rapidly and selectively on zirconia from an acidic solution
(pH 4.8) then reversibly desorbed by increasing pH up to 13. A flow system consisting of a column packed with zirconia impregnated
on cellulose fibers and an ion-selective electrode was used for the determination of fluoride. The RSD was found to be 1.6%
and the detection limit defined by S/N = 3 was 3 × 10−9 mol L−1. The interference effects of various ions, such as nitrate, sulfate, halides, alkaline, and alkaline earth ions, which may
be found in the environmental water, were studied, and it was found that they were tolerated even at high concentrations.
The method was applied to determine fluoride in drinking water, which contains ultratrace amounts of fluoride. The concentration
of fluoride was found to be 42 μg L−1, which is confirmed by spiking 2 μmol fluoride to the drinking water with a recovery of 99%.
Published in Russian in Zhurnal Analiticheskoi Khimii, 2006, Vol. 61, No. 2, pp. 179–183.
The text was submitted by the authors in English. 相似文献
10.
Khodayar Gholivand Zahra Hosseini Mehrdad Pourayoubi Zahra Shariatinia 《无机化学与普通化学杂志》2005,631(15):3074-3079
Some new N‐carbonyl, phosphoramidates with formula C6H5C(O)N(H)P(O)R2 (R = NC3H6 ( 1 ), NC6H12 ( 2 ), NHCH2CH=CH2 ( 3 ), N(C3H7)2 ( 4 )) and CCl3C(O)N(H)P(O)R′2 (R′ = NC3H6 ( 5 ), NHCH2CH=CH2 ( 6 )) were synthesized and characterized by 1H, 13C, 31P NMR and IR spectroscopy and elemental analysis. The structures were determined for compounds 1 and 2 . Compound 1 exists as two crystallographically independent molecules in crystal lattice. Both compounds 1 and 2 produced dimeric aggregates via intermolecular ‐P=O…H‐N‐ hydrogen bonds, which in compound 2 is a centrosymmetric dimer. In compounds with four‐membered ring amine groups, 3J(P,C)>2J(P,C), in agreement with our previous studies about five‐membered ring amine groups. Also, 3J(P,C) values in compounds 1 and 5 are greater than in compounds with five‐, six‐ and seven‐membered ring amine groups. 相似文献