全文获取类型
收费全文 | 381篇 |
免费 | 29篇 |
国内免费 | 1篇 |
专业分类
化学 | 267篇 |
晶体学 | 4篇 |
力学 | 28篇 |
数学 | 37篇 |
物理学 | 75篇 |
出版年
2023年 | 8篇 |
2022年 | 13篇 |
2021年 | 23篇 |
2020年 | 14篇 |
2019年 | 14篇 |
2018年 | 13篇 |
2017年 | 10篇 |
2016年 | 17篇 |
2015年 | 16篇 |
2014年 | 24篇 |
2013年 | 28篇 |
2012年 | 34篇 |
2011年 | 28篇 |
2010年 | 25篇 |
2009年 | 10篇 |
2008年 | 19篇 |
2007年 | 15篇 |
2006年 | 12篇 |
2005年 | 11篇 |
2004年 | 14篇 |
2003年 | 5篇 |
2002年 | 14篇 |
2001年 | 7篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 4篇 |
1994年 | 7篇 |
1993年 | 5篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1987年 | 1篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有411条查询结果,搜索用时 156 毫秒
111.
Zakaria Elaoud Slaheddine Kamoun Tahar Mhiri Joel Jaud 《Journal of chemical crystallography》1999,29(5):541-545
The salt triethylentetraammonium bis monohydrogenmonophosphate dihydrate is monoclinic with the following unit cell dimensions: a = 8.462(1), b = 10.500(1), c = 9.520 Å, = 99.297(1)°, space group P21/n with Z = 2. The structure was solved by the Patterson method and refined to final R value of 0.043 for 1590 independent reflections. The structure consists of infinite parallel two-dimensional [
01] planes built of mutually connected ions and water molecules by strong O—H···O and N—H···O hydrogen bonding. 相似文献
112.
Choudhury M. Zakaria George Ferguson Alan J. Lough Christopher Glidewell 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(7):m271-m274
Hexamethylenetetramine, C6H12N4, and ferrocenecarboxylic acid, C11H10FeO2, form a 1:2 adduct, (I), which is a salt, viz. hexamethylenetetraminium(2+) bis(ferrocenecarboxylate), (C6H14N4)[Fe(C5H5)(C6H4O2)]2. The dication in (I) is disordered with two orientations at a site of mm2 symmetry in space group Fmm2, while the anion lies across a mirror plane with its unsubstituted cyclopentadienyl ring disordered over two sets of sites. With ferrocene‐1,1′‐dicarboxylic acid, C12H10FeO4, hexamethylenetetramine forms a 1:1 adduct, (II), in which both components are neutral, viz. hexamethylenetetramine–ferrocene‐1,1′‐dicarboxylic acid (1/1), [Fe(C6H5O2)2]·C6H12N4. The amine component in (II) is disordered with two orientations at a site of mm2 symmetry in space group Cmcm, while the acid component is disordered with two orientations at a site of 2/m symmetry. The components in (I) are linked into a finite three‐ion aggregate by a single N—H⃛O hydrogen bond, while the components of (II) are linked into continuous chains by a single O—H⃛N hydrogen bond. 相似文献
113.
George Ferguson Alan J. Lough David M. Smith Choudhury M. Zakaria Christopher Glidewell 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(8):922-923
In the title compound, [Na(C2H3N2O3)], the Na+ cation lies on a centre of inversion in space group P21/m and all the atoms of the anion lie on a mirror plane. Na is octahedrally coordinated by four O and two N atoms from six different anions and each anion is coordinated to six different Na+ cations, forming chains of confacial octahedra which link the anion layers. Within these layers, the individual anions are linked by both O—H?O and C—H?O hydrogen bonds. 相似文献
114.
Lorenz Beckmann Uta Sandy Tretbar Reni Kitte Maik Tretbar 《Molecules (Basel, Switzerland)》2022,27(8)
Drimane and coloratane sesquiterpenoids are present in several plants, microorganisms, and marine life. Because of their cytotoxic activity, these sesquiterpenoids have received increasing attention as a source for new anticancer drugs and pharmacophores. Natural drimanes and coloratanes, as well as their semi-synthetic derivatives, showed promising results against cancer cell lines with in vitro activities in the low micro- and nanomolar range. Despite their high potential as novel anticancer agents, the mode of action and structure–activity relationships of drimanes and coloratanes have not been completely enlightened nor systematically reviewed. Our review aims to give an overview of known structures and derivatizations of this class of sesquiterpenoids, as well as their activity against cancer cells and potential modes-of-action. The cytotoxic activities of about 40 natural and 25 semi-synthetic drimanes and coloratanes are discussed. In addition to that, we give a summary about the clinical significance of drimane and coloratane sesquiterpenoids. 相似文献
115.
116.
117.
I. Hashim M.S.M. Noorani R. Ahmad S.A. Bakar E.S. Ismail A.M. Zakaria 《Chaos, solitons, and fractals》2006,28(5):1149-1158
In this paper, the Adomian decomposition method (ADM) is applied to the famous Lorenz system. The ADM yields an analytical solution in terms of a rapidly convergent infinite power series with easily computable terms. Comparisons between the decomposition solutions and the fourth-order Runge–Kutta (RK4) numerical solutions are made for various time steps. In particular we look at the accuracy of the ADM as the Lorenz system changes from a non-chaotic system to a chaotic one. 相似文献
118.
Chitosan acetate–adipic acid film polymer electrolytes have been prepared by the solution cast technique. The highest conductivity
is 1.4 × 10−9 S cm−1 for 35 wt.% of adipic acid at room temperature. The sample with highest conductivity has the lowest activation energy. Calculations
using the Rice and Roth model provide number of mobile ions, η. The conductivity is dependent on the diffusion coefficient and mobility. 相似文献
119.
This Note deals with the identifiability of non-smooth defects by boundary measurements. We prove the uniqueness of the detection by two measurements for arbitrary closed sets satisfying quasi-everywhere a conductivity assumption. This assumption is satisfied by a large class of compact sets, including all the sets which can be written as an arbitrary union of continua of positive diameter. The conductivity is a new regularity concept which is related to the thickness of the set and is to be compared to the Wiener regularity. In order to rigorously justify the numerical approach by the finite element method, we provide a stability result without any a priori smoothness assumptions. To cite this article: Z. Belhachmi, D. Bucur, C. R. Acad. Sci. Paris, Ser. I 340 (2005). 相似文献
120.
Jonathan Whitford Manish Shinde Brandon Hunt Sandy Miller Yulia Kostogorova‐Beller 《Journal of Polymer Science.Polymer Physics》2017,55(17):1278-1285
This work reveals influence of electrospinning of polyacrylonitrile–N ,N‐dimethylformamide solution of different concentrations on nanofiber web color parameters, molecular structure, and heat stability. It is found that fiber diameters depend on concentration through the power law relationship; however, the medium concentration‐based web is characterized by a green–yellow hue, representative of the chromophore color; while, the solvent‐rich and solvent‐poor solution‐based webs give rise to Stokes shifts and ultraviolet‐blue emission bands, attributed to fluorescence. The chromophore structure, present in the neat powder, undergoes changes as a result of electrospinning reflected by the enamine‐to‐ketonitrile conversion and the fraction of C?N conjugation. Blue‐shifting of the C?N conjugation is indicative of a reduction of the π‐electron system, which is coincident with the decreased color saturation value but observed only in the nanofibers prepared from the medium concentration solution. A decrease in the glass transition and an increase in cyclization temperatures also support these findings. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55 , 1278–1285 相似文献