全文获取类型
收费全文 | 1075篇 |
免费 | 44篇 |
国内免费 | 2篇 |
专业分类
化学 | 743篇 |
晶体学 | 7篇 |
力学 | 25篇 |
数学 | 221篇 |
物理学 | 125篇 |
出版年
2023年 | 7篇 |
2022年 | 15篇 |
2021年 | 40篇 |
2020年 | 18篇 |
2019年 | 18篇 |
2018年 | 6篇 |
2017年 | 11篇 |
2016年 | 46篇 |
2015年 | 38篇 |
2014年 | 37篇 |
2013年 | 67篇 |
2012年 | 78篇 |
2011年 | 78篇 |
2010年 | 63篇 |
2009年 | 47篇 |
2008年 | 58篇 |
2007年 | 54篇 |
2006年 | 59篇 |
2005年 | 53篇 |
2004年 | 37篇 |
2003年 | 40篇 |
2002年 | 34篇 |
2001年 | 23篇 |
2000年 | 9篇 |
1999年 | 12篇 |
1998年 | 6篇 |
1997年 | 11篇 |
1996年 | 11篇 |
1995年 | 10篇 |
1994年 | 20篇 |
1993年 | 7篇 |
1992年 | 9篇 |
1991年 | 6篇 |
1990年 | 8篇 |
1989年 | 7篇 |
1988年 | 9篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 7篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1973年 | 3篇 |
1966年 | 2篇 |
1954年 | 2篇 |
排序方式: 共有1121条查询结果,搜索用时 15 毫秒
101.
Mauro Epifani Elisabetta Comini Guido Faglia Jordi Arbiol Teresa Andreu Giovanni Pace Pietro Siciliano Joan R. Morante 《Journal of Sol-Gel Science and Technology》2011,60(3):254-259
A titanium chloromethoxide solution was prepared by reacting TiCl4 with methanol, followed by water addition. The starting solutions were characterized by Fourier Transform Infrared (FTIR) spectroscopy, evidencing that the in situ generated water results in early hydrolysis of the chloroalkoxide. The solution was reacted with molten dodecylamine at room temperature, obtaining a white slurry of amorphous titania nanoparticles. Stable, redispersible TiO2 nanocrystals could be prepared by subsequent solvothermal treatment in oleic acid at 250???C. The use of oleic acid was essential for obtaining crystalline structures, while other surfactants prevented crystallization. The nanocrystals were characterized by X-ray Diffraction and Transmission Electron Microscopy, confirming the formation of anatase TiO2 nanocrystals with a mean size of 3.3?nm. The TiO2 nanocrystals were used for fabricating gas-sensing devices, which were tested towards ethanol vapors. The initial small size of the nanocrystals, and the limited size growth during the high-temperature sensor operation, result in remarkable sensing performances if compared with bulk titania sensors. 相似文献
102.
Alberico E Baumann W de Vries JG Drexler HJ Gladiali S Heller D Henderickx HJ Lefort L 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(45):12683-12695
The mechanism of the asymmetric hydrogenation of methyl (Z)-2-acetamidocinnamate (mac) catalysed by [Rh(MonoPhos)(2)(nbd)]SbF(6) (MonoPhos: 3,5-dioxa-4-phosphacyclohepta[2,1-a:3,4-a']dinaphthalen-4-yl)dimethylamine) was elucidated by using (1)H, (31)P and (103)Rh NMR spectroscopy and ESI-MS. The use of nbd allows one to obtain in pure form the rhodium complex that contains two units of the ligand. In contrast to the analogous complexes that contain cis,cis-1,5-cyclooctadiene (cod), this complex shows well-resolved NMR spectroscopic signals. Hydrogenation of these catalyst precursors at 1 bar total pressure gave rise to the formation of a bimetallic complex of general formula [Rh(MonoPhos)(2)](2)(SbF(6))(2); no solvate complexes were detected. In the dimeric complex both rhodium atoms are ligated to two MonoPhos ligands but, in addition, each rhodium atom also binds to one of the binaphthyl rings of a ligand that is bound to the other rhodium metal. Upon addition of mac, a mixture of diastereomeric complexes [Rh(MonoPhos)(2)(mac)]SbF(6) is formed in which the substrate is bound in a chelate fashion to the metal. Upon hydrogenation, these adducts are converted into a new complex [Rh(MonoPhos)(2){mac(H)(2)}]SbF(6) in which the methyl phenylalaninate mac(H)(2) is bound through its aromatic ring to rhodium. Addition of mac to this complex leads to displacement of the product by the substrate. No hydride intermediates could be detected and no evidence was found for the involvement at any stage of the process of complexes with only one coordinated MonoPhos. The collected data suggest that the asymmetric hydrogenation follows a Halpern-like mechanism in which the less abundant substrate-catalyst adduct is preferentially hydrogenated to phenylalanine methyl ester. 相似文献
103.
Finocchio E Baccini I Cristiani C Dotelli G Gallo Stampino P Zampori L 《The journal of physical chemistry. A》2011,115(26):7484-7493
The intercalation of organic polymers molecules (i.e., PEGs and BRIJ) into a standard Ca-montmorillonite has been studied by XRD, TG, and IR spectroscopy. The polymer intercalation is confirmed by the increasing of the d(001) in XRD spectra as well as by the complex multisteps thermal decomposition behavior of the organo-clay materials. Mid-IR and diffuse reflectance near-IR spectra of the intercalated materials show the polymer diagnostic bands (CH stretching and deformation mode), shifted or changed in shape by the interaction with the clay matrix. Both PEG 1500 and PEG 4000 based materials are likely intercalated in an extended configuration, similar to the amorphous polymer form. BRIJ intercalated polymer spectra suggest the disordered conformation of the alkilic chain in a prevailing "gauche", poorly packed, conformation. Host montmorillonite IR bands, mainly OH and water stretching and deformation fundamentals, combination, and overtone bands, are reduced in intensity by polymer intercalation, pointing out an interaction, likely through H-bonding and/or a possible substitution of cations hydration water molecules. 相似文献
104.
In this paper, the connections between model theory and the theory of infinite permutation groups (see 11 ) are used to study the n‐existence and the n‐uniqueness for n‐amalgamation problems of stable theories. We show that, for any n ? 2, there exists a stable theory having (k + 1)‐existence and k‐uniqueness, for every k ? n, but has neither (n + 2)‐existence nor (n + 1)‐uniqueness. In particular, this generalizes the example, for n = 2, due to Hrushovski given in 3 . © 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim 相似文献
105.
We study the effect of quenched size polydispersity on the phase behavior of charged colloidal suspensions using free-energy calculations in Monte Carlo simulations. The colloids are assumed to interact with a hard-core repulsive Yukawa (screened-Coulomb) interaction with constant surface potential, so that the particles are polydisperse both in size and charge. In addition, we take the size distribution to be fixed in both the fluid and crystal phase (no size fractionation is allowed). We study the fluid-solid transition for various screening lengths and surface potentials, finding that upon increasing the size polydispersity the freezing transition shifts toward higher packing fractions and the density discontinuity between the two coexisting phases diminishes. Our results provide support for a terminal polydispersity above which the freezing transition disappears. 相似文献
106.
107.
The interplay of protein dynamics and molecular recognition is of fundamental importance in biological processes. Atomic‐resolution insights into these phenomena may provide new opportunities for drug discovery. Herein, we have combined NMR relaxation experiments and residual dipolar coupling (RDC) measurements with molecular dynamics (MD) simulations to study the effects of the anti‐inflammatory drug carbenoxolone (CBNX) on the conformational properties and on the internal dynamics of a subdomain (box A) of high‐mobility group B protein (HMGB1). 15N relaxation data show that CBNX binding enhances the fast pico‐ to nanosecond motions of a loop and partially removes the internal motional anisotropy of the first two helices of box A. Dipolar wave analysis of amide RDC data shows that ligand binding induces helical distortions. In parallel, increased mobility of the loop upon ligand binding is highlighted by the essential dynamics analysis (EDA) of MD simulations. Moreover, simulations detect two possible orientations for CBNX, which induces two possible conformations of helix H3, one being similar to the free form and the second one causing a partial helical distortion. Finally, we introduce a new approach for the analysis of the internal coordination of protein residues that is consistent with experimental data and allows us to pinpoint which substructures of box A are dynamically affected by CBNX. The observations reported here may be useful for understanding the role of protein dynamics in binding at atomic resolution. 相似文献
108.
In this paper, two different structures for inverted files are analyzed and compared, when the relational join operation is taken into account. The structures are called shared and separate inverted files. The results are given of some experiments which show that the shared inverted organization is always advantageous when the inverted files are not sorted and is almost always advantageous when the files are sorted. 相似文献
109.
Summary Observations of atmospheric temperature have been uninterruptedly carried out at Mt. Cimone (2165 m s.l.) since January 1946.
Four decades and a half of homogeneous measurements are presented in this paper giving particular emphasis to long-term change:
in the yearly temperature averages there is no evidence for secular trend as well as in the winter and summer temperature
averages. On the contrary the spring averages show a decreasing long-term trend, while the autumn averages reveal an increasing
long-term trend. We find, for the spring season, a global decrease of about −1°C and, for the autumn season, a global increase
of about +1°C. A temperature correlation analysis between Mt. Cimone and an area-box of about (200×700) km2, exceeding the Po Valley, just to the North of Mt. Cimone, is presented. Results show how long-term temperature change, representing
the mentioned area, could be powerfully monitored by operating a single station as Mt. Cimone. 相似文献