全文获取类型
收费全文 | 391篇 |
免费 | 6篇 |
专业分类
化学 | 206篇 |
力学 | 20篇 |
数学 | 39篇 |
物理学 | 132篇 |
出版年
2019年 | 4篇 |
2018年 | 3篇 |
2016年 | 3篇 |
2014年 | 6篇 |
2013年 | 17篇 |
2012年 | 21篇 |
2011年 | 17篇 |
2010年 | 5篇 |
2009年 | 7篇 |
2008年 | 12篇 |
2007年 | 18篇 |
2006年 | 22篇 |
2005年 | 16篇 |
2004年 | 25篇 |
2003年 | 9篇 |
2002年 | 11篇 |
2001年 | 16篇 |
2000年 | 16篇 |
1999年 | 9篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 10篇 |
1995年 | 7篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1992年 | 9篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 7篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1968年 | 2篇 |
1966年 | 2篇 |
1965年 | 3篇 |
1940年 | 2篇 |
1933年 | 2篇 |
1928年 | 2篇 |
1894年 | 2篇 |
1888年 | 2篇 |
排序方式: 共有397条查询结果,搜索用时 15 毫秒
391.
Fister TT Seidler GT Shirley EL Vila FD Rehr JJ Nagle KP Linehan JC Cross JO 《The Journal of chemical physics》2008,129(4):044702
New theoretical and experimental investigations of the occupied and unoccupied local electronic densities of states (DOS) are reported for alpha-Li(3)N. Band-structure and density-functional theory calculations confirm the absence of covalent bonding character. However, real-space full-multiple-scattering (RSFMS) calculations of the occupied local DOS find less extreme nominal valences than have previously been proposed. Nonresonant inelastic x-ray scattering, RSFMS calculations, and calculations based on the Bethe-Salpeter equation are used to characterize the unoccupied electronic final states local to both the Li and N sites. There is a good agreement between experiment and theory. Throughout the Li 1s near-edge region, both experiment and theory find strong similarities in the s-and p-type components of the unoccupied local final DOS projected onto an orbital angular momentum basis (l-DOS). An unexpected, significant correspondence exists between the near-edge spectra for the Li 1s and N 1s initial states. We argue that both spectra are sampling essentially the same final DOS due to the combination of long core-hole lifetimes, long photoelectron lifetimes, and the fact that orbital angular momentum is the same for all relevant initial states. Such considerations may be generally applicable for low atomic number compounds. 相似文献
392.
Can TV Sharma M Hung I Gor'kov PL Brey WW Cross TA 《Journal of the American Chemical Society》2012,134(22):9022-9025
As a small tetrameric helical membrane protein, the M2 proton channel structure is highly sensitive to its environment. As a result, structural data from a lipid bilayer environment have proven to be essential for describing the conductance mechanism. While oriented sample solid-state NMR has provided a high-resolution backbone structure in lipid bilayers, quaternary packing of the helices and many of the side-chain conformations have been poorly restrained. Furthermore, the quaternary structural stability has remained a mystery. Here, the isotropic chemical shift data and interhelical cross peaks from magic angle spinning solid-state NMR of a liposomal preparation strongly support the quaternary structure of the transmembrane helical bundle as a dimer-of-dimers structure. The data also explain how the tetrameric stability is enhanced once two charges are absorbed by the His37 tetrad prior to activation of this proton channel. The combination of these two solid-state NMR techniques appears to be a powerful approach for characterizing helical membrane protein structure. 相似文献
393.
Species identification of Crassostrea and Ostrea oysters by polymerase chain reaction amplification of the 5S rRNA gene 总被引:1,自引:0,他引:1
A specific multiplex polymerase chain reaction (PCR) was developed for the identification of Crassostrea angulata, C. gigas, Ostrea edulis, and O. stentina oyster species. Universal primers were used for the amplification of complete repetition units of 5S rDNA in each of the 4 species. The alignment of the obtained sequences was the basis for the specific design of species-specific primers (ED1, ED2, ST1, ST2, CR1, and CR2) located in the nontranscribed spacer regions. The different sizes of the species-specific amplicons, separated by agarose gel electrophoresis, allowed identification of Crassostrea and Ostrea species. A multiplex PCR with a set of the 6 designed primers showed that they did not interfere with each other and bound specifically to the DNA target. This genetic marker can be very useful for traceability of the species, application in the management of oyster cultures, and conservation of the genetic resources of the species. 相似文献
394.
Cao B Peres T Lifshitz C Cross RJ Saunders M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(8):2213-2221
Unimolecular decomposition of C70(+) and its endohedral cation N@C70(+) were studied by high-resolution mass-analyzed ion kinetic energy (MIKE) spectrometry. Information on the energetics and dynamics of these reactions was extracted. C70(+) dissociates unimolecularly by loss of a C2 unit, whereas N@C70(+) expels the endohedral N atom. Kinetic energy release distributions (KERDs) in these reactions were measured. By use of finite heat bath theory (FHBT), the binding energy for C2 emission from C70(+) and the activation energy for N elimination from N@C70(+) were deduced from KERDs in the light of a recent finding that fragmentation of fullerene cations proceeds via a very loose transition state. The activation energy measured for N extrusion from N@C70(+) was found to be lower than that for C2 evaporation, higher than the value from its neutral molecule N@C70 obtained on the basis of thermal stability measurements, and coincident with the theoretical value. The results provide confirmation that the proposed extrusion mechanism in which the N atom escapes from the cage via formation of an aza-bridged intermediate is correct. 相似文献
395.
S. J. Kane M. C. Bartholomew-Biggs M. Cross M. Dewar 《Journal of Global Optimization》2009,45(1):153-167
This paper considers the Omega function, proposed by Cascon, Keating & Shadwick as a performance measure for comparing financial
assets. We discuss the use of Omega as a basis for portfolio selection. We show that the problem of choosing portfolio weights
in order to maximize Omega typically has many local solutions and we describe some preliminary computational experience of
finding the global optimum using a NAG library implementation of the Huyer & Neumaier MCS method. 相似文献
396.
397.
Sirish K. Reddy Neil B. Cramer Allison K. O' Brien Tsali Cross Rishi Raj Christopher N. Bowman 《Macromolecular Symposia》2004,206(1):361-374
A novel thiol-ene photopolymerization reaction involving copolymerization of tetrathiol monomer with vinyl silazane is experimentally characterized and is modeled successfully. The overall polymerization rate is found to be controlled by the ratio of the propagation to chain transfer kinetic parameters. The polymerization rate of this mixture, in the presence of added photoinitiator, is approximately first order in ene functionality and is independent of thiol functional group concentration. Initiation rates in this system, when cured utilizing a light centered around 365 nm light, and in the presence of no added photoinitiator, are shown to be proportional to the ene monomer concentration. When the mixture is polymerized utilizing light centered at 254 nm light, and without photoinitiator, the initiation rates are proportional to the thiol monomer concentrations. This novel reaction scheme is further utilized to form ultra rapidly polymerizable polymer derived ceramic structures with high aspect ratios. 相似文献