全文获取类型
收费全文 | 1380篇 |
免费 | 33篇 |
国内免费 | 5篇 |
专业分类
化学 | 914篇 |
晶体学 | 3篇 |
力学 | 36篇 |
数学 | 258篇 |
物理学 | 207篇 |
出版年
2023年 | 9篇 |
2022年 | 24篇 |
2021年 | 29篇 |
2020年 | 25篇 |
2019年 | 27篇 |
2018年 | 21篇 |
2017年 | 20篇 |
2016年 | 47篇 |
2015年 | 39篇 |
2014年 | 42篇 |
2013年 | 82篇 |
2012年 | 66篇 |
2011年 | 75篇 |
2010年 | 64篇 |
2009年 | 53篇 |
2008年 | 75篇 |
2007年 | 72篇 |
2006年 | 48篇 |
2005年 | 49篇 |
2004年 | 43篇 |
2003年 | 41篇 |
2002年 | 46篇 |
2001年 | 29篇 |
2000年 | 28篇 |
1999年 | 24篇 |
1998年 | 21篇 |
1997年 | 21篇 |
1996年 | 16篇 |
1995年 | 15篇 |
1994年 | 16篇 |
1993年 | 17篇 |
1992年 | 21篇 |
1991年 | 18篇 |
1990年 | 17篇 |
1989年 | 12篇 |
1988年 | 9篇 |
1987年 | 12篇 |
1986年 | 7篇 |
1985年 | 12篇 |
1984年 | 16篇 |
1983年 | 8篇 |
1982年 | 9篇 |
1981年 | 12篇 |
1980年 | 13篇 |
1979年 | 8篇 |
1978年 | 9篇 |
1977年 | 13篇 |
1975年 | 6篇 |
1974年 | 5篇 |
1969年 | 3篇 |
排序方式: 共有1418条查询结果,搜索用时 15 毫秒
71.
Recently, a new and efficient method for total homocysteine (tHcy) quantitation in plasma using trap and release membrane introduction mass spectrometry (T&R-MIMS) with a versatile removable direct introduction membrane probe (DIMP) was described [R. Haddad, M. A. Mendes, N. F. Hoehr and M. N. Eberlin, Analyst, 2001, 126, 1212]. Herein we report on the use of the DIMP-T&R-MIMS technique for total cysteine (tCys) quantitation; hence combined tCys and tHcy quantitation in plasma or serum can be achieved. The method employs Cys and Hcy derivatization with ethyl chloroformate (after disulfide bond reduction with dithiothreitol and protein precipitation with trichloroacetic acid), preconcentration in a capillary silicone membrane, and their thermal desorption to the gas phase inside the ion source region of a mass spectrometer, at a point exactly between the two ionization filaments. Thermal desorption uses the uniform heat radiation provided by the two ionization filaments. The analytes are then ionized by electron ionization and both Cys and Hcy are quantitated by mass spectrometry using selected ion monitoring. For tCys quantitation, good linearity and reproducibility was observed for concentrations ranging from 5 to 350 microM, recovery was near 95%, and the limit of detection (LOD) was of 2 microM. This LOD is well below the mean Cys concentration in plasma, and serum samples from a large group of healthy people showed a mean tCys concentration of 132 +/- 45 microM. 相似文献
72.
Renato S. Gonnelli Mauro Tortello Dario Daghero Giovanni Alberto Ummarino Valeri A. Stepanov Jun S. Kim 《Central European Journal of Physics》2009,7(2):251-256
Point-contact Andreev-reflection (PCAR) experiments were performed in the Fe-1111 layered superconductor LaFeAsO0.9F0.1 with resistive T
c
on
∼ 27 K. The observation of two pairs of peaks in the low-temperature Andreev-reflection spectra clearly indicates the presence
of two order parameters. The behavior of the two gaps as a function of temperature, obtained by fitting the conductance curves
by means of the generalized two-band Blonder-Tinkham-Klapwijk model, shows some anomalies. A theoretical analysis performed
within the two-band Eliashberg theory with a generic electron-boson coupling can reproduce the low-temperature value of the
two gaps but generally fails in giving a satisfactory fit of their overall temperature dependence, indicating the rich and
complex physics of these newly discovered superconductors.
相似文献
73.
Weak steady Mach reflections are numerically simulated using unstructured grids by means of either “shock-fitting” or “shock-capturing”
techniques. It is shown that shock-fitting allows using coarser meshes than those required by shock-capturing, since the latter
needs mesh refinement in the direction normal to the discontinuities, which is not needed using the former approach. The shock-fitted
solution is also free from the numerical disturbances that arise along the captured discontinuities and pollute the captured
solution in the smooth flowfield region. Finally, the shock-fitting solutions show the presence of a small region next to
the Mach stem and the reflected shock downstream of the triple point, characterized by very high gradients. 相似文献
74.
The stability number α(G) for a given graph G is the size of a maximum stable set in G. The Lovász theta number provides an upper bound on α(G) and can be computed in polynomial time as the optimal value of the Lovász semidefinite program. In this paper, we show that
restricting the matrix variable in the Lovász semidefinite program to be rank-one and rank-two, respectively, yields a pair
of continuous, nonlinear optimization problems each having the global optimal value α(G). We propose heuristics for obtaining large stable sets in G based on these new formulations and present computational results indicating the effectiveness of the heuristics.
Received: December 13, 2000 / Accepted: September 3, 2002 Published online: December 19, 2002
RID="★"
ID="★" Computational results reported in this paper were obtained on an SGI Origin2000 computer at Rice University acquired
in part with support from NSF Grant DMS-9872009.
Key Words. maximum stable set – maximum clique – minimum vertex cover – semidefinite program – semidefinite relaxation – continuous
optimization heuristics – nonlinear programming
Mathematics Subject Classification (2000): 90C06, 90C27, 90C30 相似文献
75.
Cocchi M Franchini G Manfredini M Marchetti A Pigani L Seeber R Tassi L Ulrici A Vignali M Zanardi C Zannini P 《Annali di chimica》2002,92(3):177-185
A study on polythiophene coated microelectrodes is reported, the goal being that of checking the capability of these electrochemical systems to work in low conductive media. The possibility of electrochemically p-doping the polymer in the presence of very low concentrations or even in the absence of supporting electrolyte in the solution is ascertained, opening the way to the use of similar systems in pure solvent media. This result is obtained in such conditions that the presence of residual charges--and corresponding counterions--trapped inside the film coating can be reasonably hypothesised. 相似文献
76.
Skupinska KA McEachern EJ Skerlj RT Bridger GJ 《The Journal of organic chemistry》2002,67(22):7890-7893
A method to prepare amino-substituted 5,6,7,8-tetrahydroquinolines and 5,6,7,8-tetrahydroisoquinolines via catalytic hydrogenation of the corresponding acetamido-substituted quinolines and isoquinolines followed by acetamide hydrolysis is described. The yields of the products are good when the acetamido substituent is present on the pyridine ring and moderate with the acetamido substituent on the benzene ring. This method has also been applied to the regioselective reduction of quinoline substrates bearing other substituents (R = OMe, CO(2)Me, Ph). 相似文献
77.
Summary Within a framework of general algebra we firstly formulate propositions concerning the connection between irreducibility,
id est the absence of certain types of subalgebrae, and simplicity.
Then we investigate some uniqueness properties of the congruences of certain types of lattices and we apply the general propositions
to algebrae with lattice operations obtaining sufficient conditions for the simplicity of wide classes of such algebrae.
Riassunto In un contesto di algebra generale noi formuliamo dapprima proposizioni concernenti la connessione tra irriducibilità, cioè l’assenza di certi tipi di sottoalgebre, e semplicità. In seguito investighiamo alcune proprietà di unicità delle conseguenze di certi tipi di reticoli e applichiamo le proposizioni generali ad algebre con operazioni di reticolo ottenendo condizioni sufficienti per la semplicità di ampie classi di tali algebre.相似文献
78.
79.
80.
Terzi F Seeber R Pigani L Zanardi C Pasquali L Nannarone S Fabrizio M Daolio S 《The journal of physical chemistry. B》2005,109(41):19397-19402
In this article the adsorption of 3-methylthiophene on planar and nanoparticle Au surfaces is investigated. The resulting systems are compared with a benchmark system based on 1-decanethiol. The characterization data collected evidence the formation of a packed 3-methylthiophene SAM on the planar surface. In particular, spectroscopic investigations suggest that 3-methylthiophene aromatic system is not adsorbed on the surface through the pi-electron system but rather through the S atom alone. On the other hand, the behavior of 3-methylthiophene on nanoparticle surfaces is notably different from that of the alkanethiol. Only a limited fraction of the surface of Au nanoparticles results to be actually coated after purification; this notwithstanding, the nanoparticle growth seems to be strongly influenced by the presence of such a labile encapsulating agent. 相似文献