全文获取类型
收费全文 | 3162篇 |
免费 | 111篇 |
国内免费 | 32篇 |
专业分类
化学 | 2162篇 |
晶体学 | 14篇 |
力学 | 91篇 |
综合类 | 1篇 |
数学 | 623篇 |
物理学 | 414篇 |
出版年
2023年 | 19篇 |
2022年 | 79篇 |
2021年 | 88篇 |
2020年 | 79篇 |
2019年 | 66篇 |
2018年 | 70篇 |
2017年 | 50篇 |
2016年 | 124篇 |
2015年 | 108篇 |
2014年 | 125篇 |
2013年 | 189篇 |
2012年 | 242篇 |
2011年 | 269篇 |
2010年 | 169篇 |
2009年 | 164篇 |
2008年 | 240篇 |
2007年 | 211篇 |
2006年 | 200篇 |
2005年 | 149篇 |
2004年 | 125篇 |
2003年 | 113篇 |
2002年 | 99篇 |
2001年 | 32篇 |
2000年 | 29篇 |
1999年 | 27篇 |
1998年 | 19篇 |
1997年 | 11篇 |
1996年 | 24篇 |
1995年 | 18篇 |
1994年 | 14篇 |
1993年 | 16篇 |
1992年 | 14篇 |
1991年 | 7篇 |
1990年 | 11篇 |
1989年 | 4篇 |
1988年 | 10篇 |
1986年 | 8篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1974年 | 8篇 |
1973年 | 3篇 |
1971年 | 3篇 |
1970年 | 4篇 |
排序方式: 共有3305条查询结果,搜索用时 15 毫秒
991.
Natalia Hassan Pedro V. Verdes Juan M. Ruso 《The Journal of chemical thermodynamics》2011,43(3):399-404
The thermal denaturation of ovalbumin, lysozyme, myoglobin and fibrinogen at different BTS concentrations have been investigated using differential scanning calorimetry (DSC) and circular dichroism (CD) spectroscopy. Thermodynamic parameters: melting temperatures (Tm), calorimetric enthalpy (ΔH), van’t Hoff enthalpy (ΔHv) were obtained for all the systems under study. Thermal denaturation of the four proteins was completely irreversible. Changes in the protein conformation due to the adsorption of BTS molecules have been monitored by using UV-CD spectra. Greater changes in α-helical contents correspond with the BTS higher concentrations. The lysozyme denaturation temperature increases at low concentrations BTS indicating that BTS acts as a structure stabilizer; meanwhile it acts as a destabilizer at higher concentrations in all the proteins studied. The major effect is observed in the case of myoglobin, the protein with the highest α-helical secondary structure (75%). 相似文献
992.
Pedro Merino Graziella Greco Tomás Tejero Ramon Hurtado-Guerrero Rosa Matute Ugo Chiacchio Antonino Corsaro Venerando Pistarà Roberto Romeo 《Tetrahedron》2013
Diastereoselective asymmetric 1,3-dipolar cycloadditions of N-(alkoxycarbonylmethyl) nitrones derived from glycine, alanine and phenylalanine have been studied both experimentally and theoretically. Asymmetric induction is evaluated by either introducing a chiral group at the nitrone nitrogen atom or by using Oppolzer's sultam acrylamide. In both cases the sense of the asymmetric induction is the same, the (3R,5R)-isomer being preferentially obtained. The best results were observed with the chiral dipolarophile, which afforded an only isomer in all cases. The obtained isoxazolidines are easily transformed into the corresponding 5-substituted-3-hydroxypyrrolidin-2-ones. DFT studies are in a qualitative agreement with the observed experimental results. 相似文献
993.
Joana R. Bernardo Sara C.A. Sousa Pedro R. Florindo Mariusz Wolff Barbara Machura Ana C. Fernandes 《Tetrahedron》2013
This work describes the catalytic activity of 17 oxo–rhenium complexes containing heterocyclic ligands in the direct reductive amination of 4-nitrobenzaldehyde with 4-chloroaniline, using phenylsilane as reducing agent. In general, all of the catalysts tested gave excellent yields of the secondary amine, although, the best result was obtained with the catalytic system PhSiH3/ReOBr2(Hhmpbta)(PPh3) (2.5 mol %). This system was also applied to the synthesis of a large variety of secondary amines in good to excellent yields and tertiary amines in moderate yields, with tolerance of different functional groups. 相似文献
994.
Proton nuclear magnetic resonance (1H NMR) relaxometry, over about five decades in Larmor frequency, and pulsed field gradient NMR were used to study the molecular dynamics in the chromonic nematic and isotropic phases of stacked molecules of the binary mixture composed by Edicol Sunset Yellow (ESY) and deuterated water. Our results evidence that in both phases collective motions are responsible for the spin-lattice relaxation dispersion in the Larmor frequency range below 1 MHz. In the nematic phase, the collective motion are attributed to columnar undulations within the stacked molecules, while, in the isotropic phase, the results are explained by local order fluctuations due to the formation of the stacks. The high frequency dispersion was explained by individual molecular motions like rotations around and perpendicular to the stack axis, and also self-diffusion. 相似文献
995.
In this work, a thin, flexible and mechanically stable polymer conducting material (Silk‐Ion Jelly) was developed though application of Ion Jelly on to silk fabrics. Ion Jelly was prepared through jellification of a room temperature ionic liquid, 1‐butyl‐3‐methyl‐imidazolium dicyanamide ([bmim][dca]) using gelatin and water and applied to silk fabrics using two different processes: impregnation and in‐situ. Various parameters influencing ionic conductivity such as Ion Jelly composition (ratio of [bmim][dca], water and gelatin) and incorporation as well as the type of application process were thoroughly investigated. It was observed that the Ion Jelly compositions containing lower gelatin and water ratio as well as application through in‐situ process at high temperature (200 °C) led to considerable improvement in conductivity, mainly due to increased [bmim][dca] concentration, structural flexibility and reduced silk crystallinity. Silk‐Ion Jelly prepared using optimized conditions showed excellent mechanical stability and possessed high room temperature conductivity (2.9 × 10?3 S. cm?1), similar to [bmim][dca], and therefore, this novel ion conducting material may find potential applications in electrochemical devices due to its eco‐friendly preparation route using biomaterials and green solvents. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
996.
Pedro J. Sánchez Gómez 《Foundations of Chemistry》2013,15(1):103-116
In this paper we present a semantic analysis of the application of didactic constructivism to chemical education. We show that the psychological basis of constructivism yield, when applied to chemistry, an internalist semantics for the chemical names. Since these names have been presented as typical examples of an externalism for kind terms, a fundamental incompatibility ensues. We study this situation, to conclude that it affects chemical education at every level. Finally, we present a preliminary analysis of this problem from the point of view of physics. 相似文献
997.
Eloy Ramos‐Cordoba Dr. Pedro Salvador Prof. Dr. Markus Reiher 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(45):15267-15275
The electronic structure of main‐group diatomic molecules is discussed in the light of local spin analysis. A deep investigation into the origin of local spins and their coupling is presented. It is shown that the presence of significant local spins in bonded molecules flags deviations from the classical bonding prototypes. For the notorious example of the C2 molecule, the local spin analysis indicates that its ground state has all ingredients to be categorized as a diradical. 相似文献
998.
Sinova Beatriz Van Aelst Stefan Terán Pedro 《Advances in Data Analysis and Classification》2021,15(2):267-288
Advances in Data Analysis and Classification - Different approaches to robustly measure the location of data associated with a random experiment have been proposed in the literature, with the aim... 相似文献
999.
Strongly negatively invariant compact sets of set-valued autonomous and nonautonomous dynamical systems on a complete metric
space, the latter formulated in terms of processes, are shown to contain a weakly positively invariant family and hence entire
solutions. For completeness the strongly positively invariant case is also considered, where the obtained invariant family
is strongly invariant. Both discrete and continuous time systems are treated. In the nonautonomous case, the various types
of invariant families are in fact composed of subsets of the state space that are mapped onto each other by the set-valued
process. A simple example shows the usefulness of the result for showing the occurrence of a bifurcation in a set-valued dynamical
system. 相似文献
1000.
Ramírez-González PE López-Flores L Acuña-Campa H Medina-Noyola M 《Physical review letters》2011,107(15):155701
We employ the principle of dynamic equivalence between soft-sphere and hard-sphere fluids [Phys. Rev. E 68, 011405 (2003)] to describe the interplay of the effects of varying the density n, the temperature T, and the softness (characterized by a softness parameter ν(-1)) on the dynamics of glass-forming soft-sphere liquids in terms of simple scaling rules. The main prediction is the existence of a dynamic universality class associated with the hard-sphere fluid, constituted by the soft-sphere systems whose dynamic parameters depend on n, T, and ν only through the reduced density n*≡nσ(HS)(T*,ν). A number of scaling properties observed in recent experiments and simulations involving glass-forming fluids with repulsive short-range interactions are found to be a direct manifestation of this general dynamic equivalence principle. 相似文献