全文获取类型
收费全文 | 3118篇 |
免费 | 96篇 |
国内免费 | 21篇 |
专业分类
化学 | 2096篇 |
晶体学 | 20篇 |
力学 | 116篇 |
数学 | 524篇 |
物理学 | 479篇 |
出版年
2023年 | 27篇 |
2022年 | 48篇 |
2021年 | 47篇 |
2020年 | 51篇 |
2019年 | 77篇 |
2018年 | 44篇 |
2017年 | 29篇 |
2016年 | 86篇 |
2015年 | 97篇 |
2014年 | 110篇 |
2013年 | 155篇 |
2012年 | 216篇 |
2011年 | 257篇 |
2010年 | 159篇 |
2009年 | 134篇 |
2008年 | 172篇 |
2007年 | 191篇 |
2006年 | 192篇 |
2005年 | 188篇 |
2004年 | 180篇 |
2003年 | 114篇 |
2002年 | 121篇 |
2001年 | 45篇 |
2000年 | 41篇 |
1999年 | 26篇 |
1998年 | 27篇 |
1997年 | 27篇 |
1996年 | 26篇 |
1995年 | 25篇 |
1994年 | 10篇 |
1993年 | 23篇 |
1992年 | 11篇 |
1991年 | 8篇 |
1989年 | 11篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 13篇 |
1984年 | 19篇 |
1983年 | 13篇 |
1982年 | 21篇 |
1981年 | 17篇 |
1980年 | 25篇 |
1979年 | 11篇 |
1978年 | 11篇 |
1977年 | 14篇 |
1976年 | 16篇 |
1975年 | 14篇 |
1974年 | 13篇 |
1973年 | 13篇 |
1971年 | 4篇 |
排序方式: 共有3235条查询结果,搜索用时 15 毫秒
31.
Simple calculations can help to predict which derivatives in a series of organic compounds are potential lasing material. In conjugated systems, a necessary condition for lasing is that there is not less than a specific minimum energy difference between a first excited allowed and a second excited forbidden transition. This order of transition and energy spacing can be obtained by judicious substitutions even in molecules that do not meet these conditions. Lasing action in the near UV has been observed in five new compounds. 相似文献
32.
33.
Infant formula powders were analyzed by liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS) to assess the whey proteins quality, which may be altered by the heat treatment used during the processing conditions. Lactosylation was found to be the major chemical modification occurring in whey proteins. In parallel, a two-dimensional (2-D) gel electrophoresis was performed on the milk sample and the entire protein patterns were analyzed by nano-ESI-MS after cutting the different gel spots and in-gel trypsin digestion. A highly selective and specific tandem MS technique has been developed to characterize and localize up to ten lactosylation sites in beta-lactoglobulin (beta-Lg) and alpha(S2)-casein. alpha-Lactalbumin (alpha-La), with five lactosylated peptides, was found to be an interesting protein marker in the milk powder sample to detect chemical modification induced by the processing/storage conditions. 相似文献
34.
Norbert de Kimpe Bart de Corte Roland Verhe Laurent de Buyck Niceas Schamp 《Tetrahedron letters》1984,25(10):1095-1098
The reaction of organometallic reagents, e.g. alkyllithiums, cuprates and alkylcoppers, with α-haloimines gave selectively a variety of synthetically useful reactions, including coupling to 1,4-diimines, homologation, and production of heterocycles. 相似文献
35.
Laurent Serlet 《Journal of Theoretical Probability》1996,9(3):561-578
We study super-Brownian motion inR
d
starting from a nontrivial finite measure and conditioned to nonextinction as defined by Evans. If (Y
t
)
t0
denotes this process, we provide a new approach to the immortal particle representation of (Y
t
)
t0
. We then show that the measureZ onR
d
defined byZ(B)=
o
1
Y
t
(B) dt is almost surely finite on compact sets whend5 and almost surely infinite on every ball whend4. 相似文献
36.
Let Ω be an open subset of , N ? 3, containing 0. We consider the solutions of ?Δu(x) + g(u(x)) = f(x) in Ω-{0}, where g is nondecreasing and f is bounded and we study the possible singularities at 0: when u(x) = o(|x|1 ? N) we prove that u is isotropic near 0 and show that either it is a C1 function in Ω (removable singularity) or |x|N ? 2u(x) → c, c ≠ 0 (weak singularity) or |x|N ? 2 |u(x) |→ + ∞ (strong singularity). We also characterize the g's for which solutions with a weak singularity exist and improve a previous removability result of H. Brézis and L. Véron (Arch. Rational Mech. Anal.23 (1979), 153–166). 相似文献
37.
Treatment of 2-methylphenols with chloro(diphenyl)-lambda(3)-iodane led to their regioselective dearomatizing 2-phenylation into cyclohexa-2,4-dienone derivatives via a proposed ligand coupling reaction. In the same vein of investigation, treatment of 2-methylanilines with the lambda(5)-iodane 2-iodoxybenzoic acid IBX reagent led to their regioselective dearomatization into previously undescribed ortho-quinol imines. 相似文献
38.
Yaghmur A de Campo L Sagalowicz L Leser ME Glatter O 《Langmuir : the ACS journal of surfaces and colloids》2005,21(2):569-577
Self-assembled nanostructures, such as inverted type mesophases of the cubic or hexagonal geometry or reverse microemulsion phases, can be dispersed using a polymeric stabilizer, such as the PEO-PPO-PEO triblock copolymer Pluronic F127. The particles, which are described in the present study, are based on monolinolein (MLO)-water mixtures. When adding tetradecane (TC) to the MLO-water-F127 system at constant temperature, the internal nanostructure of the kinetically stabilized particles transforms from a Pn3m (cubosomes) to a H2 (hexosomes) and to a water-in-oil (W/O, L2) microemulsion phase (emulsified microemulsion (EME)). To our knowledge, this is the first time that the formation of stable emulsified microemulsion (EME) systems has been described and proven to exist even at room temperature. The same structural transitions can also be induced by increasing temperature at constant tetradecane content. The internal nanostructure of the emulsified particles is probed using small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (cryo-TEM). At each investigated composition and temperature, the internal structure of the dispersions is observed to be identical to the corresponding structure of the nondispersed, fully hydrated bulk phase. This is clear evidence for the fact that the self-assembled inner particle nanostructure is preserved during the dispersion procedure. In addition, the internal structure of the particles is in thermodynamic equilibrium with the surrounding water phase. The internal structure of the dispersed, kinetically stabilized particles is a "real" and stable self-assembled nanostructure. To emphasize this fact, we denoted this new family of colloidal particles (cubosomes, hexosomes, and EMEs) as "ISASOMES" (internally self-assembled particles or "somes"). 相似文献
39.
Wang G Huang T Murray RW Menard L Nuzzo RG 《Journal of the American Chemical Society》2005,127(3):812-813
Visible-near-IR luminescence spectra of gold MPCs that are similar, irrespective of the number of core atoms (all <2 nm diameter) and different monolayers, are reported. The luminescence can be quantitatively invoked by introducing polar ligands into nonpolar MPC monolayers and by galvanic exchange of metal atoms on the MPC core surface with different metals. The observed emissions are believed to result from surface-localized states that depend on both the core metal of the nanoparticle and the ligands attached to the metal surface. 相似文献
40.
Parac-Vogt TN Pacco A Nockemann P Laurent S Muller RN Wickleder M Meyer G Vander Elst L Binnemans K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,12(1):204-210
Proton nuclear magnetic relaxation dispersion (NMRD) profiles were recorded between 0.24 mT and 1.4 T for lanthanum(III)- and gadolinium(III)-containing [15]metallacrown-5 complexes derived from alpha-aminohydroxamic acids and with copper(II) as the ring metal. The influence of the different R-groups on the proton relaxivity was investigated, and a linear relationship between the relaxivity and the molecular mass of the metallacrown complex was found. The selectivity of the metallacrown complexes was tested by transmetalation experiments with zinc(II) ions. The crystal structure of the copper [15]metallacrown-5 gadolinium complex with glycine hydroximate ligands is reported. 相似文献