全文获取类型
收费全文 | 758篇 |
免费 | 67篇 |
国内免费 | 3篇 |
专业分类
化学 | 666篇 |
力学 | 14篇 |
数学 | 76篇 |
物理学 | 72篇 |
出版年
2023年 | 13篇 |
2022年 | 18篇 |
2021年 | 30篇 |
2020年 | 35篇 |
2019年 | 18篇 |
2018年 | 11篇 |
2017年 | 12篇 |
2016年 | 58篇 |
2015年 | 32篇 |
2014年 | 44篇 |
2013年 | 30篇 |
2012年 | 55篇 |
2011年 | 76篇 |
2010年 | 25篇 |
2009年 | 13篇 |
2008年 | 51篇 |
2007年 | 45篇 |
2006年 | 45篇 |
2005年 | 32篇 |
2004年 | 36篇 |
2003年 | 21篇 |
2002年 | 26篇 |
2001年 | 9篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1995年 | 8篇 |
1994年 | 3篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1985年 | 5篇 |
1981年 | 3篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1975年 | 2篇 |
1968年 | 2篇 |
1957年 | 3篇 |
1956年 | 3篇 |
1944年 | 2篇 |
1936年 | 1篇 |
1935年 | 1篇 |
1931年 | 1篇 |
1930年 | 1篇 |
1921年 | 1篇 |
1899年 | 2篇 |
排序方式: 共有828条查询结果,搜索用时 31 毫秒
741.
Konek CT Illg KD Al-Abadleh HA Voges AB Yin G Musorrafiti MJ Schmidt CM Geiger FM 《Journal of the American Chemical Society》2005,127(45):15771-15777
It is now known that the untreated discharge of pharmaceuticals into the environment can impact human health and development and lead to increased drug resistance in biota. Here, we present the first direct interface-specific studies that address the mobility of the widely used agricultural antibiotic morantel, which is commonly present in farm runoff. Surface-bound morantel was spectroscopically identified using second harmonic generation (SHG) via a two-photon resonance of its n-pi* transition and in the C-H stretching region by vibrational sum frequency generation (VSFG). Resonantly enhanced SHG adsorption isotherm measurements carried out at the silica/water interface between 6 x 10(-7) and 5 x 10(-5) M morantel concentration result in a free energy of adsorption of 42(2) kJ/mol at pH 7. Finally, real-time tracking of morantel interaction with the silica/water interface shows that the binding events are fully reversible, consistent with its high mobility in silica-rich soil environments. This work thus indicates that pharmaceuticals discharged into the environment can enter the groundwater supply of municipal water systems, at which point their removal is challenging. In addition, the high mobility of morantel in silica-rich soil environments could lead to developing increased interaction of this antibiotic with target organisms, which could respond by increased drug resistance. 相似文献
742.
743.
Charlotte Hertneck 《Mathematische Annalen》1962,146(5):433-455
Ohne Zusammenfassung 相似文献
744.
Charlotte Froese Fischer 《Zeitschrift für Physik A Hadrons and Nuclei》1974,266(3):161-165
Using a multi-configuration Hartree-Fock (MCHF) approximation for the stationary states, the effect of correlation on the excitation probability, Kr 4p 6 1 S→ Rb+ 4p 5 5p 1 S is studied. It is shown that the MCHF approximation equivalent to a nonorthogonal Hartree-Fock approximation, is the most important correction to the Hartree-Fock total wave function, and that the remaining correlation, though significant, has a much smaller effect. 相似文献
745.
Spline algorithms are evaluated for the non-linear, integro-differential equation describing the Hartree-Fock approximation for the He 1s21S ground state. The error in the energy decreases as h2K−2, where h is a grid parameter and K is the order of the spline. It is shown that for higher order splines, the method is fast and accurate, and contrary to the conclusion reached by Altenberger-Siczek and Gilbert, that spline methods are suitable for SCF atomic structure calculations. Accuracy and timing studies are presented as well as comparisons with other accurate procedures. 相似文献
746.
A series of unconventional twisted pi-electron system molecules has been synthesized via Suzuki cross-coupling of two sterically hindered arenes. Crystallographic analysis of these molecules reveals a large ring-ring dihedral twist angle (87 degrees ) and a highly charge-separated zwitterionic ground state. An efficient conversion of phenols into aryl halides is also reported. [reaction: see text] 相似文献
747.
The reaction between the flexible ligand (1,4-bis(pyridine-2-yl-methanethio)benzene) and Ag+ produces two novel coordination polymers with macrocyclic cages or pockets contained within their backbones, depending upon the ratio of starting materials. 相似文献
748.
The weak-link approach has been employed to synthesize a series of bimetallic Cu(I) macrocycles in high yield. Addition of phosphinoalkylether or -thioether ligands to [Cu(MeCN)4]PF6 produces "condensed" intermediates, [mu-(1,4-(PPh2CH2CH2X)2Y)2Cu2][PF6]2 (X = S, O; Y = C6H4, C6F4), containing strong P-Cu bonds and weaker O-Cu or S-Cu bonds. The weak bonds of these intermediates can be cleaved through ligand substitution reactions to generate macrocyclic structures, [mu-(1,4-(PPh2CH2CH2X)2Y)2(Z)nCu2][PF6]2 (X = S, O; Y = C6H4, C6F4; Z = pyridine, acetonitrile, diimines, isocyanide) in nearly quantitative yields. The incorporation of tetrahedral Cu(I) metal centers into these macrocycles provides a pathway to complexes that differ from analogous d8 square planar macrocycles generated via this approach in their increased air stability, small molecule reactivity, and ability to form multiple structural isomers. Solid-state structures, as determined by single-crystal X-ray diffraction studies, are presented for condensed intermediates and an open macrocycle 相似文献
749.
We report the synthesis and physical characterization of a series of peripherally functionalized porphyrazines (pz's) 1[M(1); M(2); R], where M(1) is a metal ion incorporated into the pz core, M(2) is a metal ion bound to a bis(5-tert-butyl-salicylidenimine) chelate built onto two amino nitrogen attached to the pz periphery, and R is a solubilizing group (either n-propyl (Pr) or 3,4,5-trimethoxyphenyl (TMP) group) attached to the remaining carbons of the pz periphery. The 1[M(1); M(2); R] species are prepared from precursor pz's with a selenodiazole ring; they are deprotected to form the diamino pz, which reacts with two moles of 5-tert-butyl-2-hydroxybenzaldehyde to form the Schiff base pz. This is metalated to form 1[M(1); M(2); R]. The crystal structures of 1[2H; Ni; Pr] and 1[Cu; ClMn; Pr] are presented. The EPR spectra of the M(1)-M(2) "isomers" prepared with Cu(II) (S = (1)/(2)) and ClMn(III) (S = 2) ions, 1[ClMn; Cu; Pr] and 1[Cu; ClMn; TMP], are a superposition of spectra expected for the S = (3)/(2) and S = (5)/(2) total-spin manifolds that result from strong Heisenberg coupling between the partner spins. The exchange splitting between the two manifolds, as determined by temperature-dependent magnetic susceptibility measurements, is equivalent for the two M(1)-M(2) "isomers", Delta/k(B) approximately 20-25 K, which suggests a sigma-pathway for exchange coupling. 相似文献
750.