全文获取类型
收费全文 | 643篇 |
免费 | 26篇 |
国内免费 | 4篇 |
专业分类
化学 | 529篇 |
晶体学 | 4篇 |
力学 | 5篇 |
数学 | 74篇 |
物理学 | 61篇 |
出版年
2024年 | 1篇 |
2023年 | 7篇 |
2022年 | 12篇 |
2021年 | 20篇 |
2020年 | 13篇 |
2019年 | 11篇 |
2018年 | 12篇 |
2017年 | 12篇 |
2016年 | 25篇 |
2015年 | 30篇 |
2014年 | 21篇 |
2013年 | 42篇 |
2012年 | 49篇 |
2011年 | 58篇 |
2010年 | 27篇 |
2009年 | 23篇 |
2008年 | 37篇 |
2007年 | 43篇 |
2006年 | 39篇 |
2005年 | 34篇 |
2004年 | 33篇 |
2003年 | 23篇 |
2002年 | 33篇 |
2001年 | 13篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 6篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有673条查询结果,搜索用时 9 毫秒
81.
82.
Adriana C. Casabuono Cecilia Czibener Mariela G. Del Giudice Ezequiel Valguarnera Juan E. Ugalde Alicia S. Couto 《Journal of the American Society for Mass Spectrometry》2017,28(12):2716-2723
Brucellaceae are Gram-negative bacteria that cause brucellosis, one of the most distributed worldwide zoonosis, transmitted to humans by contact with either infected animals or their products. The lipopolysaccharide exposed on the cell surface has been intensively studied and is considered a major virulence factor of Brucella. In the last years, structural studies allowed the determination of new structures in the core oligosaccharide and the O-antigen of this lipopolysaccharide. In this work, we have reinvestigated the lipid A structure isolated from B. suis and B. abortus lipopolysaccharides. A detailed study by MALDI-TOF mass spectrometry in the positive and negative ion modes of the lipid A moieties purified from both species was performed. Interestingly, a new feature was detected: the presence of a pyrophosphorylethanolamine residue substituting the backbone. LID-MS/MS analysis of some of the detected ions allowed assurance that the Lipid A structure composed by the diGlcN3N disaccharide, mainly hexa-acylated and penta-acylated, bearing one phosphate and one pyrophosphorylethanolamine residue. 相似文献
83.
84.
Comelli NC Lobayan RM Castro EA Jubert AH 《The journal of physical chemistry. A》2011,115(9):1686-1700
The conformational and electronic characteristics of the polar O(9)═C(8)-X(10) moiety in the anticonvulsant valproic acid (Vpa) drug and some of their amides and ester derivatives are analyzed at the B3LYP level using the 6-31+G(d,p) and 6-311++G(d,p) 6d,10f basis sets. Exploring the delocalization of the electron density of the O(9)═C(8)-X(10) moiety by means of ELF, NBO, and AIM calculations, we found that the bending away from coplanarity of the atoms in O(9)═C(8)-X(10) is accompanied by a three-dimensional arrangement of donor and acceptor proton units closing nearly planar pseudorings of four, five, and six members arising from stabilizing interactions around the O(9)═C(8)-X(10) backbone. From the structure-property relationship analysis, we explain the origin of the change in the structural parameters and atomic charges in the polar moiety. 相似文献
85.
Lesarri A Vega-Toribio A Suenram RD Brugh DJ Nori-Shargh D Boggs JE Grabow JU 《Physical chemistry chemical physics : PCCP》2011,13(14):6610-6618
The conformational and structural properties of the inhalational anesthetic isoflurane (1-chloro-2,2,2-trifluoroethyl difluoromethyl ether) have been probed in a supersonic jet expansion using Fourier-transform microwave (FT-MW) spectroscopy. Two conformers of the isolated molecule were identified from the rotational spectrum of the parent and several (37)Cl and (13)C isotopologues detected in natural abundance. The two most stable structures of isoflurane are characterized by an anti carbon skeleton (τ(C(1)-C(2)-O-C(3)) = 137.8(11)° or 167.4(19)°), differing in the trans (AT) or gauche (AG) orientation of the difluoromethyl group. The conformational abundances in the jet were estimated from relative intensity measurements as (AT)/(AG) ≈ 3:1. The structural preferences of the molecule have been rationalized with supporting ab initio calculations and natural-bond-orbital (NBO) analysis, which suggest that the molecule is stabilized by hyperconjugative effects. The NBO analysis of donor-acceptor (LP → σ*) interactions showed that these stereoelectronic effects decrease from the AT to AG conformations, so the conformational preferences can be accounted for in terms of the generalized anomeric effect. 相似文献
86.
Ross F. Koby Alicia M. Doerr Nicholas R. Rightmire Nathan D. Schley Dr. William W. Brennessel Prof. Brian K. Long Prof. Timothy P. Hanusa 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(31):8195-8202
Without solvents present, the often far-from-equilibrium environment in a mechanochemically driven synthesis can generate high-energy, non-stoichiometric products not observed from the same ratio of reagents used in solution. Ball milling 2 equiv. K[A’] (A’=[1,3-(SiMe3)2C3H3]−) with CaI2 yields a non-stoichiometric calciate, K[CaA’3], which initially forms a structure ( 1 ) likely containing a mixture of pi- and sigma-bound allyl ligands. Dissolved in arenes, the compound rearranges over the course of several days to a structure ( 2 ) with only η3-bound allyl ligands, and that can be crystallized as a coordination polymer. If dissolved in alkanes, however, the rearrangement of 1 to 2 occurs within minutes. The structures of 1 and 2 have been modeled with DFT calculations, and 2 initiates the anionic polymerization of methyl methacrylate and isoprene; for the latter, under the mildest conditions yet reported for a heavy Group 2 species (one-atm pressure and room temperature). 相似文献
87.
Binu Jacob Alicia Vogelaar Enrique Cadenas Julio A. Camarero 《Molecules (Basel, Switzerland)》2022,27(19)
This review provides an overview of the properties of cyclotides and their potential for developing novel peptide-based therapeutics. The selective disruption of protein–protein interactions remains challenging, as the interacting surfaces are relatively large and flat. However, highly constrained polypeptide-based molecular frameworks with cell-permeability properties, such as the cyclotide scaffold, have shown great promise for targeting those biomolecular interactions. The use of molecular techniques, such as epitope grafting and molecular evolution employing the cyclotide scaffold, has shown to be highly effective for selecting bioactive cyclotides. 相似文献
88.
Ewan Couic Alicia Tribondeau Vanessa Alphonse Alexandre Livet Noureddine Bousserrhine 《Molecules (Basel, Switzerland)》2022,27(6)
Understanding ecological trajectories after mine site rehabilitation is essential to develop relevant protocols adapted for gold mining sites. This study describes the influence of a range of mine site rehabilitation and revegetation protocols on soil physicochemical parameters and microbial activities related to carbon, nitrogen and phosphorus cycles. We sampled soil from six rehabilitated mining sites in French Guiana with different plant cover (herbaceous, Cyperaceous, monoculture of Clitoria racemosa and Acacia mangium and association of C. racemosa and A. mangium). We measured the mineralization potential of organic matter by estimating the mineralization of carbon, nitrogen and phosphorus and the microbial catabolic diversity balance. The results showed an improvement in the quality of organic matter on revegetated sites with tree cover. On restored sites with fabaceous species, the microbial biomass is three times higher than non-restored sites, improving the rates of organic matter mineralization and restoring the catabolic diversity to the level of natural Guyanese soils. These results confirm that the establishment of fabaceous species under controlled conditions significantly improves the restoration of microbial communities in mining soils. 相似文献
89.
N. V. Joshi Alicia Serfaty 《International Journal of Infrared and Millimeter Waves》1989,10(9):1077-1088
Important parameters of the photosensors such as Noise Equivalent Power (NEP) and detectivity depend upon the magnitude of the signal to noise ratio. Recent improvements in the techniques of measurement in digitized form permit to process noise statistically with a suitable procedure and increase the detection capability more than expected from the conventional definition. 相似文献
90.