全文获取类型
收费全文 | 701篇 |
免费 | 34篇 |
国内免费 | 4篇 |
专业分类
化学 | 542篇 |
力学 | 27篇 |
数学 | 103篇 |
物理学 | 67篇 |
出版年
2023年 | 9篇 |
2022年 | 12篇 |
2021年 | 10篇 |
2020年 | 12篇 |
2019年 | 23篇 |
2018年 | 15篇 |
2017年 | 10篇 |
2016年 | 29篇 |
2015年 | 29篇 |
2014年 | 13篇 |
2013年 | 35篇 |
2012年 | 49篇 |
2011年 | 57篇 |
2010年 | 22篇 |
2009年 | 30篇 |
2008年 | 36篇 |
2007年 | 56篇 |
2006年 | 32篇 |
2005年 | 36篇 |
2004年 | 36篇 |
2003年 | 28篇 |
2002年 | 26篇 |
2001年 | 6篇 |
2000年 | 7篇 |
1999年 | 9篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1996年 | 8篇 |
1995年 | 10篇 |
1994年 | 7篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1991年 | 16篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1978年 | 3篇 |
1976年 | 2篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1971年 | 2篇 |
1966年 | 1篇 |
1965年 | 1篇 |
1964年 | 1篇 |
1962年 | 3篇 |
1960年 | 2篇 |
排序方式: 共有739条查询结果,搜索用时 15 毫秒
131.
Sundaraganesan N Joshua BD 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2007,68(3):771-777
The Fourier transform Raman and Fourier transform infrared spectra of methyl benzoate (MB) were recorded in the liquid phase. The equilibrium geometry, harmonic vibrational frequencies, infrared intensities and Raman scattering activities, depolarization ratios, reduced masses were calculated by Hartree-Fock (HF) and density functional B3LYP method with the 6-311+G(d,p) basis set. The scaled theoretical wavenumbers showed very good agreement with the experimental values. The thermodynamic functions of the title compound were also performed at HF/6-311+G(d,p) and B3LYP/6-311+G(d,p) levels of theory. A detailed interpretations of the infrared and Raman spectra of methyl benzoate is reported. The theoretical spectrograms for FT-IR spectra of the title molecule have been constructed. 相似文献
132.
In S Orlov A Berg R García F Pedrosa-Jimenez S Tikhov MS Wright DS Lambert RM 《Journal of the American Chemical Society》2007,129(45):13790-13791
133.
Fürstner A Kirk D Fenster MD Aïssa C De Souza D Nevado C Tuttle T Thiel W Müller O 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(1):135-149
Deliberate digression from the blueprint of the total syntheses of latrunculin A (1) and latrunculin B (2) reported in the accompanying paper allowed for the preparation of a focused library of "latrunculin-like" compounds, in which all characteristic structural elements of these macrolides were subject to pertinent molecular editing. Although all previously reported derivatives of 1 and 2 were essentially devoid of any actin-binding capacity, the synthetic compounds presented herein remain fully functional. One of the designer molecules with a relaxed macrocyclic backbone, that is compound 44, even surpasses latrunculin B in its effect on actin while being much easier to prepare. This favorable result highlights the power of "diverted total synthesis" as compared to the much more widely practiced chemical modification of a given lead compound by conventional functional group interconversion. A computational study was carried out to rationalize the observed effects. The analysis of the structure of the binding site occupied by the individual ligands on the G-actin host shows that latrunculin A and 44 both have similar hydrogen-bond network strengths and present similar ligand distortion. In contrast, the H-bond network is weaker for latrunculin B and the distortion of the ligand from its optimum geometry is larger. From this, one may expect that the binding ability follows the order 1 >/= 44 > 2, which is in accord with the experimental data. Furthermore, the biological results provide detailed insights into structure/activity relationships characteristic for the latrunculin family. Thus, it is demonstrated that the highly conserved thiazolidinone ring of the natural products can be replaced by an oxazolidinone moiety, and that inversion of the configuration at C16 (latrunculin B numbering) is also well accommodated. From a purely chemical perspective, this study attests to the maturity of ring-closing alkyne metathesis (RCAM) catalyzed by a molybdenum alkylidyne complex generated in situ, which constitutes a valuable tool for advanced organic synthesis and natural product chemistry. 相似文献
134.
Duer MJ García F Goodman JM Hehn JP Kowenicki RA Naseri V McPartlin M Stead ML Stein R Wright DS 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(4):1251-1260
The reaction of MeAlCl2 with 'PhPLi2' in THF gives [{MeAl(PPh)3Li(4).3 THF}4(mu4-Cl)]-Li+ (1). The GaIII and InIII analogues, [{MeE(PPh)3Li(4).3 THF}4(mu4-Cl)]-Li+(THF)3 (E=Ga (2), In (3)), are obtained by the in situ reactions of MeECl2 with PhPLi2 in THF. For all of the complexes, the cage anions have an unusual cubic arrangement that is similar to a zeolite, and contain large voids (ca. 17 A). The location of the Li+ counterions in 1-3 and their coordination environment appears to subtly reflect variations in packing and lattice energy. Whereas in 1 highly mobile, loosely coordinated Li+ counterions are present, 2 and 3 contain less mobile THF-solvated counterions within the cavities. X-ray crystallographic and solid-state NMR studies are reported on 1-3, together with model DFT calculations on the selectivity of halide coordination. 相似文献
135.
Lo C Le Blanc JC Yu CK Sze KH Ng DC Chu IK 《Rapid communications in mass spectrometry : RCM》2007,21(24):4101-4108
Transgenic Arabidopsis plants were analyzed by liquid chromatography/tandem mass spectrometry (LC/MS/MS) to investigate the glycosylation patterns of resveratrol derived from expression of a sorghum stilbene synthase gene. In negative ionization mode, the different resveratrol derivatives fragmented to yield the diagnostic deprotonated resveratrol ion at m/z 227.2. The use of precursor ion scanning led to the identification of precursor ions for different resveratrol glycosides through rapid differentiation from other phytochemical constituents. Structural information was generated simultaneously from the low-collision-energy product ion spectra using hybrid linear ion-trap mass spectrometry. Three additional resveratrol-related metabolites - a resveratrol diglucoside (M1) and trans- and cis-resveratrol acetylhexosides (M2 and M3) - were detected in the crude plant extracts. The identities of M1, M2, and M3 were confirmed by accurate mass analysis on a quadrupole time-of-flight mass spectrometer as well as beta-glucosidase digestion or UV-induced isomerization. Quantitative analyses by LC/MS in multiple reaction monitoring mode revealed that resveratrol diglucoside and cis-resveratrol acetyhexoside accumulated up to 2.79 and 10.38 microg/g, respectively, while trans-resveratrol acetylhexoside was barely detectable. This study demonstrated the power of the hybrid linear ion-trap technology for simultaneous profiling and structural characterization of stilbene-related metabolites, which would be useful to understand how resveratrol is modified in sorghum and other plants. 相似文献
136.
137.
138.
139.
Michael A. Beswick Nick Choi Alexander D. Hopkins Yvonne G. Lawson Mary McPartlin Alexander Rothenberger Dietmar Stalke Andrew E. H. Wheatley Dominic S. Wright 《Angewandte Chemie (International ed. in English)》1999,38(20):3053-3055
Thermally unstable crystals of the title compound—the first bismuth phosphide complex to be structurally characterized (see picture)—are obtained by the reaction of [Bi(NMe2)3] with [tBuPHLi] (1:3) in THF/hexane. Berry pseudorotation of the pseudo-trigonal-bipyramidal [{(tBuP)3}2Bi]− ion is prevented for steric reasons. 相似文献
140.
S?ren Krach Isabelle Blümel Dominic Marjoram Tineke Lataster Lydia Krabbendam Jochen Weber Jim van Os Tilo Kircher 《BMC neuroscience》2009,10(1):1-11