全文获取类型
收费全文 | 254篇 |
免费 | 12篇 |
专业分类
化学 | 155篇 |
力学 | 1篇 |
数学 | 10篇 |
物理学 | 100篇 |
出版年
2021年 | 3篇 |
2020年 | 4篇 |
2019年 | 7篇 |
2017年 | 2篇 |
2016年 | 3篇 |
2015年 | 10篇 |
2014年 | 8篇 |
2013年 | 8篇 |
2012年 | 7篇 |
2011年 | 9篇 |
2010年 | 3篇 |
2009年 | 3篇 |
2008年 | 5篇 |
2007年 | 10篇 |
2006年 | 12篇 |
2005年 | 8篇 |
2004年 | 8篇 |
2003年 | 10篇 |
2002年 | 11篇 |
2001年 | 5篇 |
2000年 | 12篇 |
1999年 | 6篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 9篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 6篇 |
1985年 | 8篇 |
1984年 | 8篇 |
1983年 | 13篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1977年 | 6篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1971年 | 1篇 |
1967年 | 1篇 |
1963年 | 1篇 |
1916年 | 1篇 |
排序方式: 共有266条查询结果,搜索用时 46 毫秒
81.
82.
Microwave measurements of rotational transitions within vibrationally excited states of several isotopic species of HCN have given improved values for the pertinent Bv constants. These new data have been combined with infrared measurements given in the literature (ncluding Dv terms) to arrive at a set of rovibrational constants (α and γ constants) which is consistent with all available data. Bond distances resulting from several different Be approximations are intercompared to assess the variability of the re values and the importance of the γ terms. The latest r0 and rs bond distances are also given. 相似文献
83.
The microwave and millimeter wave spectra of HNCS in the three bending excited states, v4 = 1, v5 = 1, and v6 = 1, have been measured. The qR0, qR1, and qR2 branches for each of these three states and the qR3 branch for the lowest excited state have been assigned. Effective rotational and centrifugal distortion constants have been determined for each vibrational and Ka-rotational sub-state. Two local resonances, caused by the Coriolis induced asymmetry interaction and a b-type Coriolis resonance, allow unambiguous confirmation of the assignment of the state v6 = 1, the first excited state of the out-of-plane vibration. 相似文献
84.
The Doppler-limited rotational spectrum of the NH radical in its electronic (X) and vibrational ground state has been measured using the frequency stabilized Cologne side-band spectrometer in the frequency region near 2 THz. The nitrogen 14N nuclear hyperfine patterns have been observed accompanying the resolved fine (J′←J″) structure of the N=2←1 rotational transition. The observed peak frequencies were analyzed in detail together with the previously measured hyperfine frequencies of the N=1←0 rotational transition and with combination differences obtained from the high-resolution electronic spectra to derive precise rotational, centrifugal distortion, fine, and hyperfine parameters. In the numerical analysis the essential attention has been paid to partly resolved and unresolved hyperfine structures. The peak positions of the partly or fully overlapped lines were analyzed with the help of a profile simulation with estimated half-widths and calculated relative intensities and in this manner the least square fit of the unresolved and partly resolved lines was significantly improved. The NH radical is an extremely important species in nitrogen chemical reaction networks in the interstellar medium and atmospheric chemistry. 相似文献
85.
S.N. Mikhailenko VL.G. TyuterevV.I. Starikov K.K. AlbertB.P. Winnewisser M. Winnewisser G. MellauC. Camy-Peyret R. LanquetinJ.-M. Flaud J.W. Brault 《Journal of Molecular Spectroscopy》2002,213(2):91-121
Water vapor infrared spectra have been recorded at room temperature in the range 4200-6250 cm−1 at resolutions (FWHM) between 0.0053 and 0.0080 cm−1. The use of a White-type multireflection cell made large pressure × pathlength products possible up to 31.27 mbar×288.5 m. The high signal-to-noise ratio allowed us to observe lines with intensities as small as 10−26 cm−1/molecule cm−2 at T=296 K. Among about 5100 recorded water lines, about half of which are reported for the first time, 2351 lines have been assigned to the second triad of H216O (bands ν1+ν2, ν2+ν3, and 3ν2). This has allowed the determination of line positions and corresponding upper rovibrational states with considerably improved accuracy. The assignments of certain highly excited states have been confirmed by the analysis of flame spectra and hot emission spectra. New values of effective Hamiltonian parameters for the upper states {(110), (030), (011)} have been determined. The generating function model was used in the data reduction to account for the anomalously strong centrifugal distortion of the rovibrational levels and resonance interactions. The RMS standard deviation of the least-squares fit of the assigned H2O data was 5×10−3 cm−1 for line positions and 7×10−3 cm−1 for energy levels up to Jmax=20 and Ka(max)=13. Particular attention was paid to water lines in the transparency window 4200-5000 cm−1, in which existing databases are not sufficient. In this region, 1395 lines of four isotopic species of water have been recorded and over 900 accurate line positions of nine bands of H216O (ν1, ν3, 2ν2, ν1+ν2, ν2+ν3, 3ν2, 4ν2−ν2, 2ν2+ν3−ν2, ν1+2ν2−ν2) are reported in this range. A comparison of laboratory spectra with long path atmospheric spectra (20 km slant path in the mountains) in this region shows that many lines missing from available spectroscopic compilations (or considerably shifted compared to observations) are important for a proper interpretation of atmospheric observations. A comparison of the observed data with the best available predictions from the molecular electronic potential energy surface is discussed. 相似文献
86.
87.
Gisela Ohms Gisbert Grossmann Eli Breuer 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4)
Abstract As known from 31P solid-state NMR investigations of inorganic phosphates there is a correlation between chemical shift anisotropy parameters and crystal lattice parameters. For phosphonic acids and phosphonates similar correlations are not known. 相似文献
88.
Hartmut Komber Gisbert Grossmann Axel Kretschmer 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3-4):335-343
Abstract Compounds of the following structure (R1O)2(X)P[sbnd]Y–P(X)(OR2)2 (X = O, Y = Sn (n = 1–4), R1 = R2 = Me, iPr; X = S, Y = Sn (n = 1–4), R1, R2 = Me, Et, iPr, iBu; X = S, Y = S-Se-S, S-Te-S, R1 = R2 = Me were prepared and their NMR spectra were analysed. Depending on the number of sulfur atoms, bonded between the phosphorus atoms, typical ranges of the P-P coupling constants were found for the different sulfanes investigated: 2JPP from-10 to-20 Hz, 3JPP less than 3 Hz, 4JPP from +10 to +13 Hz and 5JPP less than 1 Hz. For the small vicinal coupling constants and the relatively large values of 4JPP different possibilities of their interpretation are given. 相似文献
89.
Combining On‐Chip Synthesis of a Focused Combinatorial Library with Computational Target Prediction Reveals Imidazopyridine GPCR Ligands 下载免费PDF全文
Michael Reutlinger Dr. Tiago Rodrigues Dr. Petra Schneider Prof. Dr. Gisbert Schneider 《Angewandte Chemie (International ed. in English)》2014,53(2):582-585
Using the example of the Ugi three‐component reaction we report a fast and efficient microfluidic‐assisted entry into the imidazopyridine scaffold, where building block prioritization was coupled to a new computational method for predicting ligand–target associations. We identified an innovative GPCR‐modulating combinatorial chemotype featuring ligand‐efficient adenosine A1/2B and adrenergic α1A/B receptor antagonists. Our results suggest the tight integration of microfluidics‐assisted synthesis with computer‐based target prediction as a viable approach to rapidly generate bioactivity‐focused combinatorial compound libraries with high success rates. 相似文献
90.
Michael Reutlinger Dr. Tiago Rodrigues Dr. Petra Schneider Prof. Dr. Gisbert Schneider 《Angewandte Chemie (International ed. in English)》2014,53(16):4244-4248
We present the development and application of a computational molecular de novo design method for obtaining bioactive compounds with desired on‐ and off‐target binding. The approach translates the nature‐inspired concept of ant colony optimization to combinatorial building block selection. By relying on publicly available structure–activity data, we developed a predictive quantitative polypharmacology model for 640 human drug targets. By taking reductive amination as an example of a privileged reaction, we obtained novel subtype‐selective and multitarget‐modulating dopamine D4 antagonists, as well as ligands selective for the sigma‐1 receptor with accurately predicted affinities. The nanomolar potencies of the hits obtained, their high ligand efficiencies, and an overall success rate of 90 % demonstrate that this ligand‐based computer‐aided molecular design method may guide target‐focused combinatorial chemistry. 相似文献