全文获取类型
收费全文 | 332篇 |
免费 | 7篇 |
专业分类
化学 | 188篇 |
力学 | 1篇 |
数学 | 19篇 |
物理学 | 131篇 |
出版年
2020年 | 3篇 |
2019年 | 5篇 |
2017年 | 3篇 |
2015年 | 4篇 |
2014年 | 4篇 |
2013年 | 12篇 |
2012年 | 10篇 |
2011年 | 11篇 |
2010年 | 6篇 |
2009年 | 2篇 |
2008年 | 9篇 |
2007年 | 13篇 |
2006年 | 16篇 |
2005年 | 10篇 |
2004年 | 17篇 |
2003年 | 8篇 |
2002年 | 7篇 |
2001年 | 12篇 |
2000年 | 14篇 |
1999年 | 11篇 |
1998年 | 7篇 |
1997年 | 2篇 |
1996年 | 9篇 |
1995年 | 7篇 |
1994年 | 14篇 |
1993年 | 6篇 |
1992年 | 9篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1987年 | 7篇 |
1986年 | 2篇 |
1985年 | 8篇 |
1984年 | 4篇 |
1982年 | 2篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1977年 | 8篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 4篇 |
1973年 | 2篇 |
1970年 | 3篇 |
1959年 | 2篇 |
1929年 | 2篇 |
1927年 | 4篇 |
1919年 | 2篇 |
排序方式: 共有339条查询结果,搜索用时 15 毫秒
51.
Elizabeth M. Briggs Geoffrey W. Brown Peter M. Cairns Josef Jiricny Mohamed F. Meidine 《Magnetic resonance in chemistry : MRC》1980,13(4):306-307
31P chemical shifts in N-aryliminotriphenylphosphoranes and the corresponding N-methylated phosphonium salts are presented. They can be correlated with those theories of the bonding in phosphorus-nitrogen ylides which involve partial double bonding as a result of pπ–dπ overlap. 相似文献
52.
53.
It is shown that there appears to be a significant correlation between one of the supposed minority carrier de Haas-van Alphen frequencies in graphite and the difference of the majority electron and hole frequencies. 相似文献
54.
For the first time the capture of inner-shell electrons by protons is calculated by the SPB method without further approximation and using Hartree-Slater wavefunctions. The resulting cross-section has roughly the correct shape, but is much too large. The problem is traced to a loss of normalization caused by the SPB approximation. A suitably renormalized SPB gives close agreement with experiment. 相似文献
55.
Smith EF Garcia IJ Briggs D Licence P 《Chemical communications (Cambridge, England)》2005,(45):5633-5635
The in situ monitoring of catalysis in Room Temperature Ionic Liquids (RTILs) is fundamental to the understanding of catalytic processes and the role of RTILs in catalytic turnover; we describe how XPS can be used to give information on both pure RTILs and catalytically-active RTIL-based solutions. 相似文献
56.
Podospicatin (I) and its trimethyl ether (II) have been synthesized by separate standard procedures respectively, involving in the former a rearrangement with alkali. 相似文献
57.
Summary A method has been developed for the determination of small amounts of potassium perchlorate in admixture with potassium chlorate. The method involves preliminary decomposition of the potassium chlorate by boiling with concentrated hydrochloric acid, preparing a disc from the dried residue, and measuring its absorbance at 628 cm–1.
Zusammenfassung Eine Methode zur Bestimmung kleiner Mengen Kaliumperchlorat in Gegenwart von Kaliumchlorat wurde ausgearbeitet. Sie beruht auf der vorhergehenden Zersetzung des Chlorats durch Kochen mit konz. Salzsäure, Herstellung einer Scheibe aus dem Trockenrückstand und Messung ihrer Absorption bei 628 cm–1.相似文献
58.
We present a simple formula by which the shape of the absorption spectrum of an aggregate of quantum "monomers" (cold atoms, molecules, quantum dots, nanoparticles, etc.) interacting via dipole-dipole forces can be calculated from the averaged spectrum of the quantum monomer itself. Spectral broadening, due to a wide variety of causes, is included explicitly so that the formula is applicable not only to the idealization of a discrete spectrum but also to the practical situation of a continuously broadened spectrum. In simple cases, analytic results are obtained showing the strong dependence of the aggregate spectrum on the precise nature of the broadening of the quantum monomer spectrum. The formula is compared with results of exact diagonalization of model aggregate Hamiltonians and with experiment. 相似文献
59.
Cletus A D'Souza Vikramjit Chopra Richard Varhol Yuan-Yun Xie Slavita Bohacec Yongjun Zhao Lisa LC Lee Mikhail Bilenky Elodie Portales-Casamar An He Wyeth W Wasserman Daniel Goldowitz Marco A Marra Robert A Holt Elizabeth M Simpson Steven JM Jones 《BMC neuroscience》2008,9(1):1-14
Background
We have recorded responses from single neurons in murine visual cortex to determine the effectiveness of the input from the two murine cone photoreceptor mechanisms and whether there is any unique selectivity for cone inputs at this higher region of the visual system that would support the possibility of colour vision in mice. Each eye was stimulated by diffuse light, either 370 (strong stimulus for the ultra-violet (UV) cone opsin) or 505 nm (exclusively stimulating the middle wavelength sensitive (M) cone opsin), obtained from light emitting diodes (LEDs) in the presence of a strong adapting light that suppressed the responses of rods.Results
Single cells responded to these diffuse stimuli in all areas of striate cortex. Two types of responsive cells were encountered. One type (135/323 – 42%) had little to no spontaneous activity and responded at either the on and/or the off phase of the light stimulus with a few impulses often of relatively large amplitude. A second type (166/323 – 51%) had spontaneous activity and responded tonically to light stimuli with impulses often of small amplitude. Most of the cells responded similarly to both spectral stimuli. A few (18/323 – 6%) responded strongly or exclusively to one or the other spectral stimulus and rarely in a spectrally opponent manner.Conclusion
Most cells in murine striate cortex receive excitatory inputs from both UV- and M-cones. A small fraction shows either strong selectivity for one or the other cone mechanism and occasionally cone opponent responses. Cells that could underlie chromatic contrast detection are present but extremely rare in murine striate cortex. 相似文献60.
Edward L. Briggs Arianna Tota Marco Colella Leonardo Degennaro Renzo Luisi James A. Bull 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(40):14441-14448
Sulfonimidamides are intriguing new motifs for medicinal and agrochemistry, and provide attractive bioisosteres for sulfonamides. However, there remain few operationally simple methods for their preparation. Here, the synthesis of NH‐sulfonimidamides is achieved directly from sulfenamides, themselves readily formed in one step from amines and disulfides. A highly chemoselective and one‐pot NH and O transfer is developed, mediated by PhIO in iPrOH, using ammonium carbamate as the NH source, and in the presence of 1 equivalent of acetic acid. A wide range of functional groups are tolerated under the developed reaction conditions, which also enables the functionalization of the antidepressants desipramine and fluoxetine and the preparation of an aza analogue of the drug probenecid. The reaction is shown to proceed via different and concurrent mechanistic pathways, including the formation of novel S≡N sulfanenitrile species as intermediates. Several alkoxy‐amino‐λ6‐sulfanenitriles are prepared with different alcohols, and shown to be alkylating agents to a range of nucleophiles. 相似文献