全文获取类型
收费全文 | 1003篇 |
免费 | 32篇 |
国内免费 | 6篇 |
专业分类
化学 | 854篇 |
晶体学 | 16篇 |
力学 | 7篇 |
数学 | 21篇 |
物理学 | 143篇 |
出版年
2023年 | 5篇 |
2022年 | 6篇 |
2021年 | 7篇 |
2020年 | 14篇 |
2019年 | 13篇 |
2018年 | 8篇 |
2017年 | 5篇 |
2016年 | 18篇 |
2015年 | 17篇 |
2014年 | 24篇 |
2013年 | 38篇 |
2012年 | 79篇 |
2011年 | 101篇 |
2010年 | 43篇 |
2009年 | 31篇 |
2008年 | 65篇 |
2007年 | 75篇 |
2006年 | 48篇 |
2005年 | 70篇 |
2004年 | 56篇 |
2003年 | 44篇 |
2002年 | 34篇 |
2001年 | 11篇 |
2000年 | 15篇 |
1999年 | 11篇 |
1998年 | 9篇 |
1997年 | 11篇 |
1996年 | 9篇 |
1995年 | 19篇 |
1994年 | 10篇 |
1992年 | 16篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1986年 | 5篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1978年 | 5篇 |
1974年 | 4篇 |
1971年 | 4篇 |
1969年 | 6篇 |
1968年 | 7篇 |
1967年 | 10篇 |
1966年 | 5篇 |
排序方式: 共有1041条查询结果,搜索用时 15 毫秒
61.
Synthesis of axinohydantoins 总被引:1,自引:0,他引:1
A short synthesis of the hydantoin-containing marine sponge metabolites axinohydantoins is described. A key feature of the synthesis is a putative biomimetic, intramolecular cyclization of alpha-functionalized imidazolone 5, which affords the tricyclic pyrroloazepinone framework comprising 6. In addition, the conversion of imidazolones to alpha,beta-unsaturated hydantoins is outlined and represents a new approach to these heterocyclic systems. 相似文献
62.
The 1H spectrum of (15N)acetamide has been measured in dimethyl sulphoxide (DMSO), methyl propyl ketone (MPK), 1,3-dioxane, 1,4-dioxane, D2O, acetonitrile and pyridine-d5 at various temperature intervals within the range of 278–343 K. From the temperature dependence of the NMR spectra of the amide protons, the free energy of activation, ΔG≠, for hindered rotation about the central C? N bond was determined by means of total line shape analysis in the four solvents DMSO, MPK and the two dioxanes. Observed values of ΔG≠ (298 K) (72.7 in DMSO, 70.1 in MPK, 70.0 in 1,3-dioxane and 70.1 kJ mol1 in 1,4-dioxane) were not very sensitive to the choice of solvent or concentration. The concentration dependence of the internal chemical shift between the amide protons was studied in MPK, D2O, acetonitrile and pyridine-d5. The free energy of activation and the internal chemical shift are discussed on the basis of solvent-amide and amide–amide specific hydrogen bonding interactions, and in comparison to the results of molecular orbital calculations. 相似文献
63.
Kenichi Nanbu 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1971,22(6):1167-1172
Zusammenfassung Mittels des Differenzenverfahrens wurden instationäre, laminare Grenzschichten längs eines Keiles (von verschiedenen Keilwinkeln ) gerechnet, der plötzlich aus der Ruhe herausbewegt wird. Es ist bemerkenswert, daß im Fall >0.6 die Grenzschicht an der betreffenden Stelle der Keilwand bereits vor der Ankunft der an der Vorderkante entstehenden Störungen fast stationär wird, und daß, wenn die -Zahl sich dem Wert –0.1988 nähert, es doch eine beträchtliche Zeit braucht vom Vorüberziehen dieser Störungen bis zum Erreichen des stationären Zustandes der Grenzschicht. 相似文献
64.
Hiroyuki Inouye Yoshio Takeda Shinichi Uesato Kenichi Uobe Toshiro Hashimoto Tetsuro Shingu 《Tetrahedron letters》1980,21(11):1059-1062
Hydrangenoside A, isolated along with its three congeners from Hydrangea macrophylla, was proved to have a novel type of structure which is thought to be biosynthesized through an aldol-type condensation of secologanin with a unit formed by the shikimate-malonate route followed by decarboxylation. 相似文献
65.
Hirosawa K Furumochi H Tada A Kannari F Takeoka M Sasaki M 《Physical review letters》2005,94(20):203601
To the best of our knowledge, we demonstrate for the first time the generation of photon number squeezing by spectral filtering for ultrabroadband light generated by microstructure fibers at 800 nm. A maximum squeezing of 4.6 dB is observed, corresponding to 10.3 dB after correcting for detection losses. We numerically analyzed the quantum dynamics of ultrashort laser pulse propagation through optical fibers by solving a nonlinear quantum Schr?dinger equation that included Raman scattering, especially for the quantum correlation of photon number fluctuation among frequency modes in broadband pulses. 相似文献
66.
We elaborated a versatile experimental model of chromatin which consists of a single chain of long duplex DNA that interacts with well-defined cationic nanoparticles of various sizes. We found that the DNA compaction by nanoparticles is stepwise and progressive at the single-chain level. It is controlled by the ability of DNA to wrap nanoparticles, which is more efficient for larger particles and, similar to DNA-histone interaction, is optimal at a physiological salt concentration. 相似文献
67.
68.
Yuasa M Oyaizu K Yamaguchi A Kuwakado M 《Journal of the American Chemical Society》2004,126(36):11128-11129
Cobalt(II) meso-tetrakis(4-hexadecylamidophenyl)porphyrin self-assembles in ethanol/1-propanol 2/1 (v/v) to form a rodlike micelle with nanoscale dimensions; the nanorod is a face-to-face aggregate having a hydrophobic corona around a polar core and is thus characterized as a reverse micelle. 相似文献
69.
Sadamoto R Niikura K Ueda T Monde K Fukuhara N Nishimura S 《Journal of the American Chemical Society》2004,126(12):3755-3761
UDP-MurNAc-pentapeptide derivative bacterial cell-wall precursors were synthesized as effective tools for surface display on living bacteria. Lactobacilli were incubated in the ketone-modified precursor-containing medium, and the ketone moiety was displayed on the bacterial surface through cell-wall biosynthesis. Oligomannose was coupled with the ketone moiety on the bacterial surface via a aminooxyl linker, thereby displaying this oligosaccharide on the surface of the bacteria. The increase in the adhesion of the sugar-displaying bacteria onto a concanavalin A-attached film compared to that of native bacteria was confirmed by microscopic observation and surface plasmon resonance measurement. The incorporation of the artificial cell-wall precursors was enhanced when incubated with fosfomycin, an inhibitor of cell-wall precursor biosynthesis. 相似文献
70.
[structure: see text] Synthesis and fluorescence properties of pi-conjugated compounds having alternately an aromatic ring such as benzene, pyridine, and thiophene and an enediyne unit in the backbone are described. 相似文献