全文获取类型
收费全文 | 384篇 |
免费 | 10篇 |
国内免费 | 1篇 |
专业分类
化学 | 258篇 |
晶体学 | 10篇 |
力学 | 8篇 |
综合类 | 2篇 |
数学 | 35篇 |
物理学 | 82篇 |
出版年
2021年 | 8篇 |
2020年 | 2篇 |
2019年 | 8篇 |
2018年 | 7篇 |
2017年 | 3篇 |
2016年 | 10篇 |
2015年 | 16篇 |
2014年 | 9篇 |
2013年 | 23篇 |
2012年 | 24篇 |
2011年 | 24篇 |
2010年 | 19篇 |
2009年 | 7篇 |
2008年 | 14篇 |
2007年 | 18篇 |
2006年 | 24篇 |
2005年 | 15篇 |
2004年 | 10篇 |
2003年 | 12篇 |
2002年 | 13篇 |
2001年 | 4篇 |
2000年 | 2篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 7篇 |
1994年 | 2篇 |
1993年 | 5篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1987年 | 2篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 9篇 |
1980年 | 4篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 8篇 |
1975年 | 8篇 |
1974年 | 10篇 |
1973年 | 6篇 |
1972年 | 3篇 |
1971年 | 3篇 |
1969年 | 3篇 |
1968年 | 2篇 |
1967年 | 1篇 |
1966年 | 1篇 |
1962年 | 1篇 |
排序方式: 共有395条查询结果,搜索用时 15 毫秒
91.
The particle scattering function P(k) is approximately evaluated for the Kratky–Porod wormlike chain with a circular cross section to examine the effect of chain diameter d on the scattering curve of k2P(k) versus k, the magnitude of the scattering vector, for stiff chains and also the applicability of the cross‐section plot of ln[kP(k)] versus k2 to them. In the evaluation, series expansions from the rod and coil limits up to the fifth‐order and third‐order deviations, respectively, are combined together. The major results or conclusions derived are as follows. First, the conventional equation, P(k) = P0(k) exp(?k2d2/16), for straight cylinders overestimates k2P(k) at relatively large values of k, whereas its alternative, P(k) = P0(k)[2J1(kd/2)/(kd/2)]2, is a good approximation to exact P(k) unless contour length L is shorter than 10d. Here, P0(k) denotes the scattering function for the chain contour, and J1(x) is the Bessel function of the first order. Second, as d is increased for a fixed value of L (relative to the Kuhn segment length), the k2P(k)–k curve lowers with a pronounced maximum, and the peak position shifts to a lower scattering angle. Third, if the chain is somewhat flexible, the cross‐section plot has an approximately linear region, with a slope fairly close to ?d2/16 expected from the aforementioned conventional equation. This plot for rods appreciably bends down, and thus the experimental observation of an approximately linear relation (over a wide k range) implies that, in contrast to the prevailing notion, the polymer examined is not completely rigid but instead is somewhat flexible. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1398–1407, 2004 相似文献
92.
Abstract— Using the method of polarized photochemistry, the polarization of the first daughter (K610 ) in the photocycle of light-adapted bacteriorhodopsin (bR570 ) is determined relative to the polarization of the photolysis pulse for different absorption regions of bR570 . The results are discussed in terms of recent spectroscopic assignments of bR570 , and in the 310–266 nm region, in terms of energy transfer processes between the apoprotein and the retinal. 相似文献
93.
Photolysis of 1-(2-bromo-3-hydroxy-4,5-(dimethoxyphenethyl)-1,2,3,4-tetrahydro-7-hydroxy-6-methoxy-2-methylisoquinoline (8) gave 4,5,6,6a-tetrahydro-1,12-dihydroxy-2,10,11-trimethoxy-6-methylhomoaporphine (7), which is identical with the alkaloid CC-24 isolated from Cholchicum cornigerum. 相似文献
94.
Yo Nakamura Takashi Norisuye Akio Teramoto 《Journal of Polymer Science.Polymer Physics》1991,29(2):153-159
Second virial coefficients A2 and third virial coefficients A3 for benzene solutions of ten polystyrene fractions ranging in weight-average molecular weight Mw from 104 to 2 × 107 at 25°C were determined by light scattering. The third coefficient is represented approximately by A3 = 8.0 × 10?6 M mol g?3 cm6 for Mw above 105. In this molecular weight region, the factor g defined by A3/AMw/ This trend of g is consistent with predictions of early two-parameter theories but not with those of renormalization group theories. In particular, quantitative agreement is observed between the present experiments (for Mw ? 2 × 105) and the mean-field two-parameter theory of Stockmayer and Casassa. 相似文献
95.
Tetsuji Kametani Keiichiro Fukumoto Takuo Nakano 《Journal of heterocyclic chemistry》1972,9(6):1363-1366
The indisputable benzyne reaction of 1-(5-bromo-3,4-dimethoxybenzyl)-1,2,3,4-tetrahydro-7-hydroxy-6-metlioxy-2-methylisoquinoline (II) with sodium amide in liquid ammonia afforded the following compounds, (±)-cryptaustoline iodide (VI), (±)-thaliporphine (VIII), 1 -(3,4-dimeth-oxybenzyl)- (III), and 1 -(2-amino-4,5-dimethoxybenzyl)-l,2,3,4-tetrahydro-7-hydroxy-6-meth-oxy-2-methylisoquinoline (IV). 相似文献
96.
Oikawa K Monobe H Takahashi J Tsuchiya K Heinrich B Guillon D Shimizu Y 《Chemical communications (Cambridge, England)》2005,(42):5337-5339
The carrier mobility of highly ordered lamellar mesophases was evaluated by a Time-of-Flight (TOF) method for mesogenic 1,4-di(5'-octyl-2'-thienyl)benzene (8-TPT-8) to reveal the fastest drift mobility (0.1 cm(2) V(-1) s(-1) for the lowest temperature mesophase) in calamitic liquid crystals reported to date. 相似文献
97.
Phenolic cyclization of 2-ethoxycarbonylmethylidenecyclohexanone (IV) with 3-hydroxy-4-methoxyphenethylamine (V) were performed in the process of finding a synthetic approach to dihydroerysolidine (I). Thus, 16-hydroxy-15-methoxyerythrinan-6-ene-8-one (VI) and 16-hydroxy-15-methoxyerythrinan-7-ene-8-one (VII) were synthesized, both of which were hydrogenated in the presence of Adams platinum to give the same product (XI). Furthermore, on the basis of the mass spectra of XI and XII, these compounds were assumed to be stereoisomeric at the C5- and C6-positions. 相似文献
98.
Michinori Akaiwa Hiroki Fukumoto Takakazu Yamamoto 《Journal of organometallic chemistry》2005,690(18):4192-4196
Thioamide-based tridentate ligands, 1,3-benzenedicarbothioamides (1a-c), were used to afford pincer palladium(II) complexes (Pd(1-H)Cl, 2a-c) with η3-S,C,S type coordination. The complexes exhibit strong emission in a glassy frozen state as well as in the solid state. The decay lifetime of the emission from the complexes is in a range of 8-9 × 10−5 s, which is indicative of phosphorescent emission. 相似文献
99.
The temperature and spectral dependences of the coefficients R i2* of the quadratic electro-optic effect (EOE) in triglycine sulphate crystals with 5% L-threonine admixture have been calculated using the temperature and spectral dependences of the refractive indices n i . It is established that the coefficients R i2* of the admixture-containing triglycine sulphate crystals exhibit weak spectral and temperature dependences. In the polar direction, R i2* are substantially different from the coefficients of admixture-free triglycine sulphate crystals. This indicates the occurrence of a bias field, the predominant orientation of the dipole moment of the polar defect, and a decrease in the spontaneous polarization in admixture-containing crystals. 相似文献
100.