全文获取类型
收费全文 | 846篇 |
免费 | 9篇 |
专业分类
化学 | 321篇 |
晶体学 | 1篇 |
力学 | 39篇 |
数学 | 43篇 |
物理学 | 451篇 |
出版年
2016年 | 12篇 |
2015年 | 12篇 |
2014年 | 9篇 |
2013年 | 26篇 |
2012年 | 24篇 |
2011年 | 26篇 |
2010年 | 13篇 |
2009年 | 19篇 |
2008年 | 26篇 |
2007年 | 32篇 |
2006年 | 41篇 |
2005年 | 39篇 |
2004年 | 26篇 |
2003年 | 38篇 |
2002年 | 24篇 |
2001年 | 17篇 |
2000年 | 30篇 |
1999年 | 13篇 |
1998年 | 7篇 |
1997年 | 8篇 |
1996年 | 10篇 |
1995年 | 21篇 |
1994年 | 19篇 |
1993年 | 32篇 |
1992年 | 26篇 |
1991年 | 13篇 |
1990年 | 22篇 |
1989年 | 7篇 |
1988年 | 7篇 |
1987年 | 9篇 |
1985年 | 8篇 |
1984年 | 6篇 |
1982年 | 14篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1977年 | 10篇 |
1976年 | 6篇 |
1975年 | 7篇 |
1974年 | 5篇 |
1973年 | 4篇 |
1972年 | 5篇 |
1943年 | 7篇 |
1935年 | 4篇 |
1934年 | 6篇 |
1933年 | 11篇 |
1931年 | 8篇 |
1906年 | 4篇 |
1903年 | 4篇 |
1896年 | 4篇 |
1885年 | 4篇 |
排序方式: 共有855条查询结果,搜索用时 156 毫秒
101.
Synthesis of 2‐Unsubstituted 1,3‐Selenazoles by Cyclization of Selenoformamide with α‐Bromocarbonyl Compounds 下载免费PDF全文
Harald Below Wolf‐Diethard Pfeiffer Karlheinz Geisler Ashot S. Saghyan Christine Fischer Peter Langer 《Journal of heterocyclic chemistry》2015,52(2):592-596
2‐Unsubstituted 1,3‐selenazoles were prepared by cyclization of selenoformamide with α‐bromoacetophenones. Parent 1,3‐selenazole was prepared by cyclization of selenoformamide with α‐bromoacetaldehyde. 相似文献
102.
H. H. Pfeiffer 《Rheologica Acta》1961,1(4-6):668-669
Ohne ZusammenfassungI thank Mr.Scott Blair for his answer reserving the term dilatancy for cases of real dilatation. Now it's only to wish that this terminology is used according to his Report on the principles of rheological nomenclature (Amsterdam 1949). 相似文献
103.
Unexpected Ring Enlargement of 2‐Hydrazono‐2,3‐dihydro‐1,3‐thiazoles to 1,3,4‐Thiadiazines 下载免费PDF全文
Wolf‐Diethard Pfeiffer Klaus‐Dieter Ahlers Ashot S. Saghyan Alexander Villinger Peter Langer 《Helvetica chimica acta》2014,97(1):76-87
The cyclization of thiosemicarbazide with α‐bromoacetophenone can result in the formation of isomeric 1,3,4‐thiadiazines and two different thiazoles. We studied the use of 4‐methyl‐ and 4‐ethylthiosemicarbazide as dinucleophilic building blocks. In this context, we observed an unprecedented rearrangement of a 2‐hydrazono‐2,3‐dihydrothiazole to a 1,3,4‐thiadiazine. While ring contractions of 1,3,4‐thiadiazines to thiazoles are quite common, ring enlargements are new. The course of the reaction depends on the substitution pattern of the substrate. 相似文献
104.
Cyclization of 4‐Phenylthiosemicarbazide with Phenacylbromide Revisited. Formation of 1,3,4‐Thiadiazines and of Isomeric 1,3‐Thiazoles 下载免费PDF全文
Wolf‐Diethard Pfeiffer Dieter Junghans Ashot S. Saghyan Peter Langer 《Journal of heterocyclic chemistry》2014,51(4):1063-1067
The cyclization of 4‐phenylthiosemicarbazide with phenacylbromide, carried out in refluxing ethanol, afforded 1,3,4‐thiadiazine 1 as the major product. In contrast to a previous report, 2‐phenylimino‐4‐phenyl‐2,3‐dihydro‐1,3‐thiazol‐3‐amine ( 2 ) and not 2‐hydrazono‐3,4‐diphenyl‐2,3‐dihydro‐1,3‐thiazole ( 8 ) was formed as a side‐product. This product is the main product when the reaction is carried out in concentrated hydrochloric acid. Our findings were independently confirmed by independent syntheses of the isomeric products and by a thorough study of their reactivity. It is important to note that the product distribution of the cyclization of thiosemicarbazides with haloketones strongly depends on the substitution pattern and on the reaction conditions. 相似文献
105.
Nano titanium dioxide (nTiO2), generally considered to be toxicologically inert, is manufactured in large quantities and extensively applied in consumer products. The small size and large surface area endow them with an active group or intrinsic toxicity. Advances in instrumentation are making Raman spectroscopy the tool of choice for an increasing number of (bio) chemical applications. One of the great advantages of this technique is its ability to provide information on the concentration, structure and interaction of biochemical molecules in their microenvironments within intact cells and tissues, non-destructively. Zebrafish (Danio rerio), one of the most important vertebrate model organisms used in developmental biology, are increasingly used in biomedical research, particularly as a model of human disease. In the present work, an attempt is made to study the effect of titanium dioxide, both nano and bulk, on the microenvironment of the liver tissues of Zebrafish using FT-Raman spectroscopy. The results of the present study suggest that TiO2 exposure demonstrate a marked influence on the microenvironments of the liver tissues of Zebrafish. A shift to a higher wavenumber and an increase in the intensity of the band at ∼1087 cm−1 in the TiO2 exposed tissues suggest that some of the conformational changes resulting from the alkali recovery process takes place due to TiO2 exposure. The decreased intensity ratio (I3220/I3400) observed in the titanium-exposed tissues suggests a decreased water domain size, which could be interpreted in terms of weaker hydrogen-bonded molecular species of water in the TiO2 exposed tissues. The observed shift of COO− bands to higher frequencies shows the disruption of salt bridges as a result of a change in the oppositely charged partners and due to the enhanced random coil conformation. The variation in the intensity ratio of the tyrosyl doublet (I858/I825) indicates variation in the hydrogen bonding of the phenolic hydroxyl group due to TiO2 exposure. The results further suggest that the microenvironments are greatly altered due to titanium nano exposure when compared to titanium bulk. In conclusion, the results indicate that FT-Raman spectroscopy might be a useful tool for rapid assessment of nano particle biological interactions. 相似文献
106.
The question whether a polynomial time recognition algorithm for the class of perfectly orderable graphs exists was posed by Chvátal in 1981 when he introduced the notion of perfect orders. Since then several classes of perfectly orderable graphs have been identified. In this note we prove that recognizing perfectly orderable graphs is NP-complete. 相似文献
107.
W. Pfeiffer F. Sattler S. Vogler G. Gerber J.-Y. Grand R. Möller 《Applied physics. B, Lasers and optics》1997,64(2):265-268
Direct illumination of the tunneling gap in an ultrahigh vacuum scanning tunneling microscope with ultrashort pump-probe laser
pulses may offer ultimate spatial and temporal resolution in surface experiments. The electronic bandwidth of the tunneling
gap ( 1 THz) does not limit the time resolution. Our experiments show that multiphoton photoelectron emission from the sample limits
the application of this detection scheme at high laser fluence. However, a substrate specific pump-probe effect in the photoelectron
yield with femtosecond transients is observed on Tantalum and on GaAs(110) surfaces.
Received: 5 November 1996 相似文献
108.
109.
R. Baur A. Breskin R. Chechik A. Drees C. Jacob U. Faschingbauer P. Fischer Z. Fraenkel E. Gatti P. Glässel Th. Günzel C. P. de los Heros F. Hess D. Irmscher B. Lenkeit L. H. Olsen Y. Panebrattsev A. Pfeiffer I. Ravinovich P. Rehak A. Schön J. Schukraft J. Schukraft M. Sampietro A. Shor H. J. Specht V. Steiner S. Tapprogge G. Tel-Zur I. Tserruya Th. Ullrich J. P. Wurm 《Zeitschrift fur Physik C Particles and Fields》1997,74(4):593-594
110.
G. Lhersonneau H. Gabelmann B. Pfeiffer K. -L. Kratz 《Zeitschrift für Physik A Hadrons and Nuclei》1995,352(3):293-301
The low-energy level scheme of theN=63 nucleus101Sr has been obtained from a β-decay study of101Rb. The ν[532]5/2 and ν[411]3/2 orbitals are well established as the ground state and a band head at 271.2keV, respectively. The general properties of the level scheme indicate a quadrupole deformation ofβ ? 0.4, confirming the unique feature of saturation of deformation inN ≥ 60 Sr isotopes. The energies of theK=3/2 intraband transitions in the odd-neutron neighbours99Sr61 and101Sr63 are very similar. More generally, the identical bands at low spin in98–101Sr nuclei are correlated with the mass-independent moments of inertia in this region. 相似文献