全文获取类型
收费全文 | 219篇 |
免费 | 3篇 |
专业分类
化学 | 95篇 |
力学 | 8篇 |
数学 | 32篇 |
物理学 | 87篇 |
出版年
2022年 | 2篇 |
2020年 | 3篇 |
2018年 | 2篇 |
2017年 | 2篇 |
2016年 | 2篇 |
2014年 | 4篇 |
2013年 | 5篇 |
2012年 | 8篇 |
2011年 | 2篇 |
2010年 | 4篇 |
2009年 | 10篇 |
2008年 | 9篇 |
2007年 | 9篇 |
2006年 | 14篇 |
2005年 | 10篇 |
2004年 | 4篇 |
2003年 | 6篇 |
2002年 | 11篇 |
2001年 | 3篇 |
2000年 | 9篇 |
1999年 | 5篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 5篇 |
1994年 | 3篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1983年 | 8篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1978年 | 8篇 |
1974年 | 3篇 |
1970年 | 4篇 |
1969年 | 5篇 |
1967年 | 2篇 |
1966年 | 2篇 |
1963年 | 2篇 |
1959年 | 1篇 |
1958年 | 1篇 |
1943年 | 2篇 |
1942年 | 1篇 |
1939年 | 1篇 |
1938年 | 2篇 |
1925年 | 1篇 |
1924年 | 1篇 |
排序方式: 共有222条查询结果,搜索用时 0 毫秒
1.
Microsatellite structures in the context of human evolution 总被引:2,自引:0,他引:2
Six microsatellite - or short tandem repeat (STR) - systems with uniform repetitive sequences (HumTH01, HumCD4, HumFES/FPS, HumF13B, HumTPO, HumLPL) and three compound repeat systems (HumVWA, HumFIBRA, D21S11) were used, including data from the literature, to determine genetic distances among eight populations worldwide. The TH01- and VWA homologous loci in nonhuman primates (chimpanzees, gorillas, orangutans, rhesus monkeys, ring-tailed lemurs) were compared and found to be shorter than in humans. Microsatellites of lower complexity were most efficient for the separation of major ethnic groups. The loci of higher complexity showed a leveling of the diversity differences among populations, which could be attributed to higher mutation rates. 相似文献
2.
J. B?chler J. Bartke H. Bia?kowska R. Bock D. Brinkmann R. Brockmann P. Buncic S. I. Chase I. Derado V. Eckardt et al. 《Zeitschrift fur Physik C Particles and Fields》1994,61(4):551-561
The intermittency phenomenon is investigated in proton-gold, oxygen-gold, sulphur-gold and sulphur-sulphur collisions at 200 GeV per nucleon. The data were taken with the NA 35 streamer chamber detector at the CERN SPS. The data samples are carefully corrected for double counting of tracks and for contamination from photon conversions, particle decays and secondary interactions. The analysis is carried out in terms of factorial moments, using a new definition, and of correlation integrals. Both methods show the presence of nonstatistical fluctuations (intermittency). The main conclusions are: The observation of the effect for pairs of hadrons with negative charges and its near absence for pairs of opposite charges is consistent with the assumption that Bose-Einstein correlations yield the dominant contribution. The intermittency effect is not proportional to (dn/dy)–1 which would be expected in superposition models. The measured relation between the second and third factorial moment for negative hadrons indicates that genuine 3-particle correlations are small. The predictions of a Monte Carlo simulation which is based on the Lund Fritiof model with the inclusion of Bose-Einstein correlations agree with the experimental results.Deceased 相似文献
3.
In the view of the Deutscher Kalibrierdienst (DKD) , a certifying body for reference materials can be considered to be a calibration laboratory. Therefore, accreditation of calibration laboratories in accordance with ISO/IEC 17025 is the most appropriate way to establish confidence in certificates for reference materials. If necessary, the criteria of ISO/IEC 17025 can be tailored to specific cases. There is no need to provide any new kind of reference-material specific accreditation. However, in view of the variety of reference materials and the practice existing in other countries, accreditation of testing laboratories and product certification bodies may optionally be acceptable as long as the same stringent principles with respect to traceability and measurement uncertainty are applied. Such accreditations but not accreditations of reference material producers (ISO Guide 34) are also covered by existing international mutual recognition arrangements (MRA). 相似文献
4.
Susanne Bhr Sabine Brinkmann‐Chen Marc Garcia‐Borrs John M. Roberts Dimitris E. Katsoulis K. N. Houk Frances H. Arnold 《Angewandte Chemie (International ed. in English)》2020,59(36):15507-15511
Compared to the biological world's rich chemistry for functionalizing carbon, enzymatic transformations of the heavier homologue silicon are rare. We report that a wild‐type cytochrome P450 monooxygenase (P450BM3 from Bacillus megaterium, CYP102A1) has promiscuous activity for oxidation of hydrosilanes to give silanols. Directed evolution was applied to enhance this non‐native activity and create a highly efficient catalyst for selective silane oxidation under mild conditions with oxygen as the terminal oxidant. The evolved enzyme leaves C?H bonds present in the silane substrates untouched, and this biotransformation does not lead to disiloxane formation, a common problem in silanol syntheses. Computational studies reveal that catalysis proceeds through hydrogen atom abstraction followed by radical rebound, as observed in the native C?H hydroxylation mechanism of the P450 enzyme. This enzymatic silane oxidation extends nature's impressive catalytic repertoire. 相似文献
5.
Gunnar Brinkmann 《Journal of Graph Theory》1996,23(2):139-149
In this paper an efficient algorithm to generate regular graphs with small vertex valency is presented. The running times of a program based on this algorithm and designed to generate cubic graphs are below two natural benchmarks: (a) If N(n) denotes the number of pairwise non-isomorphic cubic graphs with n vertices and T(n) the time needed for generating the list of all these graphs, then T(n)/N(n) decreases gradually for the observed values of n. This suggests that T(n)/N(n) might be uniformly bounded for all n, ignoring the time to write the outputs, but we are unable to prove this and in fact are not confident about it. (b) For programs that generate lists of non-isomorphic objects, but cannot a priori make sure to avoid the generation of isomorphic copies, the time needed to check a randomly ordered list of these objects for being non-isomorphic is a natural benchmark. Since for large lists (n ≥ 22, girth 3) existing graph isomorphism programs take longer to canonically label all of the N(n) graphs than our algorithm takes to generate them, our algorithm is probably faster than any method which does one or more isomorphism test for every graph. © 1996 John Wiley & Sons, Inc. 相似文献
6.
7.
Peter Brinkmann 《Geometriae Dedicata》2002,93(1):191-203
We present necessary and sufficient conditions for the existence of a splitting over of the mapping torus
of a free group automorphism . 相似文献
8.
Priv. Doz. Dr.-Ing. G. Brinkmann 《Rheologica Acta》1969,8(3):274-277
Ohne Zusammenfassung 相似文献
9.
U. Brinkmann J. Goschler A. Steudel H. Walther 《Zeitschrift für Physik A Hadrons and Nuclei》1969,228(4):427-439
An atomic beam source for atoms in metastable states is described. The source was used to produce metastable Ca and Sr atoms in the3 P 0,1,2 and1 D 2 and Mg atoms in the3 P 0,1,2 states. The population of these levels was high enough (about 30% of the atoms were in the3 P levels and 3% in the1 D 2 level) so that zero field level crossing experiments could be performed at highly excited levels which were populated by an optical excitation starting from the metastable states. The lifetime results obtained for Ca areτ(4s 4d 3 D 1)=(1.21±0.07)·10?8sec,τ(4s 4f1 F 3)=(2.84±0.23)· 10?8sec, andτ(3d 4p 1 F 3)=(6.15±0.62)·10?8 sec. The three lifetimes have been evaluated using theg J values forLS-coupling. The quoted uncertainties include the errors by a possible deviation fromLS-coupling. 相似文献
10.
By measuring the nuclear spin-lattice relaxation time of 127I cooperative effects in Ag diffusion have been found which point to the necessity to include mutual cation interaction in the diffusion theory. An anomalous increase of the relaxation rate within 5 K just below the transition into the superionic state is taken as dynamical evidence for a discontinuity in the number of diffusing Ag ions, i.e. for sublattice melting. 相似文献