全文获取类型
收费全文 | 246719篇 |
免费 | 1870篇 |
国内免费 | 881篇 |
专业分类
化学 | 111257篇 |
晶体学 | 3764篇 |
力学 | 13750篇 |
综合类 | 3篇 |
数学 | 50794篇 |
物理学 | 69902篇 |
出版年
2020年 | 1398篇 |
2019年 | 1553篇 |
2018年 | 12184篇 |
2017年 | 12080篇 |
2016年 | 9087篇 |
2015年 | 2706篇 |
2014年 | 3375篇 |
2013年 | 7935篇 |
2012年 | 9364篇 |
2011年 | 17024篇 |
2010年 | 10451篇 |
2009年 | 10856篇 |
2008年 | 12895篇 |
2007年 | 14932篇 |
2006年 | 6259篇 |
2005年 | 6724篇 |
2004年 | 6553篇 |
2003年 | 6491篇 |
2002年 | 5418篇 |
2001年 | 5434篇 |
2000年 | 4132篇 |
1999年 | 3096篇 |
1998年 | 2656篇 |
1997年 | 2515篇 |
1996年 | 2421篇 |
1995年 | 2226篇 |
1994年 | 2162篇 |
1993年 | 2093篇 |
1992年 | 2356篇 |
1991年 | 2306篇 |
1990年 | 2241篇 |
1989年 | 2178篇 |
1988年 | 2178篇 |
1987年 | 2179篇 |
1986年 | 2076篇 |
1985年 | 2674篇 |
1984年 | 2724篇 |
1983年 | 2417篇 |
1982年 | 2532篇 |
1981年 | 2345篇 |
1980年 | 2330篇 |
1979年 | 2469篇 |
1978年 | 2494篇 |
1977年 | 2406篇 |
1976年 | 2452篇 |
1975年 | 2376篇 |
1974年 | 2337篇 |
1973年 | 2528篇 |
1972年 | 1639篇 |
1971年 | 1345篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
M. R. Allazov Ali Riza Kul A. V. Einullaev M. B. Babanly 《Russian Journal of Inorganic Chemistry》2006,51(4):624-629
Some polythermal sections of the Ni-Bi-Se system have been investigated by DTA, X-ray powder diffraction, microstructural analysis, and microhardness measurements. The liquidus surface has been constructed for this system. The compounds NiBi2Se4 and Ni3Bi2Se2 are formed by dystectic reactions and melt at 1088 and 980 K, respectively. The regions of primary and joint phase crystallization have been determined. A commutation of Bi2Se3-based thermoelements with a metal nickel bus-bar has been proposed. 相似文献
102.
Catalytic properties of silica-supported heteropolyacids (HPA) in a mechanical mixture with reduced Me-Ce oxides (Me = Ni,
Pd) in n-hexane isomerization are studied. The role of each component of the mixed oxides (Ce and, typically, Ni and Pd) and their
optimum content has been illuminated: cerium is not only beneficial for eliminating or preventing coke deposition but is also
effective for maintaining the Keggin structure of the highly-organized HPA during the reaction and probably allows a better
dispersion of the second metal species. Nickel and palladium, present as Ni0 and Pd0, reinforce the activation of the alkane, which is difficult to obtain by means of a direct attack by an acid, and, thus,
enhance noticeably the activity of the catalyst. The best mechanical mixtures are obtained with 30–70 wt % NiCeO-HPW/SiO2 and 50–50 wt % Pd0.1CeO-HPW/SiO2. These mixtures have the highest efficiency for a Ni/(Ni + W) atomic ratio of 0.66 and a Pd/(Pd + W) ratio of 0.40, respectively.
Finally, the conversion of n-hexane is in the order HPW > HSiW > HBW, which seems to be consistent with the order of their acid strength as per the literature,
but the isomerization selectivity appears to be slightly higher on HSiW.
Published in Russian in Kinetika i Kataliz, 2006, Vol. 47, No. 1, pp. 24–28.
The text was submitted by the authors in English. 相似文献
103.
104.
105.
Palladium-catalysed three component coupling of an alkenylbromide, isonitrile and an amine or alkoxide/phenoxide affords α,β-unsaturated-amidines and -imidates. 相似文献
106.
Chris Hope 《The Journal of the Operational Research Society》2003,54(11):1167-1176
What strategy should a football (soccer, in American parlance) club adopt when deciding whether to sack its manager? This paper introduces a simple model assuming that a club's objective is to maximize the number of league points that it scores per season. The club's strategy consists of three choices: the length of the honeymoon period during which it will not consider sacking a new manager, the level of the performance trapdoor below which the manager get the sack, and the weight that it will give to more recent games compared to earlier ones. Some data from the last six seasons of the English Premiership are used to calibrate the model. At this early stage of the research, the best strategy appears to have only a short honeymoon period of eight games (much less than the actual shortest period of 12 games), to set the trapdoor at 0.74 points per game, and to put 47% of the weight on the last five games. A club adopting this strategy would obtain on average 56.8 points per season, compared to a Premiership average of 51.8 points. 相似文献
107.
108.
Dominique Fourdrinier William E. Strawderman 《Annals of the Institute of Statistical Mathematics》2003,55(4):803-816
We consider estimation of loss for generalized Bayes or pseudo-Bayes estimators of a multivariate normal mean vector, θ. In
3 and higher dimensions, the MLEX is UMVUE and minimax but is inadmissible. It is dominated by the James-Stein estimator and by many others. Johnstone (1988,
On inadmissibility of some unbiased estimates of loss,Statistical Decision Theory and Related Topics, IV (eds. S. S. Gupta and J. O. Berger), Vol. 1, 361–379, Springer, New York) considered the estimation of loss for the usual
estimatorX and the James-Stein estimator. He found improvements over the Stein unbiased estimator of risk. In this paper, for a generalized
Bayes point estimator of θ, we compare generalized Bayes estimators to unbiased estimators of loss. We find, somewhat surprisingly,
that the unbiased estimator often dominates the corresponding generalized Bayes estimator of loss for priors which give minimax
estimators in the original point estimation problem. In particular, we give a class of priors for which the generalized Bayes
estimator of θ is admissible and minimax but for which the unbiased estimator of loss dominates the generalized Bayes estimator
of loss. We also give a general inadmissibility result for a generalized Bayes estimator of loss.
Research supported by NSF Grant DMS-97-04524. 相似文献
109.
V. Bradnova M. M. Chernyavsky L. Just S. P. Kharlamov A. D. Kovalenko M. Haiduc K. A. Kotel’nikov V. A. Krasnov V. G. Larionova F. G. Lepekhin A. I. Malakhov G. I. Orlova N. G. Peresadko N. G. Polukhina P. A. Rukoyatkin V. V. Rusakova N. A. Salmanova B. B. Simonov S. Vokal P. I. Zarubin 《Physics of Atomic Nuclei》2003,66(9):1646-1650
A physical program of irradiation of emulsions in beams of relativistic nuclei named the BECQUEREL Project is reviewed. It is destined to study in detail the processes of relativistic fragmentation of light radioactive and stable nuclei. The expected results would make it possible to answer some topical questions concerning the cluster structure of light nuclei. Owing to the best spatial resolution, the nuclear emulsions would enable one to obtain unique and evident results. The most important irradiations will be performed in the secondary beams of He, Be, B, C, and N radioactive nuclei formed on the basis of JINR Nuclotron beams of stable nuclei. We present results on the charged state topology of relativistic fragmentation of the 10B nucleus at low energy-momentum transfers as the first step of the research. 相似文献
110.