全文获取类型
收费全文 | 237272篇 |
免费 | 3211篇 |
国内免费 | 1343篇 |
专业分类
化学 | 133400篇 |
晶体学 | 3339篇 |
力学 | 9179篇 |
综合类 | 61篇 |
数学 | 27383篇 |
物理学 | 68464篇 |
出版年
2020年 | 2011篇 |
2019年 | 2167篇 |
2018年 | 2844篇 |
2017年 | 2860篇 |
2016年 | 4317篇 |
2015年 | 2915篇 |
2014年 | 4071篇 |
2013年 | 9930篇 |
2012年 | 8745篇 |
2011年 | 10435篇 |
2010年 | 7282篇 |
2009年 | 7026篇 |
2008年 | 9690篇 |
2007年 | 9815篇 |
2006年 | 9217篇 |
2005年 | 8463篇 |
2004年 | 7528篇 |
2003年 | 6597篇 |
2002年 | 6447篇 |
2001年 | 7015篇 |
2000年 | 5364篇 |
1999年 | 3881篇 |
1998年 | 3208篇 |
1997年 | 3158篇 |
1996年 | 3204篇 |
1995年 | 2763篇 |
1994年 | 2882篇 |
1993年 | 2719篇 |
1992年 | 2975篇 |
1991年 | 3019篇 |
1990年 | 2838篇 |
1989年 | 2719篇 |
1988年 | 2664篇 |
1987年 | 2600篇 |
1986年 | 2616篇 |
1985年 | 3434篇 |
1984年 | 3504篇 |
1983年 | 2899篇 |
1982年 | 3141篇 |
1981年 | 2923篇 |
1980年 | 2706篇 |
1979年 | 2865篇 |
1978年 | 3068篇 |
1977年 | 3109篇 |
1976年 | 3127篇 |
1975年 | 2860篇 |
1974年 | 2946篇 |
1973年 | 3003篇 |
1972年 | 2342篇 |
1971年 | 1874篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
A new microscopic model of anomalous muonium for the elemental semiconductors is proposed. The relevant configuration consisting
of both a diamagrentic molecule Si−Mu and an unpaired orbital e− is contained into a semivacancy of the real lattice. By using the unrestricted Hartree-Fock computational method the principal
properties of the system are established. A dynamical version of the model together with a question on the formation of such
system are discussed. 相似文献
122.
123.
L. V. Veretekhina 《Journal of Mathematical Sciences》1992,60(4):1586-1590
A numerical example of the salinity regime of soils in a two-dimensional region is considered with allowance for the effect of temperature fields. The mathematical model is based on solving a system of nonlinear partial differential equations.Translated from Vychislitel'naya i Prikladnaya Matematika, No. 60, pp. 59–65, 1986. 相似文献
124.
G. M. Luke L. P. Le B. J. Sternlieb Y. J. Uemura J. H. Brewer R. Kadono R. F. Kiefl S. R. Kreitzman T. M. Riseman C. L. Seaman Y. Dalichaouch M. B. Maple J. D. Garrett 《Hyperfine Interactions》1991,64(1-4):517-522
We have performed both zero field and high transverse field measurements at dilution refrigerator temperatures on a number of heavy electron systems, examining the superconducting and magnetic properties of these interesting materials. Among the materials studied to date are UBe13, URu2Si2 and U6Fe. The magnetic field penetration depth in the superconducting state of UBe13 is greater than 10000 Å, as no increase in the transverse field relaxation rate is observed belowT c . A sharp increase in the precession frequency is seen, starting atT c . This frequency shift shows little temperature dependence at low temperature; we found no clear evidence for unconventional superconductivity in this material. Zero field measurements in URu2Si2 show the weak antiferromagnetic transition at 17.5 K. Finally, we we found no clear evidence for unconventional superconductivity in this material. Zero field measurements in URu2Si2 show the weak antiferromagnetic transition at 17.5 K. Finally, we have observed relaxation in high transverse field due to the formation of a flux lattice in U6Fe, a material where the electron effective mass is rather lighter than in other heavy fermion systems. The relaxation exhibits a sharp onset atT c=3.9 K, and is flat at low temperatures as expected for a conventional superconductor. 相似文献
125.
S. Ramos-Bernal A. Negrón-Mendoza 《Journal of Radioanalytical and Nuclear Chemistry》1992,160(2):487-492
This research addresses itself to the study of the mechanism of the acetic acid decarboxylation in Na-Montmorillonite exposed to ionizing radiation. The results obtained indicated that the decarboxylation reaction is enhanced several times by the irradiation. This behavior is probably due to an oxidation reaction at the edges of the clay. Also it is by energy transfer from the clay to adsorbed molecules by an interaction of non-equilibrium charge carriers with the adsorbed molecules. 相似文献
126.
127.
Rate constants have been measured by pulse radiolysis for the reactions of the carbonate radical, CO3·?, with a number of organic and inorganic reactants as a function of temperature, generally over the range 5 to 80°C. The reactants include the substitution-inert cyano complexes of FeII, MoIV, and WIV, the simple inorganic anions SO32?, ClO2?, NO2?, I?, and SCN?, several phenolates, ascorbate, tryptophan, cysteine, cystine, methionine, triethylamine, and allyl alcohol. The measured rate constants ranged from less than 105 to 3 × 109 M?1 s?1, the activation energies ranged from ?11.4 to 18.8 kJ mol?1, and the pre-exponential factors ranged from log A = 6.4 to 10.7. The activation energies for the metal complexes and inorganic anions generally decrease with increasing driving force for the reaction, as expected for an outer sphere electron transfer. For highly exothermic reactions, however, the activation energy appears to increase, probably reflecting the temperature dependence of diffusion. For many of the organic reactants, the activation energies were low and independent of driving force, suggesting that the oxidation is via an inner sphere mechanism. 相似文献
128.
Network location problems occur when new facilities must be located on a network, and the network distances between new and existing facilities are important. In urban, regional, or geographic contexts, there may be hundreds of thousands (or more) of existing facilities, in which case it is common to aggregate existing facilities, e.g. represent all the existing facility locations in a zip code area by a centroid. This aggregation makes the size of the problem more manageable for data collection and data processing purposes, as well as for purposes of analysis; at the same time, it introduces errors, and results in an approximating location problem being solved. There seems to be relatively little theory for doing aggregation, or evaluating the results of aggregation; most approaches are based on experimentation or computational studies. We propose a theory that has the potential to improve the means available for doing aggregation.This research was supported in part by the National Science Foundation, Grant No. DDM-9023392. 相似文献
129.
Peroxyoxalate chemiluminescence may be used for sensitive postcolumn detection of phenothiazine analytes separated by high performance liquid chromatography with appropriate optimization of measurement conditions such as solvent, pH and oxalate ester. Detectability of fluorescent analytes by chemical excitation varies greatly, but analytes with low oxidation potentials are generally more readily detected at low levels, as demonstrated for phenothiazines, an important class of fluorescent drugs. Some improvement in detection limits is observed for fluphenazine when chemiluminescence detection is compared to conventional fluorescence detection. Because of the specificity of chemical excitation, fewer interferences from fluorescent impurities in a urine matrix are observed. 相似文献
130.
A nonuniform electron density distribution is observed in La1−x− y
NdySrxCuO4 and La1−x−y
EuySrxCuO4, and long-lived magnetic fluctuations in these compounds are studied. The dynamics of the magnetic fluctuations depends strongly
on the magnetic properties of the rare-earth ions, which stabilize the low-temperature tetragonal phase.
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 5, 344–349 (10 March 1998) 相似文献