全文获取类型
收费全文 | 36934篇 |
免费 | 3967篇 |
国内免费 | 6317篇 |
专业分类
化学 | 30122篇 |
晶体学 | 1403篇 |
力学 | 828篇 |
综合类 | 256篇 |
数学 | 3871篇 |
物理学 | 10738篇 |
出版年
2024年 | 56篇 |
2023年 | 367篇 |
2022年 | 848篇 |
2021年 | 946篇 |
2020年 | 1163篇 |
2019年 | 1152篇 |
2018年 | 967篇 |
2017年 | 1312篇 |
2016年 | 1334篇 |
2015年 | 1210篇 |
2014年 | 1623篇 |
2013年 | 3062篇 |
2012年 | 2054篇 |
2011年 | 2615篇 |
2010年 | 2170篇 |
2009年 | 2643篇 |
2008年 | 2709篇 |
2007年 | 2609篇 |
2006年 | 2501篇 |
2005年 | 2235篇 |
2004年 | 1939篇 |
2003年 | 1599篇 |
2002年 | 1495篇 |
2001年 | 1235篇 |
2000年 | 1152篇 |
1999年 | 902篇 |
1998年 | 786篇 |
1997年 | 654篇 |
1996年 | 593篇 |
1995年 | 583篇 |
1994年 | 530篇 |
1993年 | 428篇 |
1992年 | 337篇 |
1991年 | 240篇 |
1990年 | 154篇 |
1989年 | 148篇 |
1988年 | 129篇 |
1987年 | 86篇 |
1986年 | 90篇 |
1985年 | 75篇 |
1984年 | 65篇 |
1983年 | 38篇 |
1982年 | 52篇 |
1981年 | 54篇 |
1980年 | 60篇 |
1979年 | 56篇 |
1978年 | 45篇 |
1977年 | 39篇 |
1976年 | 20篇 |
1973年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 578 毫秒
921.
Methyl trifluoropiruvate in trifluoroacetic acid at 20 °C rapidly C-hydroxyalkylates various phenols at thepara-positions to afford the corresponding esters ofpara-hydroxy substituted -trifluoromethylmandelic acids.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 528–530, March, 1995.The present study was carried out with the financial support of the Russian Foundation for Basic Research (Project code 93-03-22696). 相似文献
922.
C. Van den Abeele D. Ryckbosch G. De Meyer J. F. Dias L. Van Hoorebeke R. Van de Vyver J. -O. Adler K. Hansen L. Isaksson H. Ruijter P. Svensson B. Schröder 《Zeitschrift für Physik A Hadrons and Nuclei》1995,351(2):133-136
The values of the angle-integrated cross section for the decay to various low-lying states in39K following the40Ca(,) reaction at a mean photon energy of 60 MeV are reported on, together with the values of the reduced Legendre coefficientsa
i
. The40Ca(,gp) and40Ca(,n) reactions yield the same angular cross-section values and these agree with the corresponding RPA-calculations.Senior Research Associate NFWO 相似文献
923.
M. W. Evans 《Foundations of Physics Letters》1995,8(3):253-259
By using an 0(3) gauge group, a non-Abelian theory of vacuum electrodynamics is developed in which the newly discovered longitudinal vacuum fieldsB
(3) andi
E
(3) appear self-consistently with the usual plane wavesB
(1),B
(2),E
(1), andE
(2) in the circular basis (1), (2), (3), a complex representation of space. Using the charge quantization condition the vacuum Maxwell equations are given in the non-Abelian representation. 相似文献
924.
Fabian Wenger 《Zeitschrift für Physik B Condensed Matter》1995,98(2):171-185
We show that weak static random potentials have pronounced effects on the quasiparticle states of a 2Dd-wave superconductor close to a node. We prove that the vertex correction coming from the simplest crossed diagram is important even for a nonmagnetic potential. The leading frequency and momentum dependent logarithmic singularities in the self-energy are calculated exactly to second order in perturbation theory. The self-energy corrections lead to a modified low energy density of states which depends strongly on the type of random potential and which can be measured in experiments. There is an exceptional case for a potential with extremely local scatterers and opposite nodes separated by (, ) where an exact cancelation takes place eliminating the leading frequency dependent singularity in the simplest crossed diagram. A comparison of the perturbative results with a self-consistent CPA (coherent potential approximation) for the nonmagnetic disorder reveals qualitative differences in the self-energy at the smallest energies which are due to the neglectance of vertex corrections in CPA. 相似文献
925.
M. Daszewski Z. Janas W. Kurcewicz B. Szweryn 《Zeitschrift für Physik A Hadrons and Nuclei》1995,351(2):225-228
The internal bremsstrahlung spectrum of55Fe was studied using HPGe detector in low background and reduced pileup conditions. The data show that the conclusion on the presence of a heavy mass neutrino strongly depends from the experimental decay energy value taken in the analysis. The decay energy was found to beQ
EC
=231.37 ± 0.10 keV. The obtained results also show the need for the higher accuracyQ
EC
used in the analysis of the existence of a 17-keV neutrino in the55Fe decay.The authors would like to thank A. Plochocki and J. ylicz for helpful discussion and assistance. 相似文献
926.
L. I. Zakharkin I. M. Churilova G. N. Antonova P. V. Petrovskii N. S. Ikonnikov 《Russian Chemical Bulletin》1994,43(8):1360-1362
Alkylation of cyclododecanone with ,-dibromoalkanes Br(CH)
n
Br (n=3, 4, 5) under conditions of phase-transfer catalysis in the presence of KOH results in the formation of either bicyclic ketones forn=3 and 5 or a mixture of bicyclic and spirocyclic ketones forn=4.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1436–1438, August, 1994. 相似文献
927.
Chemiluminescence emission intensity is modulated by modulating the potential of a working electrode which is used to generate a key species in the electrogenerated Chemiluminescence (ECL) reaction. The emission is monitored synchronously using a lock-in amplifier. The reactions used in the characterization are luminol with hydrogen peroxide and tris(2,2-bipyridyl)ruthenium (II) (or Ru(bpy)
3
2+
) with oxalate. Modulation widths of ± 50 mV yield maximum signals for luminol when centered at 0.45 V (vs Ag/AgCl) and for Ru(bpy)
3
2+
when centered at 1.05 V. The resulting signal decreases with increasing modulation frequency and shows that luminol/H2O2 is a faster ECL system than Ru(bpy)
3
2+
/oxalate. Working curves for luminol and for oxalate have essentially the same linear range and slope with the modulated potential approach as with a DC electrode potential. This approach provides capability for differentiating the analytical signal from constant background emission or stray light. 相似文献
928.
Copolymers of -methyl styrene and 2-ethylhexyl acrylate were prepared in a benzene solution. The presence of the copolymers were confirmed by solubility, IR and NMR tests. The molecular weight and the polydispersity of the polymers were estimated by GPC. The copolymers obtained were blended with paraffinic and naphthenic base oils. The viscosity, the viscosity index (VI) the Q value as well as the stability to shear and oxidation were obtained for these blends. The results are compared with the results obtained with an oil blend containing a commonly used high temperature additive. Two of the copolymers obtained have shown to be good alternatives for specific applications.Presented at the Symposium, 76th CSC Congress, Sherbrooke, Quebec, May 30–June 3, 1993, honoring Professor Donald Patterson on the occasion of his 65th birthday. 相似文献
929.
I. E. Filatov G. L. Rusinov O. N. Chupakhin X. Solans M. Font-Bardia M. Font-Altaba 《Russian Chemical Bulletin》1994,43(7):1214-1219
The reaction of 2-chloro-3,5-dinitropyridine with two equivalents of KN3 in the presence of ROH results in stable Meisenheimer-type -adducts of 4,6-dinitrotetra-zolo[1,5-a]pyridine with RO– anions (R = H, Alk, Ph). The mechanism of -complex formation was suggested. The structure of the -adduct with R = Me was established by IR and NMR spectroscopy and by X-ray diffraction analysis.For the preliminary communication, see Ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1278–1283, July, 1994.This work was supported by the Russian Foundation for Basic Research (project code 93-03-5329). 相似文献
930.
In this paper we consider a class of systems described by singular integrodifferential equations. This type of systems appear, for example, in the modeling of certain aeroelastic control problems. We study these systems in frequency domain framework and show the existence of finite-dimensional stabilizing controllers. An algorithmic procedure is outlined for the construction of such controllers. In order to illustrate the numerical aspects of this algorithm, we present an example involving the classical Theodorsen model of an airfoil, which fits in the class of systems considered here.This work was supported in part by the National Science Foundation under Grants DMS-8907019 and MSS-9203418. 相似文献