全文获取类型
收费全文 | 26624篇 |
免费 | 4274篇 |
国内免费 | 2748篇 |
专业分类
化学 | 16884篇 |
晶体学 | 498篇 |
力学 | 302篇 |
综合类 | 151篇 |
数学 | 324篇 |
物理学 | 15487篇 |
出版年
2024年 | 45篇 |
2023年 | 181篇 |
2022年 | 567篇 |
2021年 | 586篇 |
2020年 | 669篇 |
2019年 | 576篇 |
2018年 | 647篇 |
2017年 | 719篇 |
2016年 | 938篇 |
2015年 | 936篇 |
2014年 | 1177篇 |
2013年 | 2400篇 |
2012年 | 1639篇 |
2011年 | 1578篇 |
2010年 | 1247篇 |
2009年 | 1605篇 |
2008年 | 1566篇 |
2007年 | 1892篇 |
2006年 | 1709篇 |
2005年 | 1470篇 |
2004年 | 1301篇 |
2003年 | 1253篇 |
2002年 | 1075篇 |
2001年 | 954篇 |
2000年 | 868篇 |
1999年 | 819篇 |
1998年 | 702篇 |
1997年 | 648篇 |
1996年 | 585篇 |
1995年 | 534篇 |
1994年 | 470篇 |
1993年 | 400篇 |
1992年 | 389篇 |
1991年 | 272篇 |
1990年 | 194篇 |
1989年 | 171篇 |
1988年 | 156篇 |
1987年 | 111篇 |
1986年 | 98篇 |
1985年 | 68篇 |
1984年 | 87篇 |
1983年 | 36篇 |
1982年 | 55篇 |
1981年 | 43篇 |
1980年 | 43篇 |
1979年 | 34篇 |
1978年 | 27篇 |
1976年 | 20篇 |
1975年 | 21篇 |
1973年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Alain Joye 《Journal of statistical physics》1994,75(5-6):929-952
The spectrum of the Floquet operator associated with time-periodic perturbations of discrete Hamiltonians is considered. If the gap between successive eigenvalues
j
of the unperturbed Hamiltonian grows as
j
-
j-1
j
and the multiplicity of
j
grows asj
with >0 asj tends to infinity, then the corresponding Floquet operator possesses no absolutely continuous spectrum provided the perturbation is smooth enough. 相似文献
92.
A. V. Savilov 《International Journal of Infrared and Millimeter Waves》1994,15(11):1819-1828
The negative-mass (space-charge) instability is studied within the model of a flat thin electron beam moving along the stationary uniform magnetic field in the case of nonsymmetrical perturbations. It is shown that due to the phenomenon of "phase mixing" of electron bunches the instability increments are small for perturbations with spatial scales smaller than the Larmor diameter. 相似文献
93.
94.
Polymer enhanced ultrafiltration (PEUF) is a newly developed method for the removal of heavy metals from aqueous solutions. This method was applied for the removal of mercury and cadmium with the presence of polyethyleneimine (PEI) as a water soluble polymer. After ultrafiltration experiments for metal–polymer mixtures, two separate streams, namely, retentate and permeate, former of which contains mainly metal–polymer complex and free polymer molecules while latter of which mainly contains free metal ions, were obtained. At the end of PEUF experiments, performance of operation was determined by concentration analyses which was achieved by atomic absorption spectroscopy (AAS) applied in a different way for permeate and retentate streams considering the effect of presence of polymer. For mercury analysis, cold vapor AAS was applied. It was observed that the presence of PEI did not affect the atomic absorption signal when 10% HCl was added to the sample solutions. For calcium and cadmium, flame AAS was used. It was observed that change in PEI concentration results in change in measured concentration of calcium and cadmium. Therefore, two new approaches were developed for accurate measurement of concentrations of calcium and cadmium. It was also observed that presence of other metals did not affect the accuracy of the measurement of a particular metal in the concentration range studied. 相似文献
95.
K. Premchand B. Seetharami Reddy B. Mallikarjuna Rao K. Parthasaradhi M. V. R. Murti K. S. Rao 《Il Nuovo Cimento D》1993,15(1):73-76
Summary An attempt is made to study theK
α
L
1 satellite multiplet structure of chlorine atoms in different compounds by photon excitation. A comparison of the averageK
α
L
1 group energy shift from the diagram line with those based on Dirac-Fock evaluations with different number ofM-shell electrons shows a reasonable agreement. The
intensity ratios are found to be higher than those studied in Mg compounds in general. 相似文献
96.
We extend a previous small-angle neutron scattering study of sodium octanoate (NaC8) micelles to the ternary system sodium octanoate/pentanol/water. The use of contrast variation through selective deuteration of individual components together with explicit computation of interference effects, permits us to deduce the location of pentanol (C5OH) in the micelles. Our main conclusion is that, although the micelles grow as (C5OH) is solubilised, there is no concomitant variation in the NaC8 aggregation number. At low alcohol concentrations, the C5OH is located near the NaC8 polar heads, while at higher concentration the -OH groups are distributed throughout the micellar core. 相似文献
97.
98.
JIANG Qi-Jun 《结构化学》2005,24(10):1140-1144
1 INTRODUCTION The electron-transfer reaction of C60 derivatives, especially light-induced electron-transfer reaction, has been an active research field for a long time. Many researches are focused on the long-live charge- separated state caused by electron-transfer[1]. And several electron-transfers between electron donor and C60 or intramolecular electron-transfer have been confirmed. As an example, TTF-C60 is proved to be a short-live charge-separated compound[2].Due to the excelle… 相似文献
99.
The molecular structure of samarium dibromide has been studied by electron diffraction at T
exp = 1250(50) K. The molecule has C2v symmetry; the internuclear distance Rg(Sm–Br) = 274.5(5) pm; g =131(6)°. The vibration frequencies were estimated from the experimental values of the mean square vibration amplitudes. 相似文献
100.
T. L. Luke H. Mohan V. M. Manoj P. Manoj J. P. Mittal C. T. Aravindakumar 《Research on Chemical Intermediates》2003,29(4):379-391
Reactions of sulphate radical anion (SO·4
-) with 4,6-dihydroxy-2-methyl pyrimidine (DHMP), 2,4-dimethyl-6-hydroxy pyrimidine (DMHP), 6-methyl uracil (MU) and 5,6-dimethyl uracil (DMU) have been studied by pulse radiolysis at pH 3 and at pH 10. The transient intermediate spectra were compared with those from the reaction of hydroxyl radical (·OH). It is proposed that SO·4
- produces radical cations of these pyrimidines in the initial stage. These radical cations are short-lived except in the case of DMHP where a relatively longer lived radical cation is proposed to be formed. When there is a hydrogen atom attached to the N(1) or N(3) position, a deprotonation from these sites is highly favored. When there is no hydrogen attached to these sites, deprotonation from a substituted methyl group is favored. At acidic pH, deprotonation from nitrogen is observed for DHMP, MU and DMU. At basic pH, the radical cation reacts with OH- leading to the formation of OH adducts. 相似文献