全文获取类型
收费全文 | 1050篇 |
免费 | 44篇 |
国内免费 | 3篇 |
专业分类
化学 | 730篇 |
晶体学 | 3篇 |
力学 | 27篇 |
数学 | 118篇 |
物理学 | 219篇 |
出版年
2023年 | 13篇 |
2022年 | 18篇 |
2021年 | 22篇 |
2020年 | 14篇 |
2019年 | 37篇 |
2018年 | 37篇 |
2017年 | 37篇 |
2016年 | 33篇 |
2015年 | 31篇 |
2014年 | 41篇 |
2013年 | 82篇 |
2012年 | 73篇 |
2011年 | 77篇 |
2010年 | 29篇 |
2009年 | 35篇 |
2008年 | 56篇 |
2007年 | 45篇 |
2006年 | 29篇 |
2005年 | 27篇 |
2004年 | 19篇 |
2003年 | 14篇 |
2002年 | 18篇 |
2001年 | 7篇 |
2000年 | 8篇 |
1999年 | 7篇 |
1998年 | 7篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1993年 | 9篇 |
1992年 | 5篇 |
1990年 | 11篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 10篇 |
1984年 | 13篇 |
1981年 | 10篇 |
1980年 | 12篇 |
1979年 | 13篇 |
1978年 | 13篇 |
1977年 | 16篇 |
1976年 | 7篇 |
1974年 | 10篇 |
1973年 | 9篇 |
1972年 | 8篇 |
1971年 | 8篇 |
1957年 | 7篇 |
1954年 | 5篇 |
1936年 | 4篇 |
排序方式: 共有1097条查询结果,搜索用时 15 毫秒
1.
2.
The present report describes a method suitable for the indirect assay of hydroxyl radical (OH.), which is likely to be produced during reperfusion of ischemic myocardium. Isolated rat heart perfused by the Langendorff technique was subjected to 30 min of ischemia, followed by 30 min of reperfusion. Salicylic acid (2 mM) was added to the perfusion circuit to trap any OH. radical generated during the experiment. 2,5- and 2,3-dihydroxybenzoic acids (hydroxylated products of salicylic acid) were identified by authentic standards as well as by pure OH.-generating system using high-performance liquid chromatography with electrochemical detection. In addition to serving as a chemical trap for the detection of OH., salicylate attenuated myocardial reperfusion injury as evidenced by reduced formation of creatine kinase, decreased lipid peroxidation, and improved myocardial contractile functions during reperfusion. These results thus provide direct evidence for the presence of OH. in heart and link it to the myocardial reperfusion injury. 相似文献
3.
The frequency and the amplitude of the driving AC current dependence on the harmonic behavior of the giant magneto-impedance (GMI) voltage of Co-rich amorphous wire have been studied. Single-peak, two-peak and three-peak behavior in the GMI characteristics was studied with the change of amplitude and frequency of the AC current. GMI ratio was calculated from the first harmonic signals which were initially increased and then decreased monotonically with the increase of frequency (f) and the amplitude (IAC) of the driving current. The response of the GMI voltage was found non-linear with the generation of higher harmonics at higher amplitude of the driving current. The second and third harmonic signals were also evaluated and their dependence on the driving current amplitude and frequency were presented in the paper. The experimental results were analyzed using single domain rotational model. The voltage harmonics were calculated through Fourier transform of the time derivative of the estimated circular magnetization of the sample. 相似文献
4.
The 57Fe Mössbauer technique has been used to investigate the effect of zinc oxide substitution in (25???x)MnO–xZnO–15Fe2O3–60B2O3 glass system (x?=?0, 5, 10, 15 and 20 mol% of ZnO ). Mössbauer absorption spectra for all the samples recorded at room temperature suggest the existence of the two paramagnetic quadrupole doublets. The observed variations in hyperfine parameters have been explained on the basis of cations distribution and exchange interaction at the lattice sites and it is concluded that B–B interaction increases while the metal–metal interaction decreases due to replacement of manganese oxide by zinc oxide. These results suggest that the present glass system exhibits a paramagnetic behaviour that changes towards the weak paramagnetic when manganese oxide was replaced with zinc oxide. 相似文献
5.
The collision-generated hybridization which has been found responsible for the on-site mixing of the atomic-likef-state and the band-liked states in mixed valence solids has been studied for the cerium solid. A practical expression which depends on the lattice
constant and temperature has been obtained for the collision-generated hybridization. Numerical calculations show that the
valence varies continuously with lattice constant and that temperature makes the transition smoother. The collision-generated
hybridization is found to be of significant strength in the intermediate valence regime; but over a wide range of the valence
near 3.5 it varies rather slowly without preferring a particular valence. Factors which can assist the collision-generated
hybridization in stabilizing the mixed valence phase at a particular lattice constant are discussed. 相似文献
6.
Adamovich MI Aggarwal MM Alexandrov YA Ameeva ZV Andreeva NP Anzon ZV Arora R Badyal SK Bhalla KB Bhasin A Bhatia VS Bubnov VI Burnett TH Cai X Chasnikov IY Chernova LP Chernyavski MM Dressel B Eligbaeva GZ Eremenko LE Friedlander EM Gadzhieva SI Gaitinov AS Ganssauge ER Garpman S Gerassimov SG Gill A Grote JG Gulamov KG Gulyamov UG Gupta VK Hackel S Heckman HH Haung H Judek B Kachroo S Kadyrov FG Kalyachkina GS Kanygina EK Kaul GL Kaur M Kharlamov SP Koss T Kumar V Lal P Larionova VG 《Physical review letters》1990,65(4):412-415
7.
Results are presented from a study of electrical breakdown of anodic aluminum oxide in a constant field with a platinum pressure electrode. Statistical breakdown parameters and their dependence on the magnitude and polarity of the applied voltage are obtained. Field and temperature dependences of breakdown delay time over the interval 10–6–103 sec are determined. It is shown that the experimental (E) curves can be rectified (in two segments) in the coordinates log E–1. This indicates a possible contribution to the breakdown mechanism by both tunnel injection of electrons from the cathode and subsequent avalanche multiplication of electrons within the dielectric.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 25–29, April, 1990.In conclusion, the authors thank T. V. Shmidt and E. Ya. Khanin for assistance in the study. 相似文献
8.
9.
10.
K. Lal 《Monatshefte für Chemie / Chemical Monthly》1983,114(1):33-36
Reactions of trimethylchlorosilane (Me 3SiCl) with some nitrogen donors viz. pyridine, 2-, 3- and 4-picolines, quinoline and isoquinoline in nitrobenzene have been studied conductometrically. The conductivities of the solutions during these reactions have been interpreted in terms of the formation of (Me 3Si.D)+, (Me 3SiCl2)? andMe 3SiCl.D (D=N-donor molecule) species. 相似文献