全文获取类型
收费全文 | 4107篇 |
免费 | 118篇 |
国内免费 | 4篇 |
专业分类
化学 | 2233篇 |
晶体学 | 12篇 |
力学 | 112篇 |
数学 | 695篇 |
物理学 | 1177篇 |
出版年
2023年 | 23篇 |
2021年 | 25篇 |
2020年 | 58篇 |
2019年 | 47篇 |
2018年 | 57篇 |
2017年 | 40篇 |
2016年 | 98篇 |
2015年 | 80篇 |
2014年 | 108篇 |
2013年 | 193篇 |
2012年 | 239篇 |
2011年 | 270篇 |
2010年 | 114篇 |
2009年 | 102篇 |
2008年 | 224篇 |
2007年 | 237篇 |
2006年 | 234篇 |
2005年 | 258篇 |
2004年 | 203篇 |
2003年 | 169篇 |
2002年 | 137篇 |
2001年 | 107篇 |
2000年 | 77篇 |
1999年 | 46篇 |
1998年 | 33篇 |
1997年 | 53篇 |
1996年 | 33篇 |
1995年 | 38篇 |
1994年 | 28篇 |
1993年 | 30篇 |
1992年 | 34篇 |
1991年 | 20篇 |
1990年 | 20篇 |
1989年 | 23篇 |
1988年 | 22篇 |
1987年 | 21篇 |
1986年 | 35篇 |
1985年 | 42篇 |
1984年 | 49篇 |
1983年 | 43篇 |
1982年 | 62篇 |
1981年 | 51篇 |
1980年 | 46篇 |
1979年 | 47篇 |
1978年 | 50篇 |
1977年 | 46篇 |
1976年 | 35篇 |
1975年 | 36篇 |
1974年 | 41篇 |
1973年 | 42篇 |
排序方式: 共有4229条查询结果,搜索用时 0 毫秒
41.
I. Espe B. Skaali P. O. Tjøm S. M. Lee M. Rozkoš B. Elbek 《Czechoslovak Journal of Physics》1979,29(11):1208-1214
Highly excited compound nuclei of74Kr have been formed by bombardment of58Ni with 70 MeV16O ions. The spectra of protons and -particles resulting from the decay of the compound nucleus (and several daughter nuclei) have been recorded at laboratory angles from 30° to 155°. The CM differential cross sections corresponding to definite energies for the particles emitted were calculated from the data. The charged particle spectra and the angular distributions show that evaporation processes are dominant. A study of spectral shapes and angular distributions has to some extent made it possible to distinguish primary particles from those evaporated after the emission of one or several particles.On leave fromFaculty of Mathematics and Physics, Charles University, Prague, Czechoslovakia. 相似文献
42.
Proton states in theN = 86 nuclei147Pm and149Eu populated in the (3He,d), (α,t) and (t, α) reactions
The (3He,d) and (α, t) reactions on targets of146Nd and148Sm have been studied, using beams of 24 MeV3He and 27 MeV4He from the McMaster University tandem van de Graaff accelerator. Also the (t, α) reaction on a target of148Sm has been studied, using 17 MeV tritons from the Los Alamos Scientific Laboratory tandem accelerator. The reaction products were analyzed with magnetic spectrographs. Information on thel-values was obtained from (3He,d) angular distributions and from ratios of (α,t) and (3He,d) cross sections. In each nucleus a severe fragmentation of the shell-model strength is found. In particular a total of 13(7)l=2 transitions and 6(6)l=0 transitions have been identified in147Pm(149Eu). The results are analyzed in terms of the spherical shell model, which accounts fairly well for the summed spectroscopic strengths. However, with the existence of the (t, α) data a more detailed investigation of the emptiness of individual levels observed in147Pm gives some indication that a deformed scheme might be more successful in describing these nuclei. 相似文献
43.
A. Kankainen L. Batist S. A. Eliseev V. -V. Elomaa T. Eronen U. Hager J. Hakala A. Jokinen I. Moore Yu. N. Novikov H. Penttilä K. Peräjärvi A. V. Popov S. Rahaman S. Rinta-Antila P. Ronkanen A. Saastamoinen D. M. Seliverstov T. Sonoda G. K. Vorobjev J. Äystö 《The European Physical Journal A - Hadrons and Nuclei》2006,29(3):271-280
The masses of 80, 81, 82, 83Y, 83, 84, 85, 86, 88Zr and 85, 86, 87, 88Nb have been measured with a typical precision of 7keV by using the Penning trap setup at IGISOL. The mass of 84Zr has been measured for the first time. These precise mass measurements have improved Sp and QEC values for astrophysically important nuclides. 相似文献
44.
Jesper L. Mortensen Alan McWilliam Christopher G. Leburn Peter Tidemand-Lichtenberg Morten Thorhauge Jirí Janousek Christian T.A. Brown Alexander A. Lagatsky Preben Buchhave Wilson Sibbett 《Optics Communications》2006,260(2):637-640
Efficient generation of continuous-wave (CW) tunable light in the yellow region is reported. The method is based on sum-frequency mixing of a tunable Cr4+:forsterite laser with a Nd:YVO4 laser. A periodically poled lithium niobate crystal was placed intra-cavity in a Nd:YVO4 laser, and the Cr4+:forsterite laser was single-passed through the non-linear media. With this setup, it was possible to generate up to 3 mW of yellow light smoothly tunable from 573 to 587 nm. This is the highest output demonstrated to date for a tunable diode pumped solid-state CW laser in this wavelength region. The ways to improve the efficiency further are discussed. 相似文献
45.
We present a photonic crystal fiber (PCF)-based light source for generating tunable excitation pulses (pump and Stokes) that are applicable to coherent anti-Stokes Raman scattering (CARS) microspectroscopy. The laser employed is an unamplified Ti:sapphire femtosecond laser oscillator. The CARS pump pulse is generated by spectral compression of a laser pulse in a PCF. The Stokes pulse is generated by redshifting a laser pulse in a PCF through the soliton self-frequency shift. This setup allows for probing up to 4000 cm(-1) with a spectral resolution of approximately 25 cm(-1). We characterize the stability and robustness of CARS microspectroscopy employing this light source. 相似文献
46.
47.
48.
Motivated by problems occurring in the empirical identification and modelling of a n-dimensional ARMA time series X(t) we study the possibility of obtaining a factorization (I + a1B + … + apBp) X(t) = [Πi=1p (I ? αiB)] X(t), where B is the backward shift operator. Using a result in [3] we conclude that as in the univariate case such a factorization always exists, but unlike the univariate case in general the factorization is not unique for given a1, a2,…, ap. In fact the number of possibilities is limited upwards by , there being cases, however, where this maximum is not reached. Implications for the existence and possible use of transformations which removes nonstationarity (or almost nonstationarity) of X(t) are mentioned. 相似文献
49.
Örn Helgason Haraldur P. Gunnlaugsson Siguröur Steinthorsson Steen Mørup 《Hyperfine Interactions》1992,70(1-4):981-984
Mössbauer spectroscopy of basalt lava samples, exhibiting reversible thermal magnetization (JS-T) curves with Curie temperatures of about 580°C, has revealed considerable amounts of maghemite (γ-Fe2O3) in many samples. In view of the expected instability, of maghemite at temperatures above 350°C, this reversibility is rather surprising. Here we report Mössbauer studies on heated lava samples, showing high content of maghemite. The samples were kept at 600°C in oxidizing, reducing, and inactive atmospheres, respectively, for different lengths of time, and then analyzed with Mössbauer spectroscopy at room temperature. The Mössbauer spectra showed that maghemite is stable in the oxidizing atmosphere for at least several hours. In the inactive atmosphere a considerable amount of maghemite still exists after two hours heating. In the reducing atmosphere maghemite had transformed to magnetite after only 30 minutes. 相似文献
50.
Mössbauer spectroscopy has been widely used for determining the ferric/ferrous ratio in amorphous rock samples to reveal the oxygen pressure in the melt. In the present investigation, Mössbauer spectroscopy in conjunction with melting experiments at controlled oxygen pressures was used to determine the rates of redox reactions in basaltic melts at 1300°C. The samples were kept at a fixed oxygen pressure long enough to reach equilibrium at a well established ferric/ferrous ratio. Then, the oxygen fugacity in the furnace was changed abruptly and the samples were kept for different lengths of time, from 15 min, to 4 hrs, at the new condition. At the end of each run the samples were quenched and the ferric/ferrous ratio analyzed by Mössbauer spectroscopy. A geological corollary of our results is that natural volcanic glasses, representing quenched melts, retain and reflect the oxidation state in the melt immediately prior to eruption, and hence the oxygen fugacity in the magma. 相似文献