全文获取类型
收费全文 | 672731篇 |
免费 | 6875篇 |
国内免费 | 2352篇 |
专业分类
化学 | 344598篇 |
晶体学 | 9577篇 |
力学 | 32357篇 |
综合类 | 14篇 |
数学 | 101589篇 |
物理学 | 193823篇 |
出版年
2021年 | 4762篇 |
2020年 | 5318篇 |
2019年 | 5850篇 |
2018年 | 16873篇 |
2017年 | 16532篇 |
2016年 | 16775篇 |
2015年 | 8050篇 |
2014年 | 11304篇 |
2013年 | 28136篇 |
2012年 | 24254篇 |
2011年 | 35138篇 |
2010年 | 22765篇 |
2009年 | 22970篇 |
2008年 | 29269篇 |
2007年 | 31076篇 |
2006年 | 21844篇 |
2005年 | 20760篇 |
2004年 | 19398篇 |
2003年 | 17774篇 |
2002年 | 16663篇 |
2001年 | 17858篇 |
2000年 | 13653篇 |
1999年 | 10778篇 |
1998年 | 9026篇 |
1997年 | 8759篇 |
1996年 | 8519篇 |
1995年 | 7707篇 |
1994年 | 7481篇 |
1993年 | 7376篇 |
1992年 | 8124篇 |
1991年 | 8226篇 |
1990年 | 7856篇 |
1989年 | 7691篇 |
1988年 | 7768篇 |
1987年 | 7567篇 |
1986年 | 7174篇 |
1985年 | 9477篇 |
1984年 | 9731篇 |
1983年 | 7897篇 |
1982年 | 8261篇 |
1981年 | 8107篇 |
1980年 | 7644篇 |
1979年 | 8070篇 |
1978年 | 8396篇 |
1977年 | 8153篇 |
1976年 | 8267篇 |
1975年 | 7523篇 |
1974年 | 7603篇 |
1973年 | 7862篇 |
1972年 | 5338篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
881.
882.
F. Seiffert R. Schwengner G. Winter L. Funke W. Lieberz R. Reinhardt K. P. Schmittgen D. Weil R. Wrzal K. O. Zell P. von Brentano 《Zeitschrift für Physik A Hadrons and Nuclei》1991,340(2):141-153
Excited states of73Se have been investigated up to spin, 21/2 using techniques of in-beamγ-ray spectroscopy in connection with the70Ge(α, n) reaction. Mean lifetimes of 12 levels have been determined applying Doppler-shift andγ-RF-methods. Five different bands have been identified that reflect a variety of different excitation modes. The decoupled 9/2+ band is likely to correspond to an oblate deformation while the 5/2+ band is interpreted as a strongly coupled prolate band built on the Nilsson configuration [422] 5/2+. The 3/2? band is a strongly coupled band built on the [301] 3/2} configuration.Nuclear reactions:70Ge(α,n),E=14, 16, 18, 19, 20MeV; measuredE γ,I γ,σ(E γ,θ),γγ-coin, linear polarization, DSA,γ(t).75Se deduced levels,I, π, τ, δ(E2/M1), B(σλ). Enriched targets, Ge detectors. 相似文献
883.
We review a little-used but powerful method of solving the scalar wave equation. It uses a modification of the well-known Airy functions, which are easily calculated on desktop computers. The techniques are reminiscent of the WKBJ methodology, but the solution, although approximate, is much more useful than the traditional WKBJ solution and can be used with almost as much ease. Re method is extremely powerful but, to our knowledge, is not used in the optics community. It is useful in analyzing integrated optical waveguide components. 相似文献
884.
The detection of serial changes in magnetic resonance (MR) signal intensity of the heart following acute myocardial infarction may provide a useful method of characterizing tissue healing. Fourteen patients with acute Q-wave infarction underwent T2-weighted, spin-echo cardiac imaging during hospitalization, followed by one or more additional MR studies (total 31) over a 6- to 27-wk period (mean: 3 mo). Visual assessment of the images demonstrated a gradual reduction in signal intensity and localization of the bright signal to the subendocardium of the infarction region over the three-mo study period. A quantitative measurement of signal intensity (infarction/normal myocardium) fell from 1.81 +/- 0.42 on the initial study to 1.34 +/- 0.37 (p less than 0.05) at a mean of 14 wk. Two patients had an increase in signal intensity on the follow-up study and both patients had been readmitted with acute coronary syndromes. In summary, characterization of changes in signal intensity may provide a useful method of assessing myocardial healing following acute myocardial infarction. Further studies are indicated to determine the prognostic significance of these parameters. 相似文献
885.
Summary In this paper we show that the transverse mode evolution of a FEL operating with short pulses can be treated, in the small-signal
and low-gain regime, using a relatively simple mathematical technique leading to a potentially fast numerical algorithm. We
also point out that analytical solutions can be obtained for the cases where the slippage length is small compared to the
longitudinal bunch length. 相似文献
886.
887.
N. M. Zoumakis 《Il Nuovo Cimento C》1992,15(2):247-250
Summary An approximate relationship between the gradient, Ri, and the bulk Richardson number, Rib, for unstable atmospheric conditions, is suggested. The proposed relation shows much better agreement with the estimation
provided by a numerical iterative method than the usual approximations suggested by Louis and Byun. 相似文献
888.
889.
The rate of nucleophilic substitution at the phosphorus centre of dialkyl methylphosphonates by methoxide and ethoxide has been studied to investigate the possible involvement of hexacoordinated phosphorus species in this reaction. For alkoxide concentrations less than ca. 1.5 M the rate increases with the square of alkoxide concentration. However, consideration of the activity of the alkoxides, represented by an appropriate acidity function, reveals that only one equivalent of alkoxide is involved in the rate-determining step. Thus, there is no requirement to invoke the intermediacy of a hexacoordinated species in the reaction pathway. © John Wiley & Sons, Inc. 相似文献
890.
M. Trinidad Menarguez Fernando Soria 《Rendiconti del Circolo Matematico di Palermo》1992,41(3):342-352
In this paper we study the behavior of the constants which appear in the weak type (1, 1) inequalities for maximal convolution
operators by means of discrete methods.
One of the first applications of these techniques will give us a very simple proof of the ergodic theorem. We also present
partial results in order to investigate the best constant in the weak type (1, 1) inequality for the Hardy-Littlewood centered
maximal operator in dimension one. In dimension bigger than one we also obtain some lower bounds for that constant. 相似文献