全文获取类型
收费全文 | 2734篇 |
免费 | 231篇 |
国内免费 | 119篇 |
专业分类
化学 | 1829篇 |
晶体学 | 53篇 |
力学 | 53篇 |
数学 | 278篇 |
物理学 | 871篇 |
出版年
2023年 | 14篇 |
2022年 | 38篇 |
2021年 | 48篇 |
2020年 | 48篇 |
2019年 | 45篇 |
2018年 | 61篇 |
2017年 | 49篇 |
2016年 | 97篇 |
2015年 | 76篇 |
2014年 | 86篇 |
2013年 | 183篇 |
2012年 | 211篇 |
2011年 | 238篇 |
2010年 | 118篇 |
2009年 | 154篇 |
2008年 | 191篇 |
2007年 | 190篇 |
2006年 | 146篇 |
2005年 | 122篇 |
2004年 | 118篇 |
2003年 | 92篇 |
2002年 | 94篇 |
2001年 | 59篇 |
2000年 | 53篇 |
1999年 | 34篇 |
1998年 | 18篇 |
1997年 | 24篇 |
1996年 | 24篇 |
1995年 | 22篇 |
1994年 | 24篇 |
1993年 | 20篇 |
1992年 | 18篇 |
1991年 | 13篇 |
1990年 | 24篇 |
1989年 | 29篇 |
1988年 | 17篇 |
1987年 | 12篇 |
1986年 | 18篇 |
1985年 | 16篇 |
1984年 | 23篇 |
1983年 | 18篇 |
1982年 | 15篇 |
1981年 | 26篇 |
1980年 | 17篇 |
1979年 | 16篇 |
1978年 | 21篇 |
1977年 | 17篇 |
1976年 | 19篇 |
1975年 | 18篇 |
1974年 | 11篇 |
排序方式: 共有3084条查询结果,搜索用时 13 毫秒
41.
Z. Kožíšek 《Czechoslovak Journal of Physics》1990,40(6):592-604
The kinetic equation of the classical homogeneous nucleation theory is rewritten in dimensionless form and it is shown that the numerical computation of the dimensionless kinetic equation is approximately 20 times faster in comparison with the original kinetic equation. The results are compared with known analytical results and with previous numerical results in the case of the constant and variable temperature for the model Li2O.2 SiO2 melt. It is shown, e.g., that under non-isothermal conditions the nucleation rate is greater than the quasistationary nucleation rate and the cluster distribution function is greater than the corresponding quasiequilibrium cluster distribution function. 相似文献
42.
JiŘí Kvapil Josef Kvapil Bohumil Perner Michal Košelja Helena Jelínková 《Czechoslovak Journal of Physics》1990,40(11):1283-1287
The methods of growing YAG:Nd crystals with a flat interface and YAP:Nd crystals with a sharp conical interface are described. The form of the interface was controlled by the He and H2O content in the reducing atmosphere composed mainly of Ar and H2 as well as by axial temperature gradient above the melt level. The crystals of 120–180 mm in length were machined to the high-quality slabs. 相似文献
43.
The present paper summarizes detailed investigations of Nd3+ fluorescence spectra in YAP:Nd laser crystal in the broad spectral range of 370–1100 nm at liquid nitrogen temperature. Especially, Nd3+ near UV and visible fluorescence spectra were studied for the first time in this crystal. The Nd3+ near UV and visible fluorescence spectra of this crystal consist of many narrow lines (up to 50). The Nd3+ near UV and visible fluorescence lines arise mainly from4D3/2 and2P3/2 Nd3+ terms (transitions from4D3/2,2P3/2 to lower lying Nd3+ levels are responsible for their appearance). At room temperature the fluorescence spectra consist of broad bands with narrow lines (mainly4D3/24F3/2,4F5/2 and2H9/2 transitions). 相似文献
44.
Chaotic oscillations associated with the breakup of polarization entangled coherent states in a microchip solid-state laser 总被引:1,自引:0,他引:1
We demonstrate the breakup of spatial-polarization entangled lasing patterns, which possess vector phase singularities, and the resultant dynamic instabilities featuring chaotic oscillations. The frequency splitting between a pair of Ince-Gauss (IG) lasing modes, originally forming a coherent entanglement state, and a self-excited additional nonorthogonal IG mode through a new class of transverse effect of self-injection pattern seeding, is shown to result in modal-interference-induced modulation at the beat frequency, leading to chaotic oscillations. 相似文献
45.
46.
Vossen A Seidl R Adachi I Aihara H Aushev T Balagura V Bartel W Bischofberger M Bondar A Bračko M Browder TE Chang MC Chen A Chen P Cheon BG Cho K Choi Y Eidelman S Feindt M Gaur V Gabyshev N Garmash A Golob B Perdekamp MG Haba J Hayasaka K Horii Y Hoshi Y Hou WS Hyun HJ Inami K Ishikawa A Iwabuchi M Iwasaki Y Iwashita T Joshi NJ Kichimi H Kim HO Kim MJ Ko BR Kumita T Lange JS Lee MJ Lee SH Leitgab M Li Y Liu C Liventsev D Louvot R McOnie S Miyata H Miyazaki Y Mizuk R Mohanty GB Nakano E 《Physical review letters》2011,107(7):072004
The interference fragmentation function translates the fragmentation of a quark with a transverse projection of the spin into an azimuthal asymmetry of two final-state hadrons. In e(+)e(-) annihilation the product of two interference fragmentation functions is measured. We report nonzero asymmetries for pairs of charge-ordered π(+)π(-) pairs, which indicate a significant interference fragmentation function in this channel. The results are obtained from a 672 fb(-1) data sample that contains 711 × 10(6) π(+)π(-) pairs and was collected at and near the Υ(4S) resonance, with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. 相似文献
47.
Broadband Convergence of 40 GHz-ROF and 10-Gb/s WDM-PON Systems in the Duplex Access Network 下载免费PDF全文
A broadly converged 40G-ROF and 10-Gb/s WDM-PON multi-service access system is proposed and exper- imentally demonstrated. This scheme consists of an integrated system of 40G-ROF and 10-Gb/s WDM-PON simultaneously transmitting independent 2.5-Gb/s wireless and 10-Gb/s wire signal. At the base station, it employs a remodulation scheme, which is achieved by remodulating the upstream OOK signal on the DPSK downstream signal, to reduce the cost of the base station. The transmission experiment is carried out over a 25-km-long single mode fiber (SMF-28). The results show that the sensitivities of downstream PON and ROF signal are -14.5 dBm and -21.5 dBm, respectively, and the sensitivity of upstream signal is -25.3 dBm. 相似文献
48.
Esen S Schwartz AJ Adachi I Aihara H Arinstein K Aulchenko V Aushev T Aziz T Bakich AM Balagura V Barberio E Bay A Bischofberger M Bondar A Bozek A Bračko M Browder TE Chang MC Chang P Chen A Chen P Cheon BG Chiang CC Choi Y Dalseno J Dash M Doležal Z Drásal Z Drutskoy A Eidelman S Goldenzweig P Golob B Ha H Haba J Hara T Hayasaka K Higuchi T Hoshi Y Hou WS Hsiung YB Hyun HJ Iijima T Inami K Itoh R Iwabuchi M Joshi NJ Julius T Kang JH Kawasaki T Kichimi H Kim HJ Kim HO Kim JH Kim YJ Kinoshita K 《Physical review letters》2010,105(20):201802
We have made the first observation of B(s)(0)→D(s)(*)+ D(s)(*)- decays using 23.6 fb(-1) of data recorded by the Belle experiment running on the Υ(5S) resonance. The branching fractions are measured to be B(B(s)(0)→D(s)+ D(s)-)=(1.03(-0.32-0.25)(+0.39+0.26))%, B(B(s)(0)→D(s)(*±) D(s)(?))=(2.75(-0.71)(+0.83)±0.69)%, and B(B(s)(0)→D(s)*+ D(s)*-)=(3.08(-1.04-0.86)(+1.22+0.85))%; the sum is B[B(s)(0)→D(s)(*)+ D(s)(*)-]=(6.85(-1.30-1.80)(+1.53+1.79))%. Assuming B(s)(0)→D(s)(*)+ D(s)(*)- saturates decays to CP-even final states, the branching fraction determines the ratio ΔΓ(s)/cosφ, where ΔΓ(s) is the difference in widths between the two B(s)-B(s) mass eigenstates, and φ is a CP-violating weak phase. Taking CP violation to be negligibly small, we obtain ΔΓ(s)/Γ(s)=0.147(-0.030)(+0.036)(stat)(-0.041)(+0.042)(syst), where Γ(s) is the mean decay width. 相似文献
49.
提出了不同结构的一维弹性波复合材料系统模型,包括一维周期结构声子晶体、标准Fibonacci准周期结构声子晶体、广义Fibonacci准周期结构声子晶体以及完全无序结构的复合材料系统. 采用模式匹配理论法,数值计算了弹性波通过一维复合材料系统的透射系数. 计算结果表明,利用特殊的准周期结构声子晶体可获得比周期结构声子晶体更宽的带隙范围,准周期结构排列的复合材料系统相当于在周期结构中引入了缺陷体一样,带隙内出现了丰富的局域模式. 对弹性波/声波在复合材料系统中局域态性质的研究有助于弹性波/声波滤波器、导波器
关键词:
弹性波复合材料
局域化 相似文献
50.
基于螺旋度分波分析公式 ,我们探讨在J ψ→fJ(θ1,1)、fJ→ππ(θ2 ,2 )、→K+ K-(θ3 ,3 )级联衰变过程中是否可以通过各种一维角分布投影鉴别出f0 和f2 共振态 .结果表明 ,f0 和f2 可以同时给出完全相同的 (θ1,1,θ2 ,2 )一维投影 ,但不能同时给出完全相同的 (θ1,1,θ2 ,2 ,3 )一维投影 .因此 ,要想保证从角分布的一维投影鉴别出f0 和f2 ,必须同时考虑所有三个衰变顶角的角分布信息 . 相似文献