全文获取类型
收费全文 | 50830篇 |
免费 | 8485篇 |
国内免费 | 5495篇 |
专业分类
化学 | 35516篇 |
晶体学 | 682篇 |
力学 | 3170篇 |
综合类 | 352篇 |
数学 | 6138篇 |
物理学 | 18952篇 |
出版年
2024年 | 122篇 |
2023年 | 1019篇 |
2022年 | 1494篇 |
2021年 | 1707篇 |
2020年 | 2041篇 |
2019年 | 1900篇 |
2018年 | 1683篇 |
2017年 | 1534篇 |
2016年 | 2353篇 |
2015年 | 2337篇 |
2014年 | 2745篇 |
2013年 | 3624篇 |
2012年 | 4351篇 |
2011年 | 4549篇 |
2010年 | 3081篇 |
2009年 | 3052篇 |
2008年 | 3388篇 |
2007年 | 3001篇 |
2006年 | 2829篇 |
2005年 | 2308篇 |
2004年 | 1809篇 |
2003年 | 1512篇 |
2002年 | 1430篇 |
2001年 | 1141篇 |
2000年 | 1145篇 |
1999年 | 1095篇 |
1998年 | 914篇 |
1997年 | 827篇 |
1996年 | 868篇 |
1995年 | 773篇 |
1994年 | 667篇 |
1993年 | 549篇 |
1992年 | 519篇 |
1991年 | 414篇 |
1990年 | 387篇 |
1989年 | 303篇 |
1988年 | 264篇 |
1987年 | 220篇 |
1986年 | 189篇 |
1985年 | 191篇 |
1984年 | 139篇 |
1983年 | 87篇 |
1982年 | 74篇 |
1981年 | 56篇 |
1980年 | 27篇 |
1979年 | 18篇 |
1976年 | 10篇 |
1975年 | 11篇 |
1971年 | 8篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
151.
We observe enhanced terahertz (THz) radiation generated from a Si3N4 film-coated GaAs photoconductive dipole antenna. Compared to an uncoated antenna with identical electrode geometry and optical excitation power, the Si3N4 film-coated antenna has a higher effective DC resistance and larger breakdown voltage. As a result, the peak amplitude of generated THz radiation is significantly enhanced due to the Si3N4 film-coated layer. 相似文献
152.
153.
LiAlO2 single crvstals doped with Ti at concentration 0.2at.% are grown by the Czochralskl technique with dimensions φ42×55mm. Ti ions in the crystal are quadrivalence proven by comparing the absorption and fluorescence spectra of pure LiAlO2 and Ti: LiAlO2. After air and Li-rich atmosphere annealing, the absorption peaks in the range of 600-800nm disappear. We conclude that 682 and 756nm absorption peaks are attributed to the VLi and Vo absorptions, respectively: The peaks at 716nm and 798nm may stem from the VLi^+ and absorptions. The colour-centre model can be applied to explain the experimental phenomena. Ti^4+-doping produces more lithium vacancies in the LiAlO2 crystal. The intensities of [LiO4] and the associated bonds remain unchanged, which improves the anti-hydrolyzation and thermal stability of LiAlO2 crystals. 相似文献
154.
The ρ-T curves in our single phase HgBa2Ca2Cu3O8+δ superconductor were measured as a function of temperature and magnetic field, ρ=ρ0exp(−Ueff/κBT). It can be transformed to another form d(lnρ)/d(1/T)=−Ueff+TdUeff/dT, then this becomes a plot of the activation energy Ueff as a function of temperature. Our data plotted in these ways show a clear crossover from high-temperature two-dimensional vortex-liquid to a critical region associated with the low-temperature three-dimensional vortex-glass phase transition. The critical exponents v(z−1)=3.9±1.9 in this system are little different with previous measurements in BSCCO and YBCO systems. 相似文献
155.
Feng Xu 《Communications in Mathematical Physics》1997,184(3):493-508
We build some exceptional representations of Birman–Wenzl algebras from the data of certain conformal embeddings. As a result
we construct new finite depth subfactors whose principal graphs are completely determined.
Received: 16 February 1996 / Accepted: 25 July 1996 相似文献
156.
HANXI'AN HUANGXILI 《高校应用数学学报(英文版)》1998,13(4):445-450
For two rational quadratic B-spline curves with same control vertexes, the cross ratio of four eollinear points are represented; which are any one of the vertexes, and the two points that the ray initialing from the vertex intersects with the corresponding segments of the twocurves, and the point the ray intersecting with the connecting line between the two neighboring vertexes. Different from rational quadratic Beeier curves, the value is generally related with the loeation of the ray, and the necessary and sufficient condition o5 the ratio being independent of the ray‘s loeation is showed. Alsn another cross ratio o5 the following four collinear points are suggested, i.e. one vertex, the points that the ray from the initlal vertex intersects respectivdy with the curve segmentt the line connecting the segments end points, and the line connecting the two neighboring vertexes. This cross ratio is concerned only whh the ray‘s location, butnot with the weights of the curve. Furthermore, the cross ratio is projective invariant under the projective transformation between the two segments. 相似文献
157.
对溴分子在68800-7200cm^-1范围内的两个被观察到的[^2Π3/2]4d偶宇称里堡态的转动光谱进行了计算模拟,确定了转动常数,并且证实了原先对实验光谱的传动结构和电子角动量的标识。 相似文献
158.
时滞种群模型的正周期解对所有正解的吸引性 总被引:5,自引:0,他引:5
李永昆 《高校应用数学学报(A辑)》1997,(3)
建立了对数种群模型N′(t)=N(t){r(t)-a1(t)ln[N(t)]-a2(t)ln[N(t-τ(t))]}的周期正解的存在性,并得到了正周期解对所有正解的吸引性. 相似文献
159.
Xu Tianzhou 《东北数学》1997,(1)
ModulesoverOperatorAlgebrasandItsModuleMapsXuTianzhou(许天周)(DepartmentofMathematics,NanjingUniersity,Nanjing,210093)AbstractLe... 相似文献
160.