全文获取类型
收费全文 | 13991篇 |
免费 | 3060篇 |
国内免费 | 2434篇 |
专业分类
化学 | 9173篇 |
晶体学 | 219篇 |
力学 | 1179篇 |
综合类 | 145篇 |
数学 | 390篇 |
物理学 | 8379篇 |
出版年
2024年 | 27篇 |
2023年 | 141篇 |
2022年 | 277篇 |
2021年 | 355篇 |
2020年 | 478篇 |
2019年 | 431篇 |
2018年 | 410篇 |
2017年 | 509篇 |
2016年 | 632篇 |
2015年 | 574篇 |
2014年 | 888篇 |
2013年 | 1248篇 |
2012年 | 1009篇 |
2011年 | 1039篇 |
2010年 | 835篇 |
2009年 | 1011篇 |
2008年 | 991篇 |
2007年 | 985篇 |
2006年 | 967篇 |
2005年 | 835篇 |
2004年 | 821篇 |
2003年 | 686篇 |
2002年 | 659篇 |
2001年 | 523篇 |
2000年 | 482篇 |
1999年 | 388篇 |
1998年 | 320篇 |
1997年 | 299篇 |
1996年 | 237篇 |
1995年 | 232篇 |
1994年 | 177篇 |
1993年 | 180篇 |
1992年 | 161篇 |
1991年 | 110篇 |
1990年 | 90篇 |
1989年 | 81篇 |
1988年 | 81篇 |
1987年 | 53篇 |
1986年 | 38篇 |
1985年 | 28篇 |
1984年 | 27篇 |
1983年 | 21篇 |
1982年 | 24篇 |
1981年 | 14篇 |
1980年 | 19篇 |
1979年 | 21篇 |
1978年 | 17篇 |
1977年 | 12篇 |
1976年 | 21篇 |
1973年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
103.
104.
高斯光束计算平板波导自由传输区远场分布及其修正 总被引:2,自引:2,他引:0
对近轴近似条件下求解亥姆霍兹方程得到的高斯光束显式传播公式做了分析,同时,基于基尔霍夫衍射理论,在菲涅耳近似的条件下给出了相应的高斯光束在远场的传播公式,在此基础上,对近轴近似条件做出了定量分析,给出了这个近似条件引入的误差,提出了一种计算高斯光束远场分布的修正方法,并采用有限差分-光束传播方法(FD-BPM)来检验各种方法的准确性。把这种修正方法应用到平面光集成波导器件,如阵列波导光栅(AWG)、蚀刻衍射光栅(EDG)等器件的设计和模拟中,可以大大降低工作的复杂性,同时可以得到精确的结果。 相似文献
105.
By using the methods of the matrix decomposition and expansion of the hard-edged aperture function into a finite sum of complex Gaussian functions, the recurrence propagation expressions for a flattened Gaussian beam (FGB) through multi-apertured optical imaging systems of B = 0 are derived and illustrated with numerical examples. Comparisons with the straightforward numerical integration of the Collins formula and with the previous work are made. It is shown that the main advantages of our methods and results are the more accuracy and great reduction of computer time. 相似文献
106.
D. Behera T. Mohanty S. K. Dash T. Banerjee D. Kanjilal N. C. Mishra 《Radiation measurements》2003,36(1-6):125-129
Swift heavy ions (SHI) with electronic energy loss exceeding a value of 14.4 keVnm−1 create amorphized latent tracks in YBCO type superconductors. In the low fluence regime of an ion beam where tracks do not overlap, a decrease of the superconducting transition temperature as probed through resistivity studies, is not expected due to availability of percolating current paths. The present study however shows Tc decrease by about 1–3 K in thin films of YBCO when irradiated by 250 MeVAg ions at 79 K at a fluence of 5×1010–1×1012 ionscm−2. The highest fluence used in the present study is three times less than the fluence where track overlapping becomes significant. The Tc tends to increase towards the preirradiation value on annealing the films at room temperature. To explain this unusual result, we consider the effect of ion irradiation in inducing materials modification not only through creation of amorphized latent tracks along the ion path, but also through creation of atomic disorder in the oxygen sublattice in the Cu–O chains of YBCO by the secondary electrons. These electrons are emitted radially from the tracks during the passage of the SHI. Considering the correlation between the charge state of copper and its oxygen coordination, we show in particular that the latter process is a consequence of the inelastic interaction of the SHI induced low-energy secondary electrons with the YBCO lattice, which result in chain oxygen disorder and Tc decrease. 相似文献
107.
108.
采用显微Raman光谱方法对红外目标模拟器中重掺杂Si微电阻桥单元的热传导特性进行研究,根据Si桥的实际特性建立相应的Raman散射模型,通过测量Raman峰位的移动得到高功率激光辐照下测量点的温度.对Si桥桥面分别进行了沿某些特殊线段的逐点线扫描和覆盖全部桥面的面扫描,得到各点的温升及其分布.用基于有限元分析的软件结合Si桥结构参数对各测量点的温升进行了模拟计算,其结果在热导分布的基本趋势上与实验相一致.实验细致地揭示了热导分布的局域起伏,反映出实际器件的不均匀性,为改进器件设计、优化器件性能提供了实验依据.
关键词:
Raman光谱
Si桥
温度分布
热导 相似文献
109.
YunFei Liu ShengCai Shi ShengLin Yu 《International Journal of Infrared and Millimeter Waves》2003,24(12):2069-2077
When electromagnetic waves propagate through a wire grid, there will be some evanescent space harmonics generated around the wire grid. In this paper, we mainly investigate their effects on the transmission characteristics of a Gaussian beam by cylindrical wire grids. The results are compared with those without taking account of evanescent space-harmonics. 相似文献
110.
A new method based on anion exchange resin separation and graphite furnace atomic absorption spectrometry (GFAAS) detection
is proposed for the determination of inorganic tin species. The result showed that Sn(IV) was quantitatively retained on the
resin when [HCl] = 9.0 mol · L−1, but Sn(II) could not be adsorbed on the resin under the same condition. Thus, a separation of Sn(II) and Sn(IV) has been
realized. When the concentration of NaOH solution was between 2.0–7.0 mol · L−1, Sn(IV) that adsorbed on the resin could be eluated from the resin completely. Meanwhile, under the atmosphere and the nitrogen
states, the translation between Sn(II) and Sn(IV) was investigated. Under the optimal conditions, the detection limit of Sn(IV)
is 0.40 μg · L−1 with RSD of 2.3% (n = 5, c = 2.0 μg · L−1). The proposed method was applied to the speciation analysis of tin in different water samples and the recovery of total
Sn was in the range of 98.7–101.7%. In order to verify the accuracy of the method, a certified reference water sample was
analyzed and the results obtained were in good agreement with the certified value. 相似文献