全文获取类型
收费全文 | 21397篇 |
免费 | 1999篇 |
国内免费 | 1155篇 |
专业分类
化学 | 2667篇 |
晶体学 | 110篇 |
力学 | 1346篇 |
综合类 | 96篇 |
数学 | 3333篇 |
物理学 | 6848篇 |
综合类 | 10151篇 |
出版年
2024年 | 58篇 |
2023年 | 185篇 |
2022年 | 428篇 |
2021年 | 456篇 |
2020年 | 448篇 |
2019年 | 408篇 |
2018年 | 439篇 |
2017年 | 534篇 |
2016年 | 509篇 |
2015年 | 628篇 |
2014年 | 1003篇 |
2013年 | 1247篇 |
2012年 | 1134篇 |
2011年 | 1373篇 |
2010年 | 1070篇 |
2009年 | 1371篇 |
2008年 | 1257篇 |
2007年 | 1456篇 |
2006年 | 1265篇 |
2005年 | 1045篇 |
2004年 | 946篇 |
2003年 | 898篇 |
2002年 | 809篇 |
2001年 | 674篇 |
2000年 | 627篇 |
1999年 | 527篇 |
1998年 | 514篇 |
1997年 | 469篇 |
1996年 | 421篇 |
1995年 | 326篇 |
1994年 | 325篇 |
1993年 | 234篇 |
1992年 | 270篇 |
1991年 | 189篇 |
1990年 | 169篇 |
1989年 | 177篇 |
1988年 | 144篇 |
1987年 | 108篇 |
1986年 | 79篇 |
1985年 | 64篇 |
1984年 | 40篇 |
1983年 | 21篇 |
1982年 | 39篇 |
1981年 | 18篇 |
1980年 | 22篇 |
1979年 | 24篇 |
1978年 | 27篇 |
1977年 | 13篇 |
1976年 | 16篇 |
1973年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
Under the nonresonant case where the carrier frequency of a Gaussian beam deviates from the resonant frequency of a Fabry–Perot etalon, the transmission of a Gaussian beam after incidenting nonnormally on a Fabry–Perot etalon has been investigated. The results show that under the nonresonant case, variations of the peak intensity, the position of the peak intensity and the spot size of the transmitted beam with the input angle behave differently and even with a reversed tendency compared with those obtained under the resonant case. 相似文献
82.
83.
As predicted by Haldane, spin, S=1 one-dimensional (1D) Heisenberg antiferromagnet (HAF) has an energy gap between the singlet ground state and first excited triplet. On application of magnetic field, the triplet state Zeeman splits and the energy of one of the triplet state becomes zero at a critical field, Hc. Above Hc the system recovers magnetism. Then, we expect that a quasi-1D HAF will show a magnetic long-range ordering (LRO) at low temperatures due to the inter-chain coupling. This field-induced LRO has not been observed before due to complication of the crystal structure in the materials studied so far and/or technical difficulty.From a heat capacity measurement on a single crystal of an S=1 quasi-Q1D HAF, Ni(C5H14N2)2N3(PF6), we found an anomaly at a temperature in finite fields indicating a field-induced phase transition. A magnetic LRO is confirmed by a neutron diffraction measurement on the same sample. The temperature versus magnetic field phase diagram of this compound is constructed and discussed. 相似文献
84.
The Monte Carlo ray-tracing method (MCRT) based on the concept of radiation distribution factor is extended to solve radiative heat transfer problem in turbulent fluctuating media under the optically thin fluctuation approximation. A one-dimensional non-scattering turbulent fluctuating media is considered, in which the mean temperature and absorption coefficient distribution are assumed and the shape of probability density function is given. The distribution of the time-averaged volume radiation heat source is solved by MCRT and direct integration method. It is shown that the results of MCRT based on the concept of radiation distribution factor agree with these of integration solution very well, but results of MCRT based on the concept of radiative transfer coefficient do not agree with these of integration solution. The solution of time-averaged radiative transfer equation by the concept of radiative transfer coefficient should be treated with caution. 相似文献
85.
86.
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
87.
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
88.
89.
We establish some liminf theorems on the increments of a (N,d)-Gaussian process with the usual Euclidean norm, via estimating upper bounds of large deviation probabilities on the suprema
of the (N,d)-Gaussian process.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
90.
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