首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2421篇
  免费   437篇
  国内免费   195篇
化学   617篇
晶体学   20篇
力学   257篇
综合类   31篇
数学   407篇
物理学   1721篇
  2024年   5篇
  2023年   24篇
  2022年   59篇
  2021年   58篇
  2020年   63篇
  2019年   62篇
  2018年   57篇
  2017年   91篇
  2016年   129篇
  2015年   77篇
  2014年   185篇
  2013年   178篇
  2012年   164篇
  2011年   180篇
  2010年   149篇
  2009年   168篇
  2008年   183篇
  2007年   143篇
  2006年   139篇
  2005年   122篇
  2004年   107篇
  2003年   84篇
  2002年   67篇
  2001年   65篇
  2000年   56篇
  1999年   52篇
  1998年   56篇
  1997年   49篇
  1996年   48篇
  1995年   36篇
  1994年   33篇
  1993年   27篇
  1992年   19篇
  1991年   17篇
  1990年   15篇
  1989年   18篇
  1988年   23篇
  1987年   10篇
  1986年   5篇
  1985年   7篇
  1984年   4篇
  1983年   1篇
  1982年   6篇
  1981年   1篇
  1980年   1篇
  1979年   3篇
  1978年   3篇
  1977年   2篇
  1975年   1篇
  1974年   1篇
排序方式: 共有3053条查询结果,搜索用时 15 毫秒
91.
A non-uniformity correction (NUC) method for an infrared focal plane array imaging system was proposed. The algorithm, based on compressive sensing (CS) of single image, overcame the disadvantages of “ghost artifacts” and bulk calculating costs in traditional NUC algorithms. A point-sampling matrix was designed to validate the measurements of CS on the time domain. The measurements were corrected using the midway infrared equalization algorithm, and the missing pixels were solved with the regularized orthogonal matching pursuit algorithm. Experimental results showed that the proposed method can reconstruct the entire image with only 25% pixels. A small difference was found between the correction results using 100% pixels and the reconstruction results using 40% pixels. Evaluation of the proposed method on the basis of the root-mean-square error, peak signal-to-noise ratio, and roughness index (ρ) proved the method to be robust and highly applicable.  相似文献   
92.
93.
详细地介绍了辉光放电质谱分析中的质谱干扰如同量异位素、多原子离子和多电荷离子干扰。从同位素选择、高分辨率仪器、碰撞诱导解离、离子源冷却、数学方法校正、放电气体更换和放电气体纯度提高等方面对辉光放电质谱的质谱干扰校正方法的现状进行了评述(引用文献共68篇)。  相似文献   
94.
Blood flow inside the liver plays a key role in hepatic functions, and abnormal hemodynamics are highly correlated with liver diseases. To date, the flow field in an elementary building block of the organ, the liver lobule, is difficult to determine experimentally in humans due to its complicated structure, with radially branched microvas-culature and the technical difficulties that derive from its geometric constraints. Here we established a set of 3D com-putational models for a liver lobule using porous media theory and analyzed its flow dynamics in normal, fibrotic, and cirrhotic lobules. Our simulations indicated that those approximations of ordinary flow in portal tracts (PTs) and the central vein, and of porous media flow in the sinusoidal network, were reasonable only for normal or fibrotic lobules. Models modified with high resistance in PTs and collateral vessels inside sinusoids were able to describe the flow fea-tures in cirrhotic lobules. Pressures, average velocities, and volume flow rates were profiled and the predictions compared well with experimental data. This study furthered our under-standing of the flow dynamics features of liver lobules and the differences among normal, fibrotic, and cirrhotic lobules.  相似文献   
95.
Applying the improved Rayleigh SchrSdinger perturbation theory based on an integral equation to helium-like ions in ground states and treating electron correlations as perturbations, we obtain the second-order corrections to wavefunctions consisting of a few terms and the third-order corrections to energicity. It is demonstrated that the corrected wavefunctions are bounded and quadratically integrable, and the corresponding perturbation series is convergent. The results clear off the previous distrust for the convergence in the quantum perturbation theory and show a reciprocal development on the quantum perturbation problem of the ground state helium-like systems.  相似文献   
96.
The decoherence effect on Grover algorithm has been studied numerically through a noise modelled by a depolarizing channel. Two types of error are introduced characterizing the qubit time evolution and gate application, so the noise is directly related to the quantum network construction. The numerical simulation concludes an exponential damping law for the successive probability of the maxima as time increases. We have obtained an allowed-error law for the algorithm: the error threshold for the allowed noise behaves as εth(N) ∼1/N1.1 (N being the size of the data set). As the power of N is almost one, we consider the Grover algorithm as robust to a certain extent against decoherence. This law also provides an absolute threshold: if the free evolution error is greater than 0.043, Grover algorithm does not work for any number of qubits affected by the present error model. The improvement in the probability of success, in the case of two qubits has been illustrated by using a fault-tolerant encoding of the initial state by means of the [[7,1,3]] quantum code.  相似文献   
97.
The procedure of microphase adsorption–spectral correction is applied to the interaction of eosine Y (EO) to the micelles of cetyl trimethyl ammonium bromide (CTAB). The Langmuir aggregation of EO on CTAB occurs owing to microelectrostatic attraction. The results have shown that at pH 3.8, monomeric and micellar aggregates have the structure EO5·CTAB2 and (EO5·CTAB2)39. The adsorption constant of an aggregate is 7.01·105, its molar absorption coefficient is = 8.8·104 liters·mole–1·cm–1 at 550 nm. Application of the aggregation of EO on CTAB gives satisfactory results for quantitative determination of cation surfaceactive agents (surfactants).  相似文献   
98.
光学系统时间畸变和色时间滞后的研究   总被引:1,自引:1,他引:0  
薛鸣球  黄玉金 《光子学报》1995,24(6):481-484
本文对皮秒和飞秒技术中瞬态现象测量系统所用的特殊光学系统校正时间畸变和压缩色时间滞后的问题进行了讨论。实验证明用该方法设计研制的光学系统校正效果显着。  相似文献   
99.
S N Jena  M R Behera 《Pramana》1995,44(4):357-374
A relativistic model of independent quarks based on Dirac equation with an equally mixed scalar-vector square root confining potential is used to compute the quark core contributions to the static properties like magnetic moments, charge radii and axial vector coupling constant ratios of the baryon octet. The results obtained with appropriate corrections due to centre-of-mass motion agree fairly well with experimental values. The model is also extended to the study of magnetic moments of the quark core of baryons in the charmed andb-flavoured sectors and the overall predictions so obtained compare well with other model predictions.  相似文献   
100.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号