全文获取类型
收费全文 | 477篇 |
免费 | 90篇 |
国内免费 | 55篇 |
专业分类
化学 | 161篇 |
晶体学 | 6篇 |
力学 | 37篇 |
综合类 | 1篇 |
数学 | 267篇 |
物理学 | 150篇 |
出版年
2024年 | 1篇 |
2023年 | 6篇 |
2022年 | 21篇 |
2021年 | 24篇 |
2020年 | 34篇 |
2019年 | 23篇 |
2018年 | 28篇 |
2017年 | 26篇 |
2016年 | 21篇 |
2015年 | 41篇 |
2014年 | 55篇 |
2013年 | 47篇 |
2012年 | 55篇 |
2011年 | 47篇 |
2010年 | 23篇 |
2009年 | 30篇 |
2008年 | 14篇 |
2007年 | 26篇 |
2006年 | 23篇 |
2005年 | 11篇 |
2004年 | 6篇 |
2003年 | 3篇 |
2002年 | 1篇 |
2001年 | 3篇 |
2000年 | 1篇 |
1999年 | 7篇 |
1998年 | 2篇 |
1997年 | 4篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 3篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有622条查询结果,搜索用时 15 毫秒
1.
《Chaos, solitons, and fractals》2006,27(1):97-101
Sufficient condition for the generalized synchronization of continuous chaotic system with a kind of nonlinear transformation is derived. The method is illustrated by applications to Lorenz and Duffing chaotic systems and the simulation results demonstrate the effectiveness of the proposed theorem. 相似文献
2.
《Tetrahedron letters》1987,28(44):5367-5368
Porcine pancreatic lipase in anhydrous organic solvents catalyses almost exclusively the oligomerisation reaction of unsubstituted β, δ, and ε-hydroxyacid methyl esters. In Contrast, the substituted δ-methyl- δ-hydroxyester undergoes lactonisation. 相似文献
3.
固-液结构圆柱声子晶体中弹性波的模式和带隙 总被引:2,自引:1,他引:2
利用一维固-液结构圆柱声子晶体中弹性波横向受限的条件,推导弹性波在一维固-液结构圆柱声子晶体中各个模式满足的关系式,研究各个模式弹性波的特征.并用色散函数计算各模式弹性波的带隙随模式量子数和圆柱半径的变化规律.得出一维固-液结构圆柱声子晶体的带隙由模式量子数和圆柱半径确定. 相似文献
4.
A highly efficient protocol for the synthesis of aminopropyl functionalized ganglioside GM1b has been described. The full protected ganglioside GM1b was obtained in 71% yield within 5 h. The key feature of the synthetic approach was the use of sialic acid donor that was with a C-5 trichloroacetamide moiety and with a dibenzyl phosphite residue as leaving group at the anomeric carbon. The sialyl donor gave high yields and excellent α-anomeric selectivities with a wide variety of glycosyl acceptors ranging from C-3 or C-6 hydroxyls of galactoside to C-6 hydroxyl of glucosaminoside by using TMSOTf as catalyst in a mixture solution of acetonitrile and methylene chloride. 相似文献
5.
In this paper, we propose a sinusoidal phase modulating (SPM) interferometer that is insensitive to external disturbances, and its measuring principle is analyzed theoretically. In the SPM interferometer, the interference signal is detected by a high-speed image sensor based on a low-speed CCD and a signal processing circuit is used to obtain the phase of each point on the surface. Therefore, the surface profile can be measured real-time. The experiments measuring the surface profile of a wedge-shaped optical flat show that the measurement time of the SPM interferometer is less than 10 ms, the repetitive measurement accuracy is 4.2 nm. The results show that the impacts of nonlinear distortion of the piezoelectric transducer (PZT) and part external disturbance are removed. 相似文献
6.
ZENG Xiao-Xiong HAN Yi-Wen YANG Shu-Zheng 《理论物理通讯》2009,51(1):187-189
Based on the covariant anomaly cancellation method, which is believed to be more refined than the initial approach of Robinson and Wilczek, we discuss Hawking radiation from the plane symmetric black hole. The result shows that Hawking radiation from the non-spherical symmetric black holes also can be derived from the viewpoint of anomaly. 相似文献
7.
Thermodynamics and weak cosmic censorship conjecture of BTZ black holes in extended phase space 下载免费PDF全文
As a charged fermion drops into a BTZ black hole, the laws of thermodynamics and the weak cosmic censorship conjecture are investigated in both the normal and extended phase space, where the cosmological parameter and renormalization length are regarded as extensive quantities. In the normal phase space, the first and second law of thermodynamics, and the weak cosmic censorship are found to be valid. In the extended phase space, although the first law and weak cosmic censorship conjecture remain valid, the second law is dependent on the variation of the renormalization energy d K. Moreover, in the extended phase space, the configurations of extremal and near-extremal black holes are not changed, as they are stable, while in the normal phase space, the extremal and near-extremal black holes evolve into non-extremal black holes. 相似文献
8.
Classification noise is a common byproduct of traditional data mining approaches, and no specialized approach for detecting classification noise is currently available. Methods for outlier detection are well-developed, but outliers and classification noise have characteristics different enough to make outlier detection algorithms unsuitable for classification noise detection. In this paper, a new, specialized approach to detect classification noise is proposed, named relative density based classification noise detection (RDBCND). Computational experiments in artificial data sets described herein show that RDBCND has time complexity of O(n log n), indicating greater efficiency than traditional approaches, which exhibit time complexity of at least O(n2). The use of classification noise detection to improve the generalization ability of common classifier algorithms is also described. In particular, a new unified approach based on RDBCND is compared to a cross validation approach applied to a BP neural network. Trials in both artificial and real-life datasets show that the RDBCND-based approach can greatly accelerate the process of identifying the best decision function. The novel method can also eliminate underfitting, as the algorithm simply searches for the highest training accuracy. The experiments also show that the RDBCND-based method has greater accuracy and lower cpu time in reaching global solutions than the cross-validation method. Since the relative density is a local concept, our new approach can be directly used in nonlinear datasets without data transformation. It is a great advantage compared to some linear classifier algorithms. As in current linear classifiers, the kernel functions or other transformations need to be used to make them suitable for non-linear datasets, and that will increase their complexity. 相似文献
9.
This paper reports ultrasound-assisted optical imaging of chemiluminescent probes in biological tissue. A focused low power ultrasound sonochemically enhances a peroxyoxalate chemiluminescence (CL) that involves indocyanine green (ICG) as luminescent pigments. By scanning the focus, it produces tomographic images of CL in scattering media. The authors demonstrate imaging using a slab of porcine muscle measuring 50 × 50 × 75 mm, in which a capsuled CL reagent is embedded at 25 mm depth. Spatial resolution of imaging and concentration characteristics of CL reagents to enhanced CL intensity are also studied to evaluate the potential for use in bio-imaging applications with exploring the CL enhancement mechanisms. CL enhancement ratio, defined as the ratio of ultrasonically enhanced CL intensity to the base intensity without ultrasound irradiation, was found to be constant even in varying ICG and oxidizer concentrations, implying to be applicable for quantitative determination of these molecules. 相似文献
10.
Yi-Wen Han Xiao-Xiong Zeng Shu-Zheng Yang 《International Journal of Theoretical Physics》2008,47(7):2011-2020
The recent work of Robinson and Wilczek that Hawking radiation can be determined by the compensating fluxes is extended to the charged and magnetized Reissner-Nordström de Sitter black hole. We reconstruct the electromagnetic field tensor and the Lagrangian of the field corresponding to the source with electric and magnetic charges to redefine an equivalent charge and gauge potential. We construct the effect field theory between the event horizon and cosmological horizon to respectively determine the compensating fluxes from them, which are shown to exactly equal to those of Hawking radiation, by the covariant anomaly cancellation conditions. 相似文献