全文获取类型
收费全文 | 23250篇 |
免费 | 4174篇 |
国内免费 | 2101篇 |
专业分类
化学 | 8863篇 |
晶体学 | 682篇 |
力学 | 1261篇 |
综合类 | 172篇 |
数学 | 1422篇 |
物理学 | 17125篇 |
出版年
2024年 | 51篇 |
2023年 | 194篇 |
2022年 | 413篇 |
2021年 | 462篇 |
2020年 | 495篇 |
2019年 | 401篇 |
2018年 | 445篇 |
2017年 | 724篇 |
2016年 | 860篇 |
2015年 | 740篇 |
2014年 | 1236篇 |
2013年 | 1930篇 |
2012年 | 1595篇 |
2011年 | 1696篇 |
2010年 | 1318篇 |
2009年 | 1588篇 |
2008年 | 1777篇 |
2007年 | 1738篇 |
2006年 | 1614篇 |
2005年 | 1340篇 |
2004年 | 1135篇 |
2003年 | 1018篇 |
2002年 | 917篇 |
2001年 | 796篇 |
2000年 | 745篇 |
1999年 | 638篇 |
1998年 | 541篇 |
1997年 | 512篇 |
1996年 | 400篇 |
1995年 | 387篇 |
1994年 | 375篇 |
1993年 | 275篇 |
1992年 | 227篇 |
1991年 | 176篇 |
1990年 | 128篇 |
1989年 | 111篇 |
1988年 | 88篇 |
1987年 | 76篇 |
1986年 | 54篇 |
1985年 | 61篇 |
1984年 | 54篇 |
1983年 | 16篇 |
1982年 | 48篇 |
1981年 | 26篇 |
1980年 | 28篇 |
1979年 | 17篇 |
1978年 | 8篇 |
1976年 | 13篇 |
1975年 | 8篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 546 毫秒
111.
Recently, molecular imaging has been rapidly developed to studyphysiological and pathological processes in vivo at the cellularand molecular levels. Among molecular imaging modalities, opticalimaging has attracted a major attention for its unique advantages.In this paper, we establish a mathematical framework for multispectralbioluminescence tomography (BLT) that allows simultaneous studiesof multiple optical reporters. We show solution existence, uniquenessand continuous dependence on data as well as the limiting behaviourswhen the regularization parameter approaches zero or when thepenalty parameter approaches infinity. Then, we propose twonumerical schemes for multispectral BLT and derive error estimatesfor the corresponding solutions. 相似文献
112.
Optical trapping forces of polystyrene microspheres are analyzed both theoretically and experimentally, and comparisons are
made between the two. Discrepancies are mainly caused by straight-ray approximation for axial trapping, and by trapping-position
vertical displacement due to gravity for transverse trapping. 相似文献
113.
This work proposes and demonstrates the feasibility of gray image encryption using multiple polarization encoding, in which
the cascaded twisted nematic liquid crystal devices sandwiched between a crossed polarizer pair are used to implement exclusive
OR (XOR) logical encryption and decryption. The polarization encoding scheme provides a multichannel XOR logic operation to
secure bit-plane images derived from a gray image, according to the adiabatic following properties of twisted nematic liquid
crystal devices. Experimental data reveal that the multiple polarization encoding schemes for gray image encryption and decryption
are performed with acceptable image quality by selecting appropriate polarization orientation and modulation conditions. Both
analytic and experimental results are presented and discussed. 相似文献
114.
115.
用力敏传感器测量乙醇水溶液的表面张力系数与浓度的关系 总被引:6,自引:3,他引:3
用硅压阻式力敏传感器测量了纯水、乙醇的表面张力系数,并测量了不同浓度的乙醇水溶液的表面张力系数,得到了乙醇水溶液的表面张力系数随浓度的变化曲线. 相似文献
116.
Hongrui Zhang Mingju Chao Mingyi Gao Liwen Zhang Jianquan Yao 《Optics & Laser Technology》2003,35(6):573-449
A fiber-coupled diode-single-end-pumped Nd:YVO4 laser with an Nd:YVO4 crystal of 0.3 at% doping concentration and 3×3×10 mm3 dimensions was reported. 14.850 W of continuous-wave output power in an M2 factor of 1.12 was obtained under pump power of 27.365 W, with an optical conversion efficiency of 60.49%, and a slope efficiency of 64.5%. 相似文献
117.
118.
Sean D. Brooks M. F. Mahmood J. A. Donaldson 《Journal of Mathematical Modelling and Algorithms》2004,3(1):19-29
A numerical investigation, based on the split-step Fourier transform algorithm of all optical switching of solitons in a low
birefringent optical fiber is presented. The numerical algorithm is described in detail.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
119.
M. Battabyal 《Journal of Physics and Chemistry of Solids》2004,65(11):1895-1900
Thermal conductivity (λ) of nanocrystalline La1−xAgxMnO3 (x=0.05, 0.15, 0.25, 0.3) pellets prepared by pyrophoric method is reported between 10 and 300 K. Magnitude of thermal conductivity has been found to be strongly influenced by monovalent (Ag) substitution at the La site. Silver doping in LaMnO3 enhances TC of the system to ∼299 K. Qualitative nature of the temperature variation of thermal conductivity of the silver substituted lanthanum manganites remains closely similar to that for divalent doped systems. Our analysis demonstrates that in La1−xAgxMnO3 also, the mechanism of heat conduction is predominantly by phonons. The contribution of the electronic part is only ∼1% of the total λ. The spin wave contribution is also estimated close to TC, which for all the samples lies within ∼2%. At temperatures below ∼100 K, the measured data have been analyzed using phonon relaxation time method and the strengths of the various phonon scattering processes have been estimated. Our analysis further suggests strong influence of phonon scattering by 2D like defects in the thermal conductivity of monovalent doped lanthanum manganites at low temperatures (<70 K) in the ferromagnetic region. 相似文献
120.
In this paper, we have developed an analytical model to study the temperature distributions in IR optical materials heated by laser pulses. Our model takes into account the two-photon absorption (TPA). The calculations are based on a three-dimensional model of heat diffusion in solids using the integral transform method. We find out the rigorous analytical expression of the thermal field when one considers both one- and two-photon absorption. The model is valid for any laser–solid system whose interaction can be described by the generalized Beer–Lambert law. Specific results are presented for an application of the model to ZnSe sample. We find out that TPA can produce detectable temperature variation. 相似文献