全文获取类型
收费全文 | 2432篇 |
免费 | 171篇 |
国内免费 | 153篇 |
专业分类
化学 | 352篇 |
晶体学 | 17篇 |
力学 | 74篇 |
综合类 | 7篇 |
数学 | 834篇 |
物理学 | 1472篇 |
出版年
2023年 | 10篇 |
2022年 | 12篇 |
2021年 | 28篇 |
2020年 | 19篇 |
2019年 | 36篇 |
2018年 | 25篇 |
2017年 | 33篇 |
2016年 | 29篇 |
2015年 | 31篇 |
2014年 | 43篇 |
2013年 | 57篇 |
2012年 | 58篇 |
2011年 | 149篇 |
2010年 | 155篇 |
2009年 | 331篇 |
2008年 | 309篇 |
2007年 | 247篇 |
2006年 | 236篇 |
2005年 | 142篇 |
2004年 | 78篇 |
2003年 | 102篇 |
2002年 | 109篇 |
2001年 | 75篇 |
2000年 | 73篇 |
1999年 | 81篇 |
1998年 | 57篇 |
1997年 | 12篇 |
1996年 | 26篇 |
1995年 | 22篇 |
1994年 | 18篇 |
1993年 | 15篇 |
1992年 | 21篇 |
1991年 | 12篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1985年 | 12篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1978年 | 2篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1975年 | 2篇 |
1974年 | 4篇 |
1973年 | 9篇 |
排序方式: 共有2756条查询结果,搜索用时 93 毫秒
71.
The flow and heat transfer problem of a second grade fluid film over an unsteady stretching sheet is considered. The fluid is incompressible and electrically conducting in the presence of a uniform applied magnetic field. The series solutions of the governing boundary value problems are obtained by employing homotopy analysis method (HAM). The convergence of the developed solutions is discussed explicitly. The dependence of velocity and temperature profiles on various parameters is shown and discussed through graphs. The values of skin-friction coefficient, Nusselt number and free surface temperature are given in tabular form for various emerging parameters. 相似文献
72.
B.U. Felderhof 《Physica A》2008,387(1):39-56
The problem of escape of a particle by diffusion from a square potential well across a square barrier is studied on the basis of the one-dimensional Smoluchowski equation for the space- and time-dependent probability distribution. For the model potential the Smoluchowski equation is solved exactly by a Laplace transform with respect to time. In the limit of a high barrier the rate of escape is given by an asymptotic result similar to that derived by Kramers for a curved well and a curved barrier. An approximate analytic formula is derived for the outward time-dependent probability current in terms of the width and depth of the well and the width and height of the barrier. A similar expression holds for the complete probability distribution. 相似文献
73.
B.U. Felderhof 《Physica A》2008,387(23):5752-5760
74.
Quantitative analysis of optical power budget of bismuth oxide-based erbium-doped fiber 总被引:1,自引:0,他引:1
We investigated optical power budget of Bi2O3-based erbium-doped fiber (BIEDF). Lateral spontaneous emissions and scattering laser powers in the BIEDF were measured quantitatively by using an integrating sphere. Compared with the power of amplified spontaneous emission and signal detected at the output fiber end, it was found that considerable powers were consumed by the laterally emitting lights. As an optically undetected loss limits power conversion efficiency (PCE) of the fiber amplifier, the effect of nonradiative decay from the termination level of pump excited state absorption (pump ESA) was estimated from decay rate analyses of the relevant levels. The nonradiative loss was comparable to amplified signal power in the BIEDF when pumped with a 980-nm LD. Nonradiative decay following cooperative upconversion (CUP) process is also discussed using rate equations analysis. 相似文献
75.
Sung Gap Im Byeong‐Su Kim Long Hua Lee Wyatt E. Tenhaeff Paula T. Hammond Karen K. Gleason 《Macromolecular rapid communications》2008,29(20):1648-1654
Click‐active surfaces patterned at 200 nm resolution are demonstrated using the dual functional polymeric film, poly(propargyl methacrylate) (PPMA). The commercially available monomer of propargyl methacrylate (PMA) is polymerized in a single step by initiated chemical vapor deposition (iCVD). FT‐IR and X‐ray photoelectron spectroscopy confirm retention of the click‐active acetylene functional group in the bulk and surface of the iCVD film, respectively. Treating substrates with silane coupling agents prior to deposition results in grafting of iCVD PPMA polymers onto various inorganic surfaces. This grafting technique provides the chemical and mechanical stability required for the PPMA layer to survive the subsequent wet chemical steps used for click functionalization. Successful attachment of an azido‐functionalized coumarin dye is demonstrated. Moreover, the PPMA film displays direct positive‐tone sensitivity to e‐beam irradiation, which enables e‐beam patterning without the use of a resist layer. Direct e‐beam exposure of the multifunctional PPMA iCVD layer results in a 200 nm pattern to which quantum dot nanoparticles are selectively conjugated on the substrates by click chemistry. e> e> e srcset="/cms/asset/5d393f79-227a-4b9b-85b2-a22934832e63/mgra001.jpg" media="(min-width: 1650px)"> e>e__image-full" src="/cms/asset/a370dabf-3fef-4fa6-a4ac-724919643896/mgra001.jpg" data-lg-src="/cms/asset/5d393f79-227a-4b9b-85b2-a22934832e63/mgra001.jpg" alt="image" title="image"> e>
76.
A systematic investigation on nanocrystalline LiCoO2 has been carried out using Raman spectroscopy. We synthesized nanocrystalline LiCoO2 (ca. 20-50 nm) through a combination of rapid thermal annealing at various annealing temperatures and a sol-gel method assisted with a triblock copolymer surfactant. Powder X-ray diffraction measurements revealed the formation of LiCoO2. The crystallite size of LiCoO2 from the Scherrer equation strongly depended on the annealing temperature. The crystallite size was confirmed by SEM and TEM measurements. Raman shifts of the A1g and Eg modes for nanocrystalline LiCoO2 exhibited a broadening and a frequency shift according to the crystallite size. While the frequency shift could be ascribed to a structural strain at the surface, the broadening was due to the phonon confinement effect produced by narrow crystal boundaries. 相似文献
77.
Chang-Zheng Yuan 《Frontiers of Physics》2015,10(6):101401
With its unique data samples at energies of 3.8–4.6 GeV, the BESIII experiment made a significant contribution to the study of charmonium and charmonium-like states, i.e., the XYZ states.We review the results for observations of the Zc(3900) and Zc(4020) states, the X(3872) in e+e− annihilation, and charmonium ψ(13D2) state, as well as measurements of the cross-sections of ωχcJ and ηJ/ψ, and the search for e+e−→ γχcJ and γY (4140). We also present data from BESIII that may further strengthen the study of the XYZ and conventional charmonium states, and discuss perspectives on future experiments. 相似文献
78.
Study of (e, 2e) process on potassium at 6 eV—60 eV above threshold in second-order Born approximation 下载免费PDF全文
The standard distorted wave Born approximation (DWBA) method has been extended to second-order Born amplitude in order to describe the multiple interactions between the projectile and the atomic target. Second-order DWBA calculations have been preformed to investigate the triple differential cross sections (TDCS) of coplanar doubly symmetric (e, 2e) collisions for alkali target potassium at excess energies of 6 eV-60 eV. Comparing with the first-order DWBA calculations before, the present theoretical model improves the degree of agreement with experiments, especially for backward scattering angle region of TDCS. This indicates that the present second-order Born term is capable to give a reasonable correction to DWBA model in studying coplanar symmetric (e, 2e) problems in low and intermediate energy range. 相似文献
79.
YUE Chong-Xing ZHANG Feng YANG Shuo SUN Yan-Bin 《理论物理通讯》2006,46(5):891-894
In the context of the littlest Higgs (LH) model, we estimate the production cross section of the process e^-у→ e^-H in the future high-energy linear e^+e^- collider (ILC) with the center-of-mass (CM) energy √S = 500 GeV. Our numerical results show that the contributions of the LH model Co this process are very small in most of the parameter space allowed by the electroweak precision measurement data, and are very diffcult to be detected in the future ILC experiments. 相似文献
80.
众所周知,电子相关能问题是量子化学的瓶颈问题‘’‘.为了更深人地了解和认识电子相关能的轨道本质,建立P。St-HF理论校正模型,JS等”-”应用电子对内对间电子相关模式,指出国际著名量子 相似文献