全文获取类型
收费全文 | 4218篇 |
免费 | 601篇 |
国内免费 | 257篇 |
专业分类
化学 | 732篇 |
晶体学 | 50篇 |
力学 | 1664篇 |
综合类 | 47篇 |
数学 | 625篇 |
物理学 | 1958篇 |
出版年
2024年 | 12篇 |
2023年 | 36篇 |
2022年 | 73篇 |
2021年 | 80篇 |
2020年 | 100篇 |
2019年 | 78篇 |
2018年 | 97篇 |
2017年 | 130篇 |
2016年 | 135篇 |
2015年 | 94篇 |
2014年 | 186篇 |
2013年 | 361篇 |
2012年 | 195篇 |
2011年 | 223篇 |
2010年 | 196篇 |
2009年 | 232篇 |
2008年 | 249篇 |
2007年 | 270篇 |
2006年 | 274篇 |
2005年 | 222篇 |
2004年 | 208篇 |
2003年 | 219篇 |
2002年 | 147篇 |
2001年 | 128篇 |
2000年 | 140篇 |
1999年 | 155篇 |
1998年 | 103篇 |
1997年 | 117篇 |
1996年 | 97篇 |
1995年 | 91篇 |
1994年 | 56篇 |
1993年 | 43篇 |
1992年 | 58篇 |
1991年 | 52篇 |
1990年 | 30篇 |
1989年 | 26篇 |
1988年 | 32篇 |
1987年 | 23篇 |
1986年 | 26篇 |
1985年 | 20篇 |
1984年 | 10篇 |
1983年 | 4篇 |
1982年 | 12篇 |
1981年 | 8篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1957年 | 2篇 |
排序方式: 共有5076条查询结果,搜索用时 15 毫秒
41.
A hypersingular integral equation for the curved crack problems of an elastic half-plane is introduced. Formulation of the equation is based on the usage of a modified complex potential. The potential is generally expressed in the form of a Cauchy-type integral. The modified complex potential is composed of the principal part and the complementary part. The principal part of the complex potential is actually equivalent to the original complex potential for the curved crack in an infinite plate. The role of the complementary part is to eliminate the boundary traction along the boundary of the half-plane caused by the principal part. From the assumed boundary traction condition, a hypersingular integral equation is obtained for the curved crack problems of an elastic half-plane. The curve length coordinate method is used to obtain a final solution. Several numerical examples are presented that prove the efficiency of the suggested method. 相似文献
42.
A complete set of elastic constants C ij and piezoelectric coefficients e ij of a La3Ga5SiO14 (langasite) single crystal was determined from 5.5 to 275.5?K by resonant ultrasound spectroscopy. Unlike a conventional crystal, the elastic constants C ij of the langasite crystal showed three types of temperature dependence: (i) monotonic elastic stiffening upon cooling (C 44 and C 14); (ii) monotonic elastic softening (C 66); and (iii) a stiffening-to-softening transition below 150?K (C 11, C 12, C 13 and C 33). In addition, a strong correlation between C 66 and the piezoelectric coefficient e 11 was confirmed. Group theoretical lattice dynamics analysis revealed that the novel phenomena of elastic softening and strong correlation are explained on the basis of two types of optical mode internal displacements which have the totally symmetric A 1 and doubly degenerated E symmetries in the point group D 3. 相似文献
43.
《Composite Interfaces》2013,20(2):95-125
Scattering of elastic P-waves from a nanofiber in a matrix is studied analytically throughout this paper. An inhomogeneous interphase region is considered between the nanofiber and the matrix. Dividing the interphase into homogeneous sublayers, surface elasticity effects are studied in the layers adjacent to matrix and nanofiber. Wave function expansion method is used to solve the corresponding equations in all three phases including fiber, interphase, and matrix. Dynamic stress concentration factors around the nanofiber are calculated and utilizing a parametric study, effects of different parameters, such as nanoscale interface, interphase thickness, and interphase rigidity are investigated. The results indicate that considering the effects of surface elasticity in wave scattering problems from inhomogeneous interphases show a major impact on the results. The dimensionless equations presented in this paper provide the possibility of further numerical studies. 相似文献
44.
利用离子香蕉轨道中心坐标和香蕉轨道平均算符,讨论了磁岛转动引起的沿磁力线电流分布及其对新经典撕裂模演进的影响。结果显示,考虑此电流的影响,当磁岛旋转频率ω=ω*i 时,被离子香蕉轨道宽度效应削弱的自举电流驱动项基本恢复;当ω=ω*e时,离子香蕉轨道宽度效应对自举电流驱动项的削弱则加剧。这意味着磁岛转动方向不同时,此沿力线电流能显著增大或减弱离子香蕉轨道宽度效应对自举电流驱动项的削弱作用。 相似文献
45.
Using a tangentially viewing x-ray imaging crystal spectrometer, substantial co-current rotation driven by lower hybrid current drive(LHCD) at 4.6 GHz is observed on EAST tokamak. This study presents plasma rotation behaviors with 4.6 GHz LHCD injection. Typically, the 10-20 km/s co-current rotation change and the transport of rotation velocity from edge to core are observed. The relationship between plasma parameters and rotation is also investigated, indicating that rotation decreases with increasing internal inductance(l_i) and increases with increasing safety factor(q_0). Hysteresis between rotation and T_e plasma stored energy is observed, suggesting different response times between the electron heating and rotation acceleration by LHCD. A comparison between the rotations driven by 4.6 G LHCD and 2.45 G LHCD on EAST is also presented, in which higher frequency LHCD could induce more rotation changes. 相似文献
46.
采用第一性原理研究了CdS的六方纤锌矿(WZ), 立方闪锌矿(ZB) 和岩盐矿(RS)相在高压条件下的相稳定性、 相变点、电子结构以及弹性性能.WZ相与RS 相可以在相应的压强范围内稳定存在, 而ZB相不能稳定存在.压强大于2.18 GPa时, WZ相向RS相发生金属化相变.WZ相中S原子电负性大于Cd, 且电负性差值小于1.7, CdS的WZ相为共价晶体.高压作用下, S原子半径被强烈压缩, 有效核电荷增加, 对层外电子吸引能力提高, 电负性急剧增大, 导致S与Cd的电负性差值大于1.7, CdS的RS相以离子晶体存在. WZ相的C44随压强增加呈下降趋势, 导致WZ相力学不稳定, 并向RS相转变.当压强大于2.18 GPa时, RS相C11, C12随压强增加而增大, 并且C44保持稳定, 说明RS相具有良好的高压稳定性与力学性能.
关键词:
第一性原理
相变
电子结构
弹性性质 相似文献
47.
LUO Jing ZHENG HouZhi SHEN Chao ZHANG Hao ZHU Ke ZHU Hui LIU Jian LI GuiRong JI Yang & ZHAO JianHua State Key Laboratory for Superlattices Microstructures 《中国科学:物理学 力学 天文学(英文版)》2010,(5)
We report that,by linearly polarized pumping of different wavelengths,Kerr transients appear at zero magnetic field only in the case when GaMnAs samples are initialized at 3 K by first applying a 0.8 Tesla field and then returning to zero field.We find that,instead of magnetization precession,the near-band gap excitation induces a coherent out-of-plane turning of magnetization,which shows very long relaxation dynamics with no precession.When photon energy increases,the peak value of the Kerr transient incre... 相似文献
48.
A. Schenck N.K. Sato G. Solt D. Andreica F.N. Gygax M. Pinkpank A. Amato 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(2):245-256
We report on transverse field (TF) Muon Spin Rotation (μSR) measurements on a single crystal of the hexagonal heavy fermion
superconductor UNi2Al3 between 5 K and 300 K. From the measured muon Knight shift (KS) in the easy (
a
,
b
)-plane and along the c-axis we extracted the local magnetic susceptibility tensor [0pt] , which arises from the nearest U-neighbors. By comparison with the bulk susceptibility [0pt] it is found that [0pt] and [0pt] agree well above 150 K but deviate considerably in the basal plane below 150 K, due to the disturbance introduced by the
. We succeed in reproducing both [0pt] and [0pt] on the basis of a crystalline electric field (CEF)-approach assuming U to be in the tetravalent state. The disturbance introduced by the affects the CEF-Hamiltonian in an expected manner, suggesting strongly that a CEF-picture implying a rather local 5
f-electron wave function is indeed valid. Reanalyzing older data on UPd2Al3 we arrive at the same conclusion. A necessary condition for extracting the local susceptibility was the knowledge of the
-site, this information was derived from the analysis of the TF-relaxation rates. At low temperatures we found about 30% of
the implanted at the d-site and none at this site above 200 K. The majority fraction was found to be in a tunneling state over six m (or k)-sites around the b-site. No long range diffusion was seen up to room temperature.
Received 20 April 1999 相似文献
49.
50.
采用两套旋转孔径散斑照相系统对动态三维位移场进行了研测。一次实验可把缓慢连续变形体的动态三维位移场的整个变化过程记录于两张散斑图上.对散斑图进行全场滤波可摄取所有各时刻的三个位移分量的信息。 相似文献