全文获取类型
收费全文 | 29790篇 |
免费 | 1523篇 |
国内免费 | 1458篇 |
专业分类
化学 | 6895篇 |
晶体学 | 92篇 |
力学 | 852篇 |
综合类 | 164篇 |
数学 | 3615篇 |
物理学 | 6007篇 |
综合类 | 15146篇 |
出版年
2024年 | 70篇 |
2023年 | 242篇 |
2022年 | 551篇 |
2021年 | 528篇 |
2020年 | 470篇 |
2019年 | 483篇 |
2018年 | 444篇 |
2017年 | 486篇 |
2016年 | 562篇 |
2015年 | 663篇 |
2014年 | 1180篇 |
2013年 | 1498篇 |
2012年 | 1379篇 |
2011年 | 1600篇 |
2010年 | 1262篇 |
2009年 | 1675篇 |
2008年 | 1786篇 |
2007年 | 2104篇 |
2006年 | 1901篇 |
2005年 | 1546篇 |
2004年 | 1382篇 |
2003年 | 1296篇 |
2002年 | 1235篇 |
2001年 | 1086篇 |
2000年 | 943篇 |
1999年 | 782篇 |
1998年 | 661篇 |
1997年 | 506篇 |
1996年 | 436篇 |
1995年 | 404篇 |
1994年 | 353篇 |
1993年 | 321篇 |
1992年 | 390篇 |
1991年 | 257篇 |
1990年 | 207篇 |
1989年 | 182篇 |
1988年 | 195篇 |
1987年 | 157篇 |
1986年 | 114篇 |
1985年 | 92篇 |
1984年 | 87篇 |
1983年 | 49篇 |
1982年 | 102篇 |
1981年 | 176篇 |
1980年 | 183篇 |
1979年 | 177篇 |
1978年 | 166篇 |
1977年 | 103篇 |
1976年 | 110篇 |
1973年 | 78篇 |
排序方式: 共有10000条查询结果,搜索用时 55 毫秒
91.
In this paper, we consider questions related to the structure of inverse matrices of linear bounded operators acting in infinite-dimensional complex Banach spaces. We obtain specific estimates of elements of inverse matrices for bounded operators whose matrices have a special structure. Matrices are introduced as special operator-valued functions on an index set. The matrix structure is described by the behavior of the given function on elements of a special partition of the index set. The method used for deriving the estimates is based on an analysis of Fourier series of strongly continuous periodic functions. 相似文献
92.
抓好数学建模竞赛 推动数学教学改革 总被引:5,自引:0,他引:5
本文通过近几年组织数学建模教学和指导学生参加竞赛的实践 ,探索抓好数学建模竞赛 ,促进数学教学改革 ,推动数学素质教育 ,提高人才培养质量的途径、措施和方法 相似文献
93.
简析"静止液体内部压强公式验证"实验的设计策略 总被引:1,自引:1,他引:0
“静止液体内部压强公式验证”在现行教材中有两种实验方法。通过分析实验的设计策略,说明其作用、效果及操作上的困难,指出合理的与不合理诸因素,从而提出改进实验的方法,化难为易,提高实验教学效果。 相似文献
94.
Electronic properties of model quantum-dot structures in zero and finite magnetic fields 总被引:1,自引:0,他引:1
H. Saarikoski E. Räsänen S. Siljamäki A. Harju M.J. Puska R.M. Nieminen 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(2):241-252
We have computed electronic structures and total energies of circularly confined two-dimensional quantum dots and their lateral
dimers in zero and finite uniform external magnetic fields using different theoretical schemes: the spin-density-functional
theory (SDFT), the current-and-spin-density-functional theory (CSDFT), and the variational quantum Monte Carlo (VMC) method.
The SDFT and CSDFT calculations employ a recently-developed, symmetry-unrestricted real-space algorithm allowing solutions
which break the spin symmetry. Results obtained for a six-electron dot in the weak confinement limit and in zero magnetic
field as well as in a moderate confinement and in finite magnetic fields enable us to draw conclusions about the reliability
of the more approximative SDFT and CSDFT schemes in comparison with the VMC method. The same is true for results obtained
for the two-electron quantum dot dimer as a function of inter-dot distance. The structure and role of the symmetry-breaking
solutions appearing in the SDFT and CSDFT calculations for the above systems are discussed.
Received 16 October 2001 and Received in final form 17 January 2002 相似文献
95.
Ben-Yuan Gu Yao Lu Tzong-Jer Yang 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(4):493-502
We present numerical investigations of the transmission properties of electrons in a normal quantum wire tangentially attached
to a superconductor ring threaded by magnetic flux. A point scatterer with a δ -function potential is placed at node to model
scattering effect. We find that the transmission characteristics of electrons in this structure strongly depend on the normal
or superconducting state of the ring. The transmission probability as a function of the energy of incident electrons, in the
case of a superconductor ring threaded by one quantum magnetic flux, emerges one deep dip, imposed upon the first broad bump
in spectrum. This intrinsic conductance dip originates from the superconductor state of the ring. When increasing the magnetic
flux from one quantum magnetic flux to two, the spectrum shifts toward higher energy region in the whole. This conductance
dip accordingly shifts and appears in the second bump. In the presence of a point-scatterer at the node, the spectrum is substantially
modified. Based on the condition of the formation of the standing wave functions in the ring and the broken of the time-reserve
symmetry of Schr?dinger equation after switching magnetic flux, the characteristics of transmission of electrons in this structure
can be well understood.
Received 6 November 2001 相似文献
96.
The behavior of a two-level entangled atom in an optical field with circular polarization is studied in this paper. The interaction of an optical field and one of the entangled atoms is analyzed in detail. A general solution of the SchrAo¨Gdinger equation about the motion of the entangled atom is obtained. The properties of the action are dependent on the initial state of the atom. By detecting the entangled atom out of the field, we can obtain the state of the other atom moving in the field. It is shown that the state of the atom out of the field will influence the energies of the split-levels of the atom in the field. 相似文献
97.
We calculate the loss induced in a single-mode rectangular optical waveguide by the presence of a second waveguide, perpendicular to the first, which crosses over the first waveguide at a variable distance d. Our calculation is applied to the analysis of several doped silica waveguides of practical importance for optical circuit design. 相似文献
98.
通过分析比较化工传热过程计算中的平均温度差法(MTD法)和传热单元数法(NTU法),找出了它们之间的内在联系,结合这两种方法的优点,组合成了一种新的计算方法,应用于化工传热过程的计算,可使计算过程大为简便,同时又可评价换热设备流动型式的合理性。 相似文献
99.
何瑶 《武汉科技学院学报》2002,15(5):7-10
采用蒸发和吸湿法测量多种织物的透湿速率,并且仔细研究用蒸发法时,织物润湿程度在透湿过程中的变化,发现织物在透湿过程中的润湿和放湿,以及织物的表面性状是影响其放湿速率的非常重要的因素。 相似文献
100.
We study the propagation of the light mesons σ,ω,ρ, and a0(980) in dense hadronic matter in an extended derivative scalar coupling model. Within the scheme proposed it is possible
to unambiguously define effective density-dependent couplings at the Lagrangian level. We first apply the model to study asymmetric
nuclear matter with fixed isospin asymmetry, and then we pay particular attention to hypermatter in β-equilibrium. The equation
of state and the potential contribution to the symmetry coefficient arising from the mean-field approximation are investigated.
Received: 16 October 2001 / Accepted: 10 January 2002 相似文献