全文获取类型
收费全文 | 2993篇 |
免费 | 391篇 |
国内免费 | 180篇 |
专业分类
化学 | 279篇 |
晶体学 | 35篇 |
力学 | 1590篇 |
综合类 | 64篇 |
数学 | 554篇 |
物理学 | 1042篇 |
出版年
2024年 | 12篇 |
2023年 | 21篇 |
2022年 | 31篇 |
2021年 | 50篇 |
2020年 | 78篇 |
2019年 | 53篇 |
2018年 | 68篇 |
2017年 | 84篇 |
2016年 | 105篇 |
2015年 | 55篇 |
2014年 | 125篇 |
2013年 | 256篇 |
2012年 | 154篇 |
2011年 | 128篇 |
2010年 | 111篇 |
2009年 | 142篇 |
2008年 | 166篇 |
2007年 | 188篇 |
2006年 | 200篇 |
2005年 | 172篇 |
2004年 | 143篇 |
2003年 | 150篇 |
2002年 | 101篇 |
2001年 | 101篇 |
2000年 | 93篇 |
1999年 | 108篇 |
1998年 | 84篇 |
1997年 | 92篇 |
1996年 | 77篇 |
1995年 | 73篇 |
1994年 | 46篇 |
1993年 | 31篇 |
1992年 | 52篇 |
1991年 | 48篇 |
1990年 | 23篇 |
1989年 | 13篇 |
1988年 | 27篇 |
1987年 | 20篇 |
1986年 | 20篇 |
1985年 | 16篇 |
1984年 | 8篇 |
1983年 | 3篇 |
1982年 | 10篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1971年 | 2篇 |
1957年 | 3篇 |
排序方式: 共有3564条查询结果,搜索用时 15 毫秒
21.
Twin Paradox and the Logical Foundation of Relativity Theory 总被引:3,自引:0,他引:3
We study the foundation of space-time theory in the framework of first-order logic (FOL). Since the foundation of mathematics has been successfully carried through (via set theory) in FOL, it is not entirely impossible to do the same for space-time theory (or relativity). First we recall a simple and streamlined FOL-axiomatization Specrel of special relativity from the literature. Specrel is complete with respect to questions about inertial motion. Then we ask ourselves whether we can prove the usual relativistic properties of accelerated motion (e.g., clocks in acceleration) in Specrel. As it turns out, this is practically equivalent to asking whether Specrel is strong enough to “handle” (or treat) accelerated observers. We show that there is a mathematical principle called induction (IND) coming from real analysis which needs to be added to Specrel in order to handle situations involving relativistic acceleration. We present an extended version AccRel of Specrel which is strong enough to handle accelerated motion, in particular, accelerated observers. Among others, we show that~the Twin Paradox becomes provable in AccRel, but it is not provable without IND. 相似文献
22.
牛顿碰撞球的解释与分析 总被引:1,自引:0,他引:1
对牛顿碰撞球的常规碰撞形式和混合联珠单球碰撞形式做了理论分析和解释.在常规碰撞时,将悬线(钓鱼线)先悬挂小球一段时间后组装仪器,可克服悬线的拉力.在混合联珠单球碰撞时,根据理论分析,选取大球和小球的质量比为27∶8时,演示效果较好. 相似文献
23.
Analogues of the well-known Kolosov–Muskhelishvili formulas of general representations are obtained for nonhomogeneous equations of statics in the case of the theory of elastic mixtures. It is shown that in this theory the displacement and stress vector components, as well as the stress tensor components, are represented through four arbitrary analytic functions.The usual Cauchy–Riemann conditions are generalized for homogeneous equations of statics in the theory of elastic mixtures. 相似文献
24.
用三维样边界元法分析水闸闸室结构。底板,闸墩和载水墙等为其子结构,交通桥,工作桥和胸墙等处理为内部支撑。地基和边载可以是任意的,只要能给定地表位移面力关系。在各种工况下,不论是设置平板门还是弧形门,是平底板是反拱底板,即使在稀疏剖分下也能给出高精度的位移场,应力场和地基反力场。 相似文献
25.
沈定珍 《宁波大学学报(理工版)》2006,19(3):346-349
软土地基中的支护是基础工程的关键,在节约成本的前提下,选择合理的支护结构至关重要.通过对某公司将要开发的2个基坑支护方案的项目进行的相关分析、计算和探讨,总结出了软土地基中的基坑支护方案的选择原则及其相对应的施工措施等. 相似文献
26.
27.
Elastic electron scattering on the exotic light nucleus28S is investigated in the plane wave Born approximation. The variation of the squared form factors of28S with momentum transfer is compared with that of32S. It is found that the behavior of the form factors near the second minimum (with a moderate momentum transfer) is sensitive
to the alteration of the charge density distribution of halo protons in28S. This indicates that elastic electron scattering can be a good probe of the structure of proton-halo nuclei. 相似文献
28.
A. N. Koryukin 《Algebra and Logic》2003,42(6):387-397
We generalize a well-known two-parameter quantization for the group GL
2(k) (over an arbitrary field k). Specifically, a certain class of Hopf algebras is constructed containing that quantization. The algebras are constructed given an arbitrary coalgebra and an arbitrary pair of its commuting anti-isomorphisms, and are defined by quadratic relations. They are densely linked to the compact quantum groups introduced by Woronowicz. We give examples of Hopf algebras that can be rowed up to the two-parameter quantization for GL
2(k). 相似文献
29.
Out of a total statistics of 896139La+Ag(Br) interactions, 128 interactions having multiplicity of target fragments (Z⩾1)⩾8 and projectile fragments (Z⩾2)⩾4 have been selected. They correspond to quasi-peripheral interactions. Azimuthal angle correlation between sources of
target fragments (TFs) and projectile fragments (PFs) shows the existence of bounce-off effect. Using data of La+Ag(Br) and84Kr+Ag(Br) reactions it is shown that individual helium [Z=2, PFs] and heavier fragment [Z⩾3, PFs] show different emission characteristics. Further, a two prong correlation functionT(Φ
ij
) plotted for heavier fragments and helium fragments separately, indicates the possibility of existence of different physical
conditions. This observation is supported by the different momentum widths of helium fragments and heavier fragments. From
the momentum width data of Kr+Ag(Br) reactions normalized density comes out to be ≈4.7. Using quasi-elastic kinematics for
the bounce-off nuclei, the excitation energy has been computed from the experimental data of flow angles. The strength of
bounce-off seems to decrease with the increase of excitation energy or temperature. 相似文献
30.
本文用超声相比较方法测定了高Tc超导体La1.85Sr0.15CuO4,La2CuO4和YBa2Cu3O7的纵波和横波声速,进而导出了它们的纵向模量、切变模量、杨氏模量、泊松比、德拜温度及定体比热。在La1.85Sr0.15CuO4样品上,还进行了压力实验,发现所有弹性模量都是随压强增加而增加。定体比热cV和泊松比σ在高压下则略有下降。德拜温度是随压强增加而增加的。 相似文献