全文获取类型
收费全文 | 23532篇 |
免费 | 3442篇 |
国内免费 | 1729篇 |
专业分类
化学 | 16045篇 |
晶体学 | 207篇 |
力学 | 1147篇 |
综合类 | 67篇 |
数学 | 2992篇 |
物理学 | 8245篇 |
出版年
2024年 | 66篇 |
2023年 | 434篇 |
2022年 | 809篇 |
2021年 | 876篇 |
2020年 | 839篇 |
2019年 | 867篇 |
2018年 | 834篇 |
2017年 | 659篇 |
2016年 | 1131篇 |
2015年 | 988篇 |
2014年 | 1225篇 |
2013年 | 1669篇 |
2012年 | 1991篇 |
2011年 | 2061篇 |
2010年 | 1354篇 |
2009年 | 1253篇 |
2008年 | 1481篇 |
2007年 | 1253篇 |
2006年 | 1217篇 |
2005年 | 1020篇 |
2004年 | 815篇 |
2003年 | 570篇 |
2002年 | 584篇 |
2001年 | 382篇 |
2000年 | 324篇 |
1999年 | 452篇 |
1998年 | 326篇 |
1997年 | 327篇 |
1996年 | 356篇 |
1995年 | 283篇 |
1994年 | 243篇 |
1993年 | 246篇 |
1992年 | 174篇 |
1991年 | 191篇 |
1990年 | 143篇 |
1989年 | 116篇 |
1988年 | 105篇 |
1987年 | 93篇 |
1986年 | 88篇 |
1985年 | 75篇 |
1984年 | 85篇 |
1983年 | 40篇 |
1982年 | 65篇 |
1981年 | 52篇 |
1980年 | 38篇 |
1979年 | 31篇 |
1978年 | 44篇 |
1977年 | 30篇 |
1976年 | 40篇 |
1973年 | 29篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Fe-doped TiO2 powder was prepared by high-energy ball milling, using TiO2 Degussa P-25 and α-Fe powders as the starting materials. The structure and magnetic properties of the Fe-doped TiO2 powder were studied by X-ray diffraction, 57Fe Mossbauer spectroscopy and vibrating sample magnetometer. The Reitveld refinement of XRD revealed that ball milling not only triggered incorporation of Fe in TiO2 lattice but also induced the phase transformation from anatase to rutile in TiO2 and consequently the milled Fe-doped TiO2 powder contained only rutile.57Fe Mössbauer effect measure showed that Fe atoms existed in Fe2+ and Fe3+ state, which were assigned to the solid solution FexTi1−xO2. The magnetization measurements indicated that the milled Fe-doped TiO2 powder was ferromagnetic above room temperature. The ferromagnetism in our milled Fe-doped TiO2 powder seemingly does not come from Fe and iron oxides particles/clusters but from the Fe-doped TiO2 powder matrices. 相似文献
32.
33.
34.
Phil Diamond Peter Kloeden Victor Kozyakin Alexei Pokrovskii 《Mathematische Nachrichten》1998,191(1):59-81
The finiteness of computer arithmetic can lead to some dramatic differences between the behaviour of a continuous dynamical system and a computer simulation. A thorough rigorous theoretical analysis of what may or what does happen is usually extremely difficult and to date little has been done even in relatively simple contexts. The comparative behaviour of a rotation mapping in the plane and on a uniform lattice in the plane is one such example. Simulations show that the rounding operator applied to a planar rotation mapping more or less preserves the qualitative behaviour of the original mapping, whereas the application of the truncation operator to a planar rotation can lead to quite different dynamical features. In this paper a theoretical justification of the properties of the planar rotation mappings under truncation to a, uniform integer lattice is provided, in particular properties of boundedness and dissipativity are investigated. 相似文献
35.
Studies of breakdown threshold intensity for air at various pressures in the range of 24–760 torr using 0.355, 0.532 and 1.06
μm radiation are reported. We observep
−0.8 scaling ofI
th at 1.06 μm and a weak scaling ofp
−0.4 at 0.532 and 0.355 μm radiation. Strong dependence of breakdown spot size on laser power but weak dependence on air pressure
is observed. 相似文献
36.
Jipu Ma 《中国科学A辑(英文版)》1997,40(12):1233-1238
A generalized dimension is further developed. Here subtraction and addition of two generalized dimensions are defined, so
that the operations: ∞ ± n = ∞, ∞ + ∞ = ∞, which used to play an inflexible role, are refined and moreover, ∞ - ∞, which used
to be meaningless, is done in sense. Then generalized index for semi-Fred-holm operators is developed to wholeB(H), i.e. all of bounded linear operators in Hilbert spaceH. Theorem 2.2 is proved with an example, which is in contradiction to a known proposition for semi-Fredholm operators in form,
practically a refined result of the known proposition. Then, it is proved thatB(H) is the union of countably many disjoint arewise connected sets over all the generalized dimensions ofB(H).
Project supported by the National Natural Science Foundation of China 相似文献
37.
38.
We derive the action of 2D gravity from the two-cocycle of the Virasoro group by using a previously introduced method for constructing a dynamical system from a Lie group. A natural construction and explanation of the hidden SL(2,
)-Kac-Moody symmetry, of general applicability, is provided. We also show how the proper quantization goes beyond the ordinary co-adjoint orbit method, and the possible connection with the Poisson-Lie groups. 相似文献
39.
In vitro and in vivo proton T1 data are reported that demonstrate that the paramagnetic copper-D-penicillamine complex can be applied as a potential contrast agent to magnetic resonance imaging. 相似文献
40.
Victor Pambuccian 《Mathematical Logic Quarterly》1992,38(1):345-348
We proved in the first part [1] that plane geometry over Pythagorean fields is axiomatizable by quantifier-free axioms in a language with three individual constants, one binary and three ternary operation symbols. In this paper we prove that two of these operation symbols are superfluous. 相似文献