全文获取类型
收费全文 | 17901篇 |
免费 | 3122篇 |
国内免费 | 2273篇 |
专业分类
化学 | 13451篇 |
晶体学 | 273篇 |
力学 | 1091篇 |
综合类 | 165篇 |
数学 | 2102篇 |
物理学 | 6214篇 |
出版年
2024年 | 38篇 |
2023年 | 324篇 |
2022年 | 599篇 |
2021年 | 600篇 |
2020年 | 728篇 |
2019年 | 760篇 |
2018年 | 633篇 |
2017年 | 551篇 |
2016年 | 914篇 |
2015年 | 968篇 |
2014年 | 1110篇 |
2013年 | 1333篇 |
2012年 | 1535篇 |
2011年 | 1565篇 |
2010年 | 1157篇 |
2009年 | 1043篇 |
2008年 | 1202篇 |
2007年 | 995篇 |
2006年 | 891篇 |
2005年 | 802篇 |
2004年 | 651篇 |
2003年 | 615篇 |
2002年 | 675篇 |
2001年 | 545篇 |
2000年 | 419篇 |
1999年 | 371篇 |
1998年 | 316篇 |
1997年 | 260篇 |
1996年 | 267篇 |
1995年 | 216篇 |
1994年 | 191篇 |
1993年 | 155篇 |
1992年 | 133篇 |
1991年 | 125篇 |
1990年 | 108篇 |
1989年 | 74篇 |
1988年 | 70篇 |
1987年 | 53篇 |
1986年 | 47篇 |
1985年 | 34篇 |
1984年 | 36篇 |
1983年 | 26篇 |
1982年 | 23篇 |
1981年 | 27篇 |
1980年 | 17篇 |
1979年 | 14篇 |
1978年 | 6篇 |
1975年 | 7篇 |
1974年 | 10篇 |
1970年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
该文给出了帐篷映射产生的迭代序列Cesaro平均收敛的条件.研究了它与实数二进展式度量性质之间的联系. 相似文献
52.
High-level ab initio calculations are carried out to study the relative stability of the two hydrogen bonded structures of water-hydrogen sulfide complex, one with water as the proton donor (A) and the other with hydrogen sulfide as the proton donor (B). The results show that structure A is considerably more stable than B at the correlated level, which is in contrast with previous results obtained from Hartree-Fock calculations. 相似文献
53.
For approximate wave functions, we prove the theorem that there is a one‐to‐one correspondence between the constraints of normalization and of the Fermi–Coulomb and Coulomb hole charge sum rules at each electron position. This correspondence is surprising in light of the fact that normalization depends on the probability of finding an electron at some position. In contrast, the Fermi–Coulomb hole sum rule depends on the probability of two electrons staying apart because of correlations due to the Pauli exclusion principle and Coulomb repulsion, while the Coulomb hole sum rule depends on Coulomb repulsion. We demonstrate the theorem for the ground state of the He atom by the use of two different approximate wave functions that are functionals rather than functions. The first of these wave function functionals is constructed to satisfy the constraint of normalization, and the second that of the Coulomb hole sum rule for each electron position. Each is then shown to satisfy the other corresponding sum rule. The significance of the theorem for the construction of approximate “exchange‐correlation” and “correlation” energy functionals of density functional theory is also discussed. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
54.
第一讲中子散射与散裂中子源 总被引:1,自引:0,他引:1
中子散射是研究物质微观结构和动态的理想工具之一,广泛地应用于凝聚态物质研究和应用的众多学科领域.散裂中子源能是新一代的加速器基脉冲中子源,能为中子散射提供高通量的脉冲中子.文章简明地介绍了中子散射的特点和它作为物质结构和动态探针的优越性,以及散裂中子源的基本原理、发展状况和多学科的应用优势.我国计划建设的散裂中子源CSNS中,靶站将由多片钨靶、铍/铁反射体和铁/重混凝土生物屏蔽体组成.质子束功率100kW下,脉冲中子通量约为2.4×1016n/cm2/s.第一期将设计建造高通量粉末衍射仪、高分辨粉末衍射仪、小角散射仪、多功能反射仪和直接几何非弹性散射仪等五台典型的中子散射谱仪,以覆盖大部分的中子散射研究领域. 相似文献
55.
56.
We present a semimonolithic frequency-doubler from 1080 to 540 nm with 80% doubling efficiency and up to 849-mW output power of green light. 相似文献
57.
Tensile impact experiments of EC8.0−24×7 glass fiber bundles at different low temperaturesT(14°C, −40°C and −10°C) and strain rates ɛ were carried out, and complete stress-strain curves were obtained. Within the range
of the experiment temperatures and strain rates, it is found that the initial modulusE, the ultimate strength σmax and the unstable strain ɛ
b
of the glass fiber bundles all increase with ɛ at an identicalT. At an identical ɛ, with the decrease ofT, E and σmax increase; but ɛ
b
increases when 10°C>T>−40°C and decreases when −40°C>T>−100°C. The strain-rate- and temperature-dependent bimodal Weibull statistical constitutive theory was adopted for the statistical
analysis of the experimental results, and the Weibull parameters of single fiber were obtained. The results show that the
bimodal Weibull distribution function is suitable to represent the strength distribution of the glass fiber at low temperature
and different strain rates. The differences in the mechanical properties between EC8.0−24×7 and EC5.5−12 ×14 glass fiber bundles
were also discussed.
Project supported by the National Natural Science Foundation of China (No. 19772058). 相似文献
58.
For vertical-cavity surface-emitting lasers (VCSELs) with polarization-rotated feedback, there exist several synchronization
types such as synchronizations between total powers and synchronizations between separate polarization modes. Based on the
two-mode rate equations, we study and compare numerically the performances of different synchronization types. Our results
show that three synchronization types exhibit good performances when their synchronization conditions are satisfied. They
are the complete synchronization between total powers, complete synchronization between x-polarized modes, and generalized synchronization between x-polarized and y-polarized modes. The former two types are sensitive to the injection rate and spontaneous emission, while the third type
is contrary. Synchronization type with the best performance may switch from one to another, with changing of injection rate
and spontaneous emission factor. 相似文献
59.
Wei-Yan Shao Ying-Nan Cao Wen-Jie Pan Xian-Zhang Bu Lin-Kun An Lian-Quan Gu Albert S.C. Chan 《Tetrahedron letters》2006,47(24):4085-4089
Seventeen unsymmetrical curcumin derivatives were synthesized in good yield and purity by a facile solid phase synthesis strategy. 相似文献
60.
Investigation of remelting and cladding processing with laminar plasma jets on several metals has been conducted looking for possible development of a new surface modification technique. The remelting tests illustrated that the new method could evidently improve the material microstructure and properties of cast iron. The cladding was done with Al2O3 ceramic powder on stainless steel. The energy dispersive spectra (EDS) analysis was used to determine the distribution of the major cladding element in the plasma-processed layers, for which the microstructure observations and hardness measurements were also performed. 相似文献