全文获取类型
收费全文 | 8476篇 |
免费 | 1232篇 |
国内免费 | 354篇 |
专业分类
化学 | 617篇 |
晶体学 | 30篇 |
力学 | 366篇 |
综合类 | 119篇 |
数学 | 539篇 |
物理学 | 3944篇 |
无线电 | 4447篇 |
出版年
2024年 | 27篇 |
2023年 | 55篇 |
2022年 | 117篇 |
2021年 | 152篇 |
2020年 | 141篇 |
2019年 | 119篇 |
2018年 | 140篇 |
2017年 | 262篇 |
2016年 | 291篇 |
2015年 | 307篇 |
2014年 | 488篇 |
2013年 | 471篇 |
2012年 | 507篇 |
2011年 | 579篇 |
2010年 | 433篇 |
2009年 | 482篇 |
2008年 | 621篇 |
2007年 | 606篇 |
2006年 | 611篇 |
2005年 | 557篇 |
2004年 | 499篇 |
2003年 | 410篇 |
2002年 | 372篇 |
2001年 | 305篇 |
2000年 | 273篇 |
1999年 | 222篇 |
1998年 | 189篇 |
1997年 | 141篇 |
1996年 | 144篇 |
1995年 | 100篇 |
1994年 | 95篇 |
1993年 | 71篇 |
1992年 | 57篇 |
1991年 | 60篇 |
1990年 | 53篇 |
1989年 | 20篇 |
1988年 | 26篇 |
1987年 | 13篇 |
1986年 | 11篇 |
1985年 | 12篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1977年 | 2篇 |
1969年 | 1篇 |
1959年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
We study pattern avoidance in the context of partial words. The problem of classifying the avoidable binary patterns has been solved, so we move on to ternary and more general patterns. Our results, which are based on morphisms (iterated or not), determine all the ternary patternsʼ avoidability indices or at least give bounds for them. 相似文献
172.
Zhifu Chen 《Mathematical and Computer Modelling of Dynamical Systems: Methods, Tools and Applications in Engineering and Related Sciences》2013,19(4):388-400
In this article, a new type of multi-agent system model with mixed coupling topologies is proposed for realizing pattern formations with specific geometric shapes and formation splitting. The interactions among individual agents are assumed to be universally repulsive and selectively attractive. By designing the form of attractive coupling matrix, one can obtain a variety of formations with specific shapes in the system through self-assembly of agents. Both symmetric coupling case and asymmetric coupling case are considered. Analysis and simulation results show symmetric ones result in convergent dynamics to steady-state formations, whereas, for asymmetric case, the system exhibits complex dynamic behaviours, including collective rotation and chaotic motion. By breaking the graph defined by attractive couplings into disjoint subgraphs, one can make the formation of agents to split into small sizes. The results are relevant for the design of coordination and cooperative control for multi-agent systems. 相似文献
173.
Most building services products are installed while a building is constructed, but they are not operated until the building is commissioned. The warranty of the products may cover the time starting from their installation to the end of the warranty period. Prior to the commissioning of the building, the products are at a dormant mode (i.e., not operated) but protected by the warranty. For such products, both the usage intensity and the failure patterns are different from those with continuous usage intensity and failure patterns. This paper develops warranty cost models for repairable products with a dormant mode from both the manufacturer’s and buyer’s perspectives. Relationships between the failure patterns at the dormant mode and at the operational mode are also discussed. Numerical examples and sensitivity analysis are used to demonstrate the applicability of the methodology derived in the paper. 相似文献
174.
Eugene Savov 《Complexity》2007,12(3):61-76
The solar wind makes the magnetosphere to expand and contract as indicated by the expansions and contractions of the auroral oval due to balancing of the dynamic pressure of the ambient space plasma at inner and outer magnetic lines. This self‐similar magnetospheric behavior elucidates the controversial magnetic storm‐substorm relationship and reveals the 3D‐spiral structure of magnetic interaction. The found self‐similarly evolving structure of one seen as fundamental interaction suggests dynamic fractal unifying interaction that builds a firework universe having 3D‐spiral code. The unifying interaction is described with equation drawn in new fundamental dynamic fractal framework. The equation of unifying interaction converges to the inverse square laws and the principle of uncertainty at laboratory scales. The dynamic fractal fundamental framework is made of one 3D‐spirally‐faster‐inward contracting and expanding, oscillating, basic matter. It simply accounts for observed constant speed of light and for the creation of bright and dark bands on a screen behind a tiny slit. The dynamic fractal framework is quantitatively confirmed with the orbital data for the Milky Way Galaxy, the Sun, the Earth, and the triple asteroid system 87 Sylvia. Many testable predictions are also made. The presented new fundamental dynamic fractal framework allows qualitative and quantitative modeling and simplification. © 2007 Wiley Periodicals, Inc. Complexity 12: 61–76, 2007 相似文献
175.
We developed a dynamic programming approach for computing common exact sequential and structural patterns between two RNAs, given their sequences and their secondary structures. An RNA consists of a sequence of nucleotides and a secondary structure defined via bonds linking together complementary nucleotides. It is known that secondary structures are more preserved than sequences in the evolution of RNAs.We are able to compute all patterns between two RNAs in time O(nm) and space O(nm), where n and m are the lengths of the RNAs. Our method is useful for describing and detecting local motifs. It is especially suitable for finding similar regions of large RNAs that do not share global similarities. An implementation is available in C++ and can be obtained by contacting one of the authors. 相似文献
176.
光热敏折变玻璃及其布拉格体光栅特性研究 总被引:2,自引:1,他引:2
采用高温二次化料的方法制备了一种SiO2-Al2O3-ZnO-Na2O(F、Br)玻璃体系的光热敏折变(PTR)玻璃,通过紫外曝光、透射率光谱、X射线衍射(XRD)和差热分析等方法研究了其光热敏析晶机理。研究表明,PTR玻璃的光敏区为280~350nm,工作区为400~2700nm,最佳成核温度和析晶温度分别为490℃和595℃,析晶组分为NaF晶体。采用双光束干涉方法与"两步法"的热处理工艺在PTR玻璃中制备了周期为1000mm-1的布拉格体光栅,光栅的相对衍射效率达到91%,并验证了制备的布拉格体光栅具有角选择滤波能力。 相似文献
177.
178.
179.
XU Shixiang ZHANG Hua FAN Dianyuan 《Chinese Journal of Lasers》1998,7(1):56-62
TemporalAberationoftheFocusedInhomogeneousWavefromaMisalignmentParalelGratingPairCompresorXUShixiangZHANGHuaFANDianyuan(Shang... 相似文献
180.