全文获取类型
收费全文 | 16126篇 |
免费 | 2889篇 |
国内免费 | 2069篇 |
专业分类
化学 | 12199篇 |
晶体学 | 163篇 |
力学 | 946篇 |
综合类 | 111篇 |
数学 | 1749篇 |
物理学 | 5916篇 |
出版年
2024年 | 46篇 |
2023年 | 376篇 |
2022年 | 496篇 |
2021年 | 601篇 |
2020年 | 739篇 |
2019年 | 689篇 |
2018年 | 563篇 |
2017年 | 491篇 |
2016年 | 809篇 |
2015年 | 751篇 |
2014年 | 890篇 |
2013年 | 1232篇 |
2012年 | 1460篇 |
2011年 | 1525篇 |
2010年 | 1028篇 |
2009年 | 985篇 |
2008年 | 1071篇 |
2007年 | 920篇 |
2006年 | 855篇 |
2005年 | 708篇 |
2004年 | 601篇 |
2003年 | 496篇 |
2002年 | 494篇 |
2001年 | 381篇 |
2000年 | 326篇 |
1999年 | 356篇 |
1998年 | 278篇 |
1997年 | 256篇 |
1996年 | 253篇 |
1995年 | 211篇 |
1994年 | 192篇 |
1993年 | 154篇 |
1992年 | 128篇 |
1991年 | 109篇 |
1990年 | 114篇 |
1989年 | 82篇 |
1988年 | 79篇 |
1987年 | 58篇 |
1986年 | 44篇 |
1985年 | 48篇 |
1984年 | 24篇 |
1983年 | 21篇 |
1982年 | 23篇 |
1981年 | 14篇 |
1980年 | 10篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1976年 | 7篇 |
1975年 | 8篇 |
1974年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
31.
This paper reports that the m-plane GaN layer is grown on (200)-plane LiAlO2 substrate by metal-organic chemical wpour deposition (MOCVD) method. Tetragonal-shaped crystallites appear at the smooth surface. Raman measurement illuminates the compressive stress in the layer which is released with increasing the layer's thickness. The high transmittance (80%), sharp band edge and excitonic absorption peak show that the GaN layer has good optical quality. The donor acceptor pair emission peak located at -3.41 eV with full-width at half maximum of 120 meV and no yellow peaks in the photoluminescence spectra partially show that no Li incorporated into GaN layer from the LiAlO2 substrate. 相似文献
32.
Haifeng Yang Guangming XieTianguang Chu Long Wang 《Nonlinear Analysis: Theory, Methods & Applications》2006
In the paper, commuting and stable feedback design for switched linear systems is investigated. This problem is formulated as to build up suitable state feedback controller for each subsystem such that the closed-loop systems are not only asymptotically stable but also commuting each other. A new concept, common admissible eigenvector set (CAES), is introduced to establish necessary/sufficient conditions for commuting and stable feedback controllers. For second-order systems, a necessary and sufficient condition is established. Moreover, a parametrization of the CAES is also obtained. The motivation comes from stabilization of switched linear systems which consist of a family of LTI systems and a switching law specifying the switching between them, where if all the subsystems are stable and commuting each other, then the total system is stable under arbitrary switching. 相似文献
33.
34.
35.
36.
Briand et al. (Electron. Comm. Probab. 5 (2000) 101–117) gave a counterexample and proposition to show that given g,g-expectations usually do not satisfy Jensen's inequality for most of convex functions. This yields a natural question, under which conditions on g, do g-expectations satisfy Jensen's inequality for convex functions? In this paper, we shall deal with this question in the case that g is convex and give a necessary and sufficient condition on g under which Jensen's inequality holds for convex functions. To cite this article: Z. Chen et al., C. R. Acad. Sci. Paris, Ser. I 337 (2003). 相似文献
37.
A 2D HgII coordination polymer containing ligands 1,2,4‐triazole (Htrz) and thiocyanate, [Hg(μ3‐trz)(SCN)]n ( 1 ) has been synthesized and characterized by elemental analysis and IR spectroscopy. The single‐crystal X‐ray data show the coordination number of Hg atoms is four and the ligand trz? acts as a three‐fold donor. The thermal stability of compound 1 was studied by thermal gravimetric and differential thermal analyses. The composition and formation of the complex in methanol solution were found to be in support of its solid state structure. 相似文献
38.
室温下,通过双核配合物[Cu(dppm)(NO3)]2(dppm=双二苯基膦甲烷)与四苯基硼钠在甲醇和二氯甲烷混合溶剂中反应制备了三核铜(I)配合物[Cu3(dppm)3(NO3)(OH)](NO3),经过红外光谱、热重分析、核磁和ES-MS等现代分析手段表征了配合物的物理化学性质,并进一步研究了配合物在室温下的荧光光谱特征。 相似文献
39.
黄龙 《新疆大学学报(理工版)》2003,20(2):130-132
用正电子湮没寿命谱技术研究了2.4×1O15/cm2、2.2×1016/cm2注量的85MeV19F离子辐照N型GaP和1.6×1016/cm 2注量的85MeV19F离子辐照P型InP所产生的辐照缺陷.结果表明:两种注量辐照在GaP中均产生较高浓度的单空位.其浓度随着辐照注量的增大而增加;辐照也在InP中产生较高浓度的单空位. 相似文献
40.