全文获取类型
收费全文 | 4129篇 |
免费 | 1129篇 |
国内免费 | 282篇 |
专业分类
化学 | 1082篇 |
晶体学 | 19篇 |
力学 | 781篇 |
综合类 | 56篇 |
数学 | 367篇 |
物理学 | 3235篇 |
出版年
2024年 | 7篇 |
2023年 | 41篇 |
2022年 | 121篇 |
2021年 | 137篇 |
2020年 | 136篇 |
2019年 | 127篇 |
2018年 | 130篇 |
2017年 | 186篇 |
2016年 | 237篇 |
2015年 | 186篇 |
2014年 | 318篇 |
2013年 | 308篇 |
2012年 | 300篇 |
2011年 | 315篇 |
2010年 | 212篇 |
2009年 | 238篇 |
2008年 | 279篇 |
2007年 | 263篇 |
2006年 | 240篇 |
2005年 | 214篇 |
2004年 | 161篇 |
2003年 | 174篇 |
2002年 | 158篇 |
2001年 | 140篇 |
2000年 | 123篇 |
1999年 | 119篇 |
1998年 | 82篇 |
1997年 | 76篇 |
1996年 | 86篇 |
1995年 | 65篇 |
1994年 | 48篇 |
1993年 | 43篇 |
1992年 | 41篇 |
1991年 | 34篇 |
1990年 | 20篇 |
1989年 | 24篇 |
1988年 | 16篇 |
1987年 | 23篇 |
1986年 | 16篇 |
1985年 | 16篇 |
1984年 | 18篇 |
1983年 | 12篇 |
1982年 | 17篇 |
1981年 | 5篇 |
1980年 | 8篇 |
1979年 | 10篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1973年 | 1篇 |
1957年 | 3篇 |
排序方式: 共有5540条查询结果,搜索用时 156 毫秒
1.
2.
Relationship between the spatial position of the seed and growth mode for single-crystal diamond grown with an enclosed-type holder 下载免费PDF全文
Wen-Liang Xie 《中国物理 B》2022,31(10):108106-108106
The relationship between the spatial position of the diamond seed and growth mode is investigated with an enclosed-type holder for single-crystal diamond growth using the microwave plasma chemical vapor deposition epitaxial method. The results demonstrate that there are three main regions by varying the spatial position of the seed. Due to the plasma concentration occurring at the seed edge, a larger depth is beneficial to transfer the plasma to the holder surface and suppress the polycrystalline diamond rim around the seed edge. However, the plasma density at the edge decreases drastically when the depth is too large, resulting in the growth of a vicinal grain plane and the reduction of surface area. By adopting an appropriate spatial location, the size of single-crystal diamond can be increased from 7 mm × 7 mm × 0.35 mm to 8.6 mm × 8.6 mm × 2.8 mm without the polycrystalline diamond rim. 相似文献
3.
4.
Asymmetric mode transformation in waveguide is of great significance for on-chip integrated devices with one-way effect, while it is challenging to achieve asymmetric nonlinear-mode-conversion (NMC) due to the limitations imposed by phase-matching. In this work, we theoretically proposed a new scheme for realizing asymmetric NMC by combining frequency-doubling process and periodic PT symmetric modulation in an optical waveguide. By engineering the one-way momentum from PT symmetric modulation, we have demonstrated the unidirectional conversion from pump to second harmonic with desired guided modes. Our findings offer new opportunities for manipulating nonlinear optical fields with PT symmetry, which could further boost more exploration on on-chip nonlinear devices assisted by non-Hermitian optics. 相似文献
5.
Timothy F. L. McKenna 《大分子反应工程》2019,13(2)
This review gives an overview of the evolution of the technology of condensed mode cooling, primarily for the case of ethylene polymerization on supported catalysts in fluidized bed reactors. It is well known that this mode of heat removal is quite effective in allowing polyolefin manufacturers to increase significantly production rates. What is perhaps less well understood are all of the issues that, in addition to the effect of the latent heat of vaporization of injected liquid components, also have an impact on the rate of production and behavior of the reactor. However, the liquid components injected into the reactor can vaporize rapidly under full‐scale conditions, leaving behind several heavy components (with respect to ethylene) that have numerous effects on how the particles behave, on the reaction rate, and on fluidization, fouling, and other parameters related to reactor and process performance. 相似文献
6.
Two new Zn2Dy2 complexes were constructed from Zn (II) salen‐type Schiff base complex fragment and 2,6‐pyridinedimethanol (H2pdm) or its Br‐substituted analogue (4‐bromopyridine‐2,6‐diyl)dimethanol (H2Brpdm); their molecular formulas are [Zn2Dy2(L)2(pdm)2(MeOH)2](ClO4)2 [ 1 , H2L = N, N′‐ bis(3‐methoxysalicylidene)‐1,3‐diaminopropane] and [Zn2Dy2(L)2(Brpdm)2(MeOH)2](ClO4)2 [ 2 ], the Dy (III) ions of which have a NO7 triangular dodecahedral coordination sphere. The two complexes show not only ferromagnetic interaction but also field‐induced single‐molecule magnet (SMM) behavior, which are rare Dy (III)‐containing cluster complexes with the NO7 triangular dodecahedral coordination sphere that can show good magnetic relaxation. The energy barrier value of complex 2 is higher than those of complex 1 and the Dy (III) complexes with the DyNO7 triangular dodecahedral coordination configuration reported in the literature. 相似文献
7.
8.
Laterally-coupled ridge-waveguide distributed feedback lasers fabricated without epitaxial regrowth steps have the advantages of process simplification and low cost. We present a laterally coupled grating with slots. The slots etched between the ridge and grating area are designed to suppress the lateral diffusion of carriers and to reduce the influence of the aspect-ratio-dependent-etching effect on the grating morphology in the etching process. Moreover, the grating height in this structure can be decreased to lower the aspect ratio significantly, which is advantageous over the conventional laterally coupled ridge waveguide gratings. The effects of five main structural parameters on the coupling characteristics of gratings are studied by MODE Solutions. It is found that varying the lateral width of the grating can be used as an effective way to tune the coupling strength; narrow slots (100 nm and 300 nm) and wide ridge (2 μm-4 μm) promote the stability of grating coupling coefficient and device performance. It is important to note that the grating bottom should be fabricated precisely. The comparative study of carrier distribution and mode field distribution shows that the introduction of narrow slots can strengthen the competitive advantage and stability of the fundamental mode. 相似文献
9.
结构柔度矩阵需由质量矩阵归一化振型获得,而质量矩阵归一化振型难以直接测得,限制了柔度曲率类损伤指标的应用。为分析振型归一化方法对梁结构柔度曲率类损伤指标的影响,根据梁结构的刚度、弯矩和位移曲率的关系,建立了均布荷载作用下结构损伤前后位移曲率与损伤程度的理论表达式,实现定量分析均匀荷载面曲率结构损伤程度。提出P-范数振型归一化方法,通过均匀荷载面曲率指标推导了振型质量矩阵归一化系数差x_α与损伤程度的关系。以三跨连续梁算例对理论进行了验证,结果表明,损伤程度定量指标效果良好,不同P-范数振型归一化方法下,损伤程度的偏差可由2x_α估算;2-范数振型归一化方法的损伤识别结果与质量矩阵振型归一化结果最接近,故当无法获得质量矩阵归一化振型时,可采用2-范数归一化振型代替。 相似文献
10.
In this paper, the implementation of research-oriented teaching mode in coordination chemistry was introduced, including the strategies, main contents and evaluation. 相似文献