全文获取类型
收费全文 | 194篇 |
免费 | 25篇 |
国内免费 | 21篇 |
专业分类
化学 | 137篇 |
晶体学 | 2篇 |
力学 | 14篇 |
综合类 | 1篇 |
数学 | 19篇 |
物理学 | 67篇 |
出版年
2023年 | 5篇 |
2022年 | 5篇 |
2021年 | 10篇 |
2020年 | 7篇 |
2019年 | 5篇 |
2018年 | 5篇 |
2017年 | 2篇 |
2016年 | 7篇 |
2015年 | 6篇 |
2014年 | 16篇 |
2013年 | 16篇 |
2012年 | 9篇 |
2011年 | 11篇 |
2010年 | 14篇 |
2009年 | 11篇 |
2008年 | 14篇 |
2007年 | 12篇 |
2006年 | 8篇 |
2005年 | 8篇 |
2004年 | 5篇 |
2003年 | 7篇 |
2002年 | 8篇 |
2001年 | 9篇 |
2000年 | 8篇 |
1999年 | 7篇 |
1998年 | 5篇 |
1997年 | 1篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有240条查询结果,搜索用时 765 毫秒
31.
32.
The effect of the relative growth rate between {1 1 1} and {1 0 0} faces on the growth morphology of perfect and twinned face-centered-cubic crystals was investigated with a Monte Carlo simulation considering both first-nearest-neighbor (FNN) and second-nearest-neighbor (SNN) interactions. When the bond energy ratio of SNN to FNN interactions is close to zero, the {1 1 1} twin planes make a reentrant edge, which enhances the growth rate on this plane, leading to a tabular growth shape. When the ratio is 0.25, the ridge side face of a tabular shape has the {1 0 0}/{1 0 0}/{1 1 1} structure instead of the {1 1 1}/{1 1 1} reentrant edge. In spite of disappearance of the reentrant edge, the side face has a higher growth rate than the top face because the {1 0 0} face still grows faster than the {1 1 1} face. 相似文献
33.
Yinghuai Zhu Cjin Nong Lee Richard A. Kemp Narayan S. Hosmane John A. Maguire 《化学:亚洲杂志》2008,3(4):650-662
In the last few decades, the synthesis and catalytic application of nanoscaled particles prepared from Group 8–10 (formerly Group VIIIB) elements have been widely explored and have achieved promising results. The innovative use of these nanoparticle catalysts may provide new opportunities in the efficient combination of conventionally used homogenous and heterogeneous catalysts. Conventional homogeneous catalysts pose extraction and recycling difficulties when dealing with metal complexes and/or ligands, whereas heterogeneous catalysts generally require more pressing experimental conditions, such as high temperatures and high pressures, to be effective. Therefore, to solve these problems, the synthesis and use of nanoparticle catalysts as replacements for conventional catalytic systems is a breakthrough owing to their improved handling and environmental and economic aspects. This Focus Review primarily addresses the catalytic applications of neutral Group 8–10 nanoparticles with an average size of less than 10 nm, and also includes a discussion of commonly used synthetic methodology. 相似文献
34.
Xueting Zhou Qingqin Huang Jiami Guo Dr. Lei Dai Prof. Dr. Yixin Lu 《Angewandte Chemie (International ed. in English)》2023,62(45):e202310078
Chiral α,α-diaryl ketones are structural motifs commonly present in bioactive molecules, and they are also valuable building blocks in synthetic organic chemistry. However, catalytic asymmetric synthesis of α,α-diaryl ketones bearing a tertiary stereogenic center remains largely unsolved. Herein, we report a catalytic de novo enantioselective synthesis of α,α-diaryl ketones from simple alkynes via chiral phosphoric acid (CPA) catalysis. A broad range of enolizable α,α-diaryl ketones are prepared in good yields and with excellent enantioselectivities. The described protocol also serves as an efficient deuteration method for the preparation of enantiomerically enriched deuterated α,α-diaryl ketones. Using the methodology reported, bioactive molecules, including one of the best-selling anti-breast cancer drugs, tamoxifen, are readily synthesized. 相似文献
35.
This paper treats the symmetrical bending of a uniformly loaded circular plate supported at k internal points. The boundary
displacement and slope are expanded in Fourier seriesr. The method proposed by [6] is applied. As both the governing differential
equation and boundary conditions are satisfied exactly, we therefore obtain the analytic expression of the transverse deflectional
equation of the circular plate. This is an easy and effective methed. 相似文献
36.
Mesoporousmaterialsareofgreatinteresttocatalysisbecauseoftheirlargeanduniformporesize(20~100A),whichallowstereo-hinderedmoleculesfacilediffusiontointernalactivesites.Althoughrecenteffectshavesuggestedthatitshouldbepossibletosynthesizemesoporousmateri... 相似文献
37.
鸦片的气相色谱快速分析 总被引:2,自引:0,他引:2
采用大口径毛细管柱,建立了一种气相色谱测定鸦片中生物碱的快速分析方法。样品经超声提取,HP-1(5m×0.53mm×2.65μm)毛细管色谱柱,FID测定。回收率为96.8% ̄101.1%,相对标准偏差均小于3%。方法简便,快速,准确,灵敏。 相似文献
38.
Catalytic difunctionalization of 1,3-enynes represents an efficient and versatile approach to rapidly assemble multifunctional propargylic compounds, allenes and 1,3-dienes. Controlling selectivity in such addition reactions has been a long-standing challenging task due to multiple reactive centers resulting from the conjugated structure of 1,3-enynes. Herein, we present a straightforward method for regiodivergent sulfonylarylation of 1,3-enynes via dual nickel and photoredox catalysis. Hinging on the nature of 1,3-enynes, diverse reaction pathways are feasible: synthesis of α-allenyl sulfones via 1,4-sulfonylarylation, or preparation of (E)-1,3-dienyl sulfones with high chemo-, regio- and stereoselectivity through 3,4-sulfonylarylation. Notably, this is the first example that nickel and photoredox catalysis are merged to achieve efficient and versatile difunctionalization of 1,3-enynes.A mild reaction protocol for regiodivergent sulfonylarylation of 1,3-enynes via dual nickel and photoredox catalysis has been developed, which led to efficient synthesis of α-allenyl sulfones or 1,3-dienyl sulfones. 相似文献
39.
磁镊是一种高精度的单分子技术,它用磁场对连有生物大分子的超顺磁球产生磁力,通过追踪磁球的位置来测量生物大分子的长度信息.磁镊包括横向磁镊和纵向磁镊.纵向磁镊空间精度高,但昂贵;横向磁镊简单便宜,但由于受其成像原理的限制,一般情况下只能连接较长的DNA等生物大分子,且其空间精度较差,进而限制了其应用范围.为了解决这个问题,本文改进了横向磁镊,用片层光照明的方法使光线主要被磁球散射,从而能够直接观察到吸附在样品槽侧壁上的磁球,这使得测量短连接的底物成为可能.对于实际应用的检测,首先测试了包含270 bp发卡结构的0.5μm双链DNA,用其中发卡结构的"折叠-去折叠"跳变过程证明了改进后的横向磁镊的确可以追踪短DNA等生物大分子.然后,进一步用16μm的λ-DNA检验了实验系统.最后,将新型横向磁镊与普通横向磁镊及纵向磁镊在小力和大力条件下拉伸不同长度DNA的噪声进行了比较,发现改进后的横向磁镊在空间精度上明显优于普通横向磁镊,与纵向磁镊相比也无明显差异.以上结果证明了改进后的横向磁镊的精度优势,并扩展了横向磁镊的应用范围. 相似文献
40.
In this paper, natural frequencies and mode shapes of structures with mixed random and interval parameters are investigated by using a hybrid stochastic and interval approach. Expressions for the mean value and variance of natural frequencies and mode shapes are derived by using perturbation method and random interval moment method. The bounds of these probabilistic characteristics are then determined by interval arithmetic. Two examples are given first to illustrate the feasibility of the presented method and the results are verified by Monte Carlo Simulations. The presented approach is also applicable to solve pure random and pure interval problems. This capability is demonstrated in the third and fourth examples through the comparisons with the peer research outcomes. 相似文献