全文获取类型
收费全文 | 8900篇 |
免费 | 1452篇 |
国内免费 | 637篇 |
专业分类
化学 | 4802篇 |
晶体学 | 134篇 |
力学 | 949篇 |
综合类 | 207篇 |
数学 | 1969篇 |
物理学 | 2928篇 |
出版年
2024年 | 6篇 |
2023年 | 111篇 |
2022年 | 239篇 |
2021年 | 328篇 |
2020年 | 420篇 |
2019年 | 286篇 |
2018年 | 281篇 |
2017年 | 409篇 |
2016年 | 490篇 |
2015年 | 413篇 |
2014年 | 527篇 |
2013年 | 657篇 |
2012年 | 571篇 |
2011年 | 533篇 |
2010年 | 459篇 |
2009年 | 569篇 |
2008年 | 517篇 |
2007年 | 527篇 |
2006年 | 524篇 |
2005年 | 461篇 |
2004年 | 417篇 |
2003年 | 354篇 |
2002年 | 303篇 |
2001年 | 231篇 |
2000年 | 200篇 |
1999年 | 145篇 |
1998年 | 153篇 |
1997年 | 128篇 |
1996年 | 103篇 |
1995年 | 121篇 |
1994年 | 97篇 |
1993年 | 80篇 |
1992年 | 70篇 |
1991年 | 42篇 |
1990年 | 34篇 |
1989年 | 29篇 |
1988年 | 18篇 |
1987年 | 16篇 |
1986年 | 17篇 |
1985年 | 26篇 |
1984年 | 17篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 14篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1957年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 30 毫秒
51.
In this article, we mainly consider the existence problem of a group divisible design GDD of type . We present two recursive constructions for this configuration using candelabra systems and construct explicitly a few small examples admitting given automorphism groups. As an application, several new infinite classes of GDD s of type are produced. Meanwhile a few new infinite families on candelabra quadruple systems with group sizes being odd and stem size greater than one are also obtained. 相似文献
52.
Lianghao Song Tiantian Xu Daowei Gao Prof. Xun Hu Prof. Cuncheng Li Prof. Shun Li Prof. Guozhu Chen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(26):6621-6627
CeO2-based catalysts are widely studied in catalysis fields. Developing one novel synthetic approach to increase the intimate contact between CeO2 and secondary species is of particular importance for enhancing catalytic activities. Herein, an interfacial reaction between metal–organic framework (MOF)-derived carbon and KMnO4 to synthesize CeO2−MnO2, in which carbon is derived from the pyrolysis of Ce-MOFs under an inert atmosphere, is described. The MOF-derived carbon is found to restrain the growth of CeO2 crystallites under a high calcination temperature and, more importantly, intimate contact within CeO2/C is conveyed to CeO2/MnO2 after the interfacial reaction; this is responsible for the high catalytic activity of CeO2−MnO2 towards CO oxidation. 相似文献
53.
Structures of ionic liquids (ILs) 1-decyl-3-methylimidazolium bis(trifluoromethanesulfonyl)azanide ([C10mim][TFSA]) and 1-decyl-dimethylimidazolium bis(trifluoromethanesulfonyl)azanide ([C10(mim)2](TFSA)2) in different-sized mica slits have been investigated using molecular dynamics simulations. Ion density and angular distributions for monocationic IL [C10mim][TFSA] were analysed to elucidate the IL structures under different surface charges and especially their changes in the direction perpendicular to the surfaces. [C10mim][TFSA] formes in bilayers, compatible with existing models of ILs with long alkyl chains. For dicationic IL [C10(mim)2](TFSA)2, cations adjacent to the mica surface tend to stay parallel to the surface with both positively charged rings absorbed. While near the centre of the slit, dications show the weak tendency of orientation distribution, more random than [C10mim]+ ions. Structures of [C10(mim)2](TFSA)2 cannot be described by bilayer models. Additionally, the in-plane arrangement of [C10mim][TFSA] is more ordered when K+ ions completely neutralise the negative charge of the mica surface, and [C10mim]+ ions tend to be located in hexagonal mica lattices with two aluminium atoms in replacement of silicon atoms. [TFSA]? ions are constrained by the neighbouring K+ ions absorbed onto mica lattices. 相似文献
54.
Necessary conditions for the existence of a super‐simple, decomposable, near‐resolvable ‐balanced incomplete block design (BIBD) whose 2‐component subdesigns are both near‐resolvable ‐BIBDs are (mod ) and . In this paper, we show that these necessary conditions are sufficient. Using these designs, we also establish that the necessary conditions for the existence of a super‐simple near‐resolvable ‐RBIBD, namely (mod ) and , are sufficient. A few new pairwise balanced designs are also given. 相似文献
55.
We show that the Smith normal form of a skew‐symmetric D ‐optimal design of order is determined by its order. Furthermore, we show that the Smith normal form of such a design can be written explicitly in terms of the order , thereby proving a recent conjecture of Armario. We apply our result to show that certain D ‐optimal designs of order are not equivalent to any skew‐symmetric D ‐optimal design. We also provide a correction to a result in the literature on the Smith normal form of D ‐optimal designs. 相似文献
56.
John Asplund Gregory Clark Garner Cochran va Czabarka Arran Hamm Gwen Spencer Lszl Szkely Libby Taylor Zhiyu Wang 《组合设计杂志》2019,27(10):586-597
The crossing number of a graph is the smallest number of edge crossings over all drawings of in the plane. For any , the ‐planar crossing number of , is defined as the minimum of over all graphs with . Pach et al [Comput. Geom.: Theory Appl. 68 (2018), pp. 2–6] showed that for every , we have and that this bound does not remain true if we replace the constant by any number smaller than . We improve the upper bound to as . For the class of bipartite graphs, we show that the best constant is exactly for every . The results extend to the rectilinear variant of the ‐planar crossing number. 相似文献
57.
A. Kirstin Sockwell Prof. Dr. Modi Wetzler 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(10):2380-2388
The promise of polyhydroxamic acid ligands for the selective chelation of the f-block elements is becoming increasingly more apparent. The initial studies of polyhydroxamic acid siderophores showed the formation of highly stable complexes with PuIV, but a higher preference for FeIII hindered effective applications. The development of synthetic routes toward highly pure and customizable ligands containing multiple hydroxamic acids allowed for the growth of new classes of compounds. Although the first round of these ligands focused on the incorporation of siderophore-like frameworks, the new synthetic strategies led to small molecules of various frameworks and even resins for applications in the field of f-block element separations and biological desorption. Unfortunately, a lack of consistent stability-constant data makes direct comparisons across this body of work difficult. More studies into the stability constants and separations of the f-block elements in a variety of pH ranges is necessary to truly realize the potential for polyhydroxamic acid ligands. 相似文献
58.
Dr. Francesca Arcudi Dana Emily Westmoreland Prof. Emily Allyn Weiss 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(63):14469-14474
Colloidal quantum dot (QD) photocatalysts have the electrochemical and optical properties to be highly effective for a range of redox reactions. QDs are proven photo-redox catalysts for a variety of reactions in organic solvents but are less prominent for aqueous reactions. Aqueous QD photocatalysts require hydrophilic ligand shells that provide long-term colloidal stability but are not so tight-binding as to prevent catalytic substrates from accessing the QD surface. Common thiolate ligands, which also poison many co-catalysts and undergo photo-oxidative desorption, are therefore often not an option. This paper describes a framework for the design of water-solubilizing ligands that are in dynamic exchange on and off the QD surface, but still provide long-term colloidal stability to CdS QDs. The binding affinity and inter-ligand electrostatic interactions of a bifunctional ligand, aminoethyl phosphonic acid (AEP), are tuned with the pH of the dispersion. The key to colloidal stability is electrostatic stabilization of the monolayer. This work demonstrates a means of mimicking the stabilizing power of a thiolate-bound ligand with a zwitterionic tail group, but without the thiolate binding group. 相似文献
59.
空间填充设计在计算机试验中应用十分广泛,当拟合回归模型时,正交的空间填充设计保证了因子效应估计的独立性.基于广义正交设计,文章给出了构造二阶正交拉丁超立方体设计和列正交设计的方法,新构造的设计不仅满足任意两列之间相互正交,还能保证每一列与任一列元素平方组成的列以及任两列元素相乘组成的列都正交.当某些正交的空间填充设计不存在时,具有较小相关系数的近似正交设计可作为替代设计使用.设计构造的灵活性为计算机试验在实践中的广泛应用提供了必要的支持. 相似文献
60.
为了克服太空环境的复杂性,满足航天工程的空间使用要求,研制一款2 500万像素宽光谱共焦成像的微型星载相机光学系统。该系统适应卫星发射和在轨道运行的恶劣环境,具有抗冲击震动、耐太空高温差强辐射,体积小,质量轻等优点。设计的系统可在450 nm~800 nm的谱段内清晰成像,焦距181 mm,入瞳口径45 mm,视场角10.4°,边缘相对照度0.81,轴上点MTF:0.57@55 lp/mm,0.33@110 lp/mm,畸变1.2%,镜头质量622 g,外形尺寸Φ58.3 mm×117 mm,抗辐照性能≥5 krad。通过温度适应性的模拟和优化,用户进行?30 ℃~+70 ℃光学镜头热真空试验,可正常工作。该系统已成功应用于天宫二号伴飞卫星相机中,获得的图像清晰稳定,为空间遥感实验观测发挥了重要的作用。 相似文献