全文获取类型
收费全文 | 312篇 |
免费 | 52篇 |
国内免费 | 23篇 |
专业分类
化学 | 20篇 |
晶体学 | 1篇 |
力学 | 79篇 |
综合类 | 6篇 |
数学 | 38篇 |
物理学 | 243篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 10篇 |
2021年 | 8篇 |
2020年 | 3篇 |
2019年 | 3篇 |
2018年 | 9篇 |
2017年 | 27篇 |
2016年 | 21篇 |
2015年 | 9篇 |
2014年 | 28篇 |
2013年 | 20篇 |
2012年 | 12篇 |
2011年 | 25篇 |
2010年 | 18篇 |
2009年 | 30篇 |
2008年 | 18篇 |
2007年 | 15篇 |
2006年 | 23篇 |
2005年 | 12篇 |
2004年 | 14篇 |
2003年 | 12篇 |
2002年 | 10篇 |
2001年 | 9篇 |
2000年 | 4篇 |
1999年 | 1篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 7篇 |
1995年 | 1篇 |
1993年 | 7篇 |
1992年 | 6篇 |
1991年 | 4篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1986年 | 3篇 |
1982年 | 2篇 |
1971年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有387条查询结果,搜索用时 15 毫秒
341.
342.
《Magnetic resonance in chemistry : MRC》2018,56(9):836-846
Seleno‐carbohydrates are those in which the oxygen of the glycosidic bond or the hydroxyl group is artificially replaced with selenium. This substitution changes 1H and 13C chemical shifts and produces spin coupling constants involving 77Se. Coupling constants, such as 2‐3J(77Se, 1H), are likely to be useful for conformational analyses of glycans because such couplings are never observed in natural glycans. Several papers have discussed the relationship between 2‐3J(77Se, 1H) and conformation; however, only few reports describe 1‐3J(77Se, 13C), which could also be useful. Here, we obtain 77Se coupling constants of seleno‐carbohydrates from 77Se‐selective HR‐HMBC and 77Se satellites in 1D 13C spectra and examine their conformations using the Newman projection scheme. 相似文献
343.
Improved pulsed-field gradient echo methods are presented and discussed for the direct selective excitation of the (13)C-satellite lines in overcrowded (1)H NMR spectra of small molecules. Sensitivity enhancements in (13)C spin-state selection can be achieved by combining multiple-proton-frequency excitation and Hadamard phase encoding. Several satellite-selective (SATSEL) NMR experiments are proposed and exemplified by measuring the sign and the magnitude of small, long-range proton-carbon coupling constants for (1)H resonances showing several levels of signal overlapping. 相似文献
344.
Hiroshi Goda Chuichiro Hayashi Hyun-Jong Song 《Proceedings of the American Mathematical Society》2004,132(11):3449-3456
Let be a knot in a closed orientable irreducible 3-manifold . Suppose admits a genus 1 Heegaard splitting and we denote by the splitting torus. We say is a -genus -bridge splitting of if intersects transversely in two points, and divides into two pairs of a solid torus and a boundary parallel arc in it. It is known that a -genus -bridge splitting of a satellite knot admits a satellite diagram disjoint from an essential loop on the splitting torus. If and the slope of the loop is longitudinal in one of the solid tori, then is obtained by twisting a component of a -bridge link along the other component. We give a criterion for determining whether a given -genus -bridge splitting of a knot admits a satellite diagram of a given slope or not. As an application, we show there exist counter examples for a conjecture of Ait Nouh and Yasuhara.
345.
针对新一代全球导航卫星系统(GNSS)中多级电平编码符号(MCS)信号存在的跟踪模糊问题,本文提出了一种通用的MCS信号无模糊跟踪方法.首先推导了不同MCS信号互相关函数的统一表达式,并给出了伪相关函数的定义;然后深入分析了实现无模糊跟踪需要满足的约束条件,推导了两路参考信号的通用构造方法以及相互之间的关系,为具体MCS信号的求解提供了极大的便利;进而给出了利用本文方法的GNSS接收机码跟踪环路模型.作为MCS信号的特例,分别讨论了本文方法在四种二进制偏移载波信号跟踪中的应用.仿真结果表明,本文方法能够有效解决MCS信号的跟踪模糊问题,具有良好的性能和广阔的应用前景. 相似文献
346.
347.
348.
自主运行和健康管理是航天技术发展的一个重要趋势。为确保实践十号返回式卫星在飞行中的设备安全、整星能源安全和自主运行需求,从卫星系统层面进行了自主安全控制设计。首先,可以使卫星在测控弧段之外出现地面无法反应的故障时能够启动自主安全保护模式;其次,可以使卫星自主执行程序化的功能,减轻地面人员的遥控数据上注压力。实践十号卫星在轨飞行中所采取的系统级自主安全控制策略以及工程设计经验,是对航天自主运行和健康管理技术的有益探索和尝试,对后续航天器的设计有很大的借鉴意义。 相似文献
349.
X-射线光电子能谱(XPS)振起(Shake-Up)伴峰主要是伴随主光电子的电离所导致的最高占有轨道到最低未占有轨道电子跃迁的结果.Carlson及Clark的工作声明这种振起伴峰是某些共轭π电子体系的表征,振起伴峰的相对强度与π电子共轭情况有关。 含酚酞侧基聚芳醚酮(PEK-C)是一种新型耐高温工程塑料,其主侧链均带苯环: 相似文献
350.
《Magnetic resonance in chemistry : MRC》2002,40(2):107-113
A survey of the use of 187Os satellite subspectra in 1H and 31P{1H} spectra of triosmium carbonyl clusters is reported. By varying evolution delays in HMQC spectra of [Os3(µ‐H)2(CO)10] we have selectively extracted the values for 1J(Os,H) and 2J(Os,H), respectively. An analysis of the principal modes of phosphine coordination in triosmium clusters demonstrates that 31P{1H}187Os satellite subspectra are diagnostic for equatorial coordination [1J(Os,P) = 211–223 Hz] or for axial coordination (perpendicular to the plane of the cluster) [1J(Os,P) ≈ 147 Hz]. Chelating and bridging diphosphines yield 187Os satellite subspectra which are the sum of A2X and AA′X spin systems. If significant P–P coupling is present, the AA′X component requires simulation. All observed 2J(Os,P) trans‐equatorial couplings fall in the range 38–65 Hz. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献