全文获取类型
收费全文 | 203篇 |
免费 | 59篇 |
国内免费 | 65篇 |
专业分类
化学 | 158篇 |
晶体学 | 6篇 |
力学 | 9篇 |
综合类 | 4篇 |
数学 | 23篇 |
物理学 | 127篇 |
出版年
2024年 | 3篇 |
2023年 | 7篇 |
2022年 | 17篇 |
2021年 | 12篇 |
2020年 | 15篇 |
2019年 | 12篇 |
2018年 | 13篇 |
2017年 | 9篇 |
2016年 | 12篇 |
2015年 | 9篇 |
2014年 | 20篇 |
2013年 | 15篇 |
2012年 | 18篇 |
2011年 | 16篇 |
2010年 | 18篇 |
2009年 | 18篇 |
2008年 | 22篇 |
2007年 | 13篇 |
2006年 | 8篇 |
2005年 | 10篇 |
2004年 | 2篇 |
2003年 | 7篇 |
2002年 | 9篇 |
2001年 | 4篇 |
2000年 | 6篇 |
1999年 | 5篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1980年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有327条查询结果,搜索用时 0 毫秒
171.
建立了乳及乳制品中13种β-受体激动剂类药物多残留的同位素内标-高效液相色谱串联质谱分析方法。样品经三氯乙酸沉淀蛋白,提取液经SupelcleanLC-SCX固相萃取柱净化后,用HPLC-MS/MS进行测定。采用AgilentEclipse Plus C18色谱柱(2.1×150 mm,3.5μm),0.1%甲酸水-乙腈流动相进行梯度洗脱,用电喷雾离子源正离子多反应监测(MRM)模式进行MS/MS检测。其中克伦特罗在0.05~5.0μg/kg线性范围内,其余12种分析物在0.25~10μg/kg线性范围内具有较好的线性关系,相关系数r>0.9988。方法检出限(LOD)为0.02~0.17μg/kg,定量限(LOQ)为0.05~0.48μg/kg。空白样品添加回收率为83.2%~102.6%,相对标准偏差为5.0%~13%。 相似文献
172.
A new synchronization scheme based on time division multiplexing and wavelength division multiplexing technology for practical quantum key distribution system 下载免费PDF全文
Three clock synchronization schemes for a quantum key distribution system are compared experimentally through the outdoor fibre and the interaction physical model of the the clock signal and the the quantum signal in the quantum key distribution system is analysed to propose a new synchronization scheme based on time division multiplexing and wavelength division multiplexing technology to reduce quantum bits error rates under some transmission rate conditions.The proposed synchronization scheme can not only completely eliminate noise photons from the bright background light of the the clock signal,but also suppress the fibre nonlinear crosstalk. 相似文献
173.
Good rectifying current-voltage characteristics and nanosecond photoelectric effects are observed in the p-n hereto junctions of La0.9Sr0.1 MnO3/SrNb0.01 Ti0.99O3 fabricated by laser molecular beam epitaxy. The rise time is about 26ns and the full width at half maximum is about 125ns for the open-circuit, photovoltaic pulses when the La0.9Sr0.1MnO3 film in the heterojunction is irradiated by a laser operated at wavelength 308nm with pulse duration of about 25 ns. A qualitative explanation is presented, based on an analysis of the photoelectric effect of p-n hereto junction. 相似文献
174.
175.
176.
We investigate the intensity and efficiency of a compressed echo, which is important in arbitrary waveform generation(AWG). A new model of compressed echo is proposed based on the optical Bloch equations, which exposes much more detailed parameters than the conventional model, such as the time delay of the chirp lasers, the nature of the rare-earth-iondoped crystal, etc. According to the novel model of compressed echo, we find that reducing the time delay of the chirp lasers and scanning the lasers around the center frequency of the inhomogeneously broadened spectrum, while utilizing a crystal with larger coherence time and excitation lifetime can improve the compressed echo's intensity and efficiency. The theoretical analysis is validated by numerical simulations. 相似文献
177.
建立了加速溶剂萃取结合离子色谱法测定烟草中12种无机阴离子和有机酸的分析方法.通过L16(45)正交试验优化了加速溶剂萃取的主要参数,获得最佳萃取条件为萃取温度60℃,萃取静态时间6min,冲洗体积150%,N2气吹扫时间100s,循环次数1次.采用KOH梯度淋洗进行分离测定,各目标物测定的相对标准偏差为0.32%~5.06%(n=6),方法的检出限为2.1~13.4μg.L-1.对烟草样品中的12种目标物进行萃取,回收率为84.71%~103.63%. 相似文献
178.
We show that the matrix (or more generally tensor) product states in a finite translation invariant system can be accurately constructed from a same set of local matrices (or tensors) that are determined from an infinite lattice system in one or higher dimensions. This provides an efficient approach for studying translation invariant tensor product states in finite lattice systems. Two methods are introduced to determine the size-independent local tensors. 相似文献
179.
建立了一套针板电极交流放电微等离子发生装置,以氮气作为载气,甲烷为分析气体,放电电压为1.32 kV, 放电距离为3 mm, Pt丝和Pt/MWNT复合纳米粒子修饰FTO电极为放电电极,放电频率为30 kHz,功率消耗为13 W,利用发射光谱法检测放电过程中产生的微等离子体发射光谱,用于在室温下检测甲烷气体。在交流电压下,检测到甲烷的谱线有CH,C2和Hα,以C2谱线作为甲烷分析线,发现C2谱线强度与甲烷浓度在0.5%~4.0%(φ)的范围内呈线性,检出限(S/N=3)为0.19%。以Hα谱线为分析线,Hα谱线强度与甲烷浓度在0.1%~3.0 %(φ)范围内呈线性, 检测限(S /N=3)为0.03%(φ)。对于3.2%的甲烷气体,平行测定11次,在Pt/MWNT/FTO电极上以C2谱线为分析线和以Hα谱线为分析线的相对标准偏差分别为 1.3%和1.9%。说明Pt/MWNT 纳米复合材料修饰电极提高了分析方法的重现性和精密度。以空气混合气体为稀释气体,甲烷气体放电行为与纯氮气中放电行为有较大差异,C2峰消失,只有Hα峰存在。Hα峰强度与甲烷浓度在0.5%~4%范围内有线性相关性。与其他的光发射光谱检测系统相比,该系统装置尺寸小,制备简单且在室温下操作。 相似文献
180.
To investigate the leader-following formation control, in this paper we present the design problem of control protocols and distributed observers under which the agents can achieve and maintain the desired formation from any initial states, while the velocity converges to that of the virtual leader whose velocity cannot be measured by agents in real time. The two cases of switching topologies without communication delay and fixed topology with time-varying communication delay are both considered for multi-agent networks. By using the Lyapunov stability theory, the issue of stability is analysed for multi-agent systems with switching topologies. Then, by considering the time-varying communication delay, the sufficient condition is proposed for the multi-agent systems with fixed topology. Finally, two numerical examples are given to illustrate the effectiveness of the proposed leader-following formation control protocols. 相似文献