全文获取类型
收费全文 | 9023篇 |
免费 | 678篇 |
国内免费 | 526篇 |
专业分类
化学 | 293篇 |
晶体学 | 10篇 |
力学 | 888篇 |
综合类 | 66篇 |
数学 | 2426篇 |
物理学 | 1385篇 |
综合类 | 5159篇 |
出版年
2024年 | 37篇 |
2023年 | 100篇 |
2022年 | 163篇 |
2021年 | 185篇 |
2020年 | 162篇 |
2019年 | 181篇 |
2018年 | 146篇 |
2017年 | 232篇 |
2016年 | 279篇 |
2015年 | 282篇 |
2014年 | 454篇 |
2013年 | 425篇 |
2012年 | 467篇 |
2011年 | 564篇 |
2010年 | 472篇 |
2009年 | 494篇 |
2008年 | 496篇 |
2007年 | 640篇 |
2006年 | 556篇 |
2005年 | 463篇 |
2004年 | 434篇 |
2003年 | 395篇 |
2002年 | 301篇 |
2001年 | 282篇 |
2000年 | 269篇 |
1999年 | 233篇 |
1998年 | 207篇 |
1997年 | 177篇 |
1996年 | 138篇 |
1995年 | 157篇 |
1994年 | 126篇 |
1993年 | 104篇 |
1992年 | 117篇 |
1991年 | 87篇 |
1990年 | 72篇 |
1989年 | 60篇 |
1988年 | 73篇 |
1987年 | 45篇 |
1986年 | 18篇 |
1985年 | 27篇 |
1984年 | 17篇 |
1983年 | 11篇 |
1982年 | 9篇 |
1981年 | 11篇 |
1980年 | 10篇 |
1979年 | 10篇 |
1978年 | 6篇 |
1977年 | 9篇 |
1976年 | 6篇 |
1975年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 25 毫秒
81.
世界各国的学者对电子束的聚焦性能已经做了广泛的研究,提出了许多分析电子束聚焦性能的方法,在这些方法的基础上,试图利用概率分布函数来描述电子束的聚焦过程。该方法将电子的发射看做是随机过程,并从轨迹的落点的概率分析了电子束的形状和大小,避免了杂散小峰的影响。 相似文献
82.
V. V. Sobolev 《Journal of Applied Spectroscopy》1999,66(3):319-335
The article surveys the main unsolved problems of the electronic structure of nonmetals in a wide energy region of fundamental
absorption.
Udmurtia State University, 71, Krasnogeroiskaya Str., Izhevsk, 426034, Russia. Translated from Zhurnal Prikladnoi Spektroskopii,
Vol. 66, No. 3, pp. 299–315, May–June, 1999. 相似文献
83.
研究了在相对论领域内,超强激光场的不同条件(频率、强度、脉冲波形磁场分量)对氘原子电离几率的影响,研究表明:电离几率随激光强度的增加而增加,随激光频率的增加而减少。而激光脉冲波形对电离几率的影响仅在激光无磁场分量时比较显著。激光场的磁场分量对原子的电离有一定的影响。 相似文献
84.
采用纳米多孔膜可以实现新型的具有极高热流密度的薄液膜沸腾相变传热。在薄液膜沸腾的基础研究中,通过在纳米多孔膜表面加工纳米级别厚度的铂镀层实现加热和测温。通过扫描电镜观察,发现实验样品残骸表面有“河流”状形貌形成,结合元素分析推断铂镀层局部发生热熔。本文对铂镀层进行简化并建立电网络模型,计算并分析了铂镀层局部厚度不均对整体发热极限及熔毁失效的影响。分析结果表明,镀层厚度的不均,将会使镀层在达到极限热流密度后,极易出现“河流”状熔毁,使镀层永久失效;而厚度更加均匀的铂镀层,有助于获得更高的极限热流密度。 相似文献
85.
Quantum walk search algorithm for multi-objective searching with iteration auto-controlling on hypercube 下载免费PDF全文
Yao-Yao Jiang 《中国物理 B》2022,31(4):40307-040307
Shenvi et al. have proposed a quantum algorithm based on quantum walking called Shenvi-Kempe-Whaley (SKW) algorithm, but this search algorithm can only search one target state and use a specific search target state vector. Therefore, when there are more than two target nodes in the search space, the algorithm has certain limitations. Even though a multi-objective SKW search algorithm was proposed later, when the number of target nodes is more than two, the SKW search algorithm cannot be mapped to the same quotient graph. In addition, the calculation of the optimal target state depends on the number of target states m. In previous studies, quantum computing and testing algorithms were used to solve this problem. But these solutions require more Oracle calls and cannot get a high accuracy rate. Therefore, to solve the above problems, we improve the multi-target quantum walk search algorithm, and construct a controllable quantum walk search algorithm under the condition of unknown number of target states. By dividing the Hilbert space into multiple subspaces, the accuracy of the search algorithm is improved from pc=(1/2)-O(1/n) to pc=1-O(1/n). And by adding detection gate phase, the algorithm can stop when the amplitude of the target state becomes the maximum for the first time, and the algorithm can always maintain the optimal number of iterations, so as to reduce the number of unnecessary iterations in the algorithm process and make the number of iterations reach $ t_{\rm f}=(\pi /2)\sqrt{2^{n-2}} $. 相似文献
86.
In this research paper, we propose a two-hop integrated radio frequency–visible light communication (RF–VLC) system which may provide a better option to transceive between the hospitals and some laboratory to transfer patient’s information. In the proposed system model, the data (such as patient’s lab test reports) is transmitted towards the amplify and forward (AF) relay mounted on the top of the hospital building via the RF channel. Further, the AF relay amplifies and converts the received information into corresponding optical signal using light emitting diodes (LED) and supporting circuitry. This optical signal is then forwarded towards the destination device (equipped with VLC transceiver), via the VLC channel. To analyse the performance of the system, we first derive the closed form analytical expressions for the cumulative distribution function (CDF) of the end-to-end (e2e) signal to noise ratio (SNR) of the system by using the moment generating function (MGF) of the SNR of the individual RF and VLC channels. Further, we use these statistical expressions to obtain the outage probability, average bit error rate (BER) and the average capacity of the system. Moreover, the asymptotic performance of the proposed system is also analysed to study the system’s behaviour at high SNR regimes. Finally, we studied the impact of the variations in channel parameters on the proposed system model performance through numerically simulated plots. 相似文献
87.
使用静电探针和发射光谱分析方法,测量了实验室圆柱形辉光等离子体轴向I-V曲线和发射光谱.通过电子能量概率函数方法、Fermi-Dirac模型、低气压放电的Schottky扩散理论,分别计算了等离子体的电子温度、电子激发温度和电子密度.研究了利用等离子体发射光谱计算电子激发温度、低气压放电理论估算电子密度的方法与静电探针诊断方法的内在联系,讨论了不同方法的使用特点.所研究的方法在某些特殊环境的等离子体参数诊断中具有较好的参考和应用价值.
关键词:
静电探针
发射光谱
电子能量概率函数
Fermi-Dirac模型 相似文献
88.
Electric-dipole allowed (El) and forbidden (E2, M1 and M2) transition probabilities of 4f for N+ 下载免费PDF全文
By applying systematically enlarged multi-configuration Dirac-Fock wavefunction, the transitions for electricdipole allowed (E1) and forbidden (E2, M1 and M2) lines are studied among 4f pair coupling and low-lying configurations for singly ionized nitrogen. Most important effects of relativity, electron correlation, the rearrangement of electron density, Breit interaction, and quantum electrodynamic effects are included in the computation. Then, allowed (E1) and forbidden (E2, M1 and M2) transition probabilities of 4f for N+ are obtained and compared with experimental results. Good agreement with available experimental results is found and most of the data of 4f are presented for the first time. 相似文献
89.
We study the phase probability distribution of a three-level atom interacting with a cavity field in the presence of two-photon detuning and decoherence. Anabiosis of the phase probability distribution is observed due to the presence of the Stark shift. The simulation demonstrates that there is an enhancement of the phase sensitivity as soon as the two-photon detuning is considered. The W-Wigner function is also examined and it is shown that the nonclassical effect is apparent, however, for a small value of the decoherence factor. 相似文献
90.
The well-known refinement of the Nash Equilibrium (NE) called an Evolutionarily Stable Strategy (ESS) is investigated in the quantum Prisoner's Dilemma (PD) game that is played using an Einstein-Podolsky-Rosen type setting. Earlier results report that in this scheme the classical NE remains intact as the unique solution of the quantum PD game. In contrast, we show here that interestingly in this scheme a non-classical solution for the ESS emerges for the quantum PD. 相似文献