全文获取类型
收费全文 | 10442篇 |
免费 | 1841篇 |
国内免费 | 1549篇 |
专业分类
化学 | 8012篇 |
晶体学 | 179篇 |
力学 | 642篇 |
综合类 | 97篇 |
数学 | 1351篇 |
物理学 | 3551篇 |
出版年
2024年 | 24篇 |
2023年 | 166篇 |
2022年 | 312篇 |
2021年 | 357篇 |
2020年 | 376篇 |
2019年 | 448篇 |
2018年 | 364篇 |
2017年 | 320篇 |
2016年 | 532篇 |
2015年 | 610篇 |
2014年 | 634篇 |
2013年 | 785篇 |
2012年 | 921篇 |
2011年 | 905篇 |
2010年 | 729篇 |
2009年 | 698篇 |
2008年 | 732篇 |
2007年 | 596篇 |
2006年 | 529篇 |
2005年 | 496篇 |
2004年 | 451篇 |
2003年 | 407篇 |
2002年 | 514篇 |
2001年 | 424篇 |
2000年 | 267篇 |
1999年 | 222篇 |
1998年 | 188篇 |
1997年 | 133篇 |
1996年 | 119篇 |
1995年 | 107篇 |
1994年 | 84篇 |
1993年 | 67篇 |
1992年 | 55篇 |
1991年 | 58篇 |
1990年 | 36篇 |
1989年 | 27篇 |
1988年 | 21篇 |
1987年 | 16篇 |
1986年 | 11篇 |
1985年 | 8篇 |
1984年 | 14篇 |
1983年 | 12篇 |
1982年 | 4篇 |
1981年 | 13篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1976年 | 3篇 |
1974年 | 5篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
H. M. Noor ul Huda Khan Asghar Yi Tan Shuang Shi Dachuan Jiang Shiqiang Qin Jiao Liao Shutao Wen Wei Dong Yao Liu 《Applied Physics A: Materials Science & Processing》2014,115(3):753-757
Small amounts of multicrystalline silicon were melted in an electron beam furnace in different experimental conditions in order to investigate the oxygen evaporation behavior during the electron beam melting (EBM) process. The oxygen content level before and after EBM was determined by secondary ion mass spectroscopy. The oxygen content was reduced from 6.177 to 1.629 ppmw when silicon was melted completely at 15 kW with removal efficiency up to 73.6 %. After that, it decreased continually to <0.0517 ppmw when the refining time exceeded 600 s with a removal efficiency of more than 99.08 %. During the melting process, the evaporation rate of silicon is 1.10 × 10?5 kg/s. The loss of silicon could be reduced up to 1.7 % during oxygen removal process to a desirable figure, indicating EBM is an effective method to remove oxygen from silicon and decrease the loss of silicon. 相似文献
62.
Li Huang Qin Guo Xue-xiang Xu Wen Yuan 《International Journal of Theoretical Physics》2014,53(11):3970-3980
A kind of non-Gaussian state—variable arcsine state is studied by using the input-output theories which relate the statistical properties of the output field to those of the input field. The variable arcsine state (VAS) is generated by using a variable beam splitter (BS), which means that the transmissivity (reflectivity) of the BS is adjustable continuously. The nonclassicality is investigated by studying the negativity of Wigner function (WF). It is shown that the variable arcsine state has negative values of WF when transmissivity is not equal to 1 or 0. The decoherence effect of the VAS is then studied by analytically deriving the time evolution formula of WF. 相似文献
63.
Considering the spin degree of freedom of the Dirac field, we study the entanglement behavior of a different class of communication channel and teleportation of three-dimensional single particle state in noninertial frames. Numerical analysis shows that the communication channel in our scheme can offer enough distillable entanglement for the teleportation protocol. Moreover, the teleportation protocol could work well if Rob's acceleration is not very big, but the fidelity of the teleportation is still reduced due to the Unruh effect. 相似文献
64.
65.
基于经典电动力学导出的表征简单离子磁化率的磁性点价gi所构建的分子磁性连接性指数?mF及45种碱金属化合物的摩尔磁化率χm的实测数据集,利用粒子群寻优的支持向量回归(SVR)方法,建立了基于0F和1F的碱金属化合物χm的预测模型,并与基于多元线性回归(MLR)模型的计算结果进行了比较.结果显示,基于9次交叉验证的SVR模型预测的平均绝对误差、平均相对误差绝对值以及均方根误差均比MLR模型小,表明SVR模型的回归预测能力优于MLR.研究表明,磁性连接性指数mF是一种合适的分子描述符,SVR是一种预测碱金属化合物χm的有效方法.
关键词:
碱金属化合物
摩尔磁化率
支持向量回归
预测 相似文献
66.
The superparamagnetic 8-nm Fe3O4 nanoparticles were successfully prepared by chemical oxidation process. For the complex permittivity, the dual dielectric relaxation processes have been proved by two overlapped Cole–Cole semicircles, and the natural resonance frequency is 3.03 GHz for the complex permeability. The maximum reflection loss value reaches −55.5 dB at 6.11 GHz with 3.85 mm in the thickness of the absorbers for the superparamagnetic 8-nm Fe3O4 nanoparticles which is better than that of 150 nm and 30 nm Fe3O4 nanoparticles. It is believed that the superparamagnetic 8-nm Fe3O4 nanoparticles can be used as a kind of candidate for microwave absorber. 相似文献
67.
We have modified the holographic model of Saremi and Son [12] by using a charged black brane, instead of a neutral one, such that when the bulk pseudo scalar (θ ) potential is made of θ2 and θ4 terms, parity can still be broken spontaneously in the boundary theory. In our model, the 3+1 dimensional bulk has a pseudo scalar coupled to the gravitational Chern–Simons term in the anti de Sitter charged black brane back ground. Parity could be broken spontaneously in the bulk by the pseudo scalar hairy solution and give rise to non-zero Hall viscosity at the boundary theory. 相似文献
68.
近红外微型光谱仪光学系统设计与模拟 总被引:3,自引:0,他引:3
基于光谱仪基本工作原理和光学设计理论,以系统微型化、且能满足一定光谱范围和分辨率要求为具体设计目标,提出了基于平面衍射光栅分光的交叉式C-T结构的近红外微型光谱仪光学系统结构方案。采用ZEMAX软件对近红外微型光谱仪的分光系统、成像系统进行了优化设计与模拟分析。最终设计与模拟分析结果表明,该光学系统光谱范围为900~1 700 nm,分辨率<10 nm,谱面展宽为12.74 mm,F数为8.128 388,系统体积为51.26 mm×41.81 mm×22 mm。 相似文献
69.
采用数值计算的方法,对脉冲激光二极管三向侧面抽运固体激光器中,激光晶体的温度场时变分布进行了计算. 分析了三向侧面抽运情况下晶体内光强分布,在此基础上,采用有限元法,以脉冲激光二极管侧面抽运Nd:YAG激光器为例,对单脉冲过程中晶体温度分布及其影响因素进行分析. 结果表明,晶体升温过程受到抽运条件以及散热条件的影响,但是主要受到抽运条件即抽运光强度和光束半径的影响,降温过程受到晶体热物性参数和晶体半径以及散热条件的影响. 当晶体温度达到周期性分布后,由于晶体径向温度梯度的周期性变化,引起通过晶体的平面光波的中心和边缘光线相对光程差也随时间作周期性变化. 相似文献
70.
We propose a novel transmitter and receiver for differential quadrature phase-shift keying (DQPSK) format. The impact of the first-order polarization mode dispersion (PMD) on systems using DQPSK with 100- Gb/s non-return-to-zero (NRZ) or return-to-zero (RZ) format is investigated. Through computing the eye openings of DQPSK formats under different PMD conditions, it is found that NRZ DQPSK, as compared with RZ DQPSK, incurs smaller eye opening due to PMD. Carrier-suppressed return-to-zero (CSRZ) DQPSK format has better tolerance than RZ DQPSK format to PMD for a given bit rate. 相似文献