全文获取类型
收费全文 | 15817篇 |
免费 | 1121篇 |
国内免费 | 608篇 |
专业分类
化学 | 8107篇 |
晶体学 | 260篇 |
力学 | 1081篇 |
综合类 | 17篇 |
数学 | 1785篇 |
物理学 | 6296篇 |
出版年
2023年 | 190篇 |
2022年 | 321篇 |
2021年 | 383篇 |
2020年 | 358篇 |
2019年 | 343篇 |
2018年 | 353篇 |
2017年 | 277篇 |
2016年 | 450篇 |
2015年 | 403篇 |
2014年 | 594篇 |
2013年 | 842篇 |
2012年 | 1161篇 |
2011年 | 1278篇 |
2010年 | 934篇 |
2009年 | 854篇 |
2008年 | 954篇 |
2007年 | 848篇 |
2006年 | 845篇 |
2005年 | 620篇 |
2004年 | 539篇 |
2003年 | 435篇 |
2002年 | 359篇 |
2001年 | 571篇 |
2000年 | 480篇 |
1999年 | 369篇 |
1998年 | 289篇 |
1997年 | 253篇 |
1996年 | 286篇 |
1995年 | 230篇 |
1994年 | 186篇 |
1993年 | 145篇 |
1992年 | 160篇 |
1991年 | 156篇 |
1990年 | 161篇 |
1989年 | 124篇 |
1988年 | 87篇 |
1987年 | 65篇 |
1986年 | 56篇 |
1985年 | 60篇 |
1984年 | 51篇 |
1983年 | 37篇 |
1982年 | 46篇 |
1981年 | 40篇 |
1980年 | 33篇 |
1979年 | 40篇 |
1978年 | 40篇 |
1977年 | 33篇 |
1976年 | 28篇 |
1975年 | 32篇 |
1973年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
Crystallography Reports - A di-nuclear uranyl complex with the formula of [(UO2)2(L)4(H2O)2]?4H2O (1) (HL = quinoline-6-carboxylic acid) was synthesized hydrothermally and characterized by... 相似文献
182.
C. Q. Tang 《Crystal Research and Technology》1994,29(6):865-868
The positron lifetime spectra in 0.25 at.% La-doped BaTiO3 with different Ba/Ti ratios have been measured at room temperature. It was found from the experiments that with deviating from exact stoichiometry the positron lifetime τ2 decreases and the intensity I2 increases for Ba/Ti ratio smaller than stoichiometric and they have more significantly similar changes for Ba/Ti ratio larger than stoichiometric. The non-monotonic dependence of positron lifetime parameters on Ba/Ti ratio is regarded as that the τ2 component is contributed together by positrons annihilating at the grain boundaries and Ba vacancies and/or Ti vacancies, and small deviations from exact stoichiometry would be expected to increase the concentration of defects such as Ba vacancies for Ba/Ti < and Ti vacancies for Ba/Ti > 1. 相似文献
183.
Quasielastic light (QEL) scattering studies of semidilute solutions of polystyrene in benzene and benzene plus diethyl phthalate mixed solvents have been carried out. Comparisons are made between experiment and theoretical results. It is found that the relative amplitude of the viscoelastic modes depends on the coupling parameter β (defined in the text). For the solutions with β=0, no viscoelastic component is observed in the QEL scattering spectrum, consistent with the theoretical prediction. The amplitude and a relaxation time distribution of the viscoelastic component of the QEL scattering spectrum of PS in the mixed solvent are found to depend on time. Steady state values are obtained only after the solution is equilibrated for more than a month. Time evolution of the QEL spectrum has been investigated. 相似文献
184.
深空光通信中的图像信标捕获技术 总被引:1,自引:0,他引:1
为实现深空光通信链路建立过程中精确的对准,提出了一种深空光通信系统扩展信标的捕获方案。该方案以可视地球图像作为信标,在航天器上存储一幅信标图像作为参考图像,采用天线扫描的方式在各点对所瞄准的区域成像,利用像素扫描的方式,使参考图像和实际探测图像进行相关,在天线扫描完成以后,找出相关性最大的位置,即可认为在该点捕获到地球图像。在计算两图像相关系数的过程中,由于傅里叶梅林变换幅度谱具有伸缩及旋转不变性,因此利用傅里叶梅林变换即可消除两图像相关系数因为旋转和伸缩的影响。利用蒙特卡罗方法随机产生1000个视场,仿真结果表明,3σ内正确捕获到信标图像的概率为99.6%,表明这是一种可行的方法。 相似文献
185.
He-Xia Huang Hui-Jun Tan Zheng-Kang Lin Zi-Jie Li Shu Sun Hao Chen Zhi-Xiang Xiao 《Acta Mechanica Sinica》2021,37(1):156-168
The submerged inlet is an attractive configuration for advanced helicopters due to its high stealth performance and low external drag.In this paper,a submerged ... 相似文献
186.
Oxidative desulfurization (ODS) is the promising new method for super deep desulfurization of fuel oil. The oxidative desulfurization performance of the metal-N4-chelates metallophthalocyanines (MPcs) is related to the chemical properties of conjugate structures and the central metal ions. Herein, a biomimetic catalytic system composed of metallophthalocyanines (MPcR4, M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II); R = -H, -COOH, -NO2, -NH2) and molecular O2 was performed to study the influence of MN4-type coordination structure in metallophthalocyanines for the degradation of dibenzothiophene (DBT) in model oil containing n-octane. The results reveal that the conjugate structures and the center metal ions of metallophthalocyanines played key roles in oxidative desulfurization performance. The inductive effect of different R substituents strongly affected the electron cloud distribution of the conjugate structures and the catalytic performance. Moreover, the catalytic activity of MPcs, which is related to the d electronic configuration and ligand-field effects, does not sequentially increase with the increase in the d electron number of central metal ions. 相似文献
187.
To make further understanding of terahertz(THz)wave generation from liquid water,we study THz wave emission from water lines of different diameters.The water line with a smaller diameter generates a stronger THz electric field for the diameters from 0.2 mm to 0.5 mm.The THz electric field strength and polarity change with the relative position between the incident laser and water line.Moreover,the THz energy has an optimal radiation angle of about 60°.A two-dimensional dipole array model is introduced to illustrate the phenomenon.Our observations contribute to optimizing the scheme of the liquid THz source. 相似文献
188.
Overview of finite elements simulation of temperature profile to estimate properties of materials 3D-printed by laser powder-bed fusion 下载免费PDF全文
Habimana Jean Willy 李辛未 Yong Hao Tan 陈哲 Mehmet Cagirici Ramadan Borayek Tun Seng Herng Chun Yee Aaron Ong 李朝将 丁军 《中国物理 B》2020,(4):98-109
Laser powder bed fusion(LPBF),like many other additive manufacturing techniques,offers flexibility in design expected to become a disruption to the manufacturing industry.The current cost of LPBF process does not favor a try-anderror way of research,which makes modelling and simulation a field of superior importance in that area of engineering.In this work,various methods used to overcome challenges in modeling at different levels of approximation of LPBF process are reviewed.Recent efforts made towards a reliable and computationally effective model to simulate LPBF process using finite element(FE)codes are presented.A combination of ray-tracing technique,the solution of the radiation transfer equation and absorption measurements has been used to establish an analytical equation,which gives a more accurate approximation of laser energy deposition in powder-substrate configuration.When this new analytical energy deposition model is used in in FE simulation,with other physics carefully set,it enables us to get reliable cooling curves and melt track morphology that agree well with experimental observations.The use of more computationally effective approximation,without explicit topological changes,allows to simulate wider geometries and longer scanning time leading to many applications in real engineering world.Different applications are herein presented including:prediction of printing quality through the simulated overlapping of consecutive melt tracks,simulation of LPBF of a mixture of materials and estimation of martensite inclusion in printed steel. 相似文献
189.
QiuHong Wang Abdusalam Abdukerim Wei Chen Xun Chen YunHua Chen XiangYi Cui YingJie Fan DeQing Fang ChangBo Fu LiSheng Geng Karl Giboni Franco Giuliani LinHui Gu XuYuan Guo Ke Han ChangDa He Di Huang Yan Huang YanLin Huang Zhou Huang Peng Ji XiangDong Ji YongLin Ju YiHui Lai Kun Liang HuaXuan Liu JiangLai Liu WenBo Ma YuGang Ma YaJun Mao Yue Meng Parinya Namwongsa KaiXiang Ni JinHua Ning XuYang Ning XiangXiang Ren ChangSong Shang Lin Si AnDi Tan AnQing Wang HongWei Wang Meng Wang SiGuang Wang XiuLi Wang Zhou Wang MengMeng Wu ShiYong Wu JingKai Xia MengJiao Xiao PengWei Xie BinBin Yan JiJun Yang Yong Yang ChunXu Yu Jumin Yuan Dan Zhang HongGuang Zhang Tao Zhang Li Zhao QiBin Zheng JiFang Zhou Ning Zhou XiaoPeng Zhou 《中国科学:物理学 力学 天文学(英文版)》2020,(3):54-63
In dark matter direct detection experiments,neutron is a serious source of background,which can mimic the dark matter-nucleus scattering signals.In this paper,we present an improved evaluation of the neutron background in the PandaX-II dark matter experiment by a novel approach.Instead of fully relying on the Monte Carlo simulation,the overall neutron background is determined from the neutron-induced high energy signals in the data.In addition,the probability of producing a dark-matter-like background per neutron is evaluated with a complete Monte Carlo generator,where the correlated emission of neutron(s)andγ(s)in the(α,n)reactions and spontaneous fissions is taken into consideration.With this method,the neutron backgrounds in the Run 9(26-ton-day)and Run 10(28-ton-day)data sets of PandaX-II are estimated to be(0.66±0.24)and(0.47±0.25)events,respectively. 相似文献
190.
Propagation dynamics of the cosh-Airy vortex(CAiV) beams in a chiral medium is investigated analytically with Huygens–Fresnel diffraction integral formula. The results show that the CAiV beams are split into the left circularly polarized vortex(LCPV) beams and the right circularly polarized vortex(RCPV) beams with different propagation trajectories in the chiral medium. We mainly investigate the effect of the cosh parameter on the propagation process of the CAiV beams.The propagation characteristics, including intensity distribution, propagation trajectory, peak intensity, main lobe's intensity, Poynting vector, and angular momentum are discussed in detail. We find that the cosh parameter affects the intensity distribution of the CAiV beams but not its propagation trajectory. As the cosh parameter increases, the distribution areas of the LCPV and RCPV beams become wider, and the side lobe's intensity and peak intensity become larger. Besides, the main lobe's intensity of the LCPV and RCPV beams increase with the increase of the cosh parameter at a farther propagation distance, which is confirmed by the variation trend of the Poynting vector. It is significant that we can vary the cosh parameter to control the intensity distribution, main lobe's intensity, and peak intensity of the CAiV beams without changing the propagation trajectory. Our results may provide some support for applications of the CAiV beams in optical micromanipulation. 相似文献