全文获取类型
收费全文 | 4955篇 |
免费 | 669篇 |
国内免费 | 565篇 |
专业分类
化学 | 3424篇 |
晶体学 | 33篇 |
力学 | 66篇 |
综合类 | 21篇 |
数学 | 84篇 |
物理学 | 2561篇 |
出版年
2024年 | 29篇 |
2023年 | 129篇 |
2022年 | 228篇 |
2021年 | 280篇 |
2020年 | 296篇 |
2019年 | 200篇 |
2018年 | 187篇 |
2017年 | 197篇 |
2016年 | 235篇 |
2015年 | 200篇 |
2014年 | 246篇 |
2013年 | 452篇 |
2012年 | 229篇 |
2011年 | 319篇 |
2010年 | 215篇 |
2009年 | 295篇 |
2008年 | 289篇 |
2007年 | 255篇 |
2006年 | 230篇 |
2005年 | 248篇 |
2004年 | 266篇 |
2003年 | 167篇 |
2002年 | 150篇 |
2001年 | 144篇 |
2000年 | 84篇 |
1999年 | 119篇 |
1998年 | 86篇 |
1997年 | 62篇 |
1996年 | 49篇 |
1995年 | 50篇 |
1994年 | 30篇 |
1993年 | 27篇 |
1992年 | 20篇 |
1991年 | 22篇 |
1990年 | 18篇 |
1989年 | 10篇 |
1988年 | 13篇 |
1987年 | 6篇 |
1986年 | 9篇 |
1985年 | 17篇 |
1984年 | 17篇 |
1983年 | 6篇 |
1982年 | 13篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1976年 | 4篇 |
1974年 | 4篇 |
1973年 | 4篇 |
排序方式: 共有6189条查询结果,搜索用时 15 毫秒
71.
Xin Xu Yifan Jiang Min Wang Huimeng Wang Chunhua Lu Huanghao Yang 《Particle & Particle Systems Characterization》2020,37(12):2000243
Black phosphorus nanosheet (BPNS) is a promising multifunctional material in the biomedical field with biodegradability and low side effects, however its features are always weakened severely owing to its poor stability. Here, a novel method is developed for improving the defect of BPNS based on the effective protection of poly(lactic-co-glycolic acid) (PLGA), which preserves the stable photothermal therapy (PTT) effect of BPNS and biodegradability of the material. Meanwhile, doxorubicin (DOX) is loaded on BPNS/PLGA to get BPNS/PLGA/DOX for further chemotherapy and preventing the recurrence of tumor after PTT. The presented combined therapeutic strategy exploits the strengths and improves the defects of BPNS, thus developing an efficient and safe nanoagent for cancer therapy, which affords and reveals the great potential of BPNS in nanomedicine. 相似文献
72.
A study of effective implementation of threshold activation technique for neutron spectral analysis in the environment of
an alpha-cyclotron target is presented. The activation data are analysed using LOUHI-82 code. Optimal choices of the regularization
parameters of the code are studied and discussed. Energy distribution of neutrons emitted from thick targets of Be, C and
Ta irradiated by 40–45 MeV alphas is discussed. 相似文献
73.
S Chakrabarty 《Pramana》1985,25(6):673-683
Transport coefficients of quark-gluon plasma are discussed in the framework of relativistic kinetic theory with the relaxation
time approximation of Boltzmann transport equation. The expressions for the coefficients of shear and volume viscosities and
heat conductivity are derived assuming quark-gluon plasma to be a non-reactive mixture of quarks, anti-quarks and gluons.
A lowest order in deviations from local thermal equilibrium and in plasma phase, lowest order in coupling constant are assumed.
Entropy production due to irreversible processes is discussed. 相似文献
74.
A polarised neutron study of the ferromagnetic Heusler alloy Cu2Mn0.863Al1.057 has been made. It has been concluded that the magnetic moment density is primarily situated on the Mn ions. On assigning
the Mn-moment value, the observed magnetic form factor is found to be in good agreement with the Mn2+ free ion form factor calculated by Watson and Freeman. A slight asphericity has been observed in the moment density. It is
estimated that there are about 3% excess 3d-electrons in the Eg states compared to spherical distribution. There is evidence of a very small positive polarisation of
the Cu atoms. No appreciable conduction electron polarisation is found. 相似文献
75.
The basic principle for the production of polarised thermal neutrons is discussed and the choice of various crystal monochromators
surveyed. Brief mention of broad-spectrum polarisers is made. The application of polarised neutrons to the study of magnetisation
density distributions in magnetic crystals, the dynamic concept of polarisation, principle and use of polarisation analysis,
the neutron spin-echo technique are discussed. 相似文献
76.
Matrix element of the Gallilean invariant nonrelativistic reduction of the pseudoscalar-pseudovector interaction has been
calculated for free pion absorption by a single nucleon inside the nucleus of16O. The Hartree-Fock wavefunctions obtained with the unitary-model-operator approach starting with the hard-core nucleon-nucleon
interaction have been used for the π-capturing nucleon in the initial state. The initial pion distortion in the presence of
nuclear field of the absorbing nucleus prior to its absorption together with the Coulomb interaction with the finite nuclear
size has been taken into account. The distortion of the emitted proton in the field of the residual nucleus has also been
considered. The differential cross-sections have been obtained and calculated results are compared with the previous experimental
and theoretical work. 相似文献
77.
R. J. Birgeneau R. A. Cowley G. Shirane H. Yoshizawa 《Journal of statistical physics》1984,34(5-6):817-848
Transition metal halides provide realizations of Ising,XY, and Heisenberg antiferromagnets in one, two, and three dimensions. The interactions, which are of short range, are generally well understood. By dilution with nonmagnetic species such as Zn++ or Mg++ one is able to prepare site-random alloys which correspond to random systems of particular interest in statistical mechanics. By mixing two magnetic ions such as Fe++ and Co++ one can produce magnetic crystals with competing interactions-either in the form of competing anisotropies or competing ferromagnetic and antiferromagnetic interactions. In this paper the results of a series of neutron scattering experiments on these systems carried out at Brookhaven over the past several years are briefly reviewed. First the critical behavior in Rb2Mn0.5Ni0.5F4 and FecZn1–cF2 which correspond to two-dimensional and three-dimensional random Ising systems, respectively, are discussed. Percolation phenomena have been studied in Rb2MncMgl–cF4, Rb2CocMgl–cF4, KMncZl-cF3, and MncZnl–cF2 which correspond to two-and three-dimensional Heisenberg and Ising models, respectively. In these casesc is chosen to be in the neighborhood of the nearest-neighbor percolation concentration. Application of a uniform field to the above systems generates a random staggered magnetic field; this has facilitated a systematic study of the random field problem. As we shall discuss in detail, a variety of novel, unexpected phenomena have been observed. 相似文献
78.
BNCT优化网格设计及相关算法研究 总被引:2,自引:0,他引:2
用MCNP蒙特卡罗程序模拟了硼中子俘获治疗(BNCT)3种国际基准网格模型, 并与
修正的Snyder椭球模型进行了比较. 在此基础上, 给出了一种保质量守恒、内存量少、易于产生输入文件的4种基本材料成分的BNCT网格模型. 计算结果表明, 在4mm网格下, 新模型可以达到基准模型的精度; 根据解析模型剂量随深度的变化规律, 研究构造了多网格组合模型, 在重要区域计算精度不损失的条件下, 计算时间大大缩短. 最后研究给出了一个既保证精度、又在可接受的时间内完成剂量计算的模型、样本数和相应的算法, 它基本上满足临床BNCT的要求. 相似文献
79.
80.
随着兰州重离子加速器冷却储存环(HIRFL-CSR)外靶实验终端中子墙的建立, 为实验测量高能中子提供了机遇. 为确定CSR外靶实验终端对中子流测量的可行性, 基于BUU理论模型分别对对称系统(Ni+Ni, Pb+Pb)和非对称系统(Pb+Ni)进行了模拟计算, 发现当系统能量达到几百MeV/u时, 中子流信号相当明显, 并与碰撞参数有明显的依赖关系. 模拟结果表明, 在前角20°的覆盖范围内, 可以较好地实现中子流测量所需要的反应平面确定及碰撞参数选择. 对双击事件及其对中子流的影响进行了简单的讨论. 相似文献