全文获取类型
收费全文 | 100709篇 |
免费 | 16664篇 |
国内免费 | 11767篇 |
专业分类
化学 | 71091篇 |
晶体学 | 1137篇 |
力学 | 5737篇 |
综合类 | 678篇 |
数学 | 12646篇 |
物理学 | 37851篇 |
出版年
2024年 | 226篇 |
2023年 | 1998篇 |
2022年 | 2364篇 |
2021年 | 3418篇 |
2020年 | 4116篇 |
2019年 | 3872篇 |
2018年 | 3575篇 |
2017年 | 3218篇 |
2016年 | 4847篇 |
2015年 | 4681篇 |
2014年 | 5809篇 |
2013年 | 7556篇 |
2012年 | 9120篇 |
2011年 | 9494篇 |
2010年 | 6642篇 |
2009年 | 6372篇 |
2008年 | 6692篇 |
2007年 | 5988篇 |
2006年 | 5587篇 |
2005年 | 4674篇 |
2004年 | 3655篇 |
2003年 | 2933篇 |
2002年 | 2667篇 |
2001年 | 2236篇 |
2000年 | 1955篇 |
1999年 | 2051篇 |
1998年 | 1734篇 |
1997年 | 1560篇 |
1996年 | 1552篇 |
1995年 | 1368篇 |
1994年 | 1240篇 |
1993年 | 1003篇 |
1992年 | 901篇 |
1991年 | 772篇 |
1990年 | 646篇 |
1989年 | 499篇 |
1988年 | 372篇 |
1987年 | 334篇 |
1986年 | 330篇 |
1985年 | 261篇 |
1984年 | 187篇 |
1983年 | 153篇 |
1982年 | 125篇 |
1981年 | 78篇 |
1980年 | 59篇 |
1979年 | 24篇 |
1978年 | 22篇 |
1976年 | 22篇 |
1975年 | 22篇 |
1957年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
901.
A simple and sensitive method was conducted for the determination of trace amounts of proteins with benzeneazo-8-acetylamino-1-naphthol-3,6-disulfonic acid sodium salt (azophloxine, AP) using a Rayleigh light-scattering (RLS) technique. At pH 2.60 and in the presence of an emulsifier OP microemulsion, the RLS of AP can be greatly enhanced by proteins, owing to the interaction between AP and protein. The enhanced intensity is proportional to the concentration of proteins. Four proteins, including bovine serum albumin (BSA), human serum albumin (HSA), lysozyme (Lys) and gamma globulin (gamma-G) have been tested. For example, the linear range of BSA was 0 - 0.06 microg mL(-1) with detection limits of 2.38 ng mL(-1). The method was applied to the analysis of protein in human urine and penicillin samples with satisfactory results. The relative standard deviation was in all instances less than 4.0%, and the recovery was in the range of 97.5 - 104%. 相似文献
902.
Effect of Molecular Weight on Liquid Crystal Photoalignment by Photosensitive Polyester Containing Thrifluoromethyl Moieties 下载免费PDF全文
We investigate the liquid-crystal (LC) alignment direction on photoalignment films formed from photosensitive polyester containing thrifluoromethyl moieties (PPDA) with various molecular weights by crossed polarized optical microscopy. It is found that LC alignment behaviour changes with molecular weight of PPDA. The LC alignment on PPDA irradiated films with the highest molecular weight is homogeneous, while those with low and intermediate molecular weights are homeotropic. However, surface morphologies show weak dependence on molecular weight. The surfaces are smooth and there is no clear morphological anisotropy on these aligned films observed by an atomic force microscope. The surface energies of the irradiated films are also measured by using an indirect contact-angle method where both surface energy and its polar component, increase with increasing molecular weight. Different polar surface energies can be considered as a main reason for different alignment characteristics. 相似文献
903.
现在,整个教育界都在提倡创新教育和自主探究式学习.笔者曾经尝试着在课堂上渗透让学生自主学习的思想,努力创设情景给学生多一些创新的机会,允许并鼓励他们在课堂上提出自己的看法.但课堂教学,特别是在目前仍受考试压力影响的高中课堂中,教师和学生依然面临着升学压力.无奈的现实很难在课堂上落实这些“理念”.毕竟学生这么多、课时这么少、教学任务又如此之重,作出一个教学决定又要考虑方方面面的因素, 相似文献
904.
Discrete-time GI/Geo/1 queue with multiple working vacations 总被引:2,自引:0,他引:2
Consider the discrete time GI/Geo/1 queue with working vacations under EAS and LAS schemes. The server takes the original
work at the lower rate rather than completely stopping during the vacation period. Using the matrix-geometric solution method,
we obtain the steady-state distribution of the number of customers in the system and present the stochastic decomposition
property of the queue length. Furthermore, we find and verify the closed property of conditional probability for negative
binomial distributions. Using such property, we obtain the specific expression for the steady-state distribution of the waiting
time and explain its two conditional stochastic decomposition structures. Finally, two special models are presented.
相似文献
905.
王俐 《南昌大学学报(理科版)》2007,31(6):610-611,615
提出了一种把解析几何与根轨迹法结合起来实现串联超前校正计算方法,无需精确绘图和繁琐的试凑运算,也能得到精确而又令人满意的校正效果,为线性控制系统的设计提供了一种简便而有效的途径,也为线性系统设计的计算机仿真奠定了又一基础. 相似文献
906.
VECTOR-VALUED RANDOM POWER SERIES ON THE UNIT BALL OF C^n 总被引:1,自引:0,他引:1
In this article, the authors study the vector-valued random power series on the unit ball of Cn and get vector-valued Salem-Zygmund theorem for them by using martingale technique. Further, the relationships between vector-valued random power series and several function spaces are also studied. 相似文献
907.
K. Ren Z.Y. Li X. Ren B. Cheng D. Zhang 《Applied Physics A: Materials Science & Processing》2007,87(2):181-185
This paper describes a simple hydrothermal procedure for high-yield synthesis of single-crystalline ZnO hexagonal nanoplates in a surfactant-free system at 70 °C. The structures and morphologies of the synthesized ZnO nanoplates are derived from characterisation by X-ray diffraction, and scanning and transmission electron microscopy. Their optical properties are recorded by Raman and photoluminescence spectroscopy. These ZnO hexagonal nanoplates exhibit the enhanced photocatalytic activity of phenol photodecomposition, suggesting that they could be served as an active system for the treatment of the waste water, in addition to their common applications. PACS 81.10.Dn; 61.10.Nz; 68.37.Hk; 78.55.Hx 相似文献
908.
This paper addresses a kind of risk decision-making problem existing widely in public administration and business management, which is characterized by (1) occurrence probabilities of states of nature can be estimated by analysing historical observations, but historical observations of different objects are unhomogeneous, (2) the relation between observations and occurrence probabilities of states of nature are affected by some qualitative and quantitative indicators, (3) it is a real-time decision-making problem, that is, there are many decisions for different objects to be made in a limited time, (4) considering decision's execution, impact of resource constrains is an important issue in decision-making process. In this paper, we develop a rule-based approach to address the problem. In the proposed approach, a two-step clustering method is employed to classify objects into categories, and observations in each category can be approximately viewed as homogeneous. For objects in each category, occurrence probabilities of states of nature are estimated by logistic regression, and the decision rule is obtained through solving an optimization model, which is to minimize the total decision risks while satisfying resource constrains. Effect and efficacy of our approach are illustrated through its application to China's customs inspection decision. 相似文献
909.
研究了初态为混合态的电荷量子比特与量子化光场之间的纠缠.通过求解系统的concurrence下限, 研究初态的混合度λ和失谐量Δ对系统纠缠随时间演化的影响. 在弱场中, 电荷量子比特初始是激发态的系统, 其纠缠度远远大于电荷量子比特初始是基态的系统, 并且Δ对系统的纠缠有明显的抑制作用. 在强场中, 电荷量子比特初始分别为激发态和基态时系统的纠缠演化接近一致, 初态混合度最高时系统的纠缠度最小, 并且Δ对系统纠缠的影响变弱.
关键词:
约瑟夫森结
纠缠
混合态
concurrence下限 相似文献
910.
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