全文获取类型
收费全文 | 5115篇 |
免费 | 526篇 |
国内免费 | 436篇 |
专业分类
化学 | 3453篇 |
晶体学 | 27篇 |
力学 | 350篇 |
综合类 | 49篇 |
数学 | 849篇 |
物理学 | 1349篇 |
出版年
2024年 | 13篇 |
2023年 | 73篇 |
2022年 | 162篇 |
2021年 | 171篇 |
2020年 | 201篇 |
2019年 | 149篇 |
2018年 | 160篇 |
2017年 | 210篇 |
2016年 | 214篇 |
2015年 | 195篇 |
2014年 | 228篇 |
2013年 | 414篇 |
2012年 | 329篇 |
2011年 | 333篇 |
2010年 | 242篇 |
2009年 | 306篇 |
2008年 | 281篇 |
2007年 | 323篇 |
2006年 | 271篇 |
2005年 | 257篇 |
2004年 | 220篇 |
2003年 | 177篇 |
2002年 | 144篇 |
2001年 | 116篇 |
2000年 | 118篇 |
1999年 | 103篇 |
1998年 | 93篇 |
1997年 | 67篇 |
1996年 | 70篇 |
1995年 | 64篇 |
1994年 | 53篇 |
1993年 | 62篇 |
1992年 | 41篇 |
1991年 | 34篇 |
1990年 | 30篇 |
1989年 | 21篇 |
1988年 | 21篇 |
1987年 | 10篇 |
1986年 | 8篇 |
1985年 | 13篇 |
1984年 | 16篇 |
1983年 | 10篇 |
1982年 | 12篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 11篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1973年 | 4篇 |
排序方式: 共有6077条查询结果,搜索用时 18 毫秒
1.
Xinghua Li Yuqin Yang Junjie Miao Zhendong Yin Yijing Zhai Hongmei Shi Zengning Li 《Electrophoresis》2020,41(18-19):1584-1591
In the present research, field-amplified sample injection–CZE (FASI–CZE) coupled with a diode array detector was established to determine trace level sulfa antibiotic. Sulfathiazole, sulfadiazine, sulfamethazine, sulfadimethoxine, sulfamethoxazole, and sulfisoxazole were selected as analytes for the experiments. The background electrolyte solution consisted of 70.0 mmol/L borax and 60.0 mmol/L boric acid (including 10% methanol, pH 9.1). The plug was 2.5 mmol/L borax, which was injected into the capillary at a pressure of 0.5 psi for 5 s. Then the sample was injected into the capillary at an injection voltage of –10 kV for 20 s. The electrophoretic separation was carried out under a voltage of +19 kV. The capillary temperature was maintained at 20˚C throughout the analysis, and six sulfonamides were completely separated within 35 min. Compared with pressure injection-CZE, the sensitivity of FASI-CZE was increased by 6.25–10.0 times, and the LODs were reduced from 0.2–0.5 to 0.02–0.05 μg/mL. The method was applied to the determination of sulfonamides in river water and particulate matter samples. The recoveries were 78.59–106.59%. The intraday and interday precisions were 2.89–7.35% and 2.77–7.09%, respectively. This provides a simpler and faster method for the analysis of sulfa antibiotic residues in environmental samples. 相似文献
2.
直流稳压电源可以将交流电压变换为直流电压,并使之稳定,在我们现实生活中应用很广泛,在实验中我们利用的电学知识,设计制造了一种直流稳压电源。本文简要介绍了这种直流稳压电源波形演示器的设计目的和电路原理,重点阐述了它的制作流程、滤波和稳压原理以及性能测试输出波形。 相似文献
3.
用经验赝势方法计算了体ZnSe以及ZnSe/GaAs单异质结系统中ZnSe外延层г、X、L等特殊对称点导带底能量随压力的变化。结果表明,同Si、Ge、GaAs等半导体材料不同,ZnSe的X点导带底具有正的压力系数,但比г点的压力系数小,这是ZnSe材料以及ZnSe基异质结构材料发生直接禁带向间接禁带的转变时所需转变压力较大的根本原因。研究了ZnSe/GaAs异质结构中晶格失配造成的应变对外延层г、X、L对称点压力系数的影响,表明这种晶格失配造成的应变可以极大地减小ZnSe外延层材料由直接禁带向间接禁带的转变压力。 相似文献
4.
Resistivity-temperature characteristics of sol gel YBa2Cu3Oy samples synthesized in flowing oxygen atmosphere
下载免费PDF全文
![点击此处可从《中国物理》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The relationship of resistivity versus synthesizing temperature of sol gel YBa_2Cu_3O_y samples was studied when prepared under flowing oxygen conditions. A set of high-temperature ρ-T curves was obtained for the whole process. After the sample finished the test measuring, its resistivity was ρ_{300}=9.83×10^{-3 }Ω·cm at room temperature. The ρ-T curve also showed that the orthorhombic-tetragonal phase transformation of sol-gel YBa_2Cu_3O_y sample occurred at 581℃ for the sample in the rising temperature process, but at 613℃ in the cooling process, lower than that of the samples made by using the conventional powder metallurgy methods. 相似文献
5.
Tereza C. R. dos Santos Ricardo Q. Aucélio Reinaldo C. Campos 《Mikrochimica acta》2003,142(1-2):63-66
A simple and direct spectrofluorimetric method has been developed for the determination of aluminum using alizarin red PS
(1,2,4-trihydroxy 9,10-anthraquinone-3-sulfonic acid). The method is based on the strong fluorescence (480/564 nm) of Al3+ and alizarin red. Experimental parameters such as pH, concentration of the ligand, ionic strength of the solution, reaction
time and temperature were optimized in order to maximize the analytical signal. Interferences of several ions (anions and
cations) were studied and evaluated. The linear range of the method extends from 3 to 100 μg L−1. Limit of detection (3sb) was 0.9 μg L−1. The method was tested with a silicate certified reference material. Interferences were eliminated by a liquid extraction
with cupferron.
Author for correspondence. E-mail: aucelior@rdc.puc-rio.br
Received September 10, 2002; accepted January 15, 2003
Published online May 5, 2003 相似文献
6.
A synthetic form of the mineral hewettite was prepared via a new route in aqueous medium, starting either from the crystalline compound Li1.1V3O8, or from its amorphous precursor. The anhydrous, crystalline derivative Ca0.5V3O8 was obtained by heating the synthetic hewettite at 250°C under dynamic vacuum. The diffraction studies show that the 2D structure of Ca0.5V3O8 involves the same V3O8 layers as in the hewettite or in Li1+αV3O8. The stacking of the layers is similar to that in the metahewettite. A structural model is proposed, where the Ca2+ ions occupy octahedral sites in the interlayer space. The electrochemical behavior of Ca0.5V3O8 vs. lithium insertion is presented. It is original and reveals particularly good performances in terms of stability during cycling at C/5 rate. The homologues obtained with Mg or Ba, instead of Ca, are briefly presented. 相似文献
7.
In the direct simulation Monte‐Carlo (DSMC) method for simulating rarefied gas flows, the velocities of simulator particles that cross a simulation boundary and enter the simulation space are typically generated using the acceptance–rejection procedure that samples the velocities from a truncated theoretical velocity distribution that excludes low and high velocities. This paper analyses an alternative technique, where the velocities of entering particles are obtained by extending the simulation procedures to a region adjacent to the simulation space, and considering the movement of particles generated within that region during the simulation time step. The alternative method may be considered as a form of acceptance–rejection procedure, and permits the generation of all possible velocities, although the population of high velocities is depleted with respect to the theoretical distribution. Nevertheless, this is an improvement over the standard acceptance–rejection method. Previous implementations of the alternative method gave a number flux lower than the theoretical number required. Two methods for obtaining the correct number flux are presented. For upstream boundaries in high‐speed flows, the alternative method is more computationally efficient than the acceptance–rejection method. However, for downstream boundaries, the alternative method is extremely inefficient. The alternative method, with the correct theoretical number flux, should therefore be used in DSMC computations in favour of the acceptance–rejection method for upstream boundaries in high‐speed flows. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
8.
从生物样品中检测未知物,一直以来是毒物分析中的一个难点。如何有效地提取目标化合物,并选择适合的检测手段将未知物筛选出来,GC-MS方法是快速筛选多种毒物和药物的一个简便、可靠的手段。随着MS技术的不断发展,更灵敏、更准确的特性将使其成为药物和毒物分析中必不可少的一门技术。 相似文献
9.
10.
本文介绍事后分层技术,说明了它不仅可用于简单随机抽样,而且可以用于放回PPS抽样。给出了事后分层估计量的形式,证明了它的无编性,并给出了它在交通运输抽样调查中的应用。 相似文献