全文获取类型
收费全文 | 3570篇 |
免费 | 57篇 |
国内免费 | 273篇 |
专业分类
化学 | 1662篇 |
晶体学 | 35篇 |
力学 | 43篇 |
综合类 | 1篇 |
数学 | 154篇 |
物理学 | 2005篇 |
出版年
2024年 | 4篇 |
2023年 | 35篇 |
2022年 | 36篇 |
2021年 | 24篇 |
2020年 | 48篇 |
2019年 | 39篇 |
2018年 | 33篇 |
2017年 | 47篇 |
2016年 | 52篇 |
2015年 | 50篇 |
2014年 | 67篇 |
2013年 | 152篇 |
2012年 | 176篇 |
2011年 | 202篇 |
2010年 | 187篇 |
2009年 | 224篇 |
2008年 | 198篇 |
2007年 | 296篇 |
2006年 | 234篇 |
2005年 | 166篇 |
2004年 | 183篇 |
2003年 | 173篇 |
2002年 | 134篇 |
2001年 | 135篇 |
2000年 | 118篇 |
1999年 | 136篇 |
1998年 | 100篇 |
1997年 | 99篇 |
1996年 | 89篇 |
1995年 | 82篇 |
1994年 | 58篇 |
1993年 | 68篇 |
1992年 | 43篇 |
1991年 | 60篇 |
1990年 | 27篇 |
1989年 | 22篇 |
1988年 | 15篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 9篇 |
1984年 | 11篇 |
1983年 | 8篇 |
1982年 | 12篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1973年 | 7篇 |
排序方式: 共有3900条查询结果,搜索用时 31 毫秒
101.
Self-avoiding random walks (SAWs) are studied on several hierarchical lattices in a randomly disordered environment. An analytical method to determine whether their fractal dimensionD
saw is affected by disorder is introduced. Using this method, it is found that for some lattices,D
saw is unaffected by weak disorder; while for othersD
saw changes even for infinitestimal disorder. A weak disorder exponent is defined and calculated analytically [ measures the dependence of the variance in the partition function (or in the effective fugacity per step)vL
on the end-to-end distance of the SAW,L]. For lattices which are stable against weak disorder (<0) a phase transition exists at a critical valuev=v
* which separates weak- and strong-disorder phases. The geometrical properties which contribute to the value of are discussed. 相似文献
102.
用原子吸收光谱法测下了“东北水三七”根、茎、叶的21种化学元素,结果表明,不同部位的元素含量有一定差别。 相似文献
103.
偏最小二乘法在原子吸收光谱分析中的应用——钴和铟的同时测定 总被引:4,自引:1,他引:3
本文用偏最小二乘法(PLS)校正了火焰原子吸收分析In252.137nm对Co252.136nm的吸收线重叠干扰,对混合样中Co和In的含量进行了测定,结果令人满意。 相似文献
104.
Weak separation properties for self-similar sets 总被引:5,自引:0,他引:5
Martin P. W. Zerner 《Proceedings of the American Mathematical Society》1996,124(11):3529-3539
We develop a theory for self-similar sets in that fulfil the weak separation property of Lau and Ngai, which is weaker than the open set condition of Hutchinson.
105.
Polymer enhanced ultrafiltration (PEUF) is a newly developed method for the removal of heavy metals from aqueous solutions. This method was applied for the removal of mercury and cadmium with the presence of polyethyleneimine (PEI) as a water soluble polymer. After ultrafiltration experiments for metal–polymer mixtures, two separate streams, namely, retentate and permeate, former of which contains mainly metal–polymer complex and free polymer molecules while latter of which mainly contains free metal ions, were obtained. At the end of PEUF experiments, performance of operation was determined by concentration analyses which was achieved by atomic absorption spectroscopy (AAS) applied in a different way for permeate and retentate streams considering the effect of presence of polymer. For mercury analysis, cold vapor AAS was applied. It was observed that the presence of PEI did not affect the atomic absorption signal when 10% HCl was added to the sample solutions. For calcium and cadmium, flame AAS was used. It was observed that change in PEI concentration results in change in measured concentration of calcium and cadmium. Therefore, two new approaches were developed for accurate measurement of concentrations of calcium and cadmium. It was also observed that presence of other metals did not affect the accuracy of the measurement of a particular metal in the concentration range studied. 相似文献
106.
Mattia Falconi Ruggero Gallimbeni Emanuele Paci 《Journal of computer-aided molecular design》1996,10(5):490-498
Summary Molecular dynamics (MD) simulations of 100 ps have been carried out to study the active-site behaviour of the Cu,Zn superoxide dismutase dimer (SOD) in water. The active site of each subunit was monitored during the whole simulation by calculating the distances between functional residues and the catalytic copper. The results indicate that charge orientation is maintained at each active site but the solvent accessibility varies. Analysis of the MD simulation, carried out by using the atomic displacement covariance matrix, has shown a different intra-subunit correlation pattern for the two monomers and the presence of inter-subunit correlations. The MD simulation presented here indicates an asymmetry in the two active sites and different dynamic behaviour of the two SOD subunits. 相似文献
107.
Using a new graph counting technique suitable for self-similar fractals, exact 18th-order series expansions for SAWs on some Sierpinski carpets are generated. From them, the critical fugacityx
c and critical exponents SAW and SAW are obtained. The results show a linear dependence of the critical fugacity with the average number of bonds per site of the lattices studied. We find for some carpets with low lacunarity that SAW<0.75, thus violating the relation SAW(fractal) > SAW (d) for SAWs on the fractals which are embedded in ad-dimensional Euclidean space. 相似文献
108.
An analytical method for the simultaneous determination of some trace elements (Au, Fe, Mg, Li, Sr, Zn) in human serum by inductively coupled plasma atomic emission spectrometry (ICP-AES) with flow injection is described. Physical interference caused by the change of sample viscosity is discussed. When 100 μl of serum was injected, the relevant recoveries of > 99% for Li, > 98% for Cu and Mg, > 95% for Fe were obtained for an NIST SRM with R.S.D. > 1.3% using optimized flow injection parameters. The prepared lyophilized control serum for routine analysis in clinical laboratories was analyzed and verified for the validity of the technique employed in this experiment using NIST SRM 909 as a primary reference material. 相似文献
109.
A magnetically coupled microcavity hollow cathode discharge device was evaluated for its analytical potential as a boosted atomic emission source. A magnetic field using an electromagnet was applied perpendicular to the axis of the microcavity hollow cathode. The intensity of the atomic emission of copper, aluminum and the ionic emission of magnesium increased with increasing magnetic field until it reached a maximum. A further increase in the field strength did not lead to an enhancement of these emissions. The attainment of the maxima was attributed to the increase in the electron temperature and radial diffusion of the electrons from the center of the microcavity axis. Electron temperatures in the presence of the magnetic field calculated based on the semicorona model were shown to be proportional to the square of the reduced field strength. Further, these maxima were correlated to the energies of the upper levels of the transition studied. 相似文献
110.
The present work describes a metallic hydride atomizer for atomic absorption spectrometry, by evaluating the performance of the Inconel 600® tube. For this purpose, stibine was used as the model volatile compound and antimony determination in river and lake sediments and in pharmaceutical samples was carried out to assess the metal furnace performance. Some parameters are evaluated such as those referring to the generation and transport of the hydride (such as KBH4 and acid concentrations, carrier gas flow rate, injected volume, etc.), as well as those referring to the metal furnace (such as tube hole area, flame composition, long-term stability, etc.). The method presents linear Sb concentration from 2 to 80 μg L−1 range (r > 0.998; n = 3) and the analytical frequency of ca. 140 h−1. The limit of detection (LOD) is 0.23 μg L−1 and the precision, expressed as R.S.D., is less than 5% (40 μg L−1; n = 10). The accuracy is evaluated through the reference materials, and the results are similar at 95% confidence level according to the t-test. 相似文献