全文获取类型
收费全文 | 4984篇 |
免费 | 735篇 |
国内免费 | 522篇 |
专业分类
化学 | 2010篇 |
晶体学 | 101篇 |
力学 | 419篇 |
综合类 | 40篇 |
数学 | 423篇 |
物理学 | 1625篇 |
无线电 | 1623篇 |
出版年
2024年 | 9篇 |
2023年 | 50篇 |
2022年 | 112篇 |
2021年 | 162篇 |
2020年 | 137篇 |
2019年 | 130篇 |
2018年 | 120篇 |
2017年 | 202篇 |
2016年 | 234篇 |
2015年 | 202篇 |
2014年 | 263篇 |
2013年 | 437篇 |
2012年 | 307篇 |
2011年 | 327篇 |
2010年 | 267篇 |
2009年 | 331篇 |
2008年 | 332篇 |
2007年 | 318篇 |
2006年 | 305篇 |
2005年 | 265篇 |
2004年 | 235篇 |
2003年 | 196篇 |
2002年 | 203篇 |
2001年 | 152篇 |
2000年 | 156篇 |
1999年 | 105篇 |
1998年 | 114篇 |
1997年 | 99篇 |
1996年 | 80篇 |
1995年 | 83篇 |
1994年 | 73篇 |
1993年 | 47篇 |
1992年 | 26篇 |
1991年 | 25篇 |
1990年 | 19篇 |
1989年 | 10篇 |
1988年 | 15篇 |
1987年 | 9篇 |
1986年 | 12篇 |
1985年 | 13篇 |
1984年 | 10篇 |
1983年 | 4篇 |
1982年 | 11篇 |
1981年 | 8篇 |
1980年 | 3篇 |
1979年 | 7篇 |
1978年 | 8篇 |
1976年 | 2篇 |
1973年 | 3篇 |
1971年 | 2篇 |
排序方式: 共有6241条查询结果,搜索用时 241 毫秒
41.
Transmission fluctuation spectrometry (TFS) is a method for the analysis of particle size distributions based on the statistical fluctuations of a transmission signal. Complete information on the PSD and particle concentration can be retrieved by a special transformation of the transmission signal, whereby the expectancy of the transmission square (ETS) is determined after the signal has been subjected to a procedure of spatial and temporal averaging. By varying the averaging parameters over a wide range, a spectrum of ETSs is obtained and introduced into a linear equation system, which yields the PSD. In the experimental realization presented here, variable temporal averaging is realized in the frequency domain with a series of low pass filters at different cutoff frequencies while spatial averaging inevitably occurs as the particles pass through a focused Gaussian beam of finite cross section. Experimental results on spherical particles (glass beads) and non‐spherical particles (SiC) are presented. The PSDs are resolved in 30 intervals within a particle size range from 1–1000 μm, employing a modified Chahine inversion algorithm. So far, the measurements are limited to moderate particle concentrations. Some influences affecting the measurements, especially for higher particle concentrations, are discussed in detail. 相似文献
42.
软x射线近贴显微技术 总被引:1,自引:0,他引:1
软x射线近贴显微技术不但可使活的生物样品成象,分辨率高于光学显微镜,而且人为的样品准备程序在该技术中都可避免。本文描述了用高功率激光打靶产生的等离子体作为软x射线源而进行的近贴显微研究,并得到了分辨率好于1μm的结果。 相似文献
43.
44.
45.
用方差定义的激光束横向尺寸,有着普适、简单和便于利用光学元件并行运算功能的特点.本文提出一种借助改变柱形容器内吸收液浓度来直接测量各种波长激光束横向尺寸的理论和方法. 相似文献
46.
A striking size dependence of the mean-square displacement of diffusing particles in the two-dimensional lattice gas of hard squares has been observed by Monte Carlo simulation. It is shown that the size effect is due to the formation of a stable cage structure in small lattices when the particle concentration is high. The formation of cages is governed by a new type of percolation problem related to bootstrap percolation. 相似文献
47.
N.P. Somasiri W.K. Toh X. Chen I.D. Robertson A.A. Rezazadeh 《International Journal of Infrared and Millimeter Waves》2002,23(12):1777-1785
This paper describes numerical modelling of a dual band multi-layered microstrip patch antenna operating at 35GHz on an in-house semi-insulating GaAs substrate. The simulated and measured resonant frequencies at both lower and upper resonant frequencies will be compared to check the accuracy of the different numerical modelling techniques. 相似文献
48.
本文用对数正态分布对物理显影中常用的Au、Ag及Ag_2s胶体催化剂的颗粒大小的实验分布进行了拟合。理论分布与实验分布的比较表明:本实验条件下制备的十二组胶体溶液其颗粒大小都服从了对数正态分布,并且不依赖于胶体的组成、大小及制备方法。因此,它们很可能遵从了同样的成核成长规律。 相似文献
49.
Chien-Cheng Tsai 《Applied Surface Science》2006,253(4):1898-1902
Nanotube aggregates with high porosity were prepared from hydrothermal treatment of TiO2 particles in NaOH at 130 °C, followed by HCl rinsing to different pH values. Pore structure of the aggregates, which were mainly mesoporous, was characterized by analyzing the N2 sorption isotherm with different methods including the t-plot and density function theory. The surface area, pore volume and mean pore size of the aggregates increased with the rinsing acidity to reach a maximum (e.g. 400 m2/g in surface area) at pH 1.6 and then decreased with further increase of the acidity. The crystalline phase and composition of the aggregates were, as well, significantly affected by the acidity of the post-treatment rinsing. Large-surface area aggregates were of loosely-attached nanotubes, composed of both anatase TiO2 and H2Ti2O5·H2O, obtained under a mildly acidic rinsing condition, while basic or highly acidic conditions resulted in the formation of closely coagulated dense structures consisting of different crystalline phases. 相似文献
50.