全文获取类型
收费全文 | 5044篇 |
免费 | 655篇 |
国内免费 | 498篇 |
专业分类
化学 | 1993篇 |
晶体学 | 42篇 |
力学 | 506篇 |
综合类 | 68篇 |
数学 | 1357篇 |
物理学 | 2231篇 |
出版年
2023年 | 48篇 |
2022年 | 117篇 |
2021年 | 118篇 |
2020年 | 122篇 |
2019年 | 107篇 |
2018年 | 105篇 |
2017年 | 181篇 |
2016年 | 217篇 |
2015年 | 177篇 |
2014年 | 262篇 |
2013年 | 499篇 |
2012年 | 311篇 |
2011年 | 374篇 |
2010年 | 302篇 |
2009年 | 341篇 |
2008年 | 332篇 |
2007年 | 348篇 |
2006年 | 287篇 |
2005年 | 246篇 |
2004年 | 260篇 |
2003年 | 214篇 |
2002年 | 154篇 |
2001年 | 122篇 |
2000年 | 88篇 |
1999年 | 107篇 |
1998年 | 81篇 |
1997年 | 102篇 |
1996年 | 88篇 |
1995年 | 61篇 |
1994年 | 62篇 |
1993年 | 43篇 |
1992年 | 46篇 |
1991年 | 39篇 |
1990年 | 28篇 |
1989年 | 27篇 |
1988年 | 24篇 |
1987年 | 15篇 |
1986年 | 14篇 |
1985年 | 14篇 |
1984年 | 14篇 |
1983年 | 8篇 |
1982年 | 11篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 16篇 |
1978年 | 13篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1975年 | 5篇 |
1973年 | 6篇 |
排序方式: 共有6197条查询结果,搜索用时 156 毫秒
11.
12.
The diffusion of the anti-microbial chlorhexidine digluconate (CHG) has been studied in C. albicans biofilms by time-of-flight secondary-ion mass spectrometry (TOF-SIMS). C. albicans has been shown to become resistant to common anti-microbial agents, including CHG, when growing as a biofilm. Mass transport resistance within biofilms has commonly been suggested as a resistance mechanism, but measurement of transport for most anti-microbial agents in biofilms has proven extremely difficult because of the heterogeneity of the biofilms and the difficulty in detecting these agents within an intact biofilm. In this study, TOF-SIMS has been used to study the transport of CHG and glucose in a frozen hydrated biofilm. The TOF-SIMS images reveal a progression of CHG from the top of the biofilm to its base with time. Images suggest that there are channels within the biofilm and show preferential binding of CHG to cellular components of the biofilm. Additionally, both living and dead cells can be identified in the TOF-SIMS images by the sequestration of K+ and the presence of cell markers. This study demonstrates that TOF-SIMS has the unique potential to simultaneously observe the presence of an antimicrobial agent, concentration of nutrients, and the viability of the cell population. 相似文献
13.
We consider Markov processes built from pasting together pieces of strong Markov processes which are killed at a position
dependent rate and connected via a transition kernel. We give necessary and sufficient conditions for local absolute continuity
of probability laws for such processes on a suitable path space and derive an explicit formula for the corresponding likelihood
ratio process. The main tool is the consideration of the process between successive jumps – what we call ‘elementary experiments’
– and criteria for absolute continuity of laws of the process there. We apply our results to systems of branching diffusions
with interactions and immigrations.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
14.
平行机半在线排序问题研究(Ⅰ) 总被引:15,自引:1,他引:14
对半在线平行机排序问题的研究进展作了详细综述和进一步探讨。文章给出半在线排序问题的背景、定义、分类和求解。介绍它们定义和在不同机器环境和目标函数下半在线排序问题分类,以及第一类半在线模型的近似算法的设计及其竞争比分析。 相似文献
15.
16.
Noboru Nakatani 《Optical Review》2003,10(4):206-210
This paper describes a compulsorily phase locked differential interferometer using an orthogonally polarized light source of a modulated LD with high extinction ratio to reduce non-linearity of the interferometer caused by polarization cross-talk. The current modulated LD is used as a light source to make the interferometer compact and for the scanning phase of the interferometer. The interferometer is operated compulsorily at the maximum inclination point of the fringe intensity curve by fringe scanning and an electric system. A Wollaston prism of high extinction ratio (50 dB) is used to combine the polarizing beams and to make the polarization cross-talk very small. In one light source the polarized output beams are on the same propagation axis; in the other they have a small crossing angle (2.5 mrad ∼ 10 mrad) to completely exclude non-linearity of the interferometer causded by polarization cross-talk. Using jets of a gas mixture of nitrogen and ethylene, this interferometer was demonstrated to be useful in detecting the photothermal effect of a photothermal velocimeter under phase fluctuation in a turbulent flow. 相似文献
17.
18.
19.
一种新的WDM光网中的共享链路保护策略 总被引:2,自引:2,他引:0
研究了WDM光网中的链路保护问题.提出了一种新的共享链路保护策略--基于SRLG的共享链路保护策略(SRLG-SLP).SRLG(共享风险链路组)定义了对一条工作光通道分配保护资源时的资源可用性的约束.它规定任意两条有着同样故障风险或者说处于同一个SRLG的工作光通道不能利用同样的保护资源.另外,还提出了一种更加符合实际的单链路故障模型,其中链路故障间隔时间和链路故障保持时间被考虑作为两个独立的变量.基于该链路故障模型,通过大量的仿真试验,比较了专用链路保护(DLP)、共享链路保护(SLP)和提出的SRLG-SLP保护策略的资源利用率、保护效率以及业务中断率.结果显示,我们提出的SRLG-SLP在保护效率和业务中断率方面的保护性能远好于DLP和SLP,但会牺牲一些资源利用率. 相似文献
20.