全文获取类型
收费全文 | 48353篇 |
免费 | 3537篇 |
国内免费 | 2597篇 |
专业分类
化学 | 24647篇 |
晶体学 | 310篇 |
力学 | 5497篇 |
综合类 | 752篇 |
数学 | 10629篇 |
物理学 | 12652篇 |
出版年
2024年 | 75篇 |
2023年 | 402篇 |
2022年 | 1221篇 |
2021年 | 1252篇 |
2020年 | 1251篇 |
2019年 | 1199篇 |
2018年 | 1079篇 |
2017年 | 1352篇 |
2016年 | 1812篇 |
2015年 | 1360篇 |
2014年 | 2003篇 |
2013年 | 3434篇 |
2012年 | 2782篇 |
2011年 | 2576篇 |
2010年 | 2197篇 |
2009年 | 2831篇 |
2008年 | 2797篇 |
2007年 | 3042篇 |
2006年 | 2623篇 |
2005年 | 2340篇 |
2004年 | 2262篇 |
2003年 | 1890篇 |
2002年 | 1526篇 |
2001年 | 1262篇 |
2000年 | 1191篇 |
1999年 | 1069篇 |
1998年 | 988篇 |
1997年 | 891篇 |
1996年 | 781篇 |
1995年 | 770篇 |
1994年 | 666篇 |
1993年 | 545篇 |
1992年 | 500篇 |
1991年 | 437篇 |
1990年 | 396篇 |
1989年 | 269篇 |
1988年 | 257篇 |
1987年 | 172篇 |
1986年 | 152篇 |
1985年 | 164篇 |
1984年 | 132篇 |
1983年 | 67篇 |
1982年 | 114篇 |
1981年 | 75篇 |
1980年 | 50篇 |
1979年 | 87篇 |
1978年 | 39篇 |
1977年 | 20篇 |
1976年 | 24篇 |
1975年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
Quantization of Underdamped, Critically Damped, and Overdamped Electric Circuits with a Power Source
Jeong-Ryeol Choi 《International Journal of Theoretical Physics》2002,41(10):1931-1939
We have investigated the quantum mechanical effect of the underdamped, critically damped, and overdamped electric circuits with a power source. The charge of the underdamped circuit oscillates while those of the critically damped and overdamped ones don't. The wave function of the system of overdamped circuit represented parabolic cylinder function while underdamped circuit was represented by well-known Hermite polynomial. The eigenvalues of underdamped circuit is discrete while those of the critically damped and overdamped ones are given as continuously. 相似文献
63.
64.
The high-temperature cubic phase of non-stoichiometric strontium ferrite SrFeOx (2.5≤x≤3.0) has been studied by in situ neutron powder diffraction in air over the temperature range 300-1273 K. The composition of SrFeOx changes within the range 2.56≤x≤2.81 from 1273 to 673 K, respectively.Rietveld refinements of the diffraction patterns show that the high-temperature cubic phase of SrFeOx is consistent with a face-centred Fm3c structure. This structure leads to agreement with previous density measurements. This cell allows the high-temperature structure of SrFeOx to be described in terms of a solid solution of the composition end members. Cubic SrFeOx at high temperature is found to closely obey Vegard's law. The density of cubic SrFeOx is also found to exhibit a linear relationship with composition. 相似文献
65.
66.
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
67.
68.
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
69.
70.