全文获取类型
收费全文 | 6619篇 |
免费 | 251篇 |
国内免费 | 1244篇 |
专业分类
化学 | 3419篇 |
晶体学 | 6篇 |
力学 | 511篇 |
综合类 | 214篇 |
数学 | 1257篇 |
物理学 | 2707篇 |
出版年
2023年 | 1篇 |
2021年 | 3篇 |
2020年 | 4篇 |
2019年 | 4篇 |
2018年 | 2篇 |
2017年 | 2篇 |
2016年 | 11篇 |
2015年 | 27篇 |
2014年 | 18篇 |
2013年 | 81篇 |
2012年 | 93篇 |
2011年 | 1177篇 |
2010年 | 602篇 |
2009年 | 614篇 |
2008年 | 95篇 |
2007年 | 100篇 |
2006年 | 167篇 |
2005年 | 351篇 |
2004年 | 1214篇 |
2003年 | 719篇 |
2002年 | 559篇 |
2001年 | 373篇 |
2000年 | 149篇 |
1999年 | 157篇 |
1998年 | 179篇 |
1997年 | 118篇 |
1996年 | 96篇 |
1995年 | 63篇 |
1994年 | 69篇 |
1993年 | 264篇 |
1992年 | 208篇 |
1991年 | 125篇 |
1990年 | 125篇 |
1989年 | 127篇 |
1988年 | 105篇 |
1987年 | 6篇 |
1986年 | 62篇 |
1985年 | 10篇 |
1984年 | 23篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1936年 | 2篇 |
1908年 | 1篇 |
排序方式: 共有8114条查询结果,搜索用时 15 毫秒
1.
Understanding and control of the surface properties such as molecular orientations are of great importance in numerous applications of ionic liquids. However, there remain discrepancies among the previous experimental and theoretical studies on the surface orientation and structures of room temperature ionic liquids(RTIL) systems. In this article, the orientation of 1-butyl-3-methylimidazolium([bmin]) cation at the air/liquid interface of a characteristic RTIL, 1-butyl-3-methylimidazolium hexafluorophosphate([bmim][PF6]), was investigated by the sum frequency generation vibrational spectroscopy(SFG-VS). Detailed polarization and experimental configuration analyses of the SFG-VS spectra showed the possibility of a small spectral splitting in the CH3 symmetric stretching region, which can be further attributed to the probable existence of multiple orientations for the interfacial [bmim] cations. In addition, the(N)–CH3 vibrations were absent, ruling out the prediction by several recent molecular dynamics simulations which state that portions of the [bmim] cations orient with a standing-up(N)–CH3 group at the ionic liquid surface. Hence, new realistic theoretical models have to be developed to reflect the complex nature of the ionic liquid surface. 相似文献
2.
Junshan Jing Yunfei Wu Jun Tao Huizheng Che Xiangao Xia Xiaochun Zhang Peng Yan Deming Zhao Leiming Zhang 《中国颗粒学报》2015,(1):144-154
Year-round measurements of the mass concentration and optical properties of fine aerosols(PM2.5) from June 2009 to May 2010 at an urban site in Beijing were analyzed.The annual mean values of the PM2.5 mass concentration,absorption coefficient(Ab),scattering coefficient(Sc) and single scattering albedo(SSA)at 525 nm were 67±66μg/m3,64 ±62 Mm-1,360 ±405 Mm-1 and 0.82 ±0.09,respectively.The bulk mass absorption efficiency and scattering efficiency of the PM2.5 at 525 nm were 0.78 m2/g and 5.55 m2/g,respectively.The Ab and Sc showed a similar diurnal variation with a maximum at night and a minimum in the afternoon,whereas SSA displayed an opposite diurnal pattern.Significant increases in the Ab and Sc were observed in pollution episodes caused by the accumulation of pollutants from both local and regional sources under unfavorable weather conditions.Aerosol loadings in dust events increased by several times in the spring,which had limited effects on the Ab and Sc due to the low absorption and scattering efficiency of dust particles.The frequency of haze days was the highest in autumn because of the high aerosol absorption and scattering under unfavorable weather conditions.The daily PM2.5concentration should be controlled to a level lower than 64 μg/m3 to prevent the occurrence of haze days according to its exponentially decreased relationship with visibility. 相似文献
3.
Zhen Xi 《中国科学:化学(英文版)》2015,(3):434-435
Redox-based post-translational modification of protein thiols has become an attractive strategy in cellular homeostasis and cell signaling.Due to the reductive end of the redox buffer network,the vicinal dithiol-containing proteins(VDPs)maintains an appropriate oxidation-reduction state of proteins through the reversible transformation from vicinal dithiols to disulfide,which is responsible for a variety of 相似文献
4.
5.
We describe general methods for enumerating subsemigroups of finite semigroups and techniques to improve the algorithmic efficiency of the calculations. As a particular application we use our algorithms to enumerate all transformation semigroups up to degree 4. Classification of these semigroups up to conjugacy, isomorphism and anti-isomorphism, by size and rank, provides a solid base for further investigations of transformation semigroups. 相似文献
6.
James East 《Periodica Mathematica Hungarica》2017,75(2):273-285
Let \({\mathcal {I}}^*_X\) be the dual symmetric inverse monoid on an infinite set X. We show that \({\mathcal {I}}^*_X\) may be generated by the symmetric group \({\mathcal {S}}_X\) together with two (but no fewer) additional block bijections, and we classify the pairs \(\alpha ,\beta \in {\mathcal {I}}^*_X\) for which \({\mathcal {I}}^*_X\) is generated by \({\mathcal {S}}_X\,\cup \,\{\alpha ,\beta \}\). Among other results, we show that any countable subset of \({\mathcal {I}}^*_X\) is contained in a 4-generated subsemigroup of \({\mathcal {I}}^*_X\), and that the length function on \({\mathcal {I}}^*_X\) (and its finitary power semigroup) is bounded with respect to any generating set. 相似文献
7.
Chathuranga S. L. Rathnamalala Selena Hernandez Dr. Melissa Y. Lucero Chelsea B. Swartchick Dr. Abdul Kalam Shaik Prof. Dr. Nathan I. Hammer Amanda K. East Prof. Dr. Steven R. Gwaltney Prof. Dr. Jefferson Chan Prof. Dr. Colleen N. Scott 《Angewandte Chemie (International ed. in English)》2023,62(13):e202214855
Shortwave infrared (SWIR) dyes are characterized by their ability to absorb light from 900 to 1400 nm, which is ideal for deep tissue imaging owing to minimized light scattering and interference from endogenous pigments. An approach to access such molecules is to tune the photophysical properties of known near-infrared dyes. Herein, we report the development of a series of easily accessible (three steps) SWIR xanthene dyes based on a dibenzazepine donor conjugated to thiophene ( SCR-1 ), thienothiophene ( SCR-2 ), or bithiophene ( SCR-3 ). We leverage the fact that SCR-1 undergoes a bathochromic shift when aggregated for in vivo studies by developing a ratiometric nanoparticle for NO ( rNP-NO ), which we employed to successfully visualize pathological levels of nitric oxide in a drug-induced liver injury model via deep tissue SWIR photoacoustic (PA) imaging. Our work demonstrates how easily this dye series can be utilized as a component in nanosensor designs for imaging studies. 相似文献
8.
Hideyasu China Nami Kageyama Hotaka Yatabe Naoko Takenaga Toshifumi Dohi 《Molecules (Basel, Switzerland)》2021,26(7)
We report a convenient and practical method for the preparation of nonexplosive cyclic hypervalent iodine(III) oxidants as efficient organocatalysts and reagents for various reactions using Oxone® in aqueous solution under mild conditions at room temperature. The thus obtained 2-iodosobenzoic acids (IBAs) could be used as precursors of other cyclic organoiodine(III) derivatives by the solvolytic derivatization of the hydroxy group under mild conditions of 80 °C or lower temperature. These sequential procedures are highly reliable to selectively afford cyclic hypervalent iodine compounds in excellent yields without contamination by hazardous pentavalent iodine(III) compound. 相似文献
9.
各向异性本构关系在板料成形数值模拟中的应用 总被引:7,自引:0,他引:7
对几种能表达面内各向异性的屈服准则Hill、Barlat-Lian、Barlat进行了比较。以弹性变形服从各向同性广义虎克定律的情况下,给出了基于张量算法推导的弹塑性本构关系的一般表达式,并由此导出了相应屈服准则的弹塑性本构关系的显式表达。借助ABAQUS软件本构模块用户子程序接口,分别实现了这些屈服准则在ABAQUS的嵌入。以模拟方形盒的拉延过程为例,分析了不同的屈服准则在板料成形过程数值模拟中的应用。模拟结果表明,基于弹塑性本构关系一般表达所列出的相应屈服准则的显式表达式是正确的;在采用壳元来模拟板料成形时,采用Barlat准则的模拟结果和采用Barlat-Lian准则的结果差别不大。 相似文献
10.