全文获取类型
收费全文 | 10636篇 |
免费 | 1567篇 |
国内免费 | 1247篇 |
专业分类
化学 | 7553篇 |
晶体学 | 118篇 |
力学 | 681篇 |
综合类 | 67篇 |
数学 | 1287篇 |
物理学 | 3744篇 |
出版年
2024年 | 56篇 |
2023年 | 262篇 |
2022年 | 398篇 |
2021年 | 388篇 |
2020年 | 429篇 |
2019年 | 446篇 |
2018年 | 387篇 |
2017年 | 375篇 |
2016年 | 517篇 |
2015年 | 512篇 |
2014年 | 585篇 |
2013年 | 801篇 |
2012年 | 887篇 |
2011年 | 938篇 |
2010年 | 652篇 |
2009年 | 588篇 |
2008年 | 724篇 |
2007年 | 603篇 |
2006年 | 551篇 |
2005年 | 411篇 |
2004年 | 369篇 |
2003年 | 278篇 |
2002年 | 310篇 |
2001年 | 211篇 |
2000年 | 202篇 |
1999年 | 257篇 |
1998年 | 181篇 |
1997年 | 131篇 |
1996年 | 142篇 |
1995年 | 134篇 |
1994年 | 99篇 |
1993年 | 108篇 |
1992年 | 88篇 |
1991年 | 86篇 |
1990年 | 77篇 |
1989年 | 58篇 |
1988年 | 42篇 |
1987年 | 36篇 |
1986年 | 21篇 |
1985年 | 31篇 |
1984年 | 20篇 |
1983年 | 14篇 |
1982年 | 12篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
Seventeen 1-aryl-2,2-dichlorocyclopropanes were examined by using IR, 13C NMR, and mass spectrometry. The data obtained from IR and 13C NMR spectra indicate that the bond strength of carbon-chlorine on the cyclopropane ring and the electron density of that carbon depend on the substituent. The mass fragmentation patterns of compounds in this series resemble those of the dibromo analogues. The fragmentation mechanism is proposed to involve the formation of indenium ion through an electrocyclization. 相似文献
82.
83.
Fourteen new mixed ligand complexes of lanthanide acetylacetonate and dibenzo-18- crown-6 (DB18C6) were prepared by three different methods. The composition of the complexes was shown to be Ln(acac)· DB18C6 by elemental analysis and X-ray powder diffraction. Infrared spectra of the complexes were investigated, and the results indicate that their absorption bands in the region of 400—4000 cm?1 are complicated and without much difference from each other, but in the far infrared region various absorption bands of Ln—O can be observed and they changes regularly with the atomic number of lanthanides. 相似文献
84.
该文用顺磁离子对其近邻~(13)C核的NMR吸收增宽效应,系统地研究了抗坏血酸在不同溶剂中对金属离子Mn~(2+)、Gd~(3+)的配合行为.在水溶液中,抗坏血酸可通过两种配合方式与Mn~(2+)作用,但与Gd~(3+)的作用只有一种稳定的结构.在水中抗坏血酸对金属的配位活性部位分别是1位羟基氧,3位离解的羟基氧和6位羟基氧.在DMSO中,3位羟基由于H~+对该基团的静电遮蔽而变得对金属离子Mn~(2+)表现为配位惰性,同时6位羟基配位活性较大增强.对Gd~(3+)来说,此时没有优势配位活性部位存在.文章还讨论了抗坏血酸在H_2O-DMSO混合溶剂中的~(13)C NMR谱及在DMSO中NaOH对其~(13)C NMR谱及其与金属络合结构的影响. 相似文献
85.
The black carbon aerosols are now recognized for their potential impact on climate and the halogenated compounds are thought to be very important in atmospheric chemistry. However, there are very few studies on the interactions between soot aerosols and halogenated compounds. We report the measurement of the uptake of CH3I on soot. The measured uptake coefficient is 0.0103 ± 0.0015 at a total pressure of 2–4 Torr and 298 K. The results suggest that the uptake of CH3I occurs efficiently on soot particles. The present work suggests that heterogeneous loss of CH3I on soot may influence the concentration of CH3I throughout the atmosphere. 相似文献
86.
设$(A,B,V,W,\psi,\phi)$是一个Morita Context,具有一对零态射$\psi=0$, $\phi=0$, $C =\left ( \begin{array} {cc}A & V \\W & B \end{array}\right)$是对应的Morita Context环.本文给出了$C$与$A,B,V,W$之间关于环的$\pi$-正则性、semiclean性、Mophic性和环的Exchgange性、Potent性、GM性的关系. 相似文献
87.
本文考察了以微波等离子体炬(MPT)为光源,电热钽丝环进样时,溶液中共存元素对发射信号的影响。 相似文献
88.
89.
A three-dimensional Ising-like model doped with anti-ferromagnetic (AFM) bonds is proposed to investigate the magnetic properties
of a doped triangular spin-chain system by using a Monte-Carlo simulation. The simulated results indicate that a steplike
magnetization behavior is very sensitive to the concentration of AFM bonds. A low concentration of AFM bonds can suppress
the stepwise behavior considerably, in accordance with doping experiments on Ca3Co2O6. The analysis of spin snapshots demonstrates that the AFM bond doping not only breaks the ferromagnetic ordered linear spin
chains along the hexagonal c-axis but also has a great influence upon the spin configuration in the ab-plane.
相似文献
90.
We report a new approach for the self-assembly of cuboid micro-parts onto Si substrates to construct three-dimensional microstructures. To perform assembly, the Si substrates are prepared with a deep cavity array as binding sites. An aggregate composed of hundreds of uniformly aligned micro-parts is formed at the C10F18-H2O interface. The micro-parts are arranged by passing the substrate through the aggregate of micro-parts, thus the micro-parts are left on the substrate, and then the substrate is vibrated ultrasonically in the solution, making it possible for the micro-parts to fall into the cavities on the substrate. Finally the substrate is pulled out of the solution after assembly. This technique could give a high yield of up to 70%, providing a new method for micro-assembly. 相似文献