全文获取类型
收费全文 | 28694篇 |
免费 | 1031篇 |
国内免费 | 161篇 |
专业分类
化学 | 19126篇 |
晶体学 | 233篇 |
力学 | 475篇 |
综合类 | 4篇 |
数学 | 4826篇 |
物理学 | 5222篇 |
出版年
2023年 | 175篇 |
2022年 | 305篇 |
2021年 | 535篇 |
2020年 | 500篇 |
2019年 | 540篇 |
2018年 | 546篇 |
2017年 | 504篇 |
2016年 | 987篇 |
2015年 | 833篇 |
2014年 | 916篇 |
2013年 | 1712篇 |
2012年 | 1819篇 |
2011年 | 2047篇 |
2010年 | 1259篇 |
2009年 | 1221篇 |
2008年 | 1777篇 |
2007年 | 1658篇 |
2006年 | 1551篇 |
2005年 | 1408篇 |
2004年 | 1142篇 |
2003年 | 965篇 |
2002年 | 836篇 |
2001年 | 579篇 |
2000年 | 498篇 |
1999年 | 401篇 |
1998年 | 313篇 |
1997年 | 308篇 |
1996年 | 386篇 |
1995年 | 273篇 |
1994年 | 292篇 |
1993年 | 271篇 |
1992年 | 263篇 |
1991年 | 206篇 |
1990年 | 200篇 |
1989年 | 151篇 |
1988年 | 140篇 |
1987年 | 156篇 |
1986年 | 152篇 |
1985年 | 184篇 |
1984年 | 189篇 |
1983年 | 127篇 |
1982年 | 152篇 |
1981年 | 122篇 |
1980年 | 127篇 |
1979年 | 96篇 |
1978年 | 82篇 |
1977年 | 82篇 |
1976年 | 74篇 |
1975年 | 59篇 |
1973年 | 72篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
132.
It was studied the tin phase composition of the electrodeposited alloys produced at different temperatures and current densities from an acid chloride/fluoride electrolyte and an acid chloride bath. Mössbauer spectra were consistent with a Ni3Sn4 intermetallic compound, dissolved tin, and a Cu?Sn intermetallic compound formed at the interface of the copper substrate. 相似文献
133.
Oscillatory change of pH occurs during the chromate-catalyzed decomposition of hydrogen peroxide in a weakly acidic medium at elevated temperature and at high initial concentration of hydrogen peroxide. In a closed system, there are only two or three periods, but sustained oscillation occurs in a CSTR. In a CSTR bistability is also found. In closed systems the temperature exhibits a great maximum (up to 15°C increase), in a CSTR sustained oscillation occurs at a constant stationary temperature. 相似文献
134.
By incorporating the holographic principle in a time-depending Λ-term cosmology, new physical bounds on the arbitrary parameters of the model can be obtained. Considering then the dark energy as a purely geometric entity, for which no equation of state has to be introduced, it is shown that the resulting range of allowed values for the parameters may explain both the coincidence problem and the universe accelerated expansion, without resorting to any kind of additional structures. 相似文献
135.
136.
A. Cerdán Vidal A. R. Maurí Aucejo M. Llobat Estellés C. Pascual Martí J. Simeón Martí 《Fresenius' Journal of Analytical Chemistry》1994,350(12):706-711
The possibility of identification of substances which have similar spectral behaviour by means of Apparent Content Curves has been studied. This study is carried out with absorption, excitation and emission spectra of several amphetamines of widespread pharmaceutical use. Results obtained show that amphetamine, phenylpropanolamine, pseudoephedrine, phenylephrine, epinephrine, dopamine and methoxyamphetamine can be identified with a probability of >95%. 相似文献
137.
Please forward books for review to the book review editor: Magdolna Hargittai, Structural Chemistry Research Group of the Hungarian Academy of Sciences, Eötvös University, H-1431 Budapest, Pf. 117, Hungary 相似文献
138.
R. Andreu I. Gayn J. Garín J. Orduna M. Savirn 《Journal of mass spectrometry : JMS》1994,29(6):321-325
The electron impact ionization mass spectra of 4,5-bis(alkylthio)-1,3-dithiole-2-thiones and their 1,2-dithiole-3-thione isomers were studied by accurate mass measurements and linked scans. The relative abundance of ions formed following the extrusion of S2, CS or CS2 allows an unambiguous isomer differentiation. Isomerization of molecular ions was studied by means of metastable ion analysis and collision-induced dissociation. The order of reactivity was analogous to that observed in isomerization under photochemical conditions. 相似文献
139.
The electron impact ionization mass spectra of o-, m- and p-bis(1,4-dithiafulven-6-yl)benzenes were studied by means of accurate mass measurements, metastable analysis and collision-induced dissociation. Differences observed in the spectra of the ortho isomers are due to a cyclization reaction leading to molecular ions with the same structure as those generated from certain cyclic compounds, as confirmed by comparison of linked scans at constant B/E of metastable and collisionally activated molecular ions. Parallels of this cyclization of molecular ions with their electrochemical or acid-induced isomerization are also discussed. 相似文献
140.
Oxyethylene macrocyclic compounds (crown-ethers) act as ligands of intracrystalline cations of certain layered silicates as montmorillonites. Stable intercalation materials are formed which are used to prepare organic-inorganic membranes by encapsulating these intercalation compounds with a poly-butadiene thin coating. Electrochemical Impedance Spectroscopy (EIS) is used to study the resulting composite membranes in contact with aqueous electrolytes. From the impedance plots, the ionic resistance of the membranes is obtained. The thickness of the polybutadiene coating is an important factor determining the ability of ions to pass across the membrane. Marked differences in the ionic resistance are observed as a function of the nature of the interlayer macrocyclic compound. For non-intercalated montmorillonite membranes, the ionic resistance is strongly reduced, whereas for some crown-ether intercalated materials such as 18-crown-6 and dibenzo 24-crown-8, iono-selective membranes are obtained. Concerning the nature of the electrolyte, cations exhibiting greater hydration energies show higher difficulties to pass through the membrane and, consequently, the ionic resistance increases. 相似文献