全文获取类型
收费全文 | 33224篇 |
免费 | 3510篇 |
国内免费 | 6066篇 |
专业分类
化学 | 29190篇 |
晶体学 | 1314篇 |
力学 | 791篇 |
综合类 | 232篇 |
数学 | 2080篇 |
物理学 | 9193篇 |
出版年
2024年 | 71篇 |
2023年 | 379篇 |
2022年 | 949篇 |
2021年 | 888篇 |
2020年 | 1121篇 |
2019年 | 1103篇 |
2018年 | 913篇 |
2017年 | 1258篇 |
2016年 | 1287篇 |
2015年 | 1167篇 |
2014年 | 1559篇 |
2013年 | 2820篇 |
2012年 | 1925篇 |
2011年 | 2372篇 |
2010年 | 1990篇 |
2009年 | 2263篇 |
2008年 | 2308篇 |
2007年 | 2285篇 |
2006年 | 2134篇 |
2005年 | 1993篇 |
2004年 | 1771篇 |
2003年 | 1452篇 |
2002年 | 1242篇 |
2001年 | 1051篇 |
2000年 | 999篇 |
1999年 | 805篇 |
1998年 | 682篇 |
1997年 | 602篇 |
1996年 | 516篇 |
1995年 | 526篇 |
1994年 | 466篇 |
1993年 | 396篇 |
1992年 | 306篇 |
1991年 | 218篇 |
1990年 | 138篇 |
1989年 | 135篇 |
1988年 | 118篇 |
1987年 | 72篇 |
1986年 | 75篇 |
1985年 | 67篇 |
1984年 | 52篇 |
1983年 | 33篇 |
1982年 | 43篇 |
1981年 | 46篇 |
1980年 | 49篇 |
1979年 | 43篇 |
1978年 | 32篇 |
1977年 | 27篇 |
1976年 | 14篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
Katsunori Nishimura Rie Hidaka Fumitoshi Hirayama Hidetoshi Arima Kaneto Uekama 《Journal of inclusion phenomena and macrocyclic chemistry》2006,54(1-2):85-88
Geometries, electronic properties and NMR-shielding of cucurbit[5]uril, decamethylcucurbit[5]uril, cucurbit[6]uril, cucurbit[7]uril,
and cucurbit[8]uril are investigated with DFT calculations. All molecules are highly symmetrical with a distinct geometric
flexibility. In addition with a characteristic partial charge distribution these findings account for their chemical complex
building ability. 相似文献
152.
A straightforward and effective procedure for the conversion of benzylic, allylic and aliphatic alcohols to the corresponding iodides using Ph3P/I2 under solvent-free conditions using microwave irradiation is reported. 相似文献
153.
A.G. Dobrikova M.I. Dimitrov S.G. Taneva I.B. Petkanchin 《Colloids and surfaces. B, Biointerfaces》2007,56(1-2):114-Optics
Using microelectrophoresis and electric light scattering techniques, we investigated the adsorption characteristics, surface coverage and surface electric parameters of superstructures from two isoforms of plastocyanin, PCa and PCb, in an oxidized state adsorbed on 3b2;-ferric hydrous oxide particles. The surface electric charge and electric dipole moments of the composite particles and the thickness of the protein adsorption layer are determined in a wide pH range, at different ionic strengths and concentration ratios of PC to 3b2;-FeOOH. The adsorption of the two proteins was found to shift the particles’ isoelectric point and to alter the total electric charge and the electric dipole moments of the oxide particles to different extent. A “reversal” in the direction of the permanent dipole moment is observed at lower pH for PCb- than for PCa-coated oxide particles. Strict correlation is found between the changes in the electrokinetic charge of the composite particles and the variation in their “permanent” dipole moments. Data suggest that the adsorption of the proteins is driven by electrostatic and/or hydrophobic interactions with the oxide surfaces dependent on pH. The adsorption behaviour is consistent with the involvement of the “eastern” and “northern” patches of the plastocyanin molecules in their adsorption on the oxide surfaces that are differently charged depending on pH. 相似文献
154.
用微量热法研究了Er3+、TMP{TMP=5,10,15,20-四(4-甲氧基苯基)卟啉}及其阳离子铒卟啉配合物[Er(TMP)(H2O)3]Cl对金黄色葡萄球菌生长作用的生物热动力学特征,求算了在Er3+、TMP和[Er(TMP)(H2O)3]Cl作用下,金黄色葡萄球菌生长的热动力学参数。实验结果表明:TMP对金黄色葡萄球菌生长的作用表现为单向的抑制作用,而Er3+和[Er(TMP)(H2O)3]Cl对金黄色葡萄球菌的生长有双向调节作用。在低浓度下,Er3+对金黄色葡萄球菌生长的刺激作用强于[Er(TMP)(H2O)3]Cl;在较高浓度下,[Er(TMP)(H2O)3]Cl对金黄色葡萄球菌生长的抑制作用显著强于Er3+。对金黄色葡萄球菌的抗菌活性为:[Er(TMP)(H2O)3]Cl>>TMP>Er3+。对相互作用机理做了初步探讨。 相似文献
155.
156.
本文研究了新水溶性5,10,15,20-四(4-甲氧基-3-磺酸苯基)卟啉[T(4-MOP)PS4]的反相高效液相色谱(HPLC)分离条件。采用ShimpackPREP-ODS半制备色谱柱,用含有10mmol/L四乙基碘化铵的乙腈-水(体积比25:75)为流动相,流速18mL/min,于418nm波长下检测。[T(4-MOP)PS4]与合成中生成的杂质组分完全分离。经此制备的卟啉纯度高,已成功地应用于自来水样中微量钴、锌、铜离子的HPLC测定中。 相似文献
157.
B. S. Fedorov M. A. Fadeev V. V. Arakcheeva G. V. Strukov N. I. Golovina R. F. Trofimova G. V. Shilov L. O. Atovmyan 《Russian Chemical Bulletin》1994,43(12):2087-2090
A novel heterocyclic compound, 4-acetoxy-5,6-dihydro-5,5-dinitro-2H-1,3-oxazineN-oxide, has been synthesized by the reaction of the dipotassium salt of 1,1,5,5-tetranitro-3-oxapentane with aqueous acetic acid. The synthesized compound has been studied by X-ray diffraction analysis.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2207ȁ3;2210, December, 1994.We would like to thank G. V. Lagodzinskaya (Institute of Chemical Physics in Chernogolovka, Russian Academy of Sciences) for recording and interpreting1H NMR spectra, A. M. Korolev (Institute of Chemical Physics in Chernogolovka, Russian Academy of Sciences) for helpful discussion, and V. I. Fetisov (Institute of Physiologically Active Compounds, Russian Academy of Sciences) for performing quantum-chemical calculations by the AM1 SCF MO LCAO method. 相似文献
158.
Organic chelating reagent influences upon the redox adsorption of activated carbon fibertowards Au3- were systematically investigated. The experimental results indicated that the presenceof organic chelating reagent on activated carbon fiber strongly affects adsorption capacity ofactivated carbon fiber towards Au3+. The reduction-adsorption amount of Au3+ increased three timesby the presence of 8-quinolinol. Furthermore, The reduction-adsorption amount of Au3+ depended onthe pH value of adsorption and temperature. 相似文献
159.
The solid state reaction of 3-methyl-1-phenyl-5-pyrazolone (MPP) with aromatic aldehydes and ke-tones benzil derivatives and imides,and the solid state Michael addition reaction of MPP with 4-arylidene-3-methyl-1-phenyl-5-pyrnzolone 2 were investigated.Some new solid state reactions between the reactants were found,from which a series of new compounds were obtained The structures of the products were identified by IR,1H NMR,MS,elemental analyses and also by X-ray crystal analysis,and the reaction mechanism of MPP with aromatic aldehydes and ketones was proposed 相似文献
160.
Reaction of copper powder with 2-thenoyltrifluoroacetone and PPh3 yielded the complex [Cu(C8H4O2F3S)(PPh3)2], which have been characterized by elemental analysis and IR spectra. The crystal is monoclinic, space group P21/n , a=1.0584(1), b=1.6738(1), c=2.2728(9) nm; β =94.22(2); V =4.0152 nm 3; Z=4; Dc=1.299 g3;cm-3; R=0.048, RW=0.054. Copper (Ⅰ) ion is coordinated by two O and two P atoms forming distorted tetrahedron. 相似文献