全文获取类型
收费全文 | 8857篇 |
免费 | 1124篇 |
国内免费 | 668篇 |
专业分类
化学 | 7004篇 |
晶体学 | 191篇 |
力学 | 923篇 |
综合类 | 23篇 |
数学 | 659篇 |
物理学 | 1849篇 |
出版年
2024年 | 22篇 |
2023年 | 64篇 |
2022年 | 169篇 |
2021年 | 203篇 |
2020年 | 391篇 |
2019年 | 244篇 |
2018年 | 208篇 |
2017年 | 261篇 |
2016年 | 387篇 |
2015年 | 381篇 |
2014年 | 408篇 |
2013年 | 648篇 |
2012年 | 596篇 |
2011年 | 487篇 |
2010年 | 447篇 |
2009年 | 580篇 |
2008年 | 629篇 |
2007年 | 674篇 |
2006年 | 554篇 |
2005年 | 448篇 |
2004年 | 457篇 |
2003年 | 405篇 |
2002年 | 322篇 |
2001年 | 224篇 |
2000年 | 210篇 |
1999年 | 233篇 |
1998年 | 200篇 |
1997年 | 147篇 |
1996年 | 103篇 |
1995年 | 114篇 |
1994年 | 68篇 |
1993年 | 65篇 |
1992年 | 52篇 |
1991年 | 40篇 |
1990年 | 25篇 |
1989年 | 29篇 |
1988年 | 22篇 |
1987年 | 17篇 |
1986年 | 18篇 |
1985年 | 15篇 |
1984年 | 23篇 |
1983年 | 4篇 |
1982年 | 14篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 10篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1970年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
82.
In the present paper, on the basis of our work. advances in study of the catalysts of polyacid-type hydrotalcite-like are reported and reviewed. Using polyoxometalates (POM) as pillaring species and layered double hydroxides (LDH) as host matter, a new class of catalytic materials, LDHPOM, has been synthesized by five different methods. Their acidic and oxidative catalytic properties have been investigated by several research groups. The above mentioned information is given in this review. 相似文献
83.
D. N. Dybtsev M. P. Yutkin E. V. Peresypkina A. V. Virovets Y. Hasegawa H. Nishihara V. P. Fedin 《Russian Chemical Bulletin》2007,56(9):1782-1786
The reaction of Co(NO3)2·6H2O with 1,3,5-benzenetricarboxylic acid (H3btc, trimesic acid) in DMF at 100 °C afforded the coordination polymer [Co3(dmf)6(btc)(Hbtc)(H2btc)]··9H2O (1) (dmf is N,N′-dimethylformamide, DMF). According to the X-ray diffraction study, the metal-organic coordination polymer is composed of
planar honeycomb (6,3) networks, in which the organic benzenetricarboxylate anions and the inorganic Co2+ cations play a role of three-connected nodes. Disordered water molecules are intercalated between the layers. A study of
the magnetic properties showed the presence of a weak antiferromagnetic coupling between the Co2+ ions (S = 3/2).
Dedicated to Academician G. A. Abakumov on the occasion of his 70th birthday.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1719–1723, September, 2007. 相似文献
84.
85.
The synthesis of four new oxo‐centered Fe clusters ( 1 a – c , 2 ) of the form [FeIII3(μ3‐O)(CH2=CHCOO)6] with acrylate as the bridging ligand gives rise to potentially intrinsically chiral oxo‐centered {M3} trimers that show a tendency to spontaneously resolve upon crystallization. For instance, 1 a , [FeIII3(μ3‐O)(CH2=CHCOO)6‐(H2O)3]+, crystallizes in the chiral space group P31 as a chloride salt. Crystallization of 1 b , [Fe3(μ3‐O)(C2H3CO2)6(H2O)3]NO3?4.5H2O, from aqueous solution followed by recrystallization from acetonitrile also gives rise to spontaneous resolution to yield the homochiral salt [Fe3(μ3‐O)(C2H3CO2)6‐(H2O)3]NO3?CH3CN of 1 c (space group P212121). Furthermore, the reaction of 1 a with hexamolybdate in acetonitrile gives the helical coordination polymer {[(Fe3(μ3‐O)L6(H2O))(MoO4)‐(Fe3(μ3‐O)L6(H2O)2)]?2CH3CN?H2O}∞ 2 (L: H2C?CHCOO), which crystallizes in the space group P21. The nature of the ligand geometry allows the formation of atropisomers in both the discrete ( 1 a – c ) and linked {Fe3} clusters ( 2 ), which is described along with a magnetic analysis of 1 a and 2 . 相似文献
86.
C. D. Eisenbach A. Göldel M. Terskan-Reinold U. S. Schubert 《Colloid and polymer science》1998,276(9):780-785
Transmission electron microscopy (TEM) studies on bipyridine (bpy) containing block copolymer systems showed the formation
of nanoscopic polymer–ion complexes through complexation with copper(I) ions which segregated to highly ordered columnar domains
of mesoscopic dimensions. The domains, i.e. stacks of [(bpy)2Cu(I)] complex moieties could be visualized by complementary TEM techniques. First, electron energy loss spectra (EELS) showed
the absorption edges of copper and nitrogen, which are specific for the bipyridine copper complexes. The element spectroscopic
imaging (ESI) technique allowed the imaging of the net copper and net nitrogen distribution, and the coinciding pictures exhibited
a microphase separated system in the case of a 3-block copolymer with complexed end segments. High resolution elastic bright
field images showed interference lines with a line to line distance of about 8 A which could be related to the Cu–Cu distance
in staggered Cu(I)–bipyridine complexes.
Received: 6 August 1997 Accepted: 28 April 1998 相似文献
87.
单斜层状LiMnO2的球磨-离子交换法合成及其电化学性能研究 总被引:2,自引:0,他引:2
通过球磨促进固相反应法合成出了具有单斜层状结构的前驱物NaMnO2,随后通过离子交换得到了单斜层状LiMnO2。XRD测试结果显示产物为单相。扫描电镜(SEM)和透射电镜(TEM)观测结果显示LiMnO2的粒子尺寸为300~500 nm,HRTEM分析显示干扰条纹的间距为0.485 nm,基本对应于m-LiMnO2的(001)晶面间距。红外吸收光谱(IR)和X射线光电子能谱(XPS)被用来测量m-LiMnO2中Mn-O键的伸缩和弯曲振动吸收和Mn元素的价态。合成的m-LiMnO2在电化学充放电循环初期表现了较好的电化学性能,但其循环寿命仍需要进一步改善。 相似文献
88.
89.
《Arabian Journal of Chemistry》2022,15(11):104272
Yinlan lipid regulatory capsule (YL) is a composite traditional Chinese medicine (TCM) new drug to alleviate hyperlipidemia, while its therapeutic mechanism in vivo was not clarified with nontargeted metabolomics investigation. An animal model was established in rats fed a high-fat diet, and their body weights, body mass index (BMI) and blood cholesterol levels were measured. Serum, liver and kidney tissue samples were also extracted for PXR-CYP3A4-ABCB1-FXR signaling pathway research using PCR and UHPLC–MS. The obtained plasma samples were analyzed by UHPLC-Q-TOF-MS metabolomic investigation, which revealed PXR-CYP3A4-related metabolites and changes induced by YL. Finally, the key metabolites were chosen as index components, and their levels in the serum, liver, small intestine and bile were used for simultaneous UHPLC–MS-MS determination. The results indicated that YL was effective in rebalancing blood TG and TC levels (compared to controls). With respect to the PXR-CYP3A4-ABCB1 pathway, as a result of YL’s effect, gene expression or activity of the two targets decreased significantly in both the liver and kidney. The same trend was observed in the serum samples mentioned above. Metabolomics screening and data revealed that 44 metabolites can be regarded as biomarkers related to hyperlipidemia, fatty acids synthesis, and body energy consumption, as well as synthesis, transportation and exertion of cholesterol. YL’s treatment focused on 26 of them, primarily bile acids, indicating that the antihyperlipidemic effect of this drug lies in its inhibitory activity of cholesterol metabolism. Subsequent analysis of those in vivo components revealed that significant increases (compared to the model group) occurred in the blood, liver, small intestine and bile in groups that received medium and high doses of YL (while the low dose was relatively unchanged). Those target components exhibit a close relationship with PXR and/or CYP3A4. The use of YL repressed PXR expression and subsequently decreased CYP3A4 activity. As a result, synthesis of related bile acids increased, while cholesterol levels decreased, consequently leading to the attenuation of hyperlipidemia. This study comprehensively investigated the antihyperlipidemia mechanism of YL based on its repression of PXR-CYP3A4 activity and related metabolite yield, establishing an accurate method for evaluating the therapeutic effect of YL. 相似文献
90.
Guang-Hua Cui Jian-Rong Li Ruo-Hua Zhang Xian-He Bu 《Journal of Molecular Structure》2005,740(1-3):187-191
Two new coordination polymers, [Eu2(L)3(H2O)2]n 1 and {[Tb2(L)3(H2O)2]·H2O}n 2, (H2L=succinic acid) have been synthesized by the reaction of H2L with nitrate salts of Eu(III) or Tb(III) under hydrothermal conditions. The X-ray diffraction analysis reveals that the two complexes are constructed by L bridging the chains of edge-sharing EuO8(H2O) or TbO8(H2O) polyhedra to form 3D network structure. 1 and 2 possess different topological structures due to the difference in the conformations of L. The solid photoluminescence of 1 and 2 was also investigated in room temperature. 相似文献