全文获取类型
收费全文 | 68724篇 |
免费 | 6166篇 |
国内免费 | 13170篇 |
专业分类
化学 | 59717篇 |
晶体学 | 2265篇 |
力学 | 880篇 |
综合类 | 704篇 |
数学 | 6669篇 |
物理学 | 17825篇 |
出版年
2024年 | 65篇 |
2023年 | 1074篇 |
2022年 | 1114篇 |
2021年 | 2285篇 |
2020年 | 2255篇 |
2019年 | 2087篇 |
2018年 | 1712篇 |
2017年 | 2205篇 |
2016年 | 2298篇 |
2015年 | 2007篇 |
2014年 | 2752篇 |
2013年 | 6001篇 |
2012年 | 4225篇 |
2011年 | 4521篇 |
2010年 | 3948篇 |
2009年 | 4716篇 |
2008年 | 4590篇 |
2007年 | 4796篇 |
2006年 | 4456篇 |
2005年 | 3887篇 |
2004年 | 3723篇 |
2003年 | 3072篇 |
2002年 | 2610篇 |
2001年 | 2081篇 |
2000年 | 2741篇 |
1999年 | 2155篇 |
1998年 | 1782篇 |
1997年 | 1142篇 |
1996年 | 1026篇 |
1995年 | 1076篇 |
1994年 | 951篇 |
1993年 | 789篇 |
1992年 | 743篇 |
1991年 | 555篇 |
1990年 | 371篇 |
1989年 | 353篇 |
1988年 | 306篇 |
1987年 | 206篇 |
1986年 | 153篇 |
1985年 | 185篇 |
1984年 | 169篇 |
1983年 | 61篇 |
1982年 | 108篇 |
1981年 | 152篇 |
1980年 | 123篇 |
1979年 | 105篇 |
1978年 | 81篇 |
1977年 | 75篇 |
1976年 | 45篇 |
1973年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 134 毫秒
991.
J. Howard Rytting Danny R. McHan Takeru Higuchi David J. W. Grant 《Journal of solution chemistry》1986,15(8):693-703
Henry's law constants have been determined for -butyrolactone (BL), ethyl acetate (EA), and 2-methyl-3-pentanol (MEP) in mixtures of iso-octane (ISO) and toluene (TOL), for BL, EA, TOL, and ISO in cinnamaldehyde (CIN) and for TOL and ISO in each other and in BL. From these data and published vapor pressures, the activity coefficients at infinite dilution and the standard molar Gibbs free energy of transfer, G
2
0
of the solutes from dilute solution in ISO to dilute solution in each solvent medium have been calculated. The different behavior patterns of BL and EA are attributed to differences in their abilities to exist in different conformations possessing different dipole moments. For polar solutes, G
2
0
decreases with increasing polarizability of the solvent and with increasing dipole moment of the solute, suggesting increased contributions from dipole-induced dipole (Debye) interactions. The sigmoidal plot of G
2
0
against the change in pair potential energy calculated from the classical expressions suggests that G
2
0
seriously underestimates the strength of the Debye interactions in comparison with the London interactions. 相似文献
992.
MgCl_2晶型对丙烯聚合MgCl_2载体催化剂活性的影响张明辉,肖世镜中国科学院化学研究所,北京,10080)关键词丙烯聚合、MgCl2、载体催化剂近年来,有关MgCI。载体催化剂的研究报道和综述文章不少,但涉及载体晶型对催化剂结构性能的影响却少见.... 相似文献
993.
R. V. Pisarev V. V. Kalashnikov A. I. Kotov E. B. Yagubskii 《Russian Chemical Bulletin》1996,45(3):735-736
[2+4[-Cycloaddition of 2,3-dihydro-1,4-dithiine and oligomeric 1,3-dithiol-2,4,5-trithione results in the formation of 4a,6,7,8a-tetrahydro-1,3-dithiolo[4',5':5,61-[1,4[dithiino[2,3-b[1,4-dithiine-2-thione, which is a precursor for synthesis of new organic rz-donors.Translated fromIzvestiya Akademi Nauk Seriya Khimicheskaya No. 3, pp. 775–776, March, 1996. 相似文献
994.
本文研究了Tb(Ⅲ)-1,4-双(′-苯基-3′-甲基-5′-氧代吡唑-4′-基)丁二酮-[1,4](BPMPBD)-溴化十六烷基三甲胺(CTMAB)体系的荧光性质,探讨了响影体系荧光性质的诸因素,确定了最佳实验条件。该体系中Tb(Ⅲ)浓度以2.0×10~(-5)~1.0×10~(-10)mol/L范围内与其荧光强度呈线性关系,检测限可达到5.0×10~(-11)mol/L。应用于合成样品中微量Tb(Ⅲ)的分析,结果令人满意。 相似文献
995.
A method is proposed for the estimation of absolute binding free energy of interaction between proteins and ligands. Conformational sampling of the protein-ligand complex is performed by molecular dynamics (MD) in vacuo and the solvent effect is calculated a posteriori by solving the Poisson or the Poisson-Boltzmann equation for selected frames of the trajectory. The binding free energy is written as a linear combination of the buried surface upon complexation, SASbur, the electrostatic interaction energy between the ligand and the protein, Eelec, and the difference of the solvation free energies of the complex and the isolated ligand and protein, deltaGsolv. The method uses the buried surface upon complexation to account for the non-polar contribution to the binding free energy because it is less sensitive to the details of the structure than the van der Waals interaction energy. The parameters of the method are developed for a training set of 16 HIV-1 protease-inhibitor complexes of known 3D structure. A correlation coefficient of 0.91 was obtained with an unsigned mean error of 0.8 kcal/mol. When applied to a set of 25 HIV-1 protease-inhibitor complexes of unknown 3D structures, the method provides a satisfactory correlation between the calculated binding free energy and the experimental pIC5o without reparametrization. 相似文献
996.
997.
998.
Feng-Yun Wang Soofin Cheng Chen-Hung Chung Ben-Zu Wan 《Journal of Solid State Electrochemistry》2006,10(11):879-885
Electrolytes of Ce1-x-y
Y
x
Mg
y
O2-0.5x-y
were prepared with citrate method and were characterized by inductively coupled plasma-atomic emission spectrometry, energy dispersive spectrometry, powder X-ray diffraction, and impedance spectroscopy. The effect of composition on the structure, conductivity, and stability of the electrolytes were investigated. When 0≤x≤ about 0.2 and 0≤y≤ about 0.05, the electrolytes were all single phase materials of ceria-based solid solution. However, when y> about 0.05, the electrolytes became two-phase materials, Y3+ and Mg2+ co-doped ceria-based solid solution and free MgO. The sample with nominal composition of Ce0.815Y0.065Mg0.12O2-d
showed ionic conductivity at 973 K close to or even a little higher than that of similarly prepared Ce0.9Gd0.1O1.95, but had lower cost of raw materials and a little better stability in reducing atmosphere. The existing of free MgO improved the stability of the electrolytes in reducing atmosphere, but too much free MgO reduced the conductivity. 相似文献
999.
《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
1000.
[H+]在0.01~0.70mol?L-1范围内,离子强度为1.00mol?L-1,[Fe(III)]>>[配体]、[H+]>>[配体]的条件下,研究了Fe(III)与2,3-二羟基苯磺酸钠(Tiron)的配位反应.发现当[H+]≤3.00×10-2mol?L-1时,[Fe(III)]2对反应速率有明显的贡献.求得了相关反应的动力学参数,从而揭示了FeOH2+和FeOH24+与Tiron配位的解离反应途径及FeOH32+的缔合反应机制,并提出了该配位反应的可能机理. 相似文献