全文获取类型
收费全文 | 60993篇 |
免费 | 13978篇 |
国内免费 | 5430篇 |
专业分类
化学 | 59311篇 |
晶体学 | 658篇 |
力学 | 2014篇 |
综合类 | 348篇 |
数学 | 4996篇 |
物理学 | 13074篇 |
出版年
2024年 | 71篇 |
2023年 | 578篇 |
2022年 | 955篇 |
2021年 | 1147篇 |
2020年 | 2306篇 |
2019年 | 3627篇 |
2018年 | 1957篇 |
2017年 | 1647篇 |
2016年 | 4571篇 |
2015年 | 4786篇 |
2014年 | 4906篇 |
2013年 | 5943篇 |
2012年 | 5348篇 |
2011年 | 4530篇 |
2010年 | 4479篇 |
2009年 | 4444篇 |
2008年 | 4187篇 |
2007年 | 3424篇 |
2006年 | 2927篇 |
2005年 | 2891篇 |
2004年 | 2379篇 |
2003年 | 2128篇 |
2002年 | 2917篇 |
2001年 | 2207篇 |
2000年 | 1945篇 |
1999年 | 931篇 |
1998年 | 484篇 |
1997年 | 409篇 |
1996年 | 369篇 |
1995年 | 329篇 |
1994年 | 246篇 |
1993年 | 232篇 |
1992年 | 198篇 |
1991年 | 175篇 |
1990年 | 144篇 |
1989年 | 90篇 |
1988年 | 94篇 |
1987年 | 72篇 |
1986年 | 62篇 |
1985年 | 71篇 |
1984年 | 38篇 |
1983年 | 38篇 |
1982年 | 23篇 |
1981年 | 16篇 |
1980年 | 13篇 |
1979年 | 14篇 |
1977年 | 8篇 |
1976年 | 7篇 |
1975年 | 6篇 |
1965年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
911.
阻抑动力学光度法测定痕量间苯二酚 总被引:26,自引:3,他引:26
研究发现,在硫酸介质中,Fe能催化H2O2与甲基红之间的裉色反应,加入间苯二酚后,间苯二酚又能灵敏地阻抑该氧化褪色反应,同时研究了该阻抑褪色反应的动力学条件,从而建立了一种新的测定痕量间苯二酚的方法。 相似文献
912.
Sergeev G. B. Smirnov V. V. Rostovshchikova T. N. Komissarova N. V. Indoleva Ye. V. 《Tetrahedron》1987,43(24):5853-5863
Complexes and reactions of 2-methylbutene-2 with hydrohalogen (HCl, HBr) have been studied in solid phase at 80–150 K. It has been found that 2-methylbutene-2 forms with HX complexes of 1:1 and 1:2 composition. Hydrohalogenation proceeds via the rearrangement of complex 2HX·C5H10 into complex of the addition product with HX. Kinetic equation depends on the reagents ratio. In excess of HX (1< HX:C5H10< 10) reaction can be described by the first order kinetic equation. If the ratio HX:C5H10 is more than 10, reaction is described by polychronous kinetic law. The effective activation energy of solid phase hydrohalogenation does not exceed 20 kJ/mole. The molecular mechanism of hydrohalogenation in solid phase has been proposed. 相似文献
913.
914.
915.
Feng‐You Hao Yong‐Fang Zhao Xiao‐Gong Jing Xin‐Ying Li Feng‐Li Liu 《International journal of quantum chemistry》2007,107(6):1502-1507
Ab initio quantum chemical calculations have been performed on X2Cl? and X2Cl (X = C, Si, Ge) clusters. The geometrical structures, vibrational frequencies, electronic properties and dissociation energies are investigated at the Hartree–Fock (HF), Møller–Plesset second‐ and fourth‐order (MP2, MP4), CCSD(T) level with the 6‐311+G(d) basis set. The X2Cl (X = C, Si, Ge) and X2Cl? (X = Si, Ge) take a bent shape obtained at the ground state, while C2Cl? has a linear structure. The impact on internal electron transfer between the X2Cl and the corresponding anional clusters is studied. The three different types of electron affinities (EAs) at the CCSD(T) are reported. The most reliable adiabatic electronic affinities, obtained at the CCSD(T)/cc‐pvqz level of theory, are predicted to be 3.30, 2.62, and 1.98 eV for C2Cl, Si2Cl, and Ge2Cl, respectively. The calculated EAs of C2Cl and Ge2Cl are in good agreement with theoretical results reported. The correlation effects and basis sets effects on the geometrical structures and dissociation energies are discussed. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
916.
Yubin Xue Shun‐Chang Liu Xinsheng Liu Yusi Yang Yimin Zhang Ding‐Jiang Xue Jin‐Song Hu 《中国化学》2020,38(4):356-360
Colloidal quantum dots (CQDs) are attractive absorber materials for high‐efficiency photovoltaics because of their facile solution processing, bandgap tunability due to quantum confinement effect, and multi‐exciton generation. To date, all published performance records for PbS CQDs solar cells have been based on the conventional hot‐injection synthesis method. This method usually requires relatively strict conditions such as high temperature and the utility of expensive source material (pyrophoric bis(trimethylsilyl) sulfide (TMS‐S)), limiting the potential for large‐scale and low‐cost synthesis of PbS CQDs. Here we report a facile room‐temperature synthetic method to produce high‐quality PbS CQDs through inexpensive ionic source materials including Pb(NO3)2 and Na2S in the presence of triethanolamine (TEA) as the stabilizing ligand. The PbS CQDs were successfully prepared with an average particle size of about 5 nm. Solar cells based on the as‐synthesized PbS CQDs show a preliminary power conversion efficiency of 1.82%. This room‐temperature and low‐cost synthesis of PbS CQDs will further benefit the development of solution‐processed CQD solar cells. 相似文献
917.
聚1-氨基蒽醌在二次锂电池正极材料中的应用 总被引:4,自引:0,他引:4
采用化学方法合成聚1-氨基蒽醌并用于二次锂电池正极材料,通过红外光谱、扫描电镜、粒度测试、循环伏安以及充放电测试等方法对材料的官能团结构、微观形貌、颗粒大小以及电化学性能等进行了研究与分析.实验表明,与金属锂组成二次锂电池后,聚1-氨基蒽醌达到了218.3 mAh•g-1的首次放电容量,经过25次循环后仍可保持较高的充放电效率.由于材料具有较高的能量密度且不含对环境有污染的元素S,因此是二次锂电池非常有希望的正极材料. 相似文献
918.
919.
Tandem cascade reactions of allylazides and olefinic dipolarophiles to give cis‐fused 2,3,7‐triazabicyclo [3.3.0]octenes ( 5, 6 or 7 ) are reported. Therein, an intermolecular dipolar cycloaddition of azide and alkene gave a triazoline which was followed by isomerization of the triazoline to a diazoester ( 4 ) and then an intramolecular dipolar cycloaddition from the diazo functional group and the double bond in 4 to give 5 . Compound 5 may further more undergo a Michael addition to give 7‐substituted‐ 2,3,7‐ triazabicyclo [3.3.0]oct‐2‐ene ( 6 ) or a tautomerization to give 2,3,7‐triazabicyclo[3.3.0]oct‐3‐ene ( 7 ). The reaction may be manipulated to stop at a particular stage by adopting a suit able solvent or an appropriate temperature. 相似文献
920.
Hemocompatibility is an essential aspect of blood contacting polymers. Knowledge of the relationship between polymer structure and hemocompatibility is important in designing such polymers. In this work, the effect of swelling behavior and states of water on the hemocompatibility of poly(acrylonitrile-co-N-vinyl-2-pyrrolidone) (PANCNVP) films was studied. Platelet adhesion and plasma recalcification time tests were used to evaluate the hemocompatibility of the films. Considering the importance of surface properties on the hemocompatibility of polymers, static water contact angles were measured by both sessile drop and captive bubble methods. It was found that, on the film surface of PANCNVP with a higher NVP content, adhered platelets were remarkably suppressed and the recalcification time was longer. The total water content adsorbed on the PANCNVP film was determined through swelling experiments performed at temperatures of interest. Differential scanning calorimetry and thermogravimetric analysis were used to probe the states of water in the films. Based on the results from these experiments, it was hypothesized that the better hemocompatibility of PANCNVP films with higher NVP contents was due to their higher free water content, because water molecule exchange at the polymer/liquid interface, facilitated by a high free water content, is unfavorable for the formation of surface bound water, which causes poor hemocompatibility. [diagram in text]. 相似文献