全文获取类型
收费全文 | 42039篇 |
免费 | 7678篇 |
国内免费 | 5495篇 |
专业分类
化学 | 31471篇 |
晶体学 | 499篇 |
力学 | 2396篇 |
综合类 | 335篇 |
数学 | 4448篇 |
物理学 | 16063篇 |
出版年
2024年 | 104篇 |
2023年 | 856篇 |
2022年 | 1060篇 |
2021年 | 1510篇 |
2020年 | 1849篇 |
2019年 | 1903篇 |
2018年 | 1560篇 |
2017年 | 1413篇 |
2016年 | 2156篇 |
2015年 | 2069篇 |
2014年 | 2559篇 |
2013年 | 3219篇 |
2012年 | 3885篇 |
2011年 | 3896篇 |
2010年 | 2661篇 |
2009年 | 2505篇 |
2008年 | 2853篇 |
2007年 | 2444篇 |
2006年 | 2317篇 |
2005年 | 1912篇 |
2004年 | 1544篇 |
2003年 | 1322篇 |
2002年 | 1531篇 |
2001年 | 1268篇 |
2000年 | 899篇 |
1999年 | 897篇 |
1998年 | 725篇 |
1997年 | 619篇 |
1996年 | 617篇 |
1995年 | 509篇 |
1994年 | 427篇 |
1993年 | 345篇 |
1992年 | 372篇 |
1991年 | 303篇 |
1990年 | 265篇 |
1989年 | 188篇 |
1988年 | 126篇 |
1987年 | 108篇 |
1986年 | 132篇 |
1985年 | 92篇 |
1984年 | 51篇 |
1983年 | 57篇 |
1982年 | 29篇 |
1981年 | 27篇 |
1980年 | 8篇 |
1979年 | 3篇 |
1959年 | 2篇 |
1957年 | 6篇 |
1936年 | 5篇 |
1923年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
A carbon supported Pt-Ru catalyst with uniform distribution and small average size of the Pt-Ru particles was synthesized using a two-step spray pyrolysis (SP) method; the electrocatalytic activity of the prepared catalyst for methanol oxidation is better than that of the standard commercial catalyst. 相似文献
992.
Qiong Ye Hong Zhao Xiang Xue Shie-Ming Pang 《Journal of organometallic chemistry》2005,690(2):286-290
Solvothermal treatments of W(CO)6 with 2,2′-bipyridine and 1,10-phenanthroline give [W(CO)4(bipy)] (1) and [W(CO)4(phen)] (2), respectively, which both crystallize in noncentrosymmetric space groups, suggesting that they meet the requirement of second harmonic generation (SHG) investigations. The preliminary experiment indicates that they are SHG active, and approximately estimated to be that of urea. 相似文献
993.
一种新型双亚胺吡啶铁系催化剂的乙烯低聚研究 总被引:1,自引:0,他引:1
线性α 烯烃广泛地应用于洗涤剂、增塑剂、润滑油等精细化学品的合成以及作为共单体制备线性低密度聚乙烯 (LLDPE) .目前工业上主要是应用SHOP法[1] 、Chevron工艺和Amoco工艺[2 ] 通过乙烯低聚制备 .近些年发展起来的新型高活性后过渡金属乙烯低聚催化剂能够高选择性地制备线性α 烯烃[3 ,4] .Brookhart等[4] 的研究表明 ,对于双亚胺吡啶铁系乙烯聚合催化剂而言 ,配体上苯基的邻位取代基位阻减小可以实现乙烯低聚 ,并具有高活性、高选择性以及理想的低聚产物分布 .本文的工作是从配体的空间位阻效应对催化剂… 相似文献
994.
TheacetoneselfCImassspectrumAcetoneselfCImassspectrumisgiveninTable1.Table1.MajorproductionsandtheirrelativeabundanceofacetoneselfCIMSTheformationofionatmlZ73AnotherproductionintheselfCIMSofacetoneistheionatm/z73.InselfCIMSofacetone-d6,thecounterpartistheionatInjz82.InselfCIMSofthemixtureofacetoneandacetone-d6inaratioofl:l,thecorrespondingionsaretheionsatInlz73,76,79and82.TheirCIDreactionresultsarelistedinTable2.Table2.TheCIDMSoftheionatIn/z73andanalogsOnthebasisofthedatainTab… 相似文献
995.
Chen-Zhong Dong Jin-Bao Zhao 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1992,23(3):211-213
Some terms of the 4s4p 4 configuration in RuXII, RhXIII and PdXIV ions can be improved and all the energy values of the configuration in AgXV can be predicted theoretically by means of a configuration-interaction ab initio analysis for the level structure of the 4s4p 4 configuration along the AsI sequence of KrIV-AgXV ions. Calculations of the wavelengths and oscillator strenghts are presented for the 4s 24p 3-4s4p 4 transition in AgXV. 相似文献
996.
High-quality online course materials were reconstructed through feedback from undergraduate students and online data analysis regarding constructed learning materials on the Chao Xing Learning Platform. They were used for studying organic chemistry courses online and offline in university for nationalities. This model, based on student-centered teaching, can effectively transform students from passively accepting knowledge to actively learning and internalizing knowledge. This strategy can also enhance the students' learning initiative and the effects of learning, and hopefully be helpful to the universities in multi-ethnic areas in developing fundamental disciplined construction of organic chemistry and other courses. 相似文献
997.
A strategy to incorporate and release anti-cancer drugs of daunorubicin (DNR) and doxorubicin (DOX) in preformed microcapsules is introduced, which is based on charge interaction mechanism. Oppositely charged poly(allylamine hydrochloride) (PAH) and poly(styrene sulfonate) (PSS) were assembled onto PSS doped-CaCO3 colloidal particles in a layer-by-layer manner to yield core-shell particles. After removal of the carbonate cores, hollow microcapsules with entrapped PSS were fabricated, which showed spontaneous loading ability of positively charged DNR and DOX. The drug loading was confirmed quantitatively by observations under confocal laser scanning microscopy, transmission electron microscopy and scanning force microscopy. Quantification of the drug loading was performed under different conditions, revealing that a larger amount of drugs could be incorporated at higher drug feeding concentrations and higher salt concentrations. However, putting additional polyelectrolyte layers on the microcapsules after core removal resulted in weaker drug loading efficiency. The drug release behaviors from the microcapsules with different layer numbers were studied too, revealing a diffusion controlled release mechanism at the initial stage (4 h). 相似文献
998.
Densities have been measured for the electrolyte (NaCl, NaBr and NaI)‐monosaccharide (D ‐mannose and D‐ribose)‐water solutions at 298.15 K. These data have been used to calculate the apparent molar volumes of the saccharides (VΦ,S) and electrolytes (VΦ,E) in the studied solutions. Infinite dilution apparent molar volumes, VΦ,S0 and VΦ,E0, have been evaluated, together with the standard transfer volumes of the saccharides (ΔtVS0) from water to aqueous electrolyte solutions and those of the electrolytes (ΔtVE0) from water to aqueous saccharide solutions. It was shown that both the ΔtVS0 and ΔtVE0 values are positive and increase with increasing molalities of sodium halides and saccharides, respectively. Overall, the ΔtVS0 and ΔtVE0 values have the order of NaCl > NaBr > NaI except for NaI‐ribose and NaI‐ribose. Volumetric interaction parameters for the electrolyte‐monosaccharide pairs in water were obtained and interpreted by the stereochemistry of the monosaccharide molecules and the structural interaction model. 相似文献
999.
Phosphonium or arsonium salt 1 can undergo the tandem reaction of deprotonation -oxidation-Wittig reaction with alcohol 2 in the presence of sodium hydroxide and manganese dioxide,which affords a general simplified method for the stereoselective synthesis of (E)- α-β-unsaturated esters 3. 相似文献
1000.