全文获取类型
收费全文 | 1051篇 |
免费 | 13篇 |
国内免费 | 115篇 |
专业分类
化学 | 975篇 |
晶体学 | 8篇 |
力学 | 5篇 |
综合类 | 5篇 |
物理学 | 186篇 |
出版年
2024年 | 2篇 |
2023年 | 13篇 |
2022年 | 4篇 |
2021年 | 16篇 |
2020年 | 12篇 |
2019年 | 18篇 |
2018年 | 16篇 |
2017年 | 17篇 |
2016年 | 16篇 |
2015年 | 23篇 |
2014年 | 36篇 |
2013年 | 55篇 |
2012年 | 66篇 |
2011年 | 67篇 |
2010年 | 59篇 |
2009年 | 53篇 |
2008年 | 46篇 |
2007年 | 70篇 |
2006年 | 70篇 |
2005年 | 60篇 |
2004年 | 64篇 |
2003年 | 53篇 |
2002年 | 48篇 |
2001年 | 34篇 |
2000年 | 36篇 |
1999年 | 33篇 |
1998年 | 23篇 |
1997年 | 20篇 |
1996年 | 24篇 |
1995年 | 22篇 |
1994年 | 12篇 |
1993年 | 19篇 |
1992年 | 19篇 |
1991年 | 13篇 |
1990年 | 9篇 |
1989年 | 5篇 |
1988年 | 9篇 |
1987年 | 1篇 |
1986年 | 6篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 2篇 |
1976年 | 1篇 |
1974年 | 2篇 |
1971年 | 1篇 |
排序方式: 共有1179条查询结果,搜索用时 500 毫秒
991.
992.
A general method that uses potassium organotrifluoroborates in the Suzuki-Miyaura cross-coupling reaction with ring-brominated porphyrins has been investigated. The reaction conditions tolerate various functional groups and are applicable to the meso- and β-position as well as to aryl- and alkyl-substituted porphyrins. Depending on the nature of the potassium organotrifluoroborate, the coupling products can be obtained in yields of up to 75%. 相似文献
993.
994.
实验测定了阳离子瓜儿胶水溶液的流变行为,讨论了油酸钾对其流变行为的影响.稳态剪切实验结果表明,加入油酸钾后,瓜儿胶溶液的零切黏度增加了近三个数量级,出现类似凝胶的性质.动态剪切实验结果表明,瓜儿胶溶液表观模量则随着油酸钾浓度的增加而增加,储存模量和损失模量对应的剪切模量随着油酸钾浓度的增加而减小.事实上,随着油酸钾浓度的增加,高分子交联在一起的聚集体数量逐渐减小,强度逐渐增加.温度的影响刚好相反,随着温度的升高,聚集体的数量逐渐增加,强度逐渐减小. 相似文献
995.
用微热量计对高锰酸钾测定痕量亚硝酸根在水中的液液反应进行了热动力学研究。通过实验和计算得出该反应的热力学参数(活化焓、活化熵及活化自由能)、速率常数和动力学参数(活化能、指前因子及反应级数)。结合实验数据讨论了反应的条件。 相似文献
996.
Mn2+doping-induced-effects on commensuration and incommensuration of potassium zinc chloride crystal
Undoped and Mn2+-doped with different concentrations of potassium zinc chloride (KZC) crystals were grown from aqueous solutions by slow evaporation. The dielectric constant (ε), dielectric losses (tan?δ) and ac conductivity (σac) of the crystals in the ferroelectric-commensurate, incommensurate and normal phases have been measured as a function of frequency, in the range 1–100?kHz, and temperature, in the range 300–580?K. Virgin samples were subjected to measurements of the frequency dependence at selected temperatures and measurements of the temperature dependence was then followed using the same samples. The increase of ε with T could be due to a combination of conductivity, structural variations and discommensuration (DC) formation and pinning as well. The increase of tan?δ with temperature was attributed to relaxation loss in addition to conduction loss, which increases more rapidly with temperature. The ac conductivity (σac) and tan?δ along the polar axis of KZC increased significantly with increasing Mn2+ content while ε decreased. σac changed with frequency according to a power law of the form σac?=?f? s where 0.15<s<1.27. A linear decrease of ε and tan?δ with increasing the frequency was also found. The obtained results were treated by considering the effect of Mn2+-doping on stripples nucleation, DC evolution/annihilation, DC-lattice formation and DCs pinning by the crystal lattice and/or structural defects for virgin and thermally treated samples. 相似文献
997.
Philip C. Andrews Colin L. Raston Brian W. Skelton 《Journal of organometallic chemistry》2006,691(15):3325-3330
Reaction of the bulky pyridyl based ligand 6-Me(2-Pyr)(Me3Si)2CH with nBuM (M = Na, K) in the presence of the N donors pmdta (N,N′,N′,N″,N″ pentamethyldiethylenetriamine) and tmeda (N,N,N′,N′ tetramethylethylenediamine) resulted in the formation and crystallisation of the heavy alkali metal complexes, [{6-Me(2-Pyr)}(Me3Si)2CNa(pmdta)], 1, and [{6-Me(2-Pyr)}(Me3Si)2CK]∞, 2. Single crystal X-ray diffraction studies show the sodium complex, 1, to be monomeric with a six coordinate metal centre, while the unsolvated potassium complex, 2, is polymeric, involving repeating η3 1-aza-allyl and allylic interactions of the pyridyl moiety with the potassium cation. 相似文献
998.
Dayanand A. KamblePratibha U. Karabal Pandurang V. ChouthaiwaleArumugam Sudalai 《Tetrahedron letters》2012,53(32):4195-4198
Sodium periodate and sodium azide combination has been found to be an excellent reagent system suitable for the direct diazidation of styrenes, alkenes, benzylic alcohols, and aryl ketones to produce the corresponding vicinal and geminal diazides respectively in high yields under mild reaction conditions. 相似文献
999.
《Journal of Coordination Chemistry》2012,65(9):1091-1096
The combination of iminodiacetic acid (H2ida) with cobalt(II) chloride hexahydrate in the presence of sodium hydroxide, followed by heating, produces the trans-facial isomer of K[Co(ida)2]·2H2O. This compound contains extensive intermolecular and intramolecular coordination and hydrogen bonding involving the potassium ions, and results in a complex three-dimensional structure in which each potassium ion is immediately surrounded by six cobalt centers. 相似文献
1000.
Gideon Fleminger Beka Solomon Tamar Wolf Eran Hadas 《Applied biochemistry and biotechnology》1990,26(3):231-238
A single step periodate oxidative binding of glycoproteins to synthetic polymeric matrices is proposed. By this procedure,
the glycoprotein to be immobilized is simultaneously mixed with sodium periodate and a hydrazide-containing matrix. The carbohydrate
moieties of the protein are oxidized and react with matrix. The single step reaction is faster than the commonly-used multistep
procedure and it allows conjugation of minute amounts of glycoproteins to the matrix. 相似文献