全文获取类型
收费全文 | 9282篇 |
免费 | 245篇 |
国内免费 | 899篇 |
专业分类
化学 | 5680篇 |
晶体学 | 65篇 |
力学 | 372篇 |
综合类 | 2篇 |
数学 | 641篇 |
物理学 | 3666篇 |
出版年
2024年 | 10篇 |
2023年 | 156篇 |
2022年 | 67篇 |
2021年 | 89篇 |
2020年 | 140篇 |
2019年 | 182篇 |
2018年 | 161篇 |
2017年 | 205篇 |
2016年 | 252篇 |
2015年 | 246篇 |
2014年 | 390篇 |
2013年 | 805篇 |
2012年 | 416篇 |
2011年 | 710篇 |
2010年 | 553篇 |
2009年 | 653篇 |
2008年 | 603篇 |
2007年 | 648篇 |
2006年 | 586篇 |
2005年 | 506篇 |
2004年 | 493篇 |
2003年 | 309篇 |
2002年 | 245篇 |
2001年 | 247篇 |
2000年 | 247篇 |
1999年 | 188篇 |
1998年 | 188篇 |
1997年 | 145篇 |
1996年 | 124篇 |
1995年 | 136篇 |
1994年 | 110篇 |
1993年 | 95篇 |
1992年 | 94篇 |
1991年 | 76篇 |
1990年 | 54篇 |
1989年 | 45篇 |
1988年 | 47篇 |
1987年 | 38篇 |
1986年 | 29篇 |
1985年 | 22篇 |
1984年 | 27篇 |
1983年 | 12篇 |
1982年 | 17篇 |
1981年 | 7篇 |
1980年 | 12篇 |
1979年 | 13篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 4篇 |
1973年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 233 毫秒
91.
The preparation and mesomorphic properties of a substituted bis(dithiolene)nickel complex derived from 4, 4'-dimethoxybenzil are reported. The phase transition temperatures were based on data obtained by polarized light microscopy and differential scanning calorimetry. The mesogenic phase existed over the temperature range from 77 to 175 degrees C. A novel micropacked column (1.5 or 3 m x 1 mm i.d.) prepared from the slurry of bis[1,2-bis(4-n-undecyloxyphenyl)ethane-1,2-dithiolene] nickel(II) (5%, w/w), coated on Chromosorb W was applied for the separation of dialkyl sulfides. The non-linearity (discontinuity) of Van't Hoff plots suggests that the liquid crystal property existed even in the coated phase. Factors affecting the retention and the sample selectivity on the prepared column were examined by using a flame photometric detector (FPD). The separation might be based on the mechanism of ligand exchange, shape selectivity and polarity interaction besides the vapor pressure. LOD for the determination of dialkyl sulfides was below 1 ng for most of the analytes. 相似文献
92.
Summary Chiral recognition of many enantiomeric solutes by a chiral amide stationary phase is based mainly on hydrogen bonding. A
chiral-recognition-factor CHI is proposed, given by the difference of the enthalpy change in the enantiomer discrimination,
standardized with respect to the specific interaction of the solutes with the diamide core of the stationary phase. The r?le
of the entropy part is also discussed. By extrapolation of the retention behaviour to elevated temperature, peak inversion
of enantiomers is predicted.
Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984 相似文献
93.
Summary A variety of bilipeptides has been synthesized and investigated by UV-VIS and CD spectroscopy to explore the conformational influence of peptide ligands on the covalently bound tetrapyrrol moiety. The results obtained are complemented by those reported previously. From the comprehensive data thus available several features of the peptidic chain regulating interactions with the bilatriene moiety have been elucidated. Accordingly, the presence of three amide linkages at the ligand is prerequiste for induction of pronounced conformational changes consisting either in a complete transition ofM intoP helical bilatriene species by inversion of all torsional angles, or in a stretching of the chromophore. The kind of conformational influence can be controlled by varying the position of the prolyl entity within a given peptide.Dedicated to Prof. Dr. Kurt Schaffner on occasion of his 60th birthday 相似文献
94.
报道从D-甘露醇出发合成手性双膦(2S,5S)-3,6-双(二苯膦)-1,4:3,6-双脱水-2,5-双去氧-L-艾杜醇,原位下BDPI与3种铑配合物作用生成手性非螯合型双膦铑催化剂,常压下对4种脱氢苯丙氨酸衍生物进行不对称催化化反主尖,对反应结果及e.e.值进行了讨论。 相似文献
95.
氧化铝具有许多重要的工业用途,而制备高热稳定活性氧化铝的技术也在不断地发展[1,2],因此,研究其高温烧结下的相变过程很有意义.离子深法作为新型测试手段,已成功地用于生物大分子结构与功能研究方面[‘],而在固体材料测试中的应用尚未见报道.我们以EU’“作为荧光探针,并结合**D和*nR研究了川对。在不同烧结温度下的相变过程.1实验部分样品的制备采用复盐分解法.先将Elf刀s用高纯硝酸溶解定容.以占AlzO。重量1%的量加入到硫酸铝锭溶液中,进行超声处理,冷冻干燥.再依次登于900”C、1000C、1100C、1200C的高温炉… 相似文献
97.
98.
具有C2对称轴的手性配体及其不对称催化反应 总被引:2,自引:0,他引:2
按配位原子的数目进行分类,综述了近年来研究较多的具有C2对称轴的手性配体及其相关的不对称催化反应,并对该类手性配体的设计做了分析和总结。参考文献79篇。 相似文献
99.
The carbobenzyloxy (cbz) protecting group is evaluated for it's potential to enhance the resolution of chiral amine enantiomers using high-performance liquid chromatography (HPLC) and supercritical fluid chromatography (SFC). A series of cbz derivatives of commercially available racemates was prepared and analyzed by enantioselective chromatography using a variety of mobile phases and polysaccharide and Pirkle-type chiral stationary phases (CSPs). The cbz-derivatized product consistently demonstrated enhanced chiral resolution under HPLC and SFC conditions. Improved selectivity and resolution combined with an automated preparative HPLC or SFC system can lead to the rapid generation of highly purified enantiomers of desirable starting materials, intermediates or final products. 相似文献
100.
Duringthelastdecade,1,3-dioltypechiralbuildingbIocksofvariousconfigurationshavebeensynthesizedandappliedwidelyinthetotalsynthesisofnaturalpolyenemacrolideantibiotics1'2andla,25-dihydroxyvitaminD3analogues'.RecentlyWeigandandBrucker4synthesizedachiralbuildingblock(4R,6R)-2,2-dimethyl-5-tert-butyldip4-hydroxymethyl-l,3-dioxane1inlOsteps.Herein,wereportasyntheticrouteofnewbuildingblock(4S,6S)-2,2-dimethyl-5-tert-butyldip2,anenantiomerofl,startingfromreadilyavailableandinexpensiveD( )-xylose3i… 相似文献