全文获取类型
收费全文 | 12524篇 |
免费 | 587篇 |
国内免费 | 48篇 |
专业分类
化学 | 9268篇 |
晶体学 | 41篇 |
力学 | 203篇 |
综合类 | 1篇 |
数学 | 1960篇 |
物理学 | 1686篇 |
出版年
2023年 | 79篇 |
2022年 | 100篇 |
2021年 | 169篇 |
2020年 | 242篇 |
2019年 | 210篇 |
2018年 | 159篇 |
2017年 | 134篇 |
2016年 | 446篇 |
2015年 | 405篇 |
2014年 | 433篇 |
2013年 | 570篇 |
2012年 | 736篇 |
2011年 | 772篇 |
2010年 | 550篇 |
2009年 | 455篇 |
2008年 | 727篇 |
2007年 | 669篇 |
2006年 | 610篇 |
2005年 | 618篇 |
2004年 | 527篇 |
2003年 | 399篇 |
2002年 | 355篇 |
2001年 | 184篇 |
2000年 | 155篇 |
1999年 | 176篇 |
1998年 | 139篇 |
1997年 | 194篇 |
1996年 | 141篇 |
1995年 | 146篇 |
1994年 | 154篇 |
1993年 | 123篇 |
1992年 | 116篇 |
1991年 | 92篇 |
1990年 | 71篇 |
1989年 | 108篇 |
1988年 | 86篇 |
1987年 | 68篇 |
1986年 | 68篇 |
1985年 | 94篇 |
1984年 | 93篇 |
1982年 | 96篇 |
1981年 | 80篇 |
1980年 | 68篇 |
1979年 | 60篇 |
1978年 | 84篇 |
1977年 | 78篇 |
1976年 | 57篇 |
1975年 | 60篇 |
1973年 | 62篇 |
1971年 | 54篇 |
排序方式: 共有10000条查询结果,搜索用时 765 毫秒
101.
Sc3N@C68 is assigned to isomer Sc3N@C68:6140 on the grounds of relative energies, geometrical data, and its 13C NMR pattern. Sc3N@C68:6140 is an endohedral fullerene where each Sc atom is coordinated to the center of an equatorial pentalene unit. Static and dynamic computer simulations explain the different point groups observed in NMR and X-ray experiments. Computed and experimental 13C NMR pattern are in close agreement except for one low-intensity signal. The competing isomer Sc3N@C68:6275 is found to be 409 kJ/mol less stable and shows a different 13C NMR pattern. 相似文献
102.
Rudolf O. Duthaler Peter Herold Susanne Wyler-Helfer Martin Riediker 《Helvetica chimica acta》1990,73(3):659-673
Chloro(cyclopentadienyl)bis(1,2:5,6-di-O-isopropylidene-α-D -glucofuranos-3-O-yl)titanium ( 1 ) is used for the transmetallation of Li-enolates obtained from propionyl derivatives. While such Ti-enolates of ketones and hydrazones appear to be unreactive, the (E)enolate 13 of 2,6-dimethylphenyl propionate ( 11 ) adds to the re-side of aldehydes, affording various syn-aldols 14 with high dia- and enantioselectivity (92–97% ds, 91–97% ee, cf. Scheme 2 and Table 1). Racemic syn-aldols (±)- 14 are obtained analogously from the achiral bis(2-propyloxy)-Ti-enolate 15 (Scheme 2 and Table 2). In contrast to the unstable Li-enolate 10 , the Ti-enolates 13 and 15 isomerize at ?30°, presumably to the thermodynamically more stable (Z)-enolates (Scheme 4), While the diastereoselectivity of the achiral enolate 15 is lost upon this equilibration, the chiral (Z)-enolate 27 quite unexpectedly affords anti-aldols 12 of high optical purity (94–98% ec) and, in most cases, with acceptable-to-good diastereoselectivity (82–90% ds). Notable exceptions are branched unsaturated and aromatic aldehydes which form a greater proportion of synepimers of moderate optical purity (Scheme 5 and Table 3). Consistent with these findings, re-facial-and ami -selective aldol-addition is also exhibited by the (Z)-configurated Ti-enolate 22 of N-propionyl-oxazolidi-none 19 (Scheme 3). 相似文献
103.
104.
Trace analysis of rapamycin in human blood by micellar electrokinetic chromatography 总被引:1,自引:0,他引:1
A capillary electrophoretic method with UV detection at 278 nm has been developed for analysis of the immunosuppressant rapamycin (sirolimus) in human blood at low microgram per liter levels. Separation has been achieved in an acidic carrier electrolyte containing sodium dodecylsulfate and 30% (v/v) acetonitrile. For sample clean-up and preconcentration, an off-line solid-phase extraction step using a silica-based reversed-phase material and an on-capillary focussing technique were employed. The latter allows the injection of increased sample volumes without excessive band broadening. Although this new method is less sensitive than existing liquid chromatographic procedures combined with mass spectrometry, it is fully suited to routine analysis of rapamycin in blood from patients treated with this drug. Last but not least the low costs make it an attractive alternative to established methods. 相似文献
105.
106.
Nidetzky Bernd Griessler Richard Weinhausel Andreas Haltrich Dietmar Kulbe Klaus D. 《Applied biochemistry and biotechnology》1997,(1):159-172
Some important process properties of α-l,4-D-ghican phosphorylases isolated from the bacteriumCorynebacterium callunae and potato tubers (Solatium tuberosum) were compared. Apart from minor differences in their stability and specificity (represented by the maximum degree of maltodextrin
conversion) and a 10-fold higher affinity of the plant phosphorylase for maltodextrin (K
M of 1.3 g/L at 300 mM of orthophosphate), the performances of both enzymes in a continuous ultrafiltration membrane reactor
were almost identical. Product synthesis was carried out over a time course of 300–400 h in the presence or absence of auxiliary
pullulanase (increasing the accessibility of the glucan substrate for phosphorolytic attack up to 15–20%). The effect of varied
dilution rate and reaction temperature on the resulting productivities was quantitated, and a maximum operational temperature
of 40°C was identified. 相似文献
107.
108.
Andreas Charalambous 《Analytica chimica acta》2005,547(1):53-58
This work is an investigation into the utility of bismuth-film electrodes (BiFEs) for the determination of indium in the presence of cadmium and lead by square wave anodic stripping voltammetry (SWASV). The purpose of this study was to demonstrate that, after judicious choice of the associated chemical and instrumental conditions, it is possible to achieve satisfactory separation of the relevant stripping peak and, thus, to determine simultaneously trace concentrations of cadmium, lead and indium. It was conclusively demonstrated that a BiFE performed better than the equivalent mercury-film electrode (MFE) in this particular application. 相似文献
109.
110.