全文获取类型
收费全文 | 144353篇 |
免费 | 27379篇 |
国内免费 | 14669篇 |
专业分类
化学 | 114197篇 |
晶体学 | 1612篇 |
力学 | 7184篇 |
综合类 | 837篇 |
数学 | 16149篇 |
物理学 | 46422篇 |
出版年
2024年 | 386篇 |
2023年 | 2298篇 |
2022年 | 4142篇 |
2021年 | 4370篇 |
2020年 | 5540篇 |
2019年 | 6483篇 |
2018年 | 4966篇 |
2017年 | 4330篇 |
2016年 | 8410篇 |
2015年 | 8499篇 |
2014年 | 9647篇 |
2013年 | 12109篇 |
2012年 | 12758篇 |
2011年 | 12313篇 |
2010年 | 9798篇 |
2009年 | 9519篇 |
2008年 | 9350篇 |
2007年 | 8090篇 |
2006年 | 7330篇 |
2005年 | 6467篇 |
2004年 | 5289篇 |
2003年 | 4451篇 |
2002年 | 4989篇 |
2001年 | 3862篇 |
2000年 | 3406篇 |
1999年 | 2664篇 |
1998年 | 1999篇 |
1997年 | 1761篇 |
1996年 | 1724篇 |
1995年 | 1509篇 |
1994年 | 1371篇 |
1993年 | 1099篇 |
1992年 | 983篇 |
1991年 | 867篇 |
1990年 | 722篇 |
1989年 | 551篇 |
1988年 | 415篇 |
1987年 | 368篇 |
1986年 | 353篇 |
1985年 | 280篇 |
1984年 | 201篇 |
1983年 | 167篇 |
1982年 | 134篇 |
1981年 | 96篇 |
1980年 | 69篇 |
1979年 | 33篇 |
1978年 | 27篇 |
1976年 | 25篇 |
1975年 | 24篇 |
1957年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
研究了导电聚合物聚(3-丁基噻吩)(PBT)在大气环境下的导电热稳定性。在室温至220℃范围内,测试电导率随时间及温度的变化。TGA分析以及化学分析的结果表明:掺杂态的PBT大约在140℃附近有一转化温度,低于或高于这一转化温度,电导率下降的决定因素各不相同。高于转化温度时,电导率下降的主要原因是反离子和高分子主链的解离,进而发生化学反应,影响了高分子主链的结构。XPS测试结果表明:经热处理后的P 相似文献
952.
Asiswellknown,thetheoryfornonlinearpolymerizationswasinitiatedbyFloryandStockmayer[1—3].MillerandMacosko[4—6]proposedarecursivemethodfordealingwiththeproblemofthepostgelpropertiesofthenetworkformingpolymerization.Stepto[7]investigatedthegelgelreactionofRAft… 相似文献
953.
Nicole Fietkau Fran?ois G Chevallier Li Jiang Timothy G J Jones Richard G Compton 《Chemphyschem》2006,7(10):2162-2167
The size of a glass sphere positioned in the center of a microdisk electrode is determined by using a simple electrochemical procedure and is confirmed, additionally, by a microscopical measurement of the sphere at the time of the electrochemical measurement. The cyclic voltammetric response of the naked electrode and of the electrode with the sphere positioned in its center is recorded over a wide range of scan rates (0.002-1.5 V s(-1)). The size of the sphere is then determined by comparison of the experimental voltammogram with simulations for each individual scan rate. 相似文献
954.
955.
Diastereoselective allylation of imine derived from N‐glyoxyloyl camphorpyrazolidinone and amines was treated with allyltributylstannane in the presence of triflic acid. The corresponding optically enriched homoallylic amines were obtained in reasonable to high material yields and with practical levels of stereoselectivity in 10 min at ambient temperature. 相似文献
956.
Uncoupled metabolism stimulated by chemical uncoupler and oxic-settling-anaerobic combined process to reduce excess sludge production 总被引:1,自引:0,他引:1
The effects of three uncoupled metabolic systems (conventional activated sludge process with the addition of 3,3′,4′,5-tetrachlorosalicylanilide
[TCS], oxic-settling-anaerobic [OSA] process modified by insertion of a sludge-holding tank in the sludge return line, and
TCS and OSA combined process) on reducing excess sludge production were studied. Compared with the control conventional activated
sludge process, the most effective system was the combined process, which could reduce excess sludge production by 46.90%.
The 180-d operation results confirmed that TCS is an effective chemical uncoupler in reducing the sludge yield but that it
had an adverse effect on substrate removal capability, effluent nitrogen concentration, and sludge settleability. The OSA
process decreased excess sludge production by only 26% but had less adverse effect on effluent quality and could improve sludge
settleability. The effluent total phosphorous concentration of the three systems was slightly lower than of the control unit.
Microbial populations were monitored by both microscopic and molecular biologic analysis method (polymerase chain reaction
[PCR]-denaturing gradient gel electrophoresis [DGGE]). The presence of TCS caused metazoans to disappear and decreased the
number and activity of protozoa. PCR amplification of 16S rRNA and sequent DGGE analysis found a shift in the diversity of
the predominant species. The results imply that OSA combined with the chemical uncoupler process may effectively reduce excess
sludge yield and not affect process performance significantly. 相似文献
957.
Ye Qing Li Ming Lu Chun Xu Lu Sai Jian Zhu Qi Fa Liu 《中国化学快报》2007,18(11):1313-1315
A novel and simple procedure for synthesis of azanucleoside by Mitsunobu reaction between N-(p-nitrobenzyloxycarbonyl)- trans-4-hydroxy-D-proline methyl ester obtained from trans-4-hydroxy-L-proline after six-step reaction and 2-fluoro-6-azidopurine is described,and azanucleoside is fluorinated by new fluridizer 2,2-difluoro-1,3-dimethylimidazolidine (DFI).All reactions could be carded out under mild condition. 相似文献
958.
The recent progress of wide bandgap (WBG) donor polymers for non-fullerene polymer solar cells (NF-PSCs) were reviewed in detail, which was classified by D-type and D-A type molecular backbones to discuss the related structure-property correlations and put forward an outlook for future innovations. 相似文献
959.
960.
WenXiangHU XueJunHOU QingTaoPENG 《中国化学快报》2002,13(12):1199-1202
In this paper,a new HPLC method was established to determine the earbonyl compounds in air.As the absorbent,2,4-dinitrophenylhydrazint(2,4-DNPH)reaeted with earbonyls specifieally,which form the corresponding 2,4-dinitrophenylhydrazones,then analyzed by HPLC.The chromatographic conditions,the recovery rate,stability of samples,reagent blank,sampling efficiency were all studied systematically.The results showed that this established method had high sensitivity and good selectivity compared with other analytical methods,and it can detemine ten earbonyl compounds in air in 26 min simultancously. 相似文献