全文获取类型
收费全文 | 374271篇 |
免费 | 4705篇 |
国内免费 | 1507篇 |
专业分类
化学 | 202260篇 |
晶体学 | 5279篇 |
力学 | 16134篇 |
综合类 | 8篇 |
数学 | 42706篇 |
物理学 | 114096篇 |
出版年
2020年 | 2695篇 |
2019年 | 2995篇 |
2018年 | 3400篇 |
2017年 | 3339篇 |
2016年 | 5712篇 |
2015年 | 4157篇 |
2014年 | 5889篇 |
2013年 | 17412篇 |
2012年 | 13089篇 |
2011年 | 16305篇 |
2010年 | 10464篇 |
2009年 | 10555篇 |
2008年 | 14768篇 |
2007年 | 14855篇 |
2006年 | 13877篇 |
2005年 | 12919篇 |
2004年 | 11563篇 |
2003年 | 10191篇 |
2002年 | 10021篇 |
2001年 | 11608篇 |
2000年 | 8824篇 |
1999年 | 6870篇 |
1998年 | 5608篇 |
1997年 | 5556篇 |
1996年 | 5299篇 |
1995年 | 4907篇 |
1994年 | 4628篇 |
1993年 | 4598篇 |
1992年 | 5059篇 |
1991年 | 5079篇 |
1990年 | 4674篇 |
1989年 | 4647篇 |
1988年 | 4687篇 |
1987年 | 4532篇 |
1986年 | 4301篇 |
1985年 | 6146篇 |
1984年 | 6241篇 |
1983年 | 5115篇 |
1982年 | 5561篇 |
1981年 | 5273篇 |
1980年 | 5106篇 |
1979年 | 5162篇 |
1978年 | 5410篇 |
1977年 | 5226篇 |
1976年 | 5376篇 |
1975年 | 4955篇 |
1974年 | 5006篇 |
1973年 | 5306篇 |
1972年 | 3218篇 |
1971年 | 2379篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
K.M.J. Rocha R.G. Leitão E.G. Oliveira-Barros M.A. Oliveira C.G.L. Canellas M.J. Anjos L.E. Nasciutti R.T. Lopes 《X射线光谱测定》2019,48(5):476-481
Prostate cancer is a highly prevalent disease and ranks second among malignant neoplasms that affect men around the world, behind lung cancer alone. Trace elements are very important and are involved in many cellular processes. The X-ray microfluorescence technique is an advanced tool of high spatial resolution, sensitivity, multielemental analysis, and nondestructiveness for trace element study. This study aimed to investigate the elemental distribution in spheroids obtained through the following human prostate cell lines using synchrotron X-ray microfluorescence: tumor cell line androgen independent (DU145), tumor cell line androgen dependent (LNCaP), and normal cell line (RWPE-1). The measurements were performed with a standard geometry of 45° of incidence, excited by a white beam using a pixel of 25 μm and an acquisition time of 300 ms/pixel at the X-ray fluorescence beamline at the Synchrotron Light National Laboratory (Campinas, Brazil). The synchrotron X-ray microfluorescence results showed differences between groups in all elements analyzed and suggested that further studies should be performed to understand the relationship of these trace elements with the progression and development of the disease. 相似文献
102.
Simen Gjelseth Antonsen Arne Joakim C. Bunkan Tomas Mikoviny Yngve Stenstrøm Armin Wisthaler 《Molecular physics》2020,118(15)
The kinetics of the O3, OH and NO3 radical reactions with diazomethane were studied in smog chamber experiments employing long-path FTIR and PTR-ToF-MS detection. The rate coefficients were determined to be k CH2NN+O3?=?(3.2?±?0.4)?×?10?17 and k CH2NN+OH?=?(1.68?±?0.12)?×?10?10 cm3 molecule?1 s?1 at 295?±?3?K and 1013?±?30 hPa, whereas the CH2NN?+?NO3 reaction was too fast to be determined in the static smog chamber experiments. Formaldehyde was the sole product observed in all the reactions. The experimental results are supported by CCSD(T*)-F12a/aug-cc-pVTZ//M062X/aug-cc-pVTZ calculations showing the reactions to proceed exclusively via addition to the carbon atom. The atmospheric fate of diazomethane is discussed. 相似文献
103.
104.
Ivanov K. A. Gubaidullin A. R. Morozov K. M. Sasin M. E. Kaliteevskii M. A. 《Optics and Spectroscopy》2019,126(6):787-787
Optics and Spectroscopy - 10.1134/S0030400X17050095 相似文献
105.
106.
107.
108.
Claudia Poloni Marc C. A. Stuart Pieter van der Meulen Wiktor Szymanski Ben L. Feringa 《Chemical science》2015,6(12):7311-7318
The external photocontrol over peptide folding, by the incorporation of molecular photoswitches into their structure, provides a powerful tool to study biological processes. However, it is limited so far to switches that exhibit only a rather limited geometrical change upon photoisomerization and that show thermal instability of the photoisomer. Here we describe the use of an overcrowded alkene photoswitch to control a model β-hairpin peptide. This photoresponsive unit undergoes a large conformational change and has two thermally stable isomers which has major influence on the secondary structure and the aggregation of the peptide, permitting the phototriggered formation of amyloid-like fibrils. 相似文献
109.
110.
Brian R. Holder Colleen A. McNaney David Luchetti Eric Schaeffer Dieter M. Drexler 《Biomedical chromatography : BMC》2015,29(9):1375-1379
Acetyl‐l ‐carnitine (ALCAR) is a potential biomarker for the modulation of brain neurotransmitter activity, but is also present in cerebrospinal fluid (CSF). Recent studies have utilized hydrophilic interaction liquid chromatography–tandem mass spectrometry (HILIC‐MS/MS) based assays to detect and quantify ALCAR within biofluids such as urine, plasma and serum, using various sample pretreatment procedures. In order to address the need to quantify ALCAR in CSF on a high‐throughput scale, a new and simple HILIC‐MS/MS assay has been successfully developed and validated. For rapid analysis, CSF sample pretreatment was performed via ‘dilute and shoot’ directly onto an advanced HILIC column prior to MS/MS detection. This newly developed HILIC‐MS/MS assay shows good recoveries of ALCAR without the need for chemical derivatization and multistep sample extraction procedures. The employment of this assay is suitable for the high‐throughput bioanalysis and quantification of ALCAR within the CSF of various animal models and human clinical studies. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献