全文获取类型
收费全文 | 19932篇 |
免费 | 3137篇 |
国内免费 | 2867篇 |
专业分类
化学 | 15484篇 |
晶体学 | 427篇 |
力学 | 972篇 |
综合类 | 262篇 |
数学 | 2019篇 |
物理学 | 6772篇 |
出版年
2024年 | 72篇 |
2023年 | 350篇 |
2022年 | 731篇 |
2021年 | 776篇 |
2020年 | 891篇 |
2019年 | 870篇 |
2018年 | 700篇 |
2017年 | 729篇 |
2016年 | 1020篇 |
2015年 | 1136篇 |
2014年 | 1338篇 |
2013年 | 1637篇 |
2012年 | 1852篇 |
2011年 | 1887篇 |
2010年 | 1397篇 |
2009年 | 1268篇 |
2008年 | 1456篇 |
2007年 | 1217篇 |
2006年 | 1104篇 |
2005年 | 950篇 |
2004年 | 755篇 |
2003年 | 618篇 |
2002年 | 703篇 |
2001年 | 494篇 |
2000年 | 335篇 |
1999年 | 272篇 |
1998年 | 212篇 |
1997年 | 136篇 |
1996年 | 141篇 |
1995年 | 93篇 |
1994年 | 87篇 |
1993年 | 88篇 |
1992年 | 76篇 |
1991年 | 84篇 |
1990年 | 58篇 |
1989年 | 56篇 |
1988年 | 32篇 |
1987年 | 38篇 |
1986年 | 30篇 |
1985年 | 37篇 |
1984年 | 26篇 |
1983年 | 28篇 |
1982年 | 17篇 |
1981年 | 22篇 |
1980年 | 18篇 |
1979年 | 19篇 |
1978年 | 15篇 |
1977年 | 12篇 |
1976年 | 9篇 |
1974年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
High-resolution solid-state 29Si NMR has been applied to the study of partially exchanged Li, K, and Cs NaY zeolites. The order of the 29Si chemical shifts of dehydrated samples is Li, Na-Y < Na-Y < K, Na-Y. The correlation between the 29Si chemical shift and the Li or K loading on Li, Na-Y or K, Na-Y was rationalized in terms of the interaction between the framework and the cations inside the small cages. Because of the restrictive migration of large Cs+ ions from the supercages to the small cages, the 29Si chemical shift of Cs, Na-Y was found to be similar to that of Na-Y. 相似文献
62.
Xiao Wen Hu Zhi Min Zheng Cai Hong Xu 《中国化学快报》2007,18(11):1351-1352
Three new 1,3-bis(phenylethynyl)disilazanes were synthesized from the reaction of 1,3-dichlorodisilazanes with (phenylethy- nyl)lithium,and characterized by infrared (IR) spectra,nuclear magnetic resonance (NMR) and mass spectrometry (MS). 相似文献
63.
Gil MC Lee MH Seo JI Choi YL Kim MK Jung KC Park SH Kim TJ 《Experimental & molecular medicine》2002,34(6):411-418
CD99 plays a critical role in the diapedesis of monocytes, T cell differentiation, and the transport of MHC molecules. Engagement of CD99 by agonistic monoclonal antibodies has been reported to trigger multifactorial events including T cell activation as well as cell-cell adhesion during hematopoietic cell differentiation. In this study, to identify the functional domains participating in the cellular events, we mapped the epitopes of CD99, which are recognized by two agonistic CD99 monoclonal antibodies, DN16 and YG32. Using recombinant fusion proteins of GST with whole or parts of CD99, we found that both antibodies interact with CD99 molecules independently of sugar moieties. DN16 mAb detected a linear epitope located in the amino terminal region of CD99 while YG32 mAb bound another linear epitope in the center of the extracellular domain. To confirm that the identified epitopes of CD99 are actually recognized by the two mAbs, we showed the presence of physical interaction between the mAbs and the fusion proteins or synthetic peptides containing the corresponding epitopes using surface plasmon resonance analyses. The dissociation constants of DN16 and YG32 mAbs for the antigen were calculated as 1.27 x 10(-7) and 7.08 x 10(-9) M, respectively. These studies will help understand the functional domains and the subsequent signaling mechanism of CD99. 相似文献
64.
A method incorporating high-performance liquid chromatography (HPLC) with electrospray ionization and tandem mass spectrometry, with parallel analysis by HPLC with UV detection using a diode-array detector, was developed for the qualitative characterization of flavonoids in D. odorifera. Twenty-three flavonoids, including six isoflavones, six neoflavones, four isoflavanones, three flavanones, two chalcones, one isoflavanonol and one pterocarpan, were unambiguously identified by comparing their retention times, UV and MS spectra with those of authentic compounds. Furthermore, the collision-induced dissociations of the [M-H]- ions were studied to clarify the MS behavior of the different types of flavonoids. In negative ion ESI-MS all the flavonoids yielded prominent [M-H]- ions in the first order mass spectra. Fragments involving losses of CH3*, H2O, CO, C2H2O, and CO2 were observed in the MS/MS spectra. Each of the seven types of flavonoid showed characteristic MS/MS fragmentation patterns. The isoflavanones, flavanones and chalcones were observed to undergo retro-Diels-Alder fragmentations. The spectra of almost all the neoflavonoids unexpectedly exhibited only [M-H-CH3]-* radical anions as base peaks without any further fragmentation. Substitution positions also remarkably influenced the fragmentation behavior, which could assist in distinction among the flavonoid isomers. The fragmentation rules deduced here could aid in the characterization of other flavonoids of these types. 相似文献
65.
66.
67.
68.
69.
H.-S. Kim C. Lee M. Takai S. Namba S.-K. Min 《Applied Physics A: Materials Science & Processing》1991,52(3):188-191
Microprobe photoluminescence (PL) measurements at 77 K were used to study the effect of the GaAs layer thickness on optical quality and variations in strain in GaAs/Si containing microcracks. PL peak intensities increase with the increase in thickness of GaAs layers and the peak intensity for the 5.5 m GaAs layer was a factor of 20 higher than those for the 1–2 m GaAs layers. Spatial nonuniformities in strain in the vicinity of two microcracks reveal that stress was almost released at the intersection of two microcracks and is maximum half way between two microcracks.On leave from Semiconductor Materials Lab., Korea Institute of Science and Technology (KIST) 相似文献
70.