全文获取类型
收费全文 | 98579篇 |
免费 | 27119篇 |
国内免费 | 20203篇 |
专业分类
化学 | 63757篇 |
晶体学 | 1277篇 |
力学 | 6449篇 |
综合类 | 352篇 |
数学 | 12602篇 |
物理学 | 61464篇 |
出版年
2024年 | 512篇 |
2023年 | 1143篇 |
2022年 | 1540篇 |
2021年 | 1492篇 |
2020年 | 1879篇 |
2019年 | 2350篇 |
2018年 | 2186篇 |
2017年 | 2777篇 |
2016年 | 3262篇 |
2015年 | 3506篇 |
2014年 | 3601篇 |
2013年 | 5686篇 |
2012年 | 6362篇 |
2011年 | 8000篇 |
2010年 | 10713篇 |
2009年 | 10959篇 |
2008年 | 4942篇 |
2007年 | 4281篇 |
2006年 | 3880篇 |
2005年 | 3998篇 |
2004年 | 4629篇 |
2003年 | 3703篇 |
2002年 | 3558篇 |
2001年 | 3722篇 |
2000年 | 2798篇 |
1999年 | 3000篇 |
1998年 | 2504篇 |
1997年 | 2297篇 |
1996年 | 2588篇 |
1995年 | 2970篇 |
1994年 | 3010篇 |
1993年 | 3017篇 |
1992年 | 2551篇 |
1991年 | 2243篇 |
1990年 | 1860篇 |
1989年 | 1926篇 |
1988年 | 1908篇 |
1987年 | 1199篇 |
1986年 | 1240篇 |
1985年 | 889篇 |
1984年 | 996篇 |
1982年 | 915篇 |
1981年 | 753篇 |
1980年 | 785篇 |
1979年 | 532篇 |
1978年 | 535篇 |
1977年 | 636篇 |
1976年 | 1048篇 |
1973年 | 438篇 |
1972年 | 532篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
Utilization of carbohydrates by radiation processing 总被引:2,自引:0,他引:2
Upgrading and utilization of carbohydrates such as chitosan, sodium alginate, carrageenan, cellulose, pectin have been investigated for recycling these bio-resources and reducing the environmental pollution. These carbohydrates were easily degraded by irradiation and various kinds of biological activities such as anti-microbial activity, promotion of plant growth, suppression of heavy metal stress, phytoalexins induction, etc. were induced. On the other hand, some carbohydrate derivatives, carboxymethylcellulose and carboxymethylstarch, could be crosslinked under certain radiation condition and produce the biodegradable hydrogel for medical and agricultural use. 相似文献
142.
The phase boundary theory and the contact rule of phase regions are compared, and some weaknesses of the latter are manifested.
The comparison between the Gupta’s method and the boundary theory method for constructing multicomponent isobaric sections
is also presented. 相似文献
143.
Summary High-purity indium was analysed by spark source mass spectrometry, using electrical and photoplate detection. For the calibration of the differences in elemental sensitivity, a standard sample was prepared in which 10 impurities were determined by graphite furnace atomic absorption spectrometry. In this way accuracies of less than 40% were obtained for relatively homogeneous elements at ppm and sub-ppm level. About 40 elements could be determined with detection limits of 10 to 30 ppb. Two pattern recognition methods, principal component analysis and clustering analysis, were applied to obtain information on trace element distribution, which indicated that a number of elements were strongly spatially correlated in the analysed sample.
On leave from: Department of Chemistry, Nanjing Normal University, Nanjing, People's Republic of China 相似文献
Chemische Analyse und Verteilungsbestimmung von Spurenelementen in Indium-Matrix durch Funkenquellen-Massenspektrometrie
On leave from: Department of Chemistry, Nanjing Normal University, Nanjing, People's Republic of China 相似文献
144.
Z.G. Xiao R.J. HuH.Y. Wu G.M. JinZ.Y. Li L.M. DuanH.W. Wang B.G. ZhangS.F. Wang Z.Y. WeiH.S. Xu Y.T. ZhuS.L. Li F. FuX.H. Yuan Z.Q. Feng 《Physics letters. [Part B]》2006
The inclusive reduced velocity correlation functions of the intermediate mass fragments were measured in the reactions of 36Ar + 112,124Sn at 35 MeV/u. The anti-correlation is observed to be stronger in 36Ar + 124Sn system than that in 36Ar + 112Sn. The difference of the correlation functions between the two reactions is mainly contributed by the particle pairs with high momenta. A three body Coulomb repulsive trajectory model is employed to calculate the emission time scale of the IMFs for the two systems. The time scale is 150 fm/c in 36Ar + 112Sn and 120 fm/c in the 36Ar + 124Sn, respectively. 相似文献
145.
Kj?rand Iversen Per Nilsson 《International Journal of Computers for Mathematical Learning》2007,12(2):113-133
This paper focuses on the different ways in which students in lower secondary school (14–16 year olds) experience compound
random events, presented to them in the form of combined junctions. A carefully designed ICT environment was developed enabling
the students to interact with different representations of such structures. Data for the analysis was gathered from two interview
sessions. The analysis of the interaction is based on constructivist principles on learning; i.e. we adopted a student-oriented
perspective, taking into consideration the different ways students try to make sense of chance encounters.
Our results show how some students give priority to geometrical and physical concerns, and we discuss how seeking causal explanations
of random phenomena may have encouraged this. With respect to numerically oriented models a division strategy appears to stand
out as the preferred one. 相似文献
146.
147.
A Monte Carlo simulation method is used to study thermal desorption of gas molecules from mixed adlayers containing two species. The effects of lateral interactions among adatoms and initial surface coverage on the desorption spectra are examined. It is shown that attractive lateral interactions lead to sharper peaks and that desorption occurs at high temperatures, whereas repulsive interactions lead to multiple peak spectra. It is found that interactions between unlike molecules affect the spectra for species with lower desorption energy only, and that the two species desorb together only in certain cases. Lateral interactions also affect the desorption kinetics significantly and very different behavior for the two species may be obtained. 相似文献
148.
The conversion of methanol into light olefins has been studied using the silver salt of dodecatungstosilicic acid supported on serosil. Special attention has been paid to the process of the acid sites formation during the initial reaction period and to the role of hydrogen. The significantly higher activity and stability of the supported silver salt compared with the supported free heteropoly acid is explained by a controlled formation process of acidic sites and their additional generation from hydrogen on the metallic silver surface. 相似文献
149.
The notion of balanced bipartitions of the vertices in a tree T was introduced and studied by Reid (Networks 34 (1999) 264). Reid proved that the set of balance vertices of a tree T consists of a single vertex or two adjacent vertices. In this note, we give a simple proof of that result. 相似文献
150.