全文获取类型
收费全文 | 30111篇 |
免费 | 4240篇 |
国内免费 | 2750篇 |
专业分类
化学 | 20635篇 |
晶体学 | 291篇 |
力学 | 1947篇 |
综合类 | 274篇 |
数学 | 3293篇 |
物理学 | 10661篇 |
出版年
2024年 | 105篇 |
2023年 | 594篇 |
2022年 | 909篇 |
2021年 | 960篇 |
2020年 | 1123篇 |
2019年 | 1084篇 |
2018年 | 918篇 |
2017年 | 817篇 |
2016年 | 1284篇 |
2015年 | 1278篇 |
2014年 | 1543篇 |
2013年 | 2063篇 |
2012年 | 2640篇 |
2011年 | 2674篇 |
2010年 | 1656篇 |
2009年 | 1638篇 |
2008年 | 1742篇 |
2007年 | 1663篇 |
2006年 | 1497篇 |
2005年 | 1233篇 |
2004年 | 947篇 |
2003年 | 800篇 |
2002年 | 763篇 |
2001年 | 569篇 |
2000年 | 563篇 |
1999年 | 656篇 |
1998年 | 589篇 |
1997年 | 579篇 |
1996年 | 664篇 |
1995年 | 513篇 |
1994年 | 471篇 |
1993年 | 390篇 |
1992年 | 380篇 |
1991年 | 324篇 |
1990年 | 261篇 |
1989年 | 205篇 |
1988年 | 160篇 |
1987年 | 137篇 |
1986年 | 127篇 |
1985年 | 120篇 |
1984年 | 89篇 |
1983年 | 64篇 |
1982年 | 42篇 |
1981年 | 36篇 |
1980年 | 18篇 |
1978年 | 19篇 |
1977年 | 23篇 |
1976年 | 20篇 |
1975年 | 28篇 |
1974年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
A simple model has been developed to describe the Zeeman patterns of far-infrared laser magnetic resonance spectra of the monobromomethyl radical CH2Br observed at 447.3 and 671.1μm. A satisfactory agreement between the experimental spectra of the radical and their simulation with this simple model has been achieved. This approach can be used to gain further information about the structure and the spectrum of this interesting radical. 相似文献
82.
The products from the condensation of acetone-anils ( 1 ) and TCNE reaction were characterized after separation. The main products, tricyanoethylene derivatives ( 7–9 ) were isolated with the malonodinitrile derivatives ( 10–12 ), respectively. The [2+2] cycloaddition product ( 13 ), namely 5-methoxy-3,4-(2′,2′,3′,3′-tetracyanocyclobutano)-l,2-dihydro-2,2,4-trimethylquinoline also has been isolated. The distribution of these three products is substituent dependent. 相似文献
83.
This paper presents an analysis of a portfolio model which can be used to assist a property-liability insurance company in determining the optimal composition of the insurance and investment portfolios. By introducing insurer's threshold risk and relaxing some non-realistic assumptions made in traditional chance constraint insurance and investment portfolio models, we propose a method for an insurer to maximize his return threshold for a given threshold risk level. This proposed model can be used to optimize the composition of underwriting and investment portfolios regarding the insurer's threshold risk level, as well as to generate the efficient frontier by adjusting insurer's threshold risk levels. A numerical example is given based on the industry's aggregated data for a sixteen year period. 相似文献
84.
Jing-song Huang 《Mathematische Annalen》1993,297(1):309-324
Supported in part by NSF Grant DMS-8610730 相似文献
85.
采用固源Si分子束外延,在较高的生长温度于Si(100)衬底上制备出Si1-xGex/Si量子阱发光材料。发光样品的质量和特性通过卢瑟福背散射、X射线双晶衍射及光致发光评估。背散射实验中观察到应变超晶格的反常沟道效应;X射线分析表明材料的生长是共度的、无应力释放的,结晶完整性好。低温光致发光主要是外延合金量子阱中带边激子的无声发射和横光学声子参与的激子复合。并讨论了生长温度对量于阱发光的影响。 相似文献
86.
Wang Dunhui Huang Songling Han Zhida Su Zhenghua Wang Yi Du Youwei 《Solid State Communications》2004,131(2):97-99
A series of Gd(1−x)Bx alloys have been prepared by arc melting method. After introducing small quantity of B atom in Gd, the Curie temperature of these alloys increase while the magnetic entropy changes are almost same as that of Gd. The refrigerant capacities of these alloys are also greater than that of Gd. These results suggest that Gd(1−x)Bx alloys may be utilized as refrigerant in household magnetic refrigeration. 相似文献
87.
J.S. Tsay H.W. Chang Y.L. Chiou K.T. Huang W.Y. Chan Y.D. Yao 《Journal of magnetism and magnetic materials》2006
Influences of oxygen exposure on the magnetic properties of Co/Ge(1 1 1) ultrathin films have been investigated by surface magneto-optic Kerr effect technique. As the oxygen exposure increases on Co/Ge(1 1 1) films, their magnetic properties could be modified. As an example for 15 ML Co/Ge(1 1 1) films, the coercivity increases from 730 to 920 Oe and the remanence Kerr intensity is reduced for 500 Langmuir (L) of oxygen exposure. Corresponding compositions analyzed by Auger electron spectroscopy measurement shows that the amount of oxygen on the surface layers increases with increasing the oxygen exposure time. Oxygen distributes on the topmost layers of the film. The adsorbed oxygen influences the electronic density of states of Co and results in the changes of the magnetic properties. Besides, the appearance of O/Co/Ge interface could modify the stress anisotropy, and as a result the coercivity of ultrathin Co/Ge(1 1 1) film is enhanced. 相似文献
88.
Observation of spontaneous pattern with six-fold symmetry in disk-shaped ZnO complex microstructures
L.W. Yang Y.J. Gao X.L. Wu Y.M. Yang G.S. Huang Z.Y. Zhang P.K. Chu 《Applied Physics A: Materials Science & Processing》2007,89(1):173-176
Using a simple vapor phase transport technique, we have fabricated unique complex disk-shaped ZnO microstructures comprising
a small disk coaxially grown on a large one and observed spatially perfect six-fold symmetric patterns. The observed results
can be explained based on the spontaneous nanoindentation (NI) effect under the geometric constraints and the explanation
can be extended to fathom the growth mechanism of other highly symmetrical ZnO nanostructures. Our results indicate that NI
not only can elucidate the mechanical properties of surfaces and thin films but also is an effective approach to fabricate
ordered nanostructures with high precision on the location of the building blocks.
PACS 81.16.Rf; 81.07.-b; 81.05.Dz 相似文献
89.
J. Xu J. Mei X.H. Huang X. Li Z. Li W. Li K. Chen 《Applied Physics A: Materials Science & Processing》2005,80(1):123-126
The effect of nitrogen surface doping on the electron field emission characteristics of hydrogenated amorphous carbon films was studied. It was found that the emission threshold electric field decreased after nitrogen surface doping which indicated the reduction of the emission barrier at the film surface. It was demonstrated that this improvement arose from the decrease of the effective work function due to the formation of a dipole layer induced by chemical termination and chemical structural change on the film surface. PACS 52.75.Xx; 73.30 +y; 73.61.Jc 相似文献
90.