全文获取类型
收费全文 | 30353篇 |
免费 | 4222篇 |
国内免费 | 2882篇 |
专业分类
化学 | 20864篇 |
晶体学 | 278篇 |
力学 | 2008篇 |
综合类 | 288篇 |
数学 | 3523篇 |
物理学 | 10496篇 |
出版年
2024年 | 35篇 |
2023年 | 596篇 |
2022年 | 576篇 |
2021年 | 911篇 |
2020年 | 1155篇 |
2019年 | 1119篇 |
2018年 | 925篇 |
2017年 | 822篇 |
2016年 | 1280篇 |
2015年 | 1230篇 |
2014年 | 1558篇 |
2013年 | 2061篇 |
2012年 | 2679篇 |
2011年 | 2780篇 |
2010年 | 1724篇 |
2009年 | 1712篇 |
2008年 | 1820篇 |
2007年 | 1745篇 |
2006年 | 1592篇 |
2005年 | 1316篇 |
2004年 | 991篇 |
2003年 | 825篇 |
2002年 | 781篇 |
2001年 | 587篇 |
2000年 | 585篇 |
1999年 | 676篇 |
1998年 | 604篇 |
1997年 | 591篇 |
1996年 | 651篇 |
1995年 | 522篇 |
1994年 | 471篇 |
1993年 | 398篇 |
1992年 | 366篇 |
1991年 | 322篇 |
1990年 | 251篇 |
1989年 | 205篇 |
1988年 | 157篇 |
1987年 | 137篇 |
1986年 | 126篇 |
1985年 | 119篇 |
1984年 | 87篇 |
1983年 | 60篇 |
1982年 | 41篇 |
1981年 | 37篇 |
1979年 | 17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 237 毫秒
91.
具有奇异值分解性质的代数 总被引:4,自引:0,他引:4
设F为一个域,R为一个带有对合的F-代数,如果R上每一个矩阵都有奇异值分解(简称SVD),则称R为一个有SVD性质的F-代数.本文指出:R为一个有SVD性质的F-代数的充要条件是:R同构于R~+,或R~+上二次扩域,或R~+上四元数体((-1,-1)/R~+),其中R~+为R的对称元集合,并且R~+为一个Galois序闭域. 相似文献
92.
93.
94.
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
95.
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
96.
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
97.
Determination of the arc-root position in a DC plasma torch 总被引:4,自引:0,他引:4
Seungho Paik P. C. Huang J. Heberleinand E. Pfender 《Plasma Chemistry and Plasma Processing》1993,13(3):379-397
The behavior of an arc operated in the nontransferred mode with a conical-shaped cathode and a nozzle-shaped anode is studied by applying general tyro-dimensional conservation equations and auxiliary relations for the simulation of arc channel flows. The position of the arc-root attachment at the anode surface is determined by using Steenbeck's minimum principle, which postulates a minimum arc voltage for a given current and certain given boundary conditions. The overall effects of the anode-arc root on the plasma flow are, studied by comparing the results with those of the transferred mode of operation. Specific arc-channel diameters are chosen in the simulation in order to verify flit, numerical model through comparisons with experimental results. The results show that Steenbeck's minimum principle is useful for determining the position of the arc-root attachment at the anode surface. Application of this method for control of the arc-anode attachment may be valuable in the design and operation of plasma spray torches to avoid jet instabilities. 相似文献
98.
Jing-song Huang 《Mathematische Annalen》1993,297(1):309-324
Supported in part by NSF Grant DMS-8610730 相似文献
99.
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
100.
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