全文获取类型
收费全文 | 1122篇 |
免费 | 214篇 |
国内免费 | 106篇 |
专业分类
化学 | 447篇 |
晶体学 | 7篇 |
力学 | 99篇 |
综合类 | 13篇 |
数学 | 291篇 |
物理学 | 585篇 |
出版年
2023年 | 14篇 |
2022年 | 32篇 |
2021年 | 39篇 |
2020年 | 46篇 |
2019年 | 32篇 |
2018年 | 30篇 |
2017年 | 34篇 |
2016年 | 37篇 |
2015年 | 45篇 |
2014年 | 49篇 |
2013年 | 96篇 |
2012年 | 67篇 |
2011年 | 55篇 |
2010年 | 59篇 |
2009年 | 76篇 |
2008年 | 92篇 |
2007年 | 66篇 |
2006年 | 55篇 |
2005年 | 60篇 |
2004年 | 51篇 |
2003年 | 45篇 |
2002年 | 69篇 |
2001年 | 40篇 |
2000年 | 37篇 |
1999年 | 36篇 |
1998年 | 20篇 |
1997年 | 31篇 |
1996年 | 23篇 |
1995年 | 19篇 |
1994年 | 14篇 |
1993年 | 7篇 |
1992年 | 10篇 |
1991年 | 8篇 |
1990年 | 8篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1970年 | 2篇 |
1966年 | 1篇 |
排序方式: 共有1442条查询结果,搜索用时 421 毫秒
101.
The role of crystallographic angle in characterizing and modeling apatite fission-track length data 总被引:1,自引:0,他引:1
Recent experimental work on apatite fission-track length measurement has documented a number of factors that can exert a considerable influence on determinations of mean length. The principal source of length variation is anisotropy of annealing and etching behavior with respect to crystallographic angle. Procedural and environmental factors that influence which angular populations are preferentially sampled during measurement lead to variations in mean length that exceed standard statistical predictions. This paper evaluates the possibility of using c-axis projection to remove angular effects, and thus make length data more reproducible and informative. 相似文献
102.
103.
Venkataramanarao G. Anand Simi K. Pushpan Sundararaman Venkatraman Tavarekere K. Chandrashekar 《Journal of Chemical Sciences》2003,115(5-6):711-720
Expanded porphyrins containing seven pyrrole/heterocyclic rings linked in a cyclic fashion are termed heptaphyrins. The number
ofπ-electrons in heptaphyrins depends on the number ofmeso carbon bridges used to link the heterocyclic rings, accordingly heptaphyrins with 28π-electrons and 30π-electrons are reported to date. Both condensation reactions of the appropriate precursors and acid-catalysed oxidative coupling
reactions have been utilized to synthesise the heptaphyrins. The 30π heptaphyrins exhibit rich structural diversity where some of the heterocyclic rings in the macrocycle undergo a 180° ring
flipping. An overview of the synthetic methods employed for the synthesis of heptaphyrins, their spectroscopic properties,
structural behaviour and aromatic properties are highlighted in this paper.
Dedicated to Professor C N R Rao on his 70th birthday 相似文献
104.
The structures of Y2Fe17-xCrx are simulated by the ab initio potentials. The site preference of Cr atom in Y2Fe17 is evaluated and the order is determined as 4f, 12j, which is close to the experimental result. Based on the site preference behavior, the calculated parameters and the atom sites of Y-Fe-Cr system are studied. The result corresponds well to observed data. Further, the DOS of the relaxed structures are calculated and the variation in Curie temperature is explained qualitatively by the spin-fluctuation theory. 相似文献
105.
ZHANG Jianfeng YAO Minyu PENG Can ZHANG Hongming XU Qianfan GAO Yizhi 《Chinese Journal of Lasers》2002,11(3):215-218
1 Introduction Thereisastrongcommercialpressuretoupgradethecapacityoftheexistingfibersystems.However,duetothefactthatthemajorityoftheworld’sinstalledfiberareG .6 52standardfiber,whichhasalargedispersion ( 1 7ps/nm/km )at 1 550nm ,chromaticdispersionbecomesthemajo… 相似文献
106.
非对称Abel逆变换研究及其在等离子体辐射功率分析中的应用 总被引:7,自引:5,他引:2
一、引言 在实验等离子体物理中,常遇到测量量是待求物理量沿等离子体截面弦的线积分值,为待求量,L为弦长。从测量到的I(x)值,求出i r值的Abel逆变换,在等离子体诊断的数据处理中得到了广泛应用。 在假定等离子体截面为中心对称的前提条件下,人们对Abel逆变换方法做了很多的研 相似文献
107.
From the comparison of correlation tensor in the theory of quantum network, the Alexander relation matrix in the theory of knot crystals and the identical inversion relations under the action of Pauli matrices, we show that there is a one to one correspondence between four Bell bases and four oriented links of the linkage 41 in knot theory. 相似文献
108.
Guan-quan Zhang 《计算数学(英文版)》1998,(6)
1.IntroductionInthispaperthefollowingpotentialinversionproblemisconsideredThatis,givinganimpulseatthesurfacez~0,todeterminethewavefleldpandpotentialvfromtheimpulseresponseh.Inone-dimensionalcase3byfactorizingthewaveoperator,thewavefieldcanbesplitintoupcominganddowngoingwaves,sothewaveequationcanbeeasilyreducedtoacoupledfirst-ordersystem.Thedirectproblemandthecoefficiellt-inversionproblemcanbetreatedasCauchyproblemsintimeandinthedirectionofdepthregardedasthetime-likevariable[1].Theseproblemsar… 相似文献
109.
110.
The fabrication of a periodic domain inversion in LiTaO3 and LiNbO3 using direct ion-beam writing is presented. The polarization of these materials can be reversed at room temperature by irradiating Si2+ ions into +c faces. A first-order periodic domain inversion with a 50% duty cycle, a depth of 300μ, and an interaction length of 1 mm was realized in LiTaO3. Using this structure, 300μW of blue light was generated for a conversion efficiency of 0.25%/W. 相似文献