全文获取类型
收费全文 | 34663篇 |
免费 | 972篇 |
国内免费 | 230篇 |
专业分类
化学 | 22596篇 |
晶体学 | 195篇 |
力学 | 788篇 |
综合类 | 1篇 |
数学 | 6501篇 |
物理学 | 5784篇 |
出版年
2021年 | 368篇 |
2020年 | 437篇 |
2019年 | 393篇 |
2018年 | 396篇 |
2017年 | 422篇 |
2016年 | 819篇 |
2015年 | 776篇 |
2014年 | 867篇 |
2013年 | 1797篇 |
2012年 | 1705篇 |
2011年 | 2073篇 |
2010年 | 1194篇 |
2009年 | 1032篇 |
2008年 | 1636篇 |
2007年 | 1651篇 |
2006年 | 1693篇 |
2005年 | 1514篇 |
2004年 | 1434篇 |
2003年 | 1200篇 |
2002年 | 1158篇 |
2001年 | 537篇 |
2000年 | 491篇 |
1999年 | 483篇 |
1998年 | 471篇 |
1997年 | 508篇 |
1996年 | 489篇 |
1995年 | 431篇 |
1994年 | 468篇 |
1993年 | 423篇 |
1992年 | 389篇 |
1991年 | 388篇 |
1990年 | 356篇 |
1989年 | 349篇 |
1988年 | 328篇 |
1987年 | 303篇 |
1986年 | 285篇 |
1985年 | 425篇 |
1984年 | 438篇 |
1983年 | 381篇 |
1982年 | 415篇 |
1981年 | 386篇 |
1980年 | 402篇 |
1979年 | 344篇 |
1978年 | 384篇 |
1977年 | 349篇 |
1976年 | 316篇 |
1975年 | 271篇 |
1974年 | 262篇 |
1973年 | 218篇 |
1972年 | 160篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
41.
42.
43.
44.
Given a principal value convolution on the Heisenberg group Hn = Cn×R, we study the relation between its Laguerre expansion and the Fourier-Bessel expansion of its limit on Cn. We also calculate the Dirichlet kernel for the Laguerre expansion on the group Hn. 相似文献
45.
An experimental method for determining the real-time depth of laser-drilled holes is presented. The proposed method involves
detecting the laser-induced optoacoustic waves generated during the interaction of the laser beam with the material. Our optodynamic
study involved measuring the propagation times of these waves as they traveled through the material and analyzing their temporal
behavior during the drilling process. The experimental observations revealed an exponential relationship between the propagation
time of the longitudinal stress wave and the number of consecutive laser pulses.
Received: 25 October 2001 / Accepted: 27 October 2001 / Published online: 20 December 2001 相似文献
46.
In order to investigate the relative effects of the differences between the structures and lipophilicities of 1, 10-dioxa-4, 7, 13, 16-tetra-azacyclo-octadecane (TA-18-crown-6) and the tetrabenzyl derivative of 1,10-dioxa-4, 7, 13, 16-tetra-azacyclo-octadecane (TBTA-18-crown-6) on their extraction-abilities and -selectivities for transition metal cations, constants of the overall extraction (logK
ex) of 1:1 (M:L) complexes, the distribution (K
D) for two diluents (CH2Cl2 and CHCl3) with different dielectric constants have been determined at 25 ± 0.1 °C. The magnitude of logK
ex is largely determined by that of K
D. The equilibrium constants of TA-18-crown-6 have been compared with those of TBTA-18-crown-6. It is found that:(i) logK
ex sequences of TA-18-crown-6 and TBTA-18-crown-6 for transition metals in CH2Cl2 lie in order: Fe3+ > Cu2+ > Mn2+ > Co2+ > Cd2+ > Ni2+ > Zn2+ and Fe3+ > Cu2+ > Co2+ > Mn2+ > Ni2+ > Cd2+ > Zn2+ respectively; (ii) the stability sequences of two types of tetra-aza-crown ethers with the transition metal cations in CHCl3 are the same as follows: Fe3+ > Ni2+ > Cu2+ > Co2+ > Zn2+ > Cd2+ > Mn2+, and (iii) unusual selectivities are observed for transition metal-tetra-aza-crowns, e.g. the high Fe3+/M
n+ selectivity factors (Sf) of TA-18-crown-6, except for the competitive-extractions for the special case in CHCl3 of TBTA-18-crown-6, it was found that the Mn2+/M
n+ values were relatively higher according to the other transition metal cations. A systematic sequence in these two types of solvents is not found for a given transition metal cation in terms of the variation of selectivity with the tetra-aza-crown ethers. The results provide alternatives for the rational design of other specific ligands on the transition metal cations. 相似文献
47.
Peter Otte 《Proceedings of the American Mathematical Society》2004,132(3):827-830
Motivated by the general approach due to Shargorodsky we derive enclosure results for the second-order relative spectrum of bounded selfadjoint operators by studying quadratic operator pencils. The quality of the results is discussed by means of a simple example.
48.
49.
50.
S. B. Ellis S. J. Kiehl W. S. Hughes K. Schwabe W. C. Gardiner H. L. Sanders H. Yoshimura Hanna Jablezynska-Jedrzewska J. Domański W. A. Dorfman P. Nylén Barbara Stone F. Hovorka W. C. Dearing E. Biilmann W. Kordatzki P. Wulff G. Florence A. Drilhon P. Szigeti O. Tomiček F. Poupě O. Redlich W. Stricks 《Analytical and bioanalytical chemistry》1937,111(2-4):94-104