全文获取类型
收费全文 | 482200篇 |
免费 | 3039篇 |
国内免费 | 714篇 |
专业分类
化学 | 222019篇 |
晶体学 | 6915篇 |
力学 | 27615篇 |
综合类 | 9篇 |
数学 | 73894篇 |
物理学 | 155501篇 |
出版年
2020年 | 4257篇 |
2019年 | 5050篇 |
2018年 | 12381篇 |
2017年 | 12790篇 |
2016年 | 12276篇 |
2015年 | 5152篇 |
2014年 | 8738篇 |
2013年 | 17502篇 |
2012年 | 16889篇 |
2011年 | 24649篇 |
2010年 | 17667篇 |
2009年 | 17998篇 |
2008年 | 22670篇 |
2007年 | 24855篇 |
2006年 | 14483篇 |
2005年 | 16142篇 |
2004年 | 13642篇 |
2003年 | 13049篇 |
2002年 | 12087篇 |
2001年 | 11264篇 |
2000年 | 9055篇 |
1999年 | 6670篇 |
1998年 | 6125篇 |
1997年 | 5915篇 |
1996年 | 5523篇 |
1995年 | 5008篇 |
1994年 | 5035篇 |
1993年 | 4916篇 |
1992年 | 5122篇 |
1991年 | 5629篇 |
1990年 | 5406篇 |
1989年 | 5409篇 |
1988年 | 5158篇 |
1987年 | 5153篇 |
1986年 | 4774篇 |
1985年 | 5796篇 |
1984年 | 6139篇 |
1983年 | 5198篇 |
1982年 | 5528篇 |
1981年 | 5122篇 |
1980年 | 4829篇 |
1979年 | 5404篇 |
1978年 | 5646篇 |
1977年 | 5568篇 |
1976年 | 5719篇 |
1975年 | 5344篇 |
1974年 | 5260篇 |
1973年 | 5459篇 |
1972年 | 4275篇 |
1971年 | 3855篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
241.
Archiv der Mathematik - A generalized Baumslag–Solitar group is a finitely generated group that acts on a tree with infinite cyclic edge and vertex stabilizers. A group G is residually a... 相似文献
242.
243.
Dr. Felipe L. Coelho Eduarda S. Gil Dr. Paulo F. B. Gonçalves Dr. Leandra F. Campo Dr. Paulo H. Schneider 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(34):8157-8162
In this work, a series of 2-chalcogenylindoles was synthesized by an efficient methodology, starting from chalcogenoalkynes, including a previously unreported tellurium indole derivative. For the first time, these 2-substituted chalcogenylindoles were obtained in the absence of metal catalyst or base, under thermal conditions only. In addition, the results described herein represent a methodology with inverse regioselectivity for the chalcogen functionalization of indoles. 相似文献
244.
Ortiz Adolfo Yang Jianhua Coccolo Mattia Seoane Jesús M. Sanjuán Miguel A. F. 《Nonlinear dynamics》2020,102(4):2323-2337
Nonlinear Dynamics - The main purpose of this paper is to study both the underdamped and the overdamped dynamics of the nonlinear Helmholtz oscillator with a fractional-order damping. For that... 相似文献
245.
246.
Differential inequalities for polynomials generalizing the well-known Smirnov, Rahman, Schmeisser, and Bernstein inequalities are obtained.
相似文献247.
Driven and non-equilibrium quantum states of matter have attracted growing interest in both theoretical and experimental studies in condensed matter physics. Recent progress in realizing transient collective states in driven or pumped Dirac materials (DMs) is reviewed herein. In particular, the focus is on optically pumped DMs which are a promising platform for transient excitonic instabilities. Optical pumping combined with the linear (Dirac) dispersion of the electronic spectrum offers a knob for tuning the effective interaction between the photoexcited electrons and holes, and thus provides a way of reducing the critical coupling for excitonic instability. As a result, a transient excitonic condensate could be achieved in a pumped DM while it is not feasible in equilibrium. A unifying theoretical framework is provided for describing transient collective states in 2D and 3D DMs. The experimental signatures are described and numerical estimates of the size of the dynamically induced excitonic gaps and the values of the critical temperatures for several specific systems, are summarized. In addition, general guidelines for identifying promising material candidates are discussed. Finally, comments are provided regarding recent experimental efforts in realizing transient excitonic condensate in pumped DMs, and outstanding issues and possible future directions are outlined. 相似文献
248.
Umie F.M. Haziz Rosenani A. Haque Shun-Ze Zhan Hassan H. Abdallah Mohd R. Razali 《应用有机金属化学》2020,34(10):e5818
The synthesis and characterizations for a series of dinuclear gold (I)-di-NHC complexes, 1–8 through the trans-metalation method of their respective silver (I)-di-NHC complexes, i–viii are reported (where NHC = N-heterocyclic carbene). The successful complexation of a series of unusual non-symmetrical and symmetrical di-NHC ligands, 3,3'-(ethane-1,2-diyl)-1-alkylbenzimidazolium-1'-butylbenzimidazolium (with alkyl = methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, benzyl) with the gold (I) ions are suggested by elemental analysis, Fourier transform-infrared, 1H- and 13C-NMR data. The 13C-NMR spectra of 1–8 show a singlet sharp peak in the range of 190.00–192.00 ppm, indicating the presence of a carbene carbon that bonded to the gold (I) ion. From single crystal X-ray diffraction data, the structure of complex 6 with the formula of [di-NHC-Au (I)]2·2PF6 is obtained [where NHC = 3,3'-(ethane-1,2-diyl)-1-hexylbenzimidazolium-1'-butylbenzimidazolium]. The photophysical study in solid state of 6 displays an intense photoluminescence with a strong emission maxima, λem = 480 nm, upon excitation at 340 nm at room temperature. Interestingly, the emission maximum at 77 K shows a structural character with a strong peak at 410 nm, a medium at 433 nm and a weak at 387 nm, accompanied by a tail band to about 500 nm. 相似文献
249.
Radiophysics and Quantum Electronics - We consider whether it is possible in principle to retrieve the key parameters of the mixed layer in the upper ocean (its thickness, bulk eddy viscosity and... 相似文献
250.
Lebedev V. T. Serebrov A. P. 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2020,14(1):1-5
Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques - A method for studying the magnetic dynamics of endofullerenes M@C2n (2n = 60, 70, …) and their derivatives,... 相似文献