首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   16808篇
  免费   443篇
  国内免费   136篇
化学   11667篇
晶体学   136篇
力学   513篇
数学   2548篇
物理学   2523篇
  2022年   138篇
  2021年   159篇
  2020年   223篇
  2019年   204篇
  2018年   188篇
  2017年   151篇
  2016年   323篇
  2015年   276篇
  2014年   318篇
  2013年   800篇
  2012年   789篇
  2011年   1074篇
  2010年   499篇
  2009年   457篇
  2008年   882篇
  2007年   920篇
  2006年   962篇
  2005年   889篇
  2004年   811篇
  2003年   730篇
  2002年   694篇
  2001年   235篇
  2000年   202篇
  1999年   165篇
  1998年   190篇
  1997年   201篇
  1996年   241篇
  1995年   187篇
  1994年   186篇
  1993年   150篇
  1992年   152篇
  1991年   159篇
  1990年   132篇
  1989年   115篇
  1988年   151篇
  1987年   142篇
  1986年   107篇
  1985年   213篇
  1984年   235篇
  1983年   170篇
  1982年   241篇
  1981年   220篇
  1980年   225篇
  1979年   207篇
  1978年   199篇
  1977年   182篇
  1976年   183篇
  1975年   152篇
  1974年   162篇
  1973年   155篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
971.
In a previous paper by the second author, two Markov chain Monte Carlo perfect sampling algorithms—one called coupling from the past (CFTP) and the other (FMMR) based on rejection sampling—are compared using as a case study the move‐to‐front (MTF) self‐organizing list chain. Here we revisit that case study and, in particular, exploit the dependence of FMMR on the user‐chosen initial state. We give a stochastic monotonicity result for the running time of FMMR applied to MTF and thus identify the initial state that gives the stochastically smallest running time; by contrast, the initial state used in the previous study gives the stochastically largest running time. By changing from worst choice to best choice of initial state we achieve remarkable speedup of FMMR for MTF; for example, we reduce the running time (as measured in Markov chain steps) from exponential in the length n of the list nearly down to n when the items in the list are requested according to a geometric distribution. For this same example, the running time for CFTP grows exponentially in n. © 2003 Wiley Periodicals, Inc. Random Struct. Alg., 2003  相似文献   
972.
A terahertz polarization insensitive dual band metamaterial absorber   总被引:2,自引:0,他引:2  
Metamaterial absorbers have attracted considerable attention for applications in the terahertz range. In this Letter, we report the design, fabrication, and characterization of a terahertz dual band metamaterial absorber that shows two distinct absorption peaks with high absorption. By manipulating the periodic patterned structures as well as the dielectric layer thickness of the metal-dielectric-metal structure, significantly high absorption can be obtained at specific resonance frequencies. Finite-difference time-domain modeling is used to design the structure of the absorber. The fabricated devices have been characterized using a Fourier transform IR spectrometer. The experimental results show two distinct absorption peaks at 2.7 and 5.2?THz, which are in good agreement with the simulation. The absorption magnitudes at 2.7 and 5.2?THz are 0.68 and 0.74, respectively.  相似文献   
973.
Bringing quantum science and technology to the space frontier offers exciting prospects for both fundamental physics and applications such as long-range secure communication and space-borne quantum probes for inertial sensing with enhanced accuracy and sensitivity. But despite important terrestrial pathfinding precursors on common microgravity platforms and promising proposals to exploit the significant advantages of space quantum missions, large-scale quantum test beds in space are yet to be realised due to the high costs and lead times of traditional ‘Big Space’ satellite development. But the ‘small space’ revolution, spearheaded by the rise of nanosatellites such as CubeSats, is an opportunity to greatly accelerate the progress of quantum space missions by providing easy and affordable access to space and encouraging agile development. We review space quantum science and technology, CubeSats and their rapidly developing capabilities and how they can be used to advance quantum satellite systems.  相似文献   
974.
This paper deals with the problem “Can a noisy orbit be tracked by a real orbit?” In particular, we will study the one-parameter family of tent maps and the one-parameter family of quadratic maps. We writeg μ for eitherf μ orF μ withf μ (x)=μx forx≦1/2 andf μ (x)=μ(1?x) forx≧1/2, andF μ (x)=μx(1?x). For a given μ we will say:g μ permits increased parameter shadowing if for each δ x >0 there exists someδ μ >0 and some δ f >0 such that every δ f -pseudog μ -orbit starting in some invariant interval can be δ x -shadowed by a realg α -orbit with α=μ+δ μ . We show thatg μ typically permits increased parameter shadowing.  相似文献   
975.
The photoelectric work function of nearly stoichiometric (111) and (100) hydrothermally grown UO2 was measured to be 6.28 ± 0.36 eV and 5.80 ± 0.36 eV, respectively. Candidate metals for electrical contacts are identified for both rectifying and non‐rectifying contacts based on work function, lattice compatibility, and electrical conductivity.  相似文献   
976.
A wide variety of sulphides can be readily converted to the corresponding sulphoxides in good to excellent yields by treatment with a combination of sodium chlorite, (salen)manganese(III) complex, and chromatographic alumina in dichloromethane under mild and neutral conditions.  相似文献   
977.
978.
A new electronic transition of PtS with a red degraded band head at 12 460 cm−1 was recorded and analyzed. Gas phase PtS was produced in a platinum-lined hollow cathode with a trace of SF6 gas, and the spectrum was recorded at near Doppler resolution using intracavity laser absorption spectroscopy. Molecular constants for the newly identified excited state are presented.  相似文献   
979.
980.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号