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   172422篇
  免费   36783篇
  国内免费   25381篇
化学   113968篇
晶体学   2063篇
力学   11644篇
综合类   551篇
数学   21115篇
物理学   85245篇
  2023年   2681篇
  2022年   2806篇
  2021年   3991篇
  2020年   4954篇
  2019年   5289篇
  2018年   4684篇
  2017年   4894篇
  2016年   6912篇
  2015年   6838篇
  2014年   7747篇
  2013年   11217篇
  2012年   12934篇
  2011年   14794篇
  2010年   14975篇
  2009年   14809篇
  2008年   9292篇
  2007年   8372篇
  2006年   7568篇
  2005年   7078篇
  2004年   6652篇
  2003年   5289篇
  2002年   4866篇
  2001年   4857篇
  2000年   3864篇
  1999年   4411篇
  1998年   3780篇
  1997年   3479篇
  1996年   3879篇
  1995年   3993篇
  1994年   4016篇
  1993年   3801篇
  1992年   3322篇
  1991年   2921篇
  1990年   2438篇
  1989年   2331篇
  1988年   2221篇
  1987年   1460篇
  1986年   1517篇
  1985年   1145篇
  1984年   1199篇
  1983年   495篇
  1982年   1007篇
  1981年   830篇
  1980年   840篇
  1979年   567篇
  1978年   564篇
  1977年   660篇
  1976年   1077篇
  1973年   467篇
  1972年   549篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
101.
A single-polarization filter comprising a gold-coated photonic crystal fiber based on surface plasmon resonance is designed and investigated. The pattern matching and coupled polarization characteristics analyzed by the full-vector finite element method (FEM) and losses at 1,540 nm are achieved to 1,016.01739 dB/cm (x-pol core mode) and 33.81917 dB/cm (y-pol core mode). The crosstalk (CT) value of the 1,540 nm band is ?853.12653 dB for fiber length L=1,000μm and the bandwidth is 850 nm. The working wavelength of the filter ranges from 1,280 nm to 1,540 nm by varying the diameter of outer air holes (d1), the diameter of inner air holes (d4), the metal film thickness (t), as well as the liquid refractive index (n).  相似文献   
102.
Mass spectrometry (MS) driven metabolomics is a frequently used tool in various areas of life sciences; however, the analysis of polar metabolites is less commonly included. In general, metabolomic analyses lead to the detection of the total amount of all covered metabolites. This is currently a major limitation with respect to metabolites showing high turnover rates, but no changes in their concentration. Such metabolites and pathways could be crucial metabolic nodes (e.g., potential drug targets in cancer metabolism). A stable-isotope tracing capillary electrophoresis–mass spectrometry (CE-MS) metabolomic approach was developed to cover both polar metabolites and isotopologues in a non-targeted way. An in-house developed software enables high throughput processing of complex multidimensional data. The practicability is demonstrated analyzing [U-13C]-glucose exposed prostate cancer and non-cancer cells. This CE-MS-driven analytical strategy complements polar metabolite profiles through isotopologue labeling patterns, thereby improving not only the metabolomic coverage, but also the understanding of metabolism.  相似文献   
103.
Defects play a central role in controlling the electronic properties of two-dimensional (2D) materials and realizing the industrialization of 2D electronics. However, the evaluation of charged defects in 2D materials within first-principles calculation is very challenging and has triggered a recent development of the WLZ (Wang, Li, Zhang) extrapolation method. This method lays the foundation of the theoretical evaluation of energies of charged defects in 2D materials within the first-principles framework. Herein, the vital role of defects for advancing 2D electronics is discussed, followed by an introduction of the fundamentals of the WLZ extrapolation method. The ionization energies (IEs) obtained by this method for defects in various 2D semiconductors are then reviewed and summarized. Finally, the unique defect physics in 2D dimensions including the dielectric environment effects, defect ionization process, and carrier transport mechanism captured with the WLZ extrapolation method are presented. As an efficient and reasonable evaluation of charged defects in 2D materials for nanoelectronics and other emerging applications, this work can be of benefit to the community.  相似文献   
104.
Near-field optical trapping can be realized with focused evanescent waves that are excited at the water–glass interface due to the total internal reflection, or with focused plasmonic waves excited on the water–gold interface. Herein, the performance of these two kinds of near-field optical trapping techniques is compared using the same optical microscope configuration. Experimental results show that only a single-micron polystyrene bead can be trapped by the focused evanescent waves, whereas many beads are simultaneously attracted to the center of the excited region by focused plasmonic waves. This difference in trapping behavior is analyzed from the electric field intensity distributions of these two kinds of focused surface waves and the difference in trapping behavior is attributed to photothermal effects due to the light absorption by the gold film.  相似文献   
105.
International Journal of Theoretical Physics - Designated verifier signatures are very useful in the applications such as e-voting and auction. In this paper, an identity-based quantum designated...  相似文献   
106.
We show the short-time existence and nonlinear stability of vortex sheets for the nonisentropic compressible Euler equations in two spatial dimensions, based on the weakly linear stability result of Morando and Trebeschi (2008) [20]. The missing normal derivatives are compensated through the equations of the linearized vorticity and entropy when deriving higher-order energy estimates. The proof of the resolution for this nonlinear problem follows from certain a priori tame estimates on the effective linear problem in the usual Sobolev spaces and a suitable Nash–Moser iteration scheme.  相似文献   
107.
In this paper, we propose a sufficient and necessary condition for the boundedness of all the solutions for the equation x¨+n2x+g(x)=p(t) with the critical situation that |02πp(t)e?intdt|=2|g(+)?g(?)| on g and p, where nN+, p(t) is periodic and g(x) is bounded.  相似文献   
108.
109.
110.
Floquet engineering appears as a new protocol for designing topological states of matter,and features anomalous edge modes pinned at quasi-energy π/T with vanished topological index.We propose how to predict the anomalous edge modes via the bulk Hamiltonian in frequency space,and use Zak phase to quantitatively index the topological properties.The above methods are clarified by the example of time periodic Kitaev chain with chemical potential of harmonic driving and pulse driving,and topological phase transitions are manifested at different driving frequencies.  相似文献   
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