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   6752篇
  免费   298篇
  国内免费   37篇
化学   5229篇
晶体学   32篇
力学   136篇
数学   715篇
物理学   975篇
  2023年   64篇
  2022年   100篇
  2021年   121篇
  2020年   144篇
  2019年   163篇
  2018年   133篇
  2017年   111篇
  2016年   263篇
  2015年   201篇
  2014年   205篇
  2013年   337篇
  2012年   554篇
  2011年   653篇
  2010年   298篇
  2009年   224篇
  2008年   483篇
  2007年   478篇
  2006年   483篇
  2005年   448篇
  2004年   323篇
  2003年   281篇
  2002年   232篇
  2001年   74篇
  2000年   45篇
  1999年   35篇
  1998年   37篇
  1997年   42篇
  1996年   37篇
  1995年   30篇
  1994年   27篇
  1993年   36篇
  1992年   30篇
  1991年   25篇
  1990年   19篇
  1989年   16篇
  1988年   20篇
  1987年   19篇
  1986年   14篇
  1985年   26篇
  1984年   24篇
  1983年   11篇
  1982年   12篇
  1981年   16篇
  1979年   24篇
  1978年   20篇
  1977年   16篇
  1976年   15篇
  1975年   11篇
  1974年   17篇
  1973年   16篇
排序方式: 共有7087条查询结果,搜索用时 15 毫秒
81.
82.
Lines of the 3ν23 “forbidden” band of 12C16O2 have been identified in the 2000-cm?1 region of a long-path, 0.01-cm?1 resolution laboratory absorption spectrum. This band has detectable intensity due to Δl = 2 Fermi interactions between the upper level and the nearby ν1 + ν2 and 3ν21 levels. Intensities of 18 lines of this band have been measured using a nonlinear least-squares spectral fitting technique. The intensities are enhanced at high J and an expression for the intensity distribution as derived by Toth [Appl. Opt.23, 1825–1834 (1984)] is used for the analysis. In terms of the total sample pressure, the vibrational band intensity is 0.194 ± 0.008 × 10?30 cm?1/molecule-cm?2 at 296 K. The coefficient in the F factor is analogous to the Coriolis coefficient ξ and has been determined to be ?0.0413 ± 0.0015. As expected by theory, its value is very close to that of ξ for the related ν1 + ν2 band.  相似文献   
83.
84.
A computer based numerical method is presented for the analysis of water and solute movement in unsaturated heterogeneous porous materials. Such a method is necessary since, for those field studies where solute movement is of concern, the soil profiles under consideration are invariably heterogeneous. The numerical analysis is based on a general one-dimensional finite difference soil water flow model which includes a numerical technique combining the concepts of scale heterogeneity with an interpolative soil water hysteresis model. An explicit finite difference solute movement subroutine is incorporated into the unsaturated flow model to describe the transport of nonreactive solutes. A velocity dependent longitudinal dispersion coefficient is used in the solution of the hydrodynamic dispersion equation. The resulting hysteretic scale heterogeneous solute movement model permits the study of solute dynamics during infiltrating and redistribution in realistically complex spatially varying soil profiles. Results are presented for the leaching of both coarse grading to fine and fine grading to coarse sand profiles. Both vertical and horizontal profiles are studied using either a constant flux or a constant concentration input boundary condition. The four cases studied demonstrate the versatility of the numerical method and emphasise the substantial differences in transport behavior that can arise between heterogeneous and homogeneous profiles.Now with BHP Petroleum Pty. Ltd., GPO Box 1911R, Melbourne, Vic. 3001, Australia.  相似文献   
85.
Parallel to the study of finite-dimensional Banach spaces, there is a growing interest in the corresponding local theory of operator spaces. We define a family of Hilbertian operator spaces , , generalizing the row and column Hilbert spaces and , and we show that an atomic subspace that is the range of a contractive projection on is isometrically completely contractive to an -sum of the and Cartan factors of types 1 to 4. In particular, for finite-dimensional , this answers a question posed by Oikhberg and Rosenthal. Explicit in the proof is a classification up to complete isometry of atomic w-closed -triples without an infinite-dimensional rank 1 w-closed ideal.

  相似文献   

86.
This paper exhibits an infinite collection of algebraic curves isometrically embedded in the moduli space of Riemann surfaces of genus two. These Teichmüller curves lie on Hilbert modular surfaces parameterizing Abelian varieties with real multiplication. Explicit examples, constructed from L-shaped polygons, give billiard tables with optimal dynamical properties.

  相似文献   

87.
88.
Let F(z)=∑n=1a(n)qn denote the unique weight 16 normalized cuspidal eigenform on . In the early 1970s, Serre and Swinnerton-Dyer conjectured that
  相似文献   
89.
We construct a family of partially ordered sets (posets) that are q-analogs of the set partition lattice. They are different from the q-analogs proposed by Dowling [5]. One of the important features of these posets is that their Whitney numbers of the first and second kind are just the q-Stirling numbers of the first and second kind, respectively. One member of this family [4] can be constructed using an interpretation of Milne [9] for S[n, k] as sequences of lines in a vector space over the Galois field F q. Another member is constructed so as to mirror the partial order in the subspace lattice.  相似文献   
90.
ABSTRACT

A new opposed type double-stage large volume cell has been developed to compress large volume samples to more than 100?GPa (Mbar) pressure. A pair of second-stage diamond anvils is introduced into the first-stage Paris–Edinburgh press. The double-stage large volume cell allows the generation of ultrahigh pressures using a large culet diameter of the second-stage diamond anvils (diameters of 0.5–1.2?mm). Pressure generation up to 131?GPa has been achieved by using the culet diameter of 0.5?mm. Sample volume of the double-stage large volume cell can be more than ~100 times larger than that of conventional Mbar experiment using a diamond anvil cell. The double-stage large volume cell has a large opening in the horizontal plane for X-ray measurements, which is particularly suited for the multi-angle energy dispersive X-ray diffraction measurement, thus opening a new way of in situ structural determinations of amorphous materials at Mbar pressures.  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