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   552417篇
  免费   5042篇
  国内免费   1304篇
化学   285554篇
晶体学   7804篇
力学   26408篇
综合类   17篇
数学   71392篇
物理学   167588篇
  2021年   5351篇
  2020年   5895篇
  2019年   6619篇
  2018年   8976篇
  2017年   9053篇
  2016年   12584篇
  2015年   6975篇
  2014年   11228篇
  2013年   25054篇
  2012年   20070篇
  2011年   23663篇
  2010年   17503篇
  2009年   17145篇
  2008年   22196篇
  2007年   22030篇
  2006年   19916篇
  2005年   17797篇
  2004年   16398篇
  2003年   14687篇
  2002年   14501篇
  2001年   15133篇
  2000年   11687篇
  1999年   9042篇
  1998年   7798篇
  1997年   7624篇
  1996年   7181篇
  1995年   6433篇
  1994年   6423篇
  1993年   6228篇
  1992年   6561篇
  1991年   6980篇
  1990年   6682篇
  1989年   6575篇
  1988年   6406篇
  1987年   6224篇
  1986年   5950篇
  1985年   7544篇
  1984年   7873篇
  1983年   6616篇
  1982年   6893篇
  1981年   6403篇
  1980年   6066篇
  1979年   6574篇
  1978年   6803篇
  1977年   6681篇
  1976年   6647篇
  1975年   6357篇
  1974年   6173篇
  1973年   6486篇
  1972年   4737篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
901.
The weighted oscillator strengths (gf) and the lifetimes presented in this work were carried out in a multi configuration Hartree-Fock relativistic (HFR) approach. In this calculation, the electrostatic parameters were optimized by a least-squares procedure, in order to improve the adjustment to experimental energy levels. This method produces gf-values that are in better agreement with intensity observations and lifetime values that are closer to the experimental ones. In this work, we presented all the experimentally known electric dipole S IX and S X spectral lines.  相似文献   
902.
In a recent paper, light-rail line noise exposures were predicted both in terms of maximum pass-by sound levels for comparison to APTA criteria and day-night average sound levels for comparison to FTA criteria. For the local land uses and ambient noise conditions of the project, the distances for the unmitigated pass-by noise exposures to attenuate to the APTA and FTA criteria limits were estimated and the numbers of included dwellings counted. The results found that the FTA impact-onset (i.e., “some-impact”) criterion curve yielded significantly greater noise exposed areas while the APTA criteria yielded results between those of the FTA “some”- and “severe”-impact curves. However, those results only applied to the specific project under evaluation. This paper attempts to extend and generalize the comparison by parametric computation of exposed areas using both the FTA and APTA procedures. Predicted exposures in this paper are compared as a function of background ambient sound levels, type of land use impacted, numbers of daytime and nighttime operations, and train pass-by maximum sound levels. At very low background ambient sound levels, FTA tended to predict the greatest exposure, while in very noisy environments, APTA predicted more exposure. APTA predicted more exposure with low numbers of daily and/or nighttime operations, and FTA predicted more exposure with high numbers, but the comparative exposures were strongly dependent upon background ambient sound level and land use. For train pass-by maximum sound levels, APTA tended to show more exposure for very quiet pass-bys and to be intermediate to FTA/some and FTA/severe for noisier events—with the comparative exposures strongly dependent upon background ambient and land use.  相似文献   
903.
Suppose that attached to each site z ∈ ? is a coin with bias θ(z), and only finitely many of these coins have nonzero bias. Allow a simple random walker to generate observations by tossing, at each move, the coin attached to its current position. Then we can determine the biases {θ(z)}z∈?, using only the outcomes of these coin tosses and no information about the path of the random walker, up to a shift and reflection of ?. This generalizes a result of Harris and Keane. © 2004 Wiley Periodicals, Inc. Random Struct. Alg., 2004  相似文献   
904.
905.
906.
907.
Microscopic evidence indicates that the thickness of the interfacial transition zone (ITZ) between the aggregate and the cement paste is modified when mineral admixtures partially replace portland cement. Unfortunately, there is limited information on the significance of these microscopic modifications to the mechanical properties of the ITZ. This research reports experimental results on the shear and tensile strength of the ITZ as affected by the addition of the following mineral admixtures: silica fume, fly ash, and natural pozzolan. Statistical analysis was used to identify the significant parameters affecting the tensile and shear strength of the ITZ. Experimental results indicate that not only does the incorporation of silica fume and fly ash increase the strength of the ITZ, these mineral admixtures have a greater influence on the strength increase of the ITZ than in the strength increase of the cement paste.  相似文献   
908.
909.
On the basis of diagram formalism for two-particle Green functions, the bremsstrahlung of charged particles interacting in a dense medium is investigated. In the case of production of soft photons, exact expressions for two-particle Green functions corresponding to the process of particle bremsstrahlung in the substance are obtained. The Green functions found are fully determined by the set of closed irreducible diagrams. It is shown that, in the case of radiation in a sufficiently dense medium in a far long-wave region of the spectrum, the coherent multiple particle scattering results in an additional (as compared that reported earlier in [1–13]) suppression of the bremsstrahlung photon yield.  相似文献   
910.
The effect of free carriers on the dispersion and damping of coupled phonon-plasmon modes is considered in the long-wave approximation. The electron and phonon scattering rate, as well as Landau damping, is taken into account.  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