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   318731篇
  免费   4777篇
  国内免费   1083篇
化学   172472篇
晶体学   3527篇
力学   13054篇
综合类   7篇
数学   37786篇
物理学   97745篇
  2020年   2135篇
  2019年   2056篇
  2018年   2082篇
  2017年   2004篇
  2016年   4158篇
  2015年   3511篇
  2014年   4681篇
  2013年   14487篇
  2012年   11208篇
  2011年   13939篇
  2010年   8529篇
  2009年   8497篇
  2008年   12846篇
  2007年   13085篇
  2006年   12698篇
  2005年   11560篇
  2004年   10351篇
  2003年   9147篇
  2002年   8916篇
  2001年   9886篇
  2000年   7301篇
  1999年   5662篇
  1998年   4414篇
  1997年   4442篇
  1996年   4450篇
  1995年   4376篇
  1994年   4137篇
  1993年   3992篇
  1992年   4471篇
  1991年   4293篇
  1990年   3992篇
  1989年   3822篇
  1988年   4108篇
  1987年   3773篇
  1986年   3695篇
  1985年   5358篇
  1984年   5465篇
  1983年   4420篇
  1982年   4791篇
  1981年   4841篇
  1980年   4584篇
  1979年   4714篇
  1978年   4732篇
  1977年   4713篇
  1976年   4661篇
  1975年   4559篇
  1974年   4399篇
  1973年   4561篇
  1972年   2576篇
  1971年   1867篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
Kleer  Pieter  Schäfer  Guido 《Mathematical Programming》2021,190(1-2):523-560
Mathematical Programming - We study the computation and efficiency of pure Nash equilibria in combinatorial congestion games, where the strategies of each player i are given by the binary vectors...  相似文献   
2.
Doklady Physics - The dependence of Raman spectra of the molecules containing polyene chains on the conjugation length, structure of side and end groups, and isomer type is analyzed theoretically.  相似文献   
3.
Gohl  J. A.  Thiele-Sardina  T. C.  Rencheck  M. L.  Erk  K. A.  Davis  C. S. 《Experimental Mechanics》2021,61(7):1209-1213
Background

Peel tests are frequently used to perform measurements of adhesive strength for pressure sensitive adhesive (PSA) tapes. Current lab methodologies for 90° peel tests translate the model substrate orthogonally to the peel direction in order to maintain the peel angle, precluding testing from immovable substrates.

Objective

It was our objective to develop a peel fixture capable of testing temporary pavement marking (TPM) tapes and other PSA tapes from immovable substrates such as roadways surfaces.

Methods

We present a modular peel fixture for conducting peel experiments directly on immovable substrates. The fixture was validated through a series of peel tests on consumer tapes to reproduce the linear width dependence and viscoelastic rate dependence found in traditional peeling setups. To test the capabilities of the fixture, a series of peel tests were conducted with various tapes on controlled surfaces, and a commercial tape on various immovable substrates.

Results

We demonstrate the ability of our fixture to reproduce results reported for traditional peel tests from literature. In addition, we were able to conduct peel tests directly on immovable substrates such as the benchtop.

Conclusions

This fixture shows potential for both traditional peeling tests, and for use in in-situ peel experiments from substrates relevant to the end application of the PSA tape.

  相似文献   
4.
Marconi  J.  Tiso  P.  Quadrelli  D. E.  Braghin  F. 《Nonlinear dynamics》2021,104(4):3039-3063
Nonlinear Dynamics - We present an enhanced version of the parametric nonlinear reduced-order model for shape imperfections in structural dynamics we studied in a previous work. In this model, the...  相似文献   
5.
Set-Valued and Variational Analysis - R. Tyrell Rockafellar and his collaborators introduced, in a series of works, new regression modeling methods based on the notion of superquantile (or...  相似文献   
6.
In this article, the effect of ionization on the energy spectrum of electrons within the interaction of a laser pulse with hydrogen atoms is investigated using particle-in-cell simulation codes. The results show that the behaviour of electrons' energy distribution function in the field-ionized plasma, which occurred due to the field ionization, compared with that in the pre-plasma strongly depends on the pulse shape. For short rise-time pulses (here 30 fs), due to the rapid enhancement of laser electric field, ionization occurs quickly, and as a result, there is not much difference in the electron energy in both the media. However, for pulses with rise time of 40 fs, in the pre-plasma state, the electron population reaches higher energies compared with the field-ionized plasma state. The main reason for this difference is the nonlinear wave breaking that happens earlier due to density inhomogeneity in the field-ionized plasma. On the other hand, at longer rise-time pulses (here 60 and 70 fs), electrons achieve higher energies in the field-ionized plasma than those in the case of pre-plasma. In this case, because of density fluctuations in the field-ionized plasma, the Raman backscattered radiations are seeded by a strong initial noise at the earlier times and the Mendonca condition for chaos threshold is met sooner. Therefore, the electrons gain more energy through the stochastic mechanism that is in agreement with chaotic nature of the motion.  相似文献   
7.
Kobayashi  M.  Zhang  Y.  Ishikawa  H.  Sun  J.  Oddershede  J.  Juul Jensen  D.  Miura  H. 《Experimental Mechanics》2021,61(5):817-828
Experimental Mechanics - The internal strain distribution developing during plastic deformation is important for understanding the mechanical properties of polycrystalline materials. Such...  相似文献   
8.
Journal of Applied Spectroscopy - With the COVID-19 outbreak, many challenges are posed before the scientific world to curb this pandemic. The diagnostic testing, treatment, and vaccine development...  相似文献   
9.
10.
Journal of Chemical Crystallography - Four different rare-earth oxyapatites of Ca2RE8(SiO4)6O2 (RE?=?Pr, Tb, Ho, Tm) were synthesized using a solution-based method followed by drying,...  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