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   4338篇
  免费   131篇
  国内免费   37篇
化学   2766篇
晶体学   9篇
力学   170篇
数学   933篇
物理学   628篇
  2023年   26篇
  2022年   96篇
  2021年   99篇
  2020年   103篇
  2019年   90篇
  2018年   89篇
  2017年   67篇
  2016年   180篇
  2015年   149篇
  2014年   183篇
  2013年   276篇
  2012年   317篇
  2011年   327篇
  2010年   161篇
  2009年   199篇
  2008年   270篇
  2007年   260篇
  2006年   217篇
  2005年   203篇
  2004年   205篇
  2003年   144篇
  2002年   104篇
  2001年   48篇
  2000年   38篇
  1999年   35篇
  1998年   40篇
  1997年   37篇
  1996年   49篇
  1995年   22篇
  1994年   28篇
  1993年   18篇
  1992年   32篇
  1991年   21篇
  1990年   23篇
  1989年   21篇
  1988年   22篇
  1987年   18篇
  1986年   15篇
  1985年   34篇
  1984年   29篇
  1983年   28篇
  1982年   30篇
  1981年   15篇
  1980年   20篇
  1979年   11篇
  1978年   19篇
  1977年   14篇
  1976年   14篇
  1974年   11篇
  1967年   4篇
排序方式: 共有4506条查询结果,搜索用时 0 毫秒
71.

Background  

There is fMRI evidence that women are neurally predisposed to process infant laughter and crying. Other findings show that women might be more empathic and sensitive than men to emotional facial expressions. However, no gender difference in the brain responses to persons and unanimated scenes has hitherto been demonstrated.  相似文献   
72.
We construct a countable set of prime non-homeomorphic homology spheres with Heegaard genus 2.
Sunto Si prova l'esistenza di una classe numerabile di sfere omologiche prime non omeomorfe con genere di Heegaard 2.


Work performed under the auspicies of the G.N.S.A.G.A. of the C.N.R. (National Research Council of Italy) and within the project Geometria delle Varietà Differenziabili of the M.P.I. (Italy).  相似文献   
73.
74.
75.
We define a de Rham cohomology theory for analytic varieties over a valued field K? of equal characteristic p with coefficients in a chosen untilt of the perfection of K? by means of the motivic version of Scholze's tilting equivalence. We show that this definition generalizes the usual rigid cohomology in case the variety has good reduction. We also prove a conjecture of Ayoub yielding an equivalence between rigid analytic motives with good reduction and unipotent algebraic motives over the residue field, also in mixed characteristic.  相似文献   
76.
Density Functional Theory employing hybrid and M06 functionals in combination with three different basis sets is used to calculate the ground state of a cage like (ZnO)12 nanocluster which has been consistently reported as the more stable cluster for its particular size. B3LYP and B3PW91 hybrid functionals combined with 6‐31+G*, Lanl2dz and SDD basis sets are employed to treat the ZnO molecular system. Alternatively, three M06 functionals in combination with three basis sets are employed in the nanostructure calculations. Results obtained by treating ZnO sodalite cage nanocluster with M06 functionals demonstrated comparable quality to results obtained with hybrid functionals. Within this study, efficient theoretical DFT methods with the widely known hybrid and the recently created M06 meta‐hybrid functionals are employed to study nanostructured ZnO. Our resulting parameters provide a fresh approach performance wise on the different theoretical methods to treat transition metal nanostructures, particularly, ZnO nanoclusters geometry and electronic structure.  相似文献   
77.
78.
79.

The environmental impacts associated with the exploitation and transformation of fossil resources aggravate the planet's situation in terms of climate change. Due to this, this paper studies an alternative use of mineral coal as a precursor to obtaining new materials with different properties to the starting coals. The thermal degradation of two Colombian semi-anthracites is analyzed through the thermogravimetry (TG) technique coupled to a Fourier transform infrared spectroscopy (FTIR) equipment from room temperature (25 °C) to 900 °C, at a heating rate of 10 K min?1 in an inert atmosphere. The catalytic effect of the addition of silicon to these samples before being subjected to a carbonization process is evaluated during this process. The results indicated that the primary reaction occurs in the temperature range between 400 and 680 °C, where the highest mass loss rate was observed. At the end of the heating process, the TG profile of the samples with silicon addition showed losses between 14.33 and 18.82% in mass, these values being slightly higher compared to the starting and demineralized samples. The release of water, light gases such as CO2, CH4, and species such as toluene, phenol and formic acid was identified in most of the samples. The presence of silica seems to favor the release of all these species, being more evident in one of the semi-anthracites studied. According to the results obtained, it is proved that the presence of silicon in samples subjected to carbonization processes has a catalytic effect that improves some characteristics of the new materials obtained, thus contributing to the use of carbon to get new materials.

  相似文献   
80.
Electroweak radiative corrections to muon capture on nuclei are computed and found to be sizable. They enhance the capture rates for hydrogen and helium by 2.8% and 3.0%, respectively. As a result, the value of the induced pseudoscalar coupling, g(P)(exp), extracted from a recent hydrogen 1S singlet capture experiment is increased by about 21% to g(P)(exp)=7.3+/-1.2 and brought into good agreement with the prediction of chiral perturbation theory, g(P)(theory)=8.2+/-0.2. Implications for helium capture rate predictions are also discussed.  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