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   125003篇
  免费   31955篇
  国内免费   34826篇
化学   80602篇
晶体学   3393篇
力学   8673篇
综合类   2315篇
数学   18482篇
物理学   78319篇
  2024年   579篇
  2023年   1113篇
  2022年   2629篇
  2021年   2479篇
  2020年   2577篇
  2019年   2998篇
  2018年   2894篇
  2017年   4380篇
  2016年   3609篇
  2015年   4735篇
  2014年   5148篇
  2013年   7456篇
  2012年   8076篇
  2011年   10166篇
  2010年   13718篇
  2009年   14198篇
  2008年   8620篇
  2007年   7646篇
  2006年   7210篇
  2005年   6860篇
  2004年   6776篇
  2003年   5052篇
  2002年   5059篇
  2001年   5344篇
  2000年   4849篇
  1999年   3832篇
  1998年   2752篇
  1997年   2421篇
  1996年   2714篇
  1995年   3128篇
  1994年   3159篇
  1993年   3224篇
  1992年   2758篇
  1991年   2332篇
  1990年   1969篇
  1989年   2075篇
  1988年   2033篇
  1987年   1308篇
  1986年   1330篇
  1985年   929篇
  1984年   1079篇
  1983年   449篇
  1982年   947篇
  1981年   792篇
  1980年   818篇
  1979年   591篇
  1978年   552篇
  1977年   641篇
  1976年   1047篇
  1972年   533篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
In this paper, we give the following dominated theorem: Let φ(g) ∈ L1(G//K),φε(t)=ε> 0, and the least radical decreasing dominatedfunction φ(t) = sup |φ(y)| ∈L1(G//K). If shtφ(t) is monotonically decreasingon (0, ∞), then for any f∈L1loc(G//K) , the following inequality holds:sup |φε * f(x)| ≤ Cmf(x),where mf(x) is the Hardy-Littlewood maximal function of f, and C = ||φ||1.An application of this dominated theorem is also given.  相似文献   
62.
The dielectric constant for rain medium is investigated by utilizing the system identification method. The rain rate model and frequency model of permittivity in millimeter waves band for rain medium are presented. The results obtained with models are in very good agreement with references in calculating the attenuation of electromagnetic waves induced by rain, which Shows that the obtained models are valid and practicable. The cross-polar discrimination gotten with rain rate model is in agreement with references.  相似文献   
63.
We study the infrared emission at 1.54 μm of an organolanthanide complex, Er(III)-tetraphenylporphyrin [Er(TPP)acac], both as a result of direct optical excitation and via energy transfer from host π-conjugate polymers of type poly(arylene–ethynylene) [PAE]. In the first case, the emission of the neat complex is characterized in inert transparent materials and a value of the quantum yield at 1.54 μm φIR=4×10−4 is measured. Then, fluorescence resonance transfer is investigated in blends of Er(TPP)acac with PAEs by monitoring the quenching of the polymer fluorescence along with the enhancement of both the visible emission of the ligand and the near-infrared band of Er3+. These different procedures allow a detailed analysis of the transfer efficiency within a specific implementation of the Förster model for polymeric donors. The experimental values of the critical radius R0, ranging from 1.3 to 2.5 nm for the different blends, are in good agreement with theory for a wide interval of the physical and spectroscopic parameters. This suggests that other mechanisms for excitation transfer do not play a significant role in these materials.  相似文献   
64.
Solid state nuclear track detectors are commonly used for measurements of concentrations of radon gas and/or radon progeny. All these measurements depend critically on the thickness of the removed layer during etching. However, the thickness of removed layer calculated using the etching period does not necessarily provide a sufficiently accurate measure of the thickness. For example, the bulk etch rate depends on the strength of stirring during etching for the LR 115 detector. We propose here to measure the thickness of the removed layer by using energy-dispersive X-ray fluorescence spectrometry. In the present work, a reference silver nitrate pellet is placed beneath the LR 115 detector, and the fluorescence X-ray intensity for silver is then measured. We have found a linear relationship between the X-ray intensity and the thickness of the removed layer for LR 115 detector. This provides a fast method to measure the thickness of removed layer from etching of LR 115 detector. However, this method was found to be inapplicable for the CR-39 detector. Therefore, alternative methods have yet to be explored for the CR-39 detector.  相似文献   
65.
We have simultaneously used adsorption isotherm volumetry and Fourier transform infrared spectroscopy in order to take the investigations on amorphous ice structure a step further, especially concerning porosity and annealing-induced modifications. We have studied surface reorganization during annealing and found that the number of surface sites decreases before crystallization, their relative ratios being different for amorphous and crystalline ice. We also present results confirming that ice can have a large specific surface area and nevertheless be non-microporous.  相似文献   
66.
讨论π空间可测场的谐调性问题。给出非谐调可测场的等价条件,进而对非谐调可测场进行分类,并对各类可测场给出相应的刻划。最后给出一个例子。  相似文献   
67.
68.
Synthesis of a new monomer and polymer containing both ferrocene and hydrazone moieties are reported. The obtained materials were examined by various techniques including differential scanning calorimetry, UV, IR, NMR spectroscopy, and time of flight method. These materials may be of particular interest for the development of future electrophotographic photoreceptors as electron photoemission spectra of the layers showed ionization potentials of 5.35–5.41 eV. The hole drift mobility values in compositions of the designed structures with bisphenol Z polycarbonate exceeded 10−8 cm2/Vs at strong electric fields.  相似文献   
69.
Alkyl isocyanides undergo a smooth reaction with alkylidene Meldrum’s acids in the presence of arylhydroxylamines to produce N 1-alkyl-2-(3,5-dioxo-2-aryltetrahydro-4-isoxazolyl)alkanamides in high yields.  相似文献   
70.
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