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   2235篇
  免费   191篇
  国内免费   5篇
化学   1869篇
晶体学   29篇
力学   43篇
数学   108篇
物理学   382篇
  2023年   25篇
  2022年   26篇
  2021年   43篇
  2020年   75篇
  2019年   83篇
  2018年   47篇
  2017年   31篇
  2016年   114篇
  2015年   101篇
  2014年   107篇
  2013年   136篇
  2012年   217篇
  2011年   241篇
  2010年   104篇
  2009年   76篇
  2008年   152篇
  2007年   124篇
  2006年   120篇
  2005年   104篇
  2004年   92篇
  2003年   56篇
  2002年   53篇
  2001年   22篇
  2000年   28篇
  1999年   12篇
  1998年   9篇
  1997年   9篇
  1996年   4篇
  1995年   9篇
  1994年   16篇
  1993年   15篇
  1992年   14篇
  1991年   9篇
  1990年   12篇
  1989年   10篇
  1988年   9篇
  1987年   11篇
  1986年   16篇
  1985年   15篇
  1984年   6篇
  1983年   5篇
  1982年   5篇
  1981年   6篇
  1980年   9篇
  1979年   5篇
  1978年   9篇
  1977年   5篇
  1976年   6篇
  1975年   7篇
  1974年   8篇
排序方式: 共有2431条查询结果,搜索用时 15 毫秒
321.
322.
A higher generation dendron with a long-alkyl chain thiol (DA2-SH) induced the formation of nanoparticles with a small core with quite a narrow size distribution (1.5 +/- 0.1 nm), the self-assembly of one-dimensional arrays of these gold nanoparticles (DA2-Au), and the stabilization for the formation of the radical cation of the phenothiazine of DA2-Au nanoparticles from the interfacial one-electron oxidation of the nanoparticles with NOBF4.  相似文献   
323.
The reaction of cyclohexa-2,5-dienyl-1-methylaldehyde and optically pure 1,2-diaryl-1,2-diamine followed by intramolecular bromo-amination produced a one-pot discrimination of two olefins in the cyclohexane system, which was used for the asymmetric synthesis of (-)-gamma-lycorane.  相似文献   
324.
An abasic site-containing DNA combined with lumiflavin allows amperometric determination of single nucleotide polymorphism through hydrogen bond-mediated nucleobase recognition in water by using abasic sites as a molecular recognition field.  相似文献   
325.
A sterically congested tetraphenyl-substituted dibenzo-tetraaza-isobacteriochlorinato nickel derivative unexpectedly reacts with methanol at room temperature to release internal molecular strains, leading to the formation of a ligand having a skeleton bearing two cis-methoxy substituents.  相似文献   
326.
Flattened representations are a useful approach to represent the convoluted complex surface of the neocortex of primates and other large-brained mammals. In this study, we compared the flattened representation of neocortical areas obtained from the recently published MRI and histology atlas of the rhesus monkey brain (Saleem KS, Logothetis NK. A combined MRI and histology atlas of the rhesus monkey brain in stereotaxic coordinates. London: Academic; 2007) with other previously published maps. Our results confirm that flat map representations are advantageous due to their ease of use and that current flat maps are well comparable to each other. Some differences arise due to different distinguishing criteria and here too flat maps can help to reveal them.  相似文献   
327.
Ni species on the spent NiMo catalyst from ultra‐deep hydrodesulfurization of gas oil in a commercial plant were studied by Ni K‐edge EXAFS and TEM measurement without contact of the catalysts with air. The Ni–Mo coordination shell related to the Ni–Mo–S phase was observed in the spent catalyst by quasi in situ Ni K‐edge EXAFS measurement with a newly constructed high‐pressure chamber. The coordination number of this shell was almost identical to that obtained by in situ Ni K‐edge EXAFS measurement of the fresh catalyst sulfided at 1.1 MPa. On the other hand, large agglomerates of Ni3S2 were observed only in the spent catalyst by quasi in situ TEM/EDX measurement. MoS2‐like slabs were sintered slightly on the spent catalyst, where they were destacked to form monolayer slabs. These results suggest that the Ni–Mo–S phase is preserved on the spent catalyst and Ni3S2 agglomerates are formed by sintering of Ni3S2 species originally present on the fresh catalyst.  相似文献   
328.
Quinacridone nanoparticles with a mean size of about 200 nm are successfully prepared using nanosecond near-infrared (NIR) laser ablation of its microcrystalline powders in heavy water. The absorption spectra of the formed colloidal solutions depend on the excitation wavelengths, which is eventually ascribed to number and energy of absorbed photons. β-carotene has low photostability and is easily decomposed upon UV/VIS laser ablation of its solid, while its nanoparticles are prepared utilizing this NIR laser ablation technique. The advantage of nanoparticle preparation by NIR laser ablation is discussed.  相似文献   
329.
Abstract

We consider a new two-scale problem which is given as a mathematical model for moisture transport arising in a concrete carbonation process. In research for moisture transport, it is a crucial step how to describe the relationship between the relative humidity and the degree of saturation, mathematically. Here, we have proposed the two-scale model consisting of the diffusion equation for the relative humidity in a macro domain and the free boundary problems describing the relationship in infinitely micro domains. Accordingly, the structures of the micro domains are unknown in our model. This is a significant feature of our new model to emphasize. The aim of this paper is to establish local existence in time and uniqueness of a solution to the model.  相似文献   
330.
We show that, for any given non-spherical orientable closed surface F2, there exists an optimal 1-planar graph which can be embedded on F2 as a triangulation. On the other hand, we prove that there does not exist any such graph for the nonorientable closed surfaces of genus at most 3.  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