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   712篇
  免费   21篇
  国内免费   1篇
化学   495篇
晶体学   21篇
力学   32篇
数学   67篇
物理学   119篇
  2023年   2篇
  2022年   9篇
  2021年   9篇
  2020年   18篇
  2019年   12篇
  2018年   22篇
  2017年   22篇
  2016年   20篇
  2015年   22篇
  2014年   29篇
  2013年   64篇
  2012年   48篇
  2011年   71篇
  2010年   44篇
  2009年   42篇
  2008年   48篇
  2007年   40篇
  2006年   38篇
  2005年   23篇
  2004年   19篇
  2003年   21篇
  2002年   30篇
  2001年   18篇
  2000年   10篇
  1999年   3篇
  1998年   8篇
  1997年   7篇
  1996年   7篇
  1995年   3篇
  1994年   4篇
  1993年   2篇
  1992年   3篇
  1990年   1篇
  1985年   2篇
  1984年   2篇
  1982年   4篇
  1979年   1篇
  1977年   2篇
  1976年   1篇
  1975年   2篇
  1973年   1篇
排序方式: 共有734条查询结果,搜索用时 15 毫秒
91.
Axially localized NaF dopants are coated onto Al cylindrical wire arrays in order to act as spectroscopic tracers in the stagnated z-pinch plasma. Non-local-thermodynamic-equilibrium kinetic models fit to Na K-shell lines provide an independent measurement of the density and temperature that is consistent with spectroscopic analysis of K-shell emissions from Al and an alloyed Mg dopant. Axial transport of the Na dopant is observed, enabling quantitative study of instabilities in dense z-pinch plasmas.  相似文献   
92.
93.
In this study, we used deep eutectic solvents for digestion and ultrasound-assisted emulsification liquid phase microextraction (UA-ELPME) of copper in liver samples. Different types of DESs were prepared for digestion and microextraction steps. DESs consisting of lactic acid and choline chloride for the digestion step and DESs consisting of tetrabuthylamonium chloride and decanoic acid for ultrasound-assisted emulsification liquid phase microextraction were used in this method. The liver samples were digested by using DES-based digestion method. After digestion step, Cu(II) ions in aqueous phase were complexed with sodium dimethyl dithiocarbamate (NaDMDTC) and the obtained hydrophobic complex was extracted to tetrabuthylamonium chloride-decanoic acid DES phase. A microsample injection system coupled with flame atomic absorption spectrometer (MS-FAAS) was used in the detection of copper. LOD, LOQ, PF and % RSD were determined as 4.00, 13.2 µg L??1, 10 and 3.2%, respectively. The proposed microextraction procedure was successfully applied to copper contents of the liver samples.  相似文献   
94.
95.
Kinetics and Catalysis - In this study, Langmuir–Hinshelwood and Michaelis–Menten kinetic models are applied to describe the kinetic behaviour of the Co–B catalyst in the...  相似文献   
96.
Morphological, surface and crystallographic analyses of titanosilicate ETS-4 products, with diverse habits ranging from spherulitic particles composed of submicron crystallites to large single crystals, are presented. Pole figures revealed that crystal surfaces with a-, b- and c- axes corresponded to 110, 010 and 001 directions, respectively. Thus, technologically important 8-membered ring pores and titania chains in ETS-4 run along the b-axis of single crystals and terminate at the smallest crystal face. Height of the spiral growth steps observed on 1 0 0 and 0 0 1 surfaces corresponded to the interplanar spacings associated with their crystallographic orientation, and is equivalent to the thickness of building units that form the ETS-4 framework. Data suggest that the more viscous synthesis mixtures, with a large driving force for growth, increased the two- and three-dimensional nucleation, while limiting the transport of nutrients to the growth surface. These conditions increase the tendency for stacking fault formation on 1 0 0 surfaces and small angle branching, which eventually results in spherulitic growth. The growth of high quality ETS-4 single crystals (from less viscous synthesis mixtures) occurred at lower surface nucleation rates. Data suggest that these high quality, large crystals grew due to one-dimensional nucleation at spiral hillocks, and indicate that under these conditions un-faulted growth is preferred.  相似文献   
97.
We studied the synthesis and characterization of polymeric coordination complexes of Co(II) and Ni(II) ions with pyrazine-2,3-dicarboxylic acid and 1-vinylimidazole. The e lemental analysis, infrared spectroscopy, powder X-ray diffraction, magnetic susceptibility, thermal analysis and X-ray single crystal techniques were used in the characterization. The X-ray single crystal analysis suggests that the pyrazine-2,3-dicarboxylato ligand acts as a bridging ligand through the oxygen atoms of the carboxylate groups and the nitrogen atoms on the pyrazine ring. The 1-vinylimidazole ligand behaves as a monodentate ligand via the ring nitrogen atom. Further, the H2 adsorption studies were carried out at 75 K for various increasing pressures and the highest H2 adsorption performances for Co(II) and Ni(II) complexes were estimated as 2.66 and 2.99 wt% at 87 bar. The theoretical calculations using the crystal data were also performed to determine the voids in the structure of Co(II) complex.  相似文献   
98.
N-trans-cinnamylidene-m-toluidine (1) C16H15N, and N-trans-cinnamylidene-m-chloroaniline (2) C15H12NCl form isomorphous crystals which are monoclinic, space group P2l/c, with unit cell dimensionsa=5.967(2),b=13.793(3),c=15.048(5) Å, =91.97(3)° anda=5.868(2),b=13.788(4),c=15.191(4) Å, =91.87(3)°, respectively. The single-crystal X-ray structure determinations of the title compounds revealtrans structures. Ring (A) C10–15 and ring (B) C1–6, are practically planar in both structures with dihedral angels of 61.3(3) and 63.6(2)°, respectively.1H nmr, u.v. and i.r. spectra are also reported.  相似文献   
99.
The aim of this study was to evaluate 99mTc labeled human β-defensin-1 (HBD-1) for discrimination between bacterial infection and sterile inflammation. For this purpose, HBD-1 was radiolabeled with 99mTc and its in vivo distribution was evaluated in inflamed rats with Staphylococcus aureus (S. aureus) and sterile inflamed rats with turpentine oil. After injection into inflamed and sterile inflamed rats, 99mTc-HBD-1 was rapidly removed from the circulation via the kidneys. Binding of 99mTc-HBD-1 to inflamed muscle (T/NT = 20 at 120 min) was two times higher than binding to sterile inflamed muscle (T/NT = 10 at 120 min) of rats. It was demonstrated that 99mTc-HBD-1 can be used to detect S. aureus inflammation in rats. However, the radiolabeled antimicrobial peptide showed only poor uptake in sterile inflammation with turpentine oil in rats. As a result, 99mTc-HBD-1 can be useful for detection of bacterial inflammation.  相似文献   
100.
Crystal structure of the compound entitled 2-methylamino-5-[(5-methyl-2-benzoxazolinone-3-yl)methyl]-1,3,4-thiadiazole dihydrophosphate is determined using X-ray analysis and compared with the structure obtained from semiempirical and RHF methods at various levels of theory. RHF/6-31G(d) calculations offer the best conformity with X-ray results for bond lengths and bond angles. Moreover, at the result of the comparison of various combinations of basis sets and methods, it appears that there is not much gain in accuracy by using sophisticated methods.  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