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   5870篇
  免费   359篇
  国内免费   46篇
化学   4100篇
晶体学   61篇
力学   228篇
数学   895篇
物理学   991篇
  2023年   37篇
  2022年   111篇
  2021年   200篇
  2020年   138篇
  2019年   242篇
  2018年   209篇
  2017年   145篇
  2016年   295篇
  2015年   202篇
  2014年   319篇
  2013年   605篇
  2012年   368篇
  2011年   376篇
  2010年   268篇
  2009年   246篇
  2008年   262篇
  2007年   256篇
  2006年   243篇
  2005年   204篇
  2004年   173篇
  2003年   145篇
  2002年   182篇
  2001年   79篇
  2000年   123篇
  1999年   69篇
  1998年   43篇
  1997年   52篇
  1996年   37篇
  1995年   38篇
  1994年   37篇
  1993年   41篇
  1992年   35篇
  1991年   28篇
  1990年   20篇
  1989年   32篇
  1988年   29篇
  1987年   26篇
  1986年   19篇
  1985年   35篇
  1984年   30篇
  1983年   30篇
  1982年   23篇
  1981年   31篇
  1980年   17篇
  1979年   15篇
  1978年   17篇
  1977年   11篇
  1976年   15篇
  1975年   18篇
  1959年   8篇
排序方式: 共有6275条查询结果,搜索用时 15 毫秒
991.
1‐Morpholin‐4‐yl‐5,6,7,8‐tetrahydroisoquinoline‐4‐carbonitrile ( 2 ) was synthesized from 3‐amino‐1‐thioxo‐5,6,7,8‐tetrahydro‐1H‐isothiochromene‐4‐carbonitrile ( 1 ) and used as starting material to synthesize many thienotetrahydroisoquinolines ( 4 ), which in turn were used in the synthesis of many pyrimidothienotetrahydroisoquinolines.  相似文献   
992.
A series of manganese(III) corroles were investigated as to their electrochemistry and spectroelectrochemistry in nonaqueous solvents. Up to three oxidations and one reduction were obtained for each complex depending on the solvents. The main compound discussed in this paper is the meso-substituted manganese corrole, (Mes 2PhCor)Mn, and the main points are how changes in axially coordinated anion and solvent will affect the redox potentials and UV-vis spectra of each electrogenerated species in oxidation states of Mn(III), Mn(IV), or Mn(II). The anions OAc (-), Cl (-), CN (-), and SCN (-) were found to form five-coordinate complexes with the neutral Mn(III) corrole while two OH (-) or F (-) anions were shown to bind axially in a stepwise addition to give the five- and six-coordinate complexes in nonaqueous media. In each case, complexation with one or two anionic axial ligands led to an easier oxidation and a harder reduction as compared to the uncomplexed four-coordinate species.  相似文献   
993.
Two new Cu(II) linear trinuclear Schiff base complexes, [Cu3(L)2(CH3COO)2] (1) and [Cu3(L)2(CF3COO)2] (2), have been prepared using a symmetrical Schiff base ligand H2L [where H2L = N,N'-bis(2-hydroxyacetophenone)propylenediimine]. Both of the complexes have been characterized by elemental analyses, Fourier transform IR, UV/vis, and electron paramagnetic resonance spectroscopy. Single-crystal X-ray structures show that the adjacent Cu(II) ions are linked by double phenoxo bridges and a mu(2)-eta(1):eta(1) carboxylato bridge. In each complex, the central copper atom is located in an inversion center with distorted octahedral coordination geometry, while the terminal copper atoms have square-pyramidal geometry. Cryomagnetic susceptibility measurements over a wide range of temperature exhibit a distinct antiferromagnetic interaction of J = -36.5 and -72.3 cm(-1) for 1 and 2, respectively. Density functional theory calculations (B3LYP functional) and continuous-shape measurement (CShM) studies have been performed on the trinuclear unit to provide a qualitative theoretical interpretation of the antiferromagnetic behavior shown by the complexes.  相似文献   
994.
In an unusual reaction of osmium(VIII) oxide with p-substituted aromatic amines (X-C(6)H(4)-NH(2), where X = Me, H, Cl) in heptane afforded the brown osmium(VI)-oxo complexes [OsO(L)(2)] (1a-c, L = N-aryl-1,2-arylenediamide) in moderate yields. The ligand L is formed in situ via oxidative ortho-C-N fusion of arylamines. The reaction occurs in an inert atmosphere, and a part of Os(VIII) is used up for the oxidation of aromatic amine. Single crystal X-ray structure of a representative complex 1a is solved. The structural analysis has authenticated the ortho-C-N fusion of ArNH(2) resulting in formation of the diamide ligand, L. The complex as a whole is penta-coordinated, and the coordination sphere has a distorted square pyramidal geometry (tau = 0.26). A similar reaction of osmium(VIII) oxide with the preformed N-phenyl-1,2-phenelene diamine produced the complex 1a in nearly quantitative yield. The substituted phenazine, 5-phenyl-3-phenylimino-3,5-dihydro-phenazine-2-ylamine, is obtained as a byproduct of the latter reaction. The complexes, 1a-c, can be reduced in a reversible one-electron step, as probed by cyclic voltammetry. The one electron reduced paramagnetic Os(V) intermediate is, however, Electron Paramagnetic Resonance (EPR) silent. Solution spectra of the osmium complexes show several multiple transitions in the UV-vis region. Density functional theory calculations were employed to confirm the structural features and to support the spectroscopic assignments. The complex 1a catalyzes oxidation of a wide variety of unsaturated hydrocarbons like alkenes, alkynes, and aldehydes to the corresponding carboxylic acids in the presence of tert-butylhydroperoxide (TBHP) efficiently at room temperature.  相似文献   
995.
Layered double hydroxides containing paramagnetic Ni (II) and diamagnetic/paramagnetic Al (III)/Fe (III) ions have been prepared and characterized. Ni 2Al(OH) 6(NO 3). nH 2O ( 1), Ni 2Fe(OH) 6(NO 3). nH 2O ( 2), Ni 2Fe(OH) 6(C 6H 8O 4) 0.5. nH 2O ( 3), and Ni 2Fe(OH) 6(C 10H 16O 4) 0.5. nH 2O ( 4) were prepared by coprecipitation at controlled pH as polycrystalline materials with the typical brucite-like structure, with alternating layers of hydroxide and the corresponding anions, which determine the interlayer separation. Magnetic studies show the appearance of spontaneous magnetization between 2 and 15 K for these compounds. Interestingly, the onset temperature for spontaneous magnetization follows a direct relationship with interlayer separation, since this is the only magnetic difference between compounds 2, 3, and 4. Magnetic and calorimetric data indicate that long-range magnetic ordering is not occurring in any of these materials, but rather a freezing of the magnetic system in 3D due to the magnetic disorder and competing intra- and interlayer interactions. Thus, these hydrotalcite-like magnetic materials can be regarded as spin glasses.  相似文献   
996.
Prof. Dr. Steven H. Liang  Dr. Jinshan Michael Chen  Prof. Dr. Marc D. Normandin  Dr. Jeanne S. Chang  Dr. George C. Chang  Dr. Christine K. Taylor  Dr. Patrick Trapa  Dr. Mark S. Plummer  Dr. Kimberly S. Para  Dr. Edward L. Conn  Dr. Lori Lopresti‐Morrow  Dr. Lorraine F. Lanyon  Dr. James M. Cook  Dr. Karl E. G. Richter  Dr. Charlie E. Nolan  Dr. Joel B. Schachter  Dr. Fouad Janat  Dr. Ye Che  Dr. Veerabahu Shanmugasundaram  Dr. Bruce A. Lefker  Dr. Bradley E. Enerson  Prof. Dr. Elijahu Livni  Lu Wang  Dr. Nicolas J. Guehl  Dr. Debasis Patnaik  Florence F. Wagner  Prof. Dr. Roy Perlis  Dr. Edward B. Holson  Prof. Dr. Stephen J. Haggarty  Prof. Dr. Georges El Fakhri  Dr. Ravi G. Kurumbail  Prof. Dr. Neil Vasdev 《Angewandte Chemie (International ed. in English)》2016,55(33):9601-9605
Glycogen synthase kinase‐3 (GSK‐3) regulates multiple cellular processes in diabetes, oncology, and neurology. N‐(3‐(1H‐1,2,4‐triazol‐1‐yl)propyl)‐5‐(3‐chloro‐4‐methoxyphenyl)oxazole‐4‐carboxamide (PF‐04802367 or PF‐367) has been identified as a highly potent inhibitor, which is among the most selective antagonists of GSK‐3 to date. Its efficacy was demonstrated in modulation of tau phosphorylation in vitro and in vivo. Whereas the kinetics of PF‐367 binding in brain tissues are too fast for an effective therapeutic agent, the pharmacokinetic profile of PF‐367 is ideal for discovery of radiopharmaceuticals for GSK‐3 in the central nervous system. A 11C‐isotopologue of PF‐367 was synthesized and preliminary PET imaging studies in non‐human primates confirmed that we have overcome the two major obstacles for imaging GSK‐3, namely, reasonable brain permeability and displaceable binding.  相似文献   
997.
We investigate Banach lattices on which each positive almost Dunford- Pettis operator is almost limited and conversely.  相似文献   
998.
999.
1000.
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