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   1521篇
  免费   55篇
  国内免费   3篇
化学   1270篇
晶体学   15篇
力学   18篇
数学   101篇
物理学   175篇
  2023年   5篇
  2021年   7篇
  2020年   8篇
  2019年   18篇
  2018年   20篇
  2017年   7篇
  2016年   36篇
  2015年   31篇
  2014年   41篇
  2013年   76篇
  2012年   71篇
  2011年   86篇
  2010年   57篇
  2009年   34篇
  2008年   82篇
  2007年   63篇
  2006年   80篇
  2005年   70篇
  2004年   74篇
  2003年   92篇
  2002年   75篇
  2001年   22篇
  2000年   54篇
  1999年   24篇
  1998年   18篇
  1997年   24篇
  1996年   26篇
  1995年   23篇
  1994年   22篇
  1993年   21篇
  1992年   20篇
  1991年   18篇
  1990年   15篇
  1989年   6篇
  1988年   15篇
  1987年   5篇
  1986年   5篇
  1985年   19篇
  1984年   22篇
  1983年   9篇
  1982年   20篇
  1981年   22篇
  1980年   24篇
  1979年   25篇
  1978年   22篇
  1977年   12篇
  1976年   13篇
  1974年   6篇
  1973年   7篇
  1968年   5篇
排序方式: 共有1579条查询结果,搜索用时 250 毫秒
101.
A gold nanoparticle surface-modified with amide ligands shows enhanced optical sensing of anions: the detection limit is increased by about three orders of magnitude higher than that originally expected from the anion binding ability of neutral amide ligands.  相似文献   
102.
Porphyrin dimer 1, which does not have an inside cavity and cannot interact with [60]fullerene (C60), becomes an excellent C60-acceptor with a large cavity in the presence of a Pd(II) complex.  相似文献   
103.
[structure: see text] Covalently linked dimers of amphotericin B were prepared by cross-linking its carboxylic acid. Among these, a dimer with a linkage of 1,6-hexanediamine revealed potent hemolytic activity (EC50, 0.25 microM) while its N-acetyl derivative gave rise to large K+ ion flux in phosphatidylcholine liposomes, regardless of the presence or absence of sterols, suggesting that the dimers may serve as a tool for elucidating the structure of the ion channel assemblage formed by amphotericin B.  相似文献   
104.
Dark red crystals of the halogen-substituted cyclotrigermenes [(tBu3Si)3Ge3X; X = Cl, Br, I] were obtained in good yields by the reaction of [(tBu3Si)3Ge3]+.TTFPB- (TTFPB- = tetrakis(2,3,5,6-tetrafluorophenyl)borate) with potassium halides (KCl, KBr, or KI) in diethyl ether. The crystal structures of the halogen-substituted cyclotrigermenes reveal a cis-bent Ge=Ge double bond, caused by the introduction of the electronegative halogen atom on the sp3 germanium atom of cyclotrigermene. In solution, an intramolecular halogen migration over the three-membered ring skeleton was observed. Facial stereoselectivity in the Diels-Alder reaction of new cyclotrigermenes with 2,3-dimethyl-1,3-butadiene is also reported.  相似文献   
105.
Statistical properties of fluctuations of pressure drop across the gas–liquid dispersions on the tray were analyzed using a 215 mm dia. three plates column with different trays. Hydrodynamic regimes of the froth were characterized in terms of the statistical properties evaluated. It was proved that the on-line estimation of the flow behavior of the froth was possible on the basis of the pattern recognition of the power spectral density function of the pressure fluctuations. The time-domain stochastic models for fluctuations of the pressure drop were identified so as to be available for its forecast and simulation.  相似文献   
106.
We revisit the EPR problem and make clear what is a correct comprehension of its problem. When one applies the quantum mechanics correctly, it will be shown that there is no paradox. According to these lines of thought, a quantum teleportation scheme without resort to the von Neumann projection postulate is presented.  相似文献   
107.
108.
An imaging method for partially coherent objects is proposed by the aid of the propagation law of mutual intensity, and it can be reduced to principles used in holography and radio astronomy if the coherence reaches the both extremes, i.e., perfect coherence and complete incoherence, respectively.  相似文献   
109.
Ab initio LCAO SCF MO calculations are carried out on planar Co-porphine with a basis set of roughly double zeta quality for Co and N and of single zeta quality for C and H. The net charge on Co and N and the overlap population between them are 1.78, ?0.57, and 0.06, respectively, in the 2A1g, state, which is known to be the ground state by experiment. The bonding in this complex is thus largely ionic. The first and second calculated ionization potentials are 6.51 and 6.77 eV, respectively, and are in reasonable agreement with the observed ionization potentials of 6.44 and 6.62 eV for Ni-tetraphenylporphine. CI calculations within the framework of the ligand field theory are also performed. The calculated order of the five lowest states is 4B2g4Eg, 4A2g, 2A1g, 4Eg from below and is not in agreement with the semiempirical order of 2A1g4B2G, 4A2g, 2Eg, 4Eg determined by Lin.  相似文献   
110.
The aim of this study was to investigate the effect of temporal resolution on the estimation of left ventricular (LV) function by cardiac magnetic resonance (MR) imaging using a steady-state free precession (SSFP) sequence. Left ventricular function was assessed by cine MR imaging using a segmented SSFP sequence in 10 healthy volunteers. Views per segment (VPS) were set at 8 and 20, resulting in high and low true temporal resolution, respectively. Irrespective of VPS, images were reconstructed at 40 cardiac phases, providing high apparent temporal resolution. Data were analyzed using 40, 20 and 10 phases to simulate different apparent temporal resolutions. Increasing the cardiac phases used for analysis slightly decreased mean end-systolic volume (ESV) and slightly increased mean ejection fraction (EF). No substantial difference in estimates of end-diastolic volume (EDV) was found between VPSs of 8 and 20. Imaging with a VPS of 20 yielded a larger ESV and smaller EF than imaging with a VPS of 8 when 40 phases were used. In conclusion, low true temporal resolution causes overestimation of ESV and underestimation of EF. Improvement of apparent temporal resolution mildly reduces but does not eliminate the errors caused by low true temporal resolution.  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