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   8006篇
  免费   750篇
  国内免费   702篇
化学   4633篇
晶体学   132篇
力学   457篇
综合类   48篇
数学   1605篇
物理学   2583篇
  2025年   33篇
  2024年   136篇
  2023年   306篇
  2022年   430篇
  2021年   447篇
  2020年   525篇
  2019年   318篇
  2018年   266篇
  2017年   339篇
  2016年   282篇
  2015年   298篇
  2014年   439篇
  2013年   547篇
  2012年   566篇
  2011年   489篇
  2010年   433篇
  2009年   409篇
  2008年   272篇
  2007年   350篇
  2006年   334篇
  2005年   180篇
  2004年   132篇
  2003年   117篇
  2002年   96篇
  2001年   103篇
  2000年   77篇
  1999年   100篇
  1998年   70篇
  1997年   68篇
  1996年   37篇
  1995年   46篇
  1994年   33篇
  1993年   30篇
  1992年   39篇
  1991年   33篇
  1989年   30篇
  1988年   95篇
  1987年   149篇
  1986年   173篇
  1973年   21篇
  1972年   27篇
  1971年   51篇
  1970年   34篇
  1969年   26篇
  1968年   49篇
  1967年   72篇
  1966年   39篇
  1965年   38篇
  1964年   32篇
  1963年   29篇
排序方式: 共有9458条查询结果,搜索用时 15 毫秒
1.
The two complexes [Ni(oxen)Cu(L)2](ClO4)2.xH2O (L=2,2'-bipyridyl(bpy), 1,10-phenanthroline(phen)) have been synthesized, where oxen is N,N'-bis(2-aminoethyl)oxamido di-anion. The crystal structure of [Ni(oxen)Cu(bpy)2](ClO4)2.CH3OH has been determined by X-ray diffraction method. The crystal is triclinic system, space group P1 with a=12.179(1),b=12.298(2), c=11.476(2) A, a=97.57(1), B=97.52(1), 7=80.29(2), V=1669.04(67) A3, Z=2, Dcalcd=1.667 g/cm3. The structure has been refined to final R of 0.076 and Rw of 0.080, respectively. The complexes have an extended oxamido-bridged structure and consist of Ni(Ⅱ) ion in a square planar environment and Cu(Ⅱ) ion in a distorted octahedral environment.  相似文献   
2.
A novel anion-selective electrode has been prepared by usingtetraazaporphyrinogen as the electroactive component and o-nitrophenyloctylether as the plasticizer. The electrode exhibits almost Nernstian responsecharacteristics for Pic-, ReO 4 - ,SCN-, ClO 4 - and TPB-. The linearresponse ranges towards the above-mentioned anions are 10-6 10-2, 10-5 10-2,10-5 10-2, 10-5 10-1, and 10-5 10-2mol/Land the corresponding slopes are -56.8, -57.1, -56.3, -56.1, and -59.9mV/decade with correlation coefficients of -0.99978, -0.99987, -0.99999,-0.99998, and -0.99998, respectively. The electrode shows an anti-Hofmeisterselectivity sequence: Pic- > SCN- >ReO 4 - > ClO 4 - > I- >Br- > BF 4 - > Sal->NO 3 - > Cl-. The unusual responsemechanism of the novel anion-selective electrode was investigated byexperimental observations and calculation with the MNDO method. Theelectrode was used as a TPB- and a Pic-sensitiveelectrode, respectively, and applied to the assay of levamisolehydrochloride tablets by potentiometric titration and Gran's methods. Theresults obtained are in excellent agreement with that determined by thestandard pharmacopoeia method based on nonaqueous titration.  相似文献   
3.
Stability, internal modes and internal oscillation of 12-pearled necklace solitons in photorefractive crystal with imprinted Bessel photonic lattices are investigated. It is shown that the imaginary parts of internal modes are negligible comparing with real parts. The stable solitons perform long-distance and quasi-periodic oscillation of intensity and shape under the perturbation of internal modes.  相似文献   
4.
Polyvinylpyrrolidone (PVP)-protected silver nanostructures of various shapes, including nanocubes, nanospheres, and hybrid shapes with nanospheres and nanorods, on the surface of glass or Si substrates (PVP-Ag films) are prepared by using electrostatic self-assembly. With 4-mercaptobenzoic acid (4-MBA) as a probe molecule, it is demonstrated that the PVP-protected silver nanocubes films (PVP-Ag NCs) have better surface-enhanced Raman scattering (SERS) activity with an order of magnitude larger enhancement factors (EF) than the PVP-protected silver nanospheres films and the PVP-protected silver hybrid shapes films, which is confirmed by our numerical simulations. The EF of 4-MBA on the PVP-Ag NCs film are up to ~5.38 × 106, and the detection limit is at least down to ~10?8 M. The uniformity and reproducibility of the SERS signals on PVP-Ag NCs film are tested by point-to-point and batch-to-batch measurements. Meanwhile, the PVP-Ag films are also shown to be an excellent SERS substrate with good biocompatibility for hemoglobin detection. It is shown that the PVP-Ag NCs films can be used as excellent SERS substrate with good activity, uniformity, reproducibility, and biocompatibility and are promising for a myriad of chemical and biochemical sensing applications.  相似文献   
5.
A series of double molybdates phosphors AEu(MoO4)2 (A = Li, Na, K and Ag) have been prepared by sol-gel method. Their crystal structure and luminescent properties have also been investigated in a comparable way. The crystallization processes of the phosphor precursors were characterized by X-ray diffraction (XRD) and thermogravimetry-differential thermal analysis (TG-DTA). Field emission scanning electron microscopy (FE-SEM) was also used to characterize the shape and size distribution of the phosphors. Samples except KEu(MoO4)2 showed tetragonal scheelite structure in the range of our experiments, and no phase transition appeared. Phosphor KEu(MoO4)2 possessed two structures, and the phase transition took place at about 800°C. All samples with high purity could be obtained at about 500°C for 5 hours, and they all showed intense red light peaked at 616 nm originated from 5D07F2 emission of Eu3+ under the excitation of 465 nm or 394 nm light. The excitation spectra of phosphors AEu(MoO4)2 (A = Li, Na, and K) are composed of a strong broad charge transfer (CT) band and some sharp lines, and the relative intensity of CT band, the two strongest absorption lines at 395 nm and 465 nm are comparative, so these three phosphors are good red phosphor candidates for violet or blue LEDs. For the excitation spectrum of phosphor AgEu(MoO4)2, intensities of CT band and the absorption line at 395 nm are much weaker than that of line at 465 nm, thus phosphor AgEu(MoO4)2 is only suit for GaN-based blue LED.  相似文献   
6.
Oxygen vacancy pairs have been suggested to play a role in the reduction of NO molecules on ceria and for the oxidation processes of reducible rare-earth oxides. The formation energy of the oxygen vacancy pairs and the changes in the structural and electronic properties of the ceria (110) surface with oxygen vacancy pairs are investigated using density-functional theory (DFT + U) methodology within the generalized gradient approximation. It is found that the excess electrons localize on the Ce ions neighbouring the vacancies, and the most stable structure for the oxygen vacancy pairs on the ceria (110) surface is at next-nearest-neighbour site.  相似文献   
7.
8.
The European Physical Journal Plus - The nonlocal defocusing nonlinear Schrödinger (ND-NLS) equation is comparatively studied via the Riemann–Hilbert approach. Firstly, via spectral...  相似文献   
9.
A series of Ba3Lu1 ? x Ce x (BO3)3 phosphors with different x value were prepared by a conventional high-temperature solid-state reaction method, and their spectroscopic characteristic were systematically investigated. The excitation and emission spectra indicate Ce3+ can occupy two different Lu lattice sites, and shows different luminescence properties. The spectroscopic characteristic of Ce(1) and Ce(2) which include Stokes shift and crystal field depression were investigated. The investigation indicates that Ba3Lu(BO3)3: Ce3 phosphor can have potential application in white-light emitting diodes due to the near-ultraviolet excitation band and blue light emission of Ce(2) in Ba3Lu(BO3)3.  相似文献   
10.
Chong Li 《Physics letters. A》2010,374(29):2994-10714
The effect of different vacancies on the morphology of the O-terminated Cu2O(111) surface has been studied through the first-principles calculations. Our results show that Cu and O vacancies trigger large relaxations and formation of two different facets. Our emulated STM images are in consistent with the experimental STM patterns. A sizeable magnetic moment (∼1.0 μB) was found for surfaces with either Cu or O vacancies. The calculated formation energies of surface vacancies indicate that the deficient surfaces are more stable than the stoichiometric O-terminated (1×1) surface, which is also in line with our results obtained from ab initio atomistic thermodynamics studies.  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