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   8608篇
  免费   745篇
  国内免费   1039篇
化学   5154篇
晶体学   187篇
力学   70篇
综合类   44篇
数学   190篇
物理学   4747篇
  2023年   25篇
  2022年   101篇
  2021年   90篇
  2020年   90篇
  2019年   108篇
  2018年   156篇
  2017年   162篇
  2016年   196篇
  2015年   165篇
  2014年   239篇
  2013年   757篇
  2012年   383篇
  2011年   408篇
  2010年   335篇
  2009年   515篇
  2008年   499篇
  2007年   560篇
  2006年   534篇
  2005年   457篇
  2004年   419篇
  2003年   415篇
  2002年   374篇
  2001年   342篇
  2000年   327篇
  1999年   322篇
  1998年   273篇
  1997年   237篇
  1996年   248篇
  1995年   260篇
  1994年   221篇
  1993年   176篇
  1992年   235篇
  1991年   130篇
  1990年   86篇
  1989年   80篇
  1988年   86篇
  1987年   58篇
  1986年   40篇
  1985年   36篇
  1984年   37篇
  1983年   28篇
  1982年   30篇
  1981年   19篇
  1980年   23篇
  1979年   24篇
  1978年   12篇
  1976年   18篇
  1975年   13篇
  1974年   13篇
  1973年   13篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
本文采用无催化剂直接蒸发高纯Zn粉,在800℃氧气氛条件下,在Si(111)衬底上生长得到以四角状为主的纳米ZnO(T-ZnO)。T-ZnO纳米线每个角约互成110°,长度约为1.5μm,直径100nm左右;Raman分析表明E2(H)普遍存在于各形态的ZnO;光致发光光谱表明,T-ZnO纳米线的光致发光除了与材料性质有关,还与杂质缺陷有关,蓝绿光带是ZnO的缺陷产生的。  相似文献   
22.
IR and Raman spectra of (NH4)3ZnCl5 have been recorded. The observed spectra have been analysed on the basis of the vibrations of ZnCl 4 2− and NH 4 + ions. The appearance of multiple Raman bands indicates the presence of two different types of ammonium ions. The effect of anisotropic crystalline field over the ZnCl4 and NH4 tetrahedra is also discussed. The assignment of internal modes has been verified by the potential energy distribution calculations.  相似文献   
23.
激光等离子实验中的低能X射线时间谱解谱方法   总被引:1,自引:1,他引:0  
利用快速Fourier变换(FFT)算法和反卷积原理对Dante谱议测量波形进行了回推获得了激光等离子体源区低能X射线辐射时间波形。解谱方法采用了W.N.Mcelroy等人提出的SANDⅡ解谱方法并与文献[6]中介绍的限幅迭代和周期性光滑技术相配合计算出了能谱时间关系的16分区结果,给出了1989年6月LF-12强激光装置实验的双束靶、漏靶诊断口,入射口的X射线时间谱以及辐射温度时间关系T_R(i)。  相似文献   
24.
激光沉积超导薄膜过程中出射粒子速度的飞行时间谱分析   总被引:1,自引:1,他引:0  
范永昌  安承武 《光学学报》1991,11(7):98-601
采用飞行时间谱技术,测量了准分子激光烧蚀沉积高温超导薄膜过程中,由靶面出射粒子的飞行速度。研究了粒子速度与充氧压及其激光能量密度的关系。讨论了高能粒子在薄膜原位低温外延生长中的作用。  相似文献   
25.
环丙沙星在胶束体系中的荧光特性研究及应用   总被引:9,自引:1,他引:8  
研究了环丙沙星在胶束体系中的荧光性质,发现十二烷基硫基酸对环丙沙星有较强的增敏作用。据此建立了胶束增敏荧光光谱法测定痕量环丙沙星的新方法,经样品测定,其线性范围为0.033-0.60μg.mL^-1,检出限为0.033μg.mL^-1,回收率为94.0%-98.1%相对标准偏差为1.5%-2.8%。  相似文献   
26.
We have used electronic spectroscopy in the 160–1100 nm range to study the polyvinyl alcohol-nickel(II) chloride system. Based on the results obtained, we hypothesize formation of mixed-ligand complexes of the type [Ni(H2O)6-nCln]2-n (n = 0, 1,..., 5) in the polyvinyl alcohol matrix. Transformation of the coordination sphere as the NiCl2 concentration changes is apparent both in the region of the d-d transition bands (350–1100 nm) and in the region of the charge transfer bands (160–250 nm). We propose assigning the absorption bands separated by mathematical treatment to complexes of specific compositions. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 1, pp. 136–138, January–February, 2006.  相似文献   
27.
The harmonic vibrational force fields and the IR spectrum of XSO2NCO (X= F, C1) molecules have been studied usingab initio HF/SCF method with the 6-31G’ basis set. Theab initio harmonic force fields are scaled empirically using the scaled quantum mechanical (SQM) method of Pulay. A set of scale factors are optimized by the least-squares fitting to the experimental frequencies of FSO2NCO and then are transferred to CISO2NCO to give ana priori prediction of its fundamental frequencies. The average deviations between the theoretical frequencies and the experimental values for FSO2NCO and C1SO2NCO are 3 and 5 cm-1, respectively. The assignments of the fundamentals for these two molecules are also made atcording to the potential energy distributions and theab initio IR intensities Project supported by the National Natural Science Foundation of China (Grant No. 29673029)  相似文献   
28.
Raman and IR spectra (4000-50 cm–1) of solid cyclopentadienyl zirconium and hafnium hydrides Cp2MH2, Cp2MD2, Cp2Zr(H)X, and Cp2Zr(D)X (Cp = 5-C5H5; M = Zr, Hf; X = Cl, Br) have been studied. The vibrational modes of MH groups, Cp-rings, and metal-ligand bonds are discussed and the band assignments are proposed. In the solid state, these complexes form polymers with linear hydride bridges of the M-H-M type. The force constants of the M-H and M-Cp bonds increase on going from Zr to Hf.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1604–1609, September, 1994.  相似文献   
29.
Basic regularities of electrochemical processes in the gap of an ex situ scanning tunneling microscope in conditions of condensation of air moisture at the sample surface are considered on a qualitative level. A layer of condensed moisture is viewed as an electrolyte in a two-electrode cell. The depolarizers present in this layer may experience electrochemical conversions on the tip and in an area of the sample surface near the tip. As a result, the recorded “tunneling” current includes electrochemical constituents. Depending on the electrochemical processes in the gap, various dependences of the tip-sample distance on the current and applied voltage can be expected. For preliminary diagnostics of processes in the gap it is suggested to use voltage-height spectra, whose shape and characteristic heights are sensitive to the nature and location of redox active species. Experimental data for various films on conducting supports (quasi-two-dimensional adsorbed layers of hemin and peroxidase, electrodeposited nonstoichiometric tungsten oxides, doped tin dioxide, solid electrolyte with ionic conduction) are presented as an examples.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 583–595.Original Russian Text Copyright © 2005 by Yusipovich, Vassiliev.  相似文献   
30.
A polyphosphide of the type (NaP)X 1 was obtained from red phosphorus and sodium in presence of small amounts of naphthalene in 1,2-dimethoxyethane as solvent. 1 reacts with alkyl halides in dependence on the kind of alkyl group with formation of different alkylcyclophosphanes. As definite compounds Me5P5 2 , Et5P5 3 (with not definite constitution), i-Pr4P4 4 and t-Bu4P4 5 could be isolated. 1 was identified by X-ray diffraction, 2 – 5 by means of their 1H, 13C, 31P n.m.r. and mass spectra. The molecular structure of 4 was identified by electron diffraction.  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