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   20582篇
  免费   899篇
  国内免费   139篇
化学   13125篇
晶体学   121篇
力学   533篇
数学   3323篇
物理学   4518篇
  2023年   165篇
  2022年   273篇
  2021年   361篇
  2020年   443篇
  2019年   423篇
  2018年   301篇
  2017年   271篇
  2016年   727篇
  2015年   559篇
  2014年   671篇
  2013年   1067篇
  2012年   1326篇
  2011年   1559篇
  2010年   788篇
  2009年   677篇
  2008年   1181篇
  2007年   1124篇
  2006年   1087篇
  2005年   1002篇
  2004年   840篇
  2003年   615篇
  2002年   600篇
  2001年   264篇
  2000年   221篇
  1999年   216篇
  1998年   163篇
  1997年   189篇
  1996年   234篇
  1995年   176篇
  1994年   165篇
  1993年   189篇
  1992年   161篇
  1991年   147篇
  1990年   123篇
  1989年   118篇
  1988年   133篇
  1987年   121篇
  1986年   113篇
  1985年   151篇
  1984年   160篇
  1983年   109篇
  1982年   172篇
  1981年   180篇
  1980年   138篇
  1979年   136篇
  1978年   165篇
  1977年   137篇
  1976年   123篇
  1975年   126篇
  1973年   111篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
131.
Potassium leakage was studied in liquid membrane systems containing various emulsifiers and compared with emulsion, stability in the storage test. The effects of various parameters upon emulsion stability and the leakage of standard traces are discussed. The transfer of cations can be caused by emulsion breaking, by transport with the specific carrier and/or with surfactants used as emulsifiers. The latter case becomes especially important when hydrophilic surfactants, e.g. ones containing polyoxyethylene chains, are present in liquid membranes. In systems containing hydrophobic emulsifiers the transfer of potassium is relatively low. In each case considered the effect of emulsifiers upon the transfer of the standard tracer should be checked prior to using the leakage test to characterize emulsion stability.  相似文献   
132.
Thed-dimensional, nearest-neighbor disordered Ising ferromagnet: $$H = - \sum {J_{ij} \sigma _i \sigma _j }$$ is studied as a function of both temperature,T, and a disorder parameter,λ, which measures the size of fluctuations of couplingsJ ij ≧0. A finite-size scaling correlation length,ζ f (T, λ), is defined in terms of the magnetic response of finite samples. This correlation length is shown to be equivalent, in the scaling sense, to the quenched average correlation lengthζ(T, λ), defined as the asymptotic decay rate of the quenched average two-point function. Furthermore, the magnetic response criterion which definesζ f is shown to have a scale-invariant property at the critical point. The above results enable us to prove that the quenched correlation length satisfies: $$C\left| {\log \xi (T)} \right|\xi (T) \geqq \left| {T - T_c } \right|^{ - {2 \mathord{\left/ {\vphantom {2 d}} \right. \kern-\nulldelimiterspace} d}}$$ which implies the boundv≧2/d for the quenched correlation length exponent.  相似文献   
133.
134.
An X-ray preionized, discharge-pumped XeCl laser with a variable beam cross-section of up to 6×6 cm2 is described. It uses flat electrodes and the beam width is determined by X-ray collimation. Its operation characteristics concerning reduced electric field strength (E/p) and X-ray dose are discussed in detail. The inductance of the discharge loop is minimized using a water capacitor arrangement. A very high specific optical power (90 MW/l) is achieved in an active volume of 1.2 l. The pulse energy exceeds 5 J in a 45 ns pulse (FWHM). Komatsu Ltd., Manda 1200, Hiratsuka-shi, Kanagawa 254, Japan Institute of Optics and Fine Mechanics, Department of Plasma Physics, Academia Sinica, Shanghai, P.R. China  相似文献   
135.
Ozone is generated in pure oxygen (p5 kPa), synthetic air (p7 kPa) and oxygen-argon mixtures (p3 kPa) by irradiation of these gases with the VUV light of a repetitively pulsed (f L15 Hz) F2-laser at =157.6 nm with maximum about 4 mJ/pulse. An absorption photometer measurement operating at 253.7 nm (Hg line) determines the ozone concentration as a function of oxygen and/or additive gas pressure, the repetition frequency of the laser and the wall temperature of the reaction chamber. The temporal development of the ozone concentration as a function of these parameters is calculated by means of rate equations for the species O(3 P), O2(X 3 g ), O3(1 A 1), O(1 D), O2(a 1g), O2(b 1 g + ) and vibrationally excited O 3 * (1 A 1) and the photon distribution. The maximum concentration of O3 in the sealed-off chamber reaches 1.6% in pure O2, 4.1% in air and 1.2% in a 1:5 O2-Ar mixture at 3 kPa. The annihilation of O3 by the wall and temperature dependent volume processes (300 KT395 K) is studied and the experimental and theoretical results are compared.  相似文献   
136.
Dodecaynes 1a-d have been prepared via a convergent strategy that employs Sonogashira couplings as the carbon-carbon bond-forming tool. Due to the steric bulk of the DMTS groups, 1c adopts a nonplanar conformation, the dynamics of which have been probed by VT-NMR. The cobalt-catalyzed isomerization of 1a,b produced the new conjugated phenylenes 2a,b and 3a,b, respectively. [structure: see text]  相似文献   
137.
Summary A variety of bilipeptides has been synthesized and investigated by UV-VIS and CD spectroscopy to explore the conformational influence of peptide ligands on the covalently bound tetrapyrrol moiety. The results obtained are complemented by those reported previously. From the comprehensive data thus available several features of the peptidic chain regulating interactions with the bilatriene moiety have been elucidated. Accordingly, the presence of three amide linkages at the ligand is prerequiste for induction of pronounced conformational changes consisting either in a complete transition ofM intoP helical bilatriene species by inversion of all torsional angles, or in a stretching of the chromophore. The kind of conformational influence can be controlled by varying the position of the prolyl entity within a given peptide.Dedicated to Prof. Dr. Kurt Schaffner on occasion of his 60th birthday  相似文献   
138.
Polypeptides for use in affinity chromatography of factor VIII were identified using phage display technology. Phage libraries were designed to express polypeptide fusions containing five to seven residues flanked by two cysteines that form a disulfide bond. Individual bacteriophage were selected for the ability of these polypeptides to bind factor VIII, and then release the protein under mild elution conditions. Strong consensus sequences were observed that appear to be necessary for this reversible interaction. Chemically synthesized ligands identified by this screening were immobilized onto a chromatographic support and used for affinity purification of factor VIII from a complex feedstream. A chromatographic step was developed that provided a 10000-fold reduction in host cell proteins and DNA, while providing exceptional product recovery.  相似文献   
139.
Partial least-squares regression (PLS) and radial basis function (RBF) networks are used to compute calibration models for non-invasive blood glucose determination by NIR diffuse reflectance spectroscopy. A model computation shows that even extremely small deviations of the spectra induce increased prediction errors. Since the spectral contribution of blood glucose is much smaller than deviations resulting from the non-invasive measuring process a method based on Pearson’s correlation coefficient can be used for evaluating the quality of the recorded spectra during the prediction step. Another method is based on the leverage values from the hat matrix of the RBF network. Both methods lead to a significant decrease in prediction error.  相似文献   
140.
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