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   1156篇
  免费   36篇
  国内免费   4篇
化学   995篇
晶体学   11篇
力学   11篇
数学   22篇
物理学   157篇
  2023年   4篇
  2022年   6篇
  2021年   10篇
  2020年   10篇
  2019年   15篇
  2018年   11篇
  2017年   5篇
  2016年   17篇
  2015年   26篇
  2014年   29篇
  2013年   71篇
  2012年   58篇
  2011年   55篇
  2010年   39篇
  2009年   29篇
  2008年   68篇
  2007年   88篇
  2006年   81篇
  2005年   57篇
  2004年   73篇
  2003年   54篇
  2002年   61篇
  2001年   30篇
  2000年   21篇
  1999年   25篇
  1998年   16篇
  1997年   19篇
  1996年   15篇
  1995年   10篇
  1994年   15篇
  1993年   11篇
  1992年   13篇
  1991年   8篇
  1990年   5篇
  1989年   7篇
  1988年   7篇
  1986年   3篇
  1985年   20篇
  1984年   15篇
  1983年   8篇
  1982年   10篇
  1981年   19篇
  1980年   9篇
  1979年   6篇
  1978年   4篇
  1977年   5篇
  1976年   4篇
  1975年   8篇
  1971年   3篇
  1969年   3篇
排序方式: 共有1196条查询结果,搜索用时 15 毫秒
101.
Ito H  Tada T  Sudo M  Ishida Y  Hino T  Saigo K 《Organic letters》2003,5(15):2643-2645
[reaction: see text] [60]Fullerenoacetyl chloride, one of the reactive derivatives of [60]fullerenoacetic acid, was isolated and identified for the first time. This acid chloride was easily synthesized in good yield from tert-butyl [60]fullerenoacetate through two steps. In the presence of 4-(dimethylamino)pyridine as a base, the acid chloride smoothly reacted with various alcohols under mild conditions to give the corresponding esters including [60]fullerene-biomolecule hybrids in moderate to high yields.  相似文献   
102.
We have developed a miniature double-pass cylindrical mirror electron energy analyzer (DPCMA) with an outer diameter of 26 mm. The DPCMA consists of a shield for the electric field, inner and outer cylinders, two pinholes with a diameter of 2.0 mm, and an electron multiplier. By assembling the DPCMA in a coaxially symmetric mirror electron energy analyzer (ASMA) coaxially and confocally we developed an analyzer for Auger photoelectron coincidence spectroscopy (APECS). The performance was estimated by measuring the Si-LVV-Auger Si-1s-photoelectron coincidence spectra of clean Si(1 1 1). The electron-energy resolution of the DPCMA was estimated to be EE = 20. This value is better than that of the miniature single-pass CMA (EE = 12) that was used in the previous APECS analyzer.  相似文献   
103.
I. INTRODUCTION

Recently the study of oligosaccharides has been extensively pursued in Japan after the findings of the remarkable biofunctions and usefulness of fructooligosac-charides for human health, improving the intestinal microflora and importance in livestock nutrition.  相似文献   
104.
105.
In plasma proteomics, before a proteome analysis, it is essential to prepare protein samples without high‐abundance proteins, including albumin, via specific preparation techniques, such as immunoaffinity capture. However, our preliminary experiments suggested that functional changes with use alter the ability of the immunoaffinity column. Thus, in this study, to evaluate the changes of the removal ability of abundant proteins from plasma by the immunoaffinity column, plasma proteome analysis was performed for the long‐term test for the reproducibility of the affinity column using the fluorogenic derivatization–liquid chromatography–tandem mass spectrometry method combined with an IgY column. The specific adsorption for albumin decreased with an increase in the number of the column usage before its expiration date. Moreover, it was demonstrated that hydrophobic high molecular weight compounds in plasma adsorbed onto the column materials surface contributed to the functional changes from specific immunoaffinity adsorption into hydrophobic interaction. These results suggested that, in quantitative plasma proteomics studies, it is important to keep in mind the risk of not only the nonselective loss but also the changes in the adsorption ability of the immunoafinity column. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   
106.
Serre's nonnegativity conjecture for intersection multiplicities has recently been proven by O. Gabber. In this paper we investigate Serre's positivity conjecture using the methods which he developed. We show in particular that the positivity conjecture has implications for properties of symbolic powers of prime ideals in regular local rings.  相似文献   
107.
By the reaction of 5,10-dialkyl-substituted 5,10-dihydrophenazine with hydrobromic acid in dimethyl sulfoxide at 90–110°, 10-alkyl-2(10H)-phenazinone was obtained as a major product. Brominated dihydrophenazine was isolated in the case of 1,6-dichloro-5,10-dimethyl-5,10-dihydrophenazine.  相似文献   
108.
Comb copolymers containing both hydrogenated and fluorinated side‐chains were prepared by copolymerization using acrylic or methacrylic monomers in several ratios. The crystal structures of these copolymers and layer structures of their organized molecular films were investigated by wide‐angle X‐ray diffraction (WAXD), small‐angle X‐ray scattering (SAXS), and out‐of plane X‐ray diffraction. Further, to selectively estimate the regularity of shorter fluorocarbon side‐chains, organized molecular films of copolymers were investigated by polarized near‐edge X‐ray adsorption fine structure (NEXAFS) spectroscopy. From the results of these measurements, it was inferred that these copolymers formed highly ordered layer structures, and a long spacing was predominantly determined by the arrangement of hydrogenated side‐chains, except in copolymers having extremely high fluorocarbon contents. In the case of the organized molecular films, the fluorinated side‐chains of methacrylate copolymers cannot form a highly ordered arrangement, whereas those of acrylate copolymers were oriented on monolayers. However, in both cases, the hydrogenated side‐chains predominantly formed layer structures in the organized films, and the fluorinated side‐chains did not contribute to the formation of the layer structures. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 534–546, 2008  相似文献   
109.
110.
The shape and porosity of hematite particles, produced from a forced hydrolysis reaction of acidic FeCl3 solution, were controlled by using Pluronics as nonionic surfactants (0–4 wt.%). Pluronics possess a nominal formula of (PEO) x –(PPO) y –(PEO) x . The effect of Pluronics with low hydrophilicity (PEO contents were less than 50 mol%) was small and provided spherical particles the same as that of the system without Pluronics (control system). However, Pluronics with higher hydrophilicity (PEO contents were over 50 mol%) gave ellipsoidal hematite particles. This effect on the particle morphology was enhanced by an increase in their molecular weight. On the other hand, the Pluronics possessing an opposite nominal formula [(PPO) x –(PEO) y –(PPO) x ] exhibited no effect on the particle shape; it only depressed phase transformation from ?-FeOOH to hematite. Not only the morphology but also the pore size of hematite particles was controlled from nonporous to mesoporous by using Pluronics. The N2 adsorption experiment and t-plot curve analysis revealed that the hematite particles changed from mesoporous to microporous by an increase in the concentration of Pluronics. On the other hand, in the presence of very low amounts of Pluronics molecules (0.1 wt.%), nonporous hematite particles were produced via strong aggregation of PN particles by their hydrogen bonding between hydroxyl and PEO or PPO groups. The dynamic light scattering measurement for the system with Pluronics clarified the existence of polynuclear (PN) particles with a hydrodynamic particle diameter (D a) of ca. 40 nm after these were aged for 6 h. The size of PN particles remained constant at ca. 40 nm during aging time of 12 h~3 days, but the scattering intensity was decreased. This decrease in the scattering intensity reveals that the number of PN particles is reduced by aggregation. The transmission electron microscope, inductively coupled plasma atomic emission spectroscopy, and total organic carbon analysis measurements employed on the systems produced for ellipsoidal particles elucidated that the formation of ellipsoidal hematite particles is attributed to the adsorption of Pluronics on the surfaces of PN and growing hematite particles.  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