全文获取类型
收费全文 | 4896篇 |
免费 | 293篇 |
国内免费 | 484篇 |
专业分类
化学 | 3683篇 |
晶体学 | 33篇 |
力学 | 116篇 |
综合类 | 9篇 |
数学 | 73篇 |
物理学 | 1053篇 |
无线电 | 706篇 |
出版年
2024年 | 33篇 |
2023年 | 337篇 |
2022年 | 131篇 |
2021年 | 171篇 |
2020年 | 172篇 |
2019年 | 172篇 |
2018年 | 133篇 |
2017年 | 157篇 |
2016年 | 166篇 |
2015年 | 167篇 |
2014年 | 211篇 |
2013年 | 310篇 |
2012年 | 377篇 |
2011年 | 293篇 |
2010年 | 238篇 |
2009年 | 287篇 |
2008年 | 278篇 |
2007年 | 286篇 |
2006年 | 232篇 |
2005年 | 192篇 |
2004年 | 204篇 |
2003年 | 149篇 |
2002年 | 90篇 |
2001年 | 96篇 |
2000年 | 87篇 |
1999年 | 104篇 |
1998年 | 109篇 |
1997年 | 79篇 |
1996年 | 65篇 |
1995年 | 51篇 |
1994年 | 46篇 |
1993年 | 47篇 |
1992年 | 37篇 |
1991年 | 36篇 |
1990年 | 20篇 |
1989年 | 19篇 |
1988年 | 10篇 |
1987年 | 8篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 8篇 |
1979年 | 9篇 |
1978年 | 1篇 |
1975年 | 14篇 |
1968年 | 1篇 |
排序方式: 共有5673条查询结果,搜索用时 15 毫秒
61.
采用透射电子显微术(TEM),研究了用磁控溅射技术在柔性金属基体上制备的、钇稳定的ZrO2(YSZ)为过镀层的YBa2Cu3O7-y(YBCO)薄膜的横断面结构。所得YBCO膜的超导临界转变温度Tc为91K,临界电流密度Jc=2×103A/cm2(77K,0T)。基体为Ni基合金(HasteloyC)。YSZ层为致密、均匀的细晶组织,约12μm厚,具有织构取向,并与基体紧密连接。YBCO层的厚度不均匀,约500nm;YBCO/YSZ界面有时连接较差,在该界面上有杂质出现,杂质有可能引发裂纹。 相似文献
62.
O. M. Radul M. Z. Krimer O. N. Rebrova V. N. Biyushkin I. V. Feofanova A. A. Panasenko 《Russian Chemical Bulletin》1993,42(3):522-527
The rearrangement of enol acylates of aryl 1H-1, 2, 4-triazol-1-ylmethyl ketones at 140–150°C in acetic anhydride is studied. The migration of the acyl group to the C(5) atom of the heterocycle is found to be intramolecular. The characteristics of the original and final products are presented. X-ray structural studies of the enol acetates of 2, 4-dichlorophenyl 1H-1, 2, 4-triazol-1-ylmethyl ketone and 2, 4-dichlorophenyl 5-acetyl-1H-1, 2, 4-triazol-1-ylmethyl ketone are carried out.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 560–564, March, 1993. 相似文献
63.
简要总结了我们在C=C及C=O双键低温加氢双金属催化剂方面的最新研究成果. 首先, 我们以环己烯加氢为探针反应, 证明了平行使用多种研究手段的重要性, 包括单晶表面的基础研究与DFT计算, 多晶表面的合成与表征, 负载型催化剂的制备与性能测试等. 其次, 总结了双金属催化剂在其他加氢反应, 如丙烯醛C=O双键的选择性加氢, 苯的低温加氢, 以及乙炔的选择性加氢等反应中的应用. 最后, 讨论了利用金属碳化物代替贵金属Pt以减少双金属催化剂中Pt用量的可能性. 相似文献
64.
H. Binder B. Kohlstrunk U. Brenn W. Schwieger G. Klose 《Colloid and polymer science》1998,276(12):1098-1109
Microcrystals of the metal silicate hydrate ilerite orient macroscopically on the surface of a ATR-crystals and thus, are
accessible for infrared linear dichroism measurements. We present first results which indicate that the alkyl chain packing
and the orientation of the polar group of dodecyltrimethylammoniumbromide (DTAB) intercalated between silicate layers can
be determined in terms of infrared order parameters. The properties of DTAB can be modulated by the relative humidity of the
surrounding atmosphere and by temperature. Upon heating DTAB undergoes a phase transition from a paraffin-like solid to a
fluid phase. The former is characterized by the orthorhombic perpendicular packing of the frozen alkyl chains with tilted
long axes. The interactions between the ionic groups of the surfactant and that of the host matrix stabilize the lamellar
arrangement of DTAB in the crystalline and in the fluid phases.
Received: 14 January 1998 Accepted: 27 July 1998 相似文献
65.
Jia-you Shu Mo Zhu Yi Shu Qi-jun Liu Tong Li 《高分子科学》2006,(4):395-401
The new chelate resins, abbreviated as PNBMZs and PBBMZs based on epoxide polymer, were synthesized by polycondensation of N,N-diglycidyl-4-glycidyloxyaniline or 1,4-bis(2,3-epoxypropyl)benzene with the primary amine group of 1,3-bis(benzimidazol-2yl)propylamine (BBPAH). The ion exchangers contain 2.71-3.23 mmol of the ligand contents per gram of the resin. Batch extraction capacities were determined for the metal chloride salts in buffer solutions in the pH range from -1 to 6.0. The chelate resins were very selective for Cu^2+, Zn^2+, Cd^2+ in the presence of other divalent transition metal ions. The maximum uptake capacities of PNBMZ (synthetic molar ratio = 1:1.5) under non-competitive condition were found to be 0.94 mmol/g for Cu^2+ at pH = 2, 1.3 mmol/g for Cd^2+ at pH = 1 and 1.75 mmol/g for Zn^2+ at pH = -1 respectively. While in the case of PBBMZ, it was 1.39 mmol/g for Cd〉 at pH = 1. The metal-uptake behaviors for both of them showed strong pH dependence, and their extraction capacities increase with decreasing pH. The uptake of Cu^2+ by the resin PNBMZs at pH = 1 was found to be rather fast with t1/2 = 18 min. Metal-uptake experiments under competitive conditions also confirm that the chelate resins have a high selectivity for Cu^2+, Zn^2+, Cd^2+ and the contrary pH dependence. 相似文献
66.
Fabrice Freville Tristan Richard Katell Bathany Serge Moreau 《Helvetica chimica acta》2006,89(12):2958-2974
A new strategy to cyclize short synthetic oligonucleotides on DNA or RNA target strands is described. The approach is based on metal‐templated cyclization of short synthetic oligonucleotides conjugated with two chelating 2,2′ : 6′,2′′‐terpyridine (Tpy) moieties at their 3′‐ and 5′‐ends. Cyclization after metal addition (Zn2+, Fe2+) was demonstrated by means of thermal‐denaturation experiments, MALDI‐Q‐TOF‐MS, and gel electrophoresis (PAGE). 1D‐ and 2D‐NMR Experiments were performed to analyze the association of complementary strands after metal‐mediated cyclization. Our protocol allows the efficient circularization of synthetic oligonucleotides. Thereby, the hybridization on a complementary strand was more efficient with an RNA target strand and a 2′‐O‐methylated circularized oligomer. 相似文献
67.
Conversion of adsorption properties of activated charcoal (C∗) by metal modification towards selenite, selenate and seleno-dl-methionine (Se-Met) was studied. Several metals were included in modification studies and also a procedure was developed for the separation and independent determination of microgram quantities of these selenium species in aqueous solution. Selenium species were collected one by one from the same sample solution onto collector material by adsorbing them directly or after complex formation onto different metal-loaded activated charcoals (MgC∗ and FeC∗). The mass of selenium in these collectors was measured directly by energy dispersive X-ray fluorescence spectrometry (EDXRF). Detection limits for all three selenium species were better than 6 μg corresponding to concentration of 60 μg/l with 0.100 l of initial sample volume. 相似文献
68.
多氮杂大环与许多金属离子能形成稳定的络合物。由于氮原子是三价的,因而多氮杂大环比冠醚具有更有利的结构;如果再导入羧基、膦酸基以及其他的亲水基团,则可得到一系列能形成水溶性金属络合物的配体。其中某些金属(如铜、钇等)的络合物在人体生理条件下表现出很好的稳定性,结合单原抗体技术的应用,这炎络合物在医疗、诊断方面有实用性。本文简单介绍某些代表性络合物的制备方法、物理性能和可能的应用。 相似文献
69.
Chemical modification of silica surface by immobilization of functional groups for extractive concentration of metal ions 总被引:11,自引:0,他引:11
Increased utilization of mechanically stable synthetic matrices particularly silica gel as a solid support and its surface modification either by impregnation of organic ligands directly or covalent grafting through spacer unit for extractive concentration of trace elements are highlighted in the present article. Experimental evidences for existence of surface silanol and its chemical nature have explored the idea of silica surface modification. Recent methods of development in functionalized silica synthesis by attachment of various ligands or organic reagents to the silica surface and techniques of characterization of the modified surface have been reported. Analytical applications of various modified silica surfaces, in particular, adsorption of trace elements taking separation and preconcentration into account from complex synthetic mixture as well as natural water is presented. 相似文献
70.
Metal (M) oxide (M: Ir, Os, Pd, Pt, Rh, Ru) together with MaO2 and MnO2 alone, were coated on SnO2 films and the anode behavior was examined in 1.0 N H2SO4, 1.0 N NaOH and 1.0, N NaCl aqueous solutions at 25°. The results are compared with those of DSA and of metallic Pt. 相似文献