全文获取类型
收费全文 | 43029篇 |
免费 | 4790篇 |
国内免费 | 7563篇 |
专业分类
化学 | 36504篇 |
晶体学 | 1934篇 |
力学 | 2253篇 |
综合类 | 341篇 |
数学 | 2279篇 |
物理学 | 12071篇 |
出版年
2024年 | 95篇 |
2023年 | 361篇 |
2022年 | 862篇 |
2021年 | 900篇 |
2020年 | 1245篇 |
2019年 | 1147篇 |
2018年 | 992篇 |
2017年 | 1209篇 |
2016年 | 1673篇 |
2015年 | 1603篇 |
2014年 | 1924篇 |
2013年 | 3200篇 |
2012年 | 3494篇 |
2011年 | 2465篇 |
2010年 | 2094篇 |
2009年 | 2647篇 |
2008年 | 2810篇 |
2007年 | 2923篇 |
2006年 | 2737篇 |
2005年 | 2491篇 |
2004年 | 2467篇 |
2003年 | 2109篇 |
2002年 | 2232篇 |
2001年 | 1466篇 |
2000年 | 1482篇 |
1999年 | 1199篇 |
1998年 | 1048篇 |
1997年 | 857篇 |
1996年 | 849篇 |
1995年 | 749篇 |
1994年 | 707篇 |
1993年 | 534篇 |
1992年 | 558篇 |
1991年 | 331篇 |
1990年 | 273篇 |
1989年 | 207篇 |
1988年 | 199篇 |
1987年 | 145篇 |
1986年 | 129篇 |
1985年 | 138篇 |
1984年 | 117篇 |
1983年 | 88篇 |
1982年 | 84篇 |
1981年 | 77篇 |
1980年 | 73篇 |
1979年 | 74篇 |
1978年 | 55篇 |
1977年 | 58篇 |
1974年 | 43篇 |
1973年 | 51篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Lucifer yellow and lissamine rhodamine sulfonyl hydrazine were used as the donor and the receptor, respectively, for Förster energy transfer measurements to determine the location of the subunit in the native Na,K-ATPase from pig kidney. It was found that (1) the subunits are located in one functional complex, i.e., the dimer ()2 appears to be the functional complex of Na,K-ATPase, and (2) the subunits in the functional enzyme complex in the membrane are not located next to each other but are rather well separated. The distance between fluorophores covalently attached to the subunits was found to be 5.3 nm. 相似文献
992.
Summary A simple and quantitative method for the preparation and high performance liquid chromatography (HPLC) of N-acylated fluoroquinolones has been developed. The acylation procedure was performed with four different acid anhydrides and found to be applicable to several fluoroquinolones. The acylated derivatives were chromatographed directly on a Nucleosil C18 column without the necessity of further sample manipulation. Detector response for the N-acetyl derivatives of norfloxacin, ciprofloxacin, sarafloxacin, and temafloxacin was linear to at least 50 g/mL. The retention behavior of the N-acyl derivatives can be predicted by the length of the carbon chain of the amide. 相似文献
993.
A nearly stoichiometric SrCoO3 phase had been prepared up to now only using high oxygen pressure. A new method for preparing fully stoichiometric SrCoO3 has been proposed using electrochemical oxidation. Brownmillerite-type SrCoO2.50 is oxidized into a completely stoichiometric perovskite at a potential of 500 mV for 180 hours at room temperature in alkaline media (1 M KOH). The oxidized phase has a cubic unit cell (a=383.5 pm). It is metallic and, at temperatures below T=280 K, it shows ferromagnetic behavior. The magnetic moment at 0 K is 2.1 μB. The physical properties of SrCoO3.00 have been explained in terms of partial occupancy of a σ*e band. 相似文献
994.
乙基苯基二氯化锡与2-羟基萘醛缩对甲氧基苯胺Schiff碱1∶1配合物的合成和晶体结构刘宝殿,包明,孙振刚,贺庆林,邢彦,贾恒庆,林永华(东北师范大学化学系,长春,130024)(中国科学院长春应用化学研究所,长春)关键词乙基苯基二氯化锡,Schif... 相似文献
995.
Reaction of the isodicyclopentadienide anion and its dehydro congener with Fe(II) leads to a stereochemically homogeneous ferrocene derivative in each instance. Through chemical correlation and X-ray analysis, above-plane complexation is established for both halves within the two sandwich compounds. 相似文献
996.
含吲哚核端基多甲川菁染料的合成及性能 总被引:6,自引:0,他引:6
我们曾合成了具有桥环的硫三碳菁及多甲川苯乙烯菁,并测定了光学性能。本文报道吲哚环为端基的桥链三碳菁和四甲川苯乙烯菁的合成及在有机溶剂中电子吸收光谱及溶解性能的测定。所用仪器同前,7种多甲川菁染料的合成反应如下: 相似文献
997.
A study on the ductile deformation domain of the brittle fault in the shallow level ofthe crust is a new probe field for the modern structural geology. Taking the southern Jiang-su Province area as an example the orientation measurement of quartz crystals, the com-positional texture observation of three pressure sensitive minerals and the rheological param-eter determination of dislocation densities, etc. have been demonstrated and analysed basedon typical samples in the present paper. In addition, their generation mechanisms arealso discussed from the cataclastic rheology, the dynamic differentiation and the simpleshearing, specially, from the Ode strength theory. Finally, a generative relationship betweenthe ductile deformation domain of the brittle fault system, in the regional layer--slip andthe formation of the stratabound ore deposit is shown as well. 相似文献
998.
Burton A Elomari S Chen CY Medrud RC Chan IY Bull LM Kibby C Harris TV Zones SI Vittoratos ES 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(23):5737-5748
The syntheses, structure solutions, and physicochemical and catalytic characterizations of the novel zeolites SSZ-53 and SSZ-59 are described. SSZ-53 and SSZ-59 were synthesized under hydrothermal conditions with the [1-(4-fluorophenyl)cyclopentylmethyl]trimethyl ammonium cation and 1-[1-(4-chlorophenyl)cyclopentylmethyl]-1-methyl azocanium cation, respectively, as structure-directing agents. The framework topology of SSZ-53 was solved with the FOCUS method, and the structure of SSZ-59 was determined by model building. Rietveld refinement of synchrotron X-ray powder diffraction data confirms each proposed model. SSZ-53 and SSZ-59 each possess a one-dimensional channel system delimited by 14-membered rings. Results from transmission electron microscopy, electron diffraction, catalytic experiments (spaciousness index and constraint index tests), and argon and hydrocarbon adsorption experiments are consistent with the proposed structures. 相似文献
999.
1 INTRODUCTION Recently, the low-spin square-planar nickel(II) complexes and high-spin octahedral nickel(II) complexes with Schiff base ligands have received much attention in optical materials[1~3]. Some nic- kel(II) complexes are widely used as lubricating oil, rubber industry additives, a fire-resistant additive and fungicide for leather[4~7]. Also, their adducts with nitrogen have attracted broad attention due to their potential applications as organic conductors and magnetic mate… 相似文献
1000.
For benzenoid hydrocarbons the distribution of pi-electrons amongst rings is characterized in the context of Randis mode of assignment attending to the different Kekulé structures. In particular the mean and mean deviation from the mean are considered, and the benzenoids which achieve maximum deviation are identified. 相似文献