全文获取类型
收费全文 | 10626篇 |
免费 | 2547篇 |
国内免费 | 3257篇 |
专业分类
化学 | 6214篇 |
晶体学 | 257篇 |
力学 | 1398篇 |
综合类 | 325篇 |
数学 | 1925篇 |
物理学 | 6311篇 |
出版年
2024年 | 65篇 |
2023年 | 211篇 |
2022年 | 289篇 |
2021年 | 220篇 |
2020年 | 149篇 |
2019年 | 296篇 |
2018年 | 339篇 |
2017年 | 268篇 |
2016年 | 288篇 |
2015年 | 246篇 |
2014年 | 679篇 |
2013年 | 380篇 |
2012年 | 400篇 |
2011年 | 415篇 |
2010年 | 365篇 |
2009年 | 414篇 |
2008年 | 446篇 |
2007年 | 416篇 |
2006年 | 422篇 |
2005年 | 369篇 |
2004年 | 323篇 |
2003年 | 652篇 |
2002年 | 1658篇 |
2001年 | 1444篇 |
2000年 | 618篇 |
1999年 | 592篇 |
1998年 | 484篇 |
1997年 | 383篇 |
1996年 | 420篇 |
1995年 | 411篇 |
1994年 | 365篇 |
1993年 | 373篇 |
1992年 | 354篇 |
1991年 | 291篇 |
1990年 | 307篇 |
1989年 | 257篇 |
1988年 | 101篇 |
1987年 | 102篇 |
1986年 | 100篇 |
1985年 | 89篇 |
1984年 | 71篇 |
1983年 | 56篇 |
1982年 | 63篇 |
1981年 | 48篇 |
1980年 | 23篇 |
1979年 | 20篇 |
1965年 | 15篇 |
1964年 | 14篇 |
1963年 | 13篇 |
1955年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
从江浙蝮蛇毒腺中抽提总RNA,RT-PCR进行体外扩增,获得江浙蝮蛇蛇毒蛋白C激活因子基因,克隆至pGEX-5X-3载体中,对3个重组克隆分别作DNA全序列分析,通过遗传密码推导出相应的氨基酸序列,与其它已知的丝氨酸复白酶蛇毒蛋白的氨基酸作比较,其中许多上氨基酸有很强的同源性,该基因的成功克隆,不仅推导出江浙蝮蛇蛇毒蛋白C激活因子的蛋白质序列,也为进一步开展江浙蝮蛇蛇毒蛋白C激活因子蛋白质工程的研究工作打下良好的基础。 相似文献
82.
Structural Evolution of Nanostructured γ—Ni—28Fe Alloy Investigated by Using the Internal Friction Technique
下载免费PDF全文
![点击此处可从《中国物理快报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The structural evolution of nanostructured γ-Ni-28Fe alloy(n-Ni-Fe)(grain size d-30nm),synthesized by the mechno-chemical method,was investigated by using the internal friction technique combined with differential scanning calorimetry(DSC) in the temperature range from 300K to 670K.An internal friction peak with typical characteristics of the first-order phase transition was observed in the vicinity of 620K,which corresponds to a broad exothermic process revealed by using DSC.Theses results can be explained as the structural changes from the disordering to the ordering transition in the n-Ni-Fe sample. 相似文献
83.
A water soluble crude polysaccharide has been isolated from the fruiting body of cultivated Cordyceps militarvs(L.)Link.The GC analysis indicated that it contained the monosaccharides of Gal,Man,Glc and GlcA.Their molar ratio is 1.00:1.58:7.89:0.19.The crude polysaccharide was fractionated with ethanol to get three fractions,which were CM-Ⅰand CM-Ⅲ,CM-Ⅱ was further purified to get one homogeneous fraction named CMB.The molecular weight was estimated to be 6000by means of gel filtration.CMB is a greyish white powder.The GC analysis indicated that it was composed of Gal.Man,Glc and the molar ratio is 1.00:1.38:5.10.Partial hydrolysis with an acid.periodate oxidation.Smith degradation.IR,GC and methylation analyses,GC/MS analyses were used for the structure analyses of CMB.Man,(1→6)-linked-Glc,(1→4)-linked-Glc and (1→4)-linked-Gal.Some of (1→4) -linked-Glc and all(1→4)-linked-Gal residues are substituted at 3-O and 6-O respectively,(1→4)-linked-Glc and minor(1→6)-linked-Gle.The nonreduced end is composed of Gal and Glc.The main glycosidic link of CMB is α configuration. 相似文献
84.
A convenient and large-scale preparation of retinoic acid 1 from β-ionone in five steps with 38% overall yield is described.The key steps are the epoxidization of 2 with a new methylated agent and the condensation 4 with tetraethyl methylenediphophonate in one-pot procedure to prepare 6. 相似文献
85.
86.
A theoretical and experimental study on no-guide light pen type 3D-coordinate measurement system 总被引:1,自引:0,他引:1
A novel no-guide light pen type 3D-coordinate measurement system with three sets of position sensitive devices (PSDs) to realize intersection converge imaging is introduced. It is called as the light pen type measurement system, because the measuring head is shaped as a pen with several light sources on it. The structure design, measurement principle and experimental results are presented. The theoretical analysis and experimental results prove that this system has advanced features of simple structure, high automation, and high accuracy, and can be used in the measurement fields of mechanical manufacture, robot, auto, aviation and medicine effectively. 相似文献
87.
The big bounce singularity of a simple five-dimensional cosmological model is studied.Contrary to the standard big bang space-time singularity,this big bounce singularity is found to be an event horizon at which the scale factor and the mass density of the universe are finite,while the pressure undergoes a sudden transition from negative infinity to positive infinity.By using coordinate transformation it is also shown that before the bounce the universe contracts deflationary.According to the proper-time,the universe may have existed for an infinitely long time. 相似文献
88.
The current-voltage characteristics of Ti/n-GaAs Schottky diodes measured over a temperature range of 78-299K have been interpreted on the basis of thermionic emission across an inhomogeneous Schottky contact.The experiment shows that the apparent barrier height (φap) increases from 0.437eV at 78K to 0.698eV at room temperature.the plot of φap versus 1/T does not exhibit a simple linear relationship over the whole temperature range,indicating that the barrier height distribution is more complicated than the frequently observed single Gaussian distribution.A new multi-Gaussian distribution model is developed.Our experimental results can be explained by a double Gaussian distribution of the barrier heights.The weight,the mean barrier height,and the standard deviation of the two Gaussian functions are 0.00001 and 0.99999,0.721 and 0.696,0.069 and 0.012eV,respectively. 相似文献
89.
Optical Properties of ZnFe2O4—SiO2 Granular Films Prepared by Radio—Frequency Magnetron Sputtering
下载免费PDF全文
![点击此处可从《中国物理快报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We report on the optical properties of ZnFe2O4-SiO2 granular films prepared on quartz substrates by the radio-frequency magnetron sputtering method.Post-annealing was performed at different temperatures under flow oxygen atmosphere.The morphology and Structures of ZnFe2O4 nanoparticles were characterized by x-ray different line types in the optical absorption curves of ZnFe2O4-SiO2 granular films.The critical transition of line types occurs when ZnFe2O4 changes from amorphous to crystalline,and the transition temperature increases with the increasing content of ZnFe2O4.There is an obvious blueshift of the optical absorption edge of the granular films with the decreasing annealing temperature. 相似文献
90.
Sound Field Calculations of Elliptical Pistons by the Superposition of Two—Dimensional Gaussian Beams
下载免费PDF全文
![点击此处可从《中国物理快报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We present an alternative approach to calculate the sound field of ultrasonic transducers.The distribution function of sources is expanded into the superposition of a series of two-dimensional Gaussian functions.The corresponding radiated sound field is expressed as the superposition of these two-dimensional Gaussian beams and is then reduced to the computation of these simple functions.This treatment does not require the condition that the shape of the source is of circular axial symmetry.A numerical example is presented for the uniform elliptical piston transducer and this is in good agreement with the results given by complicated computation. 相似文献