全文获取类型
收费全文 | 17083篇 |
免费 | 1897篇 |
国内免费 | 1196篇 |
专业分类
化学 | 9844篇 |
晶体学 | 211篇 |
力学 | 239篇 |
综合类 | 112篇 |
数学 | 312篇 |
物理学 | 9458篇 |
出版年
2024年 | 19篇 |
2023年 | 172篇 |
2022年 | 383篇 |
2021年 | 571篇 |
2020年 | 489篇 |
2019年 | 490篇 |
2018年 | 428篇 |
2017年 | 623篇 |
2016年 | 869篇 |
2015年 | 802篇 |
2014年 | 1063篇 |
2013年 | 1578篇 |
2012年 | 1200篇 |
2011年 | 1255篇 |
2010年 | 962篇 |
2009年 | 1184篇 |
2008年 | 979篇 |
2007年 | 1083篇 |
2006年 | 811篇 |
2005年 | 836篇 |
2004年 | 702篇 |
2003年 | 505篇 |
2002年 | 424篇 |
2001年 | 336篇 |
2000年 | 328篇 |
1999年 | 278篇 |
1998年 | 189篇 |
1997年 | 191篇 |
1996年 | 197篇 |
1995年 | 196篇 |
1994年 | 129篇 |
1993年 | 149篇 |
1992年 | 146篇 |
1991年 | 76篇 |
1990年 | 82篇 |
1989年 | 70篇 |
1988年 | 78篇 |
1987年 | 59篇 |
1986年 | 39篇 |
1985年 | 43篇 |
1984年 | 26篇 |
1983年 | 24篇 |
1982年 | 40篇 |
1981年 | 20篇 |
1980年 | 10篇 |
1979年 | 16篇 |
1978年 | 6篇 |
1976年 | 3篇 |
1973年 | 7篇 |
1971年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Capillary gas chromatography coupled to microwave-inducedplasma detection furnishes sensitivity adequate for trace analysis when the signal is monitored at a carbon emission line. Work performed with one of these systems at high electronic gain for the carbon signal has revealed solvent band widths in excess of four minutes; these impeded quantification of peaks eluting after the solvent. This report discusses two phenomena which could be related to the unexpected intensity of this solvent response: photomultiplier tube saturation and carbon deposits in the quartz plasma discharge tube. 相似文献
62.
63.
A. E. Chmel’ 《Journal of Applied Spectroscopy》1997,64(4):566-568
Using Raman spectroscopy, a quantitative analysis of the distribution of OH− ions on the boundary between a bearing pipe and a glass layer deposited from chlorides in billets for quartz fiber light
guides is carried out. Water penetrated into the light-reflecting shell to a depth of several tenths of a millimeter, depending
on the composition of the doping layer (i.e., ultimately on the temperature of the depsoition process).
A. F. Ioffe Physical-Technical Institute, Academy of Sciences of Russia, 26, Politekhnicheskaya St., St. Petersburg, 194021,
Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 4, pp. 548–550, July–August, 1997. 相似文献
64.
转动喇曼散射截面的群论计算 总被引:1,自引:1,他引:0
本文利用群链U(4)U(3)O(3)描述双原子分子N_2和O_2振转谱的对称性质,并利用群论方法计算了N_2和O_2分子转动喇曼散射的跃迁矩阵元,给出了它们的转动喇曼散射的截面。结果与实验较好地符合。 相似文献
65.
Liquid chromatography-electrospray ionisation mass spectrometry was evaluated in the high-throughput analysis of microcystins and nodularins, cyanobacterial peptide hepatotoxins. Extracts originating from cyanobacterial strains and field material were separated on a 30 mm × 4 mm I.D. Merck Purospher STAR RP-18e column using a rapid gradient of aqueous formic acid and acetonitrile, ionised by electrospray technique and analysed on a Micromass Quattro II triple-quadrupole mass spectrometer operated in the selected ion recording (SIR) mode. The total analysis time per sample was 2.8 min corresponding to 514 samples a day. The system showed good robustness during a series of 320 repetitive injections of a field sample containing three major microcystins. 相似文献
66.
67.
T. Rietmann S. Sohn M. Schröder D. Lipinsky H.F. Arlinghaus 《Applied Surface Science》2006,252(19):6640-6643
In order to improve quantification of high mass ions, the influence of cluster composition on detection efficiencies has been studied using a TOF-SIMS IV with the extended capability of postaccelerating ions up to 20 keV. In this experimental study, we focus on the comparison of detection efficiencies for three types of negatively charged secondary cluster ions: gold-alkanethiolate-clusters (AuxMy), gold-sulfur-clusters (AuxSy) and gold-clusters (Aux). The clusters were sputtered from self-assembled monolayers of hexadecanethiols on gold substrates using 10 keV Ar+ primary ions. The detection efficiencies were derived on the basis of a function for the secondary electron yield and a fourth-order approximated Poisson probability distribution for electron propagation and amplification within the microchannel plate.In addition to the well-known dependence of detection efficiencies on ion mass and energy, which has already been studied for positively charged ions, we were able to show a similar behaviour for the investigated negatively charged secondary ions. We have observed major variations among the three types of clusters at similar mass and energy as predicted in a theoretical approach. The observed differences are due to the different composition of the investigated clusters which has a major influence on the kinetic ion induced electron emission within the microchannel plate. For the first time it was possible to experimentally verify these predictions for detection efficiencies. 相似文献
68.
69.
Orotic acid (vitamin B13) is a key intermediate in biosynthesis of the pyrimidine nucleotides in living organisms, moreover, it may serve as the biological carrier for some metal ions. cis-Diammine(orotato)platinum(II), cis-[Pt(C5H2N2O4)(NH3)2] can be considered as a new potential cisplatin analogue. The FT-Raman and FT-IR spectra of the title complex are reported, for the first time. The molecular structure, vibrational frequencies, and the theoretical infrared and Raman intensities have been calculated by the density functional mPW1PW91 method. The detailed vibrational assignment has been made on the basis of the calculated potential energy distribution. The theoretically predicted IR and Raman spectra show very good agreement with experiment. Natural bond orbital (NBO) analyses were performed for cisplatin, carboplatin and the title complex. The results provided new data on the nature of platinum–ligand bonding in these compounds. Strong intramolecular hydrogen bond between the orotate ligand and the coordinated ammonia group stabilizes the structure of the platinum(II) complex. Thus, it is suggested that the orotate ligand in the title complex is more inert to the substitution reactions than the chloride ligands in cisplatin. 相似文献
70.
提出一种波长检测技术实现温度测量的方法,利用FBG传感器对温度等物理量实施监测,具有测试精度高,应用场合不受限制等特点,当环境参数发生变化时,光纤光栅的有效折射率和光栅周期会受到影响,将引起光纤光栅峰值波长的偏移,依据反射光谱结构的变化,可知道其温度的变化趋势。实验测试结果表明,在温度变化0.1°,波长变化1pm,温度和波长具有良好的线性关系。 相似文献