全文获取类型
收费全文 | 10577篇 |
免费 | 1597篇 |
国内免费 | 915篇 |
专业分类
化学 | 5749篇 |
晶体学 | 95篇 |
力学 | 517篇 |
综合类 | 36篇 |
数学 | 1007篇 |
物理学 | 3191篇 |
无线电 | 2494篇 |
出版年
2024年 | 46篇 |
2023年 | 261篇 |
2022年 | 322篇 |
2021年 | 388篇 |
2020年 | 454篇 |
2019年 | 358篇 |
2018年 | 328篇 |
2017年 | 337篇 |
2016年 | 481篇 |
2015年 | 545篇 |
2014年 | 565篇 |
2013年 | 721篇 |
2012年 | 920篇 |
2011年 | 885篇 |
2010年 | 645篇 |
2009年 | 628篇 |
2008年 | 677篇 |
2007年 | 516篇 |
2006年 | 592篇 |
2005年 | 467篇 |
2004年 | 326篇 |
2003年 | 276篇 |
2002年 | 225篇 |
2001年 | 180篇 |
2000年 | 210篇 |
1999年 | 219篇 |
1998年 | 202篇 |
1997年 | 160篇 |
1996年 | 175篇 |
1995年 | 150篇 |
1994年 | 120篇 |
1993年 | 104篇 |
1992年 | 97篇 |
1991年 | 93篇 |
1990年 | 55篇 |
1989年 | 43篇 |
1988年 | 51篇 |
1987年 | 37篇 |
1986年 | 31篇 |
1985年 | 24篇 |
1984年 | 23篇 |
1983年 | 20篇 |
1982年 | 9篇 |
1981年 | 16篇 |
1980年 | 9篇 |
1977年 | 6篇 |
1976年 | 10篇 |
1975年 | 9篇 |
1973年 | 8篇 |
1972年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
942.
Wei Zhang Yongzhai Du Zhili Feng Jun Xu 《International Journal for Ion Mobility Spectrometry》2010,13(2):65-71
Membrane-extraction Ion Mobility Spectrometry (ME-IMS) is a feasible technique for the continuous monitoring of chlorinated hydrocarbons in water. This work studies theoretically the time-dependent characteristics of sampling and detection of trichloroethylene (TCE). The sampling is configured so that aqueous contaminants permeate through a hollow polydimethylsiloxane (PDMS) membrane and are carried away by a transport gas flowing through the membrane tube into IMS analyzer. The theoretical study is based on a two-dimensional transient fluid flow and mass transport model. The model describes the TCE mixing in the water, permeation through the membrane layer, and convective diffusion in the air flow inside membrane tube. The effect of various transport gas flow rates on temporal profiles of IMS signal intensity is investigated. The results show that fast time response and high transport yield can be achieved for ME-IMS by controlling the flow rate in the extraction membrane tube. These modeled time-response profiles are important for determining duty cycles of field-deployable sensors for monitoring chlorinated hydrocarbons in water. 相似文献
943.
Dušan Berek 《Journal of separation science》2010,33(3):315-335
Size exclusion chromatography, SEC is one of the most popular methods for the separation of different kinds of macromolecules. This critical review gives concise information about macromolecules and their behavior in solution, basic understanding about principles, instrumentation, and application possibilities of SEC, and more in detail discusses drawbacks and pitfalls of the method with the emphasis on synthetic polymers. Selected practical advices are included to help enhance the quality of SEC results. 相似文献
944.
Hongyuan Yan Jingjing Du Xiguo Zhang Gengliang Yang Kyung Ho Row Yunkai Lv 《Journal of separation science》2010,33(12):1829-1835
A simple and rapid ultrasound‐assisted dispersive liquid–liquid microextraction method coupled with GC‐flame ionization detection was developed for simultaneous determination of nine pyrethroids in domestic wastewater samples. An ultrasound‐assisted process was applied to accelerate the formation of the fine cloudy solution using small volume of disperser solvent, which markedly increased the extraction efficiency and reduced the equilibrium time. Various parameters affecting the extraction efficiency were investigated, including the type and volume of extraction solvent and disperser solvent, extraction and ultrasonic time. Good linearity was obtained for all analytes in the range of 0.8–100 μg/L with the correlation coefficient (r2)≥0.998. The recoveries at three spiking levels ranged from 75.3 to 101.2% with the RSD less than 8.7% (n=5). Under the optimum condition, the enrichment factors for the nine pyrethroids ranged from 728‐ to 1725‐fold. This method offered a good alternative for routine analysis due to its simplicity and reliability. 相似文献
945.
Lei Zhang Qingqing Li Wei Tao Bohao Yu Yiping Du 《Analytical and bioanalytical chemistry》2010,398(4):1827-1832
Silver sol surface-enhanced Raman spectroscopy (SERS) was considered as a technique in the quantitative analysis of low-concentration thymine. Because of the poor stability and reproducibility of SERS signal, a polymer of polyacrylic acid sodium was selected as a stable medium to add into silver sol in order to obtain a surface-enhanced Raman spectroscopy signal. Assignments of Raman shift for solid thymine, SERS of thymine, and SERS of thymine containing stable medium were given. The comparison of Raman peaks between them showed that the addition of stable medium had a little influence on the SERS of thymine and is suitable for the quantitative analysis of low-concentration thymine. 相似文献
946.
Repická Zuzana Moncol Jan Puchoňová Miroslava Jorík Vladimír Mikloš Dušan Lis Tadeusz Padělková Zdenka Mazúr Milan Valigura Dušan 《Structural chemistry》2010,21(5):1093-1102
Novel copper(II) X-salicylate complexes with N,N-diethylnicotinamide (dena) of the formula [Cu(RCOO)2(dena)2(H2O)2] (RCOO = 3-methylsalicylate anion (3-Mesal, 1), 4-methylsalicylate anion (4-Mesal, 2), 5-methylsalicylate anion (5-Mesal, 3), 5-methoxysalicylate anion (5-MeOsal, 4) or 4-methoxysalicylate anion (4-MeOsal, 5)), and complex [Cu(3-MeOsal)2(dena)2(H2O)2]∙2H2O (3-MeOsal = 3-methoxysalicylate anion (6)) have been prepared in the crystalline forms and characterized by spectroscopic methods (IR, Vis–UV, EPR). All the compounds
according to their composition (1–5) seem to possess octahedral copper(II) stereochemistry. The complex 1 has been prepared in two different forms. X-ray analyses of the complexes 1, 4, and 5 were carried out and they featured a tetragonal-bipyramidal geometry around the copper atoms. The tetragonal planes are created
by X-salicylate anions bonded to the copper(II) atoms via unidentate carboxylate oxygen atoms and the pyridine ring nitrogen
atoms of the neutral ligand N,N-diethylnicotinamide, while in axial positions are water molecules. The two forms of complex 1 present conformation polymorphs and supramolecular isomers. 相似文献
947.
Eleven kinds of density functionals in conjunction with three different basis sets are employed to investigate the homonuclear
5d-electron dimers: Hf2, Ta2, Re2, W2 and Hg2. The computed bond lengths, vibrational frequencies and dissociation energies of these molecules are used to compare with
available experimental data to find the appropriate combination of functional and basis set. The different functionals and
basis sets favor different ground electronic state for Hf2 and Re2 molecules, indicating that these two dimers are sensitive to the functionals used. The molecular properties of Hg2 dimer depend strongly on both functionals and basis sets used. It is found that the BP86 and PBEPBE functionals are generally
successful in describing the 5d-electron dimers. For the ground states of these dimers, the bonding patterns are determined by natural bond orbital (NBO)
analysis. Natural electron configurations show that the 6s and 5d orbitals in the bonding atoms hybrid with each other for the studied dimers except for Hg2. 相似文献
948.
PbS nanotubes were successfully synthesized in bicontinuous microemulsion system containing cyclohexane, aqueous solution,
n-pentanol and surfactant OP (polyethylene glycol p-octylphenyl ether). The morphology of PbS nanotubes was confirmed by the transmission electron microscopy. The crystallinity
and structural features of PbS nanotubes were characterized by powder X-ray diffraction. The effect of key parameters, such
as the molar ratio of water to surfactant and the reactant concentration, on the resulting product has also been investigated.
The formation mechanism of PbS nanotubes and nanowires synthesized in bicontinuous microemulsion system has been discussed. 相似文献
949.
Tao Jiang Fei Du Kejin Zhang Yingjin Wei Zhe Li Chunzhong Wang Gang Chen 《Solid State Sciences》2010,12(9):1672-1676
Carbon coated and carbon free Li3V2(PO4)3 cathode materials were prepared by carbothermal reduction and H2 reduction methods, respectively. The carbon free material had a grain size about 1 μm whereas the carbon coated material was less than 100 nm. The surface carbon layer enhanced the electronic conductivity of Li3V2(PO4)3 by five orders of magnitude. In addition, the surface carbon layer also prevented the formation of SEI film, decreased the charge transfer resistance and increased the chemical diffusion coefficient of Li+ ions. All of these advantages improved the electrochemical performance of Li3V2(PO4)3. As most of intercalation materials, the low temperature performance of Li3V2(PO4)3 was poorer than that at room temperature. This was attributed to the electrochemical sluggish kinetics which caused higher charge transfer resistance and smaller chemical diffusion coefficient. The carbon coating technique was effective to eliminate these sluggish kinetics, and then improved the low temperature performance of Li3V2(PO4)3. 相似文献
950.
Yang X Sun X Lv Z Guo W Du Y Wang E 《Chemical communications (Cambridge, England)》2010,46(46):8818-8820
A new kind of silver micro-dendrites with no surfactants protected has been synthesized for the separation and detection of DNA merely by earth gravity as the density of silver is larger than that of water. Through this approach, the DNA of human T-lymphotropic virus type I (HTLV-I) can be detected down to 10 pM with the detection range from 10 pM to 100 nM. 相似文献