全文获取类型
收费全文 | 5756篇 |
免费 | 1046篇 |
国内免费 | 1365篇 |
专业分类
化学 | 5202篇 |
晶体学 | 360篇 |
力学 | 143篇 |
综合类 | 39篇 |
数学 | 20篇 |
物理学 | 2403篇 |
出版年
2024年 | 7篇 |
2023年 | 118篇 |
2022年 | 161篇 |
2021年 | 274篇 |
2020年 | 286篇 |
2019年 | 247篇 |
2018年 | 209篇 |
2017年 | 269篇 |
2016年 | 316篇 |
2015年 | 254篇 |
2014年 | 332篇 |
2013年 | 450篇 |
2012年 | 463篇 |
2011年 | 531篇 |
2010年 | 421篇 |
2009年 | 510篇 |
2008年 | 405篇 |
2007年 | 477篇 |
2006年 | 421篇 |
2005年 | 353篇 |
2004年 | 282篇 |
2003年 | 247篇 |
2002年 | 210篇 |
2001年 | 141篇 |
2000年 | 124篇 |
1999年 | 123篇 |
1998年 | 94篇 |
1997年 | 84篇 |
1996年 | 55篇 |
1995年 | 58篇 |
1994年 | 45篇 |
1993年 | 37篇 |
1992年 | 46篇 |
1991年 | 20篇 |
1990年 | 20篇 |
1989年 | 15篇 |
1988年 | 11篇 |
1987年 | 13篇 |
1986年 | 11篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 7篇 |
1981年 | 1篇 |
1979年 | 6篇 |
1975年 | 4篇 |
排序方式: 共有8167条查询结果,搜索用时 31 毫秒
31.
A method for the deposition of BN onto graphite and other substrates is described. Boron trichloride (BCl3) and ammonia (NH3) diluted with Ar were used as reacting gases. The deposition process was carried out at 1300 K as well as lower temperatures in an open system at pressures of 1 atm. The consequences of the introduction of hydrogen to the system were considered. It was demonstrated that the replacement of argon with hydrogen increases the efficiency of the process as well as the theoretical rate of BN deposition. However, the acceleration of the deposition seems to be unprofitable, because the resulting supersaturation leads to the formation of an amorphous phase. The modification of the experimental conditions were proposed.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday 相似文献
32.
The oxidation of aminoethanethiol (1) was investigated in acid solutions on a glass carbon anode. It was shown that at relatively low anode potentials thiyl radicals RS· are released into the solution, but this does not lead to binding of the oxygen in the solution. Raising the anode potential leads to binding of oxygen, which is probably due to the formation of the intermediate RS+. The oxidation of 1 was studied in Ce(SO4)2+H2SO4 solution. It was shown that under certain conditions the intermediate is RS+, which subsequently converts to a product that could not be identified as any previously described product of the oxidation of thiols. Proposals are made regarding its structure and conversion pathways.B. P. Konstantinov Institute of Nuclear Physics, Russian Academy of Sciences, 188350 Leningrad. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 2, pp. 278–288, February, 1992. 相似文献
33.
J.L. Shui 《Applied Surface Science》2006,253(5):2379-2385
Spongy-like reticular structure is a unique morphology fabricated by electrostatic spray deposition (ESD) technique. The effects of solvent, substrate temperature, precursor feeding rate, static electric field strength, and deposition time on tailoring the reticular structure were investigated. Scanning electron microscopy was used to observe the film morphology. MnOx or LiMn2O4 were selected as the model materials. It is found that in addition to the conventional solvent butyl carbitol, other kinds of solvents such as ethylene glycol and propylene glycol can also be used to obtain reticular films at a suitable substrate temperature. Porous films with a low cross-linking degree pore structure can be prepared by increasing precursor feeding rate or decreasing substrate temperature. Increasing the deposition time or the electric field strength helps to obtain reticular films with more homogeneous pore size distribution. In addition, the addition of a high boiling-point solvent in mixed alcohol solvent results in the increase of proper substrate temperature. It is concluded that the fluidity of the spray droplets on the surface of a hot substrate is an important factor to form a reticular film. 相似文献
34.
Chenghang Wang 《Applied Surface Science》2006,253(4):2282-2288
In this paper, thin films of titanium oxide imprinted with O,O-dimethyl-(2,4-dichlorophenoxyacetoxyl)(3′-nitrobenyl) methinephosphonate (Phi-NO2) were prepared via liquid phase deposition (LPD) method on a glassy carbon electrode. The imprinted molecular in the films was removed by treatment with immersion in CH2Cl2. X-ray diffraction (XRD) and electrochemical methods were introduced to show the evidence of the molecular imprinting phenomenon. It was also found that the recognition ability of the sensor depended on the substituents associated with tridimensional structures of the nitro-compounds. Under the optimized condition, the sensor showed better sensitivity, selectivity and reproducibility to the imprinted molecule and the linear relationship between the current and the concentration of analyte in the range of 0.1-50 μM was obtained. LPD proved to be a powerful method for imprinting titanium oxide thin sense films. 相似文献
35.
36.
提出了线性扫描溶出伏安法测定福美双的电分析化学方法.在 pH 5.0 HAc-NaAc缓冲溶液中福美双在汞电极上出现一还原峰,峰电位为-610 mV(vs.Ag/AgCl).采用各种电化学技术如循环伏安法和线性扫描溶出伏安法等对本体系进行研究,发现采用线性扫描溶出伏安法能得到较灵敏的还原峰,呈现不可逆电极反应现象,并具有一定的吸附性,在210 s时能达到吸附平衡.选择吸附时间为180 s时,线性范围为0.02~0.14 μg·mL-1,最低检测限为9.5 ng·mL-1.将本方法用于实际样品的测定,得到满意的结果. 相似文献
37.
Q. Liang 《Applied Surface Science》2006,252(13):4628-4631
We report a pulsed laser deposition (PLD) growth of VMn/CoCrPt bilayer with a magnetic coercivity (Hc) of 2.2 kOe and a grain size of 12 nm. The effects of VMn underlayer on magnetic properties of CoCrPt layer were studied. The coercivity, Hc, and squareness, S, of VMn/CoCrPt bilayer, is dependent on the thickness of VMn. The grain size of the CoCrPt film can also be modified by laser parameters. High laser fluence used for CoCrPt deposition produces a smaller grain size. Enhanced Hc and reduced grain size in VMn/CoCrPt is explained by more pronounced surface phase segregation during deposition at high laser fluence. 相似文献
38.
Ni + Mo + Si composite coatings were prepared by co-deposition of nickel with molybdenum and silicon powders from a nickel solution in which Mo and Si particles were suspended by stirring. The layers have been deposited on a carbon steel substrate (St3S) under galvanostatic conditions. The content of Si in deposited layers was about 2-5 wt.% depending on deposition current density and the value of electric charge. For comparison Ni + Mo composite coatings were obtained under analogous current conditions. Composite coatings of enhanced Si content (15 wt.%) were deposited from an electrolyte in which 40 g/dm3 of Si covered with electroless plated nickel was dispersed. Deposition current density was equal 0.1 A/cm2 and the value of electric charge Q = 500 C/cm2. The thickness of the coatings was about 100-300 μm depending on their kind, electric charge and the deposition current density. Surface and cross-section morphology were investigated by scanning electron microscope (SEM). All deposited coatings are characterized by great, developed surface area. No internal stresses causing their cracking were observed. Chemical composition of the layers was determined by X-ray fluorescence spectroscopy (XRF) method and quantitative X-ray analysis (QXRD). It was stated, that the content of molybdenum and silicon in Ni + Mo + Si coatings depends on deposition current density and the amount of the powder in bath. The results of structural investigation of the obtained layers by the X-ray diffraction (XRD) method show, that they consist in crystalline Mo or Mo and Si phases built into Ni matrix. Moreover, Ni + Mo + Si composite coatings were modified by thermal treatment. It has been found that the thermal treatment of Ni + Mo + Si composite coatings caused that the new phases (NiSi, Mo2Ni3Si and Ni6Mo6C1.06) were obtained. 相似文献
39.
40.
Electrolysis of dimethyl malonate or methyl cyanoacetate in methanol in the presence of LiCl in an undivided cell leads to formation of 1,1,2,2-cyclopropanetetracarboxylic derivatives.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1835–1836, October, 1994.This work was supported by the International Science Foundation (Grant No MHY 000). 相似文献