全文获取类型
收费全文 | 662篇 |
免费 | 64篇 |
国内免费 | 37篇 |
专业分类
化学 | 284篇 |
晶体学 | 23篇 |
力学 | 88篇 |
综合类 | 2篇 |
数学 | 31篇 |
物理学 | 335篇 |
出版年
2024年 | 3篇 |
2023年 | 10篇 |
2022年 | 28篇 |
2021年 | 21篇 |
2020年 | 18篇 |
2019年 | 24篇 |
2018年 | 18篇 |
2017年 | 26篇 |
2016年 | 27篇 |
2015年 | 35篇 |
2014年 | 49篇 |
2013年 | 66篇 |
2012年 | 39篇 |
2011年 | 53篇 |
2010年 | 28篇 |
2009年 | 49篇 |
2008年 | 32篇 |
2007年 | 43篇 |
2006年 | 34篇 |
2005年 | 29篇 |
2004年 | 17篇 |
2003年 | 23篇 |
2002年 | 19篇 |
2001年 | 6篇 |
2000年 | 10篇 |
1999年 | 12篇 |
1998年 | 5篇 |
1997年 | 4篇 |
1996年 | 9篇 |
1995年 | 7篇 |
1994年 | 6篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
排序方式: 共有763条查询结果,搜索用时 109 毫秒
1.
Most of the novel highly potent drugs, developed on the basis of modern molecular medicine, taking into account cell surface recognition techniques, show poor water solubility. A chemical modification of the drug substance enhancing the solubility often decreases the pharmacological activity. Thus, as an alternative an increase of the solubility can be obtained by the reduction of the size of the drug particles. Unfortunately, it is often difficult to obtain micro or nanosized drug particles by classical or more advanced crystallization using supercritical gases or by milling techniques. In addition, nanosized particles are often not physically stable and need to be stabilized in an appropriate matrix. Thus, it may be of interest to manufacture directly nanosized drug particles stabilized in an inert hydrophilic matrix, i.e. nanostructured and nanocomposite systems. Solid solutions and solid dispersions represent nanostructured and nanocomposite systems. In this context, the use of the vacuum-fluidized-bed technique for the spray-drying of a low water soluble drug cosolubilized with a hydrophilic excipient in a polar organic solvent is discussed. In order to avoid the use of organic solvents, a special spray-freeze-drying technique working at atmospheric pressure is presented. This process is very suitable for temperature and otherwise sensitive drugs such as pharmaproteins. 相似文献
2.
Jae-Yeon Lee Eugene Lubarsky Ben T. Zinn 《Proceedings of the Combustion Institute》2005,30(2):1757-1764
This paper describes an experimental investigation of the feasibility of using “slow” active control approaches, which “instantaneously” change liquid fuel spray properties, to suppress combustion instabilities. The objective of this control approach was to break up the feedback between the combustion process heat release and combustor pressure oscillations that drive the instability by changing the characteristics of the combustion process (e.g., the characteristic combustion time). To demonstrate the feasibility of such control, this study used a proprietary fuel injector (NanomiserTM), which can vary its fuel spray properties, to investigate the dependence of acoustics–combustion process coupling, i.e., the driving of combustion instabilities, upon the fuel spray properties. This study showed that by changing the spray characteristics it is possible to significantly damp combustion instabilities. Furthermore, using combustion zone chemiluminescence distributions, which were obtained by Abel’s deconvolution synchronized with measured acoustic data, it has been shown that the instabilities were mostly driven midway between the combustor centerline and wall, a short distance downstream from the flame holder, where the mean axial flow velocity is approximately zero in the vortex near the flame holder. The results of this study strongly suggest that a “slow” active control system that employs controllable fuel injectors could be effectively used to prevent the onset of detrimental combustion instabilities. 相似文献
3.
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
4.
The combination of the optical diagnostics and image processing technique has produced various methods of practical measurement in engineering. The measurement of size and velocity of droplets in fuel spray is one typical example. In general, the spray is a complicated and three-dimensional two-phase flow; therefore multi-dimensional field measurement of the spray field is indispensable. In the present paper, a technique of simultaneous measurement of droplet size and three-components of velocity is proposed and applied to spray issuing from the swirl nozzle as a practical application. The focused image of glare points is captured by a stereoscopic arrangement, and droplet size and the three-components of velocity are evaluated from the doublet image. Fundamental optical arrangements to capture the image of the glare points with a stereo view are established, and the feasibility and the accuracy of the technique are confirmed. © 2004 The Optical Society of Japan 相似文献
5.
Ha Yong Lee Se Hun Jung Soo Yong Lee Young Ho You Kyung Hyun Ko 《Applied Surface Science》2005,252(5):1891-1898
Al-Al2O3 composite coatings with different Al2O3 particle shapes were prepared on Si and Al substrate by cold spray. The powder compositions of metal (Al) and ceramic (Al2O3) having different sizes and agglomerations were varied into ratios of 10:1 wt% and 1:1 wt%. Al2O3 particles were successfully incorporated into the soft metal matrix of Al. It was found that crater formation between the coatings and substrate, which is typical characteristic signature of cold spray could be affected by initial starting Al2O3 particles. In addition, when the large hard particles of fused Al2O3 were employed, the deep and big craters were generated at the interface between coatings and hard substrates. In the case of pure soft metal coating such as Al on hard substrate, it is very hard to get proper adhesion due to lack of crater formation. Therefore, the composite coating would have certain advantages. 相似文献
6.
Benedict Ita P. Murugavel V. Ponnambalam A. R. Raju 《Journal of Chemical Sciences》2003,115(5-6):519-524
Fine powders of lanthanum iron oxide, LaFeO3, have been prepared by solid state reaction as well as sol-gel synthesis and nebulized spray pyrolysis. Structures, morphologies
and magnetic susceptibility measurements of these powders have been examined. The powders prepared by all the three low-temperature
routes contain nearly spherical particles with an average diameter of 40 nm. These samples show a lower Neel temperature than
the powder prepared by solid state reaction besides showing much lower magnetic susceptibility at low temperatures.
Dedicated to Professor C N R Rao on his 70th birthday 相似文献
7.
热喷涂技术的现状和发展 总被引:4,自引:0,他引:4
介绍了热喷涂工艺的特点,喷涂方法的种类及其技术以及热喷涂技术的应用概况,并对热喷涂技术的发展方向给予了展望。 相似文献
8.
Determination of impurities in highly pure platinum by inductively coupled plasma-atomic emission spectrometry 总被引:1,自引:0,他引:1
In this work, a cyclone spray chamber system is used in conjunction with an inductively coupled plasma-atomic emission spectrometer instead of the conventional Scott-type chamber system to reduce the lower limit of detection achieved by the instrument, and an internal standard element (Y) is introduced to eliminate the effects caused by the drift in the plasma background level. An ICP-AES method for the determination of 13 impurity elements in a highly pure platinum sample has been developed. In this method, it is not necessary either to add a platinum matrix to the calibration standard or to separate and concentrate the elements to be determined in the samples. The effect of the platinum matrix on the elements to be analyzed is corrected for by a background equivalent concentration subtraction method. The determination ranges of the method are as follows: 0.00010-0.0050% for Mg, Mn, Cu, Ag, Fe and Zn; 0.00030-0.015% for Au, Ir, Ni and Pb; 0.00050-0.025% for Rh and Al; and 0.00080-0.040% for Pd. The method is simple, rapid and accurate, and can be applied to the analysis of 99.9–99.995% pure platinum. 相似文献
9.
Krunks M. Madarász J. Leskelä T. Mere A. Niinistö L. Pokol G. 《Journal of Thermal Analysis and Calorimetry》2003,72(2):497-506
Thermal decomposition of the title compound, Zn(tu)2Cl2 (tu=thiourea), was studied up to 1200°C in dynamic inert (N2) and oxidative (air) atmospheres using simultaneous TG/DTA techniques. In addition, XRD and IR were employed ex situ to resolve
the reaction mechanism and products. Cubic ZnS (sphalerite) is formed below 300°C in both atmospheres and is observed until
760°C, whereafter it transforms in nitrogen to the hexagonal ZnS (wurtzite). EGA by FTIR revealed the complexity of the decomposition
reactions involving also the evolution of H2NCN, which reacts to form hexagonal ZnCN2 as revealed by an XRD analysis.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
PEPAMP是应用于工业循环水中的新一代高效阻垢剂.采用电喷雾电离质谱和质谱/质谱技术分析了合成产物,注射泵直接进样,正离子方式检测,方法简便、快速.通过EI-MS技术获得了目标产物PEPAMP及主要副产物的准分子离子峰,通过ESI-MS-MS技术获得了其碎片信息,并对目标化合物及主要副产物进行了精确质量测定,确定了目标化合物及主要副产物的结构. 相似文献