全文获取类型
收费全文 | 341篇 |
免费 | 12篇 |
专业分类
化学 | 236篇 |
晶体学 | 18篇 |
力学 | 10篇 |
数学 | 2篇 |
物理学 | 44篇 |
无线电 | 43篇 |
出版年
2023年 | 1篇 |
2022年 | 6篇 |
2021年 | 5篇 |
2020年 | 12篇 |
2019年 | 8篇 |
2018年 | 2篇 |
2017年 | 3篇 |
2016年 | 13篇 |
2015年 | 6篇 |
2014年 | 7篇 |
2013年 | 30篇 |
2012年 | 26篇 |
2011年 | 14篇 |
2010年 | 17篇 |
2009年 | 13篇 |
2008年 | 30篇 |
2007年 | 17篇 |
2006年 | 11篇 |
2005年 | 10篇 |
2004年 | 6篇 |
2003年 | 4篇 |
2002年 | 6篇 |
2001年 | 6篇 |
2000年 | 8篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 5篇 |
1989年 | 8篇 |
1988年 | 7篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 5篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 7篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有353条查询结果,搜索用时 31 毫秒
61.
Cooperation among various types of management functions is necessary to allow management functions to interwork in providing and using information and services for systems management. To understand these tasks from the point of view of cooperative working, this article discusses the requirements and presents the concept of cooperative system management. © 1998 John Wiley & Sons, Ltd. 相似文献
62.
63.
Results of the scanning electron microscopy (SEM), X-ray diffraction (XRD), optical absorption, photoconductivity (PC), and
photoluminescence (PL) studies for the CdSSe:CdCl2,Ho films are presented in this paper. The SEM studies of different CdSSe films show a layered growth structure. A crystalline
nature of the films is observed in the XRD studies. The regions with stacking fault were also observed in the X-ray diffractograms.
The optical absorption spectra of these films show variations corresponding to the band gaps and the grain-sizes obtained
under various deposition conditions and also with annealing. The effect of flux, impurities and annealing on the saturated
photo to dark current ratio Ipc/Idc is observed in the PC rise and decay studies. The maximum value of Ipc/Idc ∼107 is obtained for the impurity doped annealed films. The PL emission spectra of CdSSe films show two emission peaks associated
with the annihilation of free excitons and the transitions between shallow donor and deep acceptor states. In CdSSe:CdCl2,Ho films, two PL emission peaks are observed at 495 nm and 545 nm corresponding to the transitions 5S2→5I8 and 5F3→5I8, respectively, in Ho. The effect of pH on PL and grain size is also included in the present studies. 相似文献
64.
Magnesium aluminate doped with Tb3+ (MgAl2O4:Tb3+) was prepared by combustion synthesis. Three thermoluminsence (TL) peaks at 120, 220 and 340 °C were observed. PL and TL emission spectrum shows that Tb3+ acts as the luminescent centre. Optically stimulated luminescence (OSL) was observed when stimulated by 470 nm blue light.Electron spin resonance (ESR) studies were carried out to identify the defect centres responsible for the TL and OSL processes in MgAl2O4:Tb3+. Two defect centres were identified in irradiated MgAl2O4:Tb3+ phosphor by ESR measurements which was carried out at room temperature and these were assigned to V and F+ centres. V centre (hole centre) is correlated to 120 and 220 °C TL peaks and F+ centre (electron centre), which acts as a recombination centre is correlated to 120, 220 and 340 °C. 相似文献
65.
Priti N. Chaudhari Kishor S. Wani Bhushan Liladhar Chaudhari Sudhir B. Chincholkar 《Applied biochemistry and biotechnology》2009,158(1):231-241
A nonmotile, nonspore-forming, Gram-negative, aerobic, small rod-shaped bacterium, isolated from soil, was identified as Chryseobacterium gleum on the basis of 16S rRNA gene sequence analysis. It was observed to grow luxuriously at pH 9 and tolerate highly alkaline
environment up to pH 12. Orange red color was a peculiar character of these cells which on purification obtained 60–80 mg/l
and found to be sphingosine type of sulfonolipid “sulfobacin A” on the basis of infrared, nuclear magnetic resonance, and
mass spectral data. Inhibition of sulfobacin A synthesis by incorporation of l-cycloserine in culture growth medium suggested presence of serine palmitoyl transferase which is one of the important enzymes
involved in its biosynthesis. Sulfobacin A from C. gleum LMG P-22264 exhibited cytotoxicity against four cell lines tested. Maximum activity against human mammary adenocarcinoma
cells was indicative of its potential as an anticancer agent. 相似文献
66.
湍流流动中鲨鱼皮表面流体减阻研究进展 总被引:2,自引:0,他引:2
快速游动的鲨鱼, 其皮肤表面沿流动方向有序地排列着沟槽状结构, 人们认为这种结构能在湍流流动 中减小表面摩擦阻力. 人们仿真这种生物结构来进行实验研究和应用, 通过复制和改善鲨鱼皮肤表面沟槽状 结构, 使得摩擦阻力最大减小了近10%. 在实验和模拟仿真中, 人们不断讨论和研究湍流流动阻力的形成机制 和沟槽减阻的理论特性. 本文综述了沟槽减阻理论特性的一些研究方法, 并且归纳定义了沟槽减阻最优几何 形状及其尺寸; 详细考虑流体流动的特点, 给出了一种用来选择最优沟槽形状及其尺寸的方法; 综述了目前的 沟槽加工制造技术. 由于鲨鱼皮肤表面存在少量黏液, 从仿生学的角度, 文章最后综述并展望了通过局部应用 疏水性材料来改变沟槽附近流场属性, 从而达到更大程度上减小阻力的目标. 相似文献
67.
Protruded roughness geometry is generally considered to be simple, an innovative and economic technique for improving thermal performance of solar air heater. Experimental investigation has been carried to study the effect of different shapes, position, and height of protrusions on heat transfer and friction characteristics of solar air heater duct for the range of parameters. Correlations for Nusselt number and friction factor have been brought out from the experimental data which can be further used for evaluating performance of solar air heater having the considered roughness geometry. 相似文献
68.
69.
Bhushan B 《Langmuir : the ACS journal of surfaces and colloids》2012,28(3):1698-1714
Nature has evolved objects with desired functionality using commonly found materials. Nature capitalizes on hierarchical structures to achieve functionality. The understanding of the functions provided by objects and processes found in nature can guide us to produce nanomaterials, nanodevices, and processes with desirable functionality. Various natural objects which provide functionality of commercial interest have been characterized to understand how a natural object provides functionality. We have modeled and fabricated structures in the lab using nature's route and developed optimum structures. Once it is understood how nature does it, optimum structures have been fabricated using smart materials and fabrication techniques. This feature article provides an overview of four topics: Lotus effect, rose petal effect, gecko feet, and shark skin. 相似文献
70.
A high-performance liquid chromatographic (HPLC) method for enantioseparation of selenomethionine (SeMet) was developed using two isothiocyanate-based chiral derivatizing reagents [(R)-methyl benzyl isothiocyanate (MBIC) and (S)-1-(1-naphthyl) ethyl isothiocyanate (NEIC)] and UV detection. Diastereomers of selenomethionine were synthesized either via stirring (using MBIC) or by microwave irradiation (using NEIC). Derivatization conditions were optimized and the synthesized diastereomers were successfully resolved using triethyl ammonium phosphate buffer and acetonitrile on a reversed-phase column. The method was validated for accuracy, precision and limit of detection. The mechanism of separation is also discussed. 相似文献