全文获取类型
收费全文 | 1139篇 |
免费 | 54篇 |
国内免费 | 8篇 |
专业分类
化学 | 617篇 |
晶体学 | 20篇 |
力学 | 28篇 |
综合类 | 1篇 |
数学 | 40篇 |
物理学 | 236篇 |
无线电 | 259篇 |
出版年
2024年 | 3篇 |
2023年 | 18篇 |
2022年 | 68篇 |
2021年 | 62篇 |
2020年 | 38篇 |
2019年 | 50篇 |
2018年 | 33篇 |
2017年 | 24篇 |
2016年 | 47篇 |
2015年 | 34篇 |
2014年 | 52篇 |
2013年 | 86篇 |
2012年 | 86篇 |
2011年 | 77篇 |
2010年 | 50篇 |
2009年 | 45篇 |
2008年 | 47篇 |
2007年 | 48篇 |
2006年 | 43篇 |
2005年 | 42篇 |
2004年 | 40篇 |
2003年 | 29篇 |
2002年 | 18篇 |
2001年 | 11篇 |
2000年 | 10篇 |
1999年 | 7篇 |
1998年 | 11篇 |
1997年 | 7篇 |
1996年 | 6篇 |
1995年 | 4篇 |
1994年 | 10篇 |
1993年 | 6篇 |
1992年 | 10篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 7篇 |
1982年 | 3篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1976年 | 4篇 |
1972年 | 3篇 |
1963年 | 2篇 |
排序方式: 共有1201条查询结果,搜索用时 15 毫秒
81.
Robert J. Good Mojahedul Islam Robert E. Baier Anne E. Meyer 《Journal of Dispersion Science and Technology》2013,34(6-7):1163-1173
82.
S. M. Islam Sanchita Mondal Anupam Singha Roy Paramita Mondal Manir Mobarak Dildar Hossain Palash Pandit 《Transition Metal Chemistry》2010,35(3):305-313
A polymer-anchored Pd(II) Schiff base complex has been synthesized by reacting a polymeric amine with 2-pyridinecarboxaldehyde
to get the polymer-anchored Schiff base, which was then reacted with palladium acetate. The catalyst was characterized by
physicochemical and spectroscopic methods. It shows excellent catalytic activity in the Sonogashira coupling of phenylacetylene
with aryl halides using triethylamine as a base and copper iodide as a co-catalyst in water under open air at 70 °C. We have
also studied the effects of base and solvent on the coupling reaction. Sonogashira reactions of phenylacetylene with a variety
of functionalized aryl halides were performed under the optimized reaction conditions. This catalyst gives excellent yields
without the use of phosphine ligands. Further experiments showed that the catalyst can be used five times without much loss
in the catalytic activity. 相似文献
83.
Long Giang BachMd. Rafiqul Islam Yeon Tae JeongYeong Soon Gal Kwon Taek Lim 《Applied Surface Science》2012,258(7):2816-2822
The synthesis of chemically anchored adenosine with biocompatible poly(2-hydroxylethyl methacrylate) grafted gold nanoparticles (Ado-i-PHEMA-g-AuNPs) was realized by employing a simple strategy. Disulfide-containing poly(2-hydroxylethyl methacrylate) (DT-PHEMA) was initially synthesized by atom transfer radical polymerization (ATRP). The formation of DT-PHEMA was confirmed by 1H-NMR and FT-IR. The molecular weight and molecular weight distribution were found to be 9.6 kg/mol and 1.40 from GPC analysis. DT-PHEMA was subsequently used for the synthesis of PHEMA-g-AuNPs by a grafting to protocol. The grafting of DT-PHEMA on the surface of AuNPs was confirmed by FT-IR, TGA, XPS, and EDX analyses. The particle size of the PHEMA-g-AuNPs was found to be ca. 5.0 nm from HR-TEM analysis. Boronic acid was used for functionalization of PHEMA-g-AuNPs, which was then subjected for covalent immobilization with adenosine via strong interaction between free hydroxyl groups of adenosine and boronic acid. Characterization and properties of the Ado-i-PHEMA-g-AuNPs were investigated by taking advantage from FT-IR, XPS, EDX, and UV-visible spectroscopy. The Ado-i-PHEMA-g-AuNPs nanocomposite exhibits a surface plasmon resonance peak at 586 nm which is red shifted from AuNPs (521 nm), indicating significant changes of surface property upon PHEMA-adenosine immobilization onto the surface of AuNPs. 相似文献
84.
Manirul Islam Paramita Mondal Anupam Singha Roy Kazi Tuhina 《Transition Metal Chemistry》2010,35(4):427-435
A poly(3,6-dibenzaldimino N-vinyl carbazole) Pd(II) complex has been synthesized and characterized by physicochemical and spectroscopic techniques. The complex was found to be highly active toward hydrogenation reactions of various organic substrates under atmospheric pressure at ambient temperature. A tentative reaction mechanism is proposed on the basis of kinetic studies and isolation of reactive intermediates. The catalyst shows good conversion rates, thermal stability and recyclability. 相似文献
85.
In 1961, Brans and Dicke [1] provided an interesting alternative to general relativity based on Mach’s principle. To understand
the reasons leading to their field equations, we first consider homogeneous and isotropic cosmological models in the Brans-Dicke
theory. Accordingly we start with the Robertson-Walker line element and the energy tensor of a perfect fluid. The scalar field
φ is now a function of the cosmic time only.
Then we consider spatially homogeneous and anisotropic Bianchi type-I-cosmological solutions of modified Brans-Dicke theory
containing barotropic fluid. These have been obtained by imposing a condition on the cosmological parameter Λ(φ). Again we
try to focus the meaning of this cosmological term and to relate it to the time coordinate which gives us a collapse singularity
or the initial singularity. On the other hand, our solution is a generalization of the solution found by Singh and Singh [2].
As far as we are aware, such solution has not been given earlier. 相似文献
86.
Fault-tolerant switched reluctance motor drive using adaptive fuzzy logic controller 总被引:5,自引:0,他引:5
Mir S. Islam M.S. Sebastian T. Husain I. 《Power Electronics, IEEE Transactions on》2004,19(2):289-295
An adaptive fuzzy controller has been designed to develop a high-performance fault-tolerant switched reluctance motor (SRM) drive. The fuzzy controller continuously adapts its properties to regulate the machine torque as desired by the drive system even under fault conditions. The adaptation of the fuzzy membership functions results in extended conduction period and increased peak current of the healthy phases to deliver the commanded torque, as much as possible. The adaptive fuzzy controller provides smooth torque output with minimum ripple, even under fault conditions, yielding a high-performance SRM drive with fault-tolerant capability. 相似文献
87.
A microwave (MW) preheating mechanism of anisotropic conductive adhesive film (ACF) has been introduced in order to reduce the bonding temperature for flip chip technology. Thermal curing of epoxy shows a very sluggish and non-uniform curing kinetics at the beginning of the curing reaction, but the rate increases with time and hence requires higher temperature. On the other hand MW radiation has the advantage of uniform heating rate during the cycle. In view of this, MW preheating (for 2/3 s) of ACF prior to final bonding has been applied to examine the electrical and mechanical performance of the bond. Low MW power has been used (80 and 240 W) to study the effect of the MW preheating. It has been found that 170 °C can be used for flip chip bonding instead of 180 °C (standard temperature for flip chip bonding) for MW preheating time and power used in this study. The contact resistance (0.015–0.025 Ω) is low in these samples where the standard resistance is 0.017 Ω (bonded at 180 °C without prior MW preheating). The shear forces at breakage were satisfactory (152–176 N) for the samples bonded at 170 °C with MW preheating, which is very close and even higher than the standard sample (173.3 N). For MW preheating time of 2 s, final bonding at 160 °C can also be used because of its low contact resistance (0.022–0.032 Ω), but the bond strength (137.3–145 N) is somewhat inferior to the standard one. 相似文献
88.
89.
Measurement of mixed radon and thoron daughter concentrations using alpha and beta activities filtered from air 总被引:1,自引:0,他引:1
This paper presents a detailed study of integral four- and five-count filter methods for the measurement of mixed radon and thoron daughter concentrations in air. The four-count method utilizes beta activity measurement while the five-count method is based on alpha activity measurement with plastic track detectors. A good correlation between the two independent detection techniques has been observed. An adequate theoretical framework is provided by interpreting the observed data. 相似文献
90.
Cu-containing solder alloys have been used to identify their interfacial reactions with electroless NiP. As-reflowed, AuSn4 intermetallic compounds (IMCs) are formed in the Sn-Cu and Sn-Ag-Cu solders, but in the cases of Sn-Ag-Cu-In, In-Sn-Au IMCs
are formed and are uniformly distributed in the solder. Different types of IMCs such as high-Cu (>30 at.%), medium-Cu (30-15
at.%), and low-Cu (<15 at.%) containing IMCs are formed at the interface. High-Cu and medium-Cu containing ternary intermetallic
compounds (TIMCs) are found in the Sn-Cu and Sn-Ag-Cu solder joints, respectively. Medium-Cu containing quaternary intermetallic
compounds (QIMCs) are found in the Sn-Ag-Cu-In joints. Initially, TIMCs and QIMCs have higher growth rates, resulting in the
entrapment of some Pb-rich phase in the high-Cu containing TIMCs and some In-Sn-Au phase in the QIMCs. High-Cu containing
TIMCs have a lower growth rate and consume less of the NiP layer. The spalling of medium-Cu containing TIMCs in the Sn-Ag-Cu
solder increases both the growth rate of TIMCs and the consumption rate of the NiP layer. Low-Cu containing QIMCs in the Sn-Ag-Cu-In
solder are stable on P-rich Ni and reduce the dissolution rate of the NiP layer. Consumption of the NiP layer can be reduced
by adding Cu or In, because of the changes of the interfacial IMCs phases, which are stable and adhere well to the P-rich
Ni layer during reflow. 相似文献