全文获取类型
收费全文 | 2150篇 |
免费 | 61篇 |
专业分类
化学 | 1187篇 |
晶体学 | 41篇 |
力学 | 83篇 |
数学 | 135篇 |
物理学 | 765篇 |
出版年
2023年 | 15篇 |
2022年 | 28篇 |
2021年 | 32篇 |
2020年 | 46篇 |
2019年 | 41篇 |
2018年 | 48篇 |
2017年 | 34篇 |
2016年 | 84篇 |
2015年 | 44篇 |
2014年 | 64篇 |
2013年 | 140篇 |
2012年 | 142篇 |
2011年 | 148篇 |
2010年 | 87篇 |
2009年 | 74篇 |
2008年 | 129篇 |
2007年 | 106篇 |
2006年 | 95篇 |
2005年 | 108篇 |
2004年 | 74篇 |
2003年 | 47篇 |
2002年 | 44篇 |
2001年 | 38篇 |
2000年 | 23篇 |
1999年 | 19篇 |
1998年 | 12篇 |
1997年 | 15篇 |
1996年 | 27篇 |
1995年 | 32篇 |
1994年 | 21篇 |
1993年 | 30篇 |
1992年 | 17篇 |
1991年 | 20篇 |
1989年 | 18篇 |
1988年 | 19篇 |
1987年 | 13篇 |
1986年 | 18篇 |
1985年 | 35篇 |
1984年 | 16篇 |
1983年 | 15篇 |
1982年 | 27篇 |
1981年 | 25篇 |
1980年 | 10篇 |
1979年 | 10篇 |
1978年 | 10篇 |
1977年 | 10篇 |
1975年 | 9篇 |
1974年 | 14篇 |
1973年 | 10篇 |
1955年 | 12篇 |
排序方式: 共有2211条查询结果,搜索用时 62 毫秒
101.
Queueing Systems - We consider strategic arrivals to a FCFS service system that starts service at a fixed time and has to serve a fixed number of customers, for example, an airplane boarding... 相似文献
102.
For the first time, intensification of monooleoyl glycerol (MOG) synthesis has been investigated in an ultrasonic-infrared-wave (USIRW) promoted batch reactor. Esterification of octadecanoic acid (ODA) with glycerol (Gl) has been conducted [using Amberlyst 36 wet catalyst] in three different reactors, namely traditional batch reactor (TBR), infrared wave promoted batch reactor (IRWPBR), and USIRW-promoted batch reactor (USIRWPBR) to assess the relative efficacy. The energy-efficient USIRWPBR remarkably intensifies the ODA-Gl esterification as manifested through superior ODA conversion (92.5 ± 1.25%) compared to that achieved in IRWPBR (79.8 ± 1.2%) and TBR (36.39 ± 1.25%). The most favorable reaction condition for optimum ODA conversion and maximum MOG yield was identified through statistical optimization over a selected parametric range, namely 3-5 Gl/ODA mole ratio, 0.004-0.006 g/mL Amberlyst 36 catalyst concentration, 300-700 rpm impeller speed, and 333-353 K reaction temperature. The present study also reports the formulation and validation of an innovative reaction kinetics, that is, concurrent noncatalytic and heterogeneously catalyzed (CNCHC) reaction mechanism in addition to the conventional heterogeneous kinetic models (LH and Eley-Rideal mechanisms). Under combined USIRW, the CNCHC esterification mechanism could best describe ODA-Gl esterification (R2 = 0.98) compared to LH (R2 = 0.97) and Eley-Rideal (R2 = 0.88) mechanisms. The optimal product (MOG) was characterized by differential scanning calorimetry and thermogravimetric analysis to assess its crystallization property and thermal stability for possible application as plasticizer/fuel additives. 相似文献
103.
104.
We seek to develop network algorithms for function computation in sensor networks. Specifically, we want dynamic joint aggregation, routing, and scheduling algorithms that have analytically provable performance benefits due to in-network computation as compared to simple data forwarding. To this end, we define a class of functions, the Fully-Multiplexible functions, which includes several functions such as parity, MAX, and kth-order statistics. For such functions we characterize the maximum achievable refresh rate of the network in terms of an underlying graph primitive, the min-mincut. In acyclic wireline networks we show that the maximum refresh rate is achievable by a simple algorithm that is dynamic, distributed, and only dependent on local information. In the case of wireless networks we provide a MaxWeight-like algorithm with dynamic flow-splitting, which is shown to be throughput-optimal. 相似文献
105.
106.
A new AB type of monomer 4′-fluoro-3,5-dimethyl-3′-trifluoromethyl-biphenyl-4-ol has been synthesized that leads to a new poly(arylene ether) by self polycondensation reaction. The monomer and the polymer have been well characterized by elemental analyses, FT-IR and NMR spectroscopy. Both FT-IR and NMR spectra of the polymers did not show any terminal phenoxy group indicating high conversion. The polymer showed glass transition at 278°C and very good thermal stability in synthetic air. GPC results indicate high molar mass development; Mw = 53200 and MWD = 2.29. 相似文献
107.
Kinshuk Dasgupta D. Sen T. Mazumdar R. K. Lenka R. Tewari S. Mazumder J. B. Joshi S. Banerjee 《Journal of nanoparticle research》2012,14(3):728
For the first time, bamboo-shaped multiwalled carbon nanotubes, having diameter of the order of 50 nm, have been grown on
carbon black in a fluidized bed in bulk amount. The activation energy for the synthesis of the product was found out to be
around 33 kJ/mol in the temperature range of 700−900 °C. The carbon nanotubes were separated from the carbon black by preferential
oxidation of the later, the temperature of which was determined by thermogravimetry. The transmission electron microscopy
revealed different features of the nanotubes such as “Y” junction, bend, and catalyst filling inside the nanotubes. Small
angle neutron scattering was performed on the nanotubes synthesized at different temperatures. The data were fitted into a
suitable model in order to find out the average diameter, which decreases with increase in synthesis temperature. The Monte
Carlo simulation predicts the same behavior. Based on the above observations, a possible growth mechanism has been predicted.
The oscillation in carbon saturation value inside the catalyst in the fluidized bed has been indicated as the responsible
factor for the bamboo-shaped structure. 相似文献
108.
109.
Apurba Kumar Das Michael G.B. Drew Debasish Haldar Arindam Banerjee 《Supramolecular chemistry》2013,25(5):331-335
The terminally protected tripeptide Boc–Ala(1)–Leu(2)–Ala(3)–OMe 1 forms antiparallel hydrogen-bonded dimers of two different conformers in the asymmetric unit and the individual dimers then self-associate to form supramolecular β-sheet structures in crystals and amyloid-like fibrils in the solid state. 相似文献