全文获取类型
收费全文 | 2794篇 |
免费 | 73篇 |
国内免费 | 3篇 |
专业分类
化学 | 1843篇 |
晶体学 | 28篇 |
力学 | 102篇 |
数学 | 353篇 |
物理学 | 544篇 |
出版年
2023年 | 16篇 |
2022年 | 43篇 |
2021年 | 79篇 |
2020年 | 42篇 |
2019年 | 52篇 |
2018年 | 47篇 |
2017年 | 51篇 |
2016年 | 86篇 |
2015年 | 73篇 |
2014年 | 104篇 |
2013年 | 166篇 |
2012年 | 162篇 |
2011年 | 202篇 |
2010年 | 116篇 |
2009年 | 153篇 |
2008年 | 185篇 |
2007年 | 151篇 |
2006年 | 134篇 |
2005年 | 115篇 |
2004年 | 108篇 |
2003年 | 81篇 |
2002年 | 67篇 |
2001年 | 43篇 |
2000年 | 39篇 |
1999年 | 34篇 |
1998年 | 35篇 |
1997年 | 21篇 |
1996年 | 30篇 |
1995年 | 37篇 |
1994年 | 23篇 |
1993年 | 15篇 |
1992年 | 27篇 |
1991年 | 10篇 |
1990年 | 9篇 |
1989年 | 14篇 |
1988年 | 11篇 |
1987年 | 12篇 |
1986年 | 13篇 |
1985年 | 28篇 |
1984年 | 16篇 |
1983年 | 26篇 |
1982年 | 22篇 |
1981年 | 29篇 |
1980年 | 24篇 |
1979年 | 18篇 |
1978年 | 15篇 |
1976年 | 12篇 |
1974年 | 10篇 |
1972年 | 8篇 |
1969年 | 8篇 |
排序方式: 共有2870条查询结果,搜索用时 125 毫秒
131.
Daniela P. Mesquita Cristiano Leal Jorge R. Cunha Adrian Oehmen A. Luís Amaral Maria A.M. Reis Eugénio C. Ferreira 《Analytica chimica acta》2013
The present study focuses on predicting the concentration of intracellular storage polymers in enhanced biological phosphorus removal (EBPR) systems. For that purpose, quantitative image analysis techniques were developed for determining the intracellular concentrations of PHA (PHB and PHV) with Nile blue and glycogen with aniline blue staining. Partial least squares (PLS) were used to predict the standard analytical values of these polymers by the proposed methodology. Identification of the aerobic and anaerobic stages proved to be crucial for improving the assessment of PHA, PHB and PHV intracellular concentrations. Current Nile blue based methodology can be seen as a feasible starting point for further enhancement. Glycogen detection based on the developed aniline blue staining methodology combined with the image analysis data proved to be a promising technique, toward the elimination of the need for analytical off-line measurements. 相似文献
132.
133.
134.
J. M. Ferreira Liliana Caramelo R. P. Chhabra 《International Journal of Mathematical Education in Science & Technology》2013,44(4):545-552
A curve fitting model is presented which minimizes the sum of squares of relative residues and expressions for the fit coefficients and their respective errors are derived. The new model is compared to the normal least squares model, using as an example the Reynolds number-drag coefficient data for a sphere. The results show that the best fit was obtained with the new model, indicating it may provide a useful tool for data analysis. 相似文献
135.
The use of local numerical schemes,such as finite differences produces much better conditioned matrices than global collocation radial basis functions methods.However,finite difference schemes are limi... 相似文献
136.
D.A. Fogaça F.S. Navarra L.G. Ferreira Filho 《Communications in Nonlinear Science & Numerical Simulation》2013,18(2):221-235
The Kadomtsev–Petviashvili (KP) nonlinear wave equation is the three dimensional generalization of the Korteveg-de Vries (KdV) equation. We show how to obtain the cylindrical KP (cKP) and cartesian KP in relativistic fluid dynamics. The obtained KP equations describe the evolution of perturbations in the baryon density in a strongly interacting quark gluon plasma (sQGP) at zero temperature. We also show the analytical solitary wave solution of the KP equations in both cases. 相似文献
137.
The extent to which the occurrence of falls, the dominant feature of human attempts to balance a stick at their fingertip,
can be predicted is examined in the context of the “Dragon-King” hypothesis. For skilled stick balancers, fluctuations in
the controlled variable, namely the vertical displacement angle θ, exhibit power law behaviors. When stick balancing is made
less stable by either decreasing the length of the stick or by requiring the subject to balance the stick on the surface of
a table tennis racket, systematic departures from the power law behaviors are observed in the range of large θ. This observation
raises the possibility that the presence of departures from the power law in the large length scale region, possibly Dragon-Kings,
may identify situations in which the occurrence of a fall is more imminent. However, whether or not Dragon-Kings are observed,
there is a Weibull-type survival function for stick falling. The possibility that increased risk of falling can, at least
to some extent, be predicted from fluctuations in the controlled variable before the event occurs has important implications
for the development of preventative strategies for the management of phenomena ranging from earthquakes to epileptic seizures
to falls in the elderly. 相似文献
138.
Dr. Teng Zhang Dr. Yuichi Kitagawa Ryoma Moriake Pedro Paulo Ferreira da Rosa Dr. Md. Jahidul Islam Dr. Tomoki Yoneda Prof. Yasuhide Inokuma Dr. Koji Fushimi Prof. Yasuchika Hasegawa 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(58):14438-14443
In this study, we have demonstrated a two-legged, upright molecular design method for monochromatic and bright red luminescent LnIII-silica nanomaterials. A novel EuIII-silica hybrid nanoparticle was developed by using a doubly binding TPPO−Si(OEt)3 (TPPO: triphenyl phosphine oxide) linker. The TPPO−Si(OEt)3 was confirmed by 1H, 31P, 29Si NMR spectroscopy and single-crystal X-ray analysis. Luminescent Eu(hfa)3 and Eu(tfc)3 moieties (hfa: hexafluoroacetylacetonate, tfc: 3-(trifluoromethylhydroxymethylene)camphorate) were fixed onto TPPO−Si(OEt)3-modified silica nanoparticles, producing Eu(hfa)3(TPPO−Si)2-SiO2 and Eu(tfc)3(TPPO−Si)2-SiO2, respectively. Eu(hfa)3(TPPO−Si)2−SiO2 exhibited the higher intrinsic luminescence quantum yield (93 %) and longer emission lifetime (0.98 ms), which is much larger than those of previously reported EuIII-based hybrid materials. Eu(tfc)3(TPPO−Si)2−SiO2 showed an extra-large intrinsic emission quantum yield (54 %), although the emission quantum yield for the precursor Eu(tfc)3(TPPO−Si(OEt)3)2 was found to be 39 %. These results confirmed that the TPPO−Si(OEt)3 linker is a promising candidate for development of EuIII-based luminescent materials. 相似文献
139.
As part of an ongoing program directed toward the preparation of antraciclinones1 and aryl substituted lapachones2, which are important anticancer and antibiotic3 agents, we became interested in a efficient synthesis of substituted 1,4-naphthoquinones, such as juglone (3). This compound has received some attention due its activity as an allelophatic compound4. An extensive analysis of the literature procedures indicated that several methods are available starting from 1,5-dihydroxynaphthalene (1). All the procedures explored the oxidation of carbon four of the naphthyl ring by several known reagents, such as, chromium trioxide-piridine5, thallium trinitrate5, chromic acid6, peracetic acid7, dichromate8, iron (III) chloride9 and mercuric oxide10. None of the several known methods for the preparation of (3) proceeded in satisfactory yield (except for the thallium trinitrate method which gave 642 yield) and most of them gave a mixture of 1,2 and 1,4-naphthoquinone. 相似文献