全文获取类型
收费全文 | 581篇 |
免费 | 44篇 |
国内免费 | 3篇 |
专业分类
化学 | 424篇 |
晶体学 | 4篇 |
力学 | 13篇 |
数学 | 81篇 |
物理学 | 106篇 |
出版年
2023年 | 8篇 |
2022年 | 7篇 |
2021年 | 10篇 |
2020年 | 24篇 |
2019年 | 20篇 |
2018年 | 18篇 |
2017年 | 19篇 |
2016年 | 25篇 |
2015年 | 24篇 |
2014年 | 29篇 |
2013年 | 48篇 |
2012年 | 52篇 |
2011年 | 62篇 |
2010年 | 21篇 |
2009年 | 26篇 |
2008年 | 36篇 |
2007年 | 30篇 |
2006年 | 25篇 |
2005年 | 18篇 |
2004年 | 13篇 |
2003年 | 17篇 |
2002年 | 22篇 |
2001年 | 6篇 |
2000年 | 2篇 |
1999年 | 5篇 |
1998年 | 4篇 |
1997年 | 7篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1985年 | 6篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有628条查询结果,搜索用时 15 毫秒
41.
Densities and viscosities of urea in (1.0, 2.5, and 5.0) mass% of aqueous glucose solutions have been measured at T = (298.15, 303.15, 308.15, and 313.15) K, respectively. Apparent molar volumes, limiting partial molar volume, and relative viscosity have been obtained from the density and viscosity data. Limiting partial molar expansibilities have also been calculated from the temperature dependence of limiting partial molar volumes. The viscosity data has been analyzed using the Jones–Dole equation. The results are used to establish the nature of solute–solute and solute–solvent interactions. The activation parameters of viscous flow have also been calculated on the basis of transition state treatment of the relative viscosity. Result shows that the solute acts as water structure breaker and posses’ weak solute–solvent interaction. 相似文献
42.
Stable, high-power, second-harmonic-generation (SHG) of a compact CW Ytterbium (Yb) fiber laser at 1064 nm into the green
and its use as a pump source for CW singly-resonant optical parametric oscillator (SRO) is demonstrated. Using a simple single-pass
SHG configuration in MgO:sPPLT, as much as 9.6 W of single-frequency green radiation at 532 nm is generated from 30 W of fundamental
power at a conversion efficiency of 32.7% in a Gaussian spatial profile with a beam quality factor of M
2 < 1.3. Thermal effects have been investigated at different fundamental power levels and various thermal management schemes
are employed to maximize the second-harmonic power. The green source is successfully deployed to pump a CW SRO tunable over
855–1408 nm, generating up to 2.1 W of idler at 1168 nm. The peak-to-peak idler power stability is better than 10.7% over
40 min, with beam quality factor M
2 < 1.26 for the idler and M
2 < 1.52 for the signal. 相似文献
43.
Alakes Maiti Bibek Patra G.P. Samanta 《International Journal of Mathematical Education in Science & Technology》2013,44(8):1061-1076
The present article deals with the problem of combined harvesting of a
Michaelis–Menten-type ratio-dependent predator–prey system. The
problem of determining the optimal harvest policy is solved by invoking
Pontryagin's Maximum Principle. Dynamic optimization of the harvest policy is
studied by taking the combined harvest effort as a dynamic variable. Computer
simulations are carried out to illustrate our analytical findings. Biological
and bioeconomical interpretations of the results are explained critically. 相似文献
44.
Subhashis Ghosal Jayanta K. Ghosh Tapas Samanta 《Annals of the Institute of Statistical Mathematics》1999,51(3):479-497
We consider a family of models that arise in connection with sharp change in hazard rate corresponding to high initial hazard rate dropping to a more stable or slowly changing rate at an unknown change-point . Although the Bayes estimates are well behaved and are asymptotically efficient, it is difficult to compute them as the posterior distributions are generally very complicated. We obtain a simple first order asymptotic approximation to the posterior distribution of . The accuracy of the approximation is judged through simulation. The approximation performs quite well. Our method is also applied to analyze a real data set. 相似文献
45.
Immobilization of bio-macromolecules on self-assembled monolayers: methods and sensor applications 总被引:1,自引:0,他引:1
Attachment of biomolecules on gold, silicon or glass surfaces has direct implications for the development of novel biosensors in the context of nanoscale detection of pathogens and other metabolites related to issues of human health. In this critical review, we have highlighted the current developments in various techniques of immobilization of biomolecules, specifically biological macromolecules on surfaces through the modification of a functional self-assembled monolayer. The utility of such immobilized biomolecules in the area of biosensing in nanoscale has been surveyed. Merits and demerits of some of the methods with reference to sensitivity of detection and practical use have been discussed (221 references). 相似文献
46.
Mrinal Kanti Paira Tapan Kumar Mondal Elena López-Torres Joan Ribas Chittaranjan Sinha 《Polyhedron》2010
Copper(II) complexes of 3-((2-(alkylthio)phenylazo)-2,4-pentanedione, tridentate O, N, S donor ligands, are described in this work. Chloride bridged copper(II) polymers (1) and thiocyanato bridged copper(II) dimmers (2) are characterized by a single crystal X-ray diffraction study. The complexes show antiferromagnetic interactions, with J = −0.5 ± 0.1 cm−1 (1a) and −25.8 ± 0.5 cm−1 (2b), which implies stronger coupling in the –SCN-bridging compound. The spectra, redox and magnetism are explained by DFT studies. 相似文献
47.
Bikash Ranjan Sahoo Banikalyan Swain Manas Ranjan Dikhit Madhubanti Basu Aritra Bej Pallipuram Jayasankar Mrinal Samanta 《Applied biochemistry and biotechnology》2013,170(6):1282-1309
The nucleotide-binding oligomerization domain 1 (NOD1) receptor recognizes various pattern-associated structures of microbes through its leucine-rich repeat (LRR) domain and activates signaling cascades to induce innate immunity. This report describes the activation of NOD1 receptor signaling by gamma-d-glutamyl-meso-diaminopimelic acid (or γ-D-Glu-mDAP [iE-DAP]) in a commercially important fish species, rohu (Labeo rohita). It also described critical motifs in the NOD1-LRR domain that could be involved in binding iE-DAP, lipopolysaccharide (LPS), and polyinosinic:polycytidylic acid (poly I:C). The activation of NOD1 receptor signaling was studied by injecting iE-DAP, and analysis of tissue samples for NOD1 and receptor-interacting serine/threonine kinase (RICK) expression was done by quantitative real-time polymerase chain reaction (qRT-PCR) assay. To identify ligand-binding motifs in NOD1, the 3D model of NOD1-LRR was generated, followed by a 6-ns molecular dynamics simulation. Molecular docking of LPS with NOD1-LRR was executed at the Hex and PatchDock servers, and iE-DAP and poly I:C in the AutoDock 4.2, FlexX 2.1, Glide 5.5, and GOLD 4.1 programs. The results of qRT-PCR revealed significant (p?<?0.05) upregulation of NOD1 and RICK expression. Molecular docking revealed that the amino acid residues at LRR1–2, LRR3–7, and LRR8–9 could be involved in poly I:C, LPS, and iE-DAP binding, respectively. In fish, this is the first report describing the 3D structure of NOD1-LRR and its critical ligand-binding motifs. 相似文献
48.
Jiaxi Guo Purnatosh Saha Junfeng Liang Mrinal Saha Brian P. Grady 《Journal of Thermal Analysis and Calorimetry》2013,113(2):467-474
Silica has been non-covalently coated on multi-walled carbon nanotubes (MWCNTs) using the sol–gel chemistry, where tetraethoxy silane (TEOS) was used to form an inorganic silica layer immediately next to surface of MWCNTs and octyl triethoxy silane was coated over the TEOS. Transmission electron microscopy (TEM) measurements show that the diameter of MWCNTs increases with increasing the number of coating layer, indicating that the silica has been coated on MWCNTs. Quantitative analysis from thermogravimetric analysis (TG) also indicates that the inorganic and organic silica has been successfully coated on MWCNTs. Further, quantitative analysis found that the amount of silica measured by TG agrees well with the increase of thickness of coated MWCNTs obtained from TEM, indicating that little or no free silica exists in the system. The thermal conductivity of epoxy/MWCNTs composite was studied and the results show that the thermal conductivity of the composite is improved by coating MWCNTs in this manner and increases with increasing the number of coatings. 相似文献
49.
Sawalha MF Sengupta MK Ohira S Idowu AD Gill TE Rojo L Barnes M Dasgupta PK 《Talanta》2008,77(1):372-379
A gas phase chemiluminescence (GPCL)-based method for trace measurement of arsenic has been recently described for the measurement of arsenic in water. The principle is based on the reduction of inorganic As to AsH3 at a controlled pH (the choice of pH governs whether only As(III) or all inorganic As is converted) and the reaction of AsH3 with O3 to produce chemiluminescence (Idowu et al., Anal. Chem. 78 (2006) 7088-7097). The same general principle has also been used in postcolumn reaction detection of As, where As species are separated chromatographically, then converted into inorganic As by passing through a UV photochemical reactor followed by AsH3 generation and CL reaction with ozone (Idowu and Dasgupta, Anal. Chem. 79 (2007) 9197-9204). In the present paper we describe the measurement of As in different soil and dust samples by serial extraction with water, citric acid, sulfuric acid and nitric acid. We also compare parallel measurements for total As by induction coupled plasma mass spectrometry (ICP-MS). As(V) was the only species found in our samples. Because of chloride interference of isobaric ArCl+ ICP-MS analyses could only be carried out by standard addition; these results were highly correlated with direct GPCL and LC-GPCL results (r2 = 0.9935 and 1.0000, respectively). The limit of detection (LOD) in the extracts was 0.36 μg/L by direct GPCL compared to 0.1 μg/L by ICP-MS. In sulfuric acid-based extracts, the LC-GPCL method provided LODs inferior to those previously observed for water-based standards and were 2.6, 1.3, 6.7, and 6.4 μg/L for As(III), As(V), dimethylarsinic acid (DMA) and monomethylarsonic acid (MMA), respectively. 相似文献
50.
Charles Shearer Oriane Desaunay Stephen Zorc Alexis D. Richaud Shyam S. Samanta Nagalakshmi Jeedimalla Stéphane P. Roche 《Tetrahedron》2019,75(43):130606
4H-Pyrans (4H-Pys) and 1,4-dihydropyridines (1,4-DHPs) are important classes of heterocyclic scaffolds in medicinal chemistry. Herein, an indium(III)-catalyzed one-pot domino reaction for the synthesis of highly functionalized 4H-Pys, and a model of 1,4-DHP is reported. This alternative approach to the challenging Hantzsch 4-component reaction enables the synthesis of fused-tricyclic heterocycles, and the mechanistic studies underline the importance of an intercepted-Knoevenagel adduct to achieve higher chemoselectivity towards these types of unsymmetrical heterocycles. 相似文献