全文获取类型
收费全文 | 1595篇 |
免费 | 37篇 |
国内免费 | 8篇 |
专业分类
化学 | 1089篇 |
晶体学 | 7篇 |
力学 | 43篇 |
数学 | 231篇 |
物理学 | 270篇 |
出版年
2023年 | 8篇 |
2022年 | 34篇 |
2021年 | 40篇 |
2020年 | 22篇 |
2019年 | 25篇 |
2018年 | 23篇 |
2017年 | 17篇 |
2016年 | 47篇 |
2015年 | 48篇 |
2014年 | 42篇 |
2013年 | 79篇 |
2012年 | 86篇 |
2011年 | 115篇 |
2010年 | 79篇 |
2009年 | 61篇 |
2008年 | 114篇 |
2007年 | 100篇 |
2006年 | 114篇 |
2005年 | 96篇 |
2004年 | 84篇 |
2003年 | 68篇 |
2002年 | 59篇 |
2001年 | 23篇 |
2000年 | 18篇 |
1999年 | 13篇 |
1998年 | 15篇 |
1997年 | 12篇 |
1996年 | 20篇 |
1995年 | 13篇 |
1994年 | 9篇 |
1992年 | 8篇 |
1991年 | 8篇 |
1990年 | 4篇 |
1989年 | 9篇 |
1988年 | 8篇 |
1987年 | 6篇 |
1986年 | 8篇 |
1985年 | 6篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 16篇 |
1981年 | 10篇 |
1980年 | 6篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1976年 | 4篇 |
1975年 | 8篇 |
1972年 | 3篇 |
1970年 | 5篇 |
1969年 | 3篇 |
排序方式: 共有1640条查询结果,搜索用时 31 毫秒
71.
Advances in Data Analysis and Classification - The STAR model is widely used to represent the dynamics of a certain variable recorded at several locations at the same time. Its advantages are often... 相似文献
72.
Raffaele Ferrari Giuseppe Storti Massimo Morbidelli 《Journal of polymer science. Part A, Polymer chemistry》2020,58(12):1642-1654
Emulsion polymerization of the three-monomer system butyl acrylate–styrene–methacrylic acid was performed in batch using a commercial maltodextrin derived from starch degradation as stabilizer. Stable latexes with narrow particle size distributions were obtained in all examined cases. A method was developed to analyze and quantify the partitioning of the maltodextrin between the continuous phase (supernatant) and the particle phase. Significant differences between the polysaccharides adsorbed onto particles with or without emulsion polymerization reaction were observed. The possible reactions of maltodextrin in presence of a radical initiator were studied in aqueous phase, thus confirming maltodextrin degradation. The formation of copolymers involving the original monomers and the stabilizer according to two different reactive pathways was also confirmed. In terms of adsorbed maltodextrin, two different contributions were observed: maltodextrin physically adsorbed and maltodextrin chemically grafted and/or physically incorporated into the polymer. 相似文献
73.
74.
75.
The direct position analysis of parallel manipulators (PMs) brings to determine a finite number of platform poses compatible with an assigned set of actuated-joint variables’ values. Therefore, when, during functioning, the need to check the actual platform pose arises, the sensors usually located on the actuators are not sufficient and the additional pieces of information coming from ad-hoc-devised extra sensors are necessary. Here, for the first time, the actual implementation of extra sensors in underactuated parallel wrists (PWs) which contain a nonholonomic constraint is addressed. Differently from “ordinary” (i.e., non-underactuated) PWs, these PWs requires a continuous monitoring of the actual platform orientation to compensate the possible sliding in the nonholonomic constraint. Thus, in this case, the algorithms that interpret the pieces of information coming from the sensors must work in real time and must be integrated in the control software that manages the motion of the machine. All these special requirements are satisfied by the proposed algorithm. Moreover, the proposed hardware can also be implemented in some ordinary PWs with a cheap add-on kit. 相似文献
76.
Nera Cagnoli Paolo Ceccherelli Massimo Curini Maria Carla Marcotullio Ernest Wenkert 《合成通讯》2013,43(11):1261-1271
Copper oxide-catalyzed decomposition of 1-diazoacetyl-1-methyl-3-methylenecyclohexanes produces strained tricycles whose reduction or hydrolysis affords 6-bicyclo[3.2.1]octanones. 相似文献
77.
78.
Kamel Abbas Izabela Cydzik Riccardo Del Torchio Massimo Farina Efrat Forti Neil Gibson Uwe Holzwarth Federica Simonelli Wolfgang Kreyling 《Journal of nanoparticle research》2010,12(7):2435-2443
Industrially manufactured titanium dioxide nanoparticles have been successfully radiolabelled with 48V by irradiation with a cyclotron-generated proton beam. Centrifugation tests showed that the 48V radiolabels were stably bound within the nanoparticle structure in an aqueous medium, while X-ray diffraction indicated
that no major structural modifications to the nanoparticles resulted from the proton irradiation. In vitro tests of the uptake
of cold and radiolabelled nanoparticles using the human cell line Calu-3 showed no significant difference in the uptake between
both batches of nanoparticles. The uptake was quantified by Inductively Coupled Plasma Mass Spectrometry and high resolution
γ-ray spectrometry for cold and radiolabelled nanoparticles, respectively. These preliminary results indicate that alterations
to the nanoparticles’ properties introduced by proton bombardment can be controlled to a sufficient extent that their further
use as radiotracers for biological investigations can be envisaged and elaborated. 相似文献
79.
Arturo Arduini Alessandro Casnati Massimo Fabbi Patrizia Minari Andrea Pochini Anna Rita Sicuri 《Supramolecular chemistry》2013,25(3-4):235-246
Abstract The development of new synthetic methods for the monoalkylation of calix[4]arenes at the lower rim allows the synthesis of a new class of trihydroxamate siderophores. Three chelating hydroxamic acid units are introduced through a sequence of reactions which blocks the macrocycle in the cone conformation. The new ligands obtained form neutral 1:1 complexes (FeL) with iron (III), which are stable in EtOH/H2O 9:1 at pH 2–7. Calix[4]arene bis-crown ethers are prepared by exploiting the selective 1,2-(proximal) functionalization of calix[4]arenes at the lower rim. These ligands are, however, less effective in complexing alkali metal cations compared with the 1,3-calix[4]arene crown-ethers which, in their partial cone structure, offer a better shielding for the complexed cations. Rigid upper rim-bridged calix[4]arenes potentially useful for the inclusion of neutral molecules are prepared by exploiting the selective 1,3-diformylation of calix[4]arene at the upper rim. Finally a new chloromethylation method for calix[4]arenes blocked in the cone conformation is described together with the synthesis of new cavitands. 相似文献
80.
A Practical Synthesis of 1,4,7,10-Tetraaza-Cyclododecane,A Pivotal Precursor for MRI Contrast Agents
A practical preparation of the versatile macrocycle 1,4,7,10-tetraazacyclododecane (cyclen) was developed starting from cheap and easily available starting materials as ethylenediamine and glyoxal. 相似文献