全文获取类型
收费全文 | 4910篇 |
免费 | 123篇 |
国内免费 | 36篇 |
专业分类
化学 | 3218篇 |
晶体学 | 36篇 |
力学 | 244篇 |
数学 | 867篇 |
物理学 | 704篇 |
出版年
2021年 | 48篇 |
2020年 | 56篇 |
2019年 | 38篇 |
2018年 | 59篇 |
2017年 | 43篇 |
2016年 | 101篇 |
2015年 | 90篇 |
2014年 | 100篇 |
2013年 | 269篇 |
2012年 | 209篇 |
2011年 | 275篇 |
2010年 | 159篇 |
2009年 | 144篇 |
2008年 | 234篇 |
2007年 | 219篇 |
2006年 | 219篇 |
2005年 | 233篇 |
2004年 | 233篇 |
2003年 | 223篇 |
2002年 | 207篇 |
2001年 | 92篇 |
2000年 | 97篇 |
1999年 | 55篇 |
1998年 | 47篇 |
1997年 | 52篇 |
1996年 | 73篇 |
1995年 | 60篇 |
1994年 | 62篇 |
1993年 | 60篇 |
1992年 | 51篇 |
1991年 | 48篇 |
1990年 | 46篇 |
1989年 | 48篇 |
1988年 | 44篇 |
1987年 | 41篇 |
1986年 | 43篇 |
1985年 | 66篇 |
1984年 | 80篇 |
1983年 | 58篇 |
1982年 | 69篇 |
1981年 | 62篇 |
1980年 | 75篇 |
1979年 | 70篇 |
1978年 | 59篇 |
1977年 | 54篇 |
1976年 | 49篇 |
1975年 | 49篇 |
1974年 | 58篇 |
1973年 | 39篇 |
1972年 | 34篇 |
排序方式: 共有5069条查询结果,搜索用时 140 毫秒
931.
Guillaume Guérin Norbert Mercier Roger Nathan Grzegorz Adamiec Yannick Lefrais 《Radiation measurements》2012,47(9):778-785
The infinite matrix assumption is commonly used to derive dose rates in the field of paleodosimetric dating methods. The update of nuclear data allowed calculating new dose rate conversion factors and attenuation factors for taking account of grain size. The relevance of the infinite matrix assumption was found to be limited to specific cases and a discussion of potential errors in estimating dose rates to natural dosimeters in sedimentary media is proposed. A new set of geometric features is shown to be of paramount importance for estimating dose rates in sedimentary media. To quantify these effects, Monte Carlo modelling was applied and the architecture of the programmes is described. It is also shown that proper characterization of sediment samples, coupled to the modelling of radioactivity in these sediments may provide more accurate dose rates to quartz grains, down to the single grain scale. 相似文献
932.
Although quantum mechanics is one of our most successful physical theories, there has been a long-standing debate about the interpretation of the wave function--the central object of the theory. Two prominent views are that (i) it corresponds to an element of reality, i.e., an objective attribute that exists before measurement, and (ii) it is a subjective state of knowledge about some underlying reality. A recent result [M.?F. Pusey, J. Barrett, and T. Rudolph, arXiv:1111.3328] has placed the subjective interpretation into doubt, showing that it would contradict certain physically plausible assumptions, in particular, that multiple systems can be prepared such that their elements of reality are uncorrelated. Here we show, based only on the assumption that measurement settings can be chosen freely, that a system's wave function is in one-to-one correspondence with its elements of reality. This also eliminates the possibility that it can be interpreted subjectively. 相似文献
933.
Majedi FS Hasani-Sadrabadi MM Emami SH Taghipoor M Dashtimoghadam E Bertsch A Moaddel H Renaud P 《Chemical communications (Cambridge, England)》2012,48(62):7744-7746
A microfluidic platform is developed for the synthesis of monodisperse, 100 nm, chitosan based nanoparticles using nanogelation with ATP. The resulting nanoparticles tuned and enhanced transport and electrochemical properties of Nafion based nanocomposite membranes, which is highly favorable for fuel cell applications. 相似文献
934.
A Rives I Baglai V Malytskyi V Maraval N Saffon-Merceron Z Voitenko R Chauvin 《Chemical communications (Cambridge, England)》2012,48(70):8763-8765
A series of stable quadrupolar bis(p-aminophenyl)-carbo-benzenes, featuring both donor-donor-donor π-frustration and central macro-aromaticity, is described and compared to the acyclic dibutatrienylacetylene (DBA) reference series. 相似文献
935.
Gaulier C Hospital A Legeret B Delmas AF Aucagne V Cisnetti F Gautier A 《Chemical communications (Cambridge, England)》2012,48(33):4005-4007
A reducing agent-free version of CuAAC able to operate under open air conditions is reported. A readily-synthesizable, hydrophilic and highly stable Cu(I)-NHC allows the clean ligations of unprotected peptides comprising sensitive side chains, at millimolar concentrations. 相似文献
936.
Humbert A Plé K Harakat D Martinez A Haudrechy A 《Molecules (Basel, Switzerland)》2012,17(7):7709-7721
A key saggitamide intermediate corresponding to a rare sugar framework has been obtained. This approach should help to establish the overall configuration of more complex structures of the sagittamide family. 相似文献
937.
Chulida Hemtasin Alison T. Ung Somdej Kanokmedhakul Kwanjai Kanokmedhakul Roger Bishop Thanaphat Satraruji David Bishop 《Monatshefte für Chemie / Chemical Monthly》2012,42(2):955-963
Abstract
Alkaloid-like compounds containing a benzo[c]azepine core structure were successfully prepared in three steps from 5H-dibenzo[a,d]cyclohepten-5-ol via the bridging Ritter reaction. Biological studies of these compounds revealed that some of them are AChE inhibitors and antimalarial agents. 相似文献938.
Evaluation of uncertainty affecting predictions is a major trend in analytical chemistry and chemometrics. Several approximate expressions and resampling methods have been proposed for the estimation of prediction uncertainty when using multivariate calibration. This article proposes a new expression for the variance of prediction, adapted to near infrared spectroscopy specificities and particularly to the spectral error structure, induced by the high colinearity of the variables. The proposed analytical expression enables a detailed evaluation of the different contributions and components of uncertainty affecting the model. An application to real data of feedstuff near infrared spectra related to protein content has shown its advantages. 相似文献
939.
Pavlo Shpak-Kraievskyi Biaolin Yin Arnaud Martel Robert Dhal Gilles Dujardin Mathieu Y. Laurent 《Tetrahedron》2012,68(9):2179-2188
Efficient access to masked β-amino-aldehydes was performed starting from 6-alcoxy tetrahydrooxazinone 6a–d (6-ATO). Transacetalization leads to the opening of the cycle to form either unsymmetric acetal 7 or symmetric acetals 16–18. These amino acetals are key compounds, obtained with 99% ee, which can be engaged in efficient peptide coupling. This method could easily provide peptides aldehydes or small amido aldehydes as exemplified with the formal synthesis of ent-Maraviroc. 相似文献
940.
N Li F Yang HA Stock DV Dearden JD Lamb RG Harrison 《Organic & biomolecular chemistry》2012,10(36):7392-7401
Resorcinarene-based deep cavitands alanine methyl resorcinarene acid (), alanine undecyl resorcinarene acid () and glycine undecyl resorcinarene acid (), which contain chiral amino acids, have been synthesized. The upper rim of the resorcinarene host is elongated with four identical substituents topped with alanine and glycine groups. The structures of the new resorcinarenes were elucidated by nuclear magnetic resonance (NMR), mass spectrometry (MS) and the sustained off-resonance irradiation collision induced dissociation (SORI-CID) technique in FTICR-MS. These studies revealed that eight water molecules associate to the cavitand, two for each alanine group. The alanine substituent groups are proposed to form a kite-like structure around the resorcinarene scaffold. The binding of , , and with chiral R- and S-methyl benzyl amines was studied by (1)H NMR titration, and compared to that of a binary l-tartaric acid and the monoacid phthalyl alanine (). The results show that these compounds interact with amine guests; however, with four carboxylic acid groups, they bind several amine molecules strongly while the binary l-tartaric acid only binds one amine guest strongly. The simple compound , which contains one carboxylic group, shows weak binding to the amines. The (1)H NMR titration of with primary, secondary, and tertiary chiral amines showed that it can discriminate between these three types of amines and showed chiral discrimination for chiral secondary amines. 相似文献