全文获取类型
收费全文 | 1041篇 |
免费 | 55篇 |
国内免费 | 2篇 |
专业分类
化学 | 877篇 |
晶体学 | 8篇 |
力学 | 19篇 |
数学 | 86篇 |
物理学 | 108篇 |
出版年
2024年 | 1篇 |
2023年 | 15篇 |
2022年 | 58篇 |
2021年 | 64篇 |
2020年 | 41篇 |
2019年 | 42篇 |
2018年 | 32篇 |
2017年 | 23篇 |
2016年 | 58篇 |
2015年 | 53篇 |
2014年 | 42篇 |
2013年 | 64篇 |
2012年 | 74篇 |
2011年 | 91篇 |
2010年 | 51篇 |
2009年 | 45篇 |
2008年 | 57篇 |
2007年 | 57篇 |
2006年 | 53篇 |
2005年 | 50篇 |
2004年 | 26篇 |
2003年 | 26篇 |
2002年 | 17篇 |
2001年 | 3篇 |
2000年 | 10篇 |
1999年 | 6篇 |
1998年 | 9篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1911年 | 1篇 |
排序方式: 共有1098条查询结果,搜索用时 17 毫秒
991.
Stefania Garzoli Valentina Laghezza Masci Giovanni Turchetti Lorenzo Pesci Antonio Tiezzi 《Natural product research》2019,33(13):1980-1983
The pepper-tree Schinus molle is an evergreen ornamental plant with various and diversified list of medical uses. In this article we analysed the chemical composition of male and female leaves of this plant during the off-flowering and flowering seasons. The leaf extracts were obtained by using a sequential extraction with solvents of different polarities and the chemical composition was investigated by GC-MS. The results showed a total of twenty-three components, in which elemol is the most abundant constituent followed by bicyclogermacrene, γ-eudesmol, α-eudesmol, β-eudesmol and isocalamendiol. The petroleum ether and diethyl ether extracts from male and female flowering and off-flowering leaves consisted of sesquiterpene hydrocarbons as a major constituent followed by monoterpene hydrocarbons, while the acetone extracts showed a different composition. The obtained results show differences in the chemical composition between male and female and flowering and not flowering. 相似文献
992.
993.
In an attempt to obtain suitable bacterial isolates for bioleaching of copper from chalcopyrite and covellite, soil samples
taken from areas of the metal industry were screened using an enrichment procedure specially run at acidic pH and thermophilic
temperature range, to overcome the limitations of mesophiles employed for the purpose besides having economic and environmental
advantages. Of a total of 47 isolates, the most promising 3 having resistance to copper toxicity were evolved by subjecting
them to gradually increasing concentrations of CuSO4 by acclimatization runs conducted on an environmental shaker for 125 d at 65°C. The isolates, JVCu-8, JVCu-10, and JVCu-12,
exhibited significantly enhanced bioleaching and copper tolerance ability at pH 3.5 and 60–70°C. The total solubilization
of copper recorded was 87, 89.4, and 91.2% by JVCu-8, JVCu-10, and JVCu-12, respectively, and these isolates exhibited tolerance
to CuSO4 concentrations of 6.9, 7.2, and 7.2%, respectively. The isolates morphologically resembled Thiobacillus and Sulfolobus. 相似文献
994.
995.
Marengo E Robotti E Gianotti V Righetti PG Cecconi D Domenici E 《Electrophoresis》2003,24(1-2):225-236
Two-dimensional (2-D) electrophoresis is a very useful technique for the analysis of proteins in biological tissues. The complexity of the 2-D maps obtained causes many difficulties in the comparison of different samples. A new method is proposed for comparing different 2-D maps, based on five steps: (i) the digitalisation of the image; (ii) the transformation of the digitalised map in a fuzzy entity, in order to consider the variability of the 2-D electrophoretic separation; (iii) the calculation of a similarity index for each pair of maps; (iv) the analysis by multidimensional scaling of the previously obtained similarity matrix; (v) the analysis by classification or cluster analysis techniques of the resulting map co-ordinates. The method adopted was first tested on some simulated samples in order to evaluate its sensitivity to small changes in the spots position and size. The optimal setting of the method parameters was also investigated. Finally, the method was successfully applied to a series of real samples corresponding to the electrophoretic bidimensional analysis of sera from normal and nicotine-treated rats. Multidimensional scaling allowed the separation of the two classes of samples without any misclassification. 相似文献
996.
997.
Sergei. S. Goncharov Valentina. S. Harizanov Julia. F. Knight Charles F. D. McCoy 《Archive for Mathematical Logic》2003,42(3):279-291
Let 𝒜 be a computable structure and let R be a new relation on its domain. We establish a necessary and sufficient condition for the existence of a copy ℬ of 𝒜 in
which the image of R (?R, resp.) is simple (immune, resp.) relative to ℬ. We also establish, under certain effectiveness conditions on 𝒜 and R, a necessary and sufficient condition for the existence of a computable copy ℬ of 𝒜 in which the image of R (?R, resp.) is simple (immune, resp.).
Received: 4 February 2001 Published online: 5 November 2002
RID="*"
ID="*" The first three authors gratefully acknowledge support of the NFS Binational Grant DMS-0075899.
RID="*"
ID="*" The first three authors gratefully acknowledge support of the NFS Binational Grant DMS-0075899.
RID="*"
ID="*" The first three authors gratefully acknowledge support of the NFS Binational Grant DMS-0075899. 相似文献
998.
Sergey S. Goncharov Valentina S. Harizanov Michael C. Laskowski Steffen Lempp Charles F. D. McCoy 《Proceedings of the American Mathematical Society》2003,131(12):3901-3912
We prove that if is any model of a trivial, strongly minimal theory, then the elementary diagram is a model complete -theory. We conclude that all countable models of a trivial, strongly minimal theory with at least one computable model are -decidable, and that the spectrum of computable models of any trivial, strongly minimal theory is .
999.
Valentina P. Bozhkova Monika Budayova Peter Kvasnicka Natalia Cigankova Dusan Chorvat 《Journal of fluorescence》1994,4(4):369-372
Regional differences in lateral diffusion rates of fluorescence-labeled proteins have been studied in the plasma membrane of dividing eggs of the loach (Misgurnus fossilis) by fluorescence recovery after photobleaching (FRAP). Apparent animal-vegetal differences in fluorescence intensity, lateral diffusion coefficients, and fractions of mobile proteins have been found, with all these quantities being higher in the animal pole region than in the yolk region. Cyclic changes in protein diffusion coefficients and mobile fractions during the first few cell cycles have also been recorded. Soon after the end of a cleavage, the diffusion coefficient reaches its minimal value and increases rapidly before the next cleavage. 相似文献
1000.
Alberto Scrivanti Valentina Beghetto Simonetta Antonaroli Federica Mandoj Bruno Crociani 《Tetrahedron letters》2004,45(30):5861-5864
The iminophosphine-palladium(0) complex [Pd(dmfu)(P-N)] [dmfu=dimethyl fumarate; P-N=2-(PPh2)C6H4-1-CHNC6H4-4-OMe] is a very efficient catalyst for the Suzuki coupling. In the reaction of aryl bromides with phenylboronic acid, turnover numbers up to ca. 200,000 are obtained at 110 °C in 2 h. Good rates are obtained also with the sterically hindered and electronically deactivated 2-bromo-1,3,5-trimethylbenzene. The complex is able to catalyze the exhaustive arylation of 2,3,7,8,12,13,17,18-octabromo-5,10,15-triphenylcorroleCu(III) to yield the corresponding undecaaryl substituted derivative. 相似文献