全文获取类型
收费全文 | 622篇 |
免费 | 5篇 |
国内免费 | 8篇 |
专业分类
化学 | 359篇 |
晶体学 | 6篇 |
力学 | 13篇 |
数学 | 133篇 |
物理学 | 124篇 |
出版年
2022年 | 17篇 |
2021年 | 9篇 |
2020年 | 6篇 |
2019年 | 6篇 |
2018年 | 11篇 |
2017年 | 16篇 |
2016年 | 19篇 |
2015年 | 13篇 |
2014年 | 22篇 |
2013年 | 35篇 |
2012年 | 21篇 |
2011年 | 28篇 |
2010年 | 26篇 |
2009年 | 28篇 |
2008年 | 28篇 |
2007年 | 28篇 |
2006年 | 22篇 |
2005年 | 16篇 |
2004年 | 23篇 |
2003年 | 26篇 |
2002年 | 18篇 |
2001年 | 9篇 |
2000年 | 10篇 |
1999年 | 12篇 |
1998年 | 9篇 |
1997年 | 9篇 |
1996年 | 9篇 |
1995年 | 12篇 |
1994年 | 11篇 |
1993年 | 12篇 |
1992年 | 7篇 |
1991年 | 11篇 |
1990年 | 7篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 12篇 |
1986年 | 9篇 |
1985年 | 9篇 |
1984年 | 3篇 |
1982年 | 7篇 |
1981年 | 9篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1977年 | 6篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1967年 | 2篇 |
1966年 | 2篇 |
1965年 | 3篇 |
排序方式: 共有635条查询结果,搜索用时 15 毫秒
91.
Mahide Küçük Ryszard Urbański Jerzy Grzybowski Yalçın Küçük İlknur Atasever Güvenç 《Optimization》2016,65(11):1949-1961
In this study, some relationships between quasidifferentiability and weakly subdifferentiability of a function are investigated, and some results on calculating the quasidifferential in terms of weak exhausters are presented. Moreover, under some assumptions weak subdifferentiability of a quasidifferentiable function is proved and the weak subdifferential is obtained by using the quasidifferential. Under some assumptions, it is proved that a positively homogeneous and lower semicontinuous function is quasidifferentiable. It is also shown that directional differentiability and weak subdifferentiability imply quasidifferentiability. Furthermore, a method to evaluate the quasidifferential is given by using reduced weak lower exhausters. 相似文献
92.
A three-step chromatographic procedure using orthogonal separation mechanisms (size-exclusion, cation-exchange and ion-pairing reversed phase) was developed to purify three low molecular weight selenospecies, including the major compound, from the aqueous extract of monkeypot (Lecythis minor) nuts. The following reversed-phase nanoHPLC-electrospray Q-TOF-MS/MS allowed the formal standardless identification of selenocystathionine and two isoforms of gamma-glutamyl-selenocystathionine. This is the first MS and MS/MS-based formal evidence of the presence of these compounds in a biological sample. 相似文献
93.
Glutathione peroxidase (isolated from bovine erythrocytes) and its behaviour during alkylation and enzymatic digestion were
studied by various hyphenated techniques: gel electrophoresis–laser ablation (LA) inductively coupled plasma (ICP) mass spectrometry
(MS), size-exclusion liquid chromatography–ICP MS, capillary high-performance liquid chromatography (capHPLC)–ICP MS, matrix-assisted
laser desorption/ionization (MALDI) time-of-flight (TOF) MS, electrospray MS, and nanoHPLC–electrospray ionization (ESI) MS/MS.
ESI TOF MS and MALDI TOF MS allowed the determination of the molecular mass but could not confirm the presence of selenium
in the protein. The purity of the protein with respect to selenium species could be evaluated by LA ICP MS and size-exclusion
chromatography (SEC)–ICP MS under denaturating and nondenaturating conditions, respectively. SEC–ICP MS and capHPLC–ICP MS
turned out to be valuable techniques to study the enzymolysis efficiency, miscleavage and artefact formation during derivatization
and tryptic digestion. For the first time the parallel ICP MS and ESI MS/MS data are reported for the selenocysteine-containing
peptide extracted from the gel; capHPLC–ICP MS allowed the sensitive detection of the selenopeptide regardless of the matrix
and nanoHPLC–electrospray made possible its identification.
Figure Eye catching image
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
94.
95.
In this communication we present the application of a new method, which enables one to acquire 3D NMR spectra in a reasonable time and preserves high resolution in indirectly detected domains. The new method is based on random distribution of time domain data points followed by Quaternion FT with respect to two time variables in one step.The experimental examples include three-dimensional spectra of strychnine in CDCl3, TOCSY-HSQC, COSY-HMBC, and the new technique proposed here: heteronuclear single quantum multiple bond correlation (HSQMBC). The obtained spectra are compared to those recorded at the same time employing the conventional acquisition scheme. We show that high-quality 3D spectra of organic compounds can be obtained in reasonable experimental time and that they are of great interest in cases when direct analysis of 2D spectra is difficult. 相似文献
96.
Domenico Catalano Filip Defever Ryszard Deszcz Marian Hotloś Zbigniew Olszak 《Abhandlungen aus dem Mathematischen Seminar der Universit?t Hamburg》1999,69(1):59-65
For anyn ≥ 2, we give examples of almost Kähler conformally flat manifoldsM 2n which are not Kähler. We discuss the meaning of these examples in the context of the Goldberg conjecture on almost Kahler manifolds. 相似文献
97.
Photovoltaic phenomenon in tetracene and pentacene layers evaporated under the same conditions onto a glass substrate and provided with the same couple of electrodes is investigated. Comparison of the results obtained for both organic materials makes it possible to conclude that in spite of differences in mechanisms of charge carrier generation, the values of photovoltaic parameters are very similar. 相似文献
98.
Artificial neural networks have become the go-to solution for computer vision tasks, including problems of the security domain. One such example comes in the form of reidentification, where deep learning can be part of the surveillance pipeline. The use case necessitates considering an adversarial setting—and neural networks have been shown to be vulnerable to a range of attacks. In this paper, the preprocessing defences against adversarial attacks are evaluated, including block-matching convolutional neural network for image denoising used as an adversarial defence. The benefit of using preprocessing defences comes from the fact that it does not require the effort of retraining the classifier, which, in computer vision problems, is a computationally heavy task. The defences are tested in a real-life-like scenario of using a pre-trained, widely available neural network architecture adapted to a specific task with the use of transfer learning. Multiple preprocessing pipelines are tested and the results are promising. 相似文献
99.
The method for analyzing the reshuffling of polymer segments developed previously has been extended to systems involving the disproportionation of chain functionalities. The effect of interchain exchange reactions of this type, leading to the redistribution of chain lengths and of the chain functionalities (redistribution of living and dead chain ends), was analyzed by means of the Monte Carlo simulations. In the systems, in which no propagation occurs (monomer concentration equal to zero), a set of polymer chains containing one living and one dead end was taken as an initial material. A series of simulations were performed for systems with differing molecular weight distributions of the starting macromolecules. Uniform (no chain length distribution polymer – all chains are of the same length), Poisson, and the most probable (geometric) distributions were taken into consideration. Although the molecular weight distributions (MWDs) of functionally different chains of the same polymer were different apart from the eventual equilibrium conditions, the overall MWD was very close to that observed in analogous systems without disproportionation. The same was observed concerning MWDs in modeled polymerization systems, in which reshuffling and disproportionation accompanied propagation. Consequently, a method of estimating the ratio of rate constants of propagation and reshuffling (i. e. kp /k tr) in the relevant polymerization systems, using the observed polydispersity indexes, was proposed. The extent of disproportionation can be evaluated from the determined relationships of the polydispersity index and of the monofunctional chains fraction as functions of the average number of chain transformations. 相似文献
100.
Julia Pretula Krzysztof Kaluzynski Jan Libiszowski Ryszard Szymanski Stanislaw Penczek 《Journal of polymer science. Part A, Polymer chemistry》1997,35(9):1733-1742
Copolymers of 7-oxabicyclo[2.2.1] heptane (B) (and of its 2-methyl derivatives) with 1,3-dioxane (D) were obtained by cationic copolymerization initiated with benzoylium hexafluoroantimonate. Structure of copolymers was determined by 1H- and 13C-NMR. The proportion of the acetal bonds in copolymers was additionally confirmed in studies of the products of hydrolysis (only the acetal bonds hydrolyze). D is unable to homopolymerize for the thermodynamic reasons and therefore mostly pseudoperiodic copolymers (-DBx-)y are formed. Nevertheless, the reshuffling reactions are responsible for the appearance of “wrong” units. These are: the separate oxymethylene and oxy-1,3-propylene units (P, subunits of D) located between two B units. Only the acetal bonds are cleaved in the acidic hydrolysis with dilute HCl. This gives the promesogenic telechelic oligomers of mostly HO-P-Bx-OH structure. This article is the first to describe successful cationic copolymerization of a cyclic acetal with a cyclic ether. Moreover, the inability of D to homopolymerize gives the thermodynamic basis of the pseudoperiodic copolymer formation. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 1733–1742, 1997 相似文献