全文获取类型
收费全文 | 8807篇 |
免费 | 236篇 |
国内免费 | 19篇 |
专业分类
化学 | 5984篇 |
晶体学 | 69篇 |
力学 | 193篇 |
综合类 | 5篇 |
数学 | 998篇 |
物理学 | 1813篇 |
出版年
2023年 | 66篇 |
2022年 | 247篇 |
2021年 | 252篇 |
2020年 | 205篇 |
2019年 | 229篇 |
2018年 | 222篇 |
2017年 | 153篇 |
2016年 | 332篇 |
2015年 | 268篇 |
2014年 | 333篇 |
2013年 | 549篇 |
2012年 | 593篇 |
2011年 | 676篇 |
2010年 | 449篇 |
2009年 | 458篇 |
2008年 | 579篇 |
2007年 | 499篇 |
2006年 | 434篇 |
2005年 | 361篇 |
2004年 | 319篇 |
2003年 | 243篇 |
2002年 | 222篇 |
2001年 | 148篇 |
2000年 | 133篇 |
1999年 | 87篇 |
1998年 | 77篇 |
1997年 | 73篇 |
1996年 | 68篇 |
1995年 | 57篇 |
1994年 | 67篇 |
1993年 | 72篇 |
1992年 | 76篇 |
1991年 | 39篇 |
1990年 | 35篇 |
1989年 | 29篇 |
1988年 | 27篇 |
1987年 | 25篇 |
1986年 | 27篇 |
1985年 | 26篇 |
1984年 | 27篇 |
1983年 | 28篇 |
1982年 | 23篇 |
1981年 | 27篇 |
1980年 | 26篇 |
1979年 | 24篇 |
1978年 | 26篇 |
1977年 | 13篇 |
1976年 | 13篇 |
1975年 | 14篇 |
1973年 | 12篇 |
排序方式: 共有9062条查询结果,搜索用时 15 毫秒
61.
62.
63.
64.
A Garcia-Quiroz David L AzevedoE.C da Silva 《Journal of Physics and Chemistry of Solids》2002,63(10):1863-1866
Properties of oxygenated carbon nitride films have attracted the attention of physics researchers due to their magnetic and physical properties, as well as for their usefulness in the industry. The free radicals were investigated using electron paramagnetic resonance applied in the study of spin concentration due to the different mechanism of preparation of carbon nitride films by RF-discharge with different kinds of plasma. Unpaired spin concentrations, in the order of 1020 per cm3, were measured and their time recombination dependency was important in those films. The films were grown by plasma enhanced chemical vapor deposition using mixtures of hydrocarbons, N2 and O2 in different proportions. 相似文献
65.
L. S. de C. Oliveira M. T. X. Silva A. Vasquez J. A. H. da Jornada 《Hyperfine Interactions》1991,66(1-4):267-270
An exploratory Mössbauer spectroscopy study of the Fe-C system in the C rich region, prepared by high pressure-high temperature treatment near the graphite-diamond stability line, was made. The results obtained for the different processing conditions give no evidence of Fe intercalation in graphite. The presence of some water in the cell produced hydrated Fe complexes, which can explain the deleterious effect of water or hydrogen in the high pressure diamond synthesis. 相似文献
66.
Some basic concepts about curvature collineations are reviewed and the existing results on this topic are applied to the case of perfect fluids, giving a characterization of those amongst them which admit proper curvature collineations. 相似文献
67.
We expose and discussPenrose's thesis: Nature produces harnessable noncomputable processes, but none at the classical level. We then suggest a partial counterexample to it, based on aGedanken experiment about an undecidable family of integrable Hamiltonian systems that could lead to a sort of idealized solution to the Halting problem for Turing machines.1. Partially supported by a Fulbright/CNPq-Brazil grant. Permanent address after November 5, 1990: Center for the Study of Mathematical Theories of Communication, IDEA/School of Communications, Federal University of Rio de Janeiro, Av. Pasteur 250, 22290 Rio de Janeiro, RJ Brazil. 相似文献
68.
A mean-field type model with random growth and reset terms is considered. The stationary distributions resulting from the corresponding master equation are relatively easy to obtain; however, for practical applications one also needs to know the convergence to stationarity. The present work contributes to this direction, studying the transient dynamics in the discrete version of the model by two different approaches. The first method is based on mathematical induction by the recursive integration of the coupled differential equations for the discrete states. The second method transforms the coupled ordinary differential equation system into a partial differential equation for the generating function. We derive analytical results for some important, practically interesting cases and discuss the obtained results for the transient dynamics. 相似文献
69.
Danilo Santos Cruz Joo M. de Araújo Carlos A. N. da Costa Carlos C. N. da Silva 《Entropy (Basel, Switzerland)》2021,23(5)
Full waveform inversion is an advantageous technique for obtaining high-resolution subsurface information. In the petroleum industry, mainly in reservoir characterisation, it is common to use information from wells as previous information to decrease the ambiguity of the obtained results. For this, we propose adding a relative entropy term to the formalism of the full waveform inversion. In this context, entropy will be just a nomenclature for regularisation and will have the role of helping the converge to the global minimum. The application of entropy in inverse problems usually involves formulating the problem, so that it is possible to use statistical concepts. To avoid this step, we propose a deterministic application to the full waveform inversion. We will discuss some aspects of relative entropy and show three different ways of using them to add prior information through entropy in the inverse problem. We use a dynamic weighting scheme to add prior information through entropy. The idea is that the prior information can help to find the path of the global minimum at the beginning of the inversion process. In all cases, the prior information can be incorporated very quickly into the full waveform inversion and lead the inversion to the desired solution. When we include the logarithmic weighting that constitutes entropy to the inverse problem, we will suppress the low-intensity ripples and sharpen the point events. Thus, the addition of entropy relative to full waveform inversion can provide a result with better resolution. In regions where salt is present in the BP 2004 model, we obtained a significant improvement by adding prior information through the relative entropy for synthetic data. We will show that the prior information added through entropy in full-waveform inversion formalism will prove to be a way to avoid local minimums. 相似文献
70.
Rafael Dias do Espírito Santo Rosineide Costa Simas Alviclér Magalhães Vanessa Gonçalves dos Santos Thais Regiani Ana Cristina Isler Natiza Graziele Martins Marcos Nogueira Eberlin Eduardo René Pérez González 《Journal of Physical Organic Chemistry》2013,26(4):315-321
Molecules containing the guanidinic nuclei possess several pharmacological applications, and knowing the preferred isomers of a potential drug is important to understand the way it operates pharmacologically. Benzoylguanidines were synthesized in satisfactory to good yields and characterized by NMR, Electrospray Ionization Mass Spectrometry (ESI‐MS) and Fourrier Transform InfraRed Spectroscopy techniques (FTIR). E/Z isomerism of the guanidines was studied and confirmed by NMR analysis in solution (1H‐13C Heteronuclear Single Quantum Coherence (HSQC) and Heteronuclear Multiple‐Bond Correlation (HMBC), 1H‐15N HMBC, 1H‐1H Correlation Spectroscopy (COSY) and Nuclear Overhauser Effect Spectroscopy (NOESY) experiments) at low temperatures. Compounds with p‐Cl and p‐Br aniline moiety exist mainly as Z isomer with a small proportion of E isomer, whereas compounds with p‐NO2 moiety showed a decrease in proportion of isomer Z. The results are important for the application of these molecules as enzymatic inhibitors. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献