全文获取类型
收费全文 | 654篇 |
免费 | 11篇 |
国内免费 | 1篇 |
专业分类
化学 | 447篇 |
晶体学 | 1篇 |
力学 | 3篇 |
数学 | 107篇 |
物理学 | 108篇 |
出版年
2021年 | 5篇 |
2020年 | 5篇 |
2016年 | 12篇 |
2015年 | 6篇 |
2014年 | 10篇 |
2013年 | 19篇 |
2012年 | 19篇 |
2011年 | 32篇 |
2010年 | 13篇 |
2009年 | 18篇 |
2008年 | 23篇 |
2007年 | 25篇 |
2006年 | 28篇 |
2005年 | 27篇 |
2004年 | 32篇 |
2003年 | 14篇 |
2002年 | 21篇 |
2001年 | 13篇 |
2000年 | 9篇 |
1999年 | 9篇 |
1997年 | 6篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 10篇 |
1989年 | 9篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 9篇 |
1984年 | 7篇 |
1983年 | 12篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1979年 | 10篇 |
1978年 | 11篇 |
1977年 | 13篇 |
1976年 | 16篇 |
1975年 | 14篇 |
1974年 | 21篇 |
1973年 | 14篇 |
1972年 | 5篇 |
1971年 | 7篇 |
1970年 | 9篇 |
1969年 | 6篇 |
1966年 | 4篇 |
1955年 | 5篇 |
1925年 | 4篇 |
排序方式: 共有666条查询结果,搜索用时 46 毫秒
31.
Lilian F. J. Noël Ian A. Maxwell Willy J. M. Van Well Anton L. German 《Journal of polymer science. Part A, Polymer chemistry》1994,32(11):2161-2168
Recently a model has been developed capable of predicting absolute monomer concentrations and their ratios in the polymer, aqueous, and monomer droplet phases as a function of conversion in batch emulsion copolymerizations without using any adjustable parameters. In this article the sensitivity of model predictions of composition drift toward deviations of 10% in all model parameters (maximum swellabilities of monomer in the polymer phase, water solubilities, reactivity ratios, and monomer and polymer densities) was estimated using the monomer combination methyl methacrylate-styrene as an example. From the sensitivity analysis it can be concluded that the reactivity ratios are the most important parameters affecting composition drift. The effects of deviations in maximum swellabilities and monomer and polymer densities on composition drift can be neglected, while the water solubility is important only in those cases where the amount of monomer in the aqueous phase cannot be neglected as compared with the total monomer amount. © 1994 John Wiley & Sons, Inc. 相似文献
32.
Benijts T Günther W Lambert W De Leenheer A 《Rapid communications in mass spectrometry : RCM》2003,17(16):1866-1872
A sonic spray ionization liquid chromatography/mass spectrometry (LC/SSI-MS) procedure combined with off-line solid-phase extraction was optimized for the analysis of 20 endocrine-disrupting chemicals (EDCs) in water samples. Method development included a comparison of the novel sonic spray ionization (SSI) with more traditional ion sources, i.e. pneumatically assisted electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI). It was demonstrated that SSI and ESI spectra were very similar, but were more prone to the formation of solvent cluster ions as compared with APCI spectra. This phenomenon was most prominent for SSI and resulted in an increased chemical background in full-scan mass spectra. However, this chemical noise did not affect the overall sensitivity of SSI and ESI. After optimization of LC and MS parameters, the LC/SSI-MS method was validated. Recoveries ranged from 76.3 up to 113.4% for all compounds. Limits of detection (LOD) and quantitation (LOQ) were established between 3.0 and 11.5 ng/L and 9.9 and 38.0 ng/L, respectively. Within-day (n = 5) and between-day (n = 5) reproducibility were investigated at three levels and ranged from 3.3-16.5% and 7.6-19.2%, respectively. Eight-point calibration curves were established and showed linearity for all compounds (r(2) > 0.987) over a linear dynamic range of 10-10 000 ng/L. 相似文献
33.
Riccardo Gatto Benjamin Baumgartner 《Methodology and Computing in Applied Probability》2014,16(3):561-582
We analyze the insurer risk under the compound Poisson risk process perturbed by a Wiener process with infinite time horizon. In the first part of this article, we consider the capital required to have fixed probability of ruin as a measure of risk and then a coherent extension of it, analogous to the tail value at risk. We show how both measures of risk can be efficiently computed by the saddlepoint approximation. We also show how to compute the stabilities of these measures of risk with respect to variations of probability of ruin. In the second part of this article, we are interested in the computation of the probability of ruin due to claim and the probability of ruin due to oscillation. We suggest a computational method based on upper and lower bounds of the probability of ruin and we compare it to the saddlepoint and to the Fast Fourier transform methods. This alternative method can be used to evaluate the proposed measures of risk and their stabilities with heavy-tailed individual losses, where the saddlepoint approximation cannot be used. The numerical accuracy of all proposed methods is very high and therefore these measures of risk can be reliably used in actuarial risk analysis. 相似文献
34.
We define the hyperbolic order of any locally injective holomorphic function between arbitrary hyperbolic domains of the complex plane and study the relation between the hyperbolic order and the Schwarzian derivative for locally injective holomorphic functions from the unit disk into itself. 相似文献
35.
36.
T. Baumgartner D. Gudat M. Nieger E. Niecke 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1)
Abstract The extraordinary reactivity of carbenoids towards electrophilic as well as nucleophilic reagents awards them for a central importance in organic chemistry. Their unusual bonding situation has been the subject of several theoretical studies'. Having shown in previous reports' that phosphoranyl carbenoids are significantly stabilized by incorporation of the carbenoid center in delocalized n-systems, we succeeded in isolating the first stable bromo. chloro and fluoro-lithio carbenoids 21-c. 相似文献
37.
Mohammad Aghazadeh Meshgi Alexander Pcheim Judith Baumgartner Viatcheslav V. Jouikov Christoph Marschner 《Molecules (Basel, Switzerland)》2021,26(1)
A number of mono- and dioligosilanylated silocanes were prepared. Compounds included silocanes with 1-methyl-1-tris(trimethylsilyl)silyl, 1,1-bis[tris(trimethylsilyl)silyl], and 1,1-bis[tris(trimethylsilyl)germyl] substitution pattern as well as two examples where the silocane silicon atom is part of a cyclosilane or oxacyclosilane ring. The mono-tris(trimethylsilyl)silylated compound could be converted to the respective silocanylbis(trimethylsilyl)silanides by reaction with KOtBu and in similar reactions the cyclosilanes were transformed to oligosilane-1,3-diides. However, the reaction of the 1,1-bis[tris(trimethylsilyl)silylated] silocane with two equivalents of KOtBu leads to the replacement of one tris(trimethylsilyl)silyl unit with a tert-butoxy substituent followed by silanide formation via KOtBu attack at one of the SiMe3 units of remaining tris(trimethylsilyl)silyl group. For none of the silylated silocanes, signs of hypercoordinative interaction between the nitrogen and silicon silocane atoms were detected either in the solid state. by single crystal XRD analysis, nor in solution by 29Si-NMR spectroscopy. This was further confirmed by cyclic voltammetry and a DFT study, which demonstrated that the N-Si distance in silocanes is not only dependent on the energy of a potential N-Si interaction, but also on steric factors and through-space interactions of the neighboring groups at Si and N, imposing the orientation of the pz(N) orbital relative to the N-Si-X axis. 相似文献
38.
Overview of finite elements simulation of temperature profile to estimate properties of materials 3D-printed by laser powder-bed fusion
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Habimana Jean Willy 李辛未 Yong Hao Tan 陈哲 Mehmet Cagirici Ramadan Borayek Tun Seng Herng Chun Yee Aaron Ong 李朝将 丁军 《中国物理 B》2020,(4):98-109
Laser powder bed fusion(LPBF),like many other additive manufacturing techniques,offers flexibility in design expected to become a disruption to the manufacturing industry.The current cost of LPBF process does not favor a try-anderror way of research,which makes modelling and simulation a field of superior importance in that area of engineering.In this work,various methods used to overcome challenges in modeling at different levels of approximation of LPBF process are reviewed.Recent efforts made towards a reliable and computationally effective model to simulate LPBF process using finite element(FE)codes are presented.A combination of ray-tracing technique,the solution of the radiation transfer equation and absorption measurements has been used to establish an analytical equation,which gives a more accurate approximation of laser energy deposition in powder-substrate configuration.When this new analytical energy deposition model is used in in FE simulation,with other physics carefully set,it enables us to get reliable cooling curves and melt track morphology that agree well with experimental observations.The use of more computationally effective approximation,without explicit topological changes,allows to simulate wider geometries and longer scanning time leading to many applications in real engineering world.Different applications are herein presented including:prediction of printing quality through the simulated overlapping of consecutive melt tracks,simulation of LPBF of a mixture of materials and estimation of martensite inclusion in printed steel. 相似文献
39.
Guillermo A. BlancoMaria T. Baumgartner 《Tetrahedron letters》2011,52(52):7061-7063
The sulfenylation of nitroalkanes and hydroxyaryls in DMSO using aryl disulfides as sulfenylating reagents was studied. The corresponding arylthionitroalkanes and arylthiohydroxyaryls were obtained in moderate to good yields in very mild conditions, thus improving the reported procedures for the synthesis of these compounds. 相似文献
40.
Klaus Bö hmer Willy Govaerts Vladimí r Janovský . 《Mathematics of Computation》1999,68(227):1097-1108
A numerical tool for the detection of degenerated symmetry breaking bifurcation points is presented. The degeneracies are classified and numerically processed on -D restrictions of the bifurcation equation. The test functions that characterise each of the equivalence classes are constructed by means of an equivariant numerical version of the Liapunov-Schmidt reduction. The classification supplies limited qualitative information concerning the imperfect bifurcation diagrams of the detected bifurcation points.