全文获取类型
收费全文 | 2817篇 |
免费 | 77篇 |
国内免费 | 12篇 |
专业分类
化学 | 1797篇 |
晶体学 | 28篇 |
力学 | 44篇 |
数学 | 536篇 |
物理学 | 501篇 |
出版年
2023年 | 14篇 |
2022年 | 28篇 |
2021年 | 47篇 |
2020年 | 65篇 |
2019年 | 57篇 |
2018年 | 29篇 |
2017年 | 38篇 |
2016年 | 81篇 |
2015年 | 67篇 |
2014年 | 73篇 |
2013年 | 143篇 |
2012年 | 171篇 |
2011年 | 161篇 |
2010年 | 91篇 |
2009年 | 95篇 |
2008年 | 145篇 |
2007年 | 166篇 |
2006年 | 152篇 |
2005年 | 136篇 |
2004年 | 110篇 |
2003年 | 104篇 |
2002年 | 96篇 |
2001年 | 52篇 |
2000年 | 51篇 |
1999年 | 42篇 |
1998年 | 36篇 |
1997年 | 34篇 |
1996年 | 25篇 |
1995年 | 26篇 |
1994年 | 31篇 |
1993年 | 27篇 |
1992年 | 31篇 |
1991年 | 28篇 |
1990年 | 16篇 |
1988年 | 14篇 |
1987年 | 15篇 |
1986年 | 16篇 |
1985年 | 22篇 |
1984年 | 17篇 |
1983年 | 21篇 |
1982年 | 22篇 |
1981年 | 19篇 |
1978年 | 21篇 |
1977年 | 26篇 |
1976年 | 27篇 |
1975年 | 19篇 |
1974年 | 25篇 |
1972年 | 13篇 |
1971年 | 13篇 |
1926年 | 15篇 |
排序方式: 共有2906条查询结果,搜索用时 15 毫秒
111.
Marcus V. P. dos Santos Eduardo C. Aguiar João Bosco P. da Silva Ricardo L. Longo 《Journal of computational chemistry》2013,34(8):611-621
A new approach Procedure for Investigating Categories of Vibrations (PICVib) for estimating vibrational frequencies of selected modes using only the structure and energy calculations at a more demanding computational level is presented and explored. The PICVib has an excellent performance at only a small fraction of the computational demand required for a complete analytical calculation. The errors are smaller than ca. 0.5% when DFT functionals are combined with high level ab initio methods. The approach is general because it can use any quantum chemical program and electronic structure method. It is very robust because it was validated for a wide range of frequency values (ca. 20–4800 cm–1) and systems: XH3 (D3h) with X = B, Al, Ga, N, P, As, O, S, and Se, YH4 (D4h) with Y = C, Si, and Ge, conformers of RDX, SN2 and E2 reactions, [W(dppe)2(NNC5H10)] complex, carbon nanotubes, and hydrogen‐bonded complexes including guanine‐cytosine pair. © 2012 Wiley Periodicals, Inc. 相似文献
112.
FUNDAMENTALS OF TRANSMISSION FLUCTUATION SPECTROMETRY WITH VARIABLE SPATIAL AVERAGING 总被引:4,自引:0,他引:4
JianqiShen UlrichRiebel MarcusBreitenstein UdoKraeuter 《中国颗粒学报》2003,1(6):242-246
Transmission signal of radiation in suspension of particles performed with a high spatial and temporal resolution shows significant fluctuations,which are related to the physical properties of the particles and the process of spatial and temporal averaging.Exploiting this connection,it is possible to calculate the particle size distribution (PSD) and particle concentration.This paper provides an approach of transmission fluctuation spectrometry (TFS) with variable spatial averaging,The transmission fluctuations are expressed in terms of the expectancy of transmission square (ETS) and are obtained as a spectrum,which is a function of the variable beam diameter.The reversal point and the depth of the spectrum contain the information of particle size and particle concentration,respectively. 相似文献
113.
Paula R. Cable Mark Parker R. Kenneth Marcus Joseph M. Pochkowski 《Journal of the American Society for Mass Spectrometry》1995,6(2):140-147
The use of a two-dimensional charge injection device (CID) to directly image the spatial profile of impingent positively charged ions is described. By this approach, no prior conversion from an ion beam to a photon image is required. Because of the positive response of the device to plasma photons, ions that emanated from the radiofrequency glow discharge source were diverted around a photon stop and focused onto the CID. The resultant ion images were digitized via an external image processor and corrected for dark current contributions. Two-dimensional ion images and single pixel line profiles are presented. 相似文献
114.
Brian Marcus 《Israel Journal of Mathematics》1975,21(2-3):111-132
115.
Froim Marcus 《Israel Journal of Mathematics》1975,22(3-4):185-202
It is shown that Fubini’s theorem concerning the converse of Bianchi’s permutability theorem, published in 1940 in Annals of Mathematics, is true in general. There is a single exceptional case which is related to a theorem of H. Jonas, published in 1937 in Mathematische Annalen, concerningW congruences in which the necessary conditions of Fubini’s Theorem are not also sufficient. For this reason we reformulate Fubini’s theorem as follows: Letx(u, v),y(u, v) be two surfaces with a one-to-one mapping between them and such that the nets of curvesu, v on these surfaces are not osculating-related (following Jonas). If each of the three surfacesz(u, v),t(u, v),η(u, v) is a congruence transform of every one of the surfacesx(u, v),y(u, v), then the congruences generated by the lines (x, z +pt), (y, z +ρt),ρ=const are allW congruences. 相似文献
116.
Single-beam coherent anti-Stokes Raman-scattering (CARS) microspectroscopy achieves a complete CARS scheme with a femtosecond laser. Here, we introduce heterodyne detection in a simple experimental extension: the optical fields driving the CARS process and the local oscillator used for heterodyning are derived from a single beam of ultrashort laser pulses by pulse shaping. The heterodyne signal is amplified by more than 3 orders of magnitude and is linearly dependent on the concentration of Raman scatterers. This dramatically increases the sensitivity of chemically selective detection at microscopic resolution while maintaining the simplicity of the single-beam setup. 相似文献
117.
Coherent anti-Stokes Raman scattering (CARS) microscopy is emerging as a powerful method for imaging materials and biological systems, partly because of its noninvasiveness and selective chemical sensitivity. However, its full potential for species-selective imaging is limited by a restricted spectral bandwidth. Recent increases in bandwidth are promising but still are not sufficient for the level of robust component discrimination that would be needed in a chemically complex milieu found, for example, in intracellular and extracellular environments. We demonstrate a truly broadband CARS imaging instrument that we use to acquire hyperspectral images with vibrational spectra over a bandwidth of 2500 cm(-1) with a resolution of 13 cm(-1). 相似文献
118.
Marcus Richter Sebastian Hahn Dr. Evgenia Dmitrieva Dr. Frank Rominger Dr. Alexey Popov Prof. Dr. Uwe H. F. Bunz Prof. Dr. Xinliang Feng Dr. Reinhard Berger 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(5):1345-1352
Polycyclic aromatic azomethine ylides (PAMYs) are powerful building blocks in the bottom-up synthesis of internally nitrogen-containing polycyclic aromatic hydrocarbons (N-PAHs) through 1,3-cycloaddition reactions. In this work, the cycloaddition reaction of PAMYs to asymmetric ortho-quinones is presented, which, in contrast to the addition to symmetric para-quinones, facilitates subsequent condensation reactions and allows the synthesis of three helical N-PAHs with ullazine-quinoxaline ( UQ - 1 – 3 ) backbones. UQ - 1 and UQ - 2 possess two helical centers; however, single-crystal X-ray analysis together with the computational modeling of UQ - 3 elucidate the formation of only the thermodynamically most stable geometry with four helical centers in a (P,P,M,M) configuration. For the series UQ - 1 – 3 , the number of redox steps is directly correlated with the number of ullazine or quinoxaline units incorporated into the targeted molecular backbones. A detailed investigation of the spectroscopic and magnetic properties of the radical cation and anion as well as the dication and dianion species by in situ EPR/UV/Vis-NIR spectroelectrochemistry is provided. The excellent optical and redox properties combined with helical geometries render them possibly applicable as chiral emitter or ambipolar charge transport material in organic electronics. 相似文献
119.
Chelsea C. Buck Patrick B. Dennis Maneesh K. Gupta Marcus T. Grant Marquise G. Crosby Joseph M. Slocik Peter A. Mirau Kellie A. Becknell Kristen K. Comfort Rajesh R. Naik 《Macromolecular bioscience》2019,19(3)
The suckerin family of proteins, identified from the squid sucker ring teeth assembly, offers unique mechanical properties and potential advantages over other natural biomaterials. In this study, a small suckerin isoform, suckerin‐12, is used to create enzymatically crosslinked, macro‐scale hydrogels. Upon exposure to specific salt conditions, suckerin‐12 hydrogels contracted into a condensed state where mechanical properties are found to be modulated by the salt anion present. The rate of contraction is found to correlate well with the kosmotropic arm of the Hofmeister anion series. However, the observed changes in hydrogel mechanical properties are better explained by the ability of the salt to neutralize charges in suckerin‐12 by deprotonization or charge screening. Thus, by altering the anions in the condensing salt solution, it is possible to tune the mechanical properties of suckerin‐12 hydrogels. The potential for suckerins to add new properties to materials based on naturally‐derived proteins is highlighted. 相似文献
120.
Iain D. H. Oswald 《Acta Crystallographica. Section C, Structural Chemistry》2019,75(8):1021-1022
A new crystalline form of αβ‐d ‐lactose prepared by oven drying a concentrated aqueous solution of d ‐lactose is a lesson in the power of observation and the rigorous analysis of powder samples. 相似文献