全文获取类型
收费全文 | 4543篇 |
免费 | 76篇 |
国内免费 | 34篇 |
专业分类
化学 | 2784篇 |
晶体学 | 38篇 |
力学 | 77篇 |
数学 | 467篇 |
物理学 | 1287篇 |
出版年
2019年 | 34篇 |
2018年 | 21篇 |
2017年 | 24篇 |
2016年 | 67篇 |
2015年 | 43篇 |
2014年 | 57篇 |
2013年 | 182篇 |
2012年 | 179篇 |
2011年 | 227篇 |
2010年 | 95篇 |
2009年 | 87篇 |
2008年 | 207篇 |
2007年 | 223篇 |
2006年 | 201篇 |
2005年 | 201篇 |
2004年 | 190篇 |
2003年 | 169篇 |
2002年 | 151篇 |
2001年 | 139篇 |
2000年 | 127篇 |
1999年 | 67篇 |
1998年 | 61篇 |
1997年 | 47篇 |
1996年 | 91篇 |
1995年 | 72篇 |
1994年 | 95篇 |
1993年 | 105篇 |
1992年 | 99篇 |
1991年 | 58篇 |
1990年 | 57篇 |
1989年 | 80篇 |
1988年 | 56篇 |
1987年 | 51篇 |
1986年 | 59篇 |
1985年 | 73篇 |
1984年 | 56篇 |
1983年 | 34篇 |
1982年 | 57篇 |
1981年 | 53篇 |
1980年 | 57篇 |
1979年 | 49篇 |
1978年 | 55篇 |
1977年 | 66篇 |
1976年 | 44篇 |
1975年 | 43篇 |
1974年 | 50篇 |
1973年 | 49篇 |
1972年 | 31篇 |
1971年 | 26篇 |
1970年 | 24篇 |
排序方式: 共有4653条查询结果,搜索用时 15 毫秒
911.
Gourab Chatterjee Ajay Jha Alejandro Blanco-Gonzalez Vandana Tiwari Madushanka Manathunga Hong-Guang Duan Friedjof Tellkamp Valentyn I. Prokhorenko Nicolas Ferr Jyotishman Dasgupta Massimo Olivucci R. J. Dwayne Miller 《Chemical science》2022,13(32):9392
The concerted interplay between reactive nuclear and electronic motions in molecules actuates chemistry. Here, we demonstrate that out-of-plane torsional deformation and vibrational excitation of stretching motions in the electronic ground state modulate the charge-density distribution in a donor-bridge-acceptor molecule in solution. The vibrationally-induced change, visualised by transient absorption spectroscopy with a mid-infrared pump and a visible probe, is mechanistically resolved by ab initio molecular dynamics simulations. Mapping the potential energy landscape attributes the observed charge-coupled coherent nuclear motions to the population of the initial segment of a double-bond isomerization channel, also seen in biological molecules. Our results illustrate the pivotal role of pre-twisted molecular geometries in enhancing the transfer of vibrational energy to specific molecular modes, prior to thermal redistribution. This motivates the search for synthetic strategies towards achieving potentially new infrared-mediated chemistry.Channelling vibrational excitation energy to achieve ground-state charge-transfer (CT)-assisted isomerization in a donor-bridge-acceptor molecule in solution. 相似文献
912.
913.
Battiato Ilenia Ferrero V Peter T. O’ Malley Daniel Miller Cass T. Takhar Pawan S. Valdés-Parada Francisco J. Wood Brian D. 《Transport in Porous Media》2019,126(1):5-22
Transport in Porous Media - We investigate local aspects and heterogeneities of porous medium morphology and relate them to the relevant mechanisms of momentum transfer. In the inertial flow range,... 相似文献
914.
Ryan J. Scamp Edward deRamon Eric K. Paulson Scott J. Miller Jonathan A. Ellman 《Angewandte Chemie (International ed. in English)》2020,59(2):890-895
Thiostrepton is a potent antibiotic against a broad range of Gram‐positive bacteria, but its medical applications have been limited by its poor aqueous solubility. In this work, the first C(sp2)?H amidation of dehydroalanine (Dha) residues was applied to the site selective modification of thiostrepton to prepare a variety of derivatives. Unlike all prior methods for the modification of thiostrepton, the alkene framework of the Dha residue is preserved and with complete selectivity for the Z‐stereoisomer. Additionally, an aldehyde group was introduced by C?H amidation, enabling oxime ligation for the installation of an even greater range of functionality. The thiostrepton derivatives generally maintain antimicrobial activity, and importantly, eight of the derivatives displayed improved aqueous solubility (up to 28‐fold), thereby addressing a key shortcoming of this antibiotic. The exceptional functional group compatibility and site selectivity of CoIII‐catalyzed C(sp2)?H Dha amidation suggests that this approach could be generalized to other natural products and biopolymers containing Dha residues. 相似文献
915.
M. A. Miller 《Radiophysics and Quantum Electronics》1993,36(7):372-379
Institute of Applied Physics, Russian Academy of Sciences. Edited from Izvetiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 36, No. 7, pp. 576–587, July, 1993. 相似文献
916.
917.
Keith E. Miller Robert H. Krueger John M. Torkelson 《Journal of Polymer Science.Polymer Physics》1995,33(17):2343-2349
The fluorescent molecular rotor probes 4-tricyanovinyl-[N-(2-hydroxyethyl)-N-ethyl]-aniline, tricyano-4-(dimethylamino) benzylidene, and tricyanovinyljulolidene have been used as extrinsic fluorescence probes for quantitative monitoring of water uptake in polymeric coatings. The presence of water causes plasticization of the polymer, which results in increased local mobility within the film. The nonradiative decay pathways of the rotor probes are increased as local mobility increases, and the resulting decrease in fluorescence intensity of the probes is directly proportional to the amount of water sorbed. Beyond allowing for the characterization of sorbent content, this fluorescence technique can be used to determine the diffusion coefficient of water in a polymer film. The relative change in fluorescence fits well to a Fickian diffusion model, yielding a diffusion coefficient for water of 3 × 10-8 cm2/s in poly(vinyl acetate), and a value of 6 × 10-9 cm2/s in a room-temperature cured epoxypolyamide, in excellent agreement with diffusion coefficient values determined from gravimetric analysis. Preliminary studies also demonstrate the utility of molecular rotor probes to monitor water uptake in individual layers of multilayered polymer systems. © 1995 John Wiley & Sons, Inc. 相似文献
918.
919.
Myron Miller Eugene Keating Delyle Eastwood Martha Schulz Hendrk 《Spectrochimica Acta Part B: Atomic Spectroscopy》1985,40(4):593-616
Enhancement of sensitive transition metal lines by a sodium matrix is measured in a 3-electrode d.c. plasma jet. Spiking with 0.43 M NaCI causes enhancement by factors of 1.85–2.92 in ionic lines and of 1.22–1.99 in atomic lines for eight of the structurally related analyte elements, but suppresses Zn I and Zn II emissions by about 25 %. Emission response to NaCI of lines within the same spectrum, or between different spectra of like ionization stage, can be simulated to 15 % and 20–25 %, respectively, by approximations linear in energy differences. For ionic lines these differences are the absolute value of the line excitation potential minus the energy of the ion state most readily pumped by Penning ionization by argon. For atomic lines it is the difference between emitting state excitation potential and the first ionization potential. Analyses of the experimental data strongly suggest that: (1) Na acts mainly to pertub radiative transfer rather than collisional redistribution processes; (2) population pumping of excited analyte states is largely driven by Penning ionization; (3) accelerated radiative cooling due to Na is manifested in a lowering of local kinetic temperature; (4) to a first-order of approximation, ambipolar diffusion, analyte-Na collisions of the second kind, and analyte ground state spin, do not influence emission line enhancement by easily ionized elements (EIE). Approximations are developed for predicting transition metal enhancements by arbitrary Na doping concentrations, and means are sketched for extending the method to other analyte group/EIE combinations. Practical implications of the work are noted. 相似文献
920.
Chris Miller 《Israel Journal of Mathematics》1997,97(1):183-187
The Gamma function is differentially transcendental over certain differential domains of real-valued functions defined on
fixed subintervals of (0, ∞).
In memory of Lee A. Rubel
Research supported by NSF Postdoctoral Fellowship No. DMS-9407549. 相似文献