全文获取类型
收费全文 | 843篇 |
免费 | 22篇 |
国内免费 | 1篇 |
专业分类
化学 | 542篇 |
晶体学 | 3篇 |
力学 | 10篇 |
数学 | 74篇 |
物理学 | 237篇 |
出版年
2020年 | 13篇 |
2019年 | 8篇 |
2018年 | 6篇 |
2017年 | 11篇 |
2016年 | 16篇 |
2015年 | 14篇 |
2014年 | 21篇 |
2013年 | 31篇 |
2012年 | 37篇 |
2011年 | 46篇 |
2010年 | 22篇 |
2009年 | 12篇 |
2008年 | 41篇 |
2007年 | 52篇 |
2006年 | 41篇 |
2005年 | 45篇 |
2004年 | 42篇 |
2003年 | 37篇 |
2002年 | 31篇 |
2001年 | 23篇 |
2000年 | 14篇 |
1999年 | 7篇 |
1998年 | 15篇 |
1995年 | 9篇 |
1994年 | 7篇 |
1993年 | 15篇 |
1992年 | 9篇 |
1991年 | 9篇 |
1990年 | 9篇 |
1989年 | 12篇 |
1988年 | 11篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 15篇 |
1984年 | 11篇 |
1983年 | 15篇 |
1982年 | 9篇 |
1981年 | 11篇 |
1980年 | 4篇 |
1979年 | 15篇 |
1978年 | 9篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1975年 | 9篇 |
1974年 | 9篇 |
1973年 | 11篇 |
1972年 | 5篇 |
1971年 | 6篇 |
1969年 | 5篇 |
1967年 | 4篇 |
排序方式: 共有866条查询结果,搜索用时 0 毫秒
71.
Adler SS Afanasiev S Aidala C Ajitanand NN Akiba Y Alexander J Amirikas R Aphecetche L Aronson SH Averbeck R Awes TC Azmoun R Babintsev V Baldisseri A Barish KN Barnes PD Bassalleck B Bathe S Batsouli S Baublis V Bazilevsky A Belikov S Berdnikov Y Bhagavatula S Boissevain JG Borel H Borenstein S Brooks ML Brown DS Bruner N Bucher D Buesching H Bumazhnov V Bunce G Burward-Hoy JM Butsyk S Camard X Chai JS Chand P Chang WC Chernichenko S Chi CY Chiba J Chiu M Choi IJ Choi J Choudhury RK Chujo T 《Physical review letters》2003,91(17):172301
We report on the yield of protons and antiprotons, as a function of centrality and transverse momentum, in Au+Au collisions at sqrt[s(NN)]=200 GeV measured at midrapidity by the PHENIX experiment at the BNL Relativistic Heavy Ion Collider. In central collisions at intermediate transverse momenta (1.5
相似文献
72.
[reaction: see text] Readily available 5-vinyldihydropyridones 2 undergo Diels-Alder cyclization with various dienophiles to afford novel octahdroquinolines. The process is highly stereoselective and provides heterocyclic products containing synthetically useful functionality. 相似文献
73.
A procedure for the preparation of high-quality single crystals from concentrated glyme mixtures is presented. Anhydrous single crystals of LiNO(3) and LiClO(4) were prepared in this manner, and the single-crystal structure of LiClO(4) (orthorhombic, Pnma, a = 8.6447(12) A, b = 6.8512(10) A, c = 4.8254(7) A, Z = 4) was determined as an example. This procedure is expected to be widely applicable for not only salts but also a wide range of other materials solvated by glymes. 相似文献
74.
Thompson R Dytman S Kim KY Mueller J Adams GS Amaryan MJ Anciant E Anghinolfi M Asavapibhop B Auger T Audit G Avakian H Barrow S Battaglieri M Beard K Bektasoglu M Bertozzi W Bianchi N Biselli A Boiarinov S Bonner BE Briscoe WJ Brooks W Burkert VD Calarco JR Capitani G Carman DS Carnahan B Cole PL Coleman A Connelly J Cords D Corvisiero P Crabb D Crannell H Cummings J Day D Degtyarenko PV Demirchyan RA Dennis LC Deppman A De Sanctis E De Vita R Dhuga KS Djalali C Dodge GE Doughty D 《Physical review letters》2001,86(9):1702-1706
New cross sections for the reaction e p-->e p eta are reported for total center of mass energy W = 1.5--1.86 GeV and invariant momentum transfer Q2 = 0.25--1.5 (GeV/c)(2). This large kinematic range allows extraction of important new information about response functions, photocouplings, and eta N coupling strengths of baryon resonances. Newly observed structure at W approximately 1.65 GeV is shown to come from interference between S and P waves and can be interpreted with known resonances. Improved values are derived for the photon coupling amplitude for the S11(1535) resonance. 相似文献
75.
We report on the use of a single-polarization, 41 μm core-diameter, intrinsically single-mode photonic crystal fiber (PCF) to obtain high peak power (up to 800 kW), 1 ns-duration pulses in a 100:1 linearly polarized, intrinsically single-mode (M2 1.2) output. By transmitting the PCF output through nonlinear crystals, we also obtained efficient second, third, and fourth harmonic generation resulting in peak power >400 kW in the visible (green, 531 nm) and 200 kW in the UV (265.5 nm). To our knowledge these results represent the highest peak power obtained in a linearly polarized output from a fiber and the highest peak power in the visible and UV obtained through harmonic generation of the direct fiber output. 相似文献
76.
In this paper, we describe a multifrequency spectroscopic system which is ideally suited to EPR investigations of very small
single crystals. Our method utilizes oversized resonant cavities and a continuously tunable vector network analyzer. This
system provides excellent sensitivity over a broad frequency range from about 30 GHz up to about 120 GHz, and in magnetic
fields up to 33 T. 相似文献
77.
This work is concerned with the development of a technique to observe the onset of corrosion as it occurs beneath a temporary
protective layer. Such temporary protectives include paints, varnishes, greases and oils that are applied to metal surfaces
to give short-term protection from corrosion. The objective of this project was to develop a technique that could be used
to evaluate the effectiveness of various temporary protectives in different environments, without the need to remove the protective
layer, thus eliminating the possibility of any chemical changes or loss of corrosion products occurring as a result of removal.
The temporary protective layers are typically 25Μm for paints and 15Μm per layer for varnishes. The 6.3 keV fluorescence X-ray is able to penetrate such layers, but the large escape depth (∼10Μm) of the X-rays means that for a thin protective layer a large proportion of the X-rays detected will originate from deep
within the substrate and the resultant spectrum will be representative of the bulk rather than the surface. To enhance the
surface sensitivity of the CXMS technique, the near surface region must be enriched in the isotope Fe-57. To achieve this,
Fe-57 was vacuum evaporated onto the surface of mild steel substrates and subsequently diffused into the near surface region.
An approximate 20 nm Fe-57 layer was deposited onto mild steel samples. The surface enriched samples were then annealed to
allow the Fe-57 to diffuse into the near surface region of the mild steel substrate, and also to allow back diffusion of the
substrate. A diffusion model was developed to predict the surface distribution of Fe-57 as a function of annealing parameters.
The computer diffusion model allowed the ideal annealing conditions to be estimated to obtain a required near surface environment.
It was essential that the annealing conditions did not result in any surface oxidation, and did result in a surface that was
characteristic of mild steel. CEMS and CXMS spectra were recorded of samples before and after annealing, and also dynamic
Secondary Ion Mass Spectrometry (SIMS) was used to monitor the enrichment and diffusion process. Energy Dispersive X-ray Analysis
(EDXA) was also used to characterize the surface. A number of enriched samples were prepared and treated with a variety of
surface temporary protectives. The CXMS spectra were recorded before and after exposure of the coated samples to various aggressive
environments. 相似文献
78.
79.
Joshua L. Brooks Phil Olsen Lijian Chen Andrew A. Rodriguez 《Tetrahedron letters》2017,58(11):1050-1052
Herein, we describe the isolation and characterization of a UnyLinker dimer which, if left uncontrolled, can become incorporated in oligonucleotide products. The dimer is formed as a result of an unusual intermolecular osmium-catalyzed etherification. We demonstrate that by simply replacing H2O2 as the co-oxidant with NMO, none of the UnyLinker dimer impurity is formed. 相似文献
80.
Larkin JD Fossey JS James TD Brooks BR Bock CW 《The journal of physical chemistry. A》2010,114(47):12531-12539
o-(N,N-Dialkylaminomethyl)arylboronate systems are an important class of compounds in diol-sensor development. We report results from a computational investigation of fourteen o-(N,N-dialkylaminomethyl)arylboronates using second-order M?ller-Plesset (MP2) perturbation theory. Geometry optimizations were performed at the MP2/cc-pVDZ level and followed by single-point calculations at the MP2/aug-cc-pVDZ(cc-pVTZ) levels. These results are compared to those from density functional theory (DFT) at the PBE1PBE(PBE1PBE-D)/6-311++G(d,p)(aug-cc-pVDZ) levels, as well as to experiment. Results from continuum PCM and CPCM solvation models were employed to assess the effects of a bulk aqueous environment. Although the behavior of o-(N,N-dialkylaminomethyl) free acid and ester proved to be complicated, we were able to extract some important trends from our calculations: (1) for the free acids the intramolecular hydrogen-bonded B-O-H···N seven-membered ring conformers 12 and 16 are found to be slightly lower in energy than the dative-bonded N→B five-membered ring conformers 10 and 14 while conformers 13 and 17, with no direct boron-nitrogen interaction, are significantly higher in energy than 12 and 16; (2) for the esters where no intramolecular B-O-H···N bonded form is possible, the N→B conformers 18 and 21 are significantly lower in energy than the no-interaction forms 20 and 23; (3) H(2)O insertion reactions into the N→B structures 10, 14, 18, and 21 leading to the seven-membered intermolecular hydrogen-bonded B···OH(2)···N ring structures 11, 15, 19, and 22 are all energetically favorable. 相似文献