全文获取类型
收费全文 | 950篇 |
免费 | 16篇 |
国内免费 | 7篇 |
专业分类
化学 | 624篇 |
晶体学 | 16篇 |
力学 | 12篇 |
数学 | 51篇 |
物理学 | 270篇 |
出版年
2022年 | 5篇 |
2021年 | 11篇 |
2020年 | 6篇 |
2019年 | 4篇 |
2018年 | 5篇 |
2017年 | 4篇 |
2016年 | 17篇 |
2015年 | 13篇 |
2014年 | 7篇 |
2013年 | 41篇 |
2012年 | 46篇 |
2011年 | 40篇 |
2010年 | 33篇 |
2009年 | 25篇 |
2008年 | 40篇 |
2007年 | 58篇 |
2006年 | 55篇 |
2005年 | 81篇 |
2004年 | 50篇 |
2003年 | 50篇 |
2002年 | 40篇 |
2001年 | 29篇 |
2000年 | 23篇 |
1999年 | 15篇 |
1998年 | 4篇 |
1997年 | 8篇 |
1996年 | 7篇 |
1995年 | 9篇 |
1993年 | 8篇 |
1992年 | 12篇 |
1991年 | 10篇 |
1990年 | 17篇 |
1989年 | 12篇 |
1988年 | 7篇 |
1987年 | 6篇 |
1986年 | 14篇 |
1985年 | 11篇 |
1984年 | 12篇 |
1983年 | 7篇 |
1982年 | 14篇 |
1981年 | 12篇 |
1980年 | 13篇 |
1979年 | 10篇 |
1978年 | 6篇 |
1977年 | 11篇 |
1976年 | 6篇 |
1975年 | 8篇 |
1974年 | 7篇 |
1968年 | 6篇 |
1967年 | 8篇 |
排序方式: 共有973条查询结果,搜索用时 35 毫秒
181.
The simple refluxing of allenynes, having a phenylsulfonyl functionality on the allenyl group, in xylene (or mesitylene) without microwave irradiation resulted in the efficient formation of bicyclo[5.2.0]nona-1,7-dienes and bicyclo[4.2.0]octa-1,6-dienes in high yields. This method was shown to be successfully applicable to the first construction of bicyclo[6.2.0]deca-1,8-dienes. Construction of the corresponding oxa- and azabicyclo[m.2.0] frameworks could also be attained. This thermal ring-closing reaction involves the formal [2+2] cycloaddition in which the distal double bond of an allenyl moiety exclusively served as one of the pi-components regardless of the position of the phenysulfonyl functionality on the allenyl moiety. 相似文献
182.
Yasunori Igasaki Fanghong Li Narihiro Yoshida Haruyoshi Toyoda Takashi Inoue Naohisa Mukohzaka Yuji Kobayashi Tsutomu Hara 《Optical Review》1999,6(4):339-344
To realize a high efficiency electrically addressable phase-only modulator, we have coupled a liquid crystal display (LCD) to an optically addressed parallel-aligned nematic liquid crystal spatial light modulator (PAL-SLM) with a set of lenses. Phase modulation exceeding 3ϖ at 532 nm wavelength was obtained. We obtained linear transfer characteristics for phase modulation at various desired phase levels after calibration and adjustment of the transfer characteristics of the PAL-SLM and the LCD. Diffraction efficiency of 40% for binary phase grating and of 90% for 8-level blazed phase grating, which were very close to the simulation values, were observed. The power loss of the readout light was caused when passed through a half mirror, therefore, we examined a setup using an oblique readout light at the modulator. Very high diffraction efficiency was obtained from the setup by optimizing the polarization direction and optical path for this light, and the orientation of liquid crystals. Since the modulator can perform at better than 90% diffraction efficiency and at nearly 100% reflectivity, various high efficiency systems utilizing such modulators are expected. 相似文献
183.
Molecular composites, in which a small concentration of ionically modified poly(p‐phenylene terephthalamide) (PPTA) is dispersed in a poly(ethylene oxide) matrix, have been prepared. With the content of PPTA anion increasing to about 5 wt %, the glass‐transition temperature rises and the melting temperature decreases. From the equilibrium‐melting‐temperature depression data that were obtained from Hoffman–Weeks plots, the Flory–Huggins interaction parameter was determined to be negative (−1.10). These indications of enhanced miscibility between the components are attributed to intermolecular ion–dipole interactions. The presence of rigid PPTA‐anion reinforcement alters the morphology; for example, the spherulite size is reduced, and the degree of crystallinity is lowered. Possible models of how the reinforcement is incorporated into the composite are presented. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1369–1376, 2000 相似文献
184.
Molecular composites have been prepared by dispersing rigid‐rod molecules of ionically‐modified poly(p‐phenylene terephthalamide) (PPTA anion) in a polar poly(4‐vinylpyridine) (PVP) matrix. For concentrations up to 5 wt % of the rigid‐rod reinforcement, the resulting composites are transparent and possess a single glass transition temperature that increases with concentration of the PPTA anion. The mechanical properties of the molecular composites are found to increase with concentration and to attain maximum values at about 5 wt % of the PPTA anion. The enhancement in properties, and the miscibility induced between the two component polymers, is attributed to the development of specific interactions between the ionic groups of the PPTA anion and the polar units of the PVP matrix. When such interactions are not present, as in composites reinforced with non‐ionic PPTA, the samples are opaque and their properties are significantly reduced compared to those of the PPTA anion/PVP composites. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2201–2209, 1999 相似文献
185.
186.
Hidemitsu Aoki Makoto Hara Takuro Masuzumi Motaharu K. Mazumder Naoki Ooi Daisuke Watanabe Chiharu Kimura Takashi Sugino 《Applied Surface Science》2009,255(6):3719-3722
Cu electroplating is required for the fabrication of Cu/low-k interconnections. The permeation of a plating solution into low-k films during Cu electroplating is a serious challenge for 45-nm nodes and more complex devices. We investigated the influence of Cu electroplating solutions on boron carbon nitride (BCN) as a low-k film. After dipping it into a Cu electroplating solution that contained additives, the BCN film's hydrophilic surface changed to a hydrophobic surface, and the incorporation of water into the BCN film was suppressed by surfactant adsorption. Sulfuric residue was detected on the BCN sample by thermal desorption spectroscopy after treatment in the Cu electroplating solution with additives; however, it was found through electrical measurements that this solution did not affect the leakage current or the dielectric constant of the BCN film. We successfully fabricated an electroplating Cu layer on a BCN film with good adhesion, and we believe that this BCN film is a sufficiently useful material for Cu/BCN integration in LSI. 相似文献
187.
Masanori Hara Naomi Hatakeyama Kuniaki Watanabe Katsunori Mori 《Journal of magnetism and magnetic materials》2009,321(5):423-428
The magnetization of GdCu induced by hydrogen uptake was measured within the temperature range of 4.2 to 300 K, occurring phase changes were followed by X-ray diffraction measurements at ambient temperature. The prepared GdCu powder of CsCl-type structure readily absorbed hydrogen at ambient temperature, where hydrogen pressure was below 100 kPa. Hydrogenation changed the magnetism of GdCu in a complex manner from an antiferromagnetic-like type to a paramagnetic-like one. The changes in magnetic properties of GdCu by hydrogenation are governed by hydrogen-induced disproportionation. Within the composition range 0<[H]/[GdCu]<1, GdCu disproportionated according to 2GdCu+H2→GdH2+GdCu2 . The magnetization was evaluated by the expression χtotal=(1-x)χGdCu+(x/2)(χGdH2+χGdCu2). GdCu hydride was not observed. Hydrogenation beyond [H]/[GdCu]>1 gave rise to the disproportionation of GdCu2 causing the change in magnetization. 相似文献
188.
Timothy A. DeVol John P. Clements Anne Farawila Matthew J. O’Hara Oleg B. Egorov Jay W. Grate 《Journal of Radioanalytical and Nuclear Chemistry》2009,282(2):623-628
Characterization of SuperLig® 620 solid phase extraction resin was performed in order to develop an automated on-line process monitor for 90Sr. The main focus was on strontium separation from barium, with the goal of developing an automated separation process for 90Sr in high-level wastes. High-level waste contains significant 137Cs activity, of which 137mBa is of great concern as an interference to the quantification of strontium. In addition barium, yttrium and plutonium were studied as potential interferences to strontium uptake and detection. A number of complexants were studied in a series of batch Kd experiments, as SuperLig® 620 was not previously known to elute strontium in typical mineral acids. The optimal separation was found using a 2 M nitric acid load solution with a strontium elution step of ~0.49 M ammonium citrate and a barium elution step of ~1.8 M ammonium citrate. 90Sr quantification of Hanford high-level tank waste was performed on a sequential injection analysis microfluidics system coupled to a flow-cell detector. The results of the on-line procedure are compared to standard radiochemical techniques in this paper. 相似文献
189.
Kazuta Ito Yoshihiro Hara Seiji Mori Prof. Dr. Hiroyuki Kusama Dr. Nobuharu Iwasawa Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(45):12408-12416
The [3+2] cycloaddition reaction of a tungsten‐containing carbonyl ylide with methyl vinyl ether and the insertion reactions of the nonstabilized carbene complex intermediates produced have been investigated through the use of B3LYP density functional theory. The [3+2] cycloaddition reaction of the tungsten‐containing carbonyl ylide has been proven to proceed concertedly, reversibly, and with high endo selectivity. The intermolecular Si? H insertion reactions of the carbene complex intermediates have been proven to be favored over the intramolecular C? H insertion, in good agreement with experimental results. Moreover, the kinetic endo/exo ratio of the [3+2] cycloaddition reaction has been shown to determine the endo/exo selectivity of the Si? H insertion products. In addition, secondary orbital interactions involving the benzene ring and the carbonyl ligand on the metal center have turned out to strongly influence the high endo selectivity of the [3+2] cycloaddition reaction with methyl vinyl ether. 相似文献
190.
Acylglycerols (=Glycerides) from the Glandular Trichome Exudate on the Leaves of Paulownia tomentosa
Teigo Asai Noriyuki Hara Sawa Kobayashi Shiro Kohshima Yoshinori Fujimoto 《Helvetica chimica acta》2009,92(8):1473-1494
Chemical investigations of the glandular trichome exudates on the leaves of Paulownia tomentosa (Scrophulariaceae) led to the identification of the thirty acylglycerols (=glycerides) 1 – 30 , including five known ones ( 2, 3, 6, 9 , and 15 ) (Fig. 1). Spectroscopic analysis combined with GC/MS studies of the glycerides and the liberated fatty acids, in the form of trimethylsilyl ether derivatives and trimethylsilylated methyl esters, respectively, established that the constituents belonged to 1,3‐di‐O‐acetyl‐2‐O‐(fatty acyl)glycerols, 1‐O‐acetyl‐2‐O‐(fatty acyl)‐sn‐glycerols, and 2‐O‐(fatty acyl)glycerols, wherein the fatty acyl moiety was either an eicosanoyl or an octadecanoyl group bearing OH and/or AcO groups at the 3‐, 3,6‐, 3,7‐, 3,8‐, or 3,9‐positions. The 1‐O‐acetyl‐2‐O‐[(3R,6S)‐3‐(acetyloxy)‐6‐hydroxyeicosanoyl]‐sn‐glycerol ( 12 ; 20% of the total glycerides), 2‐O‐[(3R,8R)‐3,8‐bis(acetyloxy)eicosanoyl]glycerol ( 17 ; 14%), 2‐O‐[(3R,9R)‐3,9‐bis(acetyloxy)eicosanoyl]glycerol ( 18 ; 12%), and 2‐O‐[(3R)‐3‐(acetyloxy)eicosanoyl]glycerol ( 10 ; 12%) were relatively abundant constituents. The configurations of the stereogenic centers of the fatty acyl moieties were determined by 1H‐NMR analysis of the monoesters obtained from (R)‐ and (S)‐2‐(naphthalen‐2‐yl)‐2‐methoxyacetic acid ((R)‐ and (S)‐2NMA? OH and the hydroxy‐substituted fatty acid methyl esters (Fig. 2). The configuration at C(2) of the glycerol moiety of the 1‐O‐acetyl‐2‐O‐(fatty acyl)glycerols was determined to be (2S) by chemical conversion of, e.g., G‐2 (= 2 / 3 1 : 10) to (+)‐3‐O‐[tert‐butyl)diphenylsilyl]‐sn glycerol of known absolute configuration. 相似文献