全文获取类型
收费全文 | 1856篇 |
免费 | 72篇 |
国内免费 | 13篇 |
专业分类
化学 | 1392篇 |
晶体学 | 11篇 |
力学 | 49篇 |
综合类 | 1篇 |
数学 | 151篇 |
物理学 | 337篇 |
出版年
2022年 | 14篇 |
2021年 | 19篇 |
2020年 | 30篇 |
2019年 | 23篇 |
2018年 | 27篇 |
2017年 | 26篇 |
2016年 | 57篇 |
2015年 | 48篇 |
2014年 | 49篇 |
2013年 | 84篇 |
2012年 | 111篇 |
2011年 | 90篇 |
2010年 | 73篇 |
2009年 | 57篇 |
2008年 | 125篇 |
2007年 | 117篇 |
2006年 | 111篇 |
2005年 | 125篇 |
2004年 | 95篇 |
2003年 | 72篇 |
2002年 | 68篇 |
2001年 | 31篇 |
2000年 | 31篇 |
1999年 | 27篇 |
1998年 | 24篇 |
1997年 | 16篇 |
1996年 | 22篇 |
1995年 | 19篇 |
1993年 | 13篇 |
1991年 | 13篇 |
1990年 | 8篇 |
1989年 | 12篇 |
1988年 | 15篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 22篇 |
1984年 | 25篇 |
1982年 | 22篇 |
1981年 | 18篇 |
1980年 | 11篇 |
1979年 | 25篇 |
1978年 | 15篇 |
1977年 | 18篇 |
1976年 | 16篇 |
1975年 | 12篇 |
1974年 | 8篇 |
1972年 | 8篇 |
1970年 | 8篇 |
1969年 | 9篇 |
1967年 | 8篇 |
排序方式: 共有1941条查询结果,搜索用时 140 毫秒
991.
Makoto Kiso Yuji Ogawa Yushun Fujishima Minoru Fujita Shinji Tanaka Akira Hasegawa 《Journal of carbohydrate chemistry》2013,32(4):625-638
Abstract In order to elucidate further the relationship between the composition of the fatty acyl groups in the nonreducing-sugar subunit of bacterial lipid A and its biological activity, 3-O-[(3R)-3-(acyloxy)tetradecanoyl]-2-deoxy-2-[(3R)-3-hydroxytetradecanamido]-4-O-phosphono-D-glucose [GLA-63(R, R) and GLA-64(R, R)], and 3-O-[(3R)-3-(acyloxy)tetradecanoyl]-2-deoxy-4-O-phosphono-2-tetradecanamido-D-glucose [GLA-67(R), GLA-68(R) and GLA-69(R)] have been synthesized. Benzyl 2-[(3R)-3-(benzyloxymethoxy)tetradecanamido]-2-deoxy-4,6-O-isopropylidene-β-D-glucopyranoside (5) and benzyl 2-deoxy-4,6-O-isopropylidene-2-tetradecanamido-β-D-glucopyranoside (6) were each esterified with (3R)-3-dodecanoyloxytetradecanoic acid (1), (3R)-3-tetradecanoyloxytetradecanoic acid (2) or (3R)-3-hexadecanoyloxy-tetradecanoic acid (3), to give 7-11, which were then transformed, by the sequence of deisopropylidenation, 6-O-tritylation and 4-O-phosphorylation, into a series of desired compounds. 相似文献
992.
Moriyuki Sato Yuji Tada Shinji Nakashima Ken‐ichi Ishikura Makoto Handa Kuninobu Kasuga 《Journal of polymer science. Part A, Polymer chemistry》2005,43(7):1511-1525
Novel thermotropic liquid‐crystalline (LC) copolyesters were prepared with three disubstituted (4,4′‐, 3,4′‐, and 3,3′‐) dioxydiundecanol derivatives of terphenyl analogues of 1,3,4‐thiadiazole [2,5‐diphenyl‐1,3,4‐thiadiazole (DPTD)], and their optical and electrochemical properties were examined. Their structures were characterized with Fourier transform infrared, 1H NMR spectroscopy, and elemental analyses. The thermal and mesomorphic properties of the copolyesters were investigated with differential scanning calorimetry measurements, polarized microscopy observations, and X‐ray analyses; the data suggested that these copolymers formed LC smectic or nematic phases. The mesomorphic tendency decreased in the following order: 4,4′‐DPTD and 3,4′‐DPTD copolyesters > 4,4′‐DPTD and 3,3′‐DPTD copolyesters > 3,4′‐DPTD and 3,3′‐DPTD copolyesters. Solution and solid‐state ultraviolet–visible (UV–vis) and photoluminescence spectra indicated that the copolyesters displayed maximum absorbances and blue emissions according to the DPTD unit; the peak maxima of absorption and emission spectra of the copolyesters shifted to lower wavelengths in the aforementioned order for the LC properties. Cyclic voltammetry measurements indicated that the electrochemical band gaps of the polyesters estimated from the onset of reduction and oxidation processes were almost the same as the optical band gaps determined from the solid‐state UV–vis spectral data. The DPTD unit enhanced the hole‐injection barrier and improved the charge‐injection balance in these polyesters. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1511–1525, 2005 相似文献
993.
Jinqing Qu Toru Fujii Toru Katsumata Yuji Suzuki Masashi Shiotsuki Fumio Sanda Masaharu Satoh Jun Wada Toshio Masuda 《Journal of polymer science. Part A, Polymer chemistry》2007,45(23):5431-5445
2,2,6,6‐Tetramethyl‐1‐piperidinyloxy (TEMPO)‐ and 2,2,5,5‐tetramethyl‐1‐pyrrolidinyloxy (PROXYL)‐containing (R)‐1‐methylpropargyl TEMPO‐4‐carboxylate ( 1 ), (R)‐1‐methylpropargyl PROXYL‐3‐carboxylate ( 2 ), (rac)‐1‐methylpropargyl PROXYL‐3‐carboxylate ( 3 ), (S)‐1‐propargylcarbamoylethyl TEMPO‐4‐carboxylate ( 4 ), and (S)‐1‐propargyloxycarbonylethyl TEMPO‐4‐carboxylate ( 5 ) (TEMPO, PROXYL) were polymerized to afford novel polymers containing the TEMPO and PROXYL radicals at high densities. Monomers 1–3 and 5 provided polymers with moderate number‐average molecular weights of 8200–140,900 in 49–97% yields in the presence of (nbd)Rh+[η6‐C6H5B?(C6H5)3], whereas 4 gave no polymer with this catalyst but gave polymers possessing low Mn (3800–7500) in 56–61% yield with [(nbd)RhCl]2‐Et3N. Poly( 1 ), poly( 2 ), and poly( 4 ) took a helical structure with predominantly one‐handed screw sense in THF and CHCl3 as well as in film state. The helical structure of poly( 1 ) and poly( 2 ) was stable upon heating and addition of MeOH, whereas poly( 4 ) was responsive to heat and solvents. All of the free radical‐containing polymers displayed the reversible charge/discharge processes, whose capacities were in a range of 43.2–112 A h/kg. In particular, the capacities of poly( 2 )–poly( 5 )‐based cells reached about 90–100% of the theoretical values regardless of the secondary structure of the polymer, helix and random. Poly( 1 ), poly( 2 ), and poly( 4 ) taking a helical structure exhibited better capacity tolerance towards the increase of current density than nonhelical poly( 3 ) and poly( 5 ) did. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5431–5445, 2007 相似文献
994.
The jet-cooled Fourier-transform microwave spectrum of N,N-dimethylacetamide was recorded in the region of 12-24 GHz, and was analyzed to determine rotational constants and nuclear quadrupole coupling constants. Coriolis-like coupling parameters characterizing interaction between internal rotation of methyl groups and the overall rotation were also determined from internal-rotation tunneling splittings of the rotational transitions. The Coriolis-like coupling parameters permitted determination of the barrier heights to internal rotation of the three methyl groups, which were found to be 677, 237, and 183 cm−1 for the C-methyl top, the trans-N-methyl top and the cis-N-methyl top, respectively. 相似文献
995.
Maximiliano Segala Yuji Takahata Delano P. Chong 《Journal of Electron Spectroscopy and Related Phenomena》2006
Density functional theory (DFT) calculations have been performed on the gas-phase 2p core-electron binding energies (CEBEs) of Si, P, S, Cl, and Ar in 145 cases using the following procedure: ΔEKS (scalar-ZORA + Exc)/TZP//HF/6-31G(d). ΔEKS is the difference in the total Kohn–Sham energies of the 2p-ionized cation and the neutral parent molecule calculated by DFT using different exchange-correlation functionals Exc with triple-zeta polarized basis set, at molecular geometry optimized by HF/6-31G(d), and relativistic effects have been estimated by scalar zeroth-order regular approximation. Among the 26 functionals tested, the form of Exc giving the best overall performance was found to be the combination of OPTX exchange and LYP correlation functionals. For that functional, the average absolute deviation (AAD) of the 145 calculated CEBEs from experiment is 0.26 eV. There are seven other exchange-correlation functionals that led to AADs of less than 0.30 eV. Some functionals give lower AADs than Exc = OPTX-LYP for some individual elements. In the case of Si, for example, the combination of either mPW91-PBE or Becke88-Perdew86 led to an AAD of only 0.10 eV for 56 silicon-containing molecules. Another example is the case of the argon atom, for which the choice of Exc = OPTX-Perdew86 yields a value for CEBE equal to the experimental value. 相似文献
996.
Jin‐Gang Liu Yasuhiro Nakamura Yuji Shibasaki Shinji Ando Mitsuru Ueda 《Journal of polymer science. Part A, Polymer chemistry》2007,45(23):5606-5617
An aromatic sulfur‐containing diamine 4,4′‐thiobis[(p‐phenylenesulfanyl) aniline] (3SDA) was synthesized and polymerized with a sulfur‐containing dianhydride 4,4′‐[p‐thiobis(phenylenesulfanyl)]diphthalic anhydride (3SDEA) and three nonsulfur aromatic tetracarboxylic dianhydrides, respectively to afford four poly(amic acid)s (PAAs) with the inherent viscosities of 0.54–1.04 dL/g. Flexible and tough polyimide (PI) films obtained from the PAA precursors showed good thermal, mechanical, and optical properties. The glass transition temperatures (Tgs) of the PIs ranged from 179.1–227.2 °C determined by differential scanning calorimetry (DSC), and 173.8–227.3 °C by dynamic mechanical analysis (DMA), depending on the dianhydride used. The 10% weight loss temperatures were in the range of 500–536 °C, showing high intrinsic thermal‐resistant characteristics of the PI films. The PI films also showed good optical transparency above 500 nm, which agreed well with the calculated absorption spectra using the time‐dependent density functional theory. The average refractive indices (nav) measured at 632.8 nm were 1.7191–1.7482, and the in‐plane/out‐of‐plane birefringences (Δn) were 0.0068–0.0123. The high refractive indices originate from the high sulfur contents, good molecular packing, and the absence of bulky structures. The relatively small birefringence mainly results from the flexible thioether linkages structures of the diamine. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5606–5617, 2007 相似文献
997.
998.
Takafumi Uemura Shinichi Yamaguchi Akira Saito Masakazu Aono Yuji Kuwahara 《Surface science》2006,600(3):L15
Tunneling electrons from a scanning tunneling microscope were used to excite light emission from individual multiwalled carbon nanotubes adsorbed on a highly ordered pyrolytic graphite surface. In the integral photon-intensity map, spatially uniform emission in the visible region was observed along the identical multiwalled carbon nanotubes. The emission spectra for the individual nanotubes showed unique profiles which differed with each nanotube, and were classified into two types. Our results indicate that the light emission is due to not the localized electronic states at the tube ends or defects but radiative transitions of electrons between the one-dimensional van Hove singularities, indicating that the two types of spectra are attributed to metallic and semiconducting nanotubes. 相似文献
999.
Summary The long time asymptotic behavior of the occupation times on a half line is studied for a class of one-dimensional diffusion processes whose excursion intervals have very heavy tail probability 相似文献
1000.
Fumihiro Toyokawa Ken‐Ichi Fukukawa Yuji Shibasaki Shinji Ando Mitsuru Ueda 《Journal of polymer science. Part A, Polymer chemistry》2005,43(12):2527-2535
A novel poly(σ‐hydroxyamide) (PHA) based photosensitive polymer that exhibits high transparency at 365 nm wavelength (i‐line) has been developed. Time‐dependent density functional theory (TD‐DFT) calculations using the B3LYP hybrid functional were performed to predict the transparencies of various hydroxyamides in the i‐line region. Based on the calculations, 4,4′‐sulfonylbis(σ‐aminophenol) (SAP) was prepared and polymerized with 4,4′‐oxybis(benzoyl chloride) (OBBC), and the resulting PHA, which is abbreviated as PHA‐S, showed a high transparency comparable to that of PHA derived from 4,4′‐(hexafluoroisopropylidene)bis(σ‐aminophenol). Positive‐type photosensitive PHA was then formulated based on PHA‐S with a crosslinker 1,3,5‐tris[(2‐vinyloxy)ethoxy]benzene (TVEB) and a photoacid generator (5‐propylsulfonyloxyimino‐5H‐thiophen‐2‐ylidene)‐2‐(methylphenyl)acetonitrile (PTMA) (17:3:1 in weight ratio), and demonstrated photosensitivity and contrast of 14 mJ/cm2 and 2.7, respectively, when the resist film was prebaked at 120 °C for 5 min, irradiated by i‐line, post exposure baked at 120 °C for 5 min, developed with an 2.38 wt% TMAH solution for 5 s. A clear positive image featuring 10‐μm line‐and‐space was also printed in a film which was exposed to 50 mJ/cm2 of i‐line by contact‐printing. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2527–2535, 2005 相似文献