全文获取类型
收费全文 | 5028篇 |
免费 | 157篇 |
国内免费 | 7篇 |
专业分类
化学 | 3691篇 |
晶体学 | 69篇 |
力学 | 60篇 |
综合类 | 2篇 |
数学 | 188篇 |
物理学 | 1182篇 |
出版年
2023年 | 27篇 |
2022年 | 26篇 |
2021年 | 41篇 |
2020年 | 74篇 |
2019年 | 79篇 |
2018年 | 55篇 |
2017年 | 29篇 |
2016年 | 92篇 |
2015年 | 111篇 |
2014年 | 100篇 |
2013年 | 238篇 |
2012年 | 244篇 |
2011年 | 252篇 |
2010年 | 154篇 |
2009年 | 167篇 |
2008年 | 240篇 |
2007年 | 285篇 |
2006年 | 262篇 |
2005年 | 289篇 |
2004年 | 217篇 |
2003年 | 202篇 |
2002年 | 204篇 |
2001年 | 116篇 |
2000年 | 118篇 |
1999年 | 74篇 |
1998年 | 55篇 |
1997年 | 51篇 |
1996年 | 89篇 |
1995年 | 56篇 |
1994年 | 54篇 |
1993年 | 67篇 |
1992年 | 72篇 |
1991年 | 65篇 |
1990年 | 54篇 |
1989年 | 57篇 |
1988年 | 54篇 |
1987年 | 58篇 |
1986年 | 51篇 |
1985年 | 92篇 |
1984年 | 76篇 |
1983年 | 43篇 |
1982年 | 52篇 |
1981年 | 49篇 |
1980年 | 58篇 |
1979年 | 56篇 |
1978年 | 47篇 |
1977年 | 33篇 |
1976年 | 39篇 |
1974年 | 27篇 |
1973年 | 28篇 |
排序方式: 共有5192条查询结果,搜索用时 17 毫秒
991.
Minamisono T. Matsuta K. Minamisono K. Kudo S. Ogura M. Fukuda S. Sato K. Mihara M. Fukuda M. 《Hyperfine Interactions》2001,136(3-8):225-231
In order to precisely determine the |eqQ(41Sc)/h| of 41Sc(I
π=7/2−, T
1/2=0.596 s) implanted in a TiO2 single crystal the electric field gradient tensor and anisotropic chemical shift were determined by detecting the Fourier
Transformed Pulse-NMR of 45Sc(I
π=7/2−, stable) in the crystal at a high field of 7.0 T and 9.4 T. Combining the new |eqQ(41Sc)/h| value with the Q(45Sc)=−(23.6±0.2) fm2, also renewed by using the known atomic hyperfine interaction constants and Sternheimer polarization effect, the |Q(41Sc;I
π=7/2−,T
1/2=0.596 s)|=(15.6±0.3) fm2 has been precisely determined. The value is compared with the theoretical Q(41Sc) given by a shell model code.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
992.
T Sato H Yokoyama H Ohya H Kamada 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2001,153(1):113-116
An imaging technique of electrically detected magnetic resonance (EDMR) was newly developed. Because the EDMR signal is obtained from paramagnetic recombination centers, one may expect the image to represent the distribution of defect and/or impurity sites in the sample. We successfully obtained EDMR images of a light-illuminated silicon plate 8 mm in width and 15 mm in length, which was cut from a silicon wafer (n-type, 100 Omega cm), under ESR irradiation at a frequency of 890 MHz (wavelength, 340 mm). The reproducibility of the EDMR image obtained from a sample was amply satisfactory. When the oxidized surface of the silicon was removed, the EDMR signal disappeared. Although the EDMR signal reappeared when the surface of the sample became reoxidized, the EDMR image obtained was slightly different from the earlier one. This finding shows that the EDMR image obtained from the sample shows the distribution of defects at the Si/SiO(2) interface. 相似文献
993.
Thin boron nitride nanotubes with unusual large inner diameters 总被引:1,自引:0,他引:1
BN nanotubes, displaying the characteristics of few concentric layers (2–6 layers) but unusual large inner diameters (ranging from 8 to more than 10 nm), are synthesized by a chemical vapor deposition (CVD) method on -Al2O3 micrometer-range particles. The inner diameters are at least 5 nm larger than the previously reported BN nanotubes of similar layers. Some BN nanotubes are observed to be filled with B–N–O-based amorphous materials. Crystalline core fillings (in the form of boron carbide nanorods) were also discovered. The discussions suggested that the CVD growth behavior of BN nanotubes may be closely dependent on the underlying substrates, which may be helpful to the possible rational synthesis of BN nanotubes. 相似文献
994.
H Terao T Sugawara Y Kita N Sato E Kaho S Takeda 《Journal of the American Chemical Society》2001,123(43):10468-10474
The crystal structure of a hydrated crystal of bis(squaryl)biphenyl (BSQB*4H2O), in which two squaric acid moieties are connected with a 4,4'-biphenyl unit, was characterized by the presence of a one-dimensional hydrogen-bonded chain composed of BSQB and water molecules. X-ray crystallographic analysis showed that BSQB exists in a dianion form and that, on average, two of the four water molecules are protonated. The enhanced temperature dependence of the thermal parameters of the oxygen atoms of the water molecules suggested dynamic disorder of the water molecules. The solid-state magic angle spinning deuterium NMR spectrum of BSQB*4D2O revealed that deuterons are exchanged between heavy water molecules and oxonium ions with an exchange rate of ca. 700 Hz around 250 K and that deuterons start to migrate in a hydrogen-bonded cluster of water molecules. Ac dielectric measurements were also used to examine the dynamic process in the hydrated crystal. The dielectric permittivity of the crystal dramatically increased above 250 K with a distinct frequency dependence (epsilon' = 4.7 x 10(4) at 340 K and 1 kHz). The frequency dependence of tan delta at 290 K exhibited a maximum at 3.0 kHz, and this maximum shifted to lower frequencies when the temperature of the crystal decreased. These experimental results suggested that in the one-dimensional hydrogen-bonded chain of BSQB*4H2O a proton relay between oxonium ions and water molecules occurred within a cluster of four water molecules and that the relay was transmitted to the adjacent cluster mediated by the modulation of the negative charge distribution of the BSQB dianion. These phenomena were interpreted as the solitonic migration of the charged domain boundaries along the one-dimensional hydrogen-bonded chain. 相似文献
995.
A series of dendrimer-encapsulated poly(phenyleneethynylene)s 4~6 were Synthesize d. The light-harvesting antenna functions of dendrimer frameworks together with the blue-light emitting activities of 4~6 were highlighted. 相似文献
996.
A novel type of heterogenized CuCl2 catalysts was designed for the oxidative carbonylation of methanol to dimethyl carbonate (DMC) taking account of the plausible reaction mechanism and intermediates. To prevent severe corrosion of the reaction equipment materials due to Cl? while keeping the catalytic activity of the homogeneous CuCl2 catalyst, we adopted, as supports (or ligands) of CuCl2, four polymers, bearing a 2,2′-bipyridine (bpy) or pyridine (py) unit, namely, poly(2,2′-bipyridine-5,5′-diyl) (Pbpy), poly(pyridine-2,5-diyl) (Ppy), poly(N,N′-bisphenylene-2,2′-bipyridine-4,4′-dicarboxylic amide) (Bpya), and poly(4-methyl-4′-vinyl-2,2′-bipyridine) (Pvbpy), together with one chelate compound, 8-quinolinol. The catalytic activity, stability of heterogenized CuCl2 and their corrosivities to stainless steels were examined in the liquid-phase reaction of the oxidative carbonylation of methanol. These polymer-supported catalysts showed considerable catalytic activity and stability for the DMC synthesis. In particular, the Pbpy-CuCl2 and Ppy-CuCl2 catalysts exhibited high DMC yields and selectivity comparable to those of the homogeneous CuCl2 catalyst. This high activity appears to be associated with the presence of the π-conjugated system in the polymers, which affect the redox reactions of Cu involved in the catalytic reaction. All of the polymer-supported CuCl2 catalysts could be easily recycled after filtration, and the initial catalytic activity was maintained after three times of use. The corrosive characters of the catalysts were closely related to CuCl2 leaching from the supports, which reflects the ability of supports to coordinate Cu. These experimental results suggest that both the electronic structure and the coordination ability of the polymer supports are key factors for the development of an effective catalytic system. 相似文献
997.
蓝藻Trichodesmium thiebautii细胞外多糖经过DEAE-sephaeel柱层析后,经TLC、GLC.^1H-NMR分析,推定为硫酸化多糖,其组成单糖主要为D-半乳糖,其次是D-葡萄糖、D-木糖、2-脱氧核糖、L-鼠李糖,并含有葡萄糖醛酸和丙酮酸. 相似文献
998.
Eu2+-doped inorganic-organic hybrid materials, which are potentially suitable for a tunable laser in the near ultra violet and blue region, were prepared through the photoreduction of Eu3+ ions in the materials under the irradiation of the fourth harmonic wave light (266 nm) of the Nd:YAG laser. The hybrid materials doped with Eu3+ ions were prepared from Si(OCH3)4, CH3Si(OCH3)3, EuCl3 and chloropropyltrimethoxysilane (CPTM). After the prehydrolized silica sol was added to the Eu3+-containing solution, Eu3+-doped transparent inorganic-organic hybrid material was obtained by drying at 50°C. The emission peak around 450–475 nm due to the charge transfer transition (5d-4f) of Eu2+ ions increased with the laser irradiation time. Eu3+ ions were effectively photoreduced to Eu2+ ions in pore-free materials prepared at high CPTM to Eu3+ ratios. Eu2+ ions were generated by the photodecomposition of the bond between Eu3+ and Cl (Cl– or Cl(CH2)3 in CPTM). 相似文献
999.
Ashraful Alam Hidetoshi Ohta Tatsuya Yamamoto Satoshi Ogawa Ryu Sato 《Heteroatom Chemistry》2007,18(3):239-248
Naphthalene‐1‐sulfonic acid dimethylamides were treated with n‐BuLi and elemental sulfur or selenium to afford dinaphtho[1,2‐b:2′,1′‐d]thiophenes and selenophenes, respectively. This is the first example of making two C S/Se bonds and a C C bond in a single step at room temperature and also demonstrates a useful method for the synthesis of both thiophenes and selenophenes on naphthalene. In the case of the reactions of elemental selenium, diselenides were also obtained along with dinaphtho[1,2‐b:2′,1′‐d]selenophenes. The structure of dinaphtho[1,2‐b:′,1′‐d]thiophene was characterized by X‐ray crystallography as a representative molecule. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:239–248, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20291 相似文献
1000.
Akane Sato Mizuho Okada Kazuya Saito Michio Sorai 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(5):564-565
In the crystal structure of the title charge‐transfer complex, namely trans‐stilbene–2,2′‐(2,3,5,6‐tetrafluorobenzene‐1,4‐diylidene)propanedinitrile (1/1) (trans‐STB–TCNQF4), C14H12·C12F4N4, the planar STB and TCNQF4 molecules are stacked alternately. The structure is not isostructural with that of STB–TCNQ. No anomaly was found in the displacement parameters of any atoms, while the bond length of the central C=C moiety was shorter than the corresponding bond in ethylene. This suggests that the central C=C moiety of the STB molecule vibrates with a large amplitude, similar to the case in free STB and STB–TCNQ. 相似文献