全文获取类型
收费全文 | 6068篇 |
免费 | 385篇 |
国内免费 | 15篇 |
专业分类
化学 | 4819篇 |
晶体学 | 36篇 |
力学 | 69篇 |
数学 | 697篇 |
物理学 | 847篇 |
出版年
2024年 | 10篇 |
2023年 | 58篇 |
2022年 | 83篇 |
2021年 | 107篇 |
2020年 | 197篇 |
2019年 | 187篇 |
2018年 | 77篇 |
2017年 | 98篇 |
2016年 | 266篇 |
2015年 | 251篇 |
2014年 | 300篇 |
2013年 | 326篇 |
2012年 | 466篇 |
2011年 | 498篇 |
2010年 | 289篇 |
2009年 | 240篇 |
2008年 | 373篇 |
2007年 | 352篇 |
2006年 | 319篇 |
2005年 | 258篇 |
2004年 | 243篇 |
2003年 | 199篇 |
2002年 | 194篇 |
2001年 | 107篇 |
2000年 | 85篇 |
1999年 | 75篇 |
1998年 | 69篇 |
1997年 | 79篇 |
1996年 | 66篇 |
1995年 | 73篇 |
1994年 | 87篇 |
1993年 | 51篇 |
1992年 | 48篇 |
1991年 | 43篇 |
1990年 | 33篇 |
1989年 | 45篇 |
1988年 | 30篇 |
1987年 | 24篇 |
1986年 | 19篇 |
1985年 | 11篇 |
1984年 | 13篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1981年 | 15篇 |
1980年 | 19篇 |
1979年 | 13篇 |
1978年 | 16篇 |
1977年 | 14篇 |
1976年 | 8篇 |
1975年 | 3篇 |
排序方式: 共有6468条查询结果,搜索用时 281 毫秒
11.
Morenzoni E. Birke M. Hofer A. Kottmann F. Litterst J. Matthias B. Meyberg M. Niedermayer Ch. Prokscha Th. Schatz G. Wutzke Th. 《Hyperfine Interactions》1996,97(1):395-406
During the last few decades, a variety of methods has been developed which makes use of polarized positive muons as a microscopic probe of the magnetic properties of condensed matter (muon spin rotation, relaxation, resonance,SR). Until now, available beams for SR studies have delivered 100% polarized muons with energies in the MeV range, resulting in a deep penetration of the muons into the sample material under investigation. This presently limits the applications of theSR technique to the study of the bulk characteristics of matter. To be able to control the implantation depth, a very low energy beam of polarized muons is being developed at the Paul Scherrer Institute. Very slow polarized muons (kinetic energy 10 eV, polarization 90%) are obtained from the moderation of a high energy muon beam in a thin film of an appropriate condensed gas. These muons can be used as a source for a beam of tunable energy between a few tens of eV and some tens of keV. Implantation depths in the range of few to a few hundreds of nanometers can thus be achieved by varying the energy. 相似文献
12.
13.
Reactions of 2- and 3-Phenyl Substituted Alkylalkylidene Iminium Ions in the Gas Phase The collision-induced fragmentations of 2- and 3-phenyl substituted alkylalkylidene iminium ions are reported. Besides the homolytic cleavage of the azaallyl bond a nucleophilic attack of the unsubstituted phenyl group at the iminium function is observed in the gas phase, yielding carbonium ions such as cyclopropanspirobenzenium ( 3 ), indanylium ( 10 ) and indenylium ions ( 11 ). 相似文献
14.
Ernst M Detken A Böckmann A Meier BH 《Journal of the American Chemical Society》2003,125(51):15807-15810
Proteins are not always available in amounts desirable for solid-state magic-angle spinning (MAS) nuclear-magnetic resonance (NMR) spectroscopy. To maximize the signal-to-noise ratio achievable with small samples, the filling factor must be optimized by using small-diameter MAS rotors. These rotors have the added benefit of allowing higher radio frequency field amplitudes during polarization transfer steps and during decoupling periods as well as allowing higher spinning frequencies. We demonstrate the advantages of relatively fast MAS (30 kHz using a 2.5 mm rotor) compared to MAS at 12 kHz for the 10.4 kDa model protein Crh with 93 residues and show that the signal-to-noise ratio in two-dimensional correlation spectra can be significantly improved by taking advantage of optimized pulse sequences available with rapid MAS. 相似文献
15.
Sodium phosphate tellurite glasses in the system (NaPO(3))(x)(TeO(2))(1-) (x) were prepared and structurally characterized by thermal analysis, vibrational spectroscopy, X-ray photoelectron spectroscopy (XPS) and a variety of complementary solid-state nuclear magnetic resonance (NMR) techniques. Unlike the situation in other mixed-network-former glasses, the interaction between the two network formers tellurium oxide and phosphorus oxide produces no new structural units, and no sharing of the network modifier Na(2)O takes place. The glass structure can be regarded as a network of interlinked metaphosphate-type P(2) tetrahedral and TeO(4/2) antiprismatic units. The combined interpretation of the O 1s XPS data and the (31)P solid-state NMR spectra presents clear quantitative evidence for a nonstatistical connectivity distribution. Rather, the formation of homoatomic P--O--P and Te--O--Te linkages is favored over mixed P--O--Te connectivities. As a consequence of this chemical segregation effect, the spatial sodium distribution is not random, as also indicated by a detailed analysis of (31)P/(23)Na rotational echo double-resonance (REDOR) experiments. 相似文献
16.
The isoquinuclidines 7 and 8 were synthesised and tested as inhibitors of hexosaminidases from jack beans and from bovine kidney. These isoquinuclidines mimick the 1,4B‐conformer of a N‐acetyl‐glucosamine‐derived β‐d‐ glucopyranoside; they are competitive inhibitors with Ki values from 0.014 to 0.30 μM . The strong inhibition of these enzymes agrees with the hypothesis that the enzymatic hydrolysis of 2‐acetamido‐2‐deoxy‐β‐d‐ glucopyranosides proceeds via a boat‐like conformer with a pseudo‐axial scissile glycosidic bond and a pseudo‐axial acetamido substituent optimally oriented to effect an intramolecular substitution of the aglycon. 相似文献
17.
The development of a novel Pd-catalyzed synthesis of (hetero)aromatic nitriles from the corresponding aryl chlorides and potassium hexacyanoferrate(II) is described. This novel protocol avoids the use of highly toxic alkali cyanides and proceeds in the presence of small amounts of palladium catalysts. High yields and selectivities of the corresponding aryl nitriles were achieved applying di(1-adamantyl)-1-butylphosphine (cataCXium® A) as the ligand. 相似文献
18.
Structure of S-9,10-Dimethyl-1,3,5,7-tetraarsa-2,4,6,8-tetraoxaadamantane and 9,10-Diethyl-1,3,5,7-tetraarsa-2,4,6,8-tetraoxaadamantane S-9,10-Dimethyl-1,3,5,7-tetraarsa-2,4,6,8-tetraoxaadamantane ( 1 ) and 9,10-diethyl-1,3,5,7-tetraarsa-2,4,6,8-tetraoxaadamantane ( 2 ) have been prepared by the reaction of propionic acid, propionic anhydride and butyric acid, butyric anhydride, respectively, with arsenic(III)-oxide. The crystals of 1 are rhombic, a = 6.902(4), b = 11.121(5), c = 13.988(8), space group P212121. The crystals of 2 are monoclinic, a = 11.757(10), b = 11.255(10), c = 18.631 (18), β = 91.78(7), space group P21/n. The mean bond lengths and angles in 1 are AsO = 1.790 Å, AsC = 1.959 Å, OAsO = 100.60°, CAsO = 99.65°, AsOAs = 128.77°, AsCAs = 118.73°, and in 2 they are AsO = 1.780 Å, AsC = 1.978 Å, OAsO = 101.45°, CAsO = 99.55°, AsOAs = 129.64°, AsCAs = 117.72°. 相似文献
19.
[reaction: see text] A novel one-pot procedure for the three-component coupling reaction of isocyanates, aldehydes, and dienophiles (IAD reaction) has been developed. Condensation of isocyanates and aldehydes and subsequent Diels-Alder reactions with electron-deficient dienophiles furnishes endo-selective amino-substituted cyclohexenes in good yield. 相似文献
20.