全文获取类型
收费全文 | 3429篇 |
免费 | 15篇 |
国内免费 | 1篇 |
专业分类
化学 | 2153篇 |
晶体学 | 9篇 |
力学 | 38篇 |
综合类 | 1篇 |
数学 | 448篇 |
物理学 | 796篇 |
出版年
2017年 | 23篇 |
2013年 | 42篇 |
2012年 | 30篇 |
2011年 | 58篇 |
2010年 | 25篇 |
2009年 | 32篇 |
2008年 | 32篇 |
2007年 | 57篇 |
2006年 | 34篇 |
2005年 | 40篇 |
2004年 | 27篇 |
2003年 | 26篇 |
1993年 | 24篇 |
1990年 | 25篇 |
1984年 | 22篇 |
1983年 | 32篇 |
1982年 | 31篇 |
1981年 | 32篇 |
1980年 | 29篇 |
1979年 | 30篇 |
1978年 | 33篇 |
1976年 | 27篇 |
1973年 | 23篇 |
1972年 | 22篇 |
1959年 | 92篇 |
1958年 | 150篇 |
1957年 | 187篇 |
1956年 | 53篇 |
1943年 | 22篇 |
1936年 | 31篇 |
1935年 | 33篇 |
1933年 | 33篇 |
1932年 | 32篇 |
1931年 | 29篇 |
1930年 | 54篇 |
1929年 | 56篇 |
1928年 | 74篇 |
1927年 | 48篇 |
1926年 | 32篇 |
1925年 | 33篇 |
1923年 | 23篇 |
1912年 | 27篇 |
1908年 | 27篇 |
1906年 | 23篇 |
1905年 | 23篇 |
1904年 | 25篇 |
1903年 | 27篇 |
1889年 | 24篇 |
1888年 | 23篇 |
1885年 | 24篇 |
排序方式: 共有3445条查询结果,搜索用时 15 毫秒
61.
Dutz H Helbing K Krimmer J Speckner T Zeitler G Ahrens J Altieri S Annand JR Anton G Arends HJ Beck R Bock A Bradtke C Braghieri A v Drachenfels W Frommberger F Godo M Goertz S Grabmayr P Hasegawa S Hansen K Harmsen J Heid E Hillert W Holvoet H Horikawa N Iwata T Van Hoorebeke L d'Hose N Jennewein P Kiel B Klein F Kondratiev R Lang M Lannoy B Leukel R Lisin V Menze D Meyer W Michel T Naumann J Panzeri A Pedroni P Pinelli T Preobrajenski I Radtke E Reicherz G Rohlof C Rostomyan T Sauer M 《Physical review letters》2003,91(19):192001
To verify the fundamental Gerasimov-Drell-Hearn (GDH) sum rule for the first time experimentally, we measured the helicity dependent total photoabsorption cross section with circularly polarized real photons and longitudinally polarized nucleons in the photon energy range 0.68-1.82 GeV with the tagged photon facility at ELSA. The experiment was carried out with a 4pi detection system, a circularly polarized tagged photon beam, and a frozen spin polarized proton target. The contribution to the GDH sum rule in this photon energy range is [49.9+/-2.4(stat)+/-2.2(syst)] microb. 相似文献
62.
Summary Let W(t) be a standard Wiener process with occupation density (local time) (x, t). Paul Lévy showed that for each x, (x, t) is a.s. equal to the mesure du voisinage of W, i.e., to the limit as h approaches zero of h
1/2 times N(h, x, t), the number of excursions from x, exceeding h in length, that are completed by W up to time t. Recently, Edwin Perkins showed that the exceptional null sets, which may depend on x, can be combined into a single null set off which the above convergence is uniform in x. The main aim of the present paper is to estimate the rate of convergence in Perkins' theorem as h goes to zero. We also investigate the connection between N and in the case when we observe a Wiener process through a long time t and consider the number of long (but much shorter than t) excursions.Research partially supported by a NSERC Canada grant 相似文献
63.
E. Träbert P. H. Heckmann H. v. Buttlar 《Zeitschrift für Physik A Hadrons and Nuclei》1977,281(4):333-339
Electronically excited states of Si ions are created by passing a 20 MeV Si5+ beam through a thin carbon foil. The EUV-radiation (λ=13–61 nm) emitted by the beam is analyzed using a grazing-incidence spectrometer. From the decay curves, lifetimes of 24 low lying levels in Si VIII to Si XII and of the 4f and 5g levels of Si XI and Si XII are derived. Cascades from doubly excited states turn out to be an important contribution to the radiation observed. The lifetime values of this work are compared to theoretical data mainly of Wiese, Sinanoλu and Dankwort/Trefftz. Most experimental values agree with at least one of the theoretical values. The decay time 560 ps of the 2s2p 3 3 D 3 0 state of Si IX is clearly longer than the theoretical prediction (highest value 455 ps by Sinanoglu). 相似文献
64.
Reaction of aryl aldehydes with Meldrum's acid 2 in the presence of formic acid and triethylamine gives 5-arylmethyl Meldrum's acid derivatives 4 at room temperature, whereas at 80–100°C 3-arylpropanoic acids 5 are formed. 相似文献
65.
17–Esters of corticosteroids have received considerable attention due to their high topical anti-inflammatory activity. one of the best known is betamethasone 17-valerate which is widely used against a variety of skin diseases2. The relatively simple compound, hydrocortisone 17–butyrate (3a)3 proved to be as active topically as the more sophisticated corticosteroids such as triamcinolone acetonide, while its systemic activity is of the same order as that of hydrocortisone4. 相似文献
66.
Philip E. Morris Jr Donald E. Kiely Gerald S. Vigee Pavol Kòváč 《Journal of carbohydrate chemistry》2013,32(5):661-673
ABSTRACT The use of a phase transfer catalyst, benzyltriethylammonium chloride (BTEAC), is described in conjunction with the ruthenium dioxide/periodate : water/chloroform system for the oxidation of carbohydrate alcohols to the corresponding ketone, aldehyde, or carboxylic acid. The method was found to be applicable to carbohydrates appropriately protected as acetals, ethers, or containing a benzoyloxy group not positioned to readily undergo β-elimination. While the method was very suitable for the oxidation of carbohydrate secondary alcohols to ketones, it was found to be less suitable for the oxidation of a carbohydrate primary alcohol to the corresponding aldehyde or carboxylic acid. Evidence presented suggests that under the mildly basic conditions of the reaction, ruthenium tetraoxide is converted to ruthenate and perruthenate ions in the aqueous solution and then the perruthenate ion is carried by the phase transfer catalyst into the organic layer where oxidation of the substrate occurs. A number of examples illustrating the scope of the method are presented. 相似文献
67.
E.M.M. De Brabander-Van Den Berg A. Nijenhuis M. Mure J. Keulen R. Reintjens F. Vandenbooren B. Bosnian R. De Raat T. Frijns S. v.D. Wal M. Castelijns J. Put E. W. Meijer 《Macromolecular Symposia》1994,77(1):51-62
The synthesis and characterization of a new series of polypropylenimine dendrimers is reported. Using a repetition of the sequence of a Michael addition to a primary amine, followed by a heterogeneously catalyzed hydrogenation, ultra-pure polypropylenimine macromolecules with molecular weights up to 6912 are synthesized. The reaction sequence allows the preparation of these dendrimers at very large scales, whilst the availability of a simple purification in the sequence affords ultra-pure samples. The polypropylenimine dendrimers are fully characterized; apart from the first 0.5 generation they are all oils, possess a Tg in the range from −90 to −40 °C, are unexpectedly stable, and their intrinsic viscosity drops after generation 4. 相似文献
68.
The title compound with the formula C6H13 C4O2H6 C6H 4Br (HBPD) crystallizes in the monoclinic space group C 2/c with lattice parameters a = 28.48 Å, b = 5.71 Å, c = 20.19 Å, β = 97.4° and molecules per unit cell. The structure has been solved by the heavy atom method and refined to a final R value of 0.094. – The HBPD molecules adopt a fully stretched form, both the alkyl and phenyl substituent are in equatorial position with respect to the chair-shaped dioxane ring. The orientation of the phenyl group is an intermediate between the perpendicular and parallel conformation. The molecules show a nearly perfect parallel arrangement in the crystal lattice. 相似文献
69.
70.
Georg v. Alexits 《Mathematische Annalen》1928,100(1):264-277
Ohne Zusammenfassung 相似文献