全文获取类型
收费全文 | 3982篇 |
免费 | 92篇 |
国内免费 | 20篇 |
专业分类
化学 | 2667篇 |
晶体学 | 51篇 |
力学 | 64篇 |
数学 | 242篇 |
物理学 | 1070篇 |
出版年
2022年 | 24篇 |
2021年 | 29篇 |
2020年 | 43篇 |
2019年 | 51篇 |
2018年 | 36篇 |
2017年 | 31篇 |
2016年 | 62篇 |
2015年 | 73篇 |
2014年 | 68篇 |
2013年 | 220篇 |
2012年 | 187篇 |
2011年 | 214篇 |
2010年 | 120篇 |
2009年 | 138篇 |
2008年 | 205篇 |
2007年 | 231篇 |
2006年 | 222篇 |
2005年 | 187篇 |
2004年 | 145篇 |
2003年 | 141篇 |
2002年 | 155篇 |
2001年 | 101篇 |
2000年 | 112篇 |
1999年 | 70篇 |
1998年 | 43篇 |
1997年 | 43篇 |
1996年 | 66篇 |
1995年 | 46篇 |
1994年 | 35篇 |
1993年 | 47篇 |
1992年 | 68篇 |
1991年 | 45篇 |
1990年 | 45篇 |
1989年 | 42篇 |
1988年 | 63篇 |
1987年 | 45篇 |
1986年 | 51篇 |
1985年 | 63篇 |
1984年 | 62篇 |
1983年 | 28篇 |
1982年 | 44篇 |
1981年 | 38篇 |
1980年 | 40篇 |
1979年 | 41篇 |
1978年 | 36篇 |
1977年 | 44篇 |
1976年 | 22篇 |
1975年 | 32篇 |
1974年 | 31篇 |
1973年 | 24篇 |
排序方式: 共有4094条查询结果,搜索用时 31 毫秒
891.
Yoshishige Sato Thoru Takahashi Toshio Saito Toshio Sato Masaaki Takehisa 《Radiation Physics and Chemistry》1993,42(4-6):621-624
Radiation sensitivities of
. pumilus and
spores were examined to bremsstrahlung of 5 MeV EB and Cobalt -60 γ rays in order to confirm the effects of radiation and dose rate. Biological indicators (SPORTROL, NAmSA, USA) were irradiated with the X ray in the dose rate range of 4.7–47kGy/h. D-value of
spores was 1.4–1.5 kGy, and that of
was 1.1–1.3 kGy. The D-values of
and
have very small dose rate dependences to X ray, and the D-values are similar to those of γ ray. Dose distribution by X-ray and γ irradiation was measured for cartons containing 32 unit dialyzers. The Dmax./Dmin. of the X-ray irradiation (1.2) was smaller than that of γ ray (1.3). 相似文献
892.
893.
894.
895.
Summary
N,N,N,N-Tetramethylisophthalthioamide (Hmpt) was cyclopalladated with PdCl2 in hot dimethylsulphoxide to give [PdCl(mpt)]. The structure was determined by X-ray analysis. The thioamide is metallated at C(2) to act as an S528-01C528-02S tridentate anionic ligand. There is appreciable steric repulsion between the benzene ring H(4, 6) and the dimethylamino groups. The hydrogens and the methyl groups mutually deviate from the coordination plane in opposite directions. The stability of the fused 5,5-membered chelate ring formed by the S528-03C528-04S ligand seems to overcome the steric hindrance. Derivatives were prepared by replacement of the chloride ion with iodide, diethyldithiocarbamate, 4-tert-butylpyridine, or tri-n-butylphosphine, and characterized spectroscopically. The S528-05C528-06S-fused chelate ring was maintained in these derivatives. 相似文献
896.
A simple synthetic method for macrocyclic ketones based on intramolecular alkylation of carbanion, generated from protected cyanohydrin is reported. Subsequent mild treatment with acid and base of the cyclized products leads to macrocyclic ketones in high yields. The reaction is rapid and irreversible, and hence required short reaction time. The method was successfully applied to the syntheses of cyclohexadecanone and trans-2-cyclopentadecenone as a precursor of (±)-muscone and exaltone. 相似文献
897.
Kamiya S Shirahase H Yoshimi A Nakamura S Kanda M Matsui H Kasai M Takahashi K Kurahashi K 《Chemical & pharmaceutical bulletin》2000,48(6):817-827
We synthesized a series of indoline derivatives with an amide or urea moiety and examined their inhibitory effects on acyl-CoA:cholesterol acyltransferase (ACAT) activity, lipid-peroxidation and serum cholesterol levels in experimental animals. Among the derivatives synthesized, a series of N-(1-alkyl-4,6-dimethylindolin-7-yl)-2,2-dimethylpropanamides++ + potently inhibited rabbit intestinal ACAT activity and lipid-peroxidation of rat brain homogenate. The effect on ACAT activity was related to the length of the alkyl chain at the 1-position of indoline. N-(4,6-Dimethyl-1-octylindolindolin-7-yl)-2,2-dimethylpropanami de hydrochloride (55) showed inhibitory effects on intestinal and hepatic ACAT activity slightly weaker than those of YM-750, and an inhibitory effect on low density lipoprotein (LDL)-peroxidation similar to that of probucol. Compound 55 also reduced serum cholesterol at 10 mg/kg/d in hyperlipidemic rats and 20 mg/kg/d in normolipidemic hamsters. The plasma concentration of 55 reached 716 ng/ml in dogs (10 mg/kg, p.o.), which is an effective concentration against hepatic ACAT activity and LDL-peroxidation. In conclusion, compound 55 is a novel bioavailable ACAT inhibitor with anti-peroxidative activity and is thus a promising anti-atherosclerotic and anti-hyperlipidemic drug. Indoline proved to be a useful pharmacophore for molecular design of new anti-peroxidative drugs. 相似文献
898.
In the presence of zeolites, moderately deactivated arenes such as 1-nitronaphthalene, naphthonitriles, and methylated benzonitriles can be smoothly nitrated at room temperature by the combined action of nitrogen dioxide and molecular oxygen. The regioselectivity is considerably improved as compared with the conventional nitration methodology based on nitric and sulfuric acids. In some cases, the minor isomer became favoured to a significant extent, resulting in the reversal of ordinary isomer ratios of nitration products. 相似文献
899.
The electronic and ionic conduction in three kinds of potassium ferrites with β-alumina structure was studied. Undoped ferrite, K2O·6Fe2O3, prepared by sintering at 1400°C after prefiring a mixture of potassium carbonate and ferric oxide, was a mixed conductor with about 1% ionic conduction and predominantly electronic conduction. The nickel- or zinc-doped potassium ferrite showed decreasing conductivity in the range of a single phase as the content of dopant increased. Variations of the electronic conduction in the doped potassium ferrites were assigned to changes of ferrous ion concentration accompanied by structural changes in the spinel-like blocks. Potassium ion conductivities of the three sorts of samples were estimated from the total conductivities and the transport numbers obtained by dc-polarization technique and electrolysis method. The decreases of the ionic conductivities were explained by narrowing of the alkali-oxygen slot caused by doping. 相似文献
900.
Mitsuo Takasugi Shigemitsu Nagao Tadashi Masamune Akira Shirata Kokichi Takahashi 《Tetrahedron letters》1979,20(48):4675-4678
The structures and antifungal activity of four new mulberry phytoalexins, designated as moracins E, F, G, and H, are described. 相似文献