全文获取类型
收费全文 | 4207篇 |
免费 | 97篇 |
国内免费 | 23篇 |
专业分类
化学 | 3167篇 |
晶体学 | 45篇 |
力学 | 36篇 |
数学 | 152篇 |
物理学 | 927篇 |
出版年
2022年 | 20篇 |
2020年 | 33篇 |
2019年 | 55篇 |
2018年 | 28篇 |
2017年 | 28篇 |
2016年 | 61篇 |
2015年 | 59篇 |
2014年 | 74篇 |
2013年 | 181篇 |
2012年 | 189篇 |
2011年 | 188篇 |
2010年 | 121篇 |
2009年 | 125篇 |
2008年 | 203篇 |
2007年 | 204篇 |
2006年 | 217篇 |
2005年 | 181篇 |
2004年 | 203篇 |
2003年 | 179篇 |
2002年 | 171篇 |
2001年 | 98篇 |
2000年 | 76篇 |
1999年 | 61篇 |
1998年 | 39篇 |
1997年 | 49篇 |
1996年 | 59篇 |
1995年 | 63篇 |
1994年 | 41篇 |
1993年 | 60篇 |
1992年 | 64篇 |
1991年 | 55篇 |
1990年 | 37篇 |
1989年 | 43篇 |
1988年 | 51篇 |
1987年 | 40篇 |
1986年 | 28篇 |
1985年 | 97篇 |
1984年 | 95篇 |
1983年 | 61篇 |
1982年 | 67篇 |
1981年 | 62篇 |
1980年 | 61篇 |
1979年 | 58篇 |
1978年 | 54篇 |
1977年 | 56篇 |
1976年 | 58篇 |
1975年 | 44篇 |
1974年 | 36篇 |
1973年 | 40篇 |
1966年 | 20篇 |
排序方式: 共有4327条查询结果,搜索用时 406 毫秒
21.
22.
The motion of a moored floating body under the action of wave forces, which is influenced by fluid forces, shape of the floating body and mooring forces, should be analysed as a complex coupled motion system. Especially under severe storm conditions or resonant motion of the floating body it is necessary to consider finite amplitude motions of the waves, the floating body and the mooring lines as well as non-linear interactions of these finite amplitude motions. The problem of a floating body has been studied on the basis of linear wave theory by many researchers. However, the finite amplitude motion under a correlated motion system has rarely been taken into account. This paper presents a numerical method for calculating the finite amplitude motion when a floating body is moored by non-linear mooring lines such as chains and cables under severe storm conditions. 相似文献
23.
Bioavailability study of commercial sustained-release preparations of diclofenac sodium in gastrointestinal physiology regulated-dogs. 总被引:1,自引:0,他引:1
K Sagara Y Nagamatsu I Yamada M Kawata H Mizuta K Ogawa 《Chemical & pharmaceutical bulletin》1992,40(12):3303-3306
The gastrointestinal (GI) physiology of beagle dogs was regulated with a combined-treatment of intramuscular pentagastrin (10 micrograms/kg x 2) and intravenous atropine sulfate (0.02 mg/kg x 1). Here, the gastric acidity, the gastric emptying time and the small intestinal transit time in the regulated-dogs were respectively around pH 2, 0.7h and 4h, approximating those in healthy humans. The superiority of the regulated-dogs over the intact dogs was confirmed in comparative bioavailability studies by using two classes of commercial preparations. Both the conventional tablet and the sustained-release capsule of diclofenac sodium exhibited simple and similar average plasma concentration-time curves of free diclofenac in the intact dogs, while the latter preparation is reported to reveal a bimodal plasma curve of the drug in healthy humans. The regulated-dogs, however, permitted a bimodal average plasma pattern of the drug for the capsules due to an approximation of the GI physiology between humans and these classes of the dogs. The combined-treatment of beagle dogs with pentagastrin and atropine sulfate seems to supply a useful animal model in predicting the absorption characteristics of the sustained-release preparations and poor water-soluble drugs. 相似文献
24.
Photochemical deprotection of nitro-substituted benzenesulfenates via photoinduced electron transfer
Kan Wakamatsu Mitsuru Kouda Kazuyoshi Shimaoka Haruo Yamada 《Tetrahedron letters》2004,45(34):6395-6398
The photochemical deprotection of alkyl 2,4-dinitrobenzenesulfenate or alkyl 2-nitrobenzenesulfenate was successfully achieved by addition of triethylamine, while it was unsuccessful without triethylamine. The sulfur-oxygen bond cleavage is thought to occur heterolytically in the sulfenate anion radical produced by photoinduced electron transfer with triethylamine. 相似文献
25.
Norifumi Yamada 《Acta Physica Hungarica A》2004,19(3-4):329-332
Using real time Feynman histories, a quasi-distribution of tunneling time Q(τ) is introduced. For the tunneling time of resident time type, an explicit expression for Q is shown for square barriers. Q becomes oscillatory as the barrier becomes opaque. Some well-known tunneling times fall within the range of τ where Q takes non-negligible values. The formal “average” and the “variance” of the tunneling time are found to be related to known tunneling times. It is thus demonstrated that the quasi-distribution extracts the temporal information about tunneling from real time Feynman histories. 相似文献
26.
Hatsuo Yamamura Kousuke Satake Rieko Hirasawa Shinichi Yamada Masao Kawai 《Journal of inclusion phenomena and macrocyclic chemistry》2007,57(1-4):261-264
A novel cyclodextrin (CD) dimer linked with a bis(picolinyl)cystine (Cys) moiety was prepared by the coupling of Boc-protected
Cys with amino-modified CDs, followed by deprotection of the Boc groups and bispicolinylation. The dimer showed less affinity
to an organic guest molecule compared to that of a native CD monomer. It was attributed to an intramolecular inclusion of
the pyridine moiety into CD cavity. The dimer caused significant increase of its organic guest affinity by an addition of
a copper ion. The included pyridine group may come out of a CD cavity to bind the copper ion and the two CDs included cooperatively
and intermolecularly a guest molecule with high affinity. 相似文献
27.
Yan Yin Otoo Yamada Shunsuke Hayashi Kazuhiro Tanaka Hidetoshi Kita Ken‐Ichi Okamoto 《Journal of polymer science. Part A, Polymer chemistry》2006,44(12):3751-3762
A series of branched/crosslinked sulfonated polyimide (B/C‐SPI) membranes were prepared and evaluated as proton‐conducting ionomers based on the new concept of in situ crosslinking from sulfonated polyimide (SPI) oligomers and triamine monomers. Chemical branching and crosslinking in SPI oligomers with 1,3,5‐tris(4‐aminophenoxy)benzene as a crosslinker gave the polymer membranes very good water stability and mechanical properties under an accelerated aging treatment in water at 130 °C, despite their high ion‐exchange capacity (2.2–2.6 mequiv g?1). The resulting polymer electrolytes displayed high proton conductivities of 0.2–0.3 S cm?1 at 120 °C in water and reasonably high conductivities of 0.02–0.03 S cm?1 at 50% relative humidity. In a single H2/O2 fuel‐cell system at 90 °C, they exhibited high fuel‐cell performances comparable to those of Nafion 112. The B/C‐SPI membranes also displayed good performances in a direct methanol fuel cell with methanol concentrations as high as 50 wt % that were superior to those of Nafion 112. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3751–3762, 2006 相似文献
28.
29.
Nahomi Sakaguchi Keiji Yamada Shuji Matsuo Taku Matsuo Hisanobu Wakita 《Research on Chemical Intermediates》2006,32(2):171-182
Surface modification of TiO2 powders with lanthanide salts (EuCl3 or YbCl3) enhanced photocatalytic decomposition of ATP. In comparison with the unmodified catalyst, a 3-fold increase in the ATP decay
rate was observed with TiO2 powders as prepared in 5 mM EuCl3 (or YbCl3) solution. The reason was ascribed to enrichment of ATP to TiO2 powder with the lanthanide ions. Evidence was obtained by adsorption experiments where ATP concentration was monitored after
dispersing TiO2 powders into the solution. The ATP molecules adsorbed faster to TiO2 powder and strongly stabilized there in the presence of Yb3+ than otherwise. 相似文献
30.