全文获取类型
收费全文 | 1210篇 |
免费 | 31篇 |
国内免费 | 5篇 |
专业分类
化学 | 859篇 |
晶体学 | 18篇 |
力学 | 21篇 |
数学 | 50篇 |
物理学 | 298篇 |
出版年
2022年 | 6篇 |
2021年 | 8篇 |
2020年 | 10篇 |
2019年 | 9篇 |
2018年 | 14篇 |
2017年 | 10篇 |
2016年 | 25篇 |
2015年 | 18篇 |
2014年 | 20篇 |
2013年 | 40篇 |
2012年 | 57篇 |
2011年 | 69篇 |
2010年 | 40篇 |
2009年 | 41篇 |
2008年 | 74篇 |
2007年 | 54篇 |
2006年 | 68篇 |
2005年 | 66篇 |
2004年 | 61篇 |
2003年 | 56篇 |
2002年 | 60篇 |
2001年 | 21篇 |
2000年 | 29篇 |
1999年 | 15篇 |
1998年 | 9篇 |
1997年 | 11篇 |
1996年 | 15篇 |
1995年 | 11篇 |
1994年 | 15篇 |
1993年 | 12篇 |
1992年 | 19篇 |
1991年 | 11篇 |
1990年 | 19篇 |
1989年 | 11篇 |
1988年 | 9篇 |
1987年 | 15篇 |
1986年 | 15篇 |
1985年 | 20篇 |
1984年 | 22篇 |
1983年 | 15篇 |
1982年 | 13篇 |
1981年 | 13篇 |
1980年 | 12篇 |
1979年 | 11篇 |
1978年 | 17篇 |
1977年 | 9篇 |
1976年 | 13篇 |
1975年 | 7篇 |
1974年 | 16篇 |
1973年 | 7篇 |
排序方式: 共有1246条查询结果,搜索用时 734 毫秒
101.
Yasutaka Shimada Kazumasa Usuda Hirokazu Okabe Tsuguru Suzuki Kazutsugu Matsumoto 《Tetrahedron: Asymmetry》2009,20(24):2802-2808
The deracemization of 1,2-diol monotosylate derivatives is achieved by the sequential combination of enzymatic hydrolysis and Mitsunobu inversion using a polymer-bound triphenylphosphine. After the lipase-catalysed hydrolysis of the racemic 2-acetoxyhexyl tosylate, the subsequent Mitsunobu reaction without separation causes an inversion of the resulting (R)-alcohol to give the (S)-enantiomer of the acetate as a single product. In particular, the reaction using the polymer-bound triphenylphosphine also proceeds smoothly, and the product is easily separated by filtration from the polymer-bound reagent and its by-products. This deracemization process is applicable to the preparation of several optically active 1,2-diol monotosylates. 相似文献
102.
S. Hirano S. Shimada M. Kuwabara 《Applied Physics A: Materials Science & Processing》2005,80(4):783-786
We demonstrate a method for fabricating a two-dimensional hexagonal array of nanoscale barium titanate ceramic pillars. A precursor array was prepared by introducing a sol solution into an electron-beam resist mold with air holes and subsequently dry etching the unnecessary gel layer formed on the mold. A ceramic array, consisting of barium titanate ceramic pillars with a radius of 85 nm, a lattice constant of 450 nm, and a height of 500 nm, was fabricated by sintering the precursor array at 1073 K. The reflection spectra for the ceramic array in the visible range revealed the underlying photonic band gaps, which were in good agreement with results calculated using a plane-wave method. PACS 77.84.-s; 42.70.-a; 42.70.Qs 相似文献
103.
Minoru Ishikura Machiko Kamada Izumi Oda Tsukasa Ohta Masanao Terashima 《Journal of heterocyclic chemistry》1987,24(2):377-386
The reaction of various lithium tributylheteroarylborates with allylic bromides in the presence of copper(I) cyanide furnished the regioselective allylation at the heteroaryl ring. 相似文献
104.
N-Benzyl-D-glucamine dithiocarbamate (BGD), N-p-hydroxymethylbenzyl-D-glucamine dithiocarbamate (HBGD), and N-p-carboxybenzyl-D-glucamine dithiocarbamate (CBGD) were compared for their relative efficacies in the distribution and excretion of cadmium in mice exposed to cadmium. Mice were injected intraperitoneally with 109CdCl2 (1 mg of Cd/kg and 2 microCi of 109Cd/one animal). Three days later, they were injected with chelating agents (400 mumol/kg) every other day for 2 weeks. After injections of BGD and HBGD, cadmium was excreted mainly in the feces through the bile, and the fecal excretion of cadmium by HBGD was significantly higher than that by BGD or CBGD. These chelating agents increased the urinary excretion of cadmium to a small extent. The hepatic cadmium content was decreased only after HBGD injection. Also, the injection of HBGD caused a much greater decrease in renal cadmium content than did BGD or CBGD. These chelating agents did not result in the redistribution of cadmium to the brain, testes, or heart. The growth of mice was only slightly retarded by injections of these chelating agents. The results of this study indicate that the injection of HBGD to mice pretreated with cadmium can remove cadmium from the body, mainly through fecal excretion, without redistribution of cadmium to other tissues such as the brain, testes, and heart, more effectively than BGD or CBGD. 相似文献
105.
Phosphotransacetylase (PTA) is immobilized on AF-Tresyl TOYOPEARL 650 gel and used on-line in a stainless-steel column (10 × 4 mm i.d.). CoA-SH liberated enzymatically from acetyl-CoA is reacted with Ellman's reagent [5,5′-dithiobis(2-nitrobenzoic acid)] in the carrier stream. The calibration graph for acetyl-CoA is linear from 4 × 10?6 to 4 × 10?4 M and the detection limits is 8 × 10?7 M. The immobilized enzyme can be employed for over 4 months without any significant decrease in activity. The enzyme retains its activity in methanol even though the initial rate of reaction is decreased. 相似文献
106.
Naoyuki Shimada 《Tetrahedron letters》2010,51(50):6572-6575
A catalytic asymmetric synthesis of descurainin has been achieved by incorporating an enantioselective 1,3-dipolar cycloaddition, a stereoselective alkene hydrogenation, an oxidation with Fremy’s salt and a regioselective demethylation with NbCl5 as the key step. The 1,3-dipolar cycloaddition of a carbonyl ylide derived from tert-butyl 2-diazo-5-formyl-3-oxopetanoate with 4-hydroxy-3-methoxyphenylacetylene in the presence of dirhodium(II) tetrakis[N-tetrachlorophthaloyl-(R)-tert-leucinate], Rh2(R-TCPTTL)4, provided an 8-oxabicyclo[3.2.1]octane skeleton in 95% ee. 相似文献
107.
A LiMnPO4/C composite cathode was prepared by a combination of spray pyrolysis and wet ball milling. The cathode showed stable performance at various cutoff voltages up to 4.9 V. The cutoff voltage increase up to 4.9 V allowed the achievement of a high discharge capacity in galvanostatic charge–discharge tests. The discharge capacities of 153 mAh g?1 at 0.05 C and 149 mAh g?1 at 0.1 C were achieved at room temperature; the trickle-mode discharge capacities at room temperature were 132, 120 and 91 mAh g?1 at 0.1, 1 and 5 C discharge rates, respectively. The cell exhibited a good rate capability in the galvanostatic cycling up to 5 C discharge rates at both ambient temperature and 50 °C. 相似文献
108.
Tomohiro Narukawa Takayoshi Kuroiwa Izumi Narushima Yasujiro Jimbo Toshihiro Suzuki Koichi Chiba 《Analytical and bioanalytical chemistry》2010,397(2):493-499
Arsenate [As(V)] solution reference material, National Metrology Institute of Japan (NMIJ) certified reference material (CRM)
7912-a, for speciation of arsenic species was developed and certified by NMIJ, the National Institute of Advanced Industrial
Science and Technology. High-purity As2O3 reagent powder was dissolved in 0.8 M HNO3 solution and As(III) was oxidized to As(V) with HNO3 to prepare 100 mg kg-1 of As(V) candidate CRM solution. The solution was bottled in 400 bottles (50 mL each). The concentration of As(V) was determined
by four independent analytical techniques—inductively coupled plasma mass spectrometry, inductively coupled plasma optical
emission spectrometry, graphite furnace atomic absorption spectrometry, and liquid chromatography inductively coupled plasma
mass spectrometry—according to As(V) calibration solutions, which were prepared from the arsenic standard of the Japan Calibration
Service system and whose species was guaranteed to be As(V) by NMIJ. The uncertainties of all the measurements and preparation
procedures were evaluated. The certified value of As(V) in the CRM is (99.53 ± 1.67) mg kg-1 (k = 2). 相似文献
109.
Mizoshita N Yamanaka K Shimada T Tani T Inagaki S 《Chemical communications (Cambridge, England)》2010,46(48):9235-9237
Polycondensation of 9-mesityl-10-methylacridinium-bridged organosilane in the presence of a nonionic surfactant yielded a mesostructured organosilica solid with a functional framework that exhibited long-lived photoinduced charge separation. 相似文献
110.
Asako Shimada Tomoko Haraga Akiko Hoshi Yutaka Kameo Mikio Nakashima Kuniaki Takahashi 《Journal of Radioanalytical and Nuclear Chemistry》2010,286(3):765-770
In order to analyze actinide elements in radioactive metal waste, the dissolution and chemical separation conditions were optimized. The surfaces of a type 304 stainless steel plate and of pipe waste sampled from the prototype advanced thermal reactor (Fugen) were dissolved in mixed acid solution (HNO3:HCl:H2O = 1:1:4). The resulting solution was evaporated to dryness and dissolved with 2 mol/dm3 of HNO3 to prepare sample solutions. In order to analyze trivalent actinide elements in the sample solution containing a large amount of Fe(III) (>0.1 g) using TRU resin, the effect of Fe(III) concentration on the recovery of Am(III) and reduction effect of Fe(III) to Fe(II) with ascorbic acid were studied. On the basis of results of this study, chemical separation scheme was constructed and Pu and Am in the sample solutions were separated. Thorium and U in the sample solutions were separated with UTEVA resin. High recoveries for all experimented elements were obtained from the analysis of spiked sample solutions, the effectiveness of the method was confirmed. 相似文献