全文获取类型
收费全文 | 1139篇 |
免费 | 25篇 |
国内免费 | 8篇 |
专业分类
化学 | 808篇 |
晶体学 | 28篇 |
力学 | 20篇 |
数学 | 60篇 |
物理学 | 256篇 |
出版年
2022年 | 6篇 |
2021年 | 7篇 |
2020年 | 18篇 |
2019年 | 11篇 |
2018年 | 13篇 |
2017年 | 14篇 |
2016年 | 22篇 |
2015年 | 12篇 |
2014年 | 31篇 |
2013年 | 57篇 |
2012年 | 62篇 |
2011年 | 83篇 |
2010年 | 45篇 |
2009年 | 43篇 |
2008年 | 84篇 |
2007年 | 78篇 |
2006年 | 81篇 |
2005年 | 51篇 |
2004年 | 38篇 |
2003年 | 47篇 |
2002年 | 38篇 |
2001年 | 24篇 |
2000年 | 21篇 |
1999年 | 17篇 |
1998年 | 13篇 |
1997年 | 10篇 |
1996年 | 10篇 |
1995年 | 9篇 |
1994年 | 19篇 |
1993年 | 11篇 |
1992年 | 9篇 |
1991年 | 9篇 |
1990年 | 8篇 |
1989年 | 9篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1986年 | 12篇 |
1985年 | 19篇 |
1984年 | 12篇 |
1983年 | 11篇 |
1982年 | 10篇 |
1981年 | 10篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1978年 | 9篇 |
1977年 | 8篇 |
1976年 | 13篇 |
1975年 | 7篇 |
1974年 | 4篇 |
1973年 | 7篇 |
排序方式: 共有1172条查询结果,搜索用时 15 毫秒
31.
An on-line purification method for catecholamines was studied using a flow system equipped with an alumina microcolumn. The procedure involves catecholamine adsorption, column washing and catecholamine elution steps. The system is designed not to decompose catecholamines under alkaline conditions in the adsorption step. Flow-rates and times for different solutions delivered in each step (alkaline buffer for adsorption, water for washing and an acidic solution for elution), column length and sample volume to be loaded were systematically investigated by liquid chromatography. Under optimum conditions, norepinephrine, epinephrine, dopamine and 3,4- dihydroxybenzylamine (internal standard) can be purified with recoveries of ? 90% within 11 min with manual operation. This method was efficiently applied to urine samples and the results indicate the possibility that catecholamines in biological samples are automatically purified. 相似文献
32.
Yasuda K Torii T Yasui K Iida Y Tuziuti T Nakamura M Asakura Y 《Ultrasonics sonochemistry》2007,14(6):699-704
The ultrasonic reactor with dual frequency was used and the effect of frequency on the fluorescence intensity of terephthalate ion was experimentally investigated in the frequency range from 176 to 635 kHz. The sonochemical reaction fields were visualized by using sonochemical luminescence of luminol solution. Compared with the fluorescence intensity of terephthalate ion for single frequency, the fluorescence intensity for dual frequency increased. The fluorescence intensity ratio of dual frequency to single frequency had maximum value when the frequency of transducer attached at the bottom wall was comparable in magnitude to that at the side wall. In the case of dual frequency, the sonochemical reaction fields became more extensive in the reactor and more intensive around the center of the reactor. 相似文献
33.
Toru Sasahara 《Journal of Geometry and Physics》2010,60(6-8):884-895
We classify biminimal Lagrangian surfaces in complex space forms under the condition that the integral curves of Maslov vector field are geodesics. 相似文献
34.
Takahiro Egawa Kazuhisa Hirabayashi Dr. Yuichiro Koide Chiaki Kobayashi Dr. Naoya Takahashi Dr. Tomoko Mineno Dr. Takuya Terai Dr. Tasuku Ueno Dr. Toru Komatsu Dr. Yuji Ikegaya Prof. Norio Matsuki Prof. Tetsuo Nagano Dr. Kenjiro Hanaoka 《Angewandte Chemie (International ed. in English)》2013,52(14):3874-3877
35.
Naoyuki Masuda Osamu Yamamoto Masahiro Fujii Tetsuro Ohgami Ayako Moritomo Toru Kontani 《合成通讯》2013,43(17):2305-2316
Various N‐3‐alkylated thiazolidenesulfonamide derivatives were efficiently prepared by the direct endo‐selective alkylation of thiazolylsulfonamides. The effects of different bases and solvents were investigated, and the NaH–THF combination was found to be the most effective at conferring high yields and endo‐selectivity. 相似文献
36.
Hemin was physically adsorbed onto porous carbon felt (CF), a microelectrode ensemble of micro-carbon fiber (ca. 7 μm in diameter) and possessing a three-dimensional random structure. The hemin-CF exhibited a well-defined redox wave that is due to Fe(III)/Fe(II) redox process in hemin, with a formal potential of ?0.32 V (vs. Ag/AgCl) in deoxygenated buffer solution of pH 7.0. The surface coverage of the electroactive hemin molecules on the surface of the CF was calculated to be 5.0?×?10?11 mol cm?2, and the apparent heterogeneous electron transfer rate constant is 3.35 s?1. The hemin-CF electrode displays excellent electrocatalytic activity for the reduction of dissolved oxygen (DO), and the magnitude of the cathodic current increases with increasing concentrations of DO in the sample solution. The electrode was used as a flow-through detector for sensitive and rapid consecutive determination of DO. Deoxygenated pH 7.0 solutions were analyzed at a flow rate of 8.0 mL min?1 at an applied potential of ?0.2 V, and highly reproducible cathodic peak current responses to DO were observed in the 0.72 to 13.3 mg L?1 concentration range. The maximum throughput is 170 samples h?1. The hemin-CF-based amperometric flow-sensor was applied to determine the concentration of DO in environmental water samples. Graphical abstract
Hemin was physically adsorbed onto porous carbon felt (CF), a microelectrode ensemble of micro-carbon fiber (ca. 7 μm in diameter). The hemin-CF electrode was used as a flow-through detector for highly sensitive and rapid determination of dissolved oxygen. 相似文献
37.
Toru Okawara Masaaki Abe Hisashi Shimakoshi Yoshio Hisaeda 《Research on Chemical Intermediates》2013,39(1):161-176
A Pd(II) complex, Pd(TPrPc-OH) (1, TPrPc-OH = 9-hydroxy-2,7,12,17-tetrapropylporphycenato dianion), has been synthesized and characterized. 1H NMR spectroscopy revealed that compound 1 exists as its enol form in solution. The H atom of the hydroxy group in 1 was exchanged with deuterium on addition of ethanol-d 6. UV–visible spectra showed a red shift of the Q band of 1 in THF compared with that of the acetoxy derivative Pd(TPrPc-OAc) (2, TPrPc-OAc = 9-acetoxy-2,7,12,17-tetrapropylporphycenato dianion). The pK a value of the hydroxy group in 1 was determined, by means of a UV–visible titration experiment, to be 10.56. A cyclic voltammogram of 1 in a mixture of THF and Britton–Robinson buffered aqueous solution revealed one-electron and one-proton coupled transfer in the oxidation process in the pH range from 2.7 to 10.5, which was identified by pH-varying experiments and the Pourbaix diagram. Transient absorption spectroscopy revealed that an electron-transfer reaction occurred from the triplet excited-state of 1 to 2,3,5,6-tetramethyl-1,4-benzoquinone (duroquinone, DQ) upon pulse laser irradiation at 532 nm. Such an intermolecular photoinduced electron-transfer reaction was not observed between the Ni analog, Ni(TPrPc-OH), and DQ. The reaction rate constant, k q, was indicative of a kinetic isotope effect with k q(H)/k q(D) = 1.7, supporting the belief that the exited-state electron transfer from 1 to DQ is accompanied by proton transfer. 相似文献
38.
39.
Toru Oba Yubi TatenoMisaki Ihara Takanori FukusumiNatsuki Takei Satoshi Ito 《Tetrahedron letters》2014
Radical reactions of a C3-vinylated chlorophyll derivative, methyl pyropheophorbide-a, which were induced by thiols and the conventional initiator azobisisobutyronitrile (AIBN) were examined in vitro for the first time. Thiyl radicals attacked regioselectively at the sole C3-vinyl group, and the anti-Markovnikov sulfanyl adducts were obtained as major products. The other peripheral substituents, as well as the chlorin macrocycle, remained intact. The AIBN-induced radical reaction competed with co-oxidation that afforded the C3-formyl chlorin. This method can open new routes to derivatization of vinyl chlorins. 相似文献
40.
Dr. Neil J. Stewart Hitomi Nakano Shuto Sugai Mitsushi Tomohiro Yuki Kase Yoshiki Uchio Dr. Toru Yamaguchi Yujirou Matsuo Dr. Tatsuya Naganuma Dr. Norihiko Takeda Dr. Ikuya Nishimura Dr. Hiroshi Hirata Dr. Takuya Hashimoto Dr. Shingo Matsumoto 《Chemphyschem》2021,22(10):915-923
Hyperpolarized [1-13C]fumarate is a promising magnetic resonance imaging (MRI) biomarker for cellular necrosis, which plays an important role in various disease and cancerous pathological processes. To demonstrate the feasibility of MRI of [1-13C]fumarate metabolism using parahydrogen-induced polarization (PHIP), a low-cost alternative to dissolution dynamic nuclear polarization (dDNP), a cost-effective and high-yield synthetic pathway of hydrogenation precursor [1-13C]acetylenedicarboxylate (ADC) was developed. The trans-selectivity of the hydrogenation reaction of ADC using a ruthenium-based catalyst was elucidated employing density functional theory (DFT) simulations. A simple PHIP set-up was used to generate hyperpolarized [1-13C]fumarate at sufficient 13C polarization for ex vivo detection of hyperpolarized 13C malate metabolized from fumarate in murine liver tissue homogenates, and in vivo 13C MR spectroscopy and imaging in a murine model of acetaminophen-induced hepatitis. 相似文献