全文获取类型
收费全文 | 2388篇 |
免费 | 67篇 |
国内免费 | 12篇 |
专业分类
化学 | 1786篇 |
晶体学 | 43篇 |
力学 | 18篇 |
综合类 | 1篇 |
数学 | 160篇 |
物理学 | 459篇 |
出版年
2022年 | 16篇 |
2021年 | 29篇 |
2020年 | 24篇 |
2019年 | 37篇 |
2018年 | 22篇 |
2017年 | 13篇 |
2016年 | 46篇 |
2015年 | 36篇 |
2014年 | 65篇 |
2013年 | 126篇 |
2012年 | 109篇 |
2011年 | 113篇 |
2010年 | 66篇 |
2009年 | 58篇 |
2008年 | 94篇 |
2007年 | 128篇 |
2006年 | 119篇 |
2005年 | 129篇 |
2004年 | 115篇 |
2003年 | 94篇 |
2002年 | 101篇 |
2001年 | 59篇 |
2000年 | 65篇 |
1999年 | 40篇 |
1998年 | 23篇 |
1997年 | 24篇 |
1996年 | 59篇 |
1995年 | 36篇 |
1994年 | 27篇 |
1993年 | 22篇 |
1992年 | 42篇 |
1991年 | 31篇 |
1990年 | 27篇 |
1989年 | 26篇 |
1988年 | 47篇 |
1987年 | 20篇 |
1986年 | 20篇 |
1985年 | 33篇 |
1984年 | 25篇 |
1983年 | 28篇 |
1982年 | 35篇 |
1981年 | 27篇 |
1980年 | 23篇 |
1979年 | 34篇 |
1978年 | 20篇 |
1976年 | 11篇 |
1975年 | 12篇 |
1974年 | 13篇 |
1973年 | 21篇 |
1972年 | 11篇 |
排序方式: 共有2467条查询结果,搜索用时 15 毫秒
181.
Takeuchi Y Nishikawa M Hachiya H Yamamoto H 《Magnetic resonance in chemistry : MRC》2005,43(8):662-664
High-resolution solid-state magic angle spinning (73)Ge NMR spectra of some organogermanium compounds were measured. Most tetrasubstituted germanes with identical substituents exhibited signals except for one case. Tetrasubstituted germanes with two kinds of different but somewhat similar substituents exhibited broad peaks. Trisubstituted germanes failed to show signals, indicating the importance of symmetry around germanium. 相似文献
182.
Nano-sized phosphine and pyridine ligands having tetraphenylphenyl-, m-terphenyl-, poly(benzylether) moieties were synthesized. These ligands showed a remarkable effect on homogeneous transition
metal catalyzed reactions. Pd(II) complexes with tetraphenylphenyl substituted pyridine ligands show high catalytic activities
for oxidation of ketones suppressing Pd black formation and maintains the catalytic activity for a long time. Rh(I) complex
catalysts with m-terphenyl substituted phosphine ligands showed remarkable rate acceleration in the hydrosilylation of ketones. In addition,
several phosphinocalixarene ligands were synthesized and their coordination studies with Pd(II), Pt(II), Ru(II), Ir(I), and
Rh(I) metals were documented. Ir(I) and Rh(I) cationic complexes with a 1,3,5-triphosphinocalix[6]arene ligand showed dynamic
behavior with size-selective molecular recognition. 相似文献
183.
Using a technique of laser flash photolysis coupled with vacuum ultraviolet laser-induced fluorescence spectroscopy, the rate coefficients of O(1D) reactions with N2, O2, N2O, and H2O at 295 ± 2 K have been determined to be , kO2=(4.06±0.24)×10-11, kN2O=(1.35±0.08)×10-10 and . The quoted uncertainties include estimated errors and are the 95% confidence level. The kN2 and kN2O values obtained are larger than the current NASA/JPL recommendations by 26% and 16%, respectively, although they are still within the error limits associated with the recommendations. 相似文献
184.
Summary Retention behavior of anions and cations on anion-exchangers modified with dextran sulfate has been investigated. Retention
of anions was remarkably reduced by the modification, and the retention factor decreased with decreasing eluent concentration
when sodium sulfate was used as the eluent. Cations were also retained on the modified stationary phase, and alkali and alkaline-earth
metal ions were separated using copper sulfate or tris(2,2′-bipyridyl)ruthenium chloride as eluent. The size of the dextran
sulfate strongly affected the retention behavior of analyte ions. 相似文献
185.
Yuichi Komazaki Masashi Hiratsuka Yasushi Narita S. Tanaka Tomio Fujita 《Fresenius' Journal of Analytical Chemistry》1999,363(7):686-695
An automated continuous measurement system for the monitoring of formaldehyde (HCHO) and acetaldehyde (CH3CHO) in the urban atmosphere was developed by using an annular diffusion scrubber in conjunction with a high-performance liquid
chromatograph (HPLC). With this technique, atmospheric HCHO and CH3CHO were effectively collected by the annular diffusion scrubber which consists of a porous polytetrafluoroethylene (PTFE)
tube disposed concentrically within a Pyrex-glass tube and a scrubbing solution. 2,4-Dinitrophenylhydrazine (DNPH) was selected
as the scrubbing solution for collecting HCHO and CH3CHO, which are derivatized to 2,4-dinitrophenylhydrazone-formaldehyde (DNPH-HCHO) and 2,4-dinitrophenylhydrazone-acetaldehyde
(DNPH-CH3CHO), respectively. An aliquot of the sample solution was automatically injected into an HPLC equipped with a semi-micro ODS
column and a UV-VIS detector for separating and determining DNPH-HCHO and DNPH-CH3CHO. All the operations are sequenced by a programmable controller, and automated continuous measurements are performed with
a typical temporal resolution of 1 h. The collection efficiencies of HCHO and CH3CHO were about 97% and 93%, respectively, at an air flow rate of 0.2 L/min. The lower detection limits (3σ of the blank hydrazones)
of HCHO and CH3CHO were 0.05 ppbv and 0.10 ppbv, respectively, in the case of 12-L air sample volume. Analytical response of a standard
solution of DNPH-HCHO and DNPH-CH3CHO by the HPLC during a 10-day continuous measurement was unchanged and the relative standard deviation (RSD) was < 1.0%.
Interferences from O3 and NO2 were insignificant in this annular diffusion scrubber method. Both for HCHO and CH3CHO measurements, concentrations from this developed system well agreed with those measured by a DNPH Silica cartridge method.
Received: 15 July 1998 / Revised: 5 October 1998 / Accepted: 7 October 1998 相似文献
186.
187.
Toshinobu Suzuki Yasushi Nagae Keiryo Mitsuhashi 《Journal of heterocyclic chemistry》1986,23(5):1419-1421
Novel synthesis of the title compounds by the facile cyclization between 2,3-dichloro-5,6-dicyanopyrazine and various 2-aminopyridines under relatively mild conditions is described. The reactivity depended on the basicity of 2-aminopyridines. 相似文献
188.
Yoshitsugu Arai Shū-ichi Kuwayama Yoshio Takeuchi Toru Koizumi 《Tetrahedron letters》1985,26(50):6205-6208
The Diels-Alder reaction of a novel chiral dienophile, alkyl ()-2--tolylsulfinylacrylates 1 with anthracene and cyclopentadiene showed high diastereoselectivity under the chelation controlled condition. 相似文献
189.
Novel synthesis of heterocyclic spirans by tandem cycloaddition to sulfur-containing heterocumulenes
Yoshiki Ohshiro Hitoshi Nanimoto Hiroyuki Tanaka Mitsuo Komatsu Toshio Agawa Noritake Yasuoka Yasushi Kai Nobutami Kasai 《Tetrahedron letters》1985,26(25):3015-3018
Novel Ni(C0)4-promoted tandem cycloadditions of diphenylcyclo- propenone to isothiocyanates and to CS2 were found to provide new heterocyclic spirans, pyrroline-2-one-5-spiro-5′-thiolene-4′-ones and a thiolene-2-one-5-spiro-5′-thiolene-4′-one, respectively, in moderate yields. 相似文献
190.