全文获取类型
收费全文 | 7699篇 |
免费 | 2089篇 |
国内免费 | 474篇 |
专业分类
化学 | 1268篇 |
晶体学 | 37篇 |
力学 | 201篇 |
综合类 | 51篇 |
数学 | 353篇 |
物理学 | 4457篇 |
无线电 | 3895篇 |
出版年
2024年 | 23篇 |
2023年 | 57篇 |
2022年 | 103篇 |
2021年 | 158篇 |
2020年 | 166篇 |
2019年 | 152篇 |
2018年 | 169篇 |
2017年 | 235篇 |
2016年 | 282篇 |
2015年 | 327篇 |
2014年 | 592篇 |
2013年 | 513篇 |
2012年 | 674篇 |
2011年 | 674篇 |
2010年 | 575篇 |
2009年 | 530篇 |
2008年 | 588篇 |
2007年 | 609篇 |
2006年 | 553篇 |
2005年 | 488篇 |
2004年 | 421篇 |
2003年 | 397篇 |
2002年 | 317篇 |
2001年 | 257篇 |
2000年 | 214篇 |
1999年 | 207篇 |
1998年 | 172篇 |
1997年 | 164篇 |
1996年 | 155篇 |
1995年 | 99篇 |
1994年 | 79篇 |
1993年 | 64篇 |
1992年 | 60篇 |
1991年 | 59篇 |
1990年 | 25篇 |
1989年 | 30篇 |
1988年 | 12篇 |
1987年 | 19篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1980年 | 4篇 |
1979年 | 10篇 |
1977年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
42.
《Electroanalysis》2004,16(5):355-359
Water present in undiluted acetic acid can be monitored in situ with Pt and Au microelectrodes using differential pulse and square‐wave voltammetries. Both reduction and oxidation peaks can be obtained. The best quantitative analytical results were obtained for the anodic peak, the Pt microelectrode, and differential pulse voltammetry. The anodic water peak is located at +1.55 V vs. the quasi reference Pt electrode. The voltammetric peak obtained at Pt electrode is apparently not a diffusional one, however, the calibration plot obtained by employing this peak is linear over a wide concentration range, up to 4 mol dm?3. The detection limit has been estimated as 2.3 mM or 0.0043 v/v%. The developed method may be particularly useful, since the Karl Fischer method can not be used to determine water in glacial acetic acid due to the estrification reaction of acetic acid with methanol. A voltammetric wave of undiluted acetic acid could not be obtained in the positive and negative ranges of potential. 相似文献
43.
DFT calculations have been carried out for 2-, 3- and 4-methoxybenzyl alcohol radical cations (1+, 3+ and 4+, respectively) and the α-methyl derivatives 2+ and 5+ using the UB3LYP/6-31G(d) method. The theoretical results have been compared with the experimental rate constants for deprotonation of 1+-5+ under acidic and basic conditions. In acidic solution, the decay of 1+-5+ proceeds by cleavage of the C-H bond, while in the presence of −OH all the radical cations undergo deprotonation from the α-OH group. This pH-dependent change in mechanism has been interpreted qualitatively in terms of simple frontier molecular orbital theory. The −OH induced α-O-H deprotonation is consistent with a charge controlled reaction, whereas the C-H deprotonation, observed when the base is H2O, appears to be affected by frontier orbital interactions. 相似文献
44.
《Electroanalysis》2003,15(4):254-262
The new electrochemical double pulse technique, known as additive differential normal pulse voltammetry (ADNPV) when there is no restriction on the duration of both pulses, and additive differential pulse voltammetry (ADPV) when t2?t1, has been applied to a pseudo‐first‐order catalytic mechanism. The expressions obtained here are applicable to planar and spherical electrodes, of any radius. This is of great interest since the size of the electrode plays an important role in the preponderating of diffusive and kinetics processes. The signal obtained with this technique presents the same morphological characteristics as the triple pulse technique, double differential pulse voltammetry (DDPV) and is more advantageous than DDPV and than the double pulse one, differential pulse voltammetry (DPV). 相似文献
45.
The behaviour of oxazepam in adsorptive stripping voltammetry was studied taking into account those conditions which have an influence on the accumulation step (electrolyte, pH, time, potential, drop size and stirring rate), rest time and stripping step (pulse amplitude and scan rate). Oxazepam can be determined at a hanging mercury drop electrode by differential-pulse voltammetry in 0.008 M Britton-Robinson buffer at pH 2.0 with a ?0.50 V accumulation potential. Its detection limit was found to be 3.6 × 10?10 M (30-s accumulation) and the relative standard deviation for oxazepam concentrations in the range 2.8 × 10?8?4.0 × 10?7 M is lower than 2.8% (80-s accumulation). In addition, a procedure using adsorptive stripping voltammetry was developed to study the interactions occurring between human albumin and the camazepam metabolic series (camazepam, temazepam and oxazepam). The interactions decreased in the order temazepam ? oxazepam ? camazepam and the groups and structural modifications favouring interaction were determined. 相似文献
46.
47.
48.
49.
50.