全文获取类型
收费全文 | 2009篇 |
免费 | 83篇 |
国内免费 | 47篇 |
专业分类
化学 | 1237篇 |
晶体学 | 13篇 |
力学 | 64篇 |
综合类 | 4篇 |
数学 | 223篇 |
物理学 | 598篇 |
出版年
2021年 | 16篇 |
2020年 | 17篇 |
2019年 | 18篇 |
2018年 | 15篇 |
2017年 | 25篇 |
2016年 | 38篇 |
2015年 | 30篇 |
2014年 | 34篇 |
2013年 | 92篇 |
2012年 | 87篇 |
2011年 | 107篇 |
2010年 | 49篇 |
2009年 | 62篇 |
2008年 | 101篇 |
2007年 | 105篇 |
2006年 | 96篇 |
2005年 | 95篇 |
2004年 | 88篇 |
2003年 | 64篇 |
2002年 | 53篇 |
2001年 | 48篇 |
2000年 | 49篇 |
1999年 | 52篇 |
1998年 | 27篇 |
1997年 | 23篇 |
1996年 | 25篇 |
1995年 | 41篇 |
1994年 | 36篇 |
1993年 | 37篇 |
1992年 | 48篇 |
1991年 | 23篇 |
1990年 | 21篇 |
1989年 | 19篇 |
1988年 | 20篇 |
1987年 | 21篇 |
1986年 | 15篇 |
1985年 | 34篇 |
1984年 | 14篇 |
1983年 | 19篇 |
1982年 | 26篇 |
1981年 | 23篇 |
1980年 | 16篇 |
1979年 | 26篇 |
1978年 | 25篇 |
1977年 | 25篇 |
1976年 | 20篇 |
1975年 | 21篇 |
1974年 | 29篇 |
1973年 | 23篇 |
1934年 | 16篇 |
排序方式: 共有2139条查询结果,搜索用时 15 毫秒
21.
King RC Gundersdorf R Fernández-Metzler CL 《Rapid communications in mass spectrometry : RCM》2003,17(21):2413-2422
A hybrid linear ion trap/triple quadrupole mass spectrometer was used to demonstrate the value of collecting full scan qualitative data during quantitative analysis of target compounds. We present examples of the additional information that can be obtained from plasma samples analyzed primarily for target compound concentrations. This information includes detection of circulating metabolites, dosing vehicle, interfering matrix components, and potential interfering drug conjugates. Additionally, the quantitative results from selected reaction monitoring (SRM) analysis and from combined full scan and SRM analysis (SRM/EMS) were compared. The quantitative data in both scan modes are acceptable in terms of sensitivity, accuracy and precision. One can conclude from this work that the hybrid linear ion trap/triple quadrupole mass analyzer can provide in a single analysis both useful qualitative data, and accurate and precise quantitative data from the samples routinely prepared and analyzed for target drug concentrations. 相似文献
22.
Steady-state mass transfer experiments were done to determine whether certain strains of bacteria in homogeneous suspension will accumulate at the gas:liquid interface and thereby significantly increase the oxygen transfer rate to the suspension. In particular, with suspensions ofB. licheniformis, the measured transfer rates are as much as three times the rate expected for a uniform suspension. In contrast, suspensions ofM. luteus show no increase in oxygen flux above expected values. The fact thatB. licheniformis is motile, whereasM. luteus is not suggests that cell motility may play an important role in the accumulation process.
相似文献23.
Frank D. King 《Tetrahedron》2007,63(9):2053-2056
A high yielding cyclisation of the readily available N-(4,4-diethoxybutyl)-2-(3,4-dimethoxyphenyl)acetamide to 8,9-bis(methyloxy)-2,3,6,10b-tetrahydropyrrolo[2,1-a]isoquinolin-5(1H)-one is described. The latter can be reduced with either AlH3 or BH3 to (±)-crispine A in an overall yield of 55%. 相似文献
24.
[reaction: see text] Glucuronyl iodide 1 has been studied in detail as a "disarmed" glycosyl donor. In a model reaction, using N-iodosuccinimide (NIS) as a promoter and 2-phenylethanol as acceptor, best results were obtained using NIS with I(2), followed by trimethylsilyltrifluoromethanesulfonate (TMSOTf). When a series of primary and secondary alcohols was glycosylated using these conditions, yields of 60-83% of beta-glucuronides were obtained. Various "nonheavy" metal salts also effectively catalyzed the model reaction but led to significant amounts of alpha-product with less reactive secondary alcohols. 相似文献
25.
Absorption transitions to vibrational levels close to the A state dissociation limit of ICI have been examined using a two-photon sequential absorption technique. The discrete rotational structures of I37 Cl bands to within 0.7 cm?1 of the limit have been selectively excited and analysed. A value of 17557.514 ± 0.030 cm?1 has been obtained for the I(2Po) + Cl(2Po) dissociation energy De, relative to the minimum of the ICI ground state potential well. The two-photon technique can be used to excite and display separately the high resolution absorption spectra of different isotopic species of a molecule which are contained in a mixture. 相似文献
26.
The kick-out model for impurity diffusion in semiconductors is studied. The kick-out mechanism is thought to play an important rôle in a number of applications, including the diffusion of zinc and chromium in gallium arsenide. Asymptotic solutions are derived for both one- and two-dimensional surface source problems. In the one-dimensional case, a mechanism for the destruction of self-interstitials is also incorporated. The calculated diffusion profiles have shapes which are typical of diffusion systems in which the kick-out mechanism is believed to be active. For the two-dimensional problem, contours of constant impurity concentration are calculated and some are found to have the bird's beak shape which is frequently observed in experiments. 相似文献
27.
Demonstration of a fundamental quantum logic gate 总被引:1,自引:0,他引:1
28.
McFarland KS Naples D Arroyo CG Auchincloss P de Barbaro P Bazarko AO Bernstein RH Bodek A Bolton T Budd H Conrad J Drucker RB Harris DA Johnson RA Kim JH King BJ Kinnel T Koizumi G Koutsoliotas S Lamm MJ Lefmann WC Marsh W McNulty C Mishra SR Nienaber P Nussbaum M Oreglia MJ Perera L Quintas PZ Romosan A Sakumoto WK Schumm BA Sciulli FJ Seligman WG Shaevitz MH Smith WH Spentzouris P Steiner R Stern EG Vakili M Yang UK 《Physical review letters》1995,75(22):3993-3996
29.
30.
Arroyo CG King BJ Bachmann KT Bazarko AO Bolton T Foudas C Lefmann WC Leung WC Mishra SR Oltman E Quintas PZ Rabinowitz SA Sciulli FJ Seligman WG Shaevitz MH Merritt FS Oreglia MJ Schumm BA Bernstein RH Borcherding F Fisk HE Lamm MJ Marsh W Merritt KW Schellman HM Yovanovitch DD Bodek A Budd HS de Barbaro P Sakumoto WK Kinnel T Sandler PH Smith WH 《Physical review letters》1994,72(22):3452-3455