全文获取类型
收费全文 | 144742篇 |
免费 | 34197篇 |
国内免费 | 10173篇 |
专业分类
化学 | 120892篇 |
晶体学 | 1269篇 |
力学 | 8975篇 |
综合类 | 549篇 |
数学 | 14562篇 |
物理学 | 42865篇 |
出版年
2024年 | 658篇 |
2023年 | 5380篇 |
2022年 | 4955篇 |
2021年 | 6135篇 |
2020年 | 8202篇 |
2019年 | 6251篇 |
2018年 | 5467篇 |
2017年 | 3798篇 |
2016年 | 10153篇 |
2015年 | 9911篇 |
2014年 | 10488篇 |
2013年 | 12423篇 |
2012年 | 12315篇 |
2011年 | 10708篇 |
2010年 | 9578篇 |
2009年 | 9314篇 |
2008年 | 7501篇 |
2007年 | 6723篇 |
2006年 | 5578篇 |
2005年 | 4674篇 |
2004年 | 3456篇 |
2003年 | 2715篇 |
2002年 | 2451篇 |
2001年 | 2017篇 |
2000年 | 1787篇 |
1999年 | 2098篇 |
1998年 | 1872篇 |
1997年 | 1803篇 |
1996年 | 1968篇 |
1995年 | 1636篇 |
1994年 | 1544篇 |
1993年 | 1377篇 |
1992年 | 1166篇 |
1991年 | 1050篇 |
1990年 | 847篇 |
1989年 | 638篇 |
1988年 | 577篇 |
1987年 | 480篇 |
1986年 | 454篇 |
1985年 | 414篇 |
1984年 | 346篇 |
1977年 | 337篇 |
1976年 | 397篇 |
1975年 | 488篇 |
1974年 | 516篇 |
1972年 | 387篇 |
1971年 | 377篇 |
1970年 | 554篇 |
1969年 | 437篇 |
1968年 | 466篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
932.
933.
A chiral liquid chromatographic method for determination of the enantiomeric purity of both l-carnitine and acetyl-l-carnitine is described. Separation of the enantiomers of dl-carnitine and acetyl-dl-carnitine was achieved on a commercial chiral column (Chiralcel OD-R) after derivatization with (alpha-bromo)methyl phenyl ketone. Introduction of this lipophilic UV chromophoric group to the carnitine and acetylcarnitine molecules improved their retention, resolution, and UV detection. The mobile phase was 74:26 (v/v) 0.5 mol L-1 sodium perchlorate–acetonitrile, pH 3.8, and the flow rate was 0.4 mL min-1. Detection was performed at 235 nm. The method is selective and reliable for determination of the enantiomeric purity of bulk drug substances l-carnitine and acetyl-l-carnitine. 相似文献
934.
Xiangke Wang Jinzhou Du Zuyi Tao Zhongxiu Fan 《Journal of Radioanalytical and Nuclear Chemistry》2003,258(1):133-138
The migration of radionuclides 85+89Sr2+, 134Cs+, 125I- and 75SeO3
2- in calcareous soil from Yuzhong county of Gansu Province (China) at pH 7.8±0.2 and 152+154Eu(III) in red earth from Yingtan county of Jiangxi Province (China) at pH 4.6±0.2, in presence of CaCl2 was studied using column experiments. Results indicate that the negative anions, iodide and selenide are mobile nuclides while the migration of positive cations is related to the sorption capacity for the element. Iodide can be assumed to be non-reactive in calcareous soil. The breakthrough curves (BTCs) were fitted to the analytical solution or numerical solution of one-dimensional convection-dispersion transport models. Good agreements were obtained between the measured and predicted concentration profiles. 相似文献
935.
A simple and sensitive fluorimetric method for the determination of ascorbic acid (AA) is described. The method is based on the condensation reaction between AA and o-phenylenediamine (OPDA) in the absence of the oxidant. The fluorescence intensity is measured at excitation and emission wavelengths of 360 and 430 nm, respectively. Under optimum condition, a linear relationship is obtained between the fluorescence intensity and the concentration of AA in the range of 0.05-40 μg ml−1. The detection limit is 0.006 μg ml−1, which is obviously lower than that of other fluorimetric methods reported. 相似文献
936.
通过流动相中电解质浓度对毛细管电色谱柱效能的流动相平均线速度的影响,研究了CEC中双电层叠加现象。提出选择合适电解质组成的浓度及在制备色谱柱过程中避免细小和破碎的固定相颗粒进入柱中,以有效地减小双电层叠加作用。 相似文献
937.
Reaction solutions of selectfluor (1) with triphenylethylene (4a) and tetraphenylethylene (4b) were monitored by ESI-MS and ESI-MS/MS. Detection and characterization of the key radical cationic intermediates 5a.+ and 5b.+) fully supports the SET mechanism in electrophilic fluorination as depicted above. [reaction: see text] 相似文献
938.
A new element tracer technique has firstly been established to estimate the contributions of mineral aerosols from both inside and outside Beijing. The ratio of Mg/Al in aerosol is a feasible element tracer to distinguish between the sources of inside and outside Beijing. Mineral aerosol, inorganic pollution aerosol mainly as sulfate and nitrate, and organic aerosol are the major components of airborne particulates in Beijing, of which mineral aerosol accounted for 32%―67% of total suspended particles (TSP), 10%―70% of fine particles (PM2.5), and as high as 74% and 90% of TSP and PM2.5, respectively, in dust storm. The sources from outside Beijing contributed 62% (38%―86%) of the total mineral aerosols in TSP, 69% (52%―90%) in PM10, and 76% (59%―93%) in PM2.5 in spring, and 69% (52%―83%), 79% (52%―93%), and 45% (7%―79%) in TSP, PM10, and PM2.5, respectively, in winter, while only ~20% in summer and autumn. The sources from outside Beijing contributed as high as 97% during dust storm and were the dominant source of airborne particulates in Beijing. The contributions from outside Beijing in spring and winter are higher than those in summer, indicating clearly that it was related to the various meteorological factors. 相似文献
939.
Song C Wang D Gu G Lin Y Yang J Chen L Fu X Hu Z 《Journal of colloid and interface science》2004,272(2):340-344
Silver-coated poly(methyl acrylic acid) (PSA) core-shell colloid particles were prepared by an in situ chemical reduction method. Crystalline silver/titania composite hollow spheres were obtained by coating the as-prepared PSA/silver particles with an amorphous titania layer and subsequently calcining in Ar atmosphere. SEM and TEM investigation indicated that the size of the as-prepared PSA/silver and PSA/silver/TiO(2) core-shell particles and silver/titania composite hollow particles was fairly uniform and the wall thickness of the hollow spheres was in the range of 40-80 nm. UV-vis absorption spectra were recorded to investigate their optical properties. 相似文献
940.