全文获取类型
收费全文 | 34584篇 |
免费 | 2120篇 |
国内免费 | 2101篇 |
专业分类
化学 | 17305篇 |
晶体学 | 171篇 |
力学 | 771篇 |
综合类 | 613篇 |
数学 | 7185篇 |
物理学 | 12760篇 |
出版年
2023年 | 266篇 |
2022年 | 399篇 |
2021年 | 1196篇 |
2020年 | 781篇 |
2019年 | 912篇 |
2018年 | 694篇 |
2017年 | 674篇 |
2016年 | 963篇 |
2015年 | 1036篇 |
2014年 | 1320篇 |
2013年 | 2219篇 |
2012年 | 1496篇 |
2011年 | 1900篇 |
2010年 | 1688篇 |
2009年 | 2160篇 |
2008年 | 2228篇 |
2007年 | 2295篇 |
2006年 | 1830篇 |
2005年 | 1143篇 |
2004年 | 1063篇 |
2003年 | 1035篇 |
2002年 | 993篇 |
2001年 | 975篇 |
2000年 | 735篇 |
1999年 | 550篇 |
1998年 | 613篇 |
1997年 | 375篇 |
1996年 | 461篇 |
1995年 | 405篇 |
1994年 | 413篇 |
1993年 | 451篇 |
1992年 | 453篇 |
1991年 | 310篇 |
1990年 | 251篇 |
1989年 | 212篇 |
1988年 | 244篇 |
1987年 | 194篇 |
1986年 | 214篇 |
1985年 | 321篇 |
1984年 | 229篇 |
1983年 | 144篇 |
1982年 | 288篇 |
1981年 | 467篇 |
1980年 | 428篇 |
1979年 | 466篇 |
1978年 | 371篇 |
1977年 | 281篇 |
1976年 | 238篇 |
1974年 | 74篇 |
1973年 | 154篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
101.
A simple, sensitive and rapid ultra‐high‐performance liquid chromatography–electrospray ionization–tandem mass spectrometry method was developed and validated for the quantification of warfarin and 7‐hydroxy warfarin in Sprague Dawley (SD) rats. Animals were administered a single dose of warfarin sodium formulations (crystalline and amorphous) at 12 mg/kg via oral gavage and blood was drawn over a 96‐h time course. Sample process recoveries, matrix effect and analyte stability were determined. The linearity for warfarin and 7‐hydroxy warfarin was from 5 to 2000 ng/mL in blank SD rat plasma. Correlation coefficients (r2) for standard calibration curves were >.98 and analytes quantified within ±15% of target at all calibrator concentrations. The average percent accuracy and precision for intra‐ and inter‐day were 93.7%–113.8% and ≤12.1%, respectively, for warfarin and 7‐hydroxy warfarin, across the quality control standards (5, 10, 500, 1800 and 2000 ng/mL). Acceptable analytical recovery (>55%) was achieved with process efficiencies >41.5% and matrix effects <139.9% over the analytical range. Both analytes were stable in stock solution, autosampler, benchtop and three cycles of freeze–thaw with percent accuracy ≥90.2% and precision (percent relative standard deviation) ≤14%. The validated method was successfully applied to a pre‐clinical bioavailability study of crystalline and amorphous warfarin sodium formulations in SD rats. 相似文献
102.
Jinghua YANG 《数学年刊B辑(英文版)》2019,40(2):227-236
In this paper, the author gives the discrete criteria and J\o
rgensen inequalities of subgroups for the special linear group on
$\overline{\mathrm{F}}((t))$ in two and higher dimensions. 相似文献
103.
104.
105.
106.
Dr. Lingxing Zeng Biyu Kang Fenqiang Luo Yixing Fang Cheng Zheng Junbin Liu Renpin Liu Xinye Li Prof. Dr. Qinghua Chen Prof. Dr. Mingdeng Wei Prof. Dr. Qingrong Qian 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(58):13411-13421
Sodium/potassium-ion batteries (SIBs/PIBs) arouse intensive interest on account of the natural abundance of sodium/potassium resources, the competitive cost and appropriate redox potential. Nevertheless, the huge challenge for SIBs/PIBs lies in the scarcity of an anode material with high capacity and stable structure, which are capable of accommodating large-size ions during cycling. Furthermore, using sustainable natural biomass to fabricate electrodes for energy storage applications is a hot topic. Herein, an ultra-small few-layer nanostructured MoSe2 embedded on N, P co-doped bio-carbon is reported, which is synthesized by using chlorella as the adsorbent and precursor. As a consequence, the MoSe2/NP-C-2 composite represents exceedingly impressive electrochemical performance for both sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs). It displays a promising reversible capacity (523 mAh g−1 at 100 mA g−1 after 100 cycles) and impressive long-term cycling performance (192 mAh g−1 at 5 A g−1 even after 1000 cycles) in SIBs, which are some of the best properties of MoSe2-based anode materials for SIBs to date. To further probe the great potential applications, full SIBs pairing the MoSe2/NP-C-2 composite anode with a Na3V2(PO4)3 cathode also exhibits a satisfactory capacity of 215 mAh g−1 at 500 mA g−1 after 100 cycles. Moreover, it also delivers a decent reversible capacity of 131 mAh g−1 at 1 A g−1 even after 250 cycles for PIBs. 相似文献
107.
Umair Ahmed Charles Turquand d’Auzay Masaya Muto Nilanjan Chakraborty Ryoichi Kurose 《Proceedings of the Combustion Institute》2019,37(3):2821-2830
The statistical behaviour of the variances, covariance and gradients of the reaction progress variable (c), and the mixture fraction (ξ) have been analysed in a pulverised coal jet flame using a three-dimensional carrier phase direct numerical simulation (DNS) dataset. It has been observed that the Favre-probability density functions (PDFs) of c and ξ can be parametrised by the standard β function. Furthermore, the log-normal distribution has been found to accurately represent |?c| and |?ξ|. It is also found that ?c and ?ξ remain aligned throughout the flame brush. Finally the joint PDF of |?c| and |?ξ| has been compared with the product of the PDF of |?c| and PDF of |?ξ| extracted from carrier phase DNS, and it has been found that |?c| and |?ξ| are not statistically independent in the case investigated.The bivariate log-normal distributions with and without correlation have also been considered, and the former is found to be in better agreement with the carrier phase DNS data. 相似文献
108.
Rongmu YAN 《数学年刊B辑(英文版)》2020,41(3):451-464
In this paper, the author establishs a real-valued function on K¨ahler manifolds by holomorphic sectional curvature under parallel translation. The author proves if such functions are equal for two simply-connected, complete K¨ahler manifolds, then they are holomorphically isometric. 相似文献
109.
Aurelio Liguori Enrico Armentani Alcide Bertocco Andrea Formato Arcangelo Pellegrino Francesco Villecco 《Entropy (Basel, Switzerland)》2020,22(11)
This article lists some tips for reducing gear case noise. With this aim, a static analysis was carried out in order to describe how stresses resulting from meshing gears affect the acoustic emissions. Different parameters were taken into account, such as the friction, material, and lubrication, in order to validate ideas from the literature and to make several comparisons. Furthermore, a coupled Eulerian–Lagrangian (CEL) analysis was performed, which was an innovative way of evaluating the sound pressure level of the aforementioned gears. Different parameters were considered again, such as the friction, lubrication, material, and rotational speed, in order to make different research comparisons. The analytical results agreed with those in the literature, both for the static analysis and CEL analysis—for example, it was shown that changing the material from steel to ductile iron improved the gear noise, while increasing the rotational speed or the friction increased the acoustic emissions. Regarding the CEL analysis, air was considered a perfect gas, but its viscosity or another state equation could have also been taken into account. Therefore, the above allowed us to state that research into these scientific fields will bring about reliable results. 相似文献
110.