全文获取类型
收费全文 | 18349篇 |
免费 | 2529篇 |
国内免费 | 2954篇 |
专业分类
化学 | 14513篇 |
晶体学 | 280篇 |
力学 | 787篇 |
综合类 | 266篇 |
数学 | 2025篇 |
物理学 | 5961篇 |
出版年
2023年 | 180篇 |
2022年 | 271篇 |
2021年 | 447篇 |
2020年 | 521篇 |
2019年 | 564篇 |
2018年 | 469篇 |
2017年 | 421篇 |
2016年 | 736篇 |
2015年 | 793篇 |
2014年 | 928篇 |
2013年 | 1342篇 |
2012年 | 1517篇 |
2011年 | 1592篇 |
2010年 | 1208篇 |
2009年 | 1179篇 |
2008年 | 1434篇 |
2007年 | 1310篇 |
2006年 | 1204篇 |
2005年 | 999篇 |
2004年 | 930篇 |
2003年 | 834篇 |
2002年 | 935篇 |
2001年 | 752篇 |
2000年 | 576篇 |
1999年 | 449篇 |
1998年 | 289篇 |
1997年 | 293篇 |
1996年 | 229篇 |
1995年 | 218篇 |
1994年 | 188篇 |
1993年 | 186篇 |
1992年 | 170篇 |
1991年 | 121篇 |
1990年 | 106篇 |
1989年 | 93篇 |
1988年 | 56篇 |
1987年 | 56篇 |
1986年 | 41篇 |
1985年 | 40篇 |
1984年 | 27篇 |
1983年 | 17篇 |
1982年 | 14篇 |
1981年 | 15篇 |
1980年 | 13篇 |
1978年 | 12篇 |
1977年 | 8篇 |
1976年 | 9篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
921.
In vivo pharmacokinetics of and tissue distribution study of physalin B after intravenous administration in rats by liquid chromatography with tandem mass spectrometry 下载免费PDF全文
A rapid and sensitive liquid chromatography tandem mass spectrometry quantitative analysis method was established for the pharmacokinetics and tissue distribution study of physalin B in rat. Physalin B and physalin H (internal standard, IS) were separated on an Agilent Eclips XDB C8 column. MS detection was performed on a triple quadrupole tandem mass spectrometer in the multiple reaction monitoring mode with a positive eletrospray ionization source. The assay was validated in the concentration ranges of 22.6–22600 ng/mL for heart and lung and 4.52–4520 ng/mL for other tissues. The intra‐ and inter‐day precisions (RSD) were ≤9.23 and ≤12.51%, respectively, with accuracy (%) in the range of 88.07–113.2%. A pharmacokinetic study showed that physalin B has a long dwell time with a half‐life of 321.2 ± 29.5 min and clearance of 175.4 ± 25.7 mL/min/kg after intravenous administration. Additionally, physalin B showed a wide tissue distribution with a special higher penetration in lung. The data presented in this study could provide useful information for the further study of physalin B. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
922.
923.
924.
在试验设计中,一阶回归模型通常被作为合格拟合模型用来从众多因子中筛选出效应显著的特殊因子,而Q和Q_B准则能够比较简单地从大量的合格拟合模型中找出具有最优性质的设计.主要探讨了当拟合模型为一阶回归模型时,二水平的初始设计d与其Double设计(d d d -d)在Q和Q_B准则下的最优关系.给出了初始设计d的Q和Q_B值与其Double设计的Q和Q_B值之间的解析关系,从而得到在Q或Q_B准则下如果初始设计d是最优的,那么其Double设计也是最优的.此外,也分别给出了初始设计d及其Double设计的Q值和Q_B值的一个下界. 相似文献
925.
926.
Hopf bifurcation control via a dynamic state-feedback control 总被引:1,自引:0,他引:1
To relocate two Hopf bifurcation points, simultaneously, to any desired locations in n-dimensional nonlinear systems, a novel dynamic state-feedback control law is proposed. Analytical schemes to determine the control gains according to the conditions for the emergence of Hopf bifurcation are derived. To verify the effectiveness of the proposed control law, numerical examples are provided. 相似文献
927.
928.
Enantioselective Sulfoxidation Catalyzed by a Bisguanidinium Diphosphatobisperoxotungstate Ion Pair 下载免费PDF全文
Xinyi Ye Adhitya Mangala Putra Moeljadi Kek Foo Chin Prof. Dr. Hajime Hirao Dr. Lili Zong Prof. Dr. Choon‐Hong Tan 《Angewandte Chemie (International ed. in English)》2016,55(25):7101-7105
The first enantioselective tungstate‐catalyzed oxidation reaction is presented. High enantioselectivities were achieved for a variety of drug‐like phenyl and heterocyclic sulfides under mild conditions with H2O2, a cheap and environmentally friendly oxidant. Synthetic utility was demonstrated through the preparation of (S)‐Lansoprazole, a commercial proton‐pump inhibitor. The active ion‐pair catalyst was identified to be bisguanidinium diphosphatobisperoxotungstate using Raman spectroscopy and computational studies. 相似文献
929.
Hong Zhang Zuoquan Wang Ion Ghiviriga Girinath G. Pillai Farukh Jabeen Justin A. Arami Wenfeng Zhou Peter J. Steel C. Dennis Hall Alan R. Katritzky 《Tetrahedron letters》2017,58(12):1079-1085
Synthesis, characterization and energetic properties of novel, nitrogen-rich 1-methyl-1,2,4-triazolium N-aryl/N-pyridinyl ylids 3a–m are reported. 相似文献
930.
A novel flame retardant resin was prepared by modifying benzoxazines with a reactive phosphorus-containing compound, 2-(6-Oxido-6H-dibenzo[c,e][1,2]oxa-phosphorin-6-yl) 1,4-benzenediol (ODOPB). The curing reactions of the benzoxazines containing ODOPB (ODOPB-BOZ) and a type of bifunctional benzoxazine (B-BOZ) were investigated via differential scanning calorimetry. The ODOPB-BOZ precursors exhibited lower curing temperature in comparison with the B-BOZ. Through dynamic mechanical analysis tests, it was found that the glass transition temperature and storage modulus of the cured ODOPB-BOZ were lower than those of the cured B-BOZ. Moreover, the tensile and flexural properties of the cured ODOPB-BOZ were also lower than those of the cured B-BOZ. The TGA tests proved that, owing to the presence of ODOPB, the char yield of the polybenzoxazines were remarkably raised while the decomposition rates at higher temperature were reduced. It was found that the flame retardancy of cured ODOPB-BOZ attained V-0 grade upon the UL-94 tests while that of cured B-BOZ was V-1 grade. SEM images showed that more compact char layers were formed in the cured ODOPB-BOZ after combustion, resulting in the improvement of flame retardance. 相似文献