全文获取类型
收费全文 | 22287篇 |
免费 | 2921篇 |
国内免费 | 2638篇 |
专业分类
化学 | 16471篇 |
晶体学 | 273篇 |
力学 | 1045篇 |
综合类 | 204篇 |
数学 | 2642篇 |
物理学 | 7211篇 |
出版年
2023年 | 264篇 |
2022年 | 450篇 |
2021年 | 519篇 |
2020年 | 636篇 |
2019年 | 699篇 |
2018年 | 551篇 |
2017年 | 528篇 |
2016年 | 918篇 |
2015年 | 908篇 |
2014年 | 1110篇 |
2013年 | 1466篇 |
2012年 | 1715篇 |
2011年 | 1936篇 |
2010年 | 1372篇 |
2009年 | 1419篇 |
2008年 | 1641篇 |
2007年 | 1474篇 |
2006年 | 1319篇 |
2005年 | 1110篇 |
2004年 | 1032篇 |
2003年 | 853篇 |
2002年 | 958篇 |
2001年 | 768篇 |
2000年 | 624篇 |
1999年 | 423篇 |
1998年 | 312篇 |
1997年 | 246篇 |
1996年 | 295篇 |
1995年 | 223篇 |
1994年 | 232篇 |
1993年 | 207篇 |
1992年 | 164篇 |
1991年 | 142篇 |
1990年 | 131篇 |
1989年 | 103篇 |
1988年 | 112篇 |
1987年 | 79篇 |
1986年 | 82篇 |
1985年 | 108篇 |
1984年 | 76篇 |
1983年 | 79篇 |
1982年 | 52篇 |
1981年 | 53篇 |
1980年 | 50篇 |
1979年 | 43篇 |
1978年 | 38篇 |
1977年 | 39篇 |
1976年 | 38篇 |
1974年 | 51篇 |
1973年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
901.
902.
Nanorod‐assembled FHA microspheres with different F contents were for the first time prepared through a facile one‐step hydrothermal method. The effect of the reaction time and pH value of reaction solutions on the FHA morphology was investigated to elucidate the self‐assembly process of FHA microspheres. The results showed pH values had significant effect on the morphology of the formed FHA crystals, which were self‐assembled into sphere‐like sturctures at high pH conditions and rod‐like structures at low pH values. The results suggested that formation of FHA crystals with varied morphology may be directly related to Ca2+ release kinetics from EDTA‐Ca‐Na2 at different pH conditions. Furthermore, it was found that the chemical stability of FHA microspheres was dependent on the F content in the materials, and high F contents in FHA microspheres lead to improved chemical stability. These results suggest that the prepared self‐assembled FHA microspheres may be used for teeth substitution materials due to their unique hierarchical structures and controllable chemical stability. 相似文献
903.
Co (II)‐C12 alkyl carbon chain multi‐functional ionic liquid immobilized on nano‐SiO2 nano‐SiO2@CoCl3‐C12IL as an efficient cooperative catalyst for C–H activation by direct acylation of aryl halides with aldehydes 下载免费PDF全文
Nano‐silica supported ionic liquids composed of alkyl carbon chain and transition metal chlorides anions have been prepared and successfully applied as a heterogeneous catalyst in the direct aldehyde C‐H activation. Catalytic results indicated that nano‐SiO2 supported ionic liquid consisting C12 alkyl carbon chain and CoCl3 anion nano‐SiO2@CoCl3‐C12IL showed excellent catalytic properties with good to excellent yields towards the desired aryl ketones. The excellent recyclability of the supported catalyst, mild reaction conditions, low catalyst loading, and operational simplicity are the important features of this methodology. 相似文献
904.
905.
Xiao‐Lan Wei Rong Han Xiao Hu Li‐Hui Quan Chun‐Yu Liu Qi Chang Yong‐Hong Liao 《Biomedical chromatography : BMC》2013,27(5):636-640
Six esterase inhibitors, namely EDTA·2Na+, NaF, phenylmethanesulfonyl fluoride, dichlorvos, bis‐nitrophenyl phosphate (BNPP) and thenoyltrifluoroacetone, and the mixture of NaF and BNPP, were evaluated for the stabilization of labile benzoate containing zeylenone in rat plasma. The mixture appeared to exhibit the most effectively stabilizing effect with the degraded content of zeylenone decreasing from >60% (in the absence of inhibitors) to <6%. Following the stabilization by the addition of NaF (5 mm ) and BNPP (5 mm ), the analytes in rat plasma were acidified by formic acid and extracted into ethyl acetate at 0°C. After chromatographic separation, the detection of zeylenone was performed on a 3200 Q‐Trap with positive ion electrospray mode, monitoring the ion transition m/z 383.2 → 105.0. The method was validated over the range from 2.68 to 1340 ng/mL with inter‐ and intra‐run precision for the quality control samples being less than 6.8%. The assay accuracy was within 100 ± 7.0%. The validated method was successfully applied to a pharmacokinetic study in rats after the intratracheal administration of zeylenone in free drug or polymeric micellar solutions. The results showed that the pulmonary absorption of zeylenone loaded in micelles was significantly retarded compared with that of free drug solutions. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
906.
Isolation of Biphenyl and Polychlorinated Biphenyl-Degrading Bacteria and Their Degradation Pathway 总被引:1,自引:0,他引:1
Young-Cheol Chang Kazunori Takada DuBok Choi Tadashi Toyama Ken Sawada Shintaro Kikuchi 《Applied biochemistry and biotechnology》2013,170(2):381-398
Four strains of biphenyl-degrading bacteria were isolated from a sewage and identified from the Rhodococcus genus (SK-1, SK-3, and SK-4) and Aquamicrobium genus (SK-2) by 16S rRNA sequence. Among these strains, strain SK-2 was most suitable for biphenyl degradation. When 0.65, 1.3, 2.6, or 3.9 mM of biphenyl was used, the biphenyl was completely degraded within 24 and 96 h of culture, respectively. However, in the case of 6.5 and 9.75 mM of biphenyl, the biphenyl degradation yields were about 80 % and 46.7 % after 120 h of culture, respectively. The isolated strains could degrade a broad spectrum of aromatic compounds including high-chlorinated polychlorinated biphenyl (PCB) congeners in the presence of biphenyl. In addition, strain SK-2 could utilize PCB congeners containing one to six chlorine substituents such as 2,2′,4,4′,5,5′-hexachlorobiphenyl. The PCB utilization rate by the strain SK-2 was increased compared to that of other PCB congener-utilizing bacteria. The four isolates metabolized 4-chlorobiphenyl to 4-chlorobenzoic acid and 2-hydroxy-6-oxo-6-(4′-chlorophenyl)-hexa-2,4-dienoic acid. These results suggest the isolated strains might be good candidates for the bioremediation of PCB-contaminated soil, especially high-saline soils. 相似文献
907.
908.
Chih-Hung Chang Tzonelih Hwang Prosanta Gope 《International Journal of Theoretical Physics》2016,55(4):2125-2138
This article proposes a collective-noise resistant QPC protocol with the help of an almostdishonest third party (TP) who may try to perform any sort of attacks to derive participants’ private secrets except colluding with any participant. The proposed scheme has some considerable advantages over the state-of-the-art QPC protocols over collective-noise channels, where it does not require any pre-shared key between the participants (Alice and Bob). Nevertheless, the proposed scheme can resist Trojan horse attacks without consuming half of the transmitted qubits and any additional equipment (wavelength filter and PNS) support. As a consequence, the proposed QPC protocol can guarantee higher qubit efficiency as compared to the others over collective noise channels. 相似文献
909.
910.
Jang Ho Kim Woo Chang Kim Frank J. Fabozzi 《Journal of Optimization Theory and Applications》2014,161(1):103-121
Robust models have a major role in portfolio optimization for resolving the sensitivity issue of the classical mean–variance model. In this paper, we survey developments of worst-case optimization while focusing on approaches for constructing robust portfolios. In addition to the robust formulations for the Markowitz model, we review work on deriving robust counterparts for value-at-risk and conditional value-at-risk problems as well as methods for combining uncertainty in factor models. Recent findings on properties of robust portfolios are introduced, and we conclude by presenting our thoughts on future research directions. 相似文献