全文获取类型
收费全文 | 24893篇 |
免费 | 4027篇 |
国内免费 | 2379篇 |
专业分类
化学 | 17454篇 |
晶体学 | 304篇 |
力学 | 1512篇 |
综合类 | 112篇 |
数学 | 2923篇 |
物理学 | 8994篇 |
出版年
2024年 | 12篇 |
2023年 | 499篇 |
2022年 | 555篇 |
2021年 | 790篇 |
2020年 | 1010篇 |
2019年 | 984篇 |
2018年 | 804篇 |
2017年 | 708篇 |
2016年 | 1169篇 |
2015年 | 1106篇 |
2014年 | 1319篇 |
2013年 | 1760篇 |
2012年 | 2371篇 |
2011年 | 2422篇 |
2010年 | 1580篇 |
2009年 | 1506篇 |
2008年 | 1645篇 |
2007年 | 1506篇 |
2006年 | 1362篇 |
2005年 | 1154篇 |
2004年 | 844篇 |
2003年 | 646篇 |
2002年 | 611篇 |
2001年 | 446篇 |
2000年 | 434篇 |
1999年 | 519篇 |
1998年 | 429篇 |
1997年 | 440篇 |
1996年 | 440篇 |
1995年 | 355篇 |
1994年 | 302篇 |
1993年 | 236篇 |
1992年 | 233篇 |
1991年 | 199篇 |
1990年 | 170篇 |
1989年 | 143篇 |
1988年 | 99篇 |
1987年 | 110篇 |
1986年 | 87篇 |
1985年 | 82篇 |
1984年 | 47篇 |
1983年 | 43篇 |
1982年 | 35篇 |
1981年 | 18篇 |
1980年 | 11篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1976年 | 9篇 |
1975年 | 11篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Mengmeng Ma Ying Wang Nan Gao Xinping Liu Yuhuan Sun Prof. Jinsong Ren Prof. Dr. Xiaogang Qu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(51):11852-11858
Proteolysis of amyloid-β (Aβ) is a promising approach against Alzheimer's disease. However, it is not feasible to employ natural hydrolases directly because of their cumbersome preparation and purification, poor stability, and hazardous immunogenicity. Therefore, artificial enzymes have been developed as potential alternatives to natural hydrolases. Since specific cleavage sites of Aβ are usually embedded inside the β-sheet structures that restrict access by artificial enzymes, this strongly hinders their efficiency for practical applications. Herein, we construct a NIR (near-IR) controllable artificial metalloprotease (MoS2-Co) using a molybdenum disulfide nanosheet (MoS2) and a cobalt complex of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (Codota). Evidenced by detailed experimental and theoretical studies, the NIR-enhanced MoS2-Co can circumvent the restriction by simultaneously inhibition of β-sheet formation and destroying β-sheet structures of the preformed Aβ aggregates in living cell. Furthermore, our designed MoS2-Co is an easy to graft Aβ-target agent that prevents misdirected or undesirable hydrolysis reactions, and has been demonstrated to cross the blood brain barrier. This method can be adapted for hydrolysis of other kinds of amyloids. 相似文献
992.
Yaru Gong Yuteng Zhang Chao Qin Chunyi Sun Xinlong Wang Zhongmin Su 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(3):790-794
A rational synthetic strategy to construct two supramolecular isomers based on polyoxovanadate organic polyhedra with tetrahedral symmetries is presented. VMOP‐α , a low‐temperature product, has an extremely large cell volume (470 842 Å3), which is one of the top three for well‐defined MOPs. The corner‐to‐corner packing of tetrahedra leads to a quite low density of 0.174 g cm?3 with 1D channels (ca. 5.4 nm). The effective pore volume is up to 93.6 % of cell volume, nearly the largest found in MOPs. For the high‐temperature outcome, VMOP‐β , the cell volume is only 15 513 Å3. The packing mode of tetrahedra is corner‐to‐face, giving rise to a high‐density architecture (1.324 g cm?3; channel 0.8 nm). Supramolecular structural transformation between VMOP‐α and VMOP‐β can be reversibly achieved by temperature‐induced solvent‐mediated transformation. These findings give a good opportunity for understanding 3D supramolecular aggregation and crystal growth based on large molecular tectonics. 相似文献
993.
Yuan Li Li Kai Song Xin Sun Huaying Ning Ping Sun Xin 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2019,93(12):2373-2382
Russian Journal of Physical Chemistry A - The mechanism of PH3 oxidation is investigated at B3LYP/6-311+g (d, p) level using density functional theory calculation with n = 0–6 water molecules... 相似文献
994.
Ye Linglong Li Xueshan Cai Yunhao Ryu Hwa Sook Lu Guangkai Wei Donghui Sun Xiaobo Woo Han Young Tan Songting Sun Yanming 《中国科学:化学(英文版)》2020,63(4):483-489
Benzo[1,2-b:4,5-b′]dithiophene(BDT) has been widely used to construct donor-acceptor(D-A) copolymers in organic solar cells(OSCs). However, benzo[1,2-b:4,5-b′]difuran(BDF), an analogue of BDT, has received less attention than BDT. The photovoltaic performance of BDF copolymers has lagged behind that of BDT copolymers. Here, we designed and synthesized two BDF copolymers, PBF1-C and PBF1-C-2Cl. PBF1-C-2Cl, which is composed of BDF and benzo[1,2-c:4,5-c′]dithiophene-4,8-dione connected by a chlorinated thiophene π-bridge, displays a low-lying highest occupied molecular orbital energy level,which helps in yielding a high open-circuit voltage(V_(oc)) in OSCs. As a result, when blended with Y6, PBF1-C-2Cl-based devices showed a high V_(oc) of 0.83 V and a power conversion efficiency(PCE) of 13.10%. To the best of our knowledge, the PCE of 13.10% is among the highest efficiency values for OSCs based on BDF copolymers. 相似文献
995.
Yongtao Bai Lihua Song Yongheng Zhang Guoliang Dai Weidong Zhang Shanshan Song Hong Sun Wen Jing Meijuan Xu Wenzheng Ju 《Biomedical chromatography : BMC》2019,33(9)
A highly selective and efficient LC–MS/MS method was developed to determine the plasma concentration of magnolol, hesperidin, neohesperidin and geniposide following oral administration of Zhi‐Zi‐Hou‐Po decoction in normal and depressed rats. Plasma samples were pretreated by protein precipitation with methanol. Chromatographic separation was performed on an XTerra® MS C18 column using a gradient elution with a mobile phase composed of acetonitrile–0.1% aqueous formic acid. The proposed method was validated to be specific, accurate and precise for the analytes determination in plasma samples. The calibration curves displayed good linearity over definite concentration ranges for the analytes. The intra‐ and inter‐day precision of the proposed method at three different levels were all within <11.13% and the relative errors ranged from ?8.46 to 8.93%. The recovery of the four compounds ranged from 82.72 to 89.08% and no apparent matrix effect was observed during sample analysis. After full validation, the established method was successfully applied for comparing the pharmacokinetics of four components between normal and depressed rats. The results showed that the AUC and Cmax of four analytes in depressed rats were significantly different from those in normal rats and might provide helpful information to guide the clinical use of Zhi‐Zi‐Hou‐Po to treat depression. 相似文献
996.
Yunyun Wang Yajun Jian Ya Wu Huaming Sun Guofang Zhang Weiqiang Zhang Ziwei Gao 《应用有机金属化学》2019,33(7)
Bifunctional catalysts bearing two catalytic sites, Lewis acidic organometallic titanocene and Brønsted acidic COOH, have been assembled in situ from Cp2TiCl2 with carboxylic acid ligands, showing high catalytic activity over an intramolecular Mannich reaction towards synthesis of 2‐aryl‐2,3‐dihydroquinolin‐4(1H)‐ones. The determination of the bifunctional catalyst Cp2Ti(C8H4NO6)2 was elucidated by single X‐ray HR‐MS and investigation of catalytic behavior. In particular, masking the Brønsted acidic COOH catalytic site with dormant COOMe lowered the reaction yield greatly, indicating that two catalytic sites work together to maintain high catalytic efficiency. 相似文献
997.
Xiong Sun Dr. Wei Su Kaiying Shi Zhuoyi Xie Prof. Dr. Congqing Zhu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(24):5354-5359
Rare-earth metal cations have been used rarely as Lewis-acidic components in the chemistry of frustrated Lewis pairs (FLPs). Herein, we report the first cerium/phosphorus system ( 2 ) employing a heptadentate N4P3 ligand, which exhibits triple FLP-type reactivity towards a series of organic substrates, including isocyanates, isothiocyanates, diazomethane, and azides on a single rare-earth Lewis acidic Ce center. This result shows that the Ce center and three P atoms in 2 could simultaneously activate three equivalents of small molecules under mild conditions. This study broadens the diversity of FLPs and demonstrates that rare earth based FLP exhibit unique properties compared with other FLP systems. 相似文献
998.
999.
A simple,rapid and reliable liquid chromatography–mass spectrometry method for determination of methotrexate in human plasma and its application to therapeutic drug monitoring 下载免费PDF全文
Dan Wu Yixuan Wang Yan Sun Nian Ouyang Jun Qian 《Biomedical chromatography : BMC》2015,29(8):1197-1202
A simple, rapid and reliable liquid chromatography–electrospray ionization tandem mass spectrometry method was established and validated for the determination of methotrexate in human plasma. After a straightforward protein precipitation by acetonitrile–water (70:30, v/v), methotrexate (MTX) and p‐aminoacetophenone (used as internal standard, IS) were separated on a Column C18 column (50 × 2.1 mm, 3 µm; Column Technology, Fremont, CA, USA) using a gradient elution with mobile phase of acetonitrile and 0.03% acetic acid aqueous solution at a flow rate of 0.5 mL/min. The total chromatographic runtime was 5 min for each injection. Quantification detection was performed in a triple‐quadruple tandem mass spectrometer under positive mode monitoring the following mass transitions: m/z 455.3 → 308.3 for MTX and m/z 136.1 → 94.4 for IS. The calibration curve was linear over the range of 0.05–25.0 µmol/L with a lower limit of quantification of 0.05 µmol/L. The intra‐ and interday precisions were <5.2%, the accuracy varied from ?4.1 to 4.5%. The recovery was >94%. The LC‐MS/MS method showed an excellent agreement with the existing HPLC‐UV method using Passing–Bablok regression and Bland–Altman difference plot analysis. The validated LC‐MS/MS can be successfully applied to the routine therapeutic drug monitoring of MTX in clinical laboratories. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
1000.