全文获取类型
收费全文 | 7816篇 |
免费 | 1545篇 |
国内免费 | 960篇 |
专业分类
化学 | 5550篇 |
晶体学 | 116篇 |
力学 | 451篇 |
综合类 | 90篇 |
数学 | 859篇 |
物理学 | 3255篇 |
出版年
2024年 | 32篇 |
2023年 | 244篇 |
2022年 | 392篇 |
2021年 | 384篇 |
2020年 | 458篇 |
2019年 | 430篇 |
2018年 | 359篇 |
2017年 | 326篇 |
2016年 | 443篇 |
2015年 | 450篇 |
2014年 | 482篇 |
2013年 | 650篇 |
2012年 | 727篇 |
2011年 | 708篇 |
2010年 | 510篇 |
2009年 | 465篇 |
2008年 | 447篇 |
2007年 | 397篇 |
2006年 | 338篇 |
2005年 | 302篇 |
2004年 | 249篇 |
2003年 | 210篇 |
2002年 | 184篇 |
2001年 | 154篇 |
2000年 | 112篇 |
1999年 | 137篇 |
1998年 | 109篇 |
1997年 | 90篇 |
1996年 | 91篇 |
1995年 | 75篇 |
1994年 | 64篇 |
1993年 | 44篇 |
1992年 | 37篇 |
1991年 | 47篇 |
1990年 | 43篇 |
1989年 | 29篇 |
1988年 | 23篇 |
1987年 | 18篇 |
1986年 | 14篇 |
1985年 | 13篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1978年 | 2篇 |
1964年 | 1篇 |
1959年 | 1篇 |
1957年 | 2篇 |
1936年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
Voriconazole is used to prevent invasive pulmonary aspergillosis. However, little is known about the concentrations of voriconazole in human lung epithelial cells (A549), which is the target for preventing invasive pulmonary aspergillosis. The goal of this study was to develop a high-performance liquid chromatography–tandem mass spectrometry method to quantify voriconazole in A549 cells. A triple-quadrupole mass spectrometer in selected reaction monitoring mode was used with positive electrospray ionization. The total duration of each run was 5?min. The calibration curves fit a least squares model for the voriconazole concentration ranging from 0.625 to 160?ng/mL. Intraday and interday coefficients of variation were less than 10%. Recoveries at the concentrations of the quality control samples where greater than 85%, and the matrix effects showed that the ratios of the peak response exhibited a 15% suppression of the signal in the matrix compared to water. Voriconazole may penetrate A549 cells. However, the voriconazole uptake was slow in A549 cells, reaching a plateau at 2?h, where the dose-dependent intracellular voriconazole concentrations were 1.98?±?0.38, 4.43?±?0.54, and 8.14?±?0.52?ng/mg protein for extracellular voriconazole concentrations of 5, 10, and 20?µg/mL, respectively. The uptake of voriconazole by A549 cells was linear at extracellular concentrations from 0 to 20?µg/mL. This study established a rapid and sensitive method suitable for determining voriconazole in A549 cells and described the kinetic properties of the absorption of voriconazole by A549 cells. 相似文献
142.
采用高压釜合成和乙酸乙酯/水萃取提纯的模式制备出高产率、高纯度的环状烷基硫碘盐. 高压釜合成在保证产率的前提下, 大大缩短了反应时间(反应时间仅为原来的1/3)|乙酸乙酯和水的萃取提纯模式在保证产品纯度的同时, 大大缩短了提纯时间, 还避免了有毒试剂的使用. 制备出的烷基环状硫碘盐作为碘源用于配制染料敏化太阳电池用电解质, 相应电池的光电转化效率接近使用传统烷基咪唑碘盐的电池. 电化学阻抗谱(EIS)测试表明环状烷基锍阳离子相比于烷基咪唑阳离子来说, 更有利于抑制电池内部的电子复合反应, 同时还能促进对电极上电子交换反应的进行, 最终可以提高电池的开路电压和填充因子. 相似文献
143.
Qingyong Meng Hai-Bo Chang Ming-Bao Huang Hua Dong 《Theoretical chemistry accounts》2011,128(3):359-365
The N-loss predissociation mechanisms of the A 2Σ+ (2 2
A′) state of N2O+ to the first and second dissociation limits were studied in the C
s symmetry. The potential energy curves (PECs) and minimum energy crossing points (MECPs) for the C
s states of N2O+ were calculated at the CAS levels. On the basis of our CAS calculation results (CASPT2 energetic results and CASSCF spin
orbit couplings), we suggest two processes for N-loss predissociation mechanisms of A 2Σ+ (2 2
A′) to the first and second limits. The first two steps in the two processes are the same: A 2Σ+ passes through the 2 2
A′/1 4
A″ MECP and then reaches the 1 4
A″ (1 4Σ−) PEC. The 2 2
A′/1 4
A″ MECP has a bent geometry and is slightly higher in energy than the transition state along the 1 4
A″ PEC. Our mechanisms are different from the previously suggested mechanisms (via 1 4Π). 相似文献
144.
Chuiming Wan Jianxin Meng Fengjin Zhang Xiaoling Deng Chuangtao Yang 《Solid State Communications》2010,150(31-32):1493-1495
A new blue-emitting phosphor LiCaPO4: Eu2+ was synthesized by solid state reaction at a relatively low temperature of 900 °C. It gives a single intense emission band centering at 470 nm, which corresponds to the 4f65d1→4f7 transition of Eu2+. The dependence of luminescence intensities on Eu2+ concentration was investigated. The phosphor, with a single excitation band extending from 250 to 400 nm, could be efficiently excited by near-ultraviolet light-emitting diodes and is believed to be a promising blue-emitting phosphor for white light-emitting diodes. 相似文献
145.
146.
147.
天然产物Radicamines A和B是日本植物学家Kusano等从半边莲中分离到的两个新型吡咯烷型生物碱,发现它们是有效的α-葡萄糖苷酶抑制剂,根据各种光谱数据推断它们为全反式取代的吡咯烷结构,绝对构型为(2S,3S,4S,5S) [1].后来,本课题组[2]和其它课题组[3,4]分别采用不同的全合成方法纠正了Radicamines A和B的构型,确定其为(2R,3R,4R,5R)(图1).去年,另一课题组采用与我们相似的合成路线率先报道了Radicamines A和B的合成及其对三种糖苷酶的活性研究[5]. 相似文献
148.
149.
This work chooses Cu/Fe single-atom catalysts(SACs) with weak/strong oxygen affinity to clarify the effect of dual-atom configuration on oxygen reduction reaction(ORR) performance based on density functional theory(DFT) calculations. The stability and ORR activity of single or dual Cu/Fe atomic sites anchored on nitrogen-doped graphene sheets(Cu-N4-C, Cu2-N6-C, Fe-N4-C, and Fe2-N6-C) are investigated, and the results indicate the dual-atom catalysts(Cu2-N6-C and Fe2-N6-C) are thermodynamically stable enough to avoid sintering and aggregation. Compared with single-atom active sites of Cu-N4-C, which show weak oxygen affinity and poor ORR performance with a limiting potential of 0.58 V, the dual-Cu active sites of Cu2-N6-C exhibit enhanced ORR activity with a limiting potential up to 0.87 V due to strengthened oxygen affinity. Interestingly, for Fe SACs with strong oxygen affinity, the DFT results show that the dual-Fe sites stabilize the two OH* ligands structure[Fe2(OH)2-N6-C], which act as the active sites during ORR process, resulting in greatly improved ORR performance with a limiting potential of 0.90 V. This study suggests that the dual-atom design is a potential strategy to improve the ORR performance of SACs, in which the activity of the single atom active sites is limited with weak or strong oxygen affinity. 相似文献
150.
化学工业生产中,用氢气为还原剂,通过选择性加氢可以制备多种重要化学品。5-羟甲基糠醛是重要的生物质基平台化合物,而5-甲基糠醛是用途广泛的化学品。由5-羟甲基糠醛加氢得到5-甲基糠醛是一条非常理想的路径,但是选择性活化C-OH非常困难。本文设计并制备了Pt@PVP/Nb2O5(PVP: 聚乙烯吡咯烷酮)催化剂,该催化体系巧妙地结合了位阻效应、氢溢流和催化剂界面的电子效应,系统研究了该催化剂对5-羟甲基糠醛选择性加氢制备5-甲基糠醛催化性能,在最优条件下,5-甲基糠醛的选择性可达92%。利用密度泛函理论计算研究了5-羟甲基糠醛选择性加氢制备5-甲基糠醛反应路径。 相似文献