全文获取类型
收费全文 | 2609篇 |
免费 | 466篇 |
国内免费 | 301篇 |
专业分类
化学 | 1390篇 |
晶体学 | 6篇 |
力学 | 109篇 |
综合类 | 18篇 |
数学 | 245篇 |
物理学 | 851篇 |
无线电 | 757篇 |
出版年
2024年 | 9篇 |
2023年 | 69篇 |
2022年 | 84篇 |
2021年 | 120篇 |
2020年 | 108篇 |
2019年 | 110篇 |
2018年 | 79篇 |
2017年 | 81篇 |
2016年 | 94篇 |
2015年 | 124篇 |
2014年 | 144篇 |
2013年 | 167篇 |
2012年 | 256篇 |
2011年 | 279篇 |
2010年 | 187篇 |
2009年 | 174篇 |
2008年 | 173篇 |
2007年 | 152篇 |
2006年 | 159篇 |
2005年 | 132篇 |
2004年 | 78篇 |
2003年 | 67篇 |
2002年 | 78篇 |
2001年 | 55篇 |
2000年 | 54篇 |
1999年 | 49篇 |
1998年 | 42篇 |
1997年 | 38篇 |
1996年 | 26篇 |
1995年 | 21篇 |
1994年 | 21篇 |
1993年 | 12篇 |
1992年 | 22篇 |
1991年 | 16篇 |
1990年 | 18篇 |
1989年 | 10篇 |
1988年 | 4篇 |
1987年 | 11篇 |
1986年 | 7篇 |
1985年 | 6篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1969年 | 2篇 |
1957年 | 2篇 |
1906年 | 1篇 |
排序方式: 共有3376条查询结果,搜索用时 31 毫秒
91.
V Sekushin R Püttner RF Fink M Martins YH Jiang H Aksela S Aksela G Kaindl 《The Journal of chemical physics》2012,137(4):044310
High-resolution normal Auger-electron spectra of carbonyl sulfide subsequent to S 2p(-1) photoionization at photon energies of 200, 220, and 240 eV are reported along with corresponding photoelectron spectra. In addition, theoretical results are presented that take the core-hole orientation of the various spin-orbit-split and molecular-field-split S 2p(-1) states into account. Auger transitions to eight metastable dicationic final states are observed and assigned on the basis of the theoretical results. From Franck-Condon analysis, assuming Morse potentials along the normal coordinates for seven of the observed quasi-stable dicationic final states, information on the potential-energy surfaces is derived and compared with theoretical results from the literature. 相似文献
92.
WD Zhang Q Wang Y Wang XJ Wang JX Pu Y Gu R Wang 《Journal of separation science》2012,35(17):2203-2209
Lignans in the drug Fructus Schisandrae chinensis (FSC) exhibit potent biological activities such as antihepatotoxic, antiasthmatic, and antigastric ulcer. An ultrahigh-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry method has been developed to evaluate the quality of FSC through simultaneous qualitative and quantitative analysis of 15 lignans, including schizandrin A, B, and C; schizandrol A and B; gomisin B, C, D, E, G, H, J, and N; tigloylgomisin H; and angeloylgomisin H. The compounds were separated on a Zorbax Eclipse Plus C(18) (2.1 × 100 mm, 1.8 μm) column with a gradient elution of acetonitrile and 0.1% formic acid. Lignans were identified through their retention times, accurate mass data, and characteristic ions by comparison with a reference substance. All calibration curves showed perfect linear regression (r(2) > 0.99) within the test range. The limits of detection and quantitation fell in the ranges of 0.1-4 ng/mL for all the analytes with an injection of 10 μL. Good results were obtained with respect to repeatability (relative standard deviation <4.6%) and recovery (85.58-105.82%). Meanwhile, the entire sample analysis time was less than 10 min. This developed method provided a new basis for the overall assessment of the quality of FSC. 相似文献
93.
Laburnine’s dissolution behaviors in glucose and saline solution were studied by a micro-calorimetry method. The measured integral and differential heats of solution were utilized to build equations of the solute and the heat, so that dissolution thermodynamic equations and half-time periods, Δsol H m, Δsol G m, and Δsol S m were obtained. The results show that this study does not only provide a simple method for the determination of the half-life period for a drug but also offer a theoretical reference for the clinical application of laburnine. 相似文献
94.
Guang-Feng Hong Zhen-Hua Dong Yong-Mei Xiao Pu Mao Ling-Bo Qu 《Phosphorus, sulfur, and silicon and the related elements》2013,188(11):771-779
AbstractA practical metal-free procedure for the synthesis of (E)-vinyl sulfones has been developed through the coupling of β-nitrostyrenes with sodium sulfinates under microwave irradiation. This methodology provides a convenient and efficient approach to various (E)-vinyl sulfones from readily available starting materials with excellent regioselectivity. The present oxidative reaction involves an efficient denitrative radical cross-coupling of β-nitrostyrenes with sodium sulfinates via using AcOH as an additive. 相似文献
95.
Liangru Yang Yunfei Li Pu Mao Jinwei Yuan Yongmei Xiao 《Phosphorus, sulfur, and silicon and the related elements》2013,188(8):780-788
AbstractThe catalytic activity of a series of chiral heteroaryl coordinated chelating N-heterocyclic carbene (NHC) palladium complexes towards asymmetric allylic alkylation (AAA) were presented here. The effects of different N-substituents, NHC backbones and chelate rings on the catalytic activity and the enantioselectivity of the alkylation of (E)-1,3-diarylallyl acetates with dialkyl malonate were investigated. The results showed that, under the optimized conditions, complexes 3a, 3b, and 3i carrying the pyridinyl-coordinated five-membered chelate ring showed high catalytic activity and chiral induction efficiency. The corresponding alkylated products were obtained in high yields with moderate ee. Furthermore, it was found that the substituents of (E)-1,3-diarylallyl acetates and the type of the nucleophile affect the results as well. 相似文献
96.
Liu Z Pu Y Li F Shaffer CA Hoops S Tyson JJ Cao Y 《The Journal of chemical physics》2012,136(3):034105
The eukaryotic cell cycle is regulated by a complicated chemical reaction network. Although many deterministic models have been proposed, stochastic models are desired to capture noise in the cell resulting from low numbers of critical species. However, converting a deterministic model into one that accurately captures stochastic effects can result in a complex model that is hard to build and expensive to simulate. In this paper, we first apply a hybrid (mixed deterministic and stochastic) simulation method to such a stochastic model. With proper partitioning of reactions between deterministic and stochastic simulation methods, the hybrid method generates the same primary characteristics and the same level of noise as Gillespie's stochastic simulation algorithm, but with better efficiency. By studying the results generated by various partitionings of reactions, we developed a new strategy for hybrid stochastic modeling of the cell cycle. The new approach is not limited to using mass-action rate laws. Numerical experiments demonstrate that our approach is consistent with characteristics of noisy cell cycle progression, and yields cell cycle statistics in accord with experimental observations. 相似文献
97.
Xinjian Yang Zhen Liu Zhenhua Li Fang Pu Prof. Dr. Jinsong Ren Prof. Dr. Xiaogang Qu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(31):10388-10394
Hydrophobicity has been an obstacle that hinders the use of many anticancer drugs. A critical challenge for cancer therapy concerns the limited availability of effective biocompatible delivery systems for most hydrophobic therapeutic anticancer drugs. In this study, we have developed a targeted near‐infrared (NIR)‐regulated hydrophobic drug‐delivery platform based on gold nanorods incorporated within a mesoporous silica framework (AuMPs). Upon application of NIR light, the photothermal effect of the gold nanorods leads to a rapid rise in the local temperature, thus resulting in the release of the entrapped drug molecules. By integrating chemotherapy and photothermotherapy into one system, we have studied the therapeutic effects of camptothecin‐loaded AuMP‐polyethylene glycol‐folic acid nanocarrier. Results revealed a synergistic effect in vitro and in vivo, which would make it possible to enhance the therapeutic effect of hydrophobic drugs and decrease drug side effects. Studies have shown the feasibility of using this nanocarrier as a targeted and noninvasive remote‐controlled hydrophobic drug‐delivery system with high spatial/temperal resolution. Owing to these advantages, we envision that this NIR‐controlled, targeted drug‐delivery method would promote the development of high‐performance hydrophobic anticancer drug‐delivery system in future clinical applications. 相似文献
98.
Synthesis and properties of amphoteric copolymer of 5‐vinyltetrazole and vinylbenzyl phosphonic acid
Hongting Pu Haochuan Luo Decheng Wan 《Journal of polymer science. Part A, Polymer chemistry》2013,51(16):3486-3493
Amphoteric polymers have been studied for various applications such as separation of low molecular weight organic molecules from inorganic salt mixtures, selective ion transport, drug delivery through membranes of biological interest, separation of ionic drugs and proteins, and separation of alcohol and water. Typical amphoteric polymers consist of weak base and weak acid groups. In present study, the copolymerization of 5‐vinyltetrazole (VT) and diisopropyl‐p‐vinylbenzyl phosphate (DIPVBP) via free radical polymerization is studied. The reactivity ratio of VT and DIPVBP, which is calculated from Kelen‐Tudos plot, is 0.251 and 0.345, respectively. The amphoteric copolymer of VT and diisopropyl‐p‐vinylbenzyl phosphonic acid (poly(VT‐co‐VBPA)) is obtained from hydrolysis of the copolymer of VT and DIPVBP (poly(VT‐co‐DIPVBP)). Poly(VT‐co‐VBPA) is thermally stable under 190 °C. The anhydrous proton conductivity of amphoteric poly(VT‐co‐VBPA) can reach 1.54 × 10‐4 S cm?1 at 170 °C with an activation energy of 114.7 kJ mol?1. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3486–3493 相似文献
99.
Jie Wang Cuicui Ma Qiannan Li Xing Wang Yang Yang Lingjian Yang Wei Jiang Sha Liao Shixiang Wang Pu Jia Ye Zhao Xiaohui Zheng 《Biomedical chromatography : BMC》2019,33(3)
Tanshinol borneol ester (DBZ) is a potential drug candidate composed of danshensu and borneol. It shows anti‐ischemic and anti‐atherosclerosis activity. However, little is known about its metabolism in vivo. This research aimed to elucidate the metabolic profile of DBZ through analyzing its metabolites using high‐performance liquid chromatography combined with electrospray ionization quadrupole time‐of‐flight mass spectrometry. Chromatographic separation was performed on an Agilent TC‐C18 column (150 × 4.6 mm, 5.0 μm) with gradient elution using methanol and water containing 0.2% (v/v) formic acid as the mobile phase. Metabolite identification involved analyzing the retention behaviors, changes in molecular weights and MS/MS fragment patterns of DBZ and its metabolites. As a result, 20 potential metabolites were detected and tentatively identified in rat plasma, urine and feces after administration of DBZ. DBZ could be metabolized to O‐methylated DBZ, DBZ‐O‐glucuronide, O‐methylated DBZ‐O‐glucuronide, hydroxylated DBZ and danshensu. Danshensu, a hydrolysis product of DBZ, could further be transformed into 12 metabolites. The proposed method was confirmed to be a reliable and sensitive alternative for characterizing metabolic pathways of DBZ and providing valuable information on its druggability. 相似文献
100.
He X Pu W Han J Chen J Lu J Jiang C Wan C 《The journal of physical chemistry. B》2005,109(49):23141-23144
A method is proposed based on mode coupling theory in which the ion transference number is introduced into the theory. The ionic limiting molar conductivities of LiPF6, LiClO4, LiBF4, LiCF3SO3, Li(CF3SO3)2N, LiC4F9SO3, and LiAsF6 in PC(propylene carbonate), GBL(gamma-butyrolactone), PC(propylene carbonate)/EMC(ethylmethyl carbonate), and PC(propylene carbonate)/DME(dimethoxyethane) are calculated based on this method, which does not involve any adjustable parameter. The results fit well to the literature data which are calculated by an empirically adjusted formula. This presents a potential way to calculate the conductivities of Li-ion battery electrolytes. 相似文献