全文获取类型
收费全文 | 72926篇 |
免费 | 14846篇 |
国内免费 | 6385篇 |
专业分类
化学 | 66985篇 |
晶体学 | 805篇 |
力学 | 2631篇 |
综合类 | 384篇 |
数学 | 7058篇 |
物理学 | 16294篇 |
出版年
2024年 | 67篇 |
2023年 | 719篇 |
2022年 | 950篇 |
2021年 | 1399篇 |
2020年 | 2543篇 |
2019年 | 3839篇 |
2018年 | 2162篇 |
2017年 | 1811篇 |
2016年 | 4829篇 |
2015年 | 5039篇 |
2014年 | 5307篇 |
2013年 | 6567篇 |
2012年 | 6129篇 |
2011年 | 5666篇 |
2010年 | 5221篇 |
2009年 | 5168篇 |
2008年 | 4925篇 |
2007年 | 4065篇 |
2006年 | 3567篇 |
2005年 | 3398篇 |
2004年 | 2821篇 |
2003年 | 2424篇 |
2002年 | 3170篇 |
2001年 | 2329篇 |
2000年 | 2087篇 |
1999年 | 1210篇 |
1998年 | 777篇 |
1997年 | 687篇 |
1996年 | 680篇 |
1995年 | 563篇 |
1994年 | 521篇 |
1993年 | 490篇 |
1992年 | 423篇 |
1991年 | 375篇 |
1990年 | 313篇 |
1989年 | 270篇 |
1988年 | 237篇 |
1987年 | 172篇 |
1986年 | 180篇 |
1985年 | 200篇 |
1984年 | 131篇 |
1983年 | 82篇 |
1982年 | 96篇 |
1981年 | 65篇 |
1980年 | 56篇 |
1979年 | 65篇 |
1978年 | 46篇 |
1976年 | 41篇 |
1974年 | 43篇 |
1973年 | 48篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
991.
YUAN Liwei WANG Yanqiu WANG Li BAI Jiling & HE Guozhong State Key Laboratory of Molecular Reaction Dynamics Dalian Institute of Chemical Physics Chinese Academy of Sciences Dalian China 《中国科学B辑(英文版)》2004,47(4)
Dichlorobenzene is a precursor molecule of di-oxins, which are some of the most toxic chemicals and are suspected of being mutagenic with the structure of benzene rings containing different numbers of chlorine atoms. They are seriously harmful to the health of human. Therefore, it is necessary to study these aryl chemicals especially dichlorobenzene molecules in great detail. In recent years, a number of groups have investi-gated the molecules of aryl halide. The near ultraviolet absorption sp… 相似文献
992.
Gao J Fu J Lin C Lin J Han Y Yu X Pan C 《Langmuir : the ACS journal of surfaces and colloids》2004,20(22):9775-9779
Silver nanoparticles were synthesized by the use of a two-armed polymer with a crown ether core [poly(styrene)]-dibenzo-18-crown-6-[poly(styrene)] based on the flexibility of the polymer chains and the complex effect of crown ether with Ag(+) and Ag. The size of silver nanoparticles could be tailored by controlling the initial concentrations of the polymer and Ag(+), and the molecular weight of the polymer. The emission of silver nanoparticles was blue-shifted, and the intensity of the photoluminescence of silver nanoparticles stabilized by the polymer was significantly increased due to the complex effect between the crown ether embedded in the polymer and the silver nanoparticles. 相似文献
993.
Solid-phase microextraction coupled with high-performance liquid chromatography was successfully applied to the analysis of nine phenylurea herbicides (metoxuron, monuron, chlorotoluron, isoproturon, monolinuron, metobromuron, buturon, linuron, and chlorbromuron). Polydimethylsiloxane-divinylbenzene (PDMS-DVB, 60 microm) and Carbowax-templated resin (CW-TPR, 50 microm) fibers were selected from four commercial fibers for further study because of their better extraction efficiencies. The parameters of the desorption procedure were studied and optimized. The effects of the properties of analytes and fiber coatings, carryover, duration and temperature of absorption, pH, organic solvent and ionic strength of samples were also investigated. External calibration with an aqueous standard can be used for the analysis of environmental samples (lake water) using either PDMS-DVB or CW-TPR fibers. Good precisions (1.0-5.9%) are achieved for this method, and the detection limits are at the level of 0.5-5.1 ng/ml. 相似文献
994.
995.
Alexander Filosa Heng Wang Wei‐Jian Li Wenjing Zhang Ellie Ngo Jonathan E. Piccolo Hai‐Bo Yang Xiaopeng Li 《中国化学》2019,37(11):1167-1173
Porphyrins have been widely used in the self‐assembly of metallo‐supramolecules. In this study, we introduced 2,2':6,2"‐terpyridine (tpy) into a porphyrin core to synthesize a tetratopic building block with multiple conformers. During the self‐assembly with Zn(II), such a mixture of conformers was able to form a discrete nanoprism with all building blocks in one conformation. Detailed characterizations, including NMR, ESI‐MS and traveling‐wave ion mobility‐mass spectrometry (TWIM‐MS), all supported the formation of the desired assemblies. AFM and TEM further confirmed the dimensions of assembled nanoprisms. Moreover, the photophysical properties of the ligands and complexes were noticeably different depending upon size and metal ion center. 相似文献
996.
Tay-Yean Lin Charles A. Kingsbury Jules Adelfang Norman H. Cromwell 《Journal of heterocyclic chemistry》1985,22(4):1017-1020
The synthesis and spectral characteristics of certain bis(1-alkyl-3-phenyl-2-aziridinyl)ketones are reported. The reactions of 1,2,4,5-tetrabromo-1,5-diphenyl-3-pentanone ( 2 ) with primary amines are assumed to have a mechanism similar to that of a simple dibromo-ketone. The so-called cis, cis- or trans, trans-configurations of the bis-aziridinylketones were determined by 1H and 13C nmr spectra. 相似文献
997.
Haoshuang Gu Yongming Hu Hao Wang Xiangrong Yang Zhenglong Hu Ying Yuan Jin You 《Journal of Sol-Gel Science and Technology》2007,42(3):293-297
Single crystalline nanowires of lead titanate (PbTiO3) were fabricated by hydrothermal method at 200°C using lead acetate and n-tetrabutyl titanate as starting materials, where sodium hydroxide was served as a mineralizer. Crystalline phases, microstructure
and optical properties of PbTiO3 nanowires were investigated. The PbTiO3 nanowires were uniform and continuous along the long axis, and were composed of single crystalline PbTiO3 with a tetragonal perovskite structure. The diameter of a single nanowire was around 12 nm and the length reached up to 3 μm.
The chemical composition of the samples and the valence states of elements were determined by X-ray photoelectron spectroscopy
(XPS). The ultraviolet/visible absorption spectroscopic investigation suggested that the absorption edge of optical transition
of the first excitonic state occurred at around 320 nm. A blue-green light emission peaking at about 471 nm (2.63 eV) is observed
at room temperature, and the intensity of this emission increased with increasing excitation wavelength. Oxygen vacancies
are responsible for the light emission of PbTiO3 nanowires. 相似文献
998.
Two new alkaloids, i.e., (2,3‐dihydro‐1‐oxo‐1H‐pyrrolo[1,2‐a]pyrrol‐7‐yl)methyl (2S*,3S*)‐3‐[(β‐D ‐glucopyranosyl)oxy]‐2‐hydroxy‐2‐(1‐methylethyl)butanoate ( 1 ) and 1,2‐dihydro‐8‐methoxy‐2‐oxoquinoline‐4‐carboxylic acid ( 2 ), were isolated from the alcoholic extract of the whole plant of Cynoglossum gansuense, together with twelve known compounds Their structures were characterized by means of spectroscopic methods, especially by 1H‐, 13C‐, and 2D‐NMR, as well as by HR‐MS experiments and comparison with literature data. 相似文献
999.
Mangiferin (2-beta-D-glucopyranosyl-1,3,6,7-tetrahydroxyxanthen-9-one) has been isolated from the herbal root of Anemarrhena asphodeloides Bung showing antioxidative, antiviral, and anticancer effect. An in vivo microdialysis sampling method coupled to microbore high-performance liquid chromatography (HPLC) was employed for continuous monitoring of free mangiferin in rat blood. Microdialysis probes were inserted into the jugular vein/right atrium and brain striatum of Sprague-Dawley rats, and mangiferin at doses of 10, 30 or 100 mg/kg were then administered via the femoral vein. Dialysates were collected every 10 min and injected directly into a microbore HPLC system. Mangiferin was separated by a reversed-phase C18 microbore column (150 x 1 mm) from dialysate within 10 min. The mobile phase consisted of acetonitrile-0.05% phosphoric acid-tetrahydrofuran (10:75:15, v/v/v) with a flow-rate of 0.05 ml/min. The wavelength of the UV detector was set at 257 nm. The limit of quantification for mangiferin was 0.05 microg/ml and in vivo recovery of mangiferin at concentrations of 1, 5 and 10 microg/ml was in range of 37.7-39.8%. The results indicate that the pharmacokinetics of mangiferin at doses of 10-30 mg/kg reveals a linear relation, while doses of 30-100 mg/kg show a nonlinear pharmacokinetic phenomenon. Mangiferin was undetectable in brain dialysate. The proposed method provides a technique for rapid and sensitive analysis of free mangiferin in rat blood and further application in pharmacokinetic study. Furthermore, the metabolites of mangiferin in the rat bile were confirmed by LC electrospray ionization (ESI) tandem mass spectrometry (MS-MS). 相似文献
1000.
Lin Z 《Chemical Society reviews》2002,31(4):239-245
Transition metal-silane complexes containing metal-eta 2-H-Si coordination display different structural and bonding characteristics in comparison to other sigma-complexes, such as dihydrogen and alkane (agostic) complexes. The different characteristics can be related to the strong sigma*-accepting properties of the eta 2-silane ligand(s) because of the weaker H-Si sigma bond. Various examples of metal-silane complexes have been reviewed and their structural stabilities have been systematically discussed. Silyl-hydride complexes having substantial silyl-hydrido interactions have also been emphasized. 相似文献