全文获取类型
收费全文 | 17007篇 |
免费 | 766篇 |
国内免费 | 144篇 |
专业分类
化学 | 10966篇 |
晶体学 | 57篇 |
力学 | 341篇 |
综合类 | 1篇 |
数学 | 3106篇 |
物理学 | 3446篇 |
出版年
2023年 | 140篇 |
2022年 | 218篇 |
2021年 | 353篇 |
2020年 | 450篇 |
2019年 | 509篇 |
2018年 | 387篇 |
2017年 | 300篇 |
2016年 | 627篇 |
2015年 | 602篇 |
2014年 | 567篇 |
2013年 | 944篇 |
2012年 | 1153篇 |
2011年 | 1358篇 |
2010年 | 715篇 |
2009年 | 600篇 |
2008年 | 971篇 |
2007年 | 899篇 |
2006年 | 898篇 |
2005年 | 811篇 |
2004年 | 649篇 |
2003年 | 505篇 |
2002年 | 470篇 |
2001年 | 289篇 |
2000年 | 207篇 |
1999年 | 225篇 |
1998年 | 179篇 |
1997年 | 196篇 |
1996年 | 184篇 |
1995年 | 168篇 |
1994年 | 154篇 |
1993年 | 137篇 |
1992年 | 119篇 |
1991年 | 100篇 |
1990年 | 90篇 |
1989年 | 61篇 |
1988年 | 73篇 |
1987年 | 83篇 |
1986年 | 74篇 |
1985年 | 103篇 |
1984年 | 90篇 |
1983年 | 56篇 |
1982年 | 84篇 |
1981年 | 77篇 |
1980年 | 70篇 |
1979年 | 68篇 |
1978年 | 69篇 |
1977年 | 60篇 |
1976年 | 84篇 |
1974年 | 52篇 |
1973年 | 52篇 |
排序方式: 共有10000条查询结果,搜索用时 390 毫秒
971.
Evgen V. Govor Andrey B. Lysenko Alexander N. Chernega Judith A.K. Howard Andriy A. Mokhir Joachim Sieler Konstantin V. Domasevitch 《Polyhedron》2008
Reaction of copper(II) acetate, lanthanium(III) or gadolinium(III) nitrate (1/5 equiv.) with pyrazinohydroxamic acid (H2Pyzha) in DMF led to a series of new heterobimetallic 15-metallacrown-5 complexes. In a MeOH/H2O solution the complexes exist as molecular unassociated metallacrowns. In solid state their structures are more complicated as it has been confirmed by X-ray analysis: discrete molecular metallacrowns [Gd(NO3)2{Cu(pyzha)}5(DMF)4(NO3)] · 0.5C6H6 · H2O (1), [Gd(NO3)2{Cu(pyzha)}5(DMF)5](NO3) · 1.5DMF · 0.5H2O (2), [La(NO3)2{Cu(pyzha)}5(DMF)5]NO3 · 1.5DMF · 2C6H6 (3) are solvates, whereas compound [{La(NO3)2{Cu(pyzha)}5(DMF)5}2(μ2-NO3)](NO3) · 3DMF (4) is a dimer, where μ-bridged nitrate links two copper centres of the adjacent metallamacrocycles. Complex [Gd(NO3)2{Cu(pyzha)}5(DMF)2(H2O)(NO3)] · CH2Cl2 · DMF (5) self-associates into a polymer chain by means of one pyrazine moiety and the copper ring atom. Reaction of the molecular metallacrowns with excess of inorganic salts CdBr2 or Cu(OAc)2 proceeds as anion methathesis process affording heteroanionic metallacrowns: molecular [Gd(NO3)2{Cu(pyzha)}5(DMF)5] [Gd(NO3)2{Cu(pyzha)}5(DMF)4(H2O)][CdBr4] · 1.5DMF (6), and 3D hydrogen bonded polymer [La(μ2-OAc)(H2O)3{Cu(pyzha)}5 (H2O)4(NO3)](NO3) · 4H2O (7). 相似文献
972.
Amanda L. Santos Gilberto O. Chierice Kenneth S. Alexander Alan Riga Ellen Matthews 《Journal of Thermal Analysis and Calorimetry》2009,96(3):821-825
Eugenol is the main volatile compound extracted oil from clove bud, Syzygium aromaticum L., and used in traditional medicine, as a bactericide, fungicide, anesthetic, and others. Its extraction was performed using
hydrodistillation which is the most common extraction technique. Its components and thermal behavior were evaluated using
gas chromatography (GC) and differential scanning calorimetry (DSC), which provide a better characterization of these natural
compounds. This extracted product was compared to the standard eugenol results. The GC results suggested ~90% eugenol was
found in the total extracted oil, and some of its boiling characteristics were 270.1 °C for peak temperature and 244.1 J g−1 for the enthalpy variation.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
973.
974.
Vadim A. Dubskikh Anna A. Lysova Denis G. Samsonenko Alexander N. Lavrov Konstantin A. Kovalenko Danil N. Dybtsev Vladimir P. Fedin 《Molecules (Basel, Switzerland)》2021,26(5)
Three new 3D metal-organic porous frameworks based on Co(II) and 2,2′-bithiophen-5,5′-dicarboxylate (btdc2−) [Co3(btdc)3(bpy)2]·4DMF, 1; [Co3(btdc)3(pz)(dmf)2]·4DMF·1.5H2O, 2; [Co3(btdc)3(dmf)4]∙2DMF∙2H2O, 3 (bpy = 2,2′-bipyridyl, pz = pyrazine, dmf = N,N-dimethylformamide) were synthesized and structurally characterized. All compounds share the same trinuclear carboxylate building units {Co3(RCOO)6}, connected either by btdc2– ligands (1, 3) or by both btdc2– and pz bridging ligands (2). The permanent porosity of 1 was confirmed by N2, O2, CO, CO2, CH4 adsorption measurements at various temperatures (77 K, 273 K, 298 K), resulted in BET surface area 667 m2⋅g−1 and promising gas separation performance with selectivity factors up to 35.7 for CO2/N2, 45.4 for CO2/O2, 20.8 for CO2/CO, and 4.8 for CO2/CH4. The molar magnetic susceptibilities χp(T) were measured for 1 and 2 in the temperature range 1.77–330 K at magnetic fields up to 10 kOe. The room-temperature values of the effective magnetic moments for compounds 1 and 2 are μeff (300 K) ≈ 4.93 μB. The obtained results confirm the mainly paramagnetic nature of both compounds with some antiferromagnetic interactions at low-temperatures T < 20 K in 2 between the Co(II) cations separated by short pz linkers. Similar conclusions were also derived from the field-depending magnetization data of 1 and 2. 相似文献
975.
Isabel V. L. Wilkinson Kelly J. Perkins Hannah Dugdale Lee Moir Aini Vuorinen Maria Chatzopoulou Sarah E. Squire Sebastian Monecke Alexander Lomow Marcus Geese Philip D. Charles Peter Burch Jonathan M. Tinsley Graham M. Wynne Stephen G. Davies Francis X. Wilson Fraydoon Rastinejad Shabaz Mohammed Kay E. Davies Angela J. Russell 《Angewandte Chemie (International ed. in English)》2020,59(6):2420-2428
Duchenne muscular dystrophy (DMD) is a fatal muscle‐wasting disease arising from mutations in the dystrophin gene. Upregulation of utrophin to compensate for the missing dystrophin offers a potential therapy independent of patient genotype. The first‐in‐class utrophin modulator ezutromid/SMT C1100 was developed from a phenotypic screen through to a Phase 2 clinical trial. Promising efficacy and evidence of target engagement was observed in DMD patients after 24 weeks of treatment, however trial endpoints were not met after 48 weeks. The objective of this study was to understand the mechanism of action of ezutromid which could explain the lack of sustained efficacy and help development of new generations of utrophin modulators. Using chemical proteomics and phenotypic profiling we show that the aryl hydrocarbon receptor (AhR) is a target of ezutromid. Several lines of evidence demonstrate that ezutromid binds AhR with an apparent KD of 50 nm and behaves as an AhR antagonist. Furthermore, other reported AhR antagonists also upregulate utrophin, showing that this pathway, which is currently being explored in other clinical applications including oncology and rheumatoid arthritis, could also be exploited in future DMD therapies. 相似文献
976.
In Vivo Endoscopic Tissue Identification by Rapid Evaporative Ionization Mass Spectrometry (REIMS) 下载免费PDF全文
Dr. Julia Balog Dr. Sacheen Kumar James Alexander Ottmar Golf Dr. Juzheng Huang Tom Wiggins Nima Abbassi‐Ghadi Dr. Attila Enyedi Dr. Sandor Kacska James Kinross Prof. George B. Hanna Prof. Jeremy K. Nicholson Prof. Zoltan Takats 《Angewandte Chemie (International ed. in English)》2015,54(38):11059-11062
Gastrointestinal cancers are a leading cause of mortality, accounting for 23 % of cancer‐related deaths worldwide. In order to improve outcomes from these cancers, novel tissue characterization methods are needed to facilitate accurate diagnosis. Rapid evaporative ionization mass spectrometry (REIMS) is a technique developed for the in vivo classification of human tissue through mass spectrometric analysis of aerosols released during electrosurgical dissection. This ionization technique was further developed by utilizing surface induced dissociation and was integrated with an endoscopic polypectomy snare to allow in vivo analysis of the gastrointestinal tract. We tested the classification performance of this novel endoscopic REIMS method in vivo. It was shown to be capable of differentiating between healthy layers of the intestinal wall, cancer, and adenomatous polyps based on the REIMS fingerprint of each tissue type in vivo. 相似文献
977.
Strong,Thermally Superinsulating Biopolymer–Silica Aerogel Hybrids by Cogelation of Silicic Acid with Pectin 下载免费PDF全文
Dr. Shanyu Zhao Dr. Wim J. Malfait Dr. Arnaud Demilecamps Dr. Yucheng Zhang Dr. Samuel Brunner Lukas Huber Dr. Philippe Tingaut Dr. Arnaud Rigacci Dr. Tatiana Budtova Dr. Matthias M. Koebel 《Angewandte Chemie (International ed. in English)》2015,54(48):14282-14286
Silica aerogels are excellent thermal insulators, but their brittle nature has prevented widespread application. To overcome these mechanical limitations, silica–biopolymer hybrids are a promising alternative. A one‐pot process to monolithic, superinsulating pectin–silica hybrid aerogels is presented. Their structural and physical properties can be tuned by adjusting the gelation pH and pectin concentration. Hybrid aerogels made at pH 1.5 exhibit minimal dust release and vastly improved mechanical properties while remaining excellent thermal insulators. The change in the mechanical properties is directly linked to the observed “neck‐free” nanoscale network structure with thicker struts. Such a design is superior to “neck‐limited”, classical inorganic aerogels. This new class of materials opens up new perspectives for novel silica–biopolymer nanocomposite aerogels. 相似文献
978.
Nikolai V. Tsvetkov Mariya E. Mikhailova Nina G. Mikusheva Alexey A. Lezov Alexander S. Gubarev Elena V. Lebedeva 《International Journal of Polymer Analysis and Characterization》2017,22(1):27-34
Conformational and dynamo-optical properties of a homologous series of poly(cetyltrimethylammonium 2-acrylamido-2-methylpropane sulfonates) with molecular masses ranging from 80 to 700?kDa were studied in chloroform solutions by viscometry, dynamic light scattering, sedimentation, and flow birefringence. The Mark–Kuhn–Houwink Equations for this polymer in chloroform were obtained; the values of hydrodynamic diameter and the Kuhn segment length as well as the value of intrinsic anisotropy of polarizability of the monomer unit were defined. 相似文献
979.
王柏懿 《应用数学和力学(英文版)》2003,24(8):928-935
By using Lagrangian method, the flow properties of a dusty-gas point source in a supersonic free stream were studied and the particle parameters in the near-symmetry-axis region were obtained . It is demonstrated that fairly inertial particles travel along oscillating and intersecting trajectories between the bow and termination shock waves . In this region, formation of " mufti- layer structure" in panicle distribution with alternating low- and high density layers is revealed. Moreover, sharp accumulation of particles occurs near the envelopes of particle trajectories . 相似文献
980.
G. C. Eiden M. E. Cisper M. L. Alexander P. H. Hemberger N. S. Nogar 《Journal of the American Society for Mass Spectrometry》1993,4(9):706-709
Laser desorption in an ion trap mass spectrometer shows significant promise for both qualitative and trace analysis. In this work, we explore various combinations of time-varying DC and radiofrequency (RF) fields in order to optimize laser-generated signals. By judicious choice of timing between the laser desorption pulse and the rise in the applied RF trapping potential, we observed over an order of magnitude enhancement in the trapped ion signal. This new method for laser desorption has enabled us to observe mass spectra of many compounds (e.g., pyrene, dichlorobenzene, and ferrocene) that are barely detectable using previous laser desorption methods. Effects of laser timing and the magnitude of the steady-state RF potential are discussed. 相似文献