全文获取类型
收费全文 | 15134篇 |
免费 | 509篇 |
国内免费 | 96篇 |
专业分类
化学 | 9867篇 |
晶体学 | 101篇 |
力学 | 323篇 |
综合类 | 2篇 |
数学 | 2233篇 |
物理学 | 3213篇 |
出版年
2023年 | 92篇 |
2022年 | 115篇 |
2021年 | 216篇 |
2020年 | 259篇 |
2019年 | 282篇 |
2018年 | 194篇 |
2017年 | 171篇 |
2016年 | 436篇 |
2015年 | 341篇 |
2014年 | 377篇 |
2013年 | 699篇 |
2012年 | 722篇 |
2011年 | 811篇 |
2010年 | 551篇 |
2009年 | 479篇 |
2008年 | 723篇 |
2007年 | 798篇 |
2006年 | 659篇 |
2005年 | 699篇 |
2004年 | 586篇 |
2003年 | 481篇 |
2002年 | 450篇 |
2001年 | 272篇 |
2000年 | 233篇 |
1999年 | 180篇 |
1998年 | 174篇 |
1997年 | 174篇 |
1996年 | 196篇 |
1995年 | 182篇 |
1994年 | 181篇 |
1993年 | 193篇 |
1992年 | 188篇 |
1991年 | 152篇 |
1990年 | 134篇 |
1989年 | 117篇 |
1988年 | 117篇 |
1987年 | 123篇 |
1986年 | 128篇 |
1985年 | 167篇 |
1984年 | 161篇 |
1983年 | 127篇 |
1982年 | 137篇 |
1981年 | 129篇 |
1980年 | 117篇 |
1979年 | 116篇 |
1978年 | 121篇 |
1977年 | 91篇 |
1975年 | 97篇 |
1974年 | 99篇 |
1973年 | 98篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
871.
Monitoring the Transition from Spherical to Polymer‐like Surfactant Micelles Using Small‐Angle X‐Ray Scattering
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Grethe Vestergaard Jensen Dr. Reidar Lund Dr. Jérémie Gummel Dr. Theyencheri Narayanan Prof. Jan Skov Pedersen 《Angewandte Chemie (International ed. in English)》2014,53(43):11524-11528
Despite over a century of modern surfactant science, the kinetic pathways of morphological transitions in micellar systems are still not well understood. This is mainly as a result of the lack of sufficiently fast methods that can capture the structural changes of such transitions. Herein, a simple surfactant system consisting of sodium dodecyl sulfate (SDS) in aqueous NaCl solutions is investigated. Combining synchrotron radiation small‐angle X‐ray scattering (SAXS) with fast stopped‐flow mixing schemes allows monitoring the process where polymer‐like micelles are formed from globular micelles when the salt concentration is suddenly increased. The results show that “worm‐like” micelles are formed by fusion of globular micelles and short cylinders in a fashion that bears similarities to a step‐like polymerization process. 相似文献
872.
Benjamin L. Solomon Christopher P. Landee Jan L. Wikaira 《Journal of Coordination Chemistry》2014,67(23-24):3953-3971
Using 2-amino-5-chloro-3-fluoropyridine, two new copper halide coordination complexes and two new salts have been synthesized: [(3,5-FCAP)2CuCl2] (1), [(3,5-FCAP)2CuBr2](2), (3,5-FCAPH)2[CuCl4] (3) and (3,5-FCAPH)2[CuBr4] (4) [3,5-FCAP?=?2-amino-5-chloro-3-fluoropyridine; 3,5-FCAPH?=?2-amino-5-chloro-3-fluoropyridinium]. These complexes have been analyzed through single-crystal X-ray diffraction and temperature-dependent magnetic susceptibility. Compounds 1 and 2 crystallize in the triclinic space group P-1, while 3 and 4 crystallize in the monoclinic space group P21/c. All structures were distinct, with 1 giving a bihalide bridged chain, 2 yielding a halide bridged dimer, 3 forming a two-halide bridged chain via short Cl???Cl contacts, and 4 producing a rectangular sheet via short Br???Br contacts. All four compounds exhibit anti-ferromagnetic interactions and were fit to linear chain (1 and 3), dimer (2), and rectangular 2-D sheet (4) models. The resulting J/kB values are ?3.4(1), ?31.3(8), ?0.9(1), and ?9.46(6)?K with an α value (α?=?J?/J) of 0.06(2), respectively. 相似文献
873.
Synthesis and EPR/UV/Vis‐NIR Spectroelectrochemical Investigation of a Persistent Phosphanyl Radical Dication
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Kai Schwedtmann Stephen Schulz Felix Hennersdorf Prof. Dr. Thomas Strassner Dr. Evgenia Dmitrieva Prof. Dr. Jan J. Weigand 《Angewandte Chemie (International ed. in English)》2015,54(38):11054-11058
The reaction of the bis(imidazoliumyl)‐substituted PI cation [(2‐ImDipp)P(4‐ImDipp)]+ ( 10 +) (2‐Im=imidazolium‐2‐yl; 4‐Im=imidazolium‐4‐yl; Dipp=2,6‐di‐isopropylphenyl) with trifluoromethanesulfonic acid (HOTf) or methyl trifluoromethylsulfonate (MeOTf) yields the corresponding protonated [(2‐ImDipp)PH(4‐ImDipp)]2+ ( 11 2+) and methylated [(2‐ImDipp)PMe(4‐ImDipp)]2+ ( 12 2+) dications, respectively. EPR/UV/Vis‐NIR spectroelectrochemical investigation of the low‐coordinated PI cation 10 + predicted a stable and “bottleable” P‐centered radical dication [(2‐ImDipp)P(4‐ImDipp)]2+. ( 13 2+.). The reaction of 10 + with the nitrosyl salt NO[OTf] yields the persistent phosphanyl radical dication 13 2+. as triflate salt in crystalline form. Quantum chemical investigation revealed an exceptional high spin density at the P atom. 相似文献
874.
Ana Isabel González Flórez Eike Mucha Dr. Doo‐Sik Ahn Sandy Gewinner Dr. Wieland Schöllkopf Prof. Dr. Kevin Pagel Dr. Gert von Helden 《Angewandte Chemie (International ed. in English)》2016,55(10):3295-3299
Here we present a combined experimental and theoretical study on the secondary structure of isolated proteins as a function of charge state. In infrared spectra of the proteins ubiquitin and cytochrome c, amide I (C=O stretch) and amide II (N–H bend) bands can be found at positions that are typical for condensed‐phase proteins. For high charge states a new band appears, substantially red‐shifted from the amide II band observed at lower charge states. The observations are interpreted in terms of Coulomb‐driven transitions in secondary structures from mostly helical to extended C5‐type hydrogen‐bonded structures. Support for this interpretation comes from simple energy considerations as well as from quantum chemical calculations on model peptides. This transition in secondary structure is most likely universal for isolated proteins that occur in mass spectrometric experiments. 相似文献
875.
Enzyme‐ and Ruthenium‐Catalyzed Enantioselective Transformation of α‐Allenic Alcohols into 2,3‐Dihydrofurans
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Bin Yang Dr. Can Zhu Dr. Youai Qiu Prof. Dr. Jan‐E. Bäckvall 《Angewandte Chemie (International ed. in English)》2016,55(18):5568-5572
An efficient one‐pot method for the enzyme‐ and ruthenium‐catalyzed enantioselective transformation of α‐allenic alcohols into 2,3‐dihydrofurans has been developed. The method involves an enzymatic kinetic resolution and a subsequent ruthenium‐catalyzed cycloisomerization, which provides 2,3‐dihydrofurans with excellent enantioselectivity (up to >99 % ee). A ruthenium carbene species was proposed as a key intermediate in the cycloisomerization. 相似文献
876.
Eva Hoffmann GyÖrgy Marko-Varga Istvan Csiky Jan Årke JÖnsoon 《International journal of environmental analytical chemistry》2013,93(1-3):161-171
Abstract A three-column ion chromatographic system for the removal of humic substances from natural waters, and subsequent on-line concentration and determination of nitrate and sulfate using non-suppressed ion chromatography is presented. Humic substances are removed using disposable adsorption columns packed with chemically bonded amine silica material. The sample is directly transfered to an ion exchange column where the anions are concentrated ca 10 times. After reversing the flow, the ions are transferred to a third column where they are separated and quantified. The detection limit is less than 1 mg L?1 of nitrate or sulfate in water containing 45mgL?1 of humic acid. 相似文献
877.
Yoshitake T Ichinose F Yoshida H Todoroki K Kehr J Inoue O Nohta H Yamaguchi M 《Biomedical chromatography : BMC》2003,17(8):509-516
A highly sensitive, selective and simple method is described for the determination of histamine by high-performance liquid chromatography (HPLC) with fluorescence detection. The method is based on an intramolecular excimer-forming fluorescence derivatization of histamine with 4-(1-pyrene)butyric acid N-hydroxysuccinimide ester (PSE), followed by reversed-phase HPLC. Histamine, having two amino moieties in a molecule, was converted to the dipyrene-labeled derivative by reaction with PSE. The derivative afforded intramolecular excimer fluorescence (450-540 nm), which can clearly be discriminated from the monomer fluorescence (370-420 nm) emitted from PSE. Typically, a 10 micro L sample solution was mixed with 100 micro L of derivatization reagent solution, which was a mixture of 0.5 mm PSE in acetonitrile and 0.5 mm potassium carbonate in water (8:2, v/v). The derivatization was carried out at 100 degrees C for 90 min. The PSE derivative of histamine could be separated by reversed-phase ODS column with isocratic elution using acetonitrile:water (82:18, v/v) containing 0.03% triethylamine. The detection limit (singnal-to-noise ratio = 3) of histamine was 0.5 fmol for a 30 micro L injection. The method was successfully applied to the determination of histamine in human urine, and had enough selectivity and sensitivity for urinary histamine quantification. 相似文献
878.
Kamil Motyka Jan Hlavá?Miroslav Soural Pavel HradilPetr Krej?í Lubomír KvapilMiloš Weiss 《Tetrahedron letters》2011,52(6):715-717
2-(4-Amino-substituted-3-nitrophenyl)-3-hydroxyquinolin-4(1H)-ones have been studied to evaluate their fluorescence properties and possible use as molecular fluorescent probes. The amino group was substituted with various alkyl moieties possessing a suitable terminal functional group (such as hydroxy or amino group) that could serve to bind a 3-hydroxyquinolin-4(1H)-one (3HQ) fluorescence label to a biomolecule. Besides simple hydrocarbon chains, ligands containing ethylenoxy units as optimal spacers were also tested. The structure-fluorescence properties and theoretical applicability of the studied molecules are discussed. 相似文献
879.
880.
Kinga Nawalany Aleksandra Rusin Mariusz Kpczyski Alexei Mikhailov Gabriela Kramer-Marek Mirosaw
nietura Jan Potowicz Zdzisaw Krawczyk Maria Nowakowska 《Journal of photochemistry and photobiology. B, Biology》2009,97(1):8-17
Two photosensitizing systems: (1) tetrakis(4-hydroxyphenyl)porphyrin (p-THPP) encapsulated in sterically stabilized liposomes (SSL) and (2) p-THPP functionalized by covalent attachment of poly(ethylene glycol) (p-THPP–PEG2000) were studied in vitro. The dark and photo cytotoxicity of these systems were evaluated on two cell lines: HCT 116, a human colorectal carcinoma cell line, and DU 145, a prostate cancer cell line and compared with these determined for free p-THPP. It was demonstrated that both encapsulation in liposomes as well as attachment of PEG chain result in pronounced reduction of the dark cytotoxicity of the parent porphyrin. The liposomal formulation showed higher than p-THPP–PEG2000 photocytotoxicity towards both cell lines used in the studies. 相似文献