全文获取类型
收费全文 | 844篇 |
免费 | 30篇 |
国内免费 | 7篇 |
专业分类
化学 | 582篇 |
晶体学 | 3篇 |
力学 | 17篇 |
数学 | 81篇 |
物理学 | 198篇 |
出版年
2022年 | 11篇 |
2021年 | 7篇 |
2020年 | 15篇 |
2019年 | 8篇 |
2018年 | 12篇 |
2017年 | 7篇 |
2016年 | 17篇 |
2015年 | 9篇 |
2014年 | 23篇 |
2013年 | 36篇 |
2012年 | 37篇 |
2011年 | 54篇 |
2010年 | 21篇 |
2009年 | 12篇 |
2008年 | 35篇 |
2007年 | 55篇 |
2006年 | 57篇 |
2005年 | 36篇 |
2004年 | 43篇 |
2003年 | 39篇 |
2002年 | 12篇 |
2001年 | 13篇 |
2000年 | 9篇 |
1998年 | 7篇 |
1997年 | 11篇 |
1996年 | 14篇 |
1993年 | 8篇 |
1992年 | 9篇 |
1991年 | 10篇 |
1990年 | 12篇 |
1989年 | 7篇 |
1988年 | 12篇 |
1987年 | 5篇 |
1986年 | 9篇 |
1985年 | 8篇 |
1984年 | 8篇 |
1983年 | 11篇 |
1982年 | 13篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1979年 | 10篇 |
1978年 | 9篇 |
1977年 | 16篇 |
1976年 | 19篇 |
1975年 | 20篇 |
1974年 | 9篇 |
1973年 | 8篇 |
1971年 | 7篇 |
1969年 | 5篇 |
1932年 | 7篇 |
排序方式: 共有881条查询结果,搜索用时 171 毫秒
101.
Organocatalyzed Asymmetric Conjugate Addition of Heteroaryl and Aryl Trifluoroborates: a Synthetic Strategy for Discoipyrrole D 下载免费PDF全文
Jiun‐Le Shih Thien S. Nguyen Prof. Jeremy A. May 《Angewandte Chemie (International ed. in English)》2015,54(34):9931-9935
Bis‐heteroaryl or bis‐aryl stereocenters were formed by an organocatalytic enantioselective conjugate addition using the respective trifluoroborate salts as nucleophiles. Control studies suggested that fluoride dissociation is necessary in the anhydrous conditions. This strategy is applicable to the synthesis of discoipyrrole D, an inhibitor of BR5 fibroblast migration. 相似文献
102.
Lewis Acid Catalyzed Condensation–Cyclization Cascade: Direct Synthesis of Di/Trifluoromethyl‐1,2,3,4‐tetrahydroquinazolines 下载免费PDF全文
Prof. Dr. G. K. Surya Prakash Dr. Attila Papp Socrates B. Munoz Nathan May John‐Paul Jones Prof. Dr. Ralf Haiges Prof. Dr. Pierre Mothé Esteves Dr. Thomas Mathew 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(28):10170-10178
Condensed heterocycles such as quinazolines constitute the framework of many promising drugs. The great impact of the dramatic fluorine effect in pharmaceuticals prompted a great surge in the quest for fluorinated drug design resulting in over 20 % fluorine‐containing drugs in the market today. Therefore, finding an efficient and cost‐effective method for the direct synthesis of fluorine‐tagged quinazoline systems is of great significance in the pharmaceutical arena. For the first time, a one‐pot sequential condensation–cyclization reaction to form selectively the difluoro/trifluoromethylated tetrahydroquinazolines from simple components difluoro/trifluoroacetaldehyde hemiacetal and aromatic amines is reported. Our recent studies using difluoro/trifluoroacetaldehyde hemiacetal as simple and elegant difluoro/trifluoromethyl synthons and metal triflates such as gallium triflate as safe and stable Lewis acid catalysts led us to this direct synthesis protocol for the expedient and convenient synthesis of fluorinated quinazolines. DFT calculations at PCM/B3LYP/6‐31++G** were carried out for evaluating a possible reaction mechanism for this cyclization. According to the DFT calculations, product stereochemistry is thermodynamically driven, favoring the cis isomer as the major product, which is also confirmed experimentally. 相似文献
103.
Ali Bagheri Jonathan Yeow Hamidreza Arandiyan Jiangtao Xu Cyrille Boyer May Lim 《Macromolecular rapid communications》2016,37(11):905-910
The polymerization of the photocleavable monomer, o‐nitrobenzyl methacrylate (NBMA), is investigated using photoinduced electron/energy transfer reversible addition‐fragmentation chain transfer polymerization. The polymerizations under visible red (λ max = 635 nm, 0.7 mW cm−2) and yellow (λ max = 560 nm, 9.7 mW cm−2) light are performed and demonstrate rational evidence of a controlled/living radical polymerization process. Well‐defined poly(o‐nitrobenzyl methacrylate) (PNBMA) homopolymers with good control over the molecular weight and polymer dispersity are successfully synthesized by varying the irradiation time and/or targeted degree of polymerization. Chain extension of a poly(oligo(ethylene glycol) methyl ether methacrylate) macro‐chain transfer agent with NBMA is carried out to fabricate photocleavable amphiphilic block copolymers (BCP). Finally, these self‐assembled BCP rapidly dissemble under UV light suggesting the photoresponsive character of NBMA is not altered during the polymerization under yellow or red light. Such photoresponsive polymers can be potentially used for the remote‐controlled delivery of therapeutic compounds.
104.
A hybrid ion mobility-mass spectrometer (IM-MS) incorporating a variable-temperature (80–400 K) drift tube is presented. The
instrument utilizes an electron ionization (EI) source for fundamental small molecule studies. Ions are transferred to the
IM-MS analyzer stages through a quadrupole, which can operate in either broad transmission or mass-selective mode. Ion beam
modulation for the ion mobility experiment is accomplished by an electronic shutter gate. The variable-temperature ion mobility
spectrometer consists of a 30.2 cm uniform field drift tube enclosed within a thermal envelope. Subambient temperatures down
to 80 K are achievable through cryogenic cooling with liquid nitrogen, while elevated temperatures can be accessed through
resistive heating of the envelope. Mobility separated ions are mass analyzed by an orthogonal time-of-flight (TOF) mass spectrometer.
This report describes the technological considerations for operating the instrument at variable temperature, and preliminary
results are presented for IM-MS analysis of several small mass ions. Specifically, mobility separations of benzene fragment
ions generated by EI are used to illustrate significantly improved (greater than 50%) ion mobility resolution at low temperatures
resulting from decreased diffusional broadening. Preliminary results on the separation of long-lived electronic states of
Ti+ formed by EI of TiCl4 and hydration reactions of Ti+ with residual water are presented. 相似文献
105.
Wyche TP Hou Y Braun D Cohen HC Xiong MP Bugni TS 《The Journal of organic chemistry》2011,76(16):6542-6547
A marine Verrucosispora sp. isolated from the sponge Chondrilla caribensis f. caribensis was found to produce thiocoraline, a potent cytotoxic compound. Five new analogs of thiocoraline were isolated and represent the first analogs of thiocoraline. 22'-Deoxythiocoraline (2), thiochondrilline C (5), and 12'-sulfoxythiocoraline (6) demonstrated significant cytotoxicity against the A549 human cancer cell line with EC(50) values of 0.13, 2.86, and 1.26 μM, respectively. The analogs provide insight into the SAR and biosynthesis of thiocoraline. The DP4 probability method was used to analyze ab initio NMR calculations to confirm stereochemical assignments. 相似文献
106.
Schnaars DD Batista ER Gaunt AJ Hayton TW May I Reilly SD Scott BL Wu G 《Chemical communications (Cambridge, England)》2011,47(27):7647-7649
Syntheses and characterization of UCl(2)((Ar)acnac)(2), UI(2)((Ar)acnac)(2), and PuI(2)((Ar)acnac)(2) are reported ((Ar)acnac denotes a bis-phenyl β-ketoiminate ligand where Ar = 3,5-(t)Bu(2)C(6)H(3)). Structural analyses and computations show significant metal-ligand orbital interaction differences in U(IV) vs. Pu(IV) bonding. 相似文献
107.
Santos CM Tria MC Vergara RA Ahmed F Advincula RC Rodrigues DF 《Chemical communications (Cambridge, England)》2011,47(31):8892-8894
The first report on the fabrication and application of a nanocomposite containing poly-N-vinyl carbazole (PVK) polymer and graphene oxide (GO) as an antimicrobial film was demonstrated. The antimicrobial film was 90% more effective in preventing bacterial colonization relative to the unmodified surface. More importantly, the nanocomposite thin film showed higher bacterial toxicity than pure GO-modified surface. 相似文献
108.
Sharma SK May PS Jones MB Lense S Hardcastle KI MacBeth CE 《Chemical communications (Cambridge, England)》2011,47(6):1827-1829
The ligand bis(2-isobutyrylamidophenyl)amine has been prepared and used to stabilize both mononuclear and dinuclear cobalt(II) complexes. The nuclearity of the cobalt product is regulated by the deprotonation state of the ligand. Both complexes catalytically oxidize triphenylphosphine to triphenylphosphine oxide in the presence of O(2). 相似文献
109.
The blue organic dye, 2,6-dichloroindophenol (DCIP), was immobilized on PEGylated Merrifield resin after a chlorination step followed by a nucleophilic substitution reaction, using microwave-assisted methodology. The final product was a blue pigmented resin that can be reversibly reduced by ascorbic acid and changes color from blue to light yellow. Structural elucidation of this immobilized indicator was confirmed through FTIR and elemental analyses. 相似文献
110.
Christopher J. May Jeffrey C. Schank Sanjay Joshi Jonathan Tran R. J. Taylor I‐Esha Scott 《Complexity》2006,12(1):53-66
Biorobotic research continually demonstrates that behavior and cognition can be the emergent products of (1) embodied agents that are (2) dynamically embedded within an environment and (3) equipped with simple sensorimotor rules. Thigmotaxis is an orientation response to contact manifested in infant rats by wall following, corner burrowing, and group aggregation. Orientation responses have been long thought to be mediated only by sensory or central processes. Here we show that a random control architecture in a morphologically similar robot embedded in a scaled environment can reproduce thigmotaxic behaviors seen in infant rats. We conclude that (1) and (2) may play a larger role than previously thought in the generation of complex behaviors. © 2006 Wiley Periodicals, Inc. Complexity 12: 53–66, 2006 相似文献