全文获取类型
收费全文 | 15309篇 |
免费 | 569篇 |
国内免费 | 43篇 |
专业分类
化学 | 10288篇 |
晶体学 | 233篇 |
力学 | 489篇 |
综合类 | 1篇 |
数学 | 1208篇 |
物理学 | 3702篇 |
出版年
2024年 | 67篇 |
2023年 | 179篇 |
2022年 | 454篇 |
2021年 | 439篇 |
2020年 | 484篇 |
2019年 | 535篇 |
2018年 | 508篇 |
2017年 | 483篇 |
2016年 | 706篇 |
2015年 | 502篇 |
2014年 | 780篇 |
2013年 | 1300篇 |
2012年 | 1142篇 |
2011年 | 1188篇 |
2010年 | 798篇 |
2009年 | 613篇 |
2008年 | 742篇 |
2007年 | 743篇 |
2006年 | 587篇 |
2005年 | 506篇 |
2004年 | 384篇 |
2003年 | 320篇 |
2002年 | 265篇 |
2001年 | 166篇 |
2000年 | 133篇 |
1999年 | 103篇 |
1998年 | 77篇 |
1997年 | 107篇 |
1996年 | 103篇 |
1995年 | 76篇 |
1994年 | 77篇 |
1993年 | 109篇 |
1992年 | 101篇 |
1991年 | 78篇 |
1990年 | 79篇 |
1989年 | 76篇 |
1988年 | 50篇 |
1987年 | 49篇 |
1986年 | 48篇 |
1985年 | 69篇 |
1984年 | 69篇 |
1983年 | 54篇 |
1982年 | 47篇 |
1981年 | 38篇 |
1980年 | 47篇 |
1979年 | 64篇 |
1978年 | 51篇 |
1977年 | 55篇 |
1976年 | 41篇 |
1975年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Raju Suresh Kumar Abdulrahman I. Almansour Natarajan Arumugam D. Kotresha J. Carlos Menéndez Raju Ranjith Kumar 《Journal of heterocyclic chemistry》2021,58(2):580-588
A three-component, [3 + 2]-cycloaddition/annulation domino protocol is described for the synthesis in excellent yield of a polycyclic cage-like heterocyclic hybrid (PCHH) that comprises various advantaged structural units viz., α,β-unsaturated ketone moiety, 4-pyridinone and pyrroloisoquinoline in a cage-like framework. The antitumor activity of PCHH on human breast (MCF7), colon (HCT116), cervical (JURKAT) and lung (NCI-H460) malignant cell lines inhibited the propagation of all cell lines. This hybrid molecule displayed increased broad-spectrum anticancer activity with higher doses of PCHH. Furthermore, the compound induced 45.21% of early apoptosis and 46.32% of late apoptosis in the Jurkat cancer cell line. Cell cycle analysis showed that this cage-like compound caused cell cycle arrest of Jurkat cells at the S phase and sub G0/G1 phase. Additionally, it led to increased DNA fragmentation and mitochondrial membrane permeabilization through activation of caspase-3 enzyme. Present investigation demonstrates the specific cytotoxic activity of the cage-like compound and the induction of apoptosis through the intrinsic pathway of Jurkat cells. 相似文献
992.
Jena Sudipta Ray Asit Sahoo Ambika Kamila Pradeep Kumar Nayak Sanghamitra Panda Pratap Chandra 《Chemistry of Natural Compounds》2021,57(6):1147-1149
Chemistry of Natural Compounds - 相似文献
993.
Akkaraboyina Lakshmi Lavanya K. Gowri Bala Kumari K. R. S. Prasad Pradeep Kumar Brahman 《Electroanalysis》2021,33(3):591-600
In this work, an economically viable, very low cost, indigenous, ubiquitously available electrochemical sensor based on bimetallic nickel and tungsten nanoparticles modified pencil graphite electrode (NiNP-WNP@PGE) was fabricated for the sensitive and selective detection of bisphenol A (BPA). The NiNP-WNP@PGE sensor was prepared by a facile electrochemical one step co-deposition method. The prepared nanocomposite was morphologically characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX), X-ray diffraction (XRD), electrochemically by cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The proposed sensor displayed high electrocatalytic activity towards electro-oxidation of BPA with one irreversible peak. The fabricated sensor displayed a wide detection window between 0.025 μM and 250 μM with a limit of detection of 0.012 μM. PGE sensor was successfully engaged for the detection of BPA in bottled water, biological, and baby glass samples. 相似文献
994.
JPC – Journal of Planar Chromatography – Modern TLC - A water-in-oil microemulsion has been used for the first time as a mobile phase in thin-layer chromatography of amino acids. A new... 相似文献
995.
Samuel K Yin W Stearns RA Tang YS Chaudhary AG Jewell JP Lanza T Lin LS Hagmann WK Evans DC Kumar S 《Journal of mass spectrometry : JMS》2003,38(2):211-221
Metabolic activation of drug candidates to electrophilic reactive metabolites that can covalently modify cellular macromolecules may result in acute and/or idiosyncratic immune system-mediated toxicities in humans. This presents a significant potential liability for the future development of these compounds as safe therapeutic agents. We present here an example of an approach where sites of metabolic activation within a new drug candidate series were rapidly identified using online liquid chromatography/multi-stage mass spectrometry on an ion trap mass spectrometer. This was accomplished by trapping the reactive intermediates formed upon incubation of compounds with rat and human liver microsomes as their corresponding glutathione conjugates and mass spectral characterization of these thiol adducts. Based on the structures of the GSH adducts identified, potential sites and mechanisms of bioactivation within the chemical structure were proposed. These metabolism studies were interfaced with iterative structural modifications of the chemical series in order to block these bioactivation sites within the molecule. This strategy led to a significant reduction in the propensity of the compounds to undergo metabolic activation as evidenced by reductions in the irreversible binding of radioactivity to liver microsomal material upon incubation of tritium-labeled compounds with this in vitro system. With the efficiency and throughput achievable with such an approach, it appears feasible to identify and address the metabolic activation potential of new drug leads during routine metabolite identification studies in an early drug discovery setting. 相似文献
996.
Nandy JP Prabhakaran EN Kumar SK Kunwar AC Iqbal J 《The Journal of organic chemistry》2003,68(5):1679-1692
A novel chemo- and diastereoselective aerobic epoxidation of the N-cinnamoyl peptides catalyzed by polyaniline-supported cobalt(II) salen (PASCOS) is described. The N-cinnamoyl proline derived peptides 1 show a high pi-facial selectivity during these epoxidations. The origin of this diastereoselectivity in 1 has been attributed to (i) the propensity of the N-cinnamoyl proline amide to exist predominantly as trans rotamer in CDCl3, DMSO-d6, and CH3CN medium and (ii) existence of these peptides as organized structures (gamma- and beta-turns) due to the presence of intramolecular hydrogen bonds. An extensive solution NMR and MD simulation study on 1d and 1f indicates that the origin of the high pi-facial selectivity is due to the well-defined gamma- and beta-turns which result in the hindrance of one face of the cinnamoyl double bond in the transition state of the epoxidation reaction. 相似文献
997.
Garg BS Nandan Kumar D 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2003,59(2):229-234
Complexes of nickel(II) of N,N'-disalicylidene-1,2-phenylenediamine (H2dsp), N,N'-disalicylidene-3,4-diaminotoluene (H2dst), 4-nitro-N,N'-disalicylidene-1,2-phenylenediamine (H2ndsp) and N,N'-disalicylidene ethylenediamine (H2salen) have been prepared and characterised by elemental analysis, electronic, IR, magnetic susceptibility measurement, 1H NMR and thermal studies. TG studies show that the Ni(dsp) and Ni(salen) complex decomposed in one step and Ni(dst) and Ni(ndsp) complex in two steps. Kinetic and thermodynamic parameters were computed from the thermal decomposition data. The activation energy of either one step decomposition or two step decomposition of complexes lies 72-95 kJ mol(-1) range. 相似文献
998.
Mahata PK Venkatesh C Syam Kumar UK Ila H Junjappa H 《The Journal of organic chemistry》2003,68(10):3966-3975
A simple, highly efficient, and regioselective synthesis of functionalized quinolines through Vilsmeier cyclization of a variety of alpha-oxoketene-N,S-anilinoacetals has been reported. The cyclization is found to be facile with N,S-acetals bearing strongly activating groups on aniline, whereas yields of quinolines are moderate in other cases. The reaction could also be extended for the synthesis of substituted tricyclic benzo[h]quinoline, pyrido[2,3-h]quinoline, 4,7-diphenylphenanthroline, and tetracyclic quino[8,7-h]quinoline by performing a Vilsmeier reaction on N,S-acetals derived from 1-naphthylamine, m-phenylenediamine, o-phenylenediamine, and 1,5-diaminonaphthalene, respectively. A few of the newly synthesized quinolines are subjected to further transformation to afford 2-unsubstituted (Raney-Ni/Ethanol), quinoline-5,8-quinone (NBS/H(2)SO(4)), or 2-alkyl/aryl aminoquinolines through sequential m-CPBA oxidation to the corresponding (2-methylsulfonyl)quinoline followed by replacement with appropriate amines. Similarly, cycloannulation of a few 2-methylthio-3-benzoylquinolines with hydrazine hydrate under microwave irradiation afforded the corresponding substituted and fused pyrazolo[3,4-b]quinolines in excellent yields, whereas TBTH/AIBN-mediated cyclization of the corresponding 3-(2-bromobenzoyl)-2-methylthioquinolines yielded the corresponding benzothiopyrano-fused quinolines through radical translocation. 相似文献
999.
The synthesis of the title spirodione, a new class of auxiliary based chiral synthon using (−)-trans-2-phenylcyclohexanol and its application to the asymmetric Diels-Alder reaction are described. Methodology for detachment of the chiral auxiliary from the cycloadduct has been developed. 相似文献
1000.