全文获取类型
收费全文 | 3116篇 |
免费 | 115篇 |
国内免费 | 5篇 |
专业分类
化学 | 2066篇 |
晶体学 | 47篇 |
力学 | 104篇 |
数学 | 292篇 |
物理学 | 727篇 |
出版年
2023年 | 43篇 |
2022年 | 83篇 |
2021年 | 79篇 |
2020年 | 82篇 |
2019年 | 103篇 |
2018年 | 90篇 |
2017年 | 89篇 |
2016年 | 136篇 |
2015年 | 87篇 |
2014年 | 130篇 |
2013年 | 254篇 |
2012年 | 191篇 |
2011年 | 223篇 |
2010年 | 130篇 |
2009年 | 96篇 |
2008年 | 143篇 |
2007年 | 139篇 |
2006年 | 125篇 |
2005年 | 106篇 |
2004年 | 115篇 |
2003年 | 66篇 |
2002年 | 54篇 |
2001年 | 39篇 |
2000年 | 23篇 |
1999年 | 31篇 |
1998年 | 21篇 |
1997年 | 20篇 |
1996年 | 23篇 |
1995年 | 23篇 |
1994年 | 19篇 |
1993年 | 32篇 |
1992年 | 18篇 |
1991年 | 12篇 |
1990年 | 21篇 |
1989年 | 23篇 |
1988年 | 14篇 |
1987年 | 20篇 |
1986年 | 19篇 |
1985年 | 17篇 |
1984年 | 22篇 |
1983年 | 16篇 |
1982年 | 13篇 |
1981年 | 12篇 |
1980年 | 29篇 |
1979年 | 14篇 |
1978年 | 17篇 |
1977年 | 28篇 |
1976年 | 14篇 |
1975年 | 14篇 |
1973年 | 15篇 |
排序方式: 共有3236条查询结果,搜索用时 15 毫秒
171.
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
172.
Gnanasekar Rani Sarnaik Jayula S. Joseph N. C. Kadwad V. B. Mathur Anupam 《Journal of Radioanalytical and Nuclear Chemistry》2021,329(1):71-76
Journal of Radioanalytical and Nuclear Chemistry - We describe a simple, user friendly two-step radioimmunoassay (RIA) based on antibody coated tubes for the measurement of free triiodothyronine in... 相似文献
173.
Sensing of Phosphates by Using Luminescent EuIII and TbIII Complexes: Application to the Microalgal Cell Chlorella vulgaris 下载免费PDF全文
Sandeep Nadella Jashobanta Sahoo Dr. Palani S. Subramanian Abhishek Sahu Dr. Sandhya Mishra Prof. Dr. Markus Albrecht 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(20):6047-6053
Phenanthroline‐based chiral ligands L1 and L2 as well as the corresponding EuIII and TbIII complexes were synthesized and characterized. The coordination compounds show red and green emission, which was explored for the sensing of a series of anions such as F?, Cl?, Br?, I?, NO3?, NO2?, HPO42?, HSO4?, CH3COO?, and HCO3?. Among the anions, HPO42? exhibited a strong response in the emission property of both europium(III) and terbium(III) complexes. The complexes showed interactions with the nucleoside phosphates adenosine triphosphate (ATP), adenosine diphosphate (ADP), and adenosine monophosphate (AMP). Owing to this recognition, these complexes have been applied as staining agents in the microalgal cell Chlorella vulgaris. The stained microalgal cells were monitored through fluorescence microscopy and scanning electron microscopy. Initially, the complexes bind to the outer cell wall and then enter the cell wall through holes in which they probably bind to phospholipids. This leads to a quenching of the luminescence properties. 相似文献
174.
Mukaiyama–Michael Reactions with trans‐2,5‐Diarylpyrrolidine Catalysts: Enantioselectivity Arises from Attractive Noncovalent Interactions,Not from Steric Hindrance 下载免费PDF全文
Dr. Eeva K. Kemppainen Dr. Gokarneswar Sahoo Antti Piisola Andrea Hamza Bianka Kótai Dr. Imre Pápai Prof. Petri M. Pihko 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(20):5983-5993
The scope of the enantioselective Mukaiyama–Michael reactions catalyzed by trans‐2,5‐diphenylpyrrolidine has been expanded to include both α‐ and β‐substituted enals. However, the rationalization of the observed enantioselectivity is far from obvious since the catalyst is not very sterically hindered. DFT calculations were carried out to rationalize the observed stereoselectivities. Transition states of the C?C bond formation between iminium intermediates and silyloxyfurans were located and their relative energies were used to estimate the stereoselectivity data. We find excellent agreement between the predicted and observed stereoselectivities. The analysis of intermolecular forces reveals that the enantioselectivity is mostly due to stabilizing noncovalent interactions between the reacting partners, not due to steric hindrance. The role of attractive noncovalent interactions in enantioselective catalysis may be underappreciated. 相似文献
175.
Organocatalytic Asymmetric Mannich Cyclization of Hydroxylactams with Acetals: Total Syntheses of (−)‐Epilupinine, (−)‐Tashiromine,and (−)‐Trachelanthamidine 下载免费PDF全文
Dr. Dipankar Koley Yarkali Krishna Kyatham Srinivas Afsar Ali Khan Ruchir Kant 《Angewandte Chemie (International ed. in English)》2014,53(48):13196-13200
An asymmetric, organocatalytic, one‐pot Mannich cyclization between a hydroxylactam and acetal is described to provide fused, bicyclic alkaloids bearing a bridgehead N atom. Both aliphatic and aromatic substrates were used in this transformation to furnish chiral pyrrolizidinone, indolizidinone, and quinolizidinone derivatives in up to 89 % yield and 97 % ee. The total syntheses of (?)‐epilupinine, (?)‐tashiromine, and (?)‐trachelanthamidine also achieved to demonstrate the generality of the process. 相似文献
176.
Lalremsiami Hrahsel Adreeja Basu Lingaraj Sahoo Robert Thangjam 《Applied biochemistry and biotechnology》2014,172(3):1530-1539
An efficient in vitro propagation method has been developed for the first time for Musa acuminata (AAA) cv. Vaibalhla, an economically important banana cultivar of Mizoram, India. Immature male flowers were used as explants. Murashige and Skoog’s (MS) medium supplemented with plant growth regulators (PGRs) were used for the regeneration process. Out of different PGR combinations, MS medium supplemented with 2 mg L?1 6-benzylaminopurine (BAP) + 0.5 mg L?1 α-naphthalene acetic acid (NAA) was optimal for production of white bud-like structures (WBLS). On this medium, explants produced the highest number of buds per explant (4.30). The highest percentage (77.77) and number (3.51) of shoot formation from each explants was observed in MS medium supplemented with 2 mg L?1 kinetin + 0.5 mg L?1 NAA. While MS medium supplemented with a combination of 2 mg L?1 BAP + 0.5 mg L?1 NAA showed the maximum shoot length (14.44 cm). Rooting efficiency of the shoots was highest in the MS basal medium without any PGRs. The plantlets were hardened successfully in the greenhouse with 96 % survival rate. Random amplified polymorphic DNA (RAPD) and inter-simple sequence repeat (ISSR) markers were employed to assess the genetic stability of in vitro regenerated plantlets of M. acuminata (AAA) cv. Vaibalhla. Eight RAPD and 8 ISSR primers were successfully used for the analysis from the 40 RAPD and 30 ISSR primers screened initially. The amplified products were monomorphic across all the regenerated plants and were similar to the mother plant. The present standardised protocol will find application in mass production, conservation and genetic transformation studies of this commercially important banana. 相似文献
177.
Amongst various carbon sources, xylan was found to be the sole inducer of endoxylanase production by Penicillium janthinellum MTCC 10889 in submerged cultivation. Endoxylanase synthesis by a xylan induced culture was initially repressed after a simultaneous addition of xylose, probably by the inducer exclusion mechanism, but it was resumed and achieved its highest level at a much later stage of growth (at 120 h). Xylose added after 30 h of growth cannot exert its full repressive effect. Although glucose was proved to be a more potent repressor than xylose, supplementation of salicin, an alcoholic β-glycoside containing d-glucose, with pure xylan resulted in an about 3.22 fold increase in the enzyme synthesis at 72 h followed by constant high production of the enzyme at least until the 144th h of growth. Inducing capacity of salicin in a xylan induced culture was significantly reduced when it was added after 30 h of growth. Addition of salicin and xylan help to partially overcome the repressive effect of xylose and glucose. Failure of salicin in recovering the endoxylanase synthesis in actinomycin D and cyclohexamide inhibited the xylan induced culture indicating that salicin cannot initiate the de novo synthesis of the enzyme. 相似文献
178.
Sumita Rani Mukesh Kumar Sumit Sharma Dinesh Kumar 《Journal of Sol-Gel Science and Technology》2014,71(3):470-476
Fine powders of zirconium oxide (ZrO2) were prepared using zirconium oxychloride by combustion method. The crystalline size of pure ZrO2 was in range of 14–45 nm. Graphene was incorporated in ZrO2 using graphene oxide as precursor and reducing it with hydrazine hydrate. X-Ray diffraction, Fourier transform infra-red spectroscopy, thermogravimetric analysis and Raman spectroscopy methods were used to characterize the samples. The role of graphene in structural transformation of ZrO2 to monoclinic phase was clearly observed. 相似文献
179.
Inoue Kazumasa Sahoo Sarata Kumar Veerasamy Nimelan Kasahara Shogo Fukushi Masahiro 《Journal of Radioanalytical and Nuclear Chemistry》2020,324(3):1423-1434
Journal of Radioanalytical and Nuclear Chemistry - Absorbed dose rates in air for 20 residential areas in Odisha were measured using a vehicle-mounted NaI(Tl) scintillation spectrometer. The... 相似文献
180.
Hao Wang Dr. Hari Krishna Bisoyi Dr. Bing-Xiang Li Dr. Michael E. McConney Dr. Timothy J. Bunning Prof. Quan Li 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(7):2706-2709
Visible-light-driven molecular switches endowing reversible modulation of the functionalities of self-organized soft materials are currently highly sought after for fundamental scientific studies and technological applications. Reported herein are the design and synthesis of two novel halogen bond donor based chiral molecular switches that exhibit reversible photoisomerization upon exposure to visible light of different wavelengths. These chiral molecular switches induce photoresponsive helical superstructures, that is, cholesteric liquid crystals, when doped into the commercially available room-temperature achiral liquid crystal host 5CB, which also acts as a halogen-bond acceptor. The induced helical superstructure containing the molecular switch with terminal iodo atoms exhibits visible-light-driven reversible unwinding, that is, a cholesteric–nematic phase transition. Interestingly, the molecular switch with terminal bromo atoms confers reversible handedness inversion to the helical superstructure upon irradiation with visible light of different wavelengths. This visible-light-driven, reversible handedness inversion, enabled by a halogen bond donor molecular switch, is unprecedented. 相似文献