全文获取类型
收费全文 | 14720篇 |
免费 | 540篇 |
国内免费 | 42篇 |
专业分类
化学 | 9997篇 |
晶体学 | 229篇 |
力学 | 465篇 |
综合类 | 1篇 |
数学 | 1114篇 |
物理学 | 3496篇 |
出版年
2024年 | 66篇 |
2023年 | 169篇 |
2022年 | 441篇 |
2021年 | 427篇 |
2020年 | 466篇 |
2019年 | 522篇 |
2018年 | 488篇 |
2017年 | 462篇 |
2016年 | 669篇 |
2015年 | 477篇 |
2014年 | 758篇 |
2013年 | 1260篇 |
2012年 | 1107篇 |
2011年 | 1147篇 |
2010年 | 760篇 |
2009年 | 586篇 |
2008年 | 719篇 |
2007年 | 721篇 |
2006年 | 560篇 |
2005年 | 491篇 |
2004年 | 377篇 |
2003年 | 313篇 |
2002年 | 252篇 |
2001年 | 155篇 |
2000年 | 131篇 |
1999年 | 99篇 |
1998年 | 71篇 |
1997年 | 99篇 |
1996年 | 94篇 |
1995年 | 73篇 |
1994年 | 68篇 |
1993年 | 93篇 |
1992年 | 97篇 |
1991年 | 77篇 |
1990年 | 68篇 |
1989年 | 71篇 |
1988年 | 49篇 |
1987年 | 45篇 |
1986年 | 42篇 |
1985年 | 63篇 |
1984年 | 62篇 |
1983年 | 53篇 |
1982年 | 47篇 |
1981年 | 37篇 |
1980年 | 45篇 |
1979年 | 62篇 |
1978年 | 48篇 |
1977年 | 53篇 |
1976年 | 41篇 |
1975年 | 34篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Parvateesam Yenda Naresh Kumar Katari Balasubramanian Satheesh Rambabu Gundla Siva Krishna Muchakayala Vijay Kumar Rekulapally 《Journal of separation science》2023,46(11):2200770
The design of an appropriate analytical method for assessing the quality of pharmaceuticals requires a deep understanding of science, and risk evaluation approaches are appreciated. The current study discusses how a related substance method was developed for Nintedanib esylate. The best possible separation between the critical peak pairs was achieved using an X-Select charged surface hybrid Phenyl Hexyl (150 × 4.6) mm, 3.5 μm column. A mixture of water, acetonitrile, and methanol in mobile phase-A (70:20:10) and mobile phase-B (20:70:10), with 0.1% trifluoroacetic acid and 0.05% formic acid in both eluents. The set flow rate, wavelength, and injection volumes were 1.0 ml/min, 285 nm, and 5 μl, respectively, with gradient elution. The method conditions were validated as per regulatory requirements and United States Pharmacopeia general chapter < 1225 >. The correlation coefficient for all impurities from the linearity experiment was found to be > 0.999. The % relative standard deviation from the precision experiments ranged from 0.4 to 3.6. The mean %recovery from the accuracy study ranged from 92.5 to 106.5. Demonstrated the power of the stability-indicating method through degradation studies; the active drug component is more vulnerable to oxidation than other conditions. Final method conditions were further evaluated using a full-factorial design. The robust method conditions were identified using the graphical optimization from the design space. 相似文献
992.
Ainhoa Salazar Dr. Marta Moreno-Simoni Dr. Sunit Kumar Jorge Labella Prof. Tomás Torres Prof. Gema de la Torre 《Angewandte Chemie (International ed. in English)》2023,62(44):e202311255
Herein we report the first example of a supramolecular cage that works as a catalytic molecular reactor to perform transformations over fullerenes in aqueous medium. Taking advantage of the ability of metallo–organic Pd(II)-subphthalocyanine (SubPc) capsules to form stable host:guest complexes with C60, we have prepared a water-soluble cage that provides a hydrophobic environment for conducting cycloadditions over encapsulated C60, namely, Diels–Alder reactions with anthracene. Indeed, the presence of catalytic amounts of SubPc cage dissolved in water promotes co-encapsulation of insoluble C60 and anthracene substrates, allowing the reaction to occur inside the cavity under mild conditions. The lower stability of the host:guest complex with the resulting C60 cycloadduct facilitates its displacement by pristine C60, which grants catalytic turnover. Moreover, bis-addition compounds are regioselectively formed inside the cage when using excess anthracene. 相似文献
993.
Subhajit Chakraborty Risov Das Mohd Riyaz Kousik Das Ashutosh Kumar Singh Debabrata Bagchi Chathakudath P. Vinod Sebastian C. Peter 《Angewandte Chemie (International ed. in English)》2023,62(9):e202216613
We present surface reconstruction-induced C−C coupling whereby CO2 is converted into ethylene. The wurtzite phase of CuGaS2. undergoes in situ surface reconstruction, leading to the formation of a thin CuO layer over the pristine catalyst, which facilitates selective conversion of CO2 to ethylene (C2H4). Upon illumination, the catalyst efficiently converts CO2 to C2H4 with 75.1 % selectivity (92.7 % selectivity in terms of Relectron) and a 20.6 μmol g−1 h−1 evolution rate. Subsequent spectroscopic and microscopic studies supported by theoretical analysis revealed operando-generated Cu2+, with the assistance of existing Cu+, functioning as an anchor for the generated *CO and thereby facilitating C−C coupling. This study demonstrates strain-induced in situ surface reconstruction leading to heterojunction formation, which finetunes the oxidation state of Cu and modulates the CO2 reduction reaction pathway to selective formation of ethylene. 相似文献
994.
Constantine Tsounis Dr. Priyank V. Kumar Dr. Hassan Masood Rutvij Pankaj Kulkarni Prof. Gopalakrishnan Sai Gautam Prof. Christoph R. Müller Prof. Rose Amal Dr. Denis A. Kuznetsov 《Angewandte Chemie (International ed. in English)》2023,62(4):e202210828
MXenes, due to their tailorable chemistry and favourable physical properties, have great promise in electrocatalytic energy conversion reactions. To exploit fully their enormous potential, further advances specific to electrocatalysis revolving around their performance, stability, compositional discovery and synthesis are required. The most recent advances in these aspects are discussed in detail: surface functional and stoichiometric modifications which can improve performance, Pourbaix stability related to their electrocatalytic operating conditions, density functional theory and advances in machine learning for their discovery, and prospects in large scale synthesis and solution processing techniques to produce membrane electrode assemblies and integrated electrodes. This Review provides a perspective that is complemented by new density functional theory calculations which show how these recent advances in MXene material design are paving the way for effective electrocatalysts required for the transition to integrated renewable energy systems. 相似文献
995.
Dr. Mamta Yadav Dr. Devesh Kumar Singh Dr. Dharmendra Kumar Yadav Dr. Piyush Kumar Sonkar Dr. Rupali Gupta Prof. Dr. Vellaichamy Ganesan 《Chemphyschem》2023,24(19):e202300117
In the present work, the oxygen reduction reaction (ORR) is explored in an acidic medium with two different catalytic supports (multi-walled carbon nanotubes (MWCNTs) and nitrogen-doped multi-walled carbon nanotubes (NMWCNTs)) and two different catalysts (copper phthalocyanine (CuPc) and sulfonic acid functionalized CuPc (CuPc-SO3−)). The composite, NMWCNTs-CuPc-SO3− exhibits high ORR activity (assessed based on the onset potential (0.57 V vs. reversible hydrogen electrode) and Tafel slope) in comparison to the other composites. Rotating ring disc electrode (RRDE) studies demonstrate a highly selective four-electron ORR (less than 2.5 % H2O2 formation) at the NMWCNTs-CuPc-SO3−. The synergistic effect of the catalyst support (NMWCNTs) and sulfonic acid functionalization of the catalyst (in CuPc-SO3−) increase the efficiency and selectivity of the ORR at the NMWCNTs-CuPc-SO3−. The catalyst activity of NMWCNTs-CuPc-SO3− has been compared with many reported materials and found to be better than several catalysts. NMWCNTs-CuPc-SO3− shows high tolerance for methanol and very small deviation in the onset potential (10 mV) between the linear sweep voltammetry responses recorded before and after 3000 cyclic voltammetry cycles, demonstrating exceptional durability. The high durability is attributed to the stabilization of CuPc-SO3− by the additional coordination with nitrogen (Cu-Nx) present on the surface of NMWCNTs. 相似文献
996.
Avigyan Naskar Kousik Kumar Bhanja Rakesh Kumar Roy Dr. Niladri Patra 《Chemphyschem》2023,24(21):e202300306
Mutations in multi-domain leucine-rich repeat kinase 2 (LRRK2) have been an interest to researchers as these mutations are associated with Parkinson's disease. G2019S mutation in LRRK2 kinase domain leads to the formation of additional hydrogen bonds by S2019 which results in stabilization of the active state of the kinase, thereby increasing kinase activity. Two additional hydrogen bonds of S2019 are reported separately. Here, a mechanistic picture of the formation of additional hydrogen bonds of S2019 with Q1919 (also with E1920) is presented using ‘active’ Roco4 kinase as a homology model and its relationship with the stabilization of the ‘active’ G2019S LRRK2 kinase. A conformational flipping of residue Q1919 was found which helped to form stable hydrogen bond with S2019 and made ‘active’ state more stable in G2019S LRRK2. Two different states were found within the ‘active’ kinase with respect to the conformational change (flipping) in Q1919. Two doubly-mutated systems, G2019S/Q1919A and G2019S/E1920 K, were studied separately to check the effect of Q1919 and E1920. For both cases, the stable S2 state was not formed, leading to a decrease in kinase activity. These results indicate that both the additional hydrogen bonds of S2019 (with Q1919 and E1920) are necessary to stabilize the active G2019S LRRK2. 相似文献
997.
Karthikraja Esackraj Dr. Naga Venkateswara Rao Nulakani Dr. Venkata Surya Kumar Choutipalli Dr. Chandra Chowdhury Dr. Palanichamy Murugan Dr. V. G. Vaidyanathan Prof. Venkatesan Subramanian 《Chemphyschem》2023,24(11):e202300035
Generally, graphynes have been generated by the insertion of acetylenic content (−C≡C−) in the graphene network in different ratios. Also, several aesthetically pleasing architectures of two-dimensional (2D) flatlands have been reported with the incorporation of acetylenic linkers between the heteroatomic constituents. Prompted by the experimental realization of boron phosphide, which has provided new insights on the boron-pnictogen family, we have modelled novel forms of acetylene-mediated borophosphene nanosheets by joining the orthorhombic borophosphene stripes with different widths and with different atomic constituents using acetylenic linkers. Structural stabilities and properties of these novel forms have been assessed using first-principles calculations. Investigation of electronic band structure elucidates that all the novel forms show the linear band crossing closer to the Fermi level at Dirac point with distorted Dirac cones. The linearity in the hole and electronic bands impose the high Fermi velocity to the charge carriers close to that of graphene. Finally, we have also unravelled the propitious features of acetylene-mediated borophosphene nanosheets as anodes in Li-ion batteries. 相似文献
998.
The excess Gibb's free energy of mixing, GE, for ethyl iodide+toluene at 25°C have been obtained from the measured vapor pressuure data. The HE and GE values for ethyl iodide+toluene are positive throughout the ethyl iodide concentration range and GE>HE. The results have been analyzed in terms of Flory and ideal associated model theory of nonelectrolyte solutions. It has been observed that the ideal associated model approach which assumes the presence of AN and A2B molecular species describes well (within±10 J-mol–1 in the worst case) the general dependence of HE on XA (mole fraction of ethyl iodide) over the whole composition range for ethyl iodide+toluene mixtures. The equilibrium constants for A+A AB and 2A+BA2B reactions along with the enthalpies of formation of AB and A2B molecular species have been calculated. 相似文献
999.
Matthew J. Hills Irmgard Kiewitt Kumar D. Mukherjee 《Applied biochemistry and biotechnology》1991,27(2):123-129
Lipase from rape (Brassica napus L., immobilized onto celite, catalyzes esterification and transesterification reactions in hexane. The activity of the lipase is stimulated up to 35 fold by the addition of water (1.3% w/v). The activity of the lipase in hydrolysis is about 8 times higher than in the esterification reactions in hexane. Interesteri-fication reactions between mono- and diacylglycerols and transesterification reactions of mono- and diacylglycerols with alcohols were also catalyzed at relatively high rates but transesterification/esterification of these acylglycerols with fatty acids was comparatively slow. In transesterification reactions, triacylglycerols reacted rather slowly. 相似文献
1000.
Dinesh Kumar Ashu Rani D. S. N. Prasad K. S. Gupta 《Reaction Kinetics and Catalysis Letters》1991,43(1):133-141