全文获取类型
收费全文 | 1085篇 |
免费 | 46篇 |
国内免费 | 4篇 |
专业分类
化学 | 773篇 |
晶体学 | 20篇 |
力学 | 32篇 |
数学 | 76篇 |
物理学 | 234篇 |
出版年
2024年 | 7篇 |
2023年 | 15篇 |
2022年 | 20篇 |
2021年 | 26篇 |
2020年 | 36篇 |
2019年 | 28篇 |
2018年 | 23篇 |
2017年 | 27篇 |
2016年 | 45篇 |
2015年 | 22篇 |
2014年 | 50篇 |
2013年 | 59篇 |
2012年 | 79篇 |
2011年 | 99篇 |
2010年 | 41篇 |
2009年 | 42篇 |
2008年 | 60篇 |
2007年 | 56篇 |
2006年 | 53篇 |
2005年 | 16篇 |
2004年 | 35篇 |
2003年 | 41篇 |
2002年 | 25篇 |
2001年 | 12篇 |
2000年 | 12篇 |
1999年 | 9篇 |
1998年 | 4篇 |
1997年 | 8篇 |
1996年 | 9篇 |
1995年 | 9篇 |
1994年 | 12篇 |
1993年 | 7篇 |
1992年 | 14篇 |
1990年 | 5篇 |
1989年 | 8篇 |
1988年 | 4篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1985年 | 10篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 11篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1972年 | 4篇 |
排序方式: 共有1135条查询结果,搜索用时 15 毫秒
901.
902.
A. Bhaskaran C. M. Ragavan R. Sankar R. Mohankumar R. Jayavel 《Crystal Research and Technology》2007,42(5):477-482
A new nonlinear optical material tetrakis thiourea nickel chloride (TTNC) was synthesized and single crystals were grown from mixed solvent of water and isopropanol by both slow evaporation and slow cooling methods. The grown crystals were characterized by powder X‐ray diffraction analyses to confirm the crystal structure. The presence of functional groups and the coordination of metal ions to thiourea were confirmed by FTIR and Raman spectroscopy analyses. UV‐VIS spectrum was recorded to study the optical transparency of the grown crystals. Thermal properties of the crystals have been by investigated using thermo gravimetric (TG) and differential thermal analyses (DTA), which indicate that the material does not decompose before melting. The second order nonlinear optical property of the grown crystal was examined by Kurtz powder technique and mechanical behavior was studied by Vicker's microhardness test. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
903.
Deka Jyoti Prasad Sarma Amarendra K. Govindarajan A. Kulkarni Manas 《Nonlinear dynamics》2020,100(2):1629-1640
Nonlinear Dynamics - We propose a generalized parity-time ($$\mathcal {PT}$$)-symmetric Liénard oscillator with two different orders of nonlinear position-dependent dissipation. We study the... 相似文献
904.
Abir Das Rajib Mandal Harihara Subramanian Ravi Sankar Dr. Subramani Kumaran Dr. J. Richard Premkumar Dipanti Borah Prof. Dr. Basker Sundararaju 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2024,136(6):e202315005
Metal-catalyzed asymmetric C−H bond annulation strategy offers a versatile platform, allowing the construction of complex P-chiral molecules through atom- and step-economical fashion. However, regioselective insertion of π-coupling partner between M−C bond with high enantio-induction remain elusive. Using commercially available Co(II) salt and chiral-Salox ligands, we demonstrate an unusual protocol for the regio-reversal, enantioselective C−H bond annulation of phosphinamide with bromoalkyne through desymmetrization. The reaction proceeds through ligand-assisted enantiodetermining cyclocobaltation followed by regioselective insertion of bromoalkyne between Co−C, subsequent reductive elimination, and halogen exchange with carboxylate resulted in P-stereogenic compounds in excellent ee (up to >99 %). The isolation of cobaltacycle involved in the catalytic cycle and the outcome of control experiments provide support for a plausible mechanism. 相似文献
905.
Amol Chhatrapati Bisen Anjali Mishra Sristi Agrawal Sachin Nashik Sanap Arpon Biswas Sarvesh Kumar Verma Rabi Sankar Bhatta 《Journal of mass spectrometry : JMS》2024,59(6):e5031
Managing ocular microbial infections typically requires pharmacotherapy using antibiotic eye drops, such as moxifloxacin hydrochloride (MFX), combined with an antifungal agent like amphotericin B (AB). We carried out and validated an LC–MS/MS assay to quantify these compounds in rabbit tear fluid in order to look into the pharmacokinetics of these two drugs. We employed a protein precipitation technique for the extraction of drugs under examination. A Waters Symmetry C18 column was used to separate the analytes and internal standard. The composition of the mobile phase was like (A) 0.1% v/v formic acid in water and (B) methanol. The detection of MFX and AB was accomplished through the utilization of positive ion electrospray ionization under multiple reaction monitoring mode. The linearity curves for both analytes exhibited an acceptable trendline across a concentration range of 2.34–300 ng/mL for MFX and 7.81–1000 ng/mL for AB in surrogate rabbit tear fluid. The lower limit of quantitation for MFX was 2.34 ng/mL, while for AB, it was 7.81 ng/mL. The approach was strictly validated, encompassing tests of selectivity, linearity (with r2 > 0.99), precision, accuracy, matrix effects, and stability. Consequently, we employed this method to evaluate the pharmacokinetics profiles of MFX and AB in rabbit tear fluid following single topical doses. 相似文献
906.
Here, we used an unconventional idea of cooperative vibrational strong coupling of solute and solvent molecules to enhance the rate of an esterification reaction. Different derivatives of p-nitrophenyl benzoate (solute) and isopropyl acetate (solvent) are cooperatively coupled to an infrared Fabry–Perot cavity mode. The apparent rates are increased by more than six times at the ON resonance condition, and the rate enhancement follows the lineshape of the vibrational envelope. Very interestingly, a strongly coupled system doesn''t obey the Hammett relations. Thermodynamics suggests that the reaction mechanism remains intact for cavity and non-cavity conditions. Temperature-dependent experiments show an entropy-driven process for the coupled molecules. Vacuum field coupling decreases the free energy of activation by 2–5 kJ mol−1, supporting a catalysis process. The non-linear rate enhancement can be due to the reshuffling of the energy distribution between the substituents and the reaction center across the aromatic ring. These findings underline the non-equilibrium behavior of cavity catalysis.Cavity catalysis: vibrational strong coupling of solute and solvent molecules enhanced the rate of an esterification reaction. Hammett relation breaks under strong light-matter coupling conditions suggesting its potential applications in catalysis. 相似文献
907.
Sankar Prasad Dey Dilip Kumar Dey Asok Kumar Mallik Lutz Dahlenburg 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(6):o321-o322
The title compound, 2‐hydroxyphenyl 5‐(pyrrol‐2‐yl)‐3H‐pyrrolizin‐6‐yl ketone, C18H14N2O2, was isolated from the base‐catalyzed 1:2 condensation of 2‐hydroxyacetophenone with pyrrole‐2‐carbaldehyde. The pyrrole N—H and hydroxybenzoyl O—H groups are hydrogen bonded to the benzoyl O atom. The allylic C=C double bond of the 3H‐pyrrolizine system is located between ring positions 1 and 2, the C atom at position 3 (adjacent to the N atom) being single bonded. 相似文献
908.
909.
In this paper, we consider a delayed predator-prey system with intraspecific competition among predator and a strong Allee effect in prey population growth. Using the delay as bifurcation parameter, we investigate the stability of coexisting equilibrium point and show that Hopf-bifurcation can occur when the discrete delay crosses some critical magnitude. The direction of the Hopf-bifurcating periodic solution and its stability are determined by applying the normal form method and the centre manifold theory. In addition, special attention is paid to the global continuation of local Hopf bifurcations. Using the global Hopf-bifurcation result of Wu ({Trans. Am. Math. Soc.} 350:4799?C4838, 1998) for functional differential equations, we establish the global existence of periodic solutions. Numerical simulations are carried out to validate the analytical findings. 相似文献
910.
Fereshteh Rashidi Johannes Leisen Seok‐Jhin Kim Ali A. Rownaghi Christopher W. Jones Sankar Nair 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(1):242-245
New membrane‐based molecular separation processes are an essential part of the strategy for sustainable chemical production. A large literature on “hybrid” or “mixed‐matrix” membranes exists, in which nanoparticles of a higher‐performance porous material are dispersed in a polymeric matrix to boost performance. We demonstrate that the hybrid membrane concept can be redefined to achieve much higher performance if the membrane matrix and the dispersed phase are both nanoporous crystalline materials, with no polymeric phase. As the first example of such a system, we find that surface‐treated nanoparticles of the zeolite MFI can be incorporated in situ during growth of a polycrystalline membrane of the MOF ZIF‐8. The resulting all‐nanoporous hybrid membrane shows propylene/propane separation characteristics that exceed known upper‐bound performance limits defined for polymers, nanoporous materials, and polymer‐based hybrid membranes. This serves as a starting point for a new generation of chemical separation membranes containing interconnected nanoporous crystalline phases. 相似文献