全文获取类型
收费全文 | 1588篇 |
免费 | 75篇 |
国内免费 | 15篇 |
专业分类
化学 | 950篇 |
晶体学 | 17篇 |
力学 | 35篇 |
数学 | 379篇 |
物理学 | 297篇 |
出版年
2024年 | 3篇 |
2023年 | 13篇 |
2022年 | 32篇 |
2021年 | 44篇 |
2020年 | 33篇 |
2019年 | 46篇 |
2018年 | 48篇 |
2017年 | 53篇 |
2016年 | 67篇 |
2015年 | 45篇 |
2014年 | 102篇 |
2013年 | 153篇 |
2012年 | 119篇 |
2011年 | 99篇 |
2010年 | 85篇 |
2009年 | 65篇 |
2008年 | 97篇 |
2007年 | 80篇 |
2006年 | 81篇 |
2005年 | 53篇 |
2004年 | 62篇 |
2003年 | 49篇 |
2002年 | 41篇 |
2001年 | 19篇 |
2000年 | 19篇 |
1999年 | 19篇 |
1998年 | 7篇 |
1997年 | 6篇 |
1996年 | 9篇 |
1995年 | 9篇 |
1994年 | 8篇 |
1993年 | 9篇 |
1992年 | 10篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 11篇 |
1988年 | 8篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1983年 | 5篇 |
1982年 | 15篇 |
1981年 | 1篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有1678条查询结果,搜索用时 31 毫秒
181.
In this work, strongly continuous semigroups of pseudocontractions are studied based on an implicit iterative algorithm. Strong convergence theorems of fixed points are obtained in an arbitrary Banach space. 相似文献
182.
G. Chandra Sekhar Reddy A. Uma Ravi Sankar M. Veera Narayana Reddy C. Radha Rani C. Suresh Reddy 《Journal of heterocyclic chemistry》2011,48(6):1229-1233
A series of a new class of phosphorus analogue macrocycles was accomplished by condensation of N‐substituted‐[bis(3,5‐dimethyl‐2‐hydroxybenzyl)]‐amines with various phosphorus dichlorides in dry toluene in the presence of triethylamine at 0–50°C. All the title compounds were evaluated for antimicrobial activity to determine their efficacy and were effective in suppressing the growth of bacteria and fungi. The chemical structures of the title products were characterized by IR, 1H, 13C, 31P‐NMR, mass spectral studies, and elemental analysis. J. Heterocyclic Chem., (2011). 相似文献
183.
Mohd. Imran Ansari Ravi Shankar Mohd. Kamil Hussain Ruchir Kant Prakash R. Maulik K. Ravi Kumar K. Hajela 《Journal of heterocyclic chemistry》2011,48(6):1336-1341
Mono‐ and bis‐diaryl‐2H‐1,4‐benzothiazines were obtained in quantitative yields through silica‐supported perchloric acid catalyzed reaction cascade of double condensation and 1,4 addition of diaroylacetylenes with 2‐aminothiophenol at room temperature. The structures were confirmed by spectroscopic analyses and X‐ray crystallographic studies. J. Heterocyclic Chem., (2011) 相似文献
184.
P. Ravi G.M. Gore Surya P. Tewari A. K. Sikder 《International journal of quantum chemistry》2011,111(15):4352-4362
In this study, we explore the possibility that fused polynitrodiazoles act as high energy density materials. Density functional theory calculations at the B3LYP/aug‐cc‐pVDZ level were performed to predict the structure, energy of explosion (≈1.68 kcal g?1), density (≈1.98 g cm?3), detonation velocity (≈9.50 km s?1), and detonation pressure (≈41.50 GPa) of model molecules. The predicted properties have been found to be promising compared with 3,4,5‐trinitro‐1H‐pyrazole, 1,3,5‐trinitro‐1,3,5‐triazinane, and octahydro‐1,3,5,7‐tetranitro‐l,3,5,7‐tetraazocane. The nature of azoles of the molecule presumably determines the geometry, stability, sensitivity, density, and detonation performance. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 相似文献
185.
Fishkin N Maloney EK Chari RV Singh R 《Chemical communications (Cambridge, England)》2011,47(38):10752-10754
A novel pathway for ex vivo maytansinoid release from thioether linked antibody maytansinoid conjugates (AMCs) upon incubation in human plasma has been identified. A thioether succinimide-linked AMC can undergo chemical oxidation followed by sulfoxide elimination under mild aqueous conditions (pH 5.5-7.5, 37 °C). Oxidized thioether-linked AMCs exhibit high, target-specific cytotoxicity toward cancer cells. 相似文献
186.
A. J. J. van Dalen M. R. Koblischka R. Griessen M. Jirsa G. Ravi Kumar 《Physica C: Superconductivity and its Applications》1995,250(3-4):265-274
Superconducting current densities js and dynamic relaxation rates Q d ln js/d In(dBe/dt), where dBe/dt is the sweep rate of the external magnetic field Be, were measured as a function of temperature (5 K < T < 65 K) in magnetic fields up to 7 T on a twin-free DyBa2Cu3O7−δ single crystal by means of a high-sensitivity capacitance torque magnetometer. Above 15 K, we observe a “fishtail” effect, i.e. a pronounced minimum in the js(Be) curve at fields around Be = 1 T. The relaxation rate Q shows an anomalous increase at low fields which is correlated to the minimum in the js(Be) curve. Both the js versus Be and Q versus Be data are used as input parameters into the generalized inversion scheme developed by Schnack et al. [Phys. Rev. B 48 (1993) 13178] to calculate the true critical current density jc which is by definition independent of relaxation effects. Interestingly, the jc(Be, T) curves derived in this way do not show a minimum. This points clearly to a dynamic contribution to the fishtail effect. The true critical current density jc(Be, T) decreases weakly with increasing Be over the entire measured temperature and field range, as expected for single-vortex pinning. This indicates that the observed fishtail effect is not caused by a crossover from single-vortex pinning to pinning of flux bundles. The temperature dependence of jc is in good agreement with the predictions of a model based on single-vortex pinning caused by spatial fluctuations in the charge-carrier mean free path. 相似文献
187.
Moloy Sarkar Raghavendra Yellampalli Bhaswati Bhattacharya Ravi Kumar Kanaparthi Anunay Samanta 《Journal of Chemical Sciences》2007,119(2):91-97
Fluorescence behaviour of 4-benzoylamido-N-methylphthalimide (1), designed and developed for selective detection of fluoride ions, is reported. 1 displays F−-induced colour change that allows its detection with the naked eye. The F− specificity of the sensor system is evident from the fact that unlike F−, other halides do not affect the absorption characteristics of 1. Apart from the colorimetric response, the fluorescence output of 1 is also modulated by F− in a manner that permits ratiometric fluorescence signalling of F− as well. It is found that the system can detect F− in the concentration range of 10–60 μM. The results of the experiments and theoretical calculations unambiguously suggest that the changes of the electronic absorption
and fluorescence behaviour of 1, which have been exploited for signalling purpose, are due to F−-induced deprotonation of the 4-amido moiety of the sensor system. 相似文献
188.
We study two-stage, finite-scenario stochastic versions of several combinatorial optimization problems, and provide nearly
tight approximation algorithms for them. Our problems range from the graph-theoretic (shortest path, vertex cover, facility
location) to set-theoretic (set cover, bin packing), and contain representatives with different approximation ratios.
The approximation ratio of the stochastic variant of a typical problem is found to be of the same order of magnitude as its
deterministic counterpart. Furthermore, we show that common techniques for designing approximation algorithms such as LP rounding,
the primal-dual method, and the greedy algorithm, can be adapted to obtain these results. 相似文献
189.
Bao Qiang YAN Donal O'REGAN Ravi P. AGARWAL 《数学学报(英文版)》2007,23(8):1447-1456
This paper presents a lower and upper solution technique for singular second order boundary value problems on the half line. 相似文献
190.
Jae-Ou Chae Vladimir Demidiouk Jae-Won Hwang Tae Gyun Jung V. Ravi 《Reaction Kinetics and Catalysis Letters》2005,85(1):167-173
Summary A number of supported metal oxide catalysts were prepared and tested for nitrogen oxide removal from diesel engine exhaust. More than 50% of nitrogen oxides were removed using many prepared catalysts in the temperature range of 150oC-350oC. 相似文献