全文获取类型
收费全文 | 1198篇 |
免费 | 29篇 |
国内免费 | 2篇 |
专业分类
化学 | 684篇 |
晶体学 | 6篇 |
力学 | 40篇 |
数学 | 118篇 |
物理学 | 381篇 |
出版年
2022年 | 18篇 |
2021年 | 20篇 |
2020年 | 27篇 |
2019年 | 22篇 |
2018年 | 27篇 |
2017年 | 25篇 |
2016年 | 22篇 |
2015年 | 29篇 |
2014年 | 36篇 |
2013年 | 132篇 |
2012年 | 59篇 |
2011年 | 67篇 |
2010年 | 43篇 |
2009年 | 48篇 |
2008年 | 45篇 |
2007年 | 55篇 |
2006年 | 34篇 |
2005年 | 37篇 |
2004年 | 40篇 |
2003年 | 25篇 |
2002年 | 32篇 |
2001年 | 17篇 |
2000年 | 17篇 |
1999年 | 18篇 |
1998年 | 11篇 |
1997年 | 6篇 |
1996年 | 12篇 |
1995年 | 11篇 |
1994年 | 8篇 |
1993年 | 7篇 |
1992年 | 16篇 |
1991年 | 7篇 |
1990年 | 12篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 11篇 |
1986年 | 10篇 |
1985年 | 18篇 |
1984年 | 21篇 |
1983年 | 13篇 |
1982年 | 11篇 |
1981年 | 16篇 |
1980年 | 26篇 |
1979年 | 13篇 |
1978年 | 19篇 |
1977年 | 17篇 |
1976年 | 6篇 |
1975年 | 6篇 |
1973年 | 7篇 |
1972年 | 7篇 |
排序方式: 共有1229条查询结果,搜索用时 31 毫秒
91.
BRST resolution is studied for the principally graded Wakimoto module of
recently found in math.QA/0005203. The submodule structure is completely determined and irreducible representations can be obtained as the zero-th cohomology group. 相似文献
92.
A complete normal coordinate analysis was performed for five-coordinate non-rigid triarylantimony diester SbPh3(O2CR)2, known to be a bioactive molecule, using Wilson G-F matrix method and Urey Bradley force field. The study of vibrational
dynamics was performed using the concept of group frequencies and band intensities.
相似文献
93.
High power continuous wave operation of a diode face-pumped thin Nd:YAG slab laser is reported. A novel pumping geometry for
a thin Nd:YAG slab using cylindrical lens duct coupled diode laser stacks is demonstrated. In a close-coupled resonator, a
maximum laser output power of 260 W in multimode operation is obtained. This corresponds to a slope efficiency of 34% and
an optical-to-optical efficiency of 27%, respectively. In high-brightness operation, a polarized laser output of 70 W has
been obtained with a beam quality factor close to 4 in both directions. The polarization contrast ratio is >100.
PACS 42.55.Xi; 42.60.Pk; 42.60.By 相似文献
94.
Vikram Sen Neeraj Panwar G.L. Bhalla 《Journal of Physics and Chemistry of Solids》2007,68(9):1685-1691
We report here the structural, magnetotransport and morphological studies of Sb-doped La2/3Ba1/3Mn1−xSbxO3 perovskite manganites. Pristine material La2/3Ba1/3MnO3 (LBMO) shows two insulator-metal (I-M) transitions in the electrical resistivity-temperature (ρ-T) behavior. While the higher temperature transition (TP1) at ∼340 K is reminiscent of the usual I-M transition in manganites, the lower temperature transition (TP2) at ∼250 K has been ascribed to the grain boundary (GB) effects arising out of the ionic size mismatch between the ions present at the rare-earth site (La3+ and Ba2+). With Sb-doping TP1 shifts to lower temperatures while TP2 remains invariant up to 3% and shifts to lower temperature for 5%. Room temperature electrical resistivity and the peak values also increase successively with Sb-doping. Scanning electron micrographs of the samples exhibit a gradual increase in their grain sizes with Sb indicating a gradual decrease in the GB density. Shift of TP1 with doping is explained on the basis of a competition between double-exchange and super-exchange mechanisms. The overall electrical resistivity increases and the shift in the electrical resistivity hump (TP2) with Sb-doping is found related to be gradually decreasing GB density and the ensuing lattice strain increase at the GBs. The intrinsic magnetoresistance (MR) gets suppressed and extrinsic MR gets enhanced with Sb-doping. At T>TP1, the electrical resistivity is found to follow the adiabatic polaron hopping model whereas the electron-magnon scattering is found to dominate in the metallic regime (T<TP1). 相似文献
95.
Nonlinear ion-acoustic solitary waves in an electron-positron-ion plasma with relativistic positron beam 下载免费PDF全文
The propagation characteristics of nonlinear ion–acoustic(IA) solitary waves(SWs) are studied in thermal electron–positron–ion plasma considering the effect of relativistic positron beam. Starting from a set of fluid equations and using the reductive perturbation technique, we derive a Korteweg–de Vries(KdV) equation which governs the evolution of weakly nonlinear IA SWs in relativistic beam driven plasmas. The properties of the IA soliton are studied, and it is shown that the presence of relativistic positron beam significantly modifies the characteristics of IA solitons. 相似文献
96.
Mazaahir Kidwai Preeti Misra Bhavesh Dave Kumar R. Bhushan Rajendra K. Saxena Meena Singh 《Monatshefte für Chemie / Chemical Monthly》2000,17(3):1207-1212
A novel synthesis of 6-fluoro-7-(5-aryl-1,3,4-thiadiazol/oxadiazol-2-yl-sulfanyl)-4-quinolone-3-carboxylic acids from 7-chloro-6-fluoro-4-quinolone-3-carboxylic acid and 5-substituted 1,3,4-thiadiazoles/oxadiazoles on basic alumina under microwave activation is described. All compounds were screened for their in vitro antibacterial activity against B. lichenformis, 2689, K. aerogens 2281, S. typhimurium 2501, E. herbicola 2491, and P. vulgaris 2027 and found to possess activities comparable to that of the standard drug norfloxacin. 相似文献
97.
Photoinduced charge separation in donor–acceptor conjugates plays a pivotal role in technology breakthroughs, especially in the areas of efficient conversion of solar energy into electrical energy and fuels. Extending the lifetime of the charge separated species is a necessity for their practical utilization, and this is often achieved by following the mechanism of natural photosynthesis where the process of electron/hole migration occurs distantly separating the radical ion pairs. Here, we hypothesize and demonstrate a new mechanism to stabilize the charge separated states via the process of electron exchange among the different acceptor entities in multimodular donor–acceptor conjugates. For this, star-shaped, central triphenylamine derived, dimethylamine–tetracyanobutadiene conjugates have been newly designed and characterized. Electron exchange was witnessed upon electroreduction in conjugates having multiple numbers of electron acceptors. Using ultrafast spectroscopy, the occurrence of excited state charge separation, and the effect of electron exchange in prolonging the lifetime of charge separated states in the conjugates having multiple acceptors have been successfully demonstrated. This work constitutes the first example of stabilizing charge-separated states via the process of electron exchange.The significance of electron exchange in stabilizing the charge-separated state is revealed in multi-modular donor–acceptor conjugates. 相似文献
98.
The synthesis of a unique tetrasaccharide linked to the serine 61 of human clotting factor IX through an α-l-fucose residue has been achieved for the first time in excellent yield. All glycosylation and protecting group manipulation steps are high yielding and reproducible for a scale-up preparation. A sequential glycosylation strategy has been used to assemble suitably protected monosaccharide synthons for the preparation of the target tetrasaccharide. 相似文献
99.
100.
The higher order contributions to Jacobian in Fujikawa’s path integral framework is considered and the form of anomaly equation
in higher orders is established. An argument for the Adler-Bardeen theorem in this formulation is given. 相似文献