全文获取类型
收费全文 | 1548篇 |
免费 | 47篇 |
国内免费 | 15篇 |
专业分类
化学 | 724篇 |
晶体学 | 12篇 |
力学 | 31篇 |
数学 | 159篇 |
物理学 | 391篇 |
无线电 | 293篇 |
出版年
2024年 | 10篇 |
2023年 | 32篇 |
2022年 | 29篇 |
2021年 | 37篇 |
2020年 | 41篇 |
2019年 | 40篇 |
2018年 | 38篇 |
2017年 | 28篇 |
2016年 | 53篇 |
2015年 | 30篇 |
2014年 | 48篇 |
2013年 | 80篇 |
2012年 | 116篇 |
2011年 | 113篇 |
2010年 | 61篇 |
2009年 | 72篇 |
2008年 | 89篇 |
2007年 | 61篇 |
2006年 | 67篇 |
2005年 | 53篇 |
2004年 | 40篇 |
2003年 | 37篇 |
2002年 | 40篇 |
2001年 | 20篇 |
2000年 | 27篇 |
1999年 | 15篇 |
1998年 | 20篇 |
1997年 | 13篇 |
1996年 | 15篇 |
1995年 | 21篇 |
1994年 | 22篇 |
1993年 | 13篇 |
1992年 | 13篇 |
1991年 | 18篇 |
1990年 | 23篇 |
1989年 | 15篇 |
1988年 | 9篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1985年 | 18篇 |
1984年 | 16篇 |
1983年 | 12篇 |
1982年 | 10篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1979年 | 10篇 |
1978年 | 7篇 |
1976年 | 6篇 |
1975年 | 7篇 |
1973年 | 7篇 |
排序方式: 共有1610条查询结果,搜索用时 15 毫秒
201.
M. Sinha H. Dutta S.K. Pradhan 《Physica E: Low-dimensional Systems and Nanostructures》2006,33(2):367-369
Nanocrystalline Mg–Zn-ferrite is prepared by ball milling the stoichiometric powder mixture of MgO, ZnO and α-Fe2O3. A non-stoichiometric ferrite phase is noticed to form after 3 h of milling when particles of starting materials became nano-sized. After 25 h of milling, stoichiometric ferrite phase is formed with 9 nm particle size. Post annealing study of ball-milled sample reveals that the nanocrystalline ferrite phase is stable up to 873 K and then starts to decompose into individual starting phases. However, heat treatment of unmilled stoichiometric powder mixture even at 1473 K for 1 h duration does not result in formation of stoichiometric Mg–Zn-ferrite phase. 相似文献
202.
In the present paper we use a control function to define a generalized contraction in Menger spaces and obtain a unique fixed point theorem. The work is in line with the research for developing probabilistic contractions with the help of control functions and related fixed point results. We have given an example to which our theorem is applicable. Some corollaries are also discussed. 相似文献
203.
The Euler equations with two controls are discretized by using the bilinear transformation method. The discrete equations are explicit and exhibit a sufficient number of conserved quantities for integrability. The explicit solution to the discrete controlled Euler top are deduced in terms of elliptic functions. 相似文献
204.
A. Dutta 《辐射效应与固体损伤》2013,168(2):92-96
In this letter, we illustrate the importance of fluid dynamics research by considering two particular areas of study: nano- and micro-scale fluid and plasma dynamics. We show how improved scientific knowledge of nano- and micro-fluid dynamics can significantly enhance our future. Application is also discussed regarding environmental aspects. 相似文献
205.
Vivek S. Borkar Mrinal K. Ghosh‡ 《Stochastics An International Journal of Probability and Stochastic Processes》2013,85(4):221-231
The problem of ergodic control of a reflecting diffusion in a compact domain is analysed under the condition of partial degeneracy, i.e. when its transition kernel after some time is absolutely continuous with respect to the Lebesgue measure on a part of the state space. Existence of a value function and a “martingale dynamic programming principle” are established by mapping the problem to a discrete time control problem. Implications for existence of optimal controls are derived. 相似文献
206.
In this article, we address stochastic differential games of mixed type with both control and stopping times. Under standard assumptions, we show that the value of the game can be characterized as the unique viscosity solution of corresponding Hamilton-Jacobi-Isaacs (HJI) variational inequalities. 相似文献
207.
Perpetua Wanjiru Muchiri M. Agouri Sahar Abdeen Mohamed A. Abbassi S. Taj B. Manaut Ashim Dutta Junaid Khan T. Mundad Youssef Bakkour Murefah mana Al-Anazy 《International journal of quantum chemistry》2024,124(7):e27368
This research work investigates the structural, electronic, optical, and thermoelectric characteristics of VFeZ (Z = N and P) half-Heusler compounds. The study employs the full-potential linearized augmented plane wave (FP-LAPW) method integrated into the WIEN2K algorithm, serving as the underpinning framework for density functional theory (DFT) analysis. In the study, we use the PBE generalized gradient approximation (PBE-GGA) to identify numerous parameters associated with structural and elastic properties. Lattice parameter results are in agreement with previous outcomes. Moreover, computed elastic parameters satisfy the criterion for stability. In the cubic structure VFeZ (Z = N and P) is ductile, to enhance the computations of electronic characteristics, Tran and Blaha's modified Becke-Johnson potential (TB-mBJ) is used. Our simulations demonstrate that the materials exhibit semiconductor behavior, with a direct band gap for VFeZ (Z = N and P). Strong UV absorption is found via optical experiments suggest compounds are suitable for optical application. Furthermore, study of the thermoelectric properties suggests its application in the thermoelectric generators. 相似文献
208.
Suprakash Biswas Tanoy Dutta Akshay Silswal Rohit Bhowal Deepak Chopra Apurba L. Koner 《Chemical science》2021,12(28):9630
Long-term visualization of lysosomal properties is extremely crucial to evaluate diseases related to their dysfunction. However, many of the reported lysotrackers are less conducive to imaging lysosomes precisely because they suffer from fluorescence quenching and other inherent drawbacks such as pH-sensitivity, polarity insensitivity, water insolubility, slow diffusibility, and poor photostability. To overcome these limitations, we have utilized an alkyl chain length engineering strategy and synthesized a series of lysosome targeting fluorescent derivatives namely NIMCs by attaching a morpholine moiety at the peri position of the 1,8-naphthalimide (NI) ring through varying alkyl spacers between morpholine and 1,8-naphthalimide. The structural and optical properties of the synthesized NIMCs were explored by 1H-NMR, single-crystal X-ray diffraction, UV-Vis, and fluorescence spectroscopy. Afterward, optical spectroscopic measurements were carefully performed to identify a pH-tolerant, polarity sensitive, and highly photostable fluoroprobes for further live-cell imaging applications. NIMC6 displayed excellent pH-tolerant and polarity-sensitive properties. Consequently, all NIMCs were employed in kidney fibroblast cells (BHK-21) to investigate their applicability for lysosome targeting and probing lysosomal micropolarity. Interestingly, a switching of localization from lysosomes to the endoplasmic reticulum (ER) was also achieved by controlling the linker length and this phenomenon was subsequently applied in determining ER micropolarity. Additionally, the selected probe NIMC6 was also employed in BHK-21 cells for 3-D spheroid imaging and in Caenorhabditis elegans (C. elegans) for in vivo imaging, to evaluate its efficacy for imaging animal models.A series naphthalimide-based fluorophores were designed by alkyl spacer length engineering to discover a pH-tolerant lysosomal marker. This approach also allows to probe lysosome-related organelles in C. elegans and communication between organelles. 相似文献
209.
S.K. Karak J. Dutta Majumdar W. Lojkowski A. Michalski L. Ciupinski K.J. Kurzydłowski 《哲学杂志》2013,93(5):516-534
Ferritic steel with compositions 83.0Fe–13.5Cr–2.0Al–0.5Ti (alloy A), 79.0Fe–17.5Cr–2.0Al–0.5Ti (alloy B), 75.0Fe–21.5Cr–2.0Al–0.5Ti (alloy C) and 71.0Fe–25.5Cr–2.0Al–0.5Ti (alloy D) (all in wt%) each with a 1.0?wt% nano-Y2O3 dispersion were synthesized by mechanical alloying and consolidated by pulse plasma sintering at 600, 800 and 1000°C using a 75-MPa uniaxial pressure applied for 5?min and a 70-kA pulse current at 3?Hz pulse frequency. X-ray diffraction, scanning and transmission electron microscopy and energy disperse spectroscopy techniques have been used to characterize the microstructural and phase evolution of all the alloys at different stages of mechano-chemical synthesis and consolidation. Mechanical properties in terms of hardness, compressive strength, yield strength and Young's modulus were determined using a micro/nano-indenter and universal testing machine. All ferritic alloys recorded very high levels of compressive strength (850–2850?MPa), yield strength (500–1556?MPa), Young's modulus (175–250?GPa) and nanoindentation hardness (9.5–15.5?GPa), with up to 1–1.5 times greater strength than other oxide dispersion-strengthened ferritic steels (<1200?MPa). These extraordinary levels of mechanical properties can be attributed to the typical microstructure of uniform dispersion of 10–20-nm Y2Ti2O7 or Y2O3 particles in a high-alloy ferritic matrix. 相似文献
210.
ABSTRACTThe stages of crystallization of magnetron sputter-deposited Ni63Zr37 film with mostly amorphous structure have been investigated by differential scanning calorimetry (DSC) and in-situ annealing at 300°C by use of heating stage on a high-resolution transmission electron microscope (HRTEM). These results have been further confirmed by grazing incidence X-ray diffraction analyses of thin film specimens annealed ex-situ at 300°C for various durations. The temperature for crystallization found by DSC has been found to increase from 371°C to 434°C with an increase in heating rate from 3°C/min to 10°C/min, and the apparent activation energy for amorphous to crystalline transformation has been found as ~260.2?kJ/mol from the Kissinger plot. Studies on HRTEM using in-situ heating stage have shown the crystallization to occur on annealing at 300°C for ~10?min. Crystallization at a temperature lower than that found by DSC is attributed to structural relaxation with reduction of free volume due to thermal activation. It has been observed that Ni3Zr forms first due to its large negative enthalpy of formation, and is followed by the formation of Ni-rich solid solution (Niss) grains. HRTEM studies have shown grain rotation with the formation of partial dislocations at Ni3Zr-Niss interfaces as well as twinning followed by detwinning with dislocation formation in the Niss matrix possibly to reduce the interfacial energy. 相似文献