全文获取类型
收费全文 | 6256篇 |
免费 | 578篇 |
国内免费 | 360篇 |
专业分类
化学 | 1879篇 |
晶体学 | 84篇 |
力学 | 1069篇 |
综合类 | 50篇 |
数学 | 924篇 |
物理学 | 3188篇 |
出版年
2024年 | 7篇 |
2023年 | 48篇 |
2022年 | 141篇 |
2021年 | 162篇 |
2020年 | 174篇 |
2019年 | 131篇 |
2018年 | 148篇 |
2017年 | 163篇 |
2016年 | 127篇 |
2015年 | 149篇 |
2014年 | 187篇 |
2013年 | 528篇 |
2012年 | 312篇 |
2011年 | 395篇 |
2010年 | 286篇 |
2009年 | 336篇 |
2008年 | 325篇 |
2007年 | 354篇 |
2006年 | 351篇 |
2005年 | 309篇 |
2004年 | 304篇 |
2003年 | 281篇 |
2002年 | 256篇 |
2001年 | 188篇 |
2000年 | 205篇 |
1999年 | 136篇 |
1998年 | 183篇 |
1997年 | 159篇 |
1996年 | 120篇 |
1995年 | 96篇 |
1994年 | 87篇 |
1993年 | 75篇 |
1992年 | 82篇 |
1991年 | 39篇 |
1990年 | 53篇 |
1989年 | 32篇 |
1988年 | 36篇 |
1987年 | 23篇 |
1986年 | 29篇 |
1985年 | 36篇 |
1984年 | 23篇 |
1983年 | 9篇 |
1982年 | 27篇 |
1981年 | 13篇 |
1980年 | 12篇 |
1979年 | 11篇 |
1978年 | 13篇 |
1977年 | 5篇 |
1976年 | 9篇 |
1973年 | 7篇 |
排序方式: 共有7194条查询结果,搜索用时 0 毫秒
21.
22.
《Physics and Chemistry of Liquids》2012,50(2-3):131-134
Abstract Thermal Conductivity of CuSbSe2 and CuBiSe2 have been studied in the solid and liquid state in a wide range of temperatures. Measurements of thermal conductivity were carried out using the concentric cylinder method which is based on the flow of heat through a cylindrical wall. 相似文献
23.
Juan Mentado-Morales Arturo Ximello-Hernndez Javier Salinas-Luna Vera L. S. Freitas Maria D. M. C. Ribeiro da Silva 《Molecules (Basel, Switzerland)》2022,27(2)
The thermochemical study of the 1,3-bis(N-carbazolyl)benzene (NCB) and 1,4-bis(diphenylamino)benzene (DAB) involved the combination of combustion calorimetric (CC) and thermogravimetric techniques. The molar heat capacities over the temperature range of (274.15 to 332.15) K, as well as the melting temperatures and enthalpies of fusion were measured for both compounds by differential scanning calorimetry (DSC). The standard molar enthalpies of formation in the crystalline phase were calculated from the values of combustion energy, which in turn were measured using a semi-micro combustion calorimeter. From the thermogravimetric analysis (TGA), the rate of mass loss as a function of the temperature was measured, which was then correlated with Langmuir’s equation to derive the vaporization enthalpies for both compounds. From the combination of experimental thermodynamic parameters, it was possible to derive the enthalpy of formation in the gaseous state of each of the title compounds. This parameter was also estimated from computational studies using the G3MP2B3 composite method. To prove the identity of the compounds, the 1H and 13C spectra were determined by nuclear magnetic resonance (NMR), and the Raman spectra of the study compounds of this work were obtained. 相似文献
25.
This paper uses heat transfer experiments and computational fluid dynamics (CFD) simulations to investigate the conjugate heat transfer (CHT) in a high-pressure pneumatic control valve assembly. A heat transfer test rig was constructed, and time–temperature histories of five test points placed on the valve assembly’s outer surface were recorded for study validation. The Unsteady Reynolds-Averaged Navier–Stokes (URANS) CFD methods with the standard k-ε turbulence closure equations were adopted in the numerical computations. Polyhedral grids were used; time step and mesh convergence studies were conducted. Simulated and measured temperatures profile comparisons revealed a good agreement. The CHT results obtained from CFD showed huge velocity fields downstream of the valve throat and the vent hole. The airflow through the valve was icy, mainly in the supersonic flow areas. Low temperatures below 273.15 K were recorded on the internal and external walls of the valve assembly. The consistency of the measured data with the numerical results demonstrates the effectiveness of polyhedral grids in exploring the CHT using CFD methods. The local entropy production rate analysis revealed that irreversibility is mainly due to viscous dissipation. The current CHT investigation provides a potential basis for thermostress analysis and optimization. 相似文献
26.
The Soret effect (thermal diffusion) of dilute aqueous solutions of NH4Cl, Me4NCl, Et4NCl, n-Pr4NCl, and n-Bu4NCl has been investigated potentiometrically using the silver, silver chloride thermocell. The molar entropies (heats) of transport have been derived from the initial and final thermoelectric powers. The concentration dependence of the entropy of transport has been examined and the effect of the ionic size on the heat of transport is discussed. The molar entropy of tetrabutylammonium chloride exhibits a sharp minimum in the neighborhood of 0.002M, the reason of which is as yet unclear. 相似文献
27.
袁都奇 《化学物理学报(中文版)》2001,14(2):246-250
应用内可逆卡诺循环的方法,导出了各种物质在临界点附近可逆与不可逆二级相变普遍适用的比热跃变公式以及广义的爱伦菲斯特方程。对简单(P,V,T)系统、超导、电介质顺电一铁电二级相变进行了应用讨论。 相似文献
28.
Qi Wang Pengyuan Liu Fanyu Zhou Lei Gao Dandan Sun Yuhang Meng Xuebin Wang 《Molecules (Basel, Switzerland)》2022,27(4)
Low-grade heat energy recycling is the key technology of waste-heat utilization, which needs to be improved. Here, we use a zinc-assisted solid-state pyrolysis route to prepare zinc-guided 3D graphene (ZnG), a 3D porous graphene with the interconnected structure. The obtained ZnG, with a high specific surface area of 1817 m2·g−1 and abundant micropores and mesopores, gives a specific capacitance of 139 F·g−1 in a neutral electrolyte when used as electrode material for supercapacitors. At a high current density of 8 A·g−1, the capacitance retention is 93% after 10,000 cycles. When ZnG is used for thermally chargeable supercapacitors, the thermoelectric conversion of the low-grade heat energy is successfully realized. This work thus provides a demonstration for low-grade heat energy conversion. 相似文献
29.
Saeed Khojaste Effatpanah Mohammad Hossein Ahmadi Seyed Hamid Delbari Giulio Lorenzini 《Entropy (Basel, Switzerland)》2022,24(2)
In recent decades, there has been an increasing trend toward the technical development of efficient energy system assessment tools owing to the growing energy demand and subsequent greenhouse gas emissions. Accordingly, in this paper, a comprehensive emergy-based exergoeconomic (emergoeconomic) method has been developed to study the biomass combustion waste heat recovery organic Rankine cycle (BCWHR-ORC), taking into account thermodynamics, economics, and sustainability aspects. To this end, the system was formulated in Engineering Equation Solver (EES) software, and then the exergy, exergoeconomic, and emergoeconomic analyses were conducted accordingly. The exergy analysis results revealed that the evaporator unit with 55.05 kilowatts and the turbine with 89.57% had the highest exergy destruction rate and exergy efficiency, respectively. Based on the exergoeconomic analysis, the cost per exergy unit , and the cost rate of the output power of the system were calculated to be 24.13 USD/GJ and 14.19 USD/h, respectively. Next, by applying the emergoeconomic approach, the monetary emergy content of the system components and the flows were calculated to evaluate the system’s sustainability. Accordingly, the turbine was found to have the highest monetary emergy rate of capital investment, equal to , and an output power monetary emergy of . Finally, a sensitivity analysis was performed to investigate the system’s overall performance characteristics from an exergoeconomic perspective, regarding the changes in the transformation coefficients (specific monetary emergy). 相似文献
30.
Seyed Ali Salehizadeh Dariush Souri 《Journal of Physics and Chemistry of Solids》2011,72(11):1381-1385
The glass transition temperature dependence to heating rate and therefore the activation energy (ΔH?) of the glass transition of (60-x)V2O5–xNiO–40TeO2 oxide glasses with 0≤x≤20 (in mol%) were investigated at heating rates φ (=3 6, 9, 10 and 12 K/min) using differential scanning calorimetry (DSC). The heating rate dependence of Tg was used to investigate the applicability of different theoretical models describing the glass transition. Using the application of Moynihan and Kissinger et al. models to the present data, different values of (ΔH?) at each different heating-rate regions were obtained. The fragility parameter (m=ΔH?/R Tg) was ∼24.98 for x=10 mol%, suggesting that this glass may be considered as a rather strong glass (fragility index m∼>20 is an indication of fragile glass). Also the compositional dependence of Tg and ΔH? was investigated. 相似文献