全文获取类型
收费全文 | 23263篇 |
免费 | 3033篇 |
国内免费 | 2774篇 |
专业分类
化学 | 16849篇 |
晶体学 | 199篇 |
力学 | 1909篇 |
综合类 | 164篇 |
数学 | 1454篇 |
物理学 | 8495篇 |
出版年
2024年 | 33篇 |
2023年 | 210篇 |
2022年 | 408篇 |
2021年 | 676篇 |
2020年 | 798篇 |
2019年 | 666篇 |
2018年 | 582篇 |
2017年 | 681篇 |
2016年 | 830篇 |
2015年 | 884篇 |
2014年 | 1173篇 |
2013年 | 1963篇 |
2012年 | 1355篇 |
2011年 | 1700篇 |
2010年 | 1337篇 |
2009年 | 1460篇 |
2008年 | 1555篇 |
2007年 | 1566篇 |
2006年 | 1478篇 |
2005年 | 1283篇 |
2004年 | 1156篇 |
2003年 | 997篇 |
2002年 | 985篇 |
2001年 | 666篇 |
2000年 | 629篇 |
1999年 | 517篇 |
1998年 | 523篇 |
1997年 | 451篇 |
1996年 | 371篇 |
1995年 | 338篇 |
1994年 | 293篇 |
1993年 | 241篇 |
1992年 | 239篇 |
1991年 | 160篇 |
1990年 | 152篇 |
1989年 | 102篇 |
1988年 | 109篇 |
1987年 | 67篇 |
1986年 | 64篇 |
1985年 | 61篇 |
1984年 | 54篇 |
1983年 | 20篇 |
1982年 | 55篇 |
1981年 | 29篇 |
1980年 | 31篇 |
1979年 | 23篇 |
1978年 | 20篇 |
1977年 | 16篇 |
1976年 | 21篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
951.
Abstract Modifications induced by the combined application of pressure (up to 800 MPa) and temperature (up to 80° C) were studied on wet and dry semolina, and on fresh pasta as such and after cooking. Rheological and immunochemical properties of the treated products were investigated, along with parameters indicating the extent of protein denaturation. No modification occurs in semolina treated at less than 45% water, below 60°C/800MPa for 10min. Egg noodles prepared from pressure/heat treated semolina had increased protein digestibility and low recognition by anti-gliadin antibodies either before or after cooking. The same effects were observed in heat/pressure treated pasta, but were lost upon subsequent cooking, although we found decreased immunochemical reactivity after heat/pressure treatment of cooked pasta. No sensory difference was found between cooked and pressure-treated semolina products. 相似文献
952.
Fluorescence resonance energy transfer between cerium ion(III) and levofloxacin is studied in a micellar solution of cetyltrimethyl ammonium bromide. A non-fluorescent 1:2 complex was formed between excited cerium ion(III) and ground state levofloxacin. The fluorescence of cerium ion(III) is quenched by levofloxacin with the quenching in accordance with the Stern–Volmer relation. The analytical relationship was established between the ratio of the fluorescence of levofloxacin present and absent cerium ion (III) and the concentration of levofloxacin, which helped to estimate the content of levofloxacin directly. 相似文献
953.
A novel system is developed for measuring the thermal resistance across thin layers of sintered copper wicks of varying porosity. Wicks to be tested are integrated into a passive vertical thermosyphon system, and the resistance is measured for a series of input power levels. The wicks are sintered to a thermally conducting pedestal above a pool of deionized water and heated from below. The apparent thermal resistance across the wick (from the pedestal/wick interface to the vapor space) under the evaporative operating conditions encountered in heat pipes is measured using thermocouples. The apparent thermal resistance across the wick is measured to be as low as 0.01°C/W, corresponding to an evaporative heat transfer coefficient of greater than 128,000 W/m2K. 相似文献
954.
This paper outlines the development and adaptation of a coupling strategy for transient temperature analysis in a solid via a conjugate heat transfer method. This study proposes a quasi‐dynamic coupling procedure to bridge the temporal disparities between the fluid and the solid. In this approach, dynamic thermal modeling in the solid is coupled with a sequence of steady states in the fluid. This quasi‐dynamic algorithm has been applied to the problem of convective heat transfer over, and transient conduction heat transfer within, a flat plate using the severe thermal conditions of a solid propellant rocket. Two different coupled thermal computations have been performed. In the first one—referred to as the reference computation—the coupling period is equal to the smallest solid time constant. In the second one, a very large coupling period is used. The results show that the procedure can predict accurate transient temperature fields at a reasonable computational cost. The simulation CPU time is approximately reduced by up to 90%, while maintaining a very good accuracy. All the details of the numerical test case are given in the paper. This application illustrates the capabilities and the overall efficiency of this coupled approach in a solid transient problem using long term simulations of time dependent flows. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
955.
This paper investigates the rotating flow and heat transfer of a viscous fluid induced by a stretching surface. The nonlinear problem subject to a given skin friction at the boundary is solved. Analytic solution is obtained using homotopy analysis method. The velocity, temperature, and stretching velocity is calculated for different values of the rotation parameter (λ). The obtained results are compared with the well known results of rotating flow induced by a stretching surface by using four sets of boundary conditions. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
956.
In this article, we investigate the influence of heat and mass transfer on the peristaltic flow of magnetohydrodynamic second‐order fluid in a channel when the induced magnetic field effects are present. Problem formulation in a wave frame of reference is presented. The governing nonlinear analysis is carried out under the assumption of small wave number. Explicit expressions of the pressure gradient, the stream function, the magnetic force function, the axial induced magnetic field, the current density distribution, the temperature, and the concentration distribution are derived. The effects of embedded parameters are also examined. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
957.
文中通过对变频控制直接膨胀式太阳能热泵的数值模拟,指出PV/T- SAHP系统实现变频控制从而解决太阳能热泵集热器面积与压缩机的容量不匹配的关键问题是找到系统集热/蒸发器的MSS线.为变工况下太阳能热泵系统的研究提供参考. 相似文献
958.
A numerical/experimental inverse procedure was employed to estimate the temperature-dependent thermal conductivity of a solid body in which 1D heat conduction in a top heated cylindrical sample is assumed. The emphasis is focused on the issue of sensitivity of results to selected assumptions made in inverse calculations. It has been found that the accuracy of heat capacity evaluation brings the largest contribution to final errors (up to 74%). Density accounts for one-fourth to one-third of the total error of determination. The failure to ensure unidirectional heat conduction in a sample during an experiment is important only at elevated temperatures. 相似文献
959.
Investigations have been performed on convective heat transfer in water flowing through mini-channels using the non intrusive technique of laser interferometry coupled with digital image processing. Optical glass channels, fabricated with metallic heating surfaces, were studied using a Mach-Zehnder interferometer configuration. Fringe patterns captured using a high-sensitivity CCD camera were analyzed digitally based on a calculation method developed for the liquid medium. Results of parametric studies were compared and contrasted with relevant theoretical solutions from the literature. Indication of the onset of turbulence at Reynolds numbers smaller than the conventional transition Reynolds number for large channels has also been noticed in the experimental investigation. 相似文献
960.
Mass transfer from irregular-shaped naphthalene particles (100-200 inn in size) was studitd in an electrodynamic balance. Charged particles were suspended in an electrostatic field directly in line with a calibrated air jet. Mass and size change histories were obtained under ambient conditions, and under steady- and pulsed-flow conditions. For natural convection, the time-averaged Sherwood number was similar to that for spheres. Forced-convection Sherwood number under steady-flow conditions was strongly dependent on particle shape and panicle Reynolds number, and was consistently higher than values predicted for spheres at comparable Reynolds numbers. This study validates the technique and indicates the shape effect on mass transfer form single particles. 相似文献