全文获取类型
收费全文 | 9179篇 |
免费 | 1112篇 |
国内免费 | 1001篇 |
专业分类
化学 | 3260篇 |
晶体学 | 115篇 |
力学 | 1060篇 |
综合类 | 204篇 |
数学 | 2887篇 |
物理学 | 3766篇 |
出版年
2024年 | 21篇 |
2023年 | 89篇 |
2022年 | 266篇 |
2021年 | 325篇 |
2020年 | 320篇 |
2019年 | 237篇 |
2018年 | 239篇 |
2017年 | 343篇 |
2016年 | 358篇 |
2015年 | 295篇 |
2014年 | 483篇 |
2013年 | 750篇 |
2012年 | 457篇 |
2011年 | 574篇 |
2010年 | 448篇 |
2009年 | 605篇 |
2008年 | 594篇 |
2007年 | 595篇 |
2006年 | 550篇 |
2005年 | 470篇 |
2004年 | 346篇 |
2003年 | 376篇 |
2002年 | 301篇 |
2001年 | 289篇 |
2000年 | 303篇 |
1999年 | 222篇 |
1998年 | 192篇 |
1997年 | 187篇 |
1996年 | 171篇 |
1995年 | 160篇 |
1994年 | 96篇 |
1993年 | 98篇 |
1992年 | 73篇 |
1991年 | 58篇 |
1990年 | 60篇 |
1989年 | 49篇 |
1988年 | 56篇 |
1987年 | 28篇 |
1986年 | 28篇 |
1985年 | 38篇 |
1984年 | 37篇 |
1983年 | 9篇 |
1982年 | 27篇 |
1981年 | 18篇 |
1980年 | 8篇 |
1979年 | 16篇 |
1978年 | 7篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1957年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
991.
Filter cake formation is important in groundwater and oil wells where drilling contains suspended mud particles. The accumulation of these mud particles on the borehole wall creates a pressure drop in the well. Furthermore, the migration of colloidal particles into adjacent porous rock could damage the formation and cause productivity decline. In this study, numerical solutions for pore liquid pressure variation across the cake with variable total stress and associated porosity variation are obtained. Mass equations for captured and suspended particles are averaged along the mud cake thickness, taking into account conditions on the cake surface and at the filter septum. The variability of total stress in soil consolidations problem is considered to determine the pore liquid pressure along the mud cake thickness. Then, the relation between porosity and pressure is studied to determine the mud cake porosity. Experimental data obtained by various researchers is used to compare and test the validity of numerical solutions to develop guidelines for model applications. Results show that the pore liquid pressure increases with the decrease of membrane impedance value (i.e. less pervious membrane). Also, the pressure profile has a cubic function of dimensionless cake thickness. The conclusions from the sensitivity analysis conducted in this study agree with earlier conclusions. 相似文献
992.
A numerical stochastic approach allows the exact solution of the convection equation arising in network theories. We now want to show the flexibility and the limits of this approach by studying the rheological properties of different kinds of models. 相似文献
993.
介绍了一种高能材料动静态变温三轴压缩试验装置,在熔点以下温度,通过对国产单质炸药TNT在中等应变速率(2-4/s)及准静态(3×10-3/s)条件下三轴压缩力学性能的测试,得出TNT的杨氏模量E、泊松比ν和屈服极限Y,以及当加载速率和温度改变时这些参数的变化规律。并提出三轴应力状态下屈服极限的一种确定方法。该三轴压缩试验装置以及三轴压缩应力状态下力学参数的测试、分析、处理系统为研究高能材料力学性能提供了一套完整的技术和手段。 相似文献
994.
Molecular dynamics simulation of crack-tip processes in copper 总被引:1,自引:0,他引:1
The crack tip processes in copper under mode II loading have been simulated by a molecular dynamics method. The nucleation,
emission, dislocation free zone (DFZ) and pile-up of the dislocations are analyzed by using a suitable atom lattice configuration
and Finnis & Sinclair potential. The simulated results show that the dislocation emitted always exhibits a dissociated fashion.
The stress intensity factor for dislocation nucleation, DFZ and dissociated width of partial dislocations are strongly dependent
on the loading rate. The stress distributions are in agreement with the elasticity solution before the dislocation emission,
but are not in agreement after the emission. The dislocation can move at subsonic wave speed (less than the shear wave speed)
or at transonic speed (greater than the shear wave speed but less than the longitudinal wave speed), but at the longitudinal
wave speed the atom lattice breaks down.
The project supported by the National Natural Science Foundation of China 相似文献
995.
For a stable two-phase free boundary problem arising in oil production, we prove the existence of a weak solution and the continuity of the free boundary.
Sommario Si prova un teorema di esistenza di una soluzione debole per un problema stazionario a contorno libero a due fasi che interessa la produzione di petrolio. Si dimostra inoltre la continuità del contorno libero.相似文献
996.
Jin Jeong Chang Nyung Kim Baek Youn Young Saeng Kim 《International Journal of Heat and Fluid Flow》2004,25(6):1006-1014
The thermal contact resistance is a principal parameter interfering with heat transfer in a fin–tube heat exchanger. However, the thermal contact resistance in the interface between tubes and fins has not been clearly investigated. The objective of the present study is to examine the thermal contact conductance for various fin–tube heat exchangers with tube diameter of 9.52 mm and to find a correlation between the thermal contact conductance and effective factors such as expansion ratio, fin type, fin spacing and hydrophilic coating. In this study, experiments have been conducted only to measure heat transfer rate between hot and cold water. To minimize heat loss to the ambient air by the natural convection fin–tube heat exchangers have been placed in an insulated vacuum chamber. Also, a numerical scheme has been employed to calculate the thermal contact conductance with the experimental data. As a result, a new correlation including the influences of expansion ratio, slit of fin and fin coating has been introduced, and the portion of each thermal resistance has been estimated in the fin–tube heat exchangers with 9.52 mm tube. 相似文献
997.
A novel dynamic compressive experimental technique has been developed based on a split Hopkinson pressure bar. This new method
dynamically loads the ceramic specimen by two consecutive stress pulses. The first pulse determines the dynamic response of
the intact ceramic materiaal and then crushes the specimen, and the second pulse determines the dynamic compressive constitutive
behavior of the ceramic rubble. Precise pulse shaping ensures that the specimen deforms at nearly constant strain rates under
dynamic stress equilibrium during the loading by both stress pulses. Pulse shaping also controls the amplitudes of loading
pulses, the values of strain rates, the maximum strains in the rubble specimens, and the proper separation time between the
two loading pulses. The feasibility of the new technique is demonstrated by the experimental results obtained on an AD995
alumina. 相似文献
998.
Analytical solutions for cohesive zone models 总被引:2,自引:0,他引:2
Solutions are given for a cantilever beam specimen using a beam on elastic foundation model to incorporate various cohesive zone traction laws. These included both positive and negative linear slopes and constant stresses. Negative slopes give rise to multiple solutions. However, all the solutions give very similar results for energy release rate and beam root rotation confirming insensitivity to the form of the traction law. The use of these solutions to analyse peeling is discussed. 相似文献
999.
1000.
本文通过试验研究了35CrMo 合金钢三点弯曲试样疲劳短裂纹的扩展特性;用电测法得到了裂尖处的载荷—应变标定关系。试验结果表明,短裂纹的扩展速率正比于局部应力幅的幂次和裂纹长度,即 da/dN=A(?),可以较好地描述疲劳短裂纹的扩展规律。 相似文献