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991.
基于二阶矩近似反应力场方法构建的全维度势能面研究了氢分子及其同位素分子在钯表面的分解过程.在构建势能面的过程中数据库中只包含了氢分子与钯(111)表面相互作用的相关信息,该势能面在研究氢分子在钯(100)表面上的分解过程中表现出了非常好的可转移性.结果表明,氢分子及其同位素分子在钯(111)与钯(100)表面上的分解系数S0均随着入射能量的增加呈现非单调变化,并且通过固定分子取向的方法发现同核分子(H2、D2和T2)最有利分解取向角为90°,而异核分子(HD、HT和DT)受质心偏移的影响,其最有利分解取向角向大角度偏移. 相似文献
992.
基于相对论Hartree-Fock-Bogoliubov (RHFB) 近似分别探索了质量-电荷极限下的超重元素与极端中质比下的奇特原子核中的新幻数问题。研究结果表明,赝自旋对称性的守恒和破缺与超重核区球形幻数结构的形成密切相关,并分别决定了中子与质子的新幻数结构。同时,理论模型之间的差异也与之密切相关。在中重奇特核区,RHFB近似很好地再现了Ca 同位素中的新幻数N = 32,34,其中同位旋矢量道中洛伦兹张量耦合扮演了较为关键的角色。以此为例,研究证明了显式考虑交换(Fock) 项的RHFB 近似的可靠性。Recent applications of the relativistic Hartree-Fock-Bogoliubov (RHFB) approach in exploring the new magicities under extreme conditions are presented for the superheavy elements with the limits of mass and charge and for the exotic nuclei with extreme neutron-to-proton ratios. It is found that the emergence of new magic shells in superheavy region is tightly related to the restoration and violation of pseudo-spin symmetry, respectively for the neutron and proton ones, in which the model deviations are indicated and discussed. In medium-heavy exotic nuclei, the occurrence of new magicity N = 32, 34 in Ca isotopes is well reproduced by the RHFB approach, in which the isovector Lorentz tensor couplings are found to play an essential role. The results exemplify that the RHFB approach, which considers the exchange (Fock) terms explicitly, furnishes a new theoretical instrument for advancing relativistic nuclear mean-field approaches. 相似文献
993.
The aim of this research work is to address the influences of dispersion forces and rippled configuration on the instability threshold of carbon nanotube (CNT) based nanotweezers. To this end, the Dirichlet and Neumann modes of Casimir force arisen from the electric and magnetic energies is developed for cylinder–cylinder geometry. Moreover, the CNTs rippling deformation which experimentally revealed is included in the Euler-Bernoulli beam model to modify the governing equations. The differential quadrature method (DQM) in conjunction with the 4th-order Runge-Kutta algorithm is employed to numerically simulate the non-linear partial differential equations. It is interestingly demonstrated that these phenomena remarkably affect the electromechanical behavior of nanotweezers fabricated from CNTs. By taking the rippling configuration and Casimir attraction between tubes into account, the pull-in voltage decreases. On the other hand, when the gas damping effect due to low vacuum environment is taken into consideration, the pull-in value increases. The accuracy of the present modeling is compared with those experimentally published in the literature, giving excellent results. 相似文献
994.
为考察含双间隙连杆机构的动力学行为,进行了仿真和实验研究。在仿真中,基于ADAMS软件建立了一个非线性接触力模型。同时,设计和建立了一个实验装置来对仿真结果进行验证。分别讨论了间隙尺寸、加载频率和加载力幅值对接触碰撞力的影响。结果表明,间隙的存在会影响传递力曲线,使机构产生明显的振动冲击,间隙大小和加载速度是影响机构动态响应的主要因素。实验结果证明了本文模型的正确性。 相似文献
995.
In many load carrying thin shell structures, a connection section is arranged to transfer concentrated external forces to its main section. It is very important for the concentrated external forces to diffuse as uniformly as possible. Nevertheless the traditional design of uniform radial rib is not optimized. The present paper studies an integrated optimization procedure for design optimization of connection section. Variance constraint of node forces at the interface between the main section and connection section is firstly proposed as the evaluation criterion of concentrated force diffusion efficiency and introduced into the topology optimization formulation. Afterwards, for improving the manufacturability of the final design the topology optimization results are interpreted and further optimized by size or shape optimization. Two strategies of interpretation are examined. The first strategy is called strategy of making holes, which inserts a number of internal holes of regular geometric features and smooth boundary with B-spline curves in the continuum based on the topology optimization result. In the second strategy, an initial truss-like design is extracted from the characteristic of topology optimization result. Then a further shape and sizing optimization is followed to obtain the final optimal design. An example of design optimization of plane connection section is presented. The effectiveness of the present approach is demonstrated. The respective advantages and disadvantages of the two strategies are discussed. 相似文献
996.
Robot locomotion on rigid terrain or in fluids has been studied to a large extent. The locomotion dynamics on or within soft substrates such as granular material (GM) has not been fully investigated. This paper proposes a hybrid force model to simulate and evaluate the locomotion performance of a legged terrestrial robot in GM. The model incorporates an improved Resistive Force Theory (RFT) model and a failure-based model. The improved RFT model integrates the force components of individual leg elements over the curved leg portion submerged in GM at any moment during a full period of leg rotation. The failure-based model is applied in a bar drag model to yield the normal and the lateral forces of the individual RFT elements as functions of the locomotion depth and speed. The hybrid model is verified by the coincidence between the theoretical predictions and the experimental results. The hybrid model is used to analyze the effects of angular velocity and leg shape with high precision and can guide the design of the legs with any profiles. Our study reveals that the interactions between locomotor and substrate are determined by the locomotor structural characteristics, the nature of the substrate, and the control strategy. 相似文献
997.
Spatial distribution of soil forces on the surface of plough is an important aspect that can help engineers for improving efficiency of tillage implement. It was analyzed at eleven different points of the moldboard plough with the help of sensors accompanied with the virtual instrument developed in LabView software with the aid of other supporting instruments. It was observed that soil forces increased with an increase in speed and depth. Depth changed soil forces more at upper parts than lower parts whereas speed affected rear parts more than the front part of the plough. Draft forces followed almost similar trend and least value of 308.17 N experimental draft force was found at 1 m/s speed and 5 cm depth under 33% moisture content. Cumulative soil forces found too smaller than the draft as they represented the force spatial distribution of specific parts of plough. It was observed that sensor technology provided real time picture of force variation during tillage process that could save time and effort. 相似文献
998.
A kind of second-order implicit upwind fractional step finite difference methods are presented for the numerical simulation of coupled systems for enhanced(chemical)oil production with capillary force in the porous media.Some techniques,e.g.,the calculus of variations,the energy analysis method,the commutativity of the products of difference operators,the decomposition of high-order difference operators,and the theory of a priori estimate,are introduced.An optimal order error estimate in the l~2 norm is derived.The method is successfully used in the numerical simulation of the enhanced oil production in actual oilfields.The simulation results are satisfactory and interesting. 相似文献
999.
1000.
基于接触力学理论和线性互补问题的算法, 给出了一种含接触、碰撞以及库伦干摩擦, 同时具有理想定常约束(铰链约束) 和非定常约束(驱动约束) 的平面多刚体系统动力学的建模与数值计算方法. 将系统中的每个物体视为刚体, 但考虑物体接触点的局部变形, 将物体间的法向接触力表示成嵌入量与嵌入速度的非线性函数,其切向摩擦力采用库伦干摩擦模型. 利用摩擦余量和接触点的切向加速度等概念, 给出了摩擦定律的互补关系式; 并利用事件驱动法, 将接触点的黏滞-滑移状态切换的判断及黏滞状态下摩擦力的计算问题转化成线性互补问题的求解. 利用第一类拉格朗日方程和鲍姆加藤约束稳定化方法建立了系统的动力学方程, 由此可降低约束的漂移, 并可求解该系统的运动、法向接触力和切向摩擦力, 还可以求解理想铰链约束力和驱动约束力. 最后以一个类似夯机的平面多刚体系统为例, 分析了其动力学特性, 并说明了相关算法的有效性. 相似文献