首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   23537篇
  免费   1572篇
  国内免费   846篇
化学   2743篇
晶体学   66篇
力学   6659篇
综合类   95篇
数学   2616篇
物理学   3854篇
综合类   9922篇
  2024年   48篇
  2023年   234篇
  2022年   372篇
  2021年   434篇
  2020年   536篇
  2019年   429篇
  2018年   475篇
  2017年   542篇
  2016年   560篇
  2015年   723篇
  2014年   944篇
  2013年   1317篇
  2012年   1174篇
  2011年   1349篇
  2010年   957篇
  2009年   1231篇
  2008年   1157篇
  2007年   1395篇
  2006年   1226篇
  2005年   1081篇
  2004年   1045篇
  2003年   974篇
  2002年   836篇
  2001年   696篇
  2000年   720篇
  1999年   604篇
  1998年   579篇
  1997年   584篇
  1996年   517篇
  1995年   459篇
  1994年   408篇
  1993年   350篇
  1992年   357篇
  1991年   311篇
  1990年   277篇
  1989年   244篇
  1988年   192篇
  1987年   152篇
  1986年   115篇
  1985年   91篇
  1984年   71篇
  1983年   38篇
  1982年   76篇
  1981年   23篇
  1980年   12篇
  1979年   6篇
  1978年   7篇
  1976年   5篇
  1971年   6篇
  1957年   7篇
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
131.
为解决大多数的流量工程问题和网络传输中的最大流问题,该文提出了基于多协议标签交换(MPLS)解决方案,阐述了解决最大流问题的数学方法,提出一种独特的将数据流划分成“微分支”的思想和方法,并介绍微分支的建立过程;给出仿真结果。  相似文献   
132.
首次公开发行股票(IPO)定价模型的评析   总被引:4,自引:0,他引:4  
对首次公开发行股票定价的三种模型的假设条件、应用优势和局限性进行了评估.  相似文献   
133.
本文将文献[9]提出改进的通量分裂方法,应用于随时间变化的贴体网格中,建立了可用于求解非定常Euler方程的通量分裂方法.该方法是以连续的特征值分离为基础,它具有方法简单,便于推广使用的特点.同时克服了Steger-Warming通量分裂方法存在的问题.对通量分裂后的Euler方程.利用MUSCL型迎风差分建立了具有二阶精度的有限体积方程.文中以NACA64A—10翼型为例,对其在跨音速流场中进行沉浮、俯仰及带有振动控制面引起的非定常气动载荷进行了计算.部分计算结果与相应的实验结果进行了比较,吻合良好  相似文献   
134.
135.
泡沫的持液量(h,mg/cm3)是泡沫的基本特性之一.本文对形成泡沫的起泡剂浓度、增粘剂浓度、气体流量和温度等因素对H的影响及变化规律作了研究,并对H与泡沫表观粘度和泡沫半衰期的相互关系作了描述,对泡沫的实际应用具有一定的指导意义.  相似文献   
136.
137.
Relative permeability functions for immiscible displacements in porous media show a wide range of profiles. Although, this behavior is well known, its impact on the stability of the displacement process is unexplored. Our analysis clearly demonstrates for the first time that the viscous instability characteristics of two-phase flows are governed not only by their end point values, but are strongly dependent on the actual profile of relative permeability functions. Linear stability analysis predicts the capacity of the flow to develop large scale fingers which can result in substantial bypassing of the resident fluid. It is observed that relative permeability functions attributed to drainage processes yield a more unstable displacement as compared to functions related to imbibition processes. Moreover, instability is observed to increase for those relative permeability functions which result from increased wettability of the wetting fluid. High accuracy numerical simulations show agreement with these predictions and demonstrate how large amplitude viscous fingers result in significant bypassing for certain relative permeability functions. In the nonlinear regime, the finger amplitude grows at a rate ∝ t1/2 initially, drops to t1/4 at a later time and finally grows ∝ t. The basic mechanisms of finger interaction, however, are not substantially influenced by relative permeability functions.  相似文献   
138.
A particle imaging technique has been used to collect droplet displacement statistics in a round turbulent jet of air. Droplets are injected on the jet axis, and a laser sheet and position-sensitive photomultiplier tube are used to track their radial displacement and time-of-flight. Dispersion statistics can be computed which are Lagrangian or Eulerian in nature. The experiments have been simulated numerically using a second-order closure scheme for the jet and a stochastic simulation for the particle trajectories. Results are presented for non-vaporizing droplets of sizes from 35 to 160 μm. The simulations have underscored the importance of initial conditions and early droplet displacement history on the droplet trajectory for droplets with large inertia relative to the turbulence. Estimates of initial conditions have been made and their effect on dispersion is quantified.  相似文献   
139.
The majority of previous studies of the hydration of cements using heat flow calorimetry have been carried out isothermally. However, with oilwell cements the slurry is mixed on the surface at ambient temperature and then gradually increases in temperature as it is pumped down the well. A Setaram C-80 calorimeter has been used to simulate the temperature ramp in API oilwell cement test schedules. This approach has enabled cementing reactions to be studied for the first time under conditions approaching those encountered in the field, and has shown that the results obtained from isothermal experiments may be misleading.The permission of the British Petroleum Company PLC to publish this paper is gratefully acknowledged.  相似文献   
140.
A general relationship between the volume fraction and the specific interfacial area for averaged dispersed two-phase flows is proposed. This relationship, expressed as a basic set of two scalar evolution equations and two vectorial non-uniformity state equations, is an analytical result obtained by a systematic approach using the derivatives of some generalized functions and a local volume-averaging technique. The proposed set of equations was expressed for measurable macroscopic parameters of the system and has the same generality as the averaged transport equations of two-phase flows. By combination of the basic set of equations, called the averaged topological equations (ATEs), second-order ATEs for the volume fraction were found. The second-order ATEs were expressed both by a Lagrangian formulation and by a Eulerian formulation. The importance and physical meaning of the ATEs developed in this study were clarified within the framework of the theory of kinematic waves.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号