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   1483篇
  免费   35篇
  国内免费   30篇
化学   855篇
晶体学   12篇
力学   43篇
数学   240篇
物理学   398篇
  2020年   15篇
  2019年   20篇
  2018年   14篇
  2017年   12篇
  2016年   19篇
  2015年   14篇
  2014年   19篇
  2013年   74篇
  2012年   58篇
  2011年   52篇
  2010年   29篇
  2009年   36篇
  2008年   57篇
  2007年   64篇
  2006年   64篇
  2005年   40篇
  2004年   42篇
  2003年   42篇
  2002年   62篇
  2001年   43篇
  2000年   36篇
  1999年   19篇
  1998年   24篇
  1997年   26篇
  1996年   23篇
  1995年   20篇
  1994年   21篇
  1993年   28篇
  1992年   20篇
  1991年   19篇
  1990年   20篇
  1989年   24篇
  1988年   22篇
  1987年   29篇
  1986年   30篇
  1985年   39篇
  1984年   32篇
  1983年   16篇
  1982年   35篇
  1981年   14篇
  1980年   17篇
  1979年   13篇
  1978年   17篇
  1977年   12篇
  1976年   23篇
  1975年   21篇
  1974年   27篇
  1973年   19篇
  1972年   12篇
  1969年   8篇
排序方式: 共有1548条查询结果,搜索用时 15 毫秒
11.
12.
13.
The sheath motion in a capacitively coupled RF discharge is highly nonlinear. The voltage waveform on a cylindrical probe placed in the sheath region is measured as a function of position and time. A circuit model of the probe-discharge system relates the observed probe voltage to the sheath motion. The equations derived from this circuit model are solved numerically with varying nonlinear sheath motions; the resulting waveforms are compared with the experimental observations to determine the actual sheath motion. The time-varying plasma potential is also determined, indirectly, from the comparison. The authors also report observation of oscillations related to the plasma frequency, whose peak harmonic component can be calculated from a single plasma model. These oscillations can be a useful plasma diagnostic for determining plasma density. The presence of these high-frequency oscillations may significantly enhance the rate of stochastic heating of electrons  相似文献   
14.
We used Monte Carlo method to generate the configurations of disassembly of hot nucleus Au* based on the Atomic Mass Table and the conservation of mass and charge number.The resulted charge distribution of fragments was then used to calculate the conditional moments.The logarithm correlation between second and third moments of experimental charge distribution is very well reproduced by theory.It seems that no connection to the critical phenomenon of concerned system exists.  相似文献   
15.
The spleen is one of the most frequently injured organs in blunt abdominal trauma. Computed tomography (CT) is the imaging modality of choice to assess patients with blunt spleen trauma, which may include lacerations, subcapsular or parenchymal hematomas, active hemorrhage, and vascular injuries. While computer-assisted diagnosis systems exist for other conditions assessed using CT scans, the current method to detect spleen injuries involves the manual review of scans by radiologists, which is a time-consuming and repetitive process. In this study, we propose an automated spleen injury detection method using machine learning. CT scans from patients experiencing traumatic injuries were collected from Michigan Medicine and the Crash Injury Research Engineering Network (CIREN) dataset. Ninety-nine scans of healthy and lacerated spleens were split into disjoint training and test sets, with random forest (RF), naive Bayes, SVM, k-nearest neighbors (k-NN) ensemble, and subspace discriminant ensemble models trained via 5-fold cross validation. Of these models, random forest performed the best, achieving an Area Under the receiver operating characteristic Curve (AUC) of 0.91 and an F1 score of 0.80 on the test set. These results suggest that an automated, quantitative assessment of traumatic spleen injury has the potential to enable faster triage and improve patient outcomes.  相似文献   
16.
17.
18.
19.
Normal and tangential stress vectors were measured at the soil-tire interface of a pneumatic tractor tire on firm and soft soils. Stress magnitudes were determined with a transducer which was designed to measure both normal and tangential stresses. The orientation of the transducer was determined using a 3-dimensional, sonic digitizing system which was mounted inside the air cavity of the tire. Data are presented from tests conducted at zero input torque, zero net traction, and 0.15 net traction ratio which show the effects of inflation pressure, dynamic load, and soil conditions on the stress vectors.  相似文献   
20.
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