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   41119篇
  免费   3205篇
  国内免费   3045篇
  47369篇
  2024年   100篇
  2023年   531篇
  2022年   1216篇
  2021年   2249篇
  2020年   1429篇
  2019年   1802篇
  2018年   1812篇
  2017年   1246篇
  2016年   1735篇
  2015年   2518篇
  2014年   2976篇
  2013年   3228篇
  2012年   3760篇
  2011年   3308篇
  2010年   2090篇
  2009年   1723篇
  2008年   2076篇
  2007年   1822篇
  2006年   1667篇
  2005年   1348篇
  2004年   1130篇
  2003年   991篇
  2002年   837篇
  2001年   726篇
  2000年   621篇
  1999年   661篇
  1998年   376篇
  1997年   383篇
  1996年   362篇
  1995年   329篇
  1994年   362篇
  1993年   275篇
  1992年   341篇
  1991年   263篇
  1990年   225篇
  1989年   204篇
  1988年   135篇
  1987年   111篇
  1986年   98篇
  1985年   94篇
  1984年   61篇
  1983年   55篇
  1982年   38篇
  1981年   11篇
  1980年   15篇
  1979年   15篇
  1978年   2篇
  1976年   2篇
  1975年   3篇
  1965年   1篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
32.
Lochbihler  Hans  Ye  Yan  Xu  Yishen 《Plasmonics (Norwell, Mass.)》2018,13(6):2161-2167
Plasmonics - We investigate aluminum nanopatch/nanohole arrays surrounded by a dielectric material on plastic substrates for large area color printing. In this specific arrangement, metallic...  相似文献   
33.
34.
35.
36.
H. Bai  Y. Sun  N. Liu  Y. Liu  F. Xue  Y. Li  S. Xu  A. Ni  J. Ye  Y. Chen  J. Chen 《Animal genetics》2018,49(3):226-236
Beak deformity (crossed beaks) is found in several indigenous chicken breeds including Beijing‐You studied here. Birds with deformed beaks have reduced feed intake and poor production performance. Recently, copy number variation (CNV) has been examined in many species and is recognized as a source of genetic variation, especially for disease phenotypes. In this study, to unravel the genetic mechanisms underlying beak deformity, we performed genome‐wide CNV detection using Affymetrix chicken high‐density 600K data on 48 deformed‐beak and 48 normal birds using penncnv . As a result, two and eight CNV regions (CNVRs) covering 0.32 and 2.45 Mb respectively on autosomes were identified in deformed‐beak and normal birds respectively. Further RT‐qPCR studies validated nine of the 10 CNVRs. The ratios of six CNVRs were significantly different between deformed‐beak and normal birds (< 0.01). Within these six regions, three and 21 known genes were identified in deformed‐beak and normal birds respectively. Bioinformatics analysis showed that these genes were enriched in six GO terms and one KEGG pathway. Five candidate genes in the CNVRs were further validated using RT‐qPCR. The expression of LRIG2 (leucine rich repeats and immunoglobulin like domains 2) was lower in birds with deformed beaks (< 0.01). Therefore, the LRIG2 gene could be considered a key factor in view of its known functions and its potential roles in beak deformity. Overall, our results will be helpful for future investigations of the genomic structural variations underlying beak deformity in chickens.  相似文献   
37.
This paper studies a Non-convex State-dependent Linear Quadratic Regulator (NSLQR) problem, in which the control penalty weighting matrix in the performance index is state-dependent. A necessary and sufficient condition for the optimal solution is established with a rigorous proof by Euler-Lagrange Equation. It is found that the optimal solution of the NSLQR problem can be obtained by solving a Pseudo-Differential-Riccati-Equation (PDRE) simultaneously with the closed-loop system equation. A Comparison Theorem for the PDRE is given to facilitate solution methods for the PDRE. A linear time-variant system is employed as an example in simulation to verify the proposed optimal solution. As a non-trivial application, a goal pursuit process in psychology is modeled as a NSLQR problem and two typical goal pursuit behaviors found in human and animals are reproduced using different control weighting . It is found that these two behaviors save control energy and cause less stress over Conventional Control Behavior typified by the LQR control with a constant control weighting , in situations where only the goal discrepancy at the terminal time is of concern, such as in Marathon races and target hitting missions.  相似文献   
38.
39.
40.
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