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   59941篇
  免费   1480篇
  国内免费   2417篇
系统科学   2191篇
丛书文集   2156篇
教育与普及   2246篇
理论与方法论   281篇
现状及发展   331篇
研究方法   214篇
综合类   56408篇
自然研究   11篇
  2024年   382篇
  2023年   760篇
  2022年   1000篇
  2021年   1201篇
  2020年   716篇
  2019年   254篇
  2018年   456篇
  2017年   614篇
  2016年   559篇
  2015年   1269篇
  2014年   1781篇
  2013年   1606篇
  2012年   1890篇
  2011年   2189篇
  2010年   2032篇
  2009年   2497篇
  2008年   2875篇
  2007年   2760篇
  2006年   2100篇
  2005年   2127篇
  2004年   1672篇
  2003年   1391篇
  2002年   1409篇
  2001年   1603篇
  2000年   1772篇
  1999年   3210篇
  1998年   3011篇
  1997年   3139篇
  1996年   2813篇
  1995年   2445篇
  1994年   2326篇
  1993年   2005篇
  1992年   1725篇
  1991年   1528篇
  1990年   1324篇
  1989年   1181篇
  1988年   982篇
  1987年   628篇
  1986年   358篇
  1985年   134篇
  1984年   34篇
  1983年   10篇
  1982年   7篇
  1981年   5篇
  1979年   5篇
  1977年   4篇
  1975年   5篇
  1974年   6篇
  1973年   6篇
  1970年   4篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
231.
The Hamming distances of all negacyclic codes of length 28 over the Gaiois ring GR (2^α, m) are given. In particular, the Lee distances of all negacyclic codes over Z4 of length 2^s are obtained. The Gray images of such negacyclic codes over Z4 are also determined under the Gray map.  相似文献   
232.
Traditional Chinese medicine (TCM) has a rich knowledge about human health and disease by its special way evolved along a very long history. As modern medicine is achieving much progress, arguments and disputes toward TCM never end. To avoid losing precious knowledge of living TCM masters, endeavors have been engaged to systematic collection of those knowledge of TCM masters, such as their growth experiences, effective practical cases toward diseases and typical therapeutic principles and methods. Knowledge mining methods have been expected to explore some useful or hidden patterns to unveil some mysteries of the TCM system. In the paper, some computerized methods are applied toward those collected materials about some living TCM masters in China mainland to show a different way of exposing essential ideas of those TCM masters by correspondence visualization which aims to help people understand TCM holistic views toward disease and body, and facilitate tacit knowledge transfer and sense-making of the essence of TCM. The work is one kind of qualitative meta-synthesis of TCM masters' knowledge.  相似文献   
233.
在分析经典回购合约的回购价格、回构批量及最高回购率的基础上,进一步讨论当供应商实际允许执行的最高回购率风险波动时,零售商相应的订货策略。建立了回购率风险波动时以利润最大化为目标的数学模型;分别讨论了有无风险波动等3种情况下零售商及供应链总体利润变化。得出了当相关参数风险波动时,零售商相应的最优订货策略。当回购率风险波动时,供应链成员及供应链总的期望利润都会下降。而回购率风险波动零售商却不做相应订货策略调整的话,整个供应链的期望利润跟经典回购时一样,但是零售商的利润会部向供应商转移,产生利润损失。  相似文献   
234.
This paper proposes a unified clutter model incorporating the effects of range walk and array rotation for space-time adaptive processing (STAP) in airborne multi-channel early-warning radar. Based on this clutter model, STAP performance is then analyzed from the perspective of covariance matrix tapering (CMT). For STAP performance degradation due to array rotation, a determinate compensation method is proposed based on the CMT method. Numerical examples are provided to verify the analysis and the proposed compensation method.  相似文献   
235.
A compressed sensing (CS) based channel estimation algorithm is proposed by using the delay-Doppler sparsity of the fast fading channel. A compressive basis expansion channel model with sparsity in both time and frequency domains is given. The pilots in accordance with a novel random pilot matrix in both time and frequency domains are sent to measure the delay-Doppler sparsity channel. The relatively nonzero channel coefficients are tracked by random pilots at a sampling rate significantly below the Nyquist rate. The sparsity channels are estimated from a very limited number of channel measurements by the basis pursuit algorithm. The proposed algorithm can effectively improve the channel estimation performance when the number of pilot symbols is reduced with improvement of throughput efficiency.  相似文献   
236.
The problem of robust H∞ control for uncertain neutral stochastic systems with time-varying delay is discussed. The parameter uncertaintie is assumed to be time varying norm-bounded. First, the stochastic robust stabilization of the stochastic system without disturbance input is investigated by nonlinear matrix inequality method. Then, a full-order stochastic dynamic output feedback controller is designed by solving a bilinear matrix inequality (BMI), which ensures a prescribed stochastic robust H∞ performance level for the resulting closed loop system with nonzero disturbance input and for all admissible uncertainties. An illustrative example is provided to show the feasibility of the controller and the potential of the proposed technique.  相似文献   
237.
The reverse construction and analysis of the networks of molecular interactions are essential for understanding their functions within cells. In this paper, a logic network model is constructed to investigate the complicated regulation mechanism of shoot genes of Arabidopsis Thaliana in response to stimuli. The dynamics of the complicated logic network is analyzed, discussed, and simulated. The simulation results show that the logic network of the active genes of shoot eventually evolves into eleven attractors under the stimuli, including five 1-periodic and six 2-periodic attractors. Our work provides valuable reference and guidance for biologists to understand and explain Arabidopsis’ response to external stimuli by experiments.  相似文献   
238.
<正> This paper considers finite-time χ-consensus problem for a multi-agent system with firstorderindividual dynamics and switching interaction topologies.Several distributed finite-time consensusrules are constructed for multi-agent dynamics in a unified way with the help of Lyapunovfunction and graph theory as well as homogeneity.Time-invariant non-smooth forms of finite-timeneighbor-based controllers are proposed and a numerical example is shown for illustration.  相似文献   
239.
<正> This paper formulates and analyzes a line search method for general nonlinear equalityconstrained optimization based on filter methods for step acceptance and secant methods for searchdirection.The feature of the new algorithm is that the secant algorithm is used to produce a searchdirection,a backtracking line search procedure is used to generate step size,some filtered rules areused to determine step acceptance,second order correction technique is used to reduce infeasibility andovercome the Maratos effect.Global convergence properties of this method are analyzed:under mildassumptions it is showed that every limit point of the sequence of iterates generated by the algorithmis feasible,and that there exists at least one limit point that is a stationary point for the problem.Moreover,it is also established that the Maratos effect can be overcome in our new approach by addingsecond order correction steps so that fast local superlinear convergence to a second order sufficient localsolution is achieved.Finally,the results of numerical experiments are reported to show the effectivenessof the line search filter secant method.  相似文献   
240.
China's aerospace enterprises carry on the multinational operation and participate in the international competition and the international division of labor and cooperation positively. This article first analyzs China aerospace enterprises' binary multinational business control objective and constructes its model. Then the article analyzes the tangible and intangible control mechanism of China aerospace enterprises' binary multinational operation respectively. Finally, the article constructs the model of China aerospace enterprises' binary multinational operation mechanisms.  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