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   1446篇
  免费   89篇
  国内免费   4篇
电工技术   36篇
综合类   1篇
化学工业   281篇
金属工艺   39篇
机械仪表   48篇
建筑科学   31篇
能源动力   52篇
轻工业   136篇
水利工程   18篇
石油天然气   6篇
无线电   200篇
一般工业技术   270篇
冶金工业   248篇
原子能技术   19篇
自动化技术   154篇
  2023年   10篇
  2022年   11篇
  2021年   37篇
  2020年   30篇
  2019年   23篇
  2018年   39篇
  2017年   46篇
  2016年   38篇
  2015年   36篇
  2014年   61篇
  2013年   83篇
  2012年   49篇
  2011年   70篇
  2010年   60篇
  2009年   57篇
  2008年   53篇
  2007年   59篇
  2006年   62篇
  2005年   47篇
  2004年   44篇
  2003年   39篇
  2002年   33篇
  2001年   30篇
  2000年   30篇
  1999年   37篇
  1998年   89篇
  1997年   70篇
  1996年   46篇
  1995年   30篇
  1994年   28篇
  1993年   26篇
  1992年   20篇
  1991年   12篇
  1990年   18篇
  1989年   13篇
  1988年   14篇
  1987年   6篇
  1986年   9篇
  1985年   4篇
  1984年   5篇
  1983年   6篇
  1982年   4篇
  1981年   6篇
  1980年   4篇
  1979年   8篇
  1978年   6篇
  1977年   4篇
  1976年   13篇
  1973年   3篇
  1936年   2篇
排序方式: 共有1539条查询结果,搜索用时 330 毫秒
101.
National, state, and local education reform agendas have been on a fast track for more than a decade. Although some psychologists have been active in promoting psychology and psychological services in education reform initiatives, knowledge about their efforts is fragmented. In order to educate psychologists about education reform, this article highlights the impetus for the recent education reform movement, briefly reviews the latest waves of education reform, and discusses the development of the National Education Goals. Then, an argument is made for the integration of education, health, and social reform initiatives; state-level education reform principles and initiatives are highlighted, illustrated by the systemic education reform mandate in Kentucky. Next, progress toward the development and implementation of an APA-sponsored response to the National Education Goals is discussed. Finally, objectives and roles for psychologists in advancing education reform are presented, and guidelines for the education and training of future psychologists are introduced. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
102.
103.
As MOS devices are shrunk to near and submicrometer dimensions, short channel, narrow width and small geometry effects cause variations in the threshold voltage. It is critical for circuit and device designers to be able to predict these variations. This paper reviews and compares the various modeling techniques developed to determine the threshold voltage as a function of device geometry. It is hoped this review will provide insights for the development of new models for today's small devices.  相似文献   
104.
A method is indicated for obtaining electrodeposited amorphous Co-P alloys with differing anisotropies, employing an alternating current density of very low frequency. The method allows samples of a high degree of permeability to be obtained with the result that, in the case of a current density at 5 Hz with amplitude between +0.6 and -0.2 A/cm2, the magnetic properties are similar to those found by Dietz and coworkers, in samples deposited on rotating cylindrical substrates. In the case of samples without perpendicular anisotropy, there can be observed a distribution of the magnetization in the plane, with 180° domains.  相似文献   
105.
In the design of brain-machine interface (BMI) algorithms, the activity of hundreds of chronically recorded neurons is used to reconstruct a variety of kinematic variables. A significant problem introduced with the use of neural ensemble inputs for model building is the explosion in the number of free parameters. Large models not only affect model generalization but also put a computational burden on computing an optimal solution especially when the goal is to implement the BMI in low-power, portable hardware. In this paper, three methods are presented to quantitatively rate the importance of neurons in neural to motor mapping, using single neuron correlation analysis, sensitivity analysis through a vector linear model, and a model-independent cellular directional tuning analysis for comparisons purpose. Although, the rankings are not identical, up to sixty percent of the top 10 ranking cells were in common. This set can then be used to determine a reduced-order model whose performance is similar to that of the ensemble. It is further shown that by pruning the initial ensemble neural input with the ranked importance of cells, a reduced sets of cells (between 40 and 80, depending upon the methods) can be found that exceed the BMI performance levels of the full ensemble.  相似文献   
106.
Despite recent advances in the application of data-dependent liquid chromatography/tandem mass spectrometry (LC/MS/MS) to the identification of drug metabolites in complex biological matrixes, a prior knowledge of the likely routes of biotransformation of the therapeutic agent of interest greatly facilitates the detection and structural characterization of its metabolites. Thus, prediction of the [M + H]+ m/z values of expected metabolites allows for the construction of user-defined MS(n) protocols that frequently reveal the presence of minor drug metabolites, even in the presence of a vast excess of coeluting endogenous constituents. However, this approach suffers from inherent user bias, as a result of which additional "survey scans" (e.g., precursor ion and constant neutral loss scans) are required to ensure detection of as many drug-related components in the sample as possible. In the present study, a novel approach to this problem has been evaluated, in which knowledge-based predictions of metabolic pathways are first derived from a commercial database, the output from which is used to formulate a list-dependent LC/MS(n) data acquisition protocol. Using indinavir as a model drug, a substructure similarity search on the MDL metabolism database with a similarity index of 60% yielded 188 "hits", pointing to the possible operation of two hydrolytic, two N-dealkylation, three N-glucuronidation, one N-methylation, and several aromatic and aliphatic oxidation pathways. Integration of this information with data-dependent LC/MS(n) analysis using an ion trap mass spectrometer led to the identification of 18 metabolites of indinavir following incubation of the drug with human hepatic postmitochondrial preparations. This result was accomplished with only a single LC/MS(n) run, representing significant savings in instrument use and operator time, and afforded an accurate view of the complex in vitro metabolic profile of this drug.  相似文献   
107.
An adaptive trimmed mean estimator for symmetric and asymmetric distributions has been developed. The simulation sample size as small as n = 10, 25 and 50 are chosen, where the influence of the outliers increases in small sample data. The comparison of the proposed estimator and the Princeton Robust Study are made. The results show that the proposed mean estimator has lower standard deviation for symmetric distributions and has a better location estimation for asymmetric distributions.  相似文献   
108.
109.
A planar photonic crystal that allows inherently gap-guided single-mode waveguides is proposed and discussed. This novel structure consists of a two-dimensional lattice of silicon rods embedded on a thin silica slab sandwiched between two silica claddings whose refractive indices are slightly lower than the index of the silica core. The physical parameters of the structure, i.e., rod radius and core thickness, are optimized to maximize the bandgap width for odd modes. Lossless guided modes inside the bandgap and below the claddings' light cone are obtained by reducing the radius of a row of rods. The waveguide bandwidth can be increased by inserting a thin silicon dielectric waveguide instead of the row of rods. The proposed approach may overcome many of the common drawbacks in conventional holes-on-dielectric planar photonic crystal waveguides.  相似文献   
110.
This paper deals with adaptive tracking for discrete-time multiple-input-multiple-output (MIMO) nonlinear systems in presence of bounded disturbances. In this paper, a high-order neural network (HONN) structure is used to approximate a control law designed by the backstepping technique, applied to a block strict feedback form (BSFF). This paper also includes the respective stability analysis, on the basis of the Lyapunov approach, for the whole controlled system, including the extended Kalman filter (EKF)-based NN learning algorithm. Applicability of the scheme is illustrated via simulation for a discrete-time nonlinear model of an electric induction motor.  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