全文获取类型
收费全文 | 35128篇 |
免费 | 4678篇 |
国内免费 | 2832篇 |
专业分类
电工技术 | 2295篇 |
技术理论 | 3篇 |
综合类 | 3550篇 |
化学工业 | 3845篇 |
金属工艺 | 681篇 |
机械仪表 | 1489篇 |
建筑科学 | 3404篇 |
矿业工程 | 1653篇 |
能源动力 | 924篇 |
轻工业 | 1612篇 |
水利工程 | 1251篇 |
石油天然气 | 1502篇 |
武器工业 | 353篇 |
无线电 | 3485篇 |
一般工业技术 | 2144篇 |
冶金工业 | 2098篇 |
原子能技术 | 283篇 |
自动化技术 | 12066篇 |
出版年
2024年 | 135篇 |
2023年 | 547篇 |
2022年 | 938篇 |
2021年 | 1238篇 |
2020年 | 1178篇 |
2019年 | 1039篇 |
2018年 | 999篇 |
2017年 | 1232篇 |
2016年 | 1373篇 |
2015年 | 1485篇 |
2014年 | 2171篇 |
2013年 | 1974篇 |
2012年 | 2310篇 |
2011年 | 2676篇 |
2010年 | 2028篇 |
2009年 | 2149篇 |
2008年 | 2082篇 |
2007年 | 2421篇 |
2006年 | 2180篇 |
2005年 | 1776篇 |
2004年 | 1522篇 |
2003年 | 1417篇 |
2002年 | 1273篇 |
2001年 | 1047篇 |
2000年 | 819篇 |
1999年 | 684篇 |
1998年 | 467篇 |
1997年 | 369篇 |
1996年 | 306篇 |
1995年 | 277篇 |
1994年 | 235篇 |
1993年 | 149篇 |
1992年 | 121篇 |
1991年 | 85篇 |
1990年 | 109篇 |
1989年 | 61篇 |
1988年 | 64篇 |
1987年 | 48篇 |
1986年 | 49篇 |
1985年 | 156篇 |
1984年 | 255篇 |
1983年 | 302篇 |
1982年 | 212篇 |
1981年 | 321篇 |
1980年 | 129篇 |
1979年 | 46篇 |
1978年 | 48篇 |
1977年 | 19篇 |
1975年 | 25篇 |
1974年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
罗立祝 《机械工业高教研究》2008,(2):106-110
从高校招生的演变历史看,中国在1978年以前对工农阶层子女实行高校入学优惠政策主要源于国家对这一阶层的特殊偏好而实行平均主义分配政策所致。国家通过报考资格政策、优先录取政策和免试推荐入学政策人为地大幅度提高了工农阶层子女在高校大学生中所占的比例。从公平视角看,这项政策不仅违背了公平原则,而且降低了人才选拔的质量。 相似文献
82.
W. Shang B. Robrahn F. Golding M. H. J. Koch 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2004,530(3):513-520
A data acquisition system for time resolved X-ray scattering experiments using linear, quadrant or area gas proportional detectors with delay line readout based on commercially available hardware (National Instruments) is described. The system can easily be configured for recording data from point detectors (e.g. photomultipliers and photodiodes) and/or ancillary data only. Applications involving measurements with two different types of time to digital converters illustrate the features and performances of the system. 相似文献
83.
Gokhan Tur 《Machine Learning》2007,69(1):55-74
We propose three methods for extending the Boosting family of classifiers motivated by the real-life problems we have encountered. First, we propose a semisupervised learning method for exploiting the unlabeled data in Boosting. We then present a novel classification model adaptation method. The goal of adaptation is optimizing an existing model for a new target application, which is similar to the previous one but may have different classes or class distributions. Finally, we present an efficient and effective cost-sensitive classification method that extends Boosting to allow for weighted classes. We evaluated these methods for call classification in the AT&;T VoiceTone® spoken language understanding system. Our results indicate that it is possible to obtain the same classification performance by using 30% less labeled data when the unlabeled data is utilized through semisupervised learning. Using model adaptation we can achieve the same classification accuracy using less than half of the labeled data from the new application. Finally, we present significant improvements in the “important” (i.e., higher weighted) classes without a significant loss in overall performance using the proposed cost-sensitive classification method. 相似文献
84.
D. P. Phillips, T. E. Ruth, and L. M. Wagner (1993) reported that 1969-1990 California mortality data show that Chinese Americans are particularly vulnerable to diseases that Chinese astrology and traditional Chinese medicine associate with their birth years. For example, because fire is associated with the heart, a Chinese person born in a fire year (such as 1937) is more likely to die of heart disease than is a Chinese person born in a nonfire year. However, many diseases were excluded from this study, some diseases that were included have ambiguous links to birth years, and the statistical tests were indirect. A more complete statistical analysis and independent California mortality data for the years 1960-1968 and 1991-2002 did not replicate the original results. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
85.
本文详细分析了解吸塔换热器结堵的原因和对环保装置正常运行的影响,并针对性地提出了防范和处理措施。 相似文献
86.
No authorship indicated 《Canadian Metallurgical Quarterly》2003,58(11):931
Provides the biography of David W. Johnson and announces that he has won the Award for Distinguished Contributions of Applications of Psychology to Education and Training for programmatic research, comprehensive research reviews, and revision of theory over four decades of persistence that have provided the knowledge foundation for cooperative learning, constructive controversy, conflict resolution, and peer mediation training. A selected bibliography is also provided. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
87.
Finite sample properties of estimators of spatial autoregressive models with autoregressive disturbances 总被引:1,自引:0,他引:1
The article investigates the finite sample properties of estimators for spatial autoregressive models where the disturbance
terms may follow a spatial autoregressive process. In particular we investigate the finite sample behavior of the feasible
generalized spatial two-stage least squares (FGS2SLS) estimator introduced by Kelejian and Prucha (1998), the maximum likelihood
(ML) estimator, as well as that of several other estimators. We find that the FGS2SLS estimator is virtually as efficient
as the ML estimator. This is important because the ML estimator is computationally burdensome, and may even be forbidding
in large samples, while the FGS2SLS estimator remains computationally feasible in large samples.
Received: 20 January 2001 / Accepted: 31 August 2001 相似文献
88.
Riikka Susitaival Ilmari Juva Markus Peuhkuri Samuli Aalto 《Telecommunication Systems》2006,33(1-3):67-88
In this paper we analyze measurements gathered from a 2.5~Gbps link in the Finnish university network (Funet) in 2004. The
traffic is broken down into origin-destination (OD) pair components based on source and destination IP address. We study the
traffic characteristics of these components, and identify four typical representative OD pairs. For these pairs we investigate
the validity of a moving IID Gaussian model. We find that the statistical properties of these OD pairs differ significantly
from each other, with only some of them close to Gaussian. The OD pairs are also found to have some cross-correlation between
each other, contradicting an often made assumption about OD pair independence. Furthermore, the existence of a mean-variance
relation between the OD pairs is studied. We find that there is a relation between mean and variance, but for some periods
of time it is rather weak. 相似文献
89.
Seog Geun Kang 《ETRI Journal》2006,28(2):235-238
In this letter, a block code that minimizes the peak‐to‐average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signals is proposed. It is shown that peak envelope power is invariant to cyclic shift and codeword inversion. The systematic encoding rule for the proposed code is composed of searching for a seed codeword, shifting the register elements, and determining codeword inversion. This eliminates the look‐up table for one‐to‐one correspondence between the source and the coded data. Computer simulation confirms that OFDM systems with the proposed code always have the minimum PAPR. 相似文献
90.