全文获取类型
收费全文 | 32556篇 |
免费 | 3571篇 |
国内免费 | 1904篇 |
专业分类
电工技术 | 1665篇 |
综合类 | 3395篇 |
化学工业 | 3831篇 |
金属工艺 | 1119篇 |
机械仪表 | 1757篇 |
建筑科学 | 5115篇 |
矿业工程 | 1517篇 |
能源动力 | 893篇 |
轻工业 | 1551篇 |
水利工程 | 1427篇 |
石油天然气 | 2350篇 |
武器工业 | 680篇 |
无线电 | 2486篇 |
一般工业技术 | 3965篇 |
冶金工业 | 1916篇 |
原子能技术 | 582篇 |
自动化技术 | 3782篇 |
出版年
2024年 | 100篇 |
2023年 | 373篇 |
2022年 | 696篇 |
2021年 | 974篇 |
2020年 | 927篇 |
2019年 | 831篇 |
2018年 | 864篇 |
2017年 | 1092篇 |
2016年 | 1291篇 |
2015年 | 1299篇 |
2014年 | 1844篇 |
2013年 | 1784篇 |
2012年 | 1978篇 |
2011年 | 2474篇 |
2010年 | 1810篇 |
2009年 | 1910篇 |
2008年 | 1834篇 |
2007年 | 2035篇 |
2006年 | 2006篇 |
2005年 | 1680篇 |
2004年 | 1391篇 |
2003年 | 1265篇 |
2002年 | 1158篇 |
2001年 | 1012篇 |
2000年 | 765篇 |
1999年 | 632篇 |
1998年 | 456篇 |
1997年 | 365篇 |
1996年 | 322篇 |
1995年 | 274篇 |
1994年 | 218篇 |
1993年 | 173篇 |
1992年 | 144篇 |
1991年 | 134篇 |
1990年 | 124篇 |
1989年 | 75篇 |
1988年 | 68篇 |
1987年 | 56篇 |
1986年 | 50篇 |
1985年 | 153篇 |
1984年 | 251篇 |
1983年 | 286篇 |
1982年 | 211篇 |
1981年 | 309篇 |
1980年 | 129篇 |
1979年 | 45篇 |
1978年 | 38篇 |
1977年 | 13篇 |
1975年 | 21篇 |
1974年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 359 毫秒
71.
Ryba Nancy L.; Cooper Virginia G.; Zapf Patricia A. 《Canadian Metallurgical Quarterly》2003,34(5):499
What is the current standard of practice for evaluations of juvenile competence to stand trial (JCST)? The present study surveyed psychologists regarding the practices used when conducting JCST evaluations. Respondents rated the importance of 17 elements that might be included in a JCST evaluation report. Of these elements, 7 were considered essential by 70% or more of respondents, with 9 additional elements rated as either essential or recommended. A majority of respondents felt that the use of psychological and forensic instruments was important. A list of tests used is provided, and the implications for the development of standards and policy are discussed to provide practitioners with additional knowledge that will help to further the state of the discipline. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
72.
利用数模转换器可构成频率精度高并且可程控的信号发生器。本电路主要由计数器CD4029产生稳定的八路数字信号输出,经数模转换器AD7528输出模拟信号,再经运放变换,从电路的不同的输出端分别实现了三角波、矩形波、正弦波输出,从而实现了信号发生器的数字控制。 相似文献
73.
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
74.
T. A. Hall 《Journal of microscopy》1991,164(1):67-79
When a microregion in a thin section of frozen-dried and embedded tissue is analysed by the conventional electron-probe X-ray continuum-normalization method, the measured quantity is in mmol of element per kg of embedded specimen. As each microregion contains an unknown amount of embedding medium, this quantity generally lies indeterminately somewhere within the wide range between mmol of element per kg of hydrated tissue and mmol of element per kg of dehydrated tissue. However, if a ‘tag’ element is incorporated in the embedding medium, the contribution of the medium to the local continuum count in each probed field should be measurable, and the X-ray data may then unambiguously yield mmol of element per kg of dehydrated tissue. This result should not be affected by shrinkage on freeze-drying or by incomplete replacement of water by embedding medium. The same X-ray data can additionally provide estimates of mmol of element per unit volume, mmol of element per kg of hydrated tissue and local dry-mass fraction. However, these estimates are subject to errors due to tissue shrinkage, incomplete replacement of water and beam damage. 相似文献
75.
Jonathan P. Belnoue Giang D. Nguyen Alexander M. Korsunsky 《International Journal of Fracture》2007,144(1):53-60
This paper presents a new 1-D non-local damage-plasticity deformation model for ductile materials. It uses the thermodynamic
framework described in Houlsby and Puzrin (2000) and holds, nevertheless, some similarities with Lemaitre’s (1971) approach.
A 1D finite element (FE) model of a bar fixed at one end and loaded in tension at the other end is introduced. This simple
model demonstrates how the approach can be implemented within the finite element framework, and that it is capable of capturing
both the pre-peak hardening and post-peak softening (generally responsible for models instability) due to damage-induced stiffness
and strength reduction characteristic of ductile materials. It is also shown that the approach has further advantages of achieving
some degree of mesh independence, and of being able to capture deformation size effects. Finally, it is illustrated how the
model permits the calculation of essential work of rupture (EWR), i.e. the specific energy per unit cross-sectional area that
is needed to cause tensile failure of a specimen. 相似文献
76.
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
77.
新型低伤害压裂液的研究与应用 总被引:1,自引:1,他引:0
针对安棚油田特低孔特低渗、储层温度高、微裂缝发育等地质特征 ,通过室内实验 ,研制出具有耐高温、低伤害、延迟交联等特点的新型压裂液体系 ,并进行了 2 0多井次的现场试验。结果表明 ,该压裂液具有很好的适应性 ,完全可满足安棚油田特低孔特低渗储层压裂改造的要求 相似文献
78.
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
79.
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
80.
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