全文获取类型
收费全文 | 2107篇 |
免费 | 30篇 |
专业分类
电工技术 | 30篇 |
综合类 | 1篇 |
化学工业 | 251篇 |
金属工艺 | 20篇 |
机械仪表 | 37篇 |
建筑科学 | 81篇 |
矿业工程 | 5篇 |
能源动力 | 37篇 |
轻工业 | 116篇 |
水利工程 | 25篇 |
石油天然气 | 6篇 |
无线电 | 286篇 |
一般工业技术 | 298篇 |
冶金工业 | 687篇 |
原子能技术 | 25篇 |
自动化技术 | 232篇 |
出版年
2020年 | 18篇 |
2019年 | 18篇 |
2018年 | 16篇 |
2017年 | 12篇 |
2016年 | 24篇 |
2015年 | 19篇 |
2014年 | 22篇 |
2013年 | 80篇 |
2012年 | 48篇 |
2011年 | 49篇 |
2010年 | 46篇 |
2009年 | 47篇 |
2008年 | 66篇 |
2007年 | 48篇 |
2006年 | 73篇 |
2005年 | 61篇 |
2004年 | 34篇 |
2003年 | 45篇 |
2002年 | 45篇 |
2001年 | 55篇 |
2000年 | 43篇 |
1999年 | 41篇 |
1998年 | 184篇 |
1997年 | 105篇 |
1996年 | 96篇 |
1995年 | 61篇 |
1994年 | 51篇 |
1993年 | 63篇 |
1992年 | 38篇 |
1991年 | 29篇 |
1990年 | 35篇 |
1989年 | 28篇 |
1988年 | 41篇 |
1987年 | 30篇 |
1986年 | 36篇 |
1985年 | 35篇 |
1984年 | 30篇 |
1983年 | 36篇 |
1982年 | 21篇 |
1981年 | 24篇 |
1980年 | 12篇 |
1979年 | 23篇 |
1978年 | 23篇 |
1977年 | 21篇 |
1976年 | 54篇 |
1975年 | 18篇 |
1974年 | 19篇 |
1973年 | 22篇 |
1972年 | 11篇 |
1971年 | 15篇 |
排序方式: 共有2137条查询结果,搜索用时 15 毫秒
11.
Summary Sedimentation experiments and X-ray photoelectron spectroscopy (XPS or ESCA) analyses have been used to study the effect of poly(methylmethacrylate) (PMMA) tacticity on aluminum oxide powder dispersion stability in a common solvent medium. The relative trends from sedimentation densities, and from surface analyses after solvent washing show that (PMMA) adsorption is greatest with isotactic polymer, where isotactic>atactic>syndiotactic adsorption. These results suggest that surface adsorption and hence dispersion stability can be influenced by polymer chain configuration as well as by chain conformation. 相似文献
12.
The hedonic properties of delta-9-tetrahydrocannabinol (THC) were assessed in place and taste conditioning paradigms in both Lewis and Sprague-Dawley rat strains. THC produced place avoidance, taste avoidance, and aversive taste reactivity responses in both strains. The Lewis strain displayed more aversive taste reactions and a stronger taste avoidance when conditioned with lower doses of THC than did the Sprague-Dawley strain of rats. THC is an anomalous drug of abuse that appears to be aversive to rats when assessed by these measures. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
13.
STUDY DESIGN: This study retrospectively reviewed the intermediate-term clinical outcome of patients who were 50 years of age or older at the time they experienced their cervical spinal cord injury. OBJECTIVES: To establish reasonable expectations for the functional outcome in the older patient with cervical spinal cord injury. BACKGROUND DATA: The long-term morbidity and mortality of large groups of patients with spinal cord injury have been reported. The specific functional ability, disposition, morbidity, and mortality of this group of older patients injured after 50 years of age, however, have been less well defined. METHODS: Forty-one consecutive patients older than 50 years of age at the time of cervical cord injury were studied, and functional abilities, independence, need for assistance in activities of daily living, disposition, morbidity, and mortality were assessed. All patients had more than 2 years of follow-up examinations (mean, 5.5 years) by the same spine injury service. RESULTS: There were 13 complete and 28 incomplete cervical cord lesions. The mean age of the patients at follow-up examination was 67.5 years. The average follow-up period was 5.5 years after injury. None of the patients with complete cord injury improved, and all required extensive care. Twenty-one (80%) of 26 of the patients with incomplete cord injury were able to ambulate with some assistance. Nineteen of 26 patients had independent or near-independent abilities with activities of daily living. Twenty (77%) of 26 were able to return home. All patients with complete cord injury (13 of 13) had died by the time of the follow-up visit. Seventy-seven percent (10 of 13) of this patient group had died within the first year. Those surviving lived an average of 3.5 years after their injury. Fourteen of 28 patients with incomplete cord injury (50%) had died by the time of the follow-up visit. Six (43%) of the 14 deaths were attributed to complications of their spinal cord injury. CONCLUSION: The functional outcome of the person older than 50 years with a complete cervical cord injury is poor. Of the 14% who survived the first year, all required extensive attendant care, and no neurologic improvement was seen. The patient with an incomplete cord injury has an overall good outcome regarding ambulation and returning to home. 相似文献
14.
15.
16.
Dynamic digital holographic wavelength filtering 总被引:2,自引:0,他引:2
This paper describes the theory and results of a new generic technology for use in optical telecommunications and wavelength division multiplexing (WDM): dynamic digital holographic wavelength filtering. The enabling component is a polarization-insensitive ferroelectric liquid crystal (FLC) spatial light modulator (SLM) in conjunction with a highly wavelength-dispersive fixed diffractive element. The technology has been used to perform demultiplexing of single or multiple WDM signals, dynamic erbium doped fiber amplifier (EDFA) gain equalization and channel management, and used to tune an erbium-doped fiber laser (EDFL) functioning as a high power, very narrow linewidth WDM source 相似文献
17.
TL Holyoake MG Freshney L McNair AN Parker PJ McKay WP Steward E Fitzsimons GJ Graham IB Pragnell 《Canadian Metallurgical Quarterly》1996,87(11):4589-4595
The characterization of many cytokines involved in the control of hematopoiesis has led to intense investigation into their potential use in ex vivo culture to expand progenitor numbers. We have established the optimum ex vivo culture conditions that allow substantial amplification of transient engrafting murine stem cells and which, simultaneously, augment the ability to sustain serial bone marrow transplantation (BMT). Short-term incubation of unfractionated BM cells in liquid culture with stem cell factor (SCF) and interleukin-11 (IL-11) produced a 50-fold amplification of clonogenic multipotential progenitors (CFU-A). Following such ex vivo expansion, substantially fewer cells were required to rescue lethally irradiated mice. When transplanted in cell doses above threshold for engraftment, BM cells expanded ex vivo resulted in significantly more rapid hematopoietic recovery. In a serial transplantation model, unmanipulated BM was only able to consistently sustain secondary BMT recipients, but BM expanded ex vivo has sustained quaternary BMT recipients that remain alive and well more than 140 days after 4th degree BMT. These results show augmentation of both short-term recovery posttransplant and the ability to serially transplant marrow by preincubation in culture with SCF and IL-11. 相似文献
18.
Nuclear pre-messenger RNA splicing requires the action of five small nuclear (sn) RNAs, U1, U2, U4, U5 and U6, and more than 50 proteins. The mechanistic similarity of nuclear pre-mRNA splicing and group II self-splicing suggests that many of the central processes of nuclear pre-mRNA splicing are based on RNA-RNA interaction. To understand the mechanism of pre-mRNA splicing, the interactions, and their temporal relationships, that occur between the snRNAs and the pre-mRNA during splicing must be identified. Several snRNA-snRNA and snRNA-intron interactions have been demonstrated but the putative RNA-based interactions that recognize the AG dinucleotide at the 3' splice site during 3' cleavage and exon ligation are unknown. We report here the reciprocal suppression between 5' and 3' splice site mutations in the yeast actin intron, and propose that the 3' splice site is positioned for 3' cleavage and exon ligation, at least in part, through a non-Watson-Crick interaction between the guanosines at the 5' and 3' splice sites. 相似文献
19.
D.B. Shire M.A. Parker C.L. Tang 《Photonics Technology Letters, IEEE》1996,8(2):188-190
We report new experimental results demonstrating optical bistability and two-input NOR gate operation in intracavity-coupled in-plane and vertical cavity surface emitting lasers (VCSELs) fabricated from the same epitaxial material. The VCSEL (or output) section gain is controlled by separately biased in-plane laser section(s), and depending on the in-plane power output, complete quenching of stimulated emission in the VCSEL is observed. Hysteresis is present in the VCSEL output power versus in-plane laser input power characteristic, and an optical memory effect is observed in the combined device. 相似文献
20.