全文获取类型
收费全文 | 4519篇 |
免费 | 217篇 |
国内免费 | 22篇 |
专业分类
电工技术 | 60篇 |
综合类 | 8篇 |
化学工业 | 1013篇 |
金属工艺 | 84篇 |
机械仪表 | 101篇 |
建筑科学 | 85篇 |
矿业工程 | 8篇 |
能源动力 | 263篇 |
轻工业 | 300篇 |
水利工程 | 39篇 |
石油天然气 | 51篇 |
无线电 | 377篇 |
一般工业技术 | 631篇 |
冶金工业 | 1115篇 |
原子能技术 | 39篇 |
自动化技术 | 584篇 |
出版年
2024年 | 7篇 |
2023年 | 57篇 |
2022年 | 167篇 |
2021年 | 190篇 |
2020年 | 154篇 |
2019年 | 180篇 |
2018年 | 229篇 |
2017年 | 176篇 |
2016年 | 205篇 |
2015年 | 133篇 |
2014年 | 179篇 |
2013年 | 368篇 |
2012年 | 199篇 |
2011年 | 228篇 |
2010年 | 170篇 |
2009年 | 153篇 |
2008年 | 122篇 |
2007年 | 81篇 |
2006年 | 97篇 |
2005年 | 58篇 |
2004年 | 57篇 |
2003年 | 48篇 |
2002年 | 53篇 |
2001年 | 28篇 |
2000年 | 28篇 |
1999年 | 47篇 |
1998年 | 345篇 |
1997年 | 207篇 |
1996年 | 160篇 |
1995年 | 88篇 |
1994年 | 66篇 |
1993年 | 78篇 |
1992年 | 35篇 |
1991年 | 29篇 |
1990年 | 22篇 |
1989年 | 27篇 |
1988年 | 23篇 |
1987年 | 25篇 |
1986年 | 14篇 |
1985年 | 22篇 |
1984年 | 10篇 |
1983年 | 10篇 |
1982年 | 11篇 |
1981年 | 13篇 |
1980年 | 22篇 |
1979年 | 8篇 |
1978年 | 13篇 |
1977年 | 23篇 |
1976年 | 71篇 |
1971年 | 4篇 |
排序方式: 共有4758条查询结果,搜索用时 15 毫秒
21.
Cancer statistics, 1993 总被引:1,自引:0,他引:1
22.
The emission and conductivity characteristics of oxide cathodes depend largely on the activation process. In this paper, the electrical properties of new type of oxide cathodes for cathode ray tube (CRT) application, supplied by LG Philips Displays, have been investigated in relation to different cathode activation regimes. The influence of the activation process over different durations has been investigated. A temperature of T=1425 K was chosen to be higher than the optimum cathode activation temperature (T=1200 K), and the other temperature of T=1125 K was lower than that. The electron activation energy (E) was found to vary in the range from 0.58 to 2.28 eV for cathodes activated at the higher temperature regime, and from 1.08 to 1.9 eV for those activated at the lower temperature regime. Scanning electron microscopy (SEM) and electron diffraction X-ray (EDX) analyses show a structural phase transformation in the oxide material that was activated at 1125 K for a period of 1-12 hours. The SEM mapping shows a large contamination of Ba in the top layer of oxide material. The activator agents tungsten and aluminum are found to penetrate into the BaO/spl bsol/SrO layer in two different ways. 相似文献
23.
Muhammad Nabeel Ghayur Anwarul Hassan Gilani 《European Food Research and Technology》2007,224(4):477-481
In this study, we describe the tracheal-relaxant and tocolytic activities of the methanol (ME) and aqueous (AQ) crude extracts
of ginger (rhizome of Zingiber officinale) in an attempt to rationalize its traditional use in disorders of airways and uterine hyperactivity. Both of the ginger extracts
dose-dependently relaxed K+ (80 mM) and carbachol (CCh, 1 μM)-induced contractions with more potency against K+, similar to that elicited by verapamil, a Ca2+ channel blocker. In isolated uterine preparations, the extracts suppressed the K+-induced contractions with respective EC50 values of 0.03 mg/ml (0.02–0.05, 95% CI) and 0.05 mg/ml (0.04–0.06). Activity-directed fractionation of AQ yielded an organic
and an aqueous fraction with the activities concentrated in the former. Both the crude extracts were found safe in mice up
to the oral dose of 5 g/kg when tested for acute toxicity for 24 h. The study shows that ginger possesses tracheal and uterine
smooth muscle relaxant activity, possibility mediated via Ca2+ channel blockade, justifying its use in disorders such as asthma, cough as well as in dysmenorrhoea and uterine and menstrual
spasms and congestion. 相似文献
24.
A new learning model for real-time, grey-level image segmentation is presented. The model gives excellent results for images with different shapes. 相似文献
25.
26.
1. alpha-toxin of Staphylococcus aureus readily permeabilized rat uterine smooth muscle after incubation for a short time. 2. The permeabilized muscle responded to Ca2+ dose-dependently and repeatedly in the same manner. 3. The threshold concentration of Ca2+ for contraction was 0.1-0.3 microM and the maximal contraction was achieved with 1 or 3 microM Ca2+. 4. GTP gamma S or GTP augmented the contractile response to Ca2+. 5. GDP beta S or GDP suppressed the contraction. 6. The role of GTP-binding protein in sensitization of Ca(2+)-induced contractile response of smooth muscle is discussed. 相似文献
27.
A two-dimensional cross-section finite difference model is presented to simulate density dependent leachate migration in leaky aquifers. Unlike existing models, a new approach is adopted to couple the groundwater-flow equation and the hydrodynamic dispersion equation with the elimination of the intermediate step of calculating velocities. The concept of the reference density is employed, permitting increased accuracy (over pressure-based models) in the representation of the transport process. The model is then used to study the effect of several hydraulic and transport parameters on the flow pattern and plume migration which are found to be very sensitive to most of these parameters. Equiconcentration and equipotential lines are overlapped to provide a better understanding of the coupling effect. 相似文献
28.
BACKGROUND: Noncutaneous psammomatous melanotic schwannoma has recently been reported as an unusual component of Carney's complex (myxomas, spotty pigmentation, and endocrinopathy). The most common locations for this lesion include peripheral nerve roots and the gastrointestinal tract. OBSERVATIONS: A cutaneous psammomatous melanotic schwannoma is reported in a patient with known Carney's complex. This neoplasm was pseudoencapsulated, with epithelioid to spindle-shaped cells and no nuclear atypia. Immunostaining was positive for S100 protein and vimentin, as well for HMB-45 antibody. Electron microscopy showed melanosomes in cytoplasmic processes of cells that were ensheathed by layers of reduplicated basal lamina. CONCLUSIONS: Location in the superficial soft tissues is extremely unusual for psammomatous melanotic schwannomas. Recognition of this new cutaneous marker as a part of this complex may aid in identification of individuals at risk for cardiac myxomas. It is also important that this lesion is not mistaken for melanoma, given the strong HMB-45 positivity. 相似文献
29.
30.
The authors suggest that effective algorithms for spectrum search, such as those used for detecting spread spectrum signals, may be derived by selecting suboptimal algorithms and then recovering some of the lost efficacy through parallelisation methods. This thesis is motivated by considering a simple yet meaningful example of a spectrum search technique that exhibits what at first may seem to be counterintuitive behaviour.<> 相似文献