全文获取类型
收费全文 | 238012篇 |
免费 | 4123篇 |
国内免费 | 647篇 |
专业分类
电工技术 | 3722篇 |
综合类 | 176篇 |
化学工业 | 35634篇 |
金属工艺 | 8692篇 |
机械仪表 | 6733篇 |
建筑科学 | 5956篇 |
矿业工程 | 1374篇 |
能源动力 | 5820篇 |
轻工业 | 22039篇 |
水利工程 | 2609篇 |
石油天然气 | 4194篇 |
武器工业 | 12篇 |
无线电 | 25158篇 |
一般工业技术 | 46495篇 |
冶金工业 | 47969篇 |
原子能技术 | 5246篇 |
自动化技术 | 20953篇 |
出版年
2021年 | 2400篇 |
2020年 | 1840篇 |
2019年 | 2194篇 |
2018年 | 3970篇 |
2017年 | 4042篇 |
2016年 | 4225篇 |
2015年 | 2817篇 |
2014年 | 4383篇 |
2013年 | 11453篇 |
2012年 | 7227篇 |
2011年 | 8988篇 |
2010年 | 7166篇 |
2009年 | 7746篇 |
2008年 | 8058篇 |
2007年 | 7931篇 |
2006年 | 6644篇 |
2005年 | 6123篇 |
2004年 | 5835篇 |
2003年 | 5621篇 |
2002年 | 5179篇 |
2001年 | 5068篇 |
2000年 | 4972篇 |
1999年 | 5320篇 |
1998年 | 14790篇 |
1997年 | 10151篇 |
1996年 | 7718篇 |
1995年 | 5443篇 |
1994年 | 4926篇 |
1993年 | 4715篇 |
1992年 | 3419篇 |
1991年 | 3280篇 |
1990年 | 3088篇 |
1989年 | 3154篇 |
1988年 | 3017篇 |
1987年 | 2555篇 |
1986年 | 2484篇 |
1985年 | 2911篇 |
1984年 | 2666篇 |
1983年 | 2460篇 |
1982年 | 2247篇 |
1981年 | 2356篇 |
1980年 | 2175篇 |
1979年 | 2241篇 |
1978年 | 2227篇 |
1977年 | 2570篇 |
1976年 | 3630篇 |
1975年 | 1915篇 |
1974年 | 1829篇 |
1973年 | 1847篇 |
1972年 | 1482篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
W. F. Flanagan Lijun Zhong B. D. Lichter 《Metallurgical and Materials Transactions A》1993,24(3):553-559
A model is proposed to explain transgranular-stress corrosion cracking (T-SCC) in face-centered cubic (fcc) materials. Crack
propagation is shown to be anisotropic, in that growth near {110} < 001> is discontinuous due to crack arrest by dislocation
blunting whereas growth away from this growth orientation is continuous. For the former case, renucleation of arrested cracks
involves active dissolution of shear bands at the crack tip, which changes the stress state at Lomer-Cottrell locks, causing
them to fail by cleavage. Once the crack is nucleated, its instantaneous macroscopic crack-growth velocity is considered to
be comprised of multiple nucleation of microcracks with intervening arrests. This microcracking results from the interaction
of the stress fields from neighboring cracks which are forming simultaneously, the crack-opening constraint due to ligaments
which act as “bridges” behind the crack front, and the localized dissolution at the microcrack tip which affectsK
IC and leads to the “cobblestone” appearance. Experimental evidence and theoretical considerations are presented to support
the model. The system studied was Cu-25 at. pct Au in 0.6 M NaCl solution at potentials between 300 and 400 mV (sce), which
precludes hydrogen embrittlement.
This article is based on a presentation made in the symposium “Quasi-Brittle Fracture” presented during the TMS fall meeting,
Cincinnati, OH, October 21–24, 1991, under the auspices of the TMS Mechanical Metallurgy Committee and the ASM/MSD Flow and
Fracture Committee. 相似文献
142.
Summary The synthesis of new high optical abrasion resistance coating materials has been undertaken by functionalizing melamine and
tris(m-aminophenyl)phosphine oxide with a triethoxysilane containing reagent. These highly functionalized compounds have been
used for coating a bis-phenol-A polycarbonate substrate by the sol-gel method. Preliminary data shows the abrasion resistance
of the polymer substrate is considerably improved when it is coated by these optically clear materials. 相似文献
143.
144.
Fractal error for detecting man-made features in aerial images 总被引:3,自引:0,他引:3
A technique is proposed for aiding photointerpreters in detecting man-made features in aerial reconnaissance images. The technique, which uses a metric called fractal error, is based on the observed propensity of natural image features to fit a fractional Brownian motion model. Man-made features usually do not fit this model well, and consequently the fractal error metric may be used as a discriminant function for detecting man-made scene features 相似文献
145.
146.
The quality of analgesia, patient satisfaction and incidence of side effects following a single bolus of epidural morphine were compared with patient-controlled epidural analgesia (PCEA) with meperidine during the first 24 hr after elective Caesarean section. Seventy-five women were randomly assigned to three equal groups. Group I received 30 mg epidural meperidine after delivery and PCEA with meperidine; Group 2 received 3 mg epidural morphine after delivery and PCEA with saline in a double-blind fashion. Group 3 received 3 mg epidural morphine after delivery without saline PCEA. Visual analogue pain scores (VAS) were higher with PCEA meperidine from 8-16 hr post-operatively (P < 0.05) than in both epidural morphine groups. Two patients in Group 1 and one in Group 3 required supplemental parental analgesia. The incidence of nausea was 16% in Group 1, compared with 52% in Group 2 and 56% in Group 3 (P < 0.01). Pruritus occurred in 24% of Group 1 patients, 84% of patients in Group 2 and 68% of patients in Group 3 (P < 0.001). Forty-six percent of patients in Group 1 were very satisfied with pain management, compared with 77% in Group 2 and 79% in Group 3. Nurse workload was higher in the PCEA study groups than in Group 3 (P < 0.05). A single bolus of epidural morphine provides superior analgesia and satisfaction at low cost, but with a higher incidence of nausea and pruritus than PCEA with meperidine. 相似文献
147.
148.
María P. Albano Liliana B. Garrido 《Journal of Materials Synthesis and Processing》2002,10(4):211-218
Si3N4powders coated with 6 wt% Y2O3and 4 wt% Al2O3were prepared by coprecipitation. The resulting powders were dispersed in water at different pH values and with addition of various amounts of ammonium polyacrylate (NH4PA) to produce 32 vol% slips. The influence of the amount of NH4PA solution added and pH on the rheological properties of 32 vol% coated Si3N4slips were studied. In addition, the sintered density of cast samples was determined and related to the degree of slip dispersion. The adsorption of the NH4PA on the coated particle surface was rather high and the surface became saturated near 0.86 mg/m2at pH 9.2. High NH4PA concentrations (1.7–3 wt%) were necessary to obtain well dispersed 32 vol% coated Si3N4slips at pH 9.2. The best stabilization was obtained with the addition of 2.3 wt% NH4PA; in this condition, the viscosity reached a minimum value of 35 mPa.s at 100 s–1. The slip viscosity increased with increasing pH from 9.2 to 10.2. Slips with low viscosities gave a more dense packing of cast samples and consequently higher sintered density values. 相似文献
149.
Bagdonavicius V.B. Gerville-Reache L. Nikulin M.S. 《Reliability, IEEE Transactions on》2002,51(1):27-31
Applications of the additive accumulation of damages (AAD) or the accelerated failure time (AFT) and the proportional hazards (PH) models in accelerated life testing with step-stresses are discussed. A new model including AAD and PH models is proposed. It is more reasonable than the PH model and wider then the AAD model. Constructing the maximum likelihood function is discussed 相似文献
150.
Metal Science and Heat Treatment - 相似文献