全文获取类型
收费全文 | 1424篇 |
免费 | 8篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 2篇 |
化学工业 | 29篇 |
金属工艺 | 6篇 |
机械仪表 | 12篇 |
建筑科学 | 8篇 |
能源动力 | 14篇 |
轻工业 | 38篇 |
水利工程 | 1篇 |
无线电 | 15篇 |
一般工业技术 | 31篇 |
冶金工业 | 1235篇 |
原子能技术 | 18篇 |
自动化技术 | 24篇 |
出版年
2021年 | 3篇 |
2019年 | 3篇 |
2018年 | 6篇 |
2017年 | 4篇 |
2016年 | 4篇 |
2014年 | 6篇 |
2013年 | 15篇 |
2012年 | 5篇 |
2011年 | 10篇 |
2010年 | 4篇 |
2009年 | 11篇 |
2008年 | 6篇 |
2007年 | 9篇 |
2006年 | 11篇 |
2005年 | 10篇 |
2004年 | 3篇 |
2003年 | 8篇 |
2002年 | 8篇 |
2001年 | 15篇 |
2000年 | 5篇 |
1999年 | 31篇 |
1998年 | 385篇 |
1997年 | 197篇 |
1996年 | 137篇 |
1995年 | 87篇 |
1994年 | 70篇 |
1993年 | 74篇 |
1992年 | 9篇 |
1991年 | 19篇 |
1990年 | 17篇 |
1989年 | 21篇 |
1988年 | 22篇 |
1987年 | 10篇 |
1986年 | 23篇 |
1985年 | 10篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 9篇 |
1980年 | 15篇 |
1978年 | 4篇 |
1977年 | 22篇 |
1976年 | 79篇 |
1975年 | 3篇 |
1973年 | 3篇 |
1970年 | 2篇 |
1969年 | 2篇 |
1966年 | 2篇 |
1964年 | 3篇 |
1960年 | 2篇 |
1955年 | 2篇 |
排序方式: 共有1433条查询结果,搜索用时 0 毫秒
1.
The implementation of Medicare's prospective payment system in acute care has coincided with a steady increase in medically unstable admissions to our freestanding rehabilitation facility. We investigated the consequences of these admissions by collecting medical information regarding transfers beginning in 1983. Patients requiring transfer back to the acute setting within 1 day of admission were considered medically unstable and their charts were reviewed. The number of patients requiring transfer back within 1 day increased from 1.5% of all first admissions to 3.1% in 1988 (Mantel - Haenszel chi 2 = 8.03, (df = 1), p < .01), but the increase among Medicare patients alone was not significant. This progressive increase was most pronounced in the cerebrovascular accident and spinal cord injury populations. Beginning in 1988, an intensified preadmission evaluation program was implemented, resulting in a significant decline in unstable patient transfers from hospitals where our consultants were on staff. Physiatric consultations at referral institutions decreased the number of unstable patients at admission. 相似文献
2.
The purpose of this study was to identify family physicians' firearm safety counseling beliefs and behaviors. A survey was mailed to a random sample of 600 members of the American Academy of Family Physicians. A three wave mailing technique was used to maximize the response rate and yielded 271 usable surveys (55% response rate). Outcome measures included training experience in firearm safety counseling, the prevalence of firearm safety counseling by family physicians, and their perceptions regarding such counseling. The majority (78%) of family physicians lacked formal training on how to counsel patients about firearm safety and 49% believed more time should be spent in residency programs on firearm safety counseling. The majority (84%) of respondents never or rarely counseled patients on firearm safety and 50% believed firearm safety counseling should be a low priority in their delivery of primary care. The majority of respondents did not regularly counsel patients about firearm safety, did not believe firearm safety counseling should be a priority, and did not believe firearm safety counseling would be effective in reducing firearm-related trauma. 相似文献
3.
MA Lindorfer CS Myung Y Savino H Yasuda R Khazan JC Garrison 《Canadian Metallurgical Quarterly》1998,273(51):34429-34436
The G protein beta5 subunit differs substantially in amino acid sequence from the other known beta subunits suggesting that beta gamma dimers containing this protein may play specialized roles in cell signaling. To examine the functional properties of the beta5 subunit, recombinant beta5 gamma2 dimers were purified from baculovirus-infected Sf9 insect cells using a strategy based on two affinity tags (hexahistidine and FLAG) engineered into the N terminus of the gamma2 subunit (gamma2HF). The function of the pure beta5 gamma2HF dimers was examined in three assays: activation of pure phospholipase C-beta in lipid vesicles; activation of recombinant, type II adenylyl cyclase expressed in Sf9 cell membranes; and coupling of alpha subunits to the endothelin B (ETB) and M1 muscarinic receptors. In each case, the efficacy of the beta5 gamma2HF dimer was compared with that of the beta1 gamma2HF dimer, which has demonstrated activity in these assays. The beta5 gamma2HF dimer activated phospholipase C-beta with a potency and efficacy similar to that of beta1 gamma2 or beta1 gamma2HF; however, it was markedly less effective than the beta1 gamma2HF or beta1 gamma2 dimer in its ability to activate type II adenylyl cyclase (EC50 of approximately 700 nM versus 25 nM). Both the beta5 gamma2HF and the beta1 gamma2HF dimers supported coupling of M1 muscarinic receptors to the Gq alpha subunit. The ETB receptor coupled effectively to both the Gi and Gq alpha subunits in the presence of the beta1 gamma2HF dimer. In contrast, the beta5 gamma2HF dimer only supported coupling of the Gq alpha subunits to the ETB receptor and did not support coupling of the Gi alpha subunit. These results suggest that the beta5 gamma2HF dimer binds selectively to Gq alpha subunits and does not activate the same set of effectors as dimers containing the beta1 subunit. Overall, the data support a specialized role for the beta5 subunit in cell signaling. 相似文献
4.
5.
6.
Neudorf E.G. Kiguel D.L. Hamoud G.A. Porretta B. Stephenson W.M. Sparks R.W. Logan D.M. Bhavaraju M.P. Billinton R. Garrison D.L. 《Power Systems, IEEE Transactions on》1995,10(3):1667-1675
There is an emerging recognition that utility investments and other decisions that affect electric service reliability should be explicitly evaluated on the basis of their cost and benefit implications. A cost-benefit approach that quantifies the reliability benefits of alternatives in terms of the reduction in costs resulting from unserved energy enables the evaluation of generation and transmission capacity additions on a consistent, economic basis. This approach has been applied to two utility case studies. In a case study for Pacific Gas and Electric Company, it was used to evaluate three options for maintaining reliability in a major load center-two involving local generation, and the third, a new 230 kV transmission connection. In a case study for Duke Power Company, the approach was used to evaluate alternative designs for proposed additions to a transmission station. This paper describes the methodology and presents the two utility studies 相似文献
7.
OBJECTIVE: Highly sulfated glycosaminoglycans (GAG) have been demonstrated in every form of amyloid examined to date. Based on temporal studies in murine amyloidogenesis heparan sulfate is deposited coincidentally with the amyloid protein. Our purpose was to follow in vivo GAG synthesis by monitoring 35SO4 incorporation during amyloidogenesis. Several necessary previously unexamined nonamyloidogenic controls were also examined. METHODS: Murine splenic amyloid was induced with lipopolysaccharide (LPS) and amyloid enhancing factor (AEF). Splenic GAG synthesis was monitored by 35SO4 incorporation. Corrections were made for alterations in SO4 metabolism which occur during inflammation. RESULTS: All animals with an inflammatory reaction had a marked increase in GAG synthesis. Those animals receiving AEF, or AEF+LPS, had a significant increase in heparan sulfate synthesis. This was particularly profound in the group developing amyloid (i.e., AEF+LPS). CONCLUSION: Our results indicate that critical factors in amyloid deposition include quantitative as well as qualitative changes that take place in tissue GAG synthesis. A distinct metabolic effect of AEF is demonstrated for the first time. 相似文献
8.
The association of antiphospholipid antibodies with unexplained thrombo-occlusive vascular disease is well known but often remains unrecognized. The most well-studied clinical manifestation is venous thrombosis, but arterial occlusive disease involving multiple sites is also well documented. Twenty-six cases of thrombo-occlusive disease were observed in 22 patients over a 3-year period. Magnetic resonance imaging and angiography were used to make the diagnoses. None of the patients who underwent angiography or venography developed thrombolytic disease related to the puncture site. This group of patients with antiphospholipid antibody syndrome had a wide distribution of arterial and venous thrombotic disease. Radiologists should consider antiphospholipid antibody syndrome in the differential diagnosis when evaluating thrombo-occlusive vascular disease that is unexpected or occurs without risk factors. Knowledge of antiphospholipid antibody status has important implications for prognosis and therapy. 相似文献
9.
AW Jones 《Canadian Metallurgical Quarterly》1993,39(9):1837-1844
The concentration-time profiles of ethanol were determined for capillary blood, end-expired breath, and saliva after 21 healthy men ingested ethanol at 0.68 g/kg body weight. Near the time of obtaining body fluids, the volunteers estimated their feelings of intoxication, and body sway (with open and closed eyes), hand tremor, positional alcohol nystagmus (PAN), and roving ocular movements (ROM) were quantitatively recorded. The concentration-time profiles of ethanol in blood, breath, and saliva agreed well within individuals but there were large variations between subjects. The mean saliva-ethanol profiles ran slightly above those for blood and breath. Subjective ratings of intoxication and impairment of body function (standing steadiness and hand steadiness) were highest at the time of reaching the peak concentrations of ethanol in body fluids. PAN was evident in most subjects between 60 and 120 min after the start of drinking, whereas ROM appeared mainly during the postabsorptive phase of ethanol kinetics (120-420 min). The blood ethanol concentration thresholds were between 500 and 700 mg/L (50-70 mg/dL) when the diminished performance had recovered to baseline values. 相似文献
10.
Perchloric acid (70%) was used to create simulated periapical lesions in tooth sockets of 15 dentate cadaver jaw specimens. Using the Trophy USA direct digital radiographic system, linear images were captured at selected time intervals after initial acid application and altered by contrast reversal, pseudocolor enhancement, and two forms of histogram equalization. The 525 total images were randomized for display on a computer monitor for evaluation by five endodontists. Images were evaluated twice by each rater, with viewings 1 to 2 wk apart. Statistical analysis determined interrater variability, intrarater reproducibility, and the relative merits of each enhancement technique. At 8, 12, 16, and 24 h after acid application, both techniques of histogram equalization yielded a statistically significant improvement over reverse contrast in perception of periapical patholais. Linear and pseudocolor-enhanced images were also significantly more diagnostic than reverse contrast at 12, 16, and 24 h. Intrarater reproducibility showed moderate agreement, but analysis showed only a fair level of interrater agreement. 相似文献