全文获取类型
收费全文 | 3421篇 |
免费 | 6篇 |
专业分类
综合类 | 1篇 |
化学工业 | 22篇 |
机械仪表 | 2篇 |
建筑科学 | 3篇 |
轻工业 | 11篇 |
无线电 | 6篇 |
一般工业技术 | 10篇 |
冶金工业 | 3363篇 |
自动化技术 | 9篇 |
出版年
2020年 | 1篇 |
2017年 | 4篇 |
2016年 | 1篇 |
2014年 | 2篇 |
2012年 | 4篇 |
2011年 | 2篇 |
2010年 | 1篇 |
2009年 | 1篇 |
2008年 | 3篇 |
2007年 | 5篇 |
2006年 | 3篇 |
2005年 | 3篇 |
2004年 | 1篇 |
2003年 | 8篇 |
2002年 | 3篇 |
2001年 | 3篇 |
2000年 | 1篇 |
1999年 | 127篇 |
1998年 | 1147篇 |
1997年 | 591篇 |
1996年 | 413篇 |
1995年 | 197篇 |
1994年 | 187篇 |
1993年 | 175篇 |
1992年 | 38篇 |
1991年 | 33篇 |
1990年 | 44篇 |
1989年 | 43篇 |
1988年 | 39篇 |
1987年 | 35篇 |
1986年 | 33篇 |
1985年 | 39篇 |
1984年 | 1篇 |
1983年 | 5篇 |
1982年 | 13篇 |
1981年 | 13篇 |
1980年 | 17篇 |
1979年 | 1篇 |
1978年 | 6篇 |
1977年 | 52篇 |
1976年 | 125篇 |
1975年 | 3篇 |
1972年 | 2篇 |
1964年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有3427条查询结果,搜索用时 15 毫秒
91.
92.
JW Erdman AJ Thatcher NE Hofmann JD Lederman SS Block CM Lee S Mokady 《Canadian Metallurgical Quarterly》1998,128(11):2009-2013
The algae Dunaliella bardawil and Dunaliella salina naturally contain large concentrations of all-trans and 9-cis beta-carotene (betaC). The purpose of this study was to compare the relative serum and tissue accumulation of all-trans and 9-cis betaC in ferrets fed different ratios of all-trans/9-cis betaC derived from two commercial sources, D. bardawil or D. salina (Betatene). Male ferrets (7 wk old) were fed carotene-free, pelleted diets for 27 d. Beginning on d 18, groups of ferrets (n = 6 or 7) received daily, one of six oral supplements varying in ratios of 9-cis and all-trans betaC mixed with approximately 1.0mL of Ensure. Four supplements containing 5.2-8.3 micromol total betaC were prepared from a 20% Betatene preparation, D. bardawil, a high-cis Betatene preparation, and Betatene further enriched in 9-cis betaC with all-trans betaC/9-cis betaC ratios of 2.2, 1.5, 0.6 and 0.4, respectively. Two control supplements, high and low betaC, were prepared from commercial betaC beadlets. The high control supplement had an all-trans/9-cis ratio of 19.0, whereas 9-cis betaC was not detected in the low supplement. On d 27, serum and tissues were obtained for HPLC analysis of betaC and its isomers. Analysis of livers showed that all-trans betaC was the primary isomer present, but 9-cis and other isomers were also detected in all groups. The hepatic all-trans/9-cis ratios were 5.9, 4.9, 2.5, 1.4, 52.2 and47.5, respectively, for the groups listed above. Lower amounts of all-trans and 9-cis betaC were found in kidneys compared with the liver, but ratios of all-trans/9-cis were not different among groups. Only trace amounts of 9-cis betaC were found in serum. These results demonstrate that the algae D. bardawil and D. salina provide a bioavailable source of betaC isomers, but, as in humans, absorption of 9-cis betaC is poor and any 9-cis betaC absorbed is apparently cleared by the liver. 相似文献
93.
The paper describes a method of fractionating vegetable, animal and fish oils, and in particular palm oil. The method involves
addition of a medium comprising two common solvents to the semisolid oils. On centrifugation, the olein and stearin are separated
by the medium in the middle. Thirteen media made up from binary combinations of nine solvents, viz. water, propylene glycol,
glycerine, methanol, ethanol,n-propanol, isopropanol (IPA), acetone and butanone, are found to be effective in olein-stearin separation. However, only the
water/IPA and water/methanol systems have been studied in detail. The aqueous IPA provides a higher yield of olein than water/
methanol but intersolubility between oil and medium is also greater. The fractionation process can be carried out at any suitable
temperature. Fractionation of the special prime bleached (SPB) palm oil at 16 C yields an olein with a cloud point of 4.8
C. Some hybrid palm oils produce a large quantity of low cloud point olein which can be bleached readily. The process can
be extended to include degumming and neutralization by using an alkaline medium for centrifugation. The olein fractions obtained
have been found to be free of phosphatides and the free fatty acids reduced to as low as 0.02%. Metal-scavenging agents have
also been added to the medium in an attempt to remove copper and iron. The development of this process into a continuous one
has been demonstrated on the AlfaLaval LAPX 202 Separator. Fractionation of crude palm oil using a density gradient provides
seven fractions of different characteristics. The iodine values vary from 37.5 to 57.4 and the unsaturated fatty acids range
from 32.7% to 51.2%. Triglyceride analysis by carbon numbers shows great differences in the C48 and C52 constituents of the fractions.
aThe volume ratio of oil to medium in each case was 1:1.
The separation involved the oil and wax. 相似文献
94.
Microemulsions with a palm oil-based emollient, i.e., medium-chain triglyceride (MCT), and water or glycerol, stabilized by
two oppositely charged ionic surfactants and a medium-chain alcohol, were investigated. The results showed that only the water-in-MCT
or the glycerol-in-MCT microemulsions were prominent. The maximum solubilization of the MCT emollient was higher in cetyltrimethyl
ammonium bromide, i.e., the positively charged surfactant that contained a nitrogen atom, than the negatively charged surfactant
sodium dodecyl sulfate. However, the results did not lend themselves for selecting any decisive factor that would explain
the different solubilization behavior encountered in the investigated aqueous and nonaqueous systems. 相似文献
95.
Treatment of airways disease is directed towards improving patients' health and well-being. Measurements of airways function do not reflect all the disease activity present in the airways that may affect the patient. Spirometry correlates poorly with health. Physicians appear to estimate their patients' health using criteria different from the patients themselves. Quality of life questionnaires provide a method of quantifying the effect of disease on patients' lives. They can summarize a number of aspects of the disease and provide an overall estimate of the effect of disease and benefits due to therapy. They have the potential to identify a threshold response to treatment that may be considered "worthwhile", and allow comparison between therapies with respect to the health gain that each provides. 相似文献
96.
CM Luetje 《Canadian Metallurgical Quarterly》1994,120(12):1395-1396
Tympanoplasty for sinus tympani retraction may result in delayed recurrence of the original problem. This is especially true in children with marginal eustachian tube function. Autogenous tragal cartilage, scored on one surface with perichondrium attached on the other, produces a "natural bend" in the cartilage. When placed in the middle ear, with the scored convex surface facing the promontory, retraction into the sinus tympani can be prevented. This simple, yet effective, surgical technique is outlined. 相似文献
97.
CM Otto MC Mickel JW Kennedy EL Alderman TM Bashore PC Block JA Brinker D Diver J Ferguson DR Holmes 《Canadian Metallurgical Quarterly》1994,89(2):642-650
BACKGROUND: To identify predictors of long-term outcome after balloon aortic valvuloplasty, we analyzed data on 674 adults (mean age, 78 +/- 9 years; 56% were women) undergoing this procedure at 24 clinical centers who had a mean initial increase in aortic valve area of 0.3 cm2. METHODS AND RESULTS: Baseline data included clinical, echocardiographic, and catheterization variables. Follow-up data included mortality, cause of death, rehospitalization, 6-month echocardiography, and functional status. Kaplan-Meier curves and log-rank tests were used to evaluate survival in subgroups. Multivariate Cox regression models were used to identify independent predictors of survival. Overall survival was 55% at 1 year, 35% at 2 years, and 23% at 3 years, with the majority of deaths (70%) classified as cardiac by an independent review committee. Rehospitalization was common (64%), although 61% of survivors at 2 years reported improved symptoms. Echocardiography at 6 months (n = 115) showed restenosis from the postprocedural valve area of 0.78 +/- 0.31 cm2 to 0.65 +/- 0.25 cm2 (P < .0001). With stepwise multivariate analysis, sequentially adding clinical, echocardiographic, and catheterization variables, the overall model identified independent predictors of survival as baseline functional status, baseline cardiac output, renal function, cachexia, female gender, left ventricular systolic function, and mitral regurgitation. Baseline and postprocedural variables were examined to identify which subgroup of patients has the best outcome after aortic valvuloplasty. A "lower-risk" subgroup (28% of the study population), defined by normal left ventricular systolic function and mild clinical functional limitation, had a 3-year survival of 36% compared with 17% in the remainder of the study group. CONCLUSIONS: Long-term survival after balloon aortic valvuloplasty is poor with 1- and 3-year survival rates of 55% and 23%, respectively. Although survivors report fewer symptoms, early restenosis and recurrent hospitalization are common. 相似文献
98.
The objective of the present study was to determine the duration of elevated concentrations of progesterone necessary to induce atresia of persistent ovarian follicles. Heifers were administered 25 mg of PGF2alpha on d 6 and 7 (d 0 = d of synchronized estrus) and a norgestomet implant from d 6 to 14. Ovaries were monitored by ultrasonography, and blood samples were collected on d 3, 5, 7, 9, 11, and 12 and daily from d 14 until ovulation. On d 12, heifers received either two progesterone-releasing intravaginal devices (PRID) for 6 h (6-h; n = 5), two PRID for 24 h (24-h; n = 5), or no treatment (CON; n = 5). Blood samples were collected at 15-min intervals from h -6 to 30 (PRID insertion = h 0) and analyzed for concentrations of LH. Characteristics of LH secretion were determined for consecutive 6-h periods (Period 0 to 5). Hourly blood samples, collected from h 0 to 29, were analyzed for concentrations of 17beta-estradiol (estradiol) and progesterone. The dominant ovarian follicles present on d 7 increased in size to 15.4+/-.3 mm on d 12 ("persistent follicle"). Following removal of the PRID and norgestomet implants, atresia of persistent follicles and ovulation of new follicles were induced in one of five and in four of five heifers in the 6-h and 24-h treatments, respectively. Persistent follicles ovulated after withdrawal of norgestomet in all other heifers. Concentrations of progesterone were increased from h 1 to 7 in the 6-h and h 1 to 26 in the 24-h treatment. Frequency of LH pulses was reduced (P < .05) during Periods 1 to 2 in the 6-h and Periods 1 to 5 in the 24-h treatment relative to the CON treatment. By h 10, concentrations of estradiol in the 6-h and 24-h treatments were lower (P < . 05) than in the CON treatment. This suppression continued through h 29 in the 24-h treatment (P < .05), whereas concentrations in the 6-h treatment were intermediate to those of the CON and 24-h treatments after h 14. Suppression of pulsatile LH release and estradiol secretion was evident with 6 and 24 h of treatment with progesterone, but only the 24-h treatment induced atresia of persistent follicles in a majority of the heifers. 相似文献
99.
A Castro Beiras JL Escudero Pereira A Juffe Stein CM Sánchez J Caramés Bouzán 《Canadian Metallurgical Quarterly》1998,51(8):611-619
The present work describes the process by which the pilot project of clinical management of the Hospital Complex Juan Canalejo, designated as "Heart Area", was implemented. In the first section, the needs and reasons that led to the undertaking of this project are explained. The project's objectives and operative strategies are listed. In the Material and Methods section, three basic aspects of the "Heart Area" are described: selection criteria of the "Area", its structure and function, and its foundation and development. In the Results section, we compare the activity undertaken in the "Area" to the situation present prior to its implementation, in relation to quality and costs. Finally, in the Conclusions, we comment on the important implications that our project can have within the Hospital Complex Juan Canalejo as well as in the health care field in general. 相似文献
100.
S Brady CM Hiam R Saemann L Humbert MZ Fleming K Dawkins-Brickhouse 《Canadian Metallurgical Quarterly》1996,32(6):573-578
The treatment of "dual diagnosis", co-occurring substance abuse and mental illness, calls for addressing two serious and often confounding problems. The authors introduce an expanded version of the transtheoretical model of change as formulated by J.O. Prochaska and C.C. DiClemente, and suggest that this new version offers a pragmatic approach to the conceptualization and treatment of dual diagnosis. The potential utility of the treatment model is presented through the authors' experiences in working with inner-city, chronic mentally ill individuals with substance abuse problems. Practical guidelines for dual diagnosis group therapy are discussed. 相似文献