首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   422篇
  免费   0篇
化学工业   2篇
机械仪表   1篇
轻工业   1篇
冶金工业   418篇
  2009年   1篇
  2004年   2篇
  2001年   1篇
  1999年   8篇
  1998年   110篇
  1997年   62篇
  1996年   54篇
  1995年   28篇
  1994年   22篇
  1993年   32篇
  1992年   5篇
  1991年   8篇
  1990年   6篇
  1989年   5篇
  1988年   7篇
  1987年   7篇
  1986年   6篇
  1985年   7篇
  1983年   1篇
  1982年   3篇
  1981年   1篇
  1980年   1篇
  1978年   2篇
  1977年   18篇
  1976年   24篇
  1960年   1篇
排序方式: 共有422条查询结果,搜索用时 78 毫秒
31.
We measured effects of continuous vs twice-daily feeding, the addition of unsaturated fat to the diet, and monensin on milk production, milk composition, feed intake, and CO2-methane production in four experiments in a herd of 88 to 109 milking Holsteins. Methane and CO2 production increased with twice-daily feeding, but the CO2:CH4 ratio remained unchanged. Soybean oil did not affect the milkfat percentages, but fatty acid composition was changed. All saturated fatty acids up to and including 16:0 decreased (P < .01), whereas 18:0 and trans 18:1 increased (P < .001). The 18:2 conjugated dienes also increased (P < .01) when the cows were fed soybean oil. Monensin addition to the diet at 24 ppm decreased methane production (P < .01); the CO2:CH4 ratios reached 15, milk production increased (P < .01), and milkfat percentage and total milkfat output decreased (P < .01), as did feed consumption, compared with cows fed diets without monensin (P < .05). Milk fatty acid composition showed evidence of depressed ruminal biohydrogenation: saturated fatty acids (P < .05) decreased and 18:1 increased (P < .001); most of the increase was seen in the trans 18:1 isomer. As with soybean oil feeding, addition of monensin also increased (P < .05) the concentration of conjugated dienes. The monensin feeding trial was repeated 161 d later with 88 cows, of which 67 received monensin in the diet in the first trial and 21 cows were newly freshened and had never received monensin. Methane production again decreased (P < .05), but this time the CO2:CH4 ratio did not change and all other monensin-related effects were absent. The ruminal microflora in the cows that had previously received monensin seemed to have undergone some adaptive changes and no longer responded as before.  相似文献   
32.
BACKGROUND: Open pelvic fractures represent one of the most devastating injuries in orthopedic trauma. The purpose of this study was to document the injury characteristics, complications, mortality, and long-term, health-related quality of life outcomes in patients with open pelvic fractures. METHODS: The trauma registry at an adult trauma center was used to identify all multiple system blunt trauma patients with a pelvic fracture from January of 1987 to August of 1995 (n = 1,179). Demographic data, mechanism of injury, and fracture type were determined from hospital records. Short-term outcome measures included infectious complications, mortality, and length of stay in hospital. Long-term outcomes of survivors were obtained by telephone interview using the SF-36 Health Survey and the Functional Independence Measure. RESULTS: Open pelvic fractures were uncommon, occurring in 44 patients (4%). Patients with open fractures were about 9 years younger, on average, than patients with closed fractures (30 vs. 39, p < 0.001). Similarly, patients with open fractures were more likely to be male (75 vs. 57%, p < 0.02), more likely to have been involved in a motorcycle crash (27 vs. 6%, p < 0.001), and more likely to have an unstable pelvic ring disruption (45 vs. 25%, p < 0.001). Open pelvic fracture patients required more blood than closed pelvic fracture patients, both in the first day (16 vs. 4 units, p < 0.001) and during the total hospital admission (29 vs. 9 units, p < 0.001). Five patients with perineal wounds did not receive a diverting colostomy; in turn, these individuals had a total of six pelvic infectious complications (one abscess, two with osteomyelitis, and three perineal wound infections). Overall, 11 patients died, six patients were lost to follow-up, and 27 were long-term survivors (mean duration of 4 years). Chronic disability was common after a pelvic fracture, with problems related to physical role performance and physical functioning, and was particularly severe after an open pelvic fracture (p < 0.05 for both as measured by the SF-36). CONCLUSIONS: Patients with open pelvic fractures often survive, need to be treated with massive blood transfusions, and often require a colostomy. They are frequently left with chronic pain and residual disabilities in physical functioning and physical roles, and many remain unemployed years after injury.  相似文献   
33.
The findings are presented of a conference on Outcomes of Hand Surgery organized by the audit committee of British Society for Surgery of the Hand in 1993. Measures of outcome in terms of movement, power, sensibility, pain, activities of daily living, complications and patient satisfaction are considered, and an example of a patient evaluation measure given as an appendix.  相似文献   
34.
As part of a class action suit, the author was asked to assess the quality of mental health services in eight prisons in Georgia. This paper describes the background to the suit, reviews selected literature on assessing quality of correctional mental health care, and describes methods used to survey prison mental health services. A standardized survey instrument was developed with probe questions to assess the quality of services. Individual cases were reviewed, inmates were interviewed, and the quality of mental health structures, processes, and outcomes were assessed. Key findings from the survey are summarized. The author concluded that the quality of mental health services in the prisons surveyed was so low overall as to constitute a pattern of deliberate indifference, and that the services were constitutionally inadequate.  相似文献   
35.
36.
OBJECTIVE: The purpose of this study was to evaluate a hydroxylapatite-based material and calcium sulfate when each was used under a resin-modified glass ionomer cement to repair furcation perforations. STUDY DESIGN: Perforations of pulp chamber floors were made in 72 teeth of 9 dogs. Perforations were divided into 3 equal-sized groups and repaired with resin-modified glass ionomer either alone or over an artificial floor. The artificial floor was either a hydroxylapatite-based material or calcium sulfate. Three dogs were killed at each of 3 intervals (1, 3, and 6 months). The tissue response to the tested materials was evaluated clinically, radiographically, and histologically. RESULTS: The hydroxylapatite-based material showed the highest radiographic success; this was followed by calcium sulfate and glass ionomer. From histologic evaluation, the average success rate was found to be 67% for calcium sulfate, 62% for the hydroxylapatite-based material, and 59% for glass ionomer. However, there was no statistical significant difference with the resin-modified glass ionomer when it was used alone and when it was used over a barrier. There was also no significant difference between the hydroxylapatite-based material and the calcium sulfate when they were used as artificial floors. CONCLUSION: The use of an artificial floor may not be necessary when flowable resin-modified glass ionomer cements are used.  相似文献   
37.
The kdr and super-kdr point mutations found in the insect sodium channel gene are postulated to confer knockdown resistance (kdr) to pyrethroids. Using an allele-specific PCR assay to detect these mutations in individual horn flies, Haematobia irritans (L.), we determined the allelic frequency of the kdr and super-kdr mutations in several wild and laboratory populations. Wild populations with very similar allelic frequencies had resistance levels that ranged widely from 3- to 18-fold relative to a susceptible population. Conversely, the kdr allele frequency in a lab population with 17-fold resistance was nearly double that found in a heavily pressured wild population with 18-fold resistance. We conclude that, although the kdr mutation confers significant levels of pyrethroid resistance, a substantial component of resistance in insecticidally pressured populations is conferred by mechanisms that are PBO-suppressible. High super-kdr allele frequencies were detected in two resistant lab populations, but in wild populations with equivalent resistance the super-kdr allele frequency was very low. Interestingly, in over 1200 individuals assayed, the super-kdr mutation was never detected in the absence of the kdr mutation.  相似文献   
38.
PURPOSE: To examine how common patient factors affect screening mammographic sensitivity and cancer stage at diagnosis. MATERIALS AND METHODS: The authors used a population-based database of 183,134 screening mammograms and a statewide tumor registry to identify 807 breast cancers detected at screening mammography. RESULTS: Sensitivity varied significantly with ethnicity, use of estrogen replacement therapy, mammographic breast density, and age. Sensitivity was 54% (13 of 24) in women younger than 40 years, 77% (121 of 157) in women aged 40-49 years, 78% (224 of 286) in women aged 50-64 years, and 81% (277 of 340) in women older than 64 years. Sensitivity was 68% (162 of 237) for dense breasts and 85% (302 of 356) for nondense breasts and 74% (180 of 244) in estrogen replacement therapy users and 81% (417 of 513) in nonusers. Sensitivity was most markedly reduced with the combination of dense breasts and estrogen replacement therapy use; there was little difference when only one factor was present. Median cancer size and the percentage of early cancers showed little change with any factors. CONCLUSION: Age is a minor determinant of mammographic sensitivity in women aged 40 years or older. Sensitivity is substantially decreased with the combination of higher breast density and estrogen replacement therapy use. There was not a notable shift in cancer outcomes in the groups with lower mammographic sensitivity. These data do not support different screening recommendations in women aged 40-49 years or in estrogen replacement therapy users.  相似文献   
39.
Induction of mucosal tolerance by inhalation of soluble peptides with defined T cell epitopes is receiving much attention as a means of specifically down-regulating pathogenic T cell reactivities in autoimmune and allergic disorders. Experimental autoimmune encephalomyelitis (EAE) induced in the Lewis rat by immunization with myelin basic protein (MBP) and Freund's adjuvant (CFA) is mediated by CD4+ T cells specific for the MBP amino acid sequences 68-86 and 87-99. To further define the principles of nasal tolerance induction, we generated three different MBP peptides (MBP 68-86, 87-99 and the non-encephalitogenic peptide 110-128), and evaluated whether their nasal administration on day -11, -10, -9, -8 and -7 prior to immunization with guinea pig MBP (gp-MBP) + CFA confers protection to Lewis rat EAE. Protection was achieved with the encephalitogenic peptides MBP 68-86 and 87-99, MBP 68-86 being more potent, but not with MBP 110-128. Neither MBP 68-86 nor 87-99 at doses used conferred complete protection to gp-MBP-induced EAE. In contrast, nasal administration of a mixture of MBP 68-86 and 87-99 completely blocked gp-MBP-induced EAE even at lower dosage compared to that being used for individual peptides. Rats tolerized with MBP 68-86 + 87-99 nasally showed decreased T cell responses to MBP reflected by lymphocyte proliferation and IFN-gamma ELISPOT assays. Rats tolerized with MBP 68-86 + 87-99 also had abrogated MBP-reactive IFN-gamma and tumor necrosis factor-alpha mRNA expression in lymph node cells compared to rats receiving MBP 110-128 nasally, while similar low levels of MBP-reactive transforming growth factor-beta and IL-4 mRNA expressing cells were observed in the two groups. Nasal administration of MBP 68-86 + 87-99 only slightly inhibited guinea pig spinal cord homogenate-induced EAE, and passive transfer of spleen mononuclear cells from MBP 68-86 + 87-99-tolerized rats did not protect na?ve rats from EAE. Finally, we show that nasal administration of MBP 68-86 + 87-99 can reverse ongoing EAE induced with gp-MBP, although higher doses are required compared to the dosage needed for prevention. In conclusion, nasal administration of encephalitogenic MBP peptides can induce antigen-specific T cell tolerance and confer incomplete protection to gp-MBP-induced EAE, and MBP 68-86 and 87-99 have synergistic effects. Non-regulatory mechanisms are proposed to be responsible for tolerance development after nasal peptide administration.  相似文献   
40.
The systematic modification of the ETA selective N-(5-isoxazolyl)benzene-sulfonamide endothelin antagonists to give ETB selective antagonists is reported. The reversal in selectivity was brought about by substitution of the 4-position with aryl and substituted aryl groups. Of all the aromatic substituents studied, the para-tolyl group gave rise to the most active and selective ETB antagonist. Larger substituents caused a decrease in both ETB activity and selectivity. A similar trend was observed by substitution at the 5-position of the N-(5-isoxazolyl)-2-thiophenesulfonamide ETA receptor antagonists. The para-tolyl group was again found to be optimal for the ETB activity and selectivity. The structural features that were found to be favorable for binding to the ETB receptor, that is, the presence of a linear, conjugated pi-system of definite shape and size, have been successfully incorporated into the design of ETB selective polycyclic aromatic sulfonamides antagonists.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号