全文获取类型
收费全文 | 1266篇 |
免费 | 0篇 |
专业分类
电工技术 | 1篇 |
综合类 | 4篇 |
化学工业 | 7篇 |
金属工艺 | 2篇 |
机械仪表 | 6篇 |
建筑科学 | 2篇 |
能源动力 | 1篇 |
轻工业 | 3篇 |
水利工程 | 1篇 |
无线电 | 2篇 |
一般工业技术 | 9篇 |
冶金工业 | 1215篇 |
自动化技术 | 13篇 |
出版年
2015年 | 2篇 |
2014年 | 4篇 |
2013年 | 7篇 |
2012年 | 1篇 |
2011年 | 1篇 |
2010年 | 4篇 |
2009年 | 1篇 |
2008年 | 2篇 |
2006年 | 6篇 |
2005年 | 2篇 |
2004年 | 1篇 |
2003年 | 5篇 |
2002年 | 1篇 |
2001年 | 1篇 |
1999年 | 30篇 |
1998年 | 394篇 |
1997年 | 204篇 |
1996年 | 147篇 |
1995年 | 67篇 |
1994年 | 61篇 |
1993年 | 73篇 |
1992年 | 6篇 |
1991年 | 20篇 |
1990年 | 11篇 |
1989年 | 22篇 |
1988年 | 13篇 |
1987年 | 12篇 |
1986年 | 11篇 |
1985年 | 10篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 7篇 |
1981年 | 9篇 |
1980年 | 6篇 |
1978年 | 2篇 |
1977年 | 36篇 |
1976年 | 77篇 |
1975年 | 2篇 |
1928年 | 1篇 |
1909年 | 1篇 |
1885年 | 4篇 |
排序方式: 共有1266条查询结果,搜索用时 15 毫秒
991.
OBJECTIVES: This study examined the impact of French routine programs urging the combined measles-mumps-rubella immunization of 15-month-old children. METHODS: We applied a cohort analysis to surveillance data collected by general practitioners to estimate the cumulative incidence rate per 1000 unvaccinated children and the proportion of susceptible children, by age and for each birth cohort between 1985 and 1995. RESULTS: More than 70% of unvaccinated children born in 1985 and 1986 had measles by the age of 10. This incidence rate dramatically decreased after implementation of the routine measles-mumps-rubella immunization program in 1989, but the proportion of 5-year-olds susceptible to measles has not decreased appreciably. In 1996, more than 15% of the children born between 1990 and 1995 were susceptible. CONCLUSIONS: The measles vaccine coverage achieved by the French routine immunization program remains insufficient as regards reducing the number of susceptible children. 相似文献
992.
DL Johnson JS Wiebe SM Gold NC Andreasen RD Hichwa GL Watkins LL Boles Ponto 《Canadian Metallurgical Quarterly》1999,156(2):252-257
OBJECTIVE: To determine current practice patterns of obtaining informed consent for infertility treatment by reproductive endocrinologists and to assess changes in response to reports of an association between ovulation induction and ovarian cancer. METHODS: Board-certified reproductive endocrinologists (n = 575) were surveyed by mail regarding how they informed patients and obtained consent for infertility treatments and how their practices had been influenced by studies suggesting a link between ovulation induction and ovarian cancer. Data were analyzed using chi2 and logistic regression analyses. RESULTS: The return rate was 62.1% (357 of 575 surveys). Most respondents (92%) used discussions with physicians to inform their patients of risks and benefits of all infertility treatments. Additional means, such as audiovisual aids, were used significantly more often for assisted reproductive technologies (including intracytoplasmic sperm injection and use of donated eggs) than for less invasive therapies (31-43% versus 4-11%, P < .001). Most physicians (46-66%) used verbal consent alone for hysterosalpingogram, intrauterine insemination, and ovulation induction. Formal written consent was used significantly more often for the various assisted reproductive technologies than for hysterosalpingogram, intrauterine insemination, or ovulation induction (94-95% versus 26-44%). Although most physicians (70%) did not believe that ovulation induction increases the risk of ovarian cancer, 83% addressed this risk when obtaining consent and 47% reported changing their practices since an association was reported. Common changes included limiting length of treatment and addressing ovarian cancer risk. CONCLUSION: Current practice patterns of obtaining informed consent for various infertility treatments by board-certified reproductive endocrinologists show, as expected, that informed consent is more rigorous for assisted reproductive technologies. Although most surveyed did not believe that ovulation induction increases risk of ovarian cancer, the majority of physicians addressed that risk when obtaining consent and nearly half changed their practices on the basis of a possible association. 相似文献
993.
DJ Madden TG Turkington JM Provenzale LL Denny TC Hawk LR Gottlob RE Coleman 《Canadian Metallurgical Quarterly》1999,7(2):115-135
Adult age differences are frequently observed in the performance of memory tasks, but the changes in neural function mediating these differences are largely unknown. We used (H2)15O positron emission tomography (PET) to measure changes in regional cerebral blood flow (rCBF) during Encoding, Baseline, and Retrieval conditions of a recognition memory task. Twelve young adults (20-29 years) and 12 older adults (62-79 years) participated. During each task condition, participants made a two-choice manual response to each of 64 words. Analyses of the performance data yielded evidence of age-related slowing of encoding and retrieval processes, and an age-related decline in the accuracy of yes/no recognition (d'). The rCBF activation associated with both encoding and retrieval was greater for older adults than for young adults, but this pattern was more clearly evident for memory retrieval. For young adults, rCBF activation during retrieval occurred primarily in right prefrontal cortex, whereas older adults exhibited a more bilateral pattern of prefrontal activation. Regression analyses predicting reaction time in the memory task from regional PET counts confirmed that the neural system mediating memory retrieval is more widely distributed for older adults than for young adults. Both age groups exhibited some decrease in rCBF activation in the second half of the test session, relative to the first half. The practice-related decrease in rCBF activation was more prominent for young adults, suggesting that the older adults' recruitment of additional neural systems reflects a more continual allocation of attention to support task performance. 相似文献
994.
This study was designed to test the hypothesis that consumption of diets enriched in polyunsaturated fatty acids beginning at birth and continuing into young adulthood would lower the risk for atherosclerotic coronary heart disease early in life through their effects on plasma lipid and apolipoprotein concentrations while supporting good health and normal development. Accordingly, African green monkeys (n = 140) were raised on atherogenic diets (0.8 mg cholesterol per kcal) enriched with either saturated or n-6 polyunsaturated fatty acids. Breast milk from mothers fed the polyunsaturated fat diet became enriched in polyunsaturated fatty acids relative to the saturated group; thus, the period of nursing also reflected the dietary fatty acid shift. Age, gender, and dietary fat type independently affected plasma lipid and apolipoprotein concentrations. Age effects were similar for all lipid and lipoprotein variables; the concentrations were low immediately after birth, increased dramatically during the first 4-6 months of life, and then attained levels similar to those of adult animals by 2 years of age. Significant differences by gender were found such that females maintained lower total plasma cholesterol concentrations and higher high density lipoprotein (HDL) cholesterol and apolipoprotein (apo) A-I concentrations. Dietary fat effects were age dependent. Before weaning at 5 months of age, total plasma cholesterol and apoB concentrations were lower in animals consuming polyunsaturated fat, and this pattern was maintained into young adulthood. Lower concentrations of plasma triglycerides, HDL cholesterol, and apoA-I for polyunsaturated fat-fed animals were found only in the postweaning period (6-60 months of age). Since this pattern of response to dietary polyunsaturated fat in the juvenile animals was similar to that for adult animals fed these same diets in which there was less atherosclerosis and because subsequent studies have documented less coronary artery atherosclerosis in the polyunsaturated fat-fed juveniles, we conclude that early dietary intervention was beneficial in this group for lowering the risk of coronary artery atherosclerosis. The results in this primate model support the concept that intervention to modify coronary heart disease risk that is initiated early in childhood will have beneficial effects. 相似文献
995.
D Steinmetz M Walsh LL Gabel PT Williams 《Canadian Metallurgical Quarterly》1993,2(7):753-60; discussion 761
OBJECTIVE: To determine family physicians' perceptions of the difficulty in caring for dying patients and how prepared they are to provide such care relative to strategies used with difficulties encountered, personal need for support and development, and cooperation with other caregivers. DESIGN: Exploratory. SETTING: Physicians' offices. SUBJECTS: Thirty-five randomly selected family physicians (doctors of medicine and doctors of osteopathy) representative of family physicians practicing in Franklin County, Ohio. INTERVENTIONS: None. MAJOR OUTCOME MEASURES: A semistructured interview guide corresponding to a three-dimensional theoretical model developed prior to the study was used to determine family physicians' perceptions regarding care of dying patients and their families. The three dimensions include family physicians' involvement with dying patients and their families, their personal needs and development, and their cooperation with other caregivers. RESULTS: Participants agreed that the care of dying patients and their families is an important and special component of practicing family medicine. Generally seeing themselves as adequately prepared, they still found such care difficult and desired more education and training to increase comfort of their patients and of themselves. Their perceptions regarding the care of dying patients and their families could be categorized in terms of communication as part of the care process, family issues, legal and ethical issues, coordination of care, physicians' feelings, and physicians' influence and support. CONCLUSIONS: Family physicians require formal training in death issues and need to find a way to maximize learning through personal experiences. Discussion of cases in a support group may be beneficial. 相似文献
996.
Variances and covariances were estimated for birth weight (BWT), weaning weight (WW), yearling gain (YG), yearling weight (YW), yearling height (YH), relative growth from birth to weaning (RGW) and weaning to yearling (RGY), and mature weight (MW). Field records on 572,446 Polled Hereford cattle were analyzed. Because multiple dam weights were collected on a cow the MW used in the analysis was calculated using a nonlinear regression correction factor computed by fitting a quadratic with a plateau to the data. If the cow had an observation(s) beyond the inflection point (IP), the closest weight to that point was used. If the cow only had observation(s) before the IP the closest weight to that point was nonlinearly adjusted to the plateau. The IP for this data set was 1,506 d and the plateau was 554.7 kg. Heritabilities and genetic and environmental correlations were calculated from the appropriate (co)variances and phenotypic correlations were computed. Heritability estimates for BWT, WW, YG, YW, YH, RGW, RGY, and MW were .49, .24, .23, .30, .59, .24, .15, and .52, respectively. Genetic correlations between MW with BWT, WW, YG, YW, YH, RGW, and RGY were .64, .80, .76, .89, .73, -.29, and .35, respectively, environmental correlations were .15, .43, .05, .40, 1.03, .32, and -.10, respectively, and phenotypic correlations were .33, .32, .28, .46, .70, .00, and .07, respectively. 相似文献
997.
The copulatory behavior of sexually experienced male Japanese quail was tested using taxidermic models with varying proportions of natural and artificial features. Completely artificial models exerted little control over copulatory behavior, and whole natural body models reliably elicited copulatory behavior. In single model presentation tests, a model containing a natural head and neck with an artificial body was as effective in eliciting copulatory behavior as a whole body model, but a model containing a natural body with an artificial head and neck was largely ineffective. In choice tests, however, males clearly preferred a whole model over a natural head and neck model, and a natural body model over a completely artificial model. These data indicate male Japanese quail do attend to features of body plumage. Furthermore, test procedures can influence conclusions about effective controlling stimuli. 相似文献
998.
999.
1000.