全文获取类型
收费全文 | 2833篇 |
免费 | 12篇 |
专业分类
电工技术 | 11篇 |
化学工业 | 52篇 |
金属工艺 | 8篇 |
机械仪表 | 3篇 |
建筑科学 | 12篇 |
能源动力 | 12篇 |
轻工业 | 87篇 |
水利工程 | 4篇 |
无线电 | 94篇 |
一般工业技术 | 83篇 |
冶金工业 | 2406篇 |
原子能技术 | 14篇 |
自动化技术 | 59篇 |
出版年
2022年 | 5篇 |
2021年 | 5篇 |
2020年 | 4篇 |
2019年 | 8篇 |
2018年 | 7篇 |
2017年 | 5篇 |
2016年 | 6篇 |
2014年 | 11篇 |
2013年 | 20篇 |
2012年 | 22篇 |
2011年 | 20篇 |
2010年 | 12篇 |
2009年 | 22篇 |
2008年 | 26篇 |
2007年 | 27篇 |
2006年 | 17篇 |
2005年 | 21篇 |
2004年 | 10篇 |
2003年 | 16篇 |
2002年 | 15篇 |
2001年 | 21篇 |
2000年 | 9篇 |
1999年 | 86篇 |
1998年 | 771篇 |
1997年 | 467篇 |
1996年 | 269篇 |
1995年 | 139篇 |
1994年 | 106篇 |
1993年 | 132篇 |
1992年 | 23篇 |
1991年 | 28篇 |
1990年 | 26篇 |
1989年 | 36篇 |
1988年 | 39篇 |
1987年 | 24篇 |
1986年 | 26篇 |
1985年 | 20篇 |
1984年 | 7篇 |
1983年 | 7篇 |
1982年 | 16篇 |
1981年 | 9篇 |
1980年 | 22篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 70篇 |
1976年 | 158篇 |
1975年 | 13篇 |
1974年 | 7篇 |
1973年 | 6篇 |
1955年 | 3篇 |
排序方式: 共有2845条查询结果,搜索用时 0 毫秒
91.
92.
93.
W Martínez-López EM Boccardo GA Folle V Porro G Obe 《Canadian Metallurgical Quarterly》1998,150(5):585-592
BACKGROUND: We recently demonstrated that arachidonic:linoleic acid ratio of erythrocytes of essential hypertension patients is greater than normal. OBJECTIVE: To investigate fatty acid composition, capability for adhesion to biological substrate and expression of beta2 integrins of leucocytes obtained from peripheral blood and skin window exudate of essential hypertension patients. DESIGN: Neutrophil activation state was evaluated by reproducing the various conditions occurring in vivo during the life of the cell (i.e. under the 'resting' condition, such as in peripheral blood, and 'primed' condition, such as after transmigration through the endothelium and after administration of specific chemo-attractants). Because both peripheral blood and skin window leucocytes of the subjects were obtained on the same day, we could be sure that there had been no dietary influences on changes in levels of fatty acid. Thus, the observed changes should reliably reflect the metabolic rate of utilization of fatty acids coupled to the activation and migration of cells. RESULTS: Leucocytes from essential hypertension patients were richer in arachidonic acid than were the corresponding cells from normotensive subjects; this difference was also evident for functionally activated skin window leucocytes, in spite of there having been a greater loss of poly-unsaturated fatty acids and arachidonic acid after migration. Moreover, a greater than normal arachidonic acid:linoleic acid ratio was shown for the first time to apply for leucocytes of essential hypertension patients, so extending our previous findings on the erythrocytes. Leucocytes from essential hypertension patients, collected both from peripheral blood and from skin window exudate, proved far more adhesive than the corresponding cells from age-matched and sex-matched controls, but this was not associated with a quantitative hyperexpression of beta2 integrins. CONCLUSIONS: The results suggest that an increase in availability of arachidonic acid in leucocytes could be a further expression of the generalized disturbance of fatty acid levels associated with essential hypertension and that a condition of hyperadhesion of neutrophils could occur spontaneously in vivo during the course of hypertension. 相似文献
94.
RD Evans EM Addison JY Villeneuve KS MacDonald DG Joachim 《Canadian Metallurgical Quarterly》1998,213(1-3):239-245
Hair samples were collected from otter (Lutra canadensis) trapped in several parts of south-central Ontario, Canada. The concentrations of total Hg in hair were compared with methyl mercury concentrations in liver tissues from the same individuals to determine if hair is a suitable monitoring tissue. Hg in the two tissues was significantly correlated. Hair was used to monitor Hg in 51 individuals from four townships. The concentrations of total Hg in hair ranged from 4 to 20 micrograms/g. No significant variation among the four sample regions existed. Generally the highest concentrations were found in the youngest members of the population. Some possible explanations for the observations are presented. 相似文献
95.
S Pursiheimo E Rintam?ki E Baena-Gonzalez EM Aro 《Canadian Metallurgical Quarterly》1998,423(2):178-182
A 32-year-old, previously healthy woman with a diffuse, complex tumoral process is described. While she was being evaluated for primary infertility, a laparoscopic procedure revealed a disseminated peritoneal process associated with bilateral ovarian lesions. A clinical diagnosis of stage III ovarian cancer was made and total hysterectomy, bilateral salpingo-oophorectomy, and omentectomy were performed. Pathologic studies showed an admixture of leiomyomatosis peritonealis disseminata (LPD) endometriosis, and an extensive multicystic mesothelial proliferation. Although endometriosis is known to occur in conjunction with either LPD or multicystic mesothelioma, to our knowledge this is the first report of all three lesions occurring simultaneously. 相似文献
96.
Retroperitoneoscope was introduced through the 11 and 10 intercostal space by linea axillaris media and anterior Differences of the accesses between each other and between those in lumbocostal angle are statistically significant. The access to 11 intercostal space was proved to be the most convenient one for the examination of the entire kidney surface, while the one to 10 intercostal space-for the endoscopy of adrenals and caudal region of the pancreas. The caput of the pancreas may be examined both through 11 intercostal space and lumbocostal angle. Clinical observations of 129 patients, operated by means of retroperitoneoscope through 11 intercostal space confirmed the effectivity of the method. Positive effects of retroperitoneoscopy_-minimal traumatization of tissues, normal postoperative period and good cosmetic effect make it suitable for wide introduction into the surgical practice. 相似文献
97.
98.
Characterization of a Schwann cell neurite-promoting activity that directs motoneuron axon outgrowth
The aim of the study described here was to correlate coronary artery (CA) stenosis pressure gradients calculated by quantitative coronary arteriography (QCA) to invasively measured transstenotic pressure drops in patients with anginal symptoms and with known or suspected coronary artery disease. Furthermore, the known mathematical models are improved by introducing (1) pressure catheter-corrected minimal stenosis area, (2) modification of flow assumptions, and (3) stenosis exit angle. Included in the study were 45 patients with 61 stenoses. The visually estimated CA lesion severity in these non-complex stenoses was in the equivocal range of 40-70%. All measurements were performed after intracoronary administration of nifedipine and nitroglycerin. Stenosis dimensions were assessed from magnified cinefilms, using hand-held calipers. Highly significant overall correlation was found between measured and calculated pressure gradients with correction for the impact of the intracoronary catheter (P < 0.00001, r = 0.84). In particular, a substantial number of stenoses with haemodynamically-insignificant pressure gradients were identified by hydrodynamic calculations. In conclusion, the great majority of the coronary artery stenoses could be classified reliably by QCA as being haemodynamically insignificant or significant, respectively. 相似文献
99.
RN Clayton M Boggild AS Bates J Bicknell D Simpson W Farrell 《Canadian Metallurgical Quarterly》1997,47(4-6):185-193
Abnormal cell proliferation is controlled by opposing actions of oncogene products (stimulatory) and tumour suppressor gene (TSG) products (inhibitory). The former are dominantly acting, i.e. only one copy needed for tumorigenesis, whilst for TSG both copies of the gene must be inactivated so these are recessive at a cellular level. For anterior pituitary tumours only one oncogene (Gsp) has been identified in a variable proportion (4-40%) of a single tumour subtype (somatotrophinomas). Contrariwise, allelic deletion studies, using a PCR-based microsatellite polymorphism analysis of DNA extracted from archival specimens, have shown significant loss of heterozygosity in 20-40% of all tumour subtypes at the locus of the putative MEN-1 gene (chr. 11q13); the retinoblastoma gene (chr. 13q 12-14), and 10q26. Moreover, these DNA microdeletions were concentrated in radiologically invasive tumours compared to noninvasive tumours (modified Hardy gdes 3 and 4 vs. 1 + 2). In addition, 50% of Cushing's adenomas showed presence of p53 immunopositivity, though no point mutations in exons 4-9 were found, by SSCP analysis, to account for this. These studies show that analysis of TSGs in pituitary adenomas may provide clues to their pathogenesis, and more importantly relate to clinical behaviour of the tumour, and hence aid decisions regarding management. 相似文献
100.
EH Thall NN Stone DL Cheng EL Cohen EM Fine I Leventhal RA Aldoroty 《Canadian Metallurgical Quarterly》1996,77(4):512-517
This study examines whether, while controlling for local economic conditions, job design and other organizational factors affect facility aide turnover rates in a sample of 250 nursing homes from 10 states. Facility characteristics were largely based on administrator and director of nursing interviews conducted in 1993 as part of the Health Care Financing Administration's evaluation of the Resident Assessment Instrument (RAI) implementation. Aide turnover was significantly reduced by involvement in interdisciplinary care plan meetings. Turnover rates were higher in for-profit homes. Aide involvement in assessments, aide training and workload, case mix severity, payor source mix, and facility size were not significantly related to aide turnover. 相似文献