全文获取类型
收费全文 | 1684篇 |
免费 | 22篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 6篇 |
综合类 | 3篇 |
化学工业 | 57篇 |
金属工艺 | 11篇 |
机械仪表 | 20篇 |
建筑科学 | 25篇 |
矿业工程 | 3篇 |
能源动力 | 17篇 |
轻工业 | 26篇 |
水利工程 | 2篇 |
无线电 | 66篇 |
一般工业技术 | 73篇 |
冶金工业 | 1279篇 |
原子能技术 | 3篇 |
自动化技术 | 117篇 |
出版年
2023年 | 6篇 |
2021年 | 7篇 |
2020年 | 6篇 |
2019年 | 8篇 |
2018年 | 6篇 |
2017年 | 7篇 |
2016年 | 10篇 |
2015年 | 9篇 |
2014年 | 11篇 |
2013年 | 51篇 |
2012年 | 19篇 |
2011年 | 27篇 |
2010年 | 13篇 |
2009年 | 16篇 |
2008年 | 19篇 |
2007年 | 24篇 |
2006年 | 16篇 |
2005年 | 12篇 |
2004年 | 16篇 |
2003年 | 15篇 |
2002年 | 14篇 |
2001年 | 6篇 |
2000年 | 11篇 |
1999年 | 44篇 |
1998年 | 376篇 |
1997年 | 205篇 |
1996年 | 159篇 |
1995年 | 77篇 |
1994年 | 68篇 |
1993年 | 81篇 |
1992年 | 18篇 |
1991年 | 18篇 |
1990年 | 29篇 |
1989年 | 29篇 |
1988年 | 32篇 |
1987年 | 23篇 |
1986年 | 25篇 |
1985年 | 15篇 |
1984年 | 7篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 13篇 |
1980年 | 14篇 |
1977年 | 38篇 |
1976年 | 68篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1966年 | 3篇 |
1948年 | 3篇 |
排序方式: 共有1708条查询结果,搜索用时 285 毫秒
1.
Marco Bocchetti Maria Grazia Ferraro Filippo Ricciardiello Alessandro Ottaiano Amalia Luce Alessia Maria Cossu Marianna Scrima Wing-Yan Leung Marianna Abate Paola Stiuso Michele Caraglia Silvia Zappavigna Tung On Yau 《International journal of molecular sciences》2021,22(8)
Colorectal cancer (CRC) is the third most deadly cancer worldwide, and inflammatory bowel disease (IBD) is one of the critical factors in CRC carcinogenesis. IBD is responsible for an unphysiological and sustained chronic inflammation environment favoring the transformation. MicroRNAs (miRNAs) belong to a class of highly conserved short single-stranded segments (18–25 nucleotides) non-coding RNA and have been extensively discussed in both CRC and IBD. However, the role of miRNAs in the development of colitis-associated CRC (CAC) is less clear. The aim of this review is to summarize the major upregulated (miR-18a, miR-19a, miR-21, miR-31, miR-155 and miR-214) and downregulated (miR-124, miR-193a-3p and miR-139-5p) miRNAs in CAC, and their roles in genes’ expression modulation in chronic colonic-inflammation-induced carcinogenesis, including programmed cell-death pathways. These miRNAs dysregulation could be applied for early CAC diagnosis, to predict therapy efficacy and for precision treatment. 相似文献
2.
Multifilament Ag-sheathed BiPbSrCaCuO (2223) superconducting tapes containing 49 filaments were fabricated by the powder-in-tube route and the roll-anneal process. The transport critical current densityJ
c
was 1.3×104 A cm–2 at 77 K and 7×104 A cm–2 at 4.2 K in self-field. A 12-m-long tape was used to construct superconducting solenoids (50, 28, and 14 mm internal diameters) generating dc fields 380–1070 G at 4.2 K. Measurements of the variation ofJ
c
with field (0–1.6 T) and bend strain (0–5%) are used to explain the performance of the solenoids. The critical bend strain of tapes was about 1.5%. 相似文献
3.
DC Reynolds CE Leak KK Bajaj CE Stutz RL Jones KR Evans PW Yu WM Theis 《Canadian Metallurgical Quarterly》1989,40(9):6210-6217
4.
5.
6.
7.
PJ Jenkins MA Satta M Simmgen WM Drake C Williamson DG Lowe K Britton SL Chew RV Thakker GM Besser 《Canadian Metallurgical Quarterly》1997,47(6):747-751
We report a patient with a metastatic parathyroid carcinoma and medullary carcinoma of the thyroid. This patient represents a variation of the multiple endocrine neoplasia syndrome (MEN) type 2A. There was no evidence of a phaeochromocytoma. The case illustrates the difficulties that may be encountered in localising the source of PTH secretion; the patient underwent four unsuccessful exploratory operations of the neck and mediastinum before further investigations revealed a single metastatic deposit of parathyroid carcinoma involving the first thoracic vertebra. PCR amplification and sequencing of the RET oncogene from the metastatic parathyroid carcinoma and genomic DNA revealed a heterozygous mutation (Cys634Tyr) in exon 11, as has previously been described to occur in MEN 2A. In addition, loss of tumour heterozygosity was demonstrated at loci from chromosomes 1, 2, 3p, 13q and 16p. This represents the first report of a parathyroid carcinoma in a MEN2A patient, in which the multiple allelic deletions are consistent with the generalised losses observed in aggressive tumours. 相似文献
8.
Cholesterol 7 alpha-hydroxylase, the rate-limiting enzyme in the bile acid biosynthetic pathway, is thought to be regulated by hydrophobic bile acids through negative feedback control. The role of cholesterol in the regulation of cholesterol 7 alpha-hydroxylase is more controversial, in part because of incomplete understanding of the relationship between the pathways of cholesterol synthesis and degradation. The main objective of this study was to define the interaction between these two pathways in an experimental model in which the supply of newly synthesized cholesterol was interrupted by sustained infusion of mevinolin (lovastatin), an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase) or accelerated by a continuous infusion of mevalonate, a cholesterol precursor. The study was carried out in rats subjected to short-term bile fistula. In one set of experiments, rats were treated postoperatively with mevinolin (5 mg/kg loading dose followed by 2 mg/kg/hr infusion), mevalonate (180 mumol/hr infusion) or both for up to 96 hr. In a separate set of experiments, rats were infused intraduodenally with taurocholate (36 mumol/100 gm/hr for up to 96 hr). We determined cholesterol 7 alpha-hydroxylase- and HMG-CoA reductase specific activities at those time intervals, whereas bile acid synthesis rates were determined throughout the study. Compared with rats not subjected to surgery, rats with short-term biliary diversion had increases in cholesterol 7 alpha-hydroxylase activity of 259% and 827% at 48 and 96 hr, respectively. The increase in bile acid biosynthesis was less pronounced. Continuous infusion of mevinolin completely prevented increases in cholesterol 7 alpha-hydroxylase specific activity and bile acid biosynthesis at both time intervals.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
9.
10.
BACKGROUND: Previous studies have documented greater use of health services by depressed persons and have postulated that health care costs could be reduced overall through better recognition and treatment of depression. OBJECTIVE: To determine whether a greater burden of medical illness contributes to excess charges for diagnostic tests among older adults with symptoms of depression. DESIGN: Prospective cohort study. SETTING: A primary care group practice at an academic institution. PATIENTS: 3767 patients 60 years of age and older who completed testing on the Centers for Epidemiologic Studies Depression Scale (CES-D) during routine office visits. MEASUREMENTS: Charges for all inpatient and ambulatory diagnostic testing for 2 years, including clinical pathology, diagnostic imaging, and special procedures; number of visits to the ambulatory care center or emergency department; and number of hospitalizations. The Ambulatory Care Group case-mix approach, which is based on ambulatory diagnoses, was used as a measure of health status and expected resource consumption. RESULTS: Patients with symptoms of depression (CES-D scores > or = 16) were significantly younger (66.6 compared with 68.1 years; P < 0.001), more likely to be white (50.5% compared with 33.9%; P = 0.001), and more likely to be female (75.8% compared with 67.6%; P = 0.001) than were those without these symptoms (CES-D scores < 16). They also had more nonpsychiatric comorbid conditions, had more visits to the ambulatory care center (9.2 compared with 7.8; P < 0.001), were more likely to use the emergency department (52.3% compared with 40%; P = 0.001), were more likely to be hospitalized (22.4% compared with 17%; P = 0.002), and had greater median total diagnostic test charges for a period of 1 year ($583 compared with $387; P < 0.001). The difference in charges, most of which were clinical pathology charges (54.2%), persisted into the second year. Ambulatory Care Group assignment was independently associated with diagnostic test charges. The CES-D summary score was not independently associated with diagnostic test charges when controlling for Ambulatory Care Group assignment. CONCLUSIONS: Patients with symptoms of depression accrue greater average diagnostic test charges. However, these data suggest that such patients also have a greater burden of comorbid nonpsychiatric illness. Efforts to improve outcome and decrease cost for patients who have late-life depression must target interventions to improve the care of psychiatric and medical illness concurrently. 相似文献