全文获取类型
收费全文 | 4043篇 |
免费 | 25篇 |
国内免费 | 12篇 |
专业分类
电工技术 | 12篇 |
综合类 | 15篇 |
化学工业 | 33篇 |
金属工艺 | 10篇 |
机械仪表 | 19篇 |
建筑科学 | 34篇 |
矿业工程 | 12篇 |
能源动力 | 5篇 |
轻工业 | 70篇 |
水利工程 | 4篇 |
石油天然气 | 6篇 |
武器工业 | 1篇 |
无线电 | 30篇 |
一般工业技术 | 35篇 |
冶金工业 | 3748篇 |
原子能技术 | 10篇 |
自动化技术 | 36篇 |
出版年
2023年 | 3篇 |
2022年 | 7篇 |
2021年 | 14篇 |
2020年 | 9篇 |
2019年 | 12篇 |
2018年 | 4篇 |
2016年 | 7篇 |
2015年 | 9篇 |
2014年 | 12篇 |
2013年 | 24篇 |
2012年 | 18篇 |
2011年 | 19篇 |
2010年 | 18篇 |
2009年 | 16篇 |
2008年 | 18篇 |
2007年 | 15篇 |
2006年 | 16篇 |
2005年 | 26篇 |
2004年 | 14篇 |
2003年 | 11篇 |
2002年 | 16篇 |
2001年 | 7篇 |
2000年 | 6篇 |
1999年 | 113篇 |
1998年 | 1224篇 |
1997年 | 707篇 |
1996年 | 413篇 |
1995年 | 251篇 |
1994年 | 195篇 |
1993年 | 211篇 |
1992年 | 41篇 |
1991年 | 25篇 |
1990年 | 46篇 |
1989年 | 37篇 |
1988年 | 51篇 |
1987年 | 39篇 |
1986年 | 41篇 |
1985年 | 38篇 |
1984年 | 3篇 |
1983年 | 6篇 |
1982年 | 16篇 |
1981年 | 22篇 |
1980年 | 25篇 |
1979年 | 3篇 |
1978年 | 12篇 |
1977年 | 85篇 |
1976年 | 149篇 |
1975年 | 12篇 |
1965年 | 2篇 |
1955年 | 4篇 |
排序方式: 共有4080条查询结果,搜索用时 140 毫秒
31.
MH Skiadopoulos S Surman JM Tatem M Paschalis SL Wu SA Udem AP Durbin PL Collins BR Murphy 《Canadian Metallurgical Quarterly》1999,73(2):1374-1381
32.
J Engle HJ Safi CC Miller MP Campbell SA Harlin GV Letsou KS Lloyd MD DB Root 《Canadian Metallurgical Quarterly》1999,29(1):150-156
PURPOSE: The relationship of the division of the diaphragm during thoracoabdominal aortic repair to prolonged ventilator support has not been studied. The purpose of this study was (1) to determine whether preservation of diaphragm integrity has a significant effect on postoperative ventilator duration and (2) to elucidate other pulmonary risk factors related to thoracoabdominal aortic surgery and to study the relationship of these factors to the intact diaphragm technique. METHODS:Between February 1991 and January 1997, we repaired 397 descending and thoracoabdominal aortic aneurysms. Descending thoracic aneurysms were not included in the study because their repair does not include the diaphragm. A total of 256 patients participated in this study. The diaphragm was divided in 150 patients and left intact in 106 patients. Examined as potential risk factors were patient demographics, history and physical findings, aneurysm extent, urgency of the procedure, acute dissection, cross-clamp time, homologous and autologous blood product consumption, and adjunctive operative techniques. FEV1 also was considered in the 197 patients for whom preoperative spirometry was available. Prolonged mechanical ventilation was defined as ventilator support for >72 hours. Data were analyzed by univariate contingency table and multiple logistic regression methods. RESULTS: Increasing age (odds ratio [OR], 1.02/y; P <.02), current smoking (OR, 2.6; P <.0008), total cross-clamp time (OR, 1.0/min; P <.008), units packed red blood cells transfused (OR, 1.06/unit; P <.008), and division of the diaphragm (OR, 2.03; P <.02) were significant, independent predictors of prolonged ventilation. Sixty-seven percent of patients (71 of 106) whose diaphragms were preserved were extubated in <72 hours compared with 52% of patients (78 of 150) who underwent diaphragm division (OR, 0.53; P <.02). CONCLUSION: Independently of well known pulmonary risk factors, an intact diaphragm during thoracoabdominal aortic repair results in a higher probability of early ventilator weaning. 相似文献
33.
SA Stranford J Skurnick D Louria D Osmond SY Chang J Sninsky G Ferrari K Weinhold C Lindquist JA Levy 《Canadian Metallurgical Quarterly》1999,96(3):1030-1035
Individuals repeatedly exposed to HIV, but who remain uninfected, form a population enriched for persons likely to have either natural or acquired resistance to the virus. We have studied four such exposed uninfected cohorts, representing 60 individuals, for evidence of protective immunity. This population included participants exposed to HIV through anal or vaginal receptive intercourse on multiple occasions over many years. We observed CD8(+)-cell noncytotoxic inhibition of HIV replication in acutely infected CD4(+) cells in the vast majority of individuals most recently exposed to the virus (within 1 year). The levels of this CD8(+)-cell response were sufficient to inhibit the in vitro infection of the exposed subjects' peripheral blood mononuclear cells. We found no evidence of a significant role for CCR5 Delta32 mutation in this population, nor did CD4(+) cell susceptibility to infection or HIV-specific cytotoxic T-lymphocytes correlate with resistance to infection in the individuals tested. Therefore, the observed strong noncytotoxic CD8(+)-cell anti-HIV responses may be an antiviral immune activity contributing to the apparent protection from infection in these exposed uninfected individuals. 相似文献
34.
分层介质动态力学性能的实验研究 总被引:1,自引:0,他引:1
采用Φ75mm分离式霍普金森压杆实验装置,对由普通混凝土与泡沫混凝土组合的分层介质的动态力学性能进行了研究。结果表明,应力波通过普通混凝土时的衰减仅为其原来峰值的5%~10%,应力波通过泡沫混凝土时其峰值衰减为原来的1/5。由此说明在含泡沫混凝土与普通混凝土的分层介质中,泡沫混凝土提供削波与延缓应力波作用时间的作用,普通混凝土则为其提供较高强度。通过对分层介质应力衰减和动量变化的分析表明,分层介质在动态力学行为上表现为较大的塑性和应变率相关性,其应力衰减主要取决于泡沫混凝土材料。 相似文献
35.
Howard W. Emmons 《Fire Technology》1965,1(3):175-181
Man's qualitative understanding of fire phenomena has enabled him to develop the fire prevention, control, and extinguishment methods in use today Quantitative understanding derived from the application of engineering science has resulted in significant improvements in many areas of technology. Would not the same approach, the author asks, benefit fire protection engineering? 相似文献
36.
Iron regulatory proteins (IRPs) control the synthesis of several proteins in iron metabolism by binding to iron-responsive elements (IREs), a hairpin structure in the untranslated region (UTR) of corresponding mRNAs. Binding of IRPs to IREs in the 5' UTR inhibits translation of ferritin heavy and light chain, erythroid aminolevulinic acid synthase, mitochondrial aconitase, and Drosophila succinate dehydrogenase b, whereas IRP binding to IREs in the 3' UTR of transferrin receptor mRNA prolongs mRNA half-life. To identify new targets of IRPs, we devised a method to enrich IRE-containing mRNAs by using recombinant IRP-1 as an affinity matrix. A cDNA library established from enriched mRNA was screened by an RNA-protein band shift assay. This revealed a novel IRE-like sequence in the 3' UTR of a liver-specific mouse mRNA. The newly identified cDNA codes for a protein with high homology to plant glycolate oxidase (GOX). Recombinant protein expressed in bacteria displayed enzymatic GOX activity. Therefore, this cDNA represents the first vertebrate GOX homologue. The IRE-like sequence in mouse GOX exhibited strong binding to IRPs at room temperature. However, it differs from functional IREs by a mismatch in the middle of its upper stem and did not confer iron-dependent regulation in cells. 相似文献
37.
一、引言在研究链式反应系统的各种性质时,常常用到具有类似裂变中子能谱的中子源。模拟裂变中子源主要由~(210)Po的α粒子轰击F,Be,Li,B等轻元素产生中子,随着靶元素成份以及结构的差异,中子能谱也不完全相同。应本院同位素处的要求,我们测量了一模拟裂变中子源的能谱,其源强约10~4n/s,靶成份为天然Li 24.16%,F66.14%,B 9.4%, 相似文献
38.
39.
40.