全文获取类型
收费全文 | 2282篇 |
免费 | 19篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 3篇 |
化学工业 | 114篇 |
金属工艺 | 33篇 |
机械仪表 | 14篇 |
建筑科学 | 24篇 |
矿业工程 | 2篇 |
能源动力 | 22篇 |
轻工业 | 77篇 |
水利工程 | 5篇 |
石油天然气 | 3篇 |
无线电 | 47篇 |
一般工业技术 | 130篇 |
冶金工业 | 1702篇 |
原子能技术 | 7篇 |
自动化技术 | 121篇 |
出版年
2023年 | 5篇 |
2021年 | 14篇 |
2019年 | 5篇 |
2018年 | 12篇 |
2017年 | 8篇 |
2016年 | 10篇 |
2015年 | 12篇 |
2014年 | 17篇 |
2013年 | 57篇 |
2012年 | 35篇 |
2011年 | 20篇 |
2010年 | 21篇 |
2009年 | 27篇 |
2008年 | 26篇 |
2007年 | 29篇 |
2006年 | 24篇 |
2005年 | 34篇 |
2004年 | 19篇 |
2003年 | 28篇 |
2002年 | 19篇 |
2001年 | 10篇 |
2000年 | 15篇 |
1999年 | 56篇 |
1998年 | 559篇 |
1997年 | 307篇 |
1996年 | 211篇 |
1995年 | 107篇 |
1994年 | 92篇 |
1993年 | 106篇 |
1992年 | 17篇 |
1991年 | 22篇 |
1990年 | 18篇 |
1989年 | 32篇 |
1988年 | 10篇 |
1987年 | 17篇 |
1986年 | 15篇 |
1985年 | 27篇 |
1984年 | 12篇 |
1983年 | 16篇 |
1982年 | 16篇 |
1981年 | 14篇 |
1980年 | 15篇 |
1979年 | 7篇 |
1978年 | 10篇 |
1977年 | 36篇 |
1976年 | 96篇 |
1975年 | 7篇 |
1974年 | 7篇 |
1973年 | 4篇 |
1971年 | 3篇 |
排序方式: 共有2304条查询结果,搜索用时 31 毫秒
1.
BACKGROUND & AIMS: The molecular mechanisms underlying pancreatitis are largely unknown. The goal of this study was to identify an early genetic event that correlated with pancreatitis. METHODS: Differential display of messenger RNAs (mRNAs) was conducted on normal pancreas vs. those of animals with secretagogue-induced pancreatitis. Northern blots from normal animals and animals with experimental acute pancreatitis were probed with cloned complementary DNAs for chemokines. Pancreatitis was induced with cerulein and by retrograde injection of bile salts. Immunocytochemistry was used to identify the source of chemokine expression. Pyrrolidine dithiocarbamate was tested for effects on chemokine expression and pancreatitis. RESULTS: A differentially amplified band was consistently observed early after cerulein hyperstimulation. This band was identified as a portion of the mob-1 gene, an alpha-chemokine. Northern analysis indicated that mRNAs for mob-1 and another chemokine, mcp-1, were induced after cerulein hyperstimulation in vivo. mob-1 mRNA was also induced by retrograde injection of bile salts and by cerulein in acinar cells in vitro. mob-1 protein was localized to exocrine cells in pancreata of diseased animals. Pyrrolidine dithiocarbamate inhibited both chemokine gene expression and early inflammatory characteristics of pancreatitis. CONCLUSIONS: Chemokines are induced in acinar cells by treatments that induce pancreatitis and may play an important role in the early stages of the disease. 相似文献
2.
Axillary lymphadenectomy in breast conservation surgery is associated with substantial morbidity in either seroma formation or infection. Seroma formation in the axilla requiring aspiration occurs in up to 42 per cent of patients treated without drainage. Prolonged outpatient suction drainage reduces but does not eliminate the incidence of seroma formation, while increasing cost, discomfort, and possibly infection rates. We studied the efficacy of overnight closed suction drainage in patients undergoing breast conservation surgery. Fifty consecutive patients undergoing a standard axillary dissection for breast cancer were studied. The axilla was drained with a 7-French closed suction drain. All drains were removed within 23 hours of surgery and prior to discharge from the outpatient surgical center. Patients were examined by the operating surgeon 7 to 10 days after surgery. One patient (2%) experienced a seroma postoperatively. No infections were observed in all 50 patients, and the remaining 49 patients did not experience visible or symptomatic seromas. The number of lymph nodes removed ranged between 5 and 33 with a mean of 15.5 +/- 0.6. Nine out of 50 (18%) patients had metastatic breast cancer to the axillary lymph nodes. Patients undergoing breast conservation surgery benefit from overnight closed suction drainage of the axilla. This short-term method reduces the incidence and the inherent morbidity of axillary seroma formation. 相似文献
3.
4.
5.
A.S. Fraser 《Journal of Great Lakes research》1980,6(1):83-87
An apparent decrease in total phosphorus concentrations of approximately 4.l μgP/L has been reported recently for the spring values of 1977 and 1978 in Lake Ontario. Investigation of the loading reduction for this period independent of sedimentation factors can account for only 10% of the change. The results indicate that changes in the sedimentation rate of total phosphorus during this period offer an explanation for the majority of the change in concentration. 相似文献
6.
7.
8.
A new simultaneous synthesis approach for mass exchange networks (MENs) is presented. The technique is adapted from the interval based mixed integer non-linear program (MINLP) superstructure (IBMS) synthesis of heat exchanger networks (HENs). The superstructure interval boundary compositions are defined by the supply and target compositions of either the rich or lean set of streams. Each rich and lean stream in the superstructure has the potential of exchanging mass with streams of opposite kind in each interval based on mass transfer feasibility. The model harnesses the strengths of the stagewise superstructure and the pinch technology methods for mass exchange network synthesis (MENS). The IBMS approach simultaneously trades-off the capital and operating costs for MENs. The superstructure composition interval defining approach introduced in this paper enforces the mixing of split streams at equal compositions, hence there is no need to include mixing equations in the model. Fixing the interval boundaries helps to eliminate the complexities involved in initialisations, thus the region of search for the optimum solution is reduced. The IBMS model is applied to MENS problems involving continuous contact and staged columns. It is also extended to problems involving multiple mass separating agents (MSAs) and regeneration. The results obtained compare well with those in the literature. 相似文献
9.
CD Wroe 《Canadian Metallurgical Quarterly》1997,51(7):463-465
Cardiac dysrhythmias in septic patients often reflect hypovolaemia, hypokalaemia or endocarditis as cardiac manifestation of the infection, but may be indicative for underlying cardiac pathology previously undiagnosed. We report on the case of a patient with severe peritonitis, on whom transoesophageal echocardiography (TEE) had been performed intraoperatively due to progressive circulatory instability. TEE revealed first diagnosis of asymmetric hypertrophic cardiomyopathy, which complicated the features of septic syndrome. Further perioperative treatment to support the circulation was successfully adjusted on the grounds of this diagnosis. 相似文献
10.
Discrimination of simple visual attributes can improve significantly with practice. We have trained human observers to perform peripherally presented tasks involving the localization of short line segments and examined the specificity of the learning for the visual location, orientation, and geometric arrangement of the trained stimulus. Several weeks of training resulted in dramatic threshold reductions. The learning was specific for the orientation and location of the trained stimulus, indicating the involvement of the earliest cortical stages in the visual pathway where the orientation and location of stimuli are mapped with highest resolution. Furthermore, improvement was also specific for both the configuration of the trained stimulus and the attribute of the stimulus that was under scrutiny during training. This degree of specificity suggests that the learning cannot be achieved by cortical recruitment alone, as proposed in current models, but is likely to involve a refinement of lateral interactions within the cortex and possibly a gating of lower level changes by attentional mechanisms. 相似文献