全文获取类型
收费全文 | 5484篇 |
免费 | 107篇 |
国内免费 | 18篇 |
专业分类
电工技术 | 55篇 |
综合类 | 16篇 |
化学工业 | 674篇 |
金属工艺 | 47篇 |
机械仪表 | 66篇 |
建筑科学 | 45篇 |
矿业工程 | 3篇 |
能源动力 | 139篇 |
轻工业 | 283篇 |
水利工程 | 18篇 |
石油天然气 | 15篇 |
无线电 | 317篇 |
一般工业技术 | 601篇 |
冶金工业 | 2919篇 |
原子能技术 | 25篇 |
自动化技术 | 386篇 |
出版年
2023年 | 29篇 |
2022年 | 66篇 |
2021年 | 114篇 |
2020年 | 74篇 |
2019年 | 77篇 |
2018年 | 94篇 |
2017年 | 81篇 |
2016年 | 100篇 |
2015年 | 53篇 |
2014年 | 95篇 |
2013年 | 167篇 |
2012年 | 127篇 |
2011年 | 153篇 |
2010年 | 117篇 |
2009年 | 100篇 |
2008年 | 117篇 |
2007年 | 113篇 |
2006年 | 97篇 |
2005年 | 89篇 |
2004年 | 62篇 |
2003年 | 62篇 |
2002年 | 48篇 |
2001年 | 28篇 |
2000年 | 42篇 |
1999年 | 115篇 |
1998年 | 969篇 |
1997年 | 512篇 |
1996年 | 377篇 |
1995年 | 216篇 |
1994年 | 184篇 |
1993年 | 229篇 |
1992年 | 68篇 |
1991年 | 57篇 |
1990年 | 52篇 |
1989年 | 45篇 |
1988年 | 55篇 |
1987年 | 45篇 |
1986年 | 43篇 |
1985年 | 51篇 |
1984年 | 32篇 |
1983年 | 15篇 |
1982年 | 32篇 |
1981年 | 29篇 |
1980年 | 45篇 |
1978年 | 22篇 |
1977年 | 69篇 |
1976年 | 138篇 |
1975年 | 15篇 |
1974年 | 21篇 |
1972年 | 13篇 |
排序方式: 共有5609条查询结果,搜索用时 31 毫秒
31.
MH Thornton DB Johns JD Campeau F Hoehler GS DiZerega 《Canadian Metallurgical Quarterly》1998,13(6):1480-1485
The objective of this study was to assess the safety and to make a preliminary assessment of the efficacy of 0.5% ferric hyaluronate adhesion prevention gel in reducing adhesions in patients undergoing peritoneal cavity surgery by laparotomy, with a planned 'second-look' laparoscopy. The study was a randomized, open-label, placebo-controlled, parallel-group design in patients desirous of fertility at the Women's and Children's Hospital, Department of Obstetrics and Gynecology, University of Southern California School of Medicine, Los Angeles, California. Female patients aged 24 to 41 years received 300 ml 0.5% ferric hyaluronate adhesion prevention gel or lactated Ringer's solution as an intraperitoneal instillate at the completion of the laparotomy procedure. At second-look laparoscopy 4-12 weeks after the laparotomy, the presence of adhesions was evaluated. Haematology and serum chemistry were determined throughout the study interval. All patients tolerated the procedures well and did not manifest any serious adverse events. At second-look laparoscopy, patients treated with 0.5% ferric hyaluronate adhesion prevention gel had significantly fewer adhesions than control patients. When adhesions did form, they were significantly less extensive and less severe in patients who received 0.5% ferric hyaluronate adhesion prevention gel. In conclusion, 0.5% ferric hyaluronate adhesion prevention gel was safe and highly efficacious in the reduction of the number, severity and extent of adhesions throughout the entire abdomen following peritoneal cavity surgery. 相似文献
32.
MH Kollef 《Canadian Metallurgical Quarterly》1994,106(6):1906-1908
Two patients are described with hemorrhagic thoracic effusions who required central venous catheterization. Presumed subclavian and internal jugular vein cannulation, ipsilateral to the hemorrhagic thoracic effusions, was confirmed by the operators in each case by the persistent aspiration of blood. Subsequent clinical and radiologic evaluation revealed that the vascular catheters were introduced into the pleural space. In both individuals, the persistent aspiration of extravascular hemorrhagic fluid mimicked intravascular catheter positioning. Physicians treating patients with hemorrhagic thoracic effusions need to be aware of this potential complication that can result in the delayed resuscitation of hemodynamically unstable patients. 相似文献
33.
34.
Small-scale models of reinforced concrete beam-column joint were subjected to large cyclic displacements at two rates: 2.5×10−3 and 1.0 Hz. To assess damage, free-vibration tests were conducted. The reliability of the modelling techniques was established
by comparison of the results for the slower rate with those obtained from the full-scale tests on prototype. The higher rate
of loading caused a greater damage than that at the lower rate. This was evidenced by the measurements of the energy absorbed
in the hysteresis loops, equivalent damping, and the stiffness and damping obtained from the free-vibration test. The relatively
greater extent of damage appears to result from the different bond behaviour at different rates of loading. 相似文献
35.
Nisar Ahmad Shah Syed Zaffer Iqbal Basharat Parveen 《AEUE-International Journal of Electronics and Communications》2005,59(7):410-412
A new topology simultaneously implementing lowpass (LP) and bandpass (BP) transadmittance filtering signals using a single operational amplifier (OA), one capacitor, and two resistors is presented. The input impedance is very high which is essential for cascading without employment of buffers. The circuit uses absolute minimum number of active and passive components. The filter employs pole-model of OA and as such has acquired suitability for extended frequency operation. The circuit permits separate adjustment of natural frequency (ω0) and quality factor (Q) in an orthogonal manner. The circuit has low sensitivity figures unlike the reported single amplifier biquads. The PSPICE simulation results are included. 相似文献
36.
Shah R. Ramzan Z. Jain R. Dendukuri R. Anjum F. 《Mobile Computing, IEEE Transactions on》2004,3(4):394-408
There has been a surge of interest in the delivery of personalized information to users (e.g., personalized stocks or travel information), particularly as mobile users with limited terminal device capabilities increasingly desire updated and targeted information in real time. When the number of information recipients is large and there is sufficient commonality in their interests, as is often the case, IP multicast is an efficient way of delivering the information. However, IP multicast services do not consider the structure and semantics of the information in the multicast process. We propose the use of Content-Based Multicast (CBM) where extra content filtering is performed at the interior nodes of the IP multicast tree; this will reduce network bandwidth usage and delivery delay, as well as the computation required at the sources and sinks. We evaluate the situations in which CBM is advantageous. The benefits of CBM depend critically upon how well filters are placed at interior nodes of the IP multicast tree and the costs depend upon those introduced by filters themselves. Further, we consider the benefits of allowing the filters to be mobile so as to respond to user mobility or changes in user interests and the corresponding costs of filter mobility. The criterion that we consider is the total network bandwidth utilization. For this criterion, we develop an optimal filter placement algorithm, as well as a heuristic that executes faster than the optimal algorithm. We evaluate the algorithms by means of simulation experiments. Our results indicate that filters can be effective in substantially reducing bandwidth. We also find filter mobility is worthwhile if there is marked large-scale user mobility. We conclude with suggestions for further work. 相似文献
37.
38.
TG Orsière MM Chauvet MH Dell''Amico MJ Bourdeaux 《Canadian Metallurgical Quarterly》1995,291(3):237-243
Hepatocyte growth factor (HGF) is a potent mitogen for the maturation of hepatocytes in vitro which plays a role in liver regeneration in vivo. In addition, transforming growth factor-beta 1 (TGF-beta 1) is also a potent regulator of liver regeneration. In attempting to clarify the mechanisms related to liver regeneration after partial hepatectomy, we investigated the expression of HGF and TGF-beta 1 in rats with liver cirrhosis (LC). A rat model of LC was prepared using carbon tetrachloride (CCl4). The expression of HGF mRNA in both the LC and control groups showed a similar time-course with the highest expression seen at 18h after a 70% hepatectomy. The expression of TGF-beta 1 mRNA peaked at 18h after partial hepatectomy in the LC group and at 48h in the control group. The 5-bromo-2'-deoxyuridine (BrdU) labeling index for the LC group at 24, 48, and 72 h after partial hepatectomy was 9.2%, 5.9%, and 1.8%, while for the control group it was 7.0%, 11.7%, and 6.8%, respectively. The BrdU labeling index in the LC group was thus suppressed earlier than that in the control group. We therefore postulate that regeneration of the remnant liver in the presence of LC accelerates immediately after partial hepatectomy, but the extent of regeneration is insufficient because of an early cessation due to an early expression of TGF-beta 1. 相似文献
39.
40.
Y Sun A Hildesheim LA Brinton PC Nasca CL Trimble RJ Kurman RP Viscidi KV Shah 《Canadian Metallurgical Quarterly》1996,63(2):200-203
We describe a case of positional dyspnea due to compression of the tracheobronchial tree by an extensive thoracic aneurysm. In a 77-year-old woman with long-standing systemic hypertension, intermittent anterior chest pain gradually developed over several years. She had no history of asthma or thoracic trauma. She was admitted to our hospital because of sudden, severe shortness of breath. The breathlessness was markedly worse when she lay on her back or on her right side. On physical examination, she was in acute respiratory distress with cyanosis, severe hypertension (180/110 mmHg), tachycardia, and inspiratory stridor. A chest X-ray film showed loss of volume and nearly complete radiopacity of the left hemithorax. Arterial blood gas analysis revealed an arterial oxygen partial pressure of 54.8 mmHg, a carbon dioxide partial pressure of 39.8 mmHg, and an oxygen saturation of 84.5 percent on room air. Computed tomographic examination of the thorax showed dilation of the aortic arch and descending aorta, and marked compression of the trachea and the left main bronchus. Examination with a fiberoptic bronchoscope revealed extrinsic compression of the trachea just proximal to the carina. The patient's symptoms stabilized. However, she did not undergo surgery because of her age and because of the size of the aneurysm. She died due to rupture of the aneurysm. 相似文献