全文获取类型
收费全文 | 2774篇 |
免费 | 4篇 |
专业分类
化学工业 | 89篇 |
金属工艺 | 28篇 |
机械仪表 | 19篇 |
建筑科学 | 15篇 |
能源动力 | 9篇 |
轻工业 | 18篇 |
水利工程 | 6篇 |
无线电 | 9篇 |
一般工业技术 | 64篇 |
冶金工业 | 2496篇 |
原子能技术 | 1篇 |
自动化技术 | 24篇 |
出版年
2022年 | 3篇 |
2021年 | 3篇 |
2019年 | 4篇 |
2018年 | 7篇 |
2017年 | 5篇 |
2016年 | 3篇 |
2015年 | 5篇 |
2014年 | 20篇 |
2013年 | 22篇 |
2012年 | 6篇 |
2011年 | 32篇 |
2010年 | 36篇 |
2009年 | 7篇 |
2008年 | 8篇 |
2007年 | 9篇 |
2006年 | 11篇 |
2005年 | 11篇 |
2004年 | 6篇 |
2003年 | 5篇 |
2002年 | 6篇 |
2001年 | 4篇 |
2000年 | 6篇 |
1999年 | 65篇 |
1998年 | 713篇 |
1997年 | 387篇 |
1996年 | 266篇 |
1995年 | 148篇 |
1994年 | 123篇 |
1993年 | 165篇 |
1992年 | 36篇 |
1991年 | 26篇 |
1990年 | 34篇 |
1989年 | 36篇 |
1988年 | 39篇 |
1987年 | 40篇 |
1986年 | 36篇 |
1985年 | 49篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 19篇 |
1981年 | 19篇 |
1980年 | 35篇 |
1979年 | 6篇 |
1978年 | 15篇 |
1977年 | 75篇 |
1976年 | 200篇 |
1975年 | 7篇 |
1964年 | 2篇 |
1961年 | 1篇 |
1955年 | 2篇 |
排序方式: 共有2778条查询结果,搜索用时 9 毫秒
141.
BACKGROUND: Arteriovenous malformations (AVMs) are an abnormal communication between arterial and venous structures. Pelvic AVMs have been infrequently described in the literature and represent an uncommon cause of a palpable pelvic mass. CASE: A case of pelvic AVM with ureteral obstruction occurred. The location and radiologic appearance of the AVM suggested a complex adnexal mass. During exploration and resection of the mass, significant bleeding was encountered. The diagnosis of AVM was made only retrospectively, with histologic examination of the specimen. CONCLUSION: AVMs are an uncommon and unique cause of pelvic pathology. Preoperative diagnosis will alert the surgeon as to the technically difficult resection that may be encountered and to the massive bleeding that can be associated with their removal. 相似文献
142.
143.
We have developed a flexible physiological monitoring and analysis system for physiological studies in which data are obtained over extended periods. Our system uses low-cost personal computer hardware to concentrate data from existing multiple monitoring devices. All monitored parameters are displayed on a single screen and recorded in a single file. The system automates the process of physiological record keeping by providing continuous displays of vital signs. In addition, audible and visual alarms are produced when vital signs are outside of acceptable ranges, prompting the experimenter to take corrective actions. The central element of the system is a program running in a dedicated manner on an IBM PC-compatible computer. The program is written in the C language and makes use of a graphics library to display traces and analysis results in real time on any standard display for the PC. This program assigns the analog channels of an A/D board to particular physiological parameters by initially reading a configuration file, which also describes the alarm conditions and analysis routine for each parameter. All hardware specific code is isolated into well-defined modules. The program is both highly flexible with regard to different sets of parameters and highly portable for different experimental and computer environments. 相似文献
144.
RS Bagley TV Baszler ML Harrington GE Pluhar MP Moore RD Keegan SA Greene 《Canadian Metallurgical Quarterly》1995,24(2):122-127
Longitudinal division of the corpus callosum was performed in six normal beagles to determine surgical morbidity. The corpus callosum was divided sagittally on the midline and the effect on neurological function was determined. Five of six dogs were clinically normal within 14 days or less after surgery. One dog had persistent but improving clinical signs consistent with a forebrain disturbance at 30 days after surgery. Overall, minimal morbidity and no mortality was associated with this surgical procedure. Further study is indicated to determine the efficacy of this surgical treatment for seizure control in dogs with idiopathic epilepsy. 相似文献
145.
In the presence of interferon-gamma (IFN-gamma), human tumor necrosis factor-alpha (Hu-TNF-alpha), which binds to murine TNF-alpha receptor type 1 (TNF-R1) but not to murine TNF-R2, was effective in inducing nitric oxide (NO) production in spleen-derived macrophages (M phi), albeit at concentrations 12.5-fold greater than those required by murine TNF-alpha (Mu-TNF-alpha), to achieve the same result. Addition of anti-TNF-R1 completely inhibited the Mu-TNF-alpha-mediated induction of NO, demonstrating that TNF-R1 is critical to the IFN-gamma-dependent TNF-alpha-mediated induction of M phi effector function. However, treatment with anti-TNF-R2 resulted in a partial inhibition of M phi activation. Spleen-derived M phi were more dependent on TNF-R2 than RAW 264.7 or peritoneal M phi based on their responsiveness to Hu-TNF-alpha. Priming of spleen-derived M phi with either IFN-gamma or granulocyte-macrophage colony-stimulating factor (GM-CSF) heightened the maximal responses to both TNF-alpha species and increased the overall effectiveness of Hu-TNF-alpha without increasing expression of either TNF-alpha receptor. The dependence of spleen-derived M phi on both TNF-alpha receptors for signaling the induction of effector function supports an active signaling role for TNF-R2 in its synergy with TNF-R1 rather than a passive ligand passing role. 相似文献
146.
This case describes ventricular proarrhythmia as a result of a synchronized internal atrial defibrillation shock in a 29-year-old man with Ebstein's anomaly referred for radiofrequency ablation of a right posterior accessory pathway. During the electrophysiologic study, atrial fibrillation was induced and 3/3 msec shocks of various strengths were delivered between two decapolar defibrillation catheters in the coronary sinus and right atrial appendage. A 2.0-J biphasic shock synchronized to an R wave after a short-long-short ventricular cycle length pattern with a preshock coupling interval of 245 msec induced ventricular fibrillation, which was externally defibrillated with 200 J. This observation has implications for the development of implantable atrial defibrillators. 相似文献
147.
148.
RD Kortschak H Reimann M Zimmer HJ Eyre R Saint DE Jenne 《Canadian Metallurgical Quarterly》1998,51(2):288-292
A 2-year trial was conducted to evaluate the cost-effectiveness of heliotherapy for psoriasis. The course and cost of psoriasis of 46 Finnish patients were first closely monitored for 1 year, then the patients received a 4-week supervised heliotherapy treatment in the Canary Islands, Spain, after which they continued to be followed for another year. Heliotherapy dramatically reduced the severity of psoriasis and also seemed to have favourable long-term effects on psoriasis. The mean direct cost of the 4-week heliotherapy for one patient was FIM12,289 (1 Pound = FIM7.0 in 1989). The cost of flights and half-board in Spain formed nearly 60% (FIM7033) of the total cost. In the year preceding heliotherapy, the mean direct annual cost of antipsoriasis therapy was FIM7335 and in the year after FIM5700, a reduction of 22% in annual costs; this change was not statistically significant because there were large variations in costs among patients. The costs of heliotherapy exceeded manyfold the mean monthly cost of conventional psoriasis therapy. There were no overall savings using heliotherapy in those patients suffering mainly from moderately severe psoriasis. Heliotherapy saved costs only in those patients with severe psoriasis that required expensive medication or ward treatment. Although heliotherapy cannot be regarded as an economical treatment for the average patients with psoriasis, it clears psoriasis effectively and is preferred by patients. Thus, heliotherapy constitutes an alternative for patients suffering severe psoriasis. 相似文献
149.
It has been suggested that adenosine cardioprotection occurs via adenosine A1 receptor-mediated activation of protein kinase C (PKC). However, adenosine has well-known vasodilatory effects in the myocardium, whereas PKC is a vasoconstrictor. This study examined whether adenosine A1 receptor activation alters the effects of the PKC activator. 1,2-dioctanoyl-s,n-glycerol (DOG) in isolated perfused rat hearts (left-ventricular developed pressure) and rat ventricular myocytes ([Ca2+]i and cell shortening). Exposure to DOG decreased left-ventricular developed pressure by 30%, an effect that was completely reversible. Pretreatment of isolated hearts with either the PKC inhibitor chelerythrine or the adenosine A1 agonist 2-chloro-N6-cyclo-cyclo-isolated pentlyadenosine (CCPA) attenuated the negative inotropic effects of DOG. In the isolated myocytes, DOG decreased [Ca2+]i and cell shortening by 25 and 28%, respectively, effects that were attenuated by both chelerythrine and CCPA. The CCPA attenuation of the DOG-induced decrease in [Ca2+]i and cell shortening was blocked by pretreating the myocytes with the adenosine A1 antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX). These results indicate that in rat ventricular myocardium, adenosine A1 receptor activation attenuates the apparent PKC-dependent negative inotropic effects of DOG via preservation of [Ca2+]i levels. 相似文献
150.
CT Baker FG Salituro JJ Court DD Deininger EE Kim B Li PM Novak BG Rao S Pazhanisamy WC Schairer RD Tung 《Canadian Metallurgical Quarterly》1998,8(24):3631-3636
A combination of structure-based design and both solution, and solid-phase synthesis were utilized to derive a potent (nM) series of HIV-1 protease inhibitors bearing a structurally novel backbone. Detailed structural analysis of several inhibitors prepared in this series has suggested that rigidification of the P1/P2 region of this class of molecules may result in compounds with improved potency. 相似文献