全文获取类型
收费全文 | 327179篇 |
免费 | 5186篇 |
国内免费 | 1194篇 |
专业分类
电工技术 | 5382篇 |
综合类 | 2671篇 |
化学工业 | 47552篇 |
金属工艺 | 13201篇 |
机械仪表 | 9406篇 |
建筑科学 | 7561篇 |
矿业工程 | 1469篇 |
能源动力 | 7166篇 |
轻工业 | 25703篇 |
水利工程 | 3263篇 |
石油天然气 | 3420篇 |
武器工业 | 19篇 |
无线电 | 38672篇 |
一般工业技术 | 60693篇 |
冶金工业 | 57795篇 |
原子能技术 | 4106篇 |
自动化技术 | 45480篇 |
出版年
2022年 | 1571篇 |
2021年 | 2572篇 |
2020年 | 1853篇 |
2019年 | 2230篇 |
2018年 | 17437篇 |
2017年 | 16294篇 |
2016年 | 13288篇 |
2015年 | 3388篇 |
2014年 | 4514篇 |
2013年 | 11273篇 |
2012年 | 9918篇 |
2011年 | 17884篇 |
2010年 | 15083篇 |
2009年 | 13253篇 |
2008年 | 14793篇 |
2007年 | 15570篇 |
2006年 | 7287篇 |
2005年 | 7756篇 |
2004年 | 7405篇 |
2003年 | 7182篇 |
2002年 | 6282篇 |
2001年 | 6041篇 |
2000年 | 5688篇 |
1999年 | 6260篇 |
1998年 | 18843篇 |
1997年 | 12300篇 |
1996年 | 9408篇 |
1995年 | 6635篇 |
1994年 | 5748篇 |
1993年 | 5693篇 |
1992年 | 3662篇 |
1991年 | 3547篇 |
1990年 | 3426篇 |
1989年 | 3289篇 |
1988年 | 3014篇 |
1987年 | 2445篇 |
1986年 | 2492篇 |
1985年 | 2906篇 |
1984年 | 2543篇 |
1983年 | 2263篇 |
1982年 | 2064篇 |
1981年 | 2255篇 |
1980年 | 2003篇 |
1979年 | 1801篇 |
1978年 | 1777篇 |
1977年 | 2312篇 |
1976年 | 3337篇 |
1975年 | 1535篇 |
1974年 | 1461篇 |
1973年 | 1454篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
J Sánchez A Torres J Serrano J Román C Martín L Pérula F Martínez P Gómez 《Canadian Metallurgical Quarterly》1997,20(5):403-408
BACKGROUND: Locally advanced thyroid cancer invading the tracheal cartilage represents a difficult treatment dilemma during thyroidectomy. METHODS: A retrospective chart review was performed to determine the results of laryngotracheal resection or tracheal cartilage shave with adjuvant radiotherapy in patients with locally advanced thyroid cancer invading the upper airway. RESULTS: Of 597 patients undergoing thyroidectomy for thyroid cancer, 40 were found to have laryngotracheal invasion. Thirty-five patients with superficial invasion underwent cartilage shave procedures with adjuvant radiotherapy; five with full-thickness invasion underwent radical resection, including tracheal sleeve resection (n = 3) or total laryngectomy (n = 2). Histologic subtypes included papillary (n = 32), follicular (n = 2), Hurthle cell (n = 1), medullary (n = 3), and anaplastic (n = 2). Of the cartilage shave group, 25 are currently alive with no evidence of disease at a mean follow-up of 81 months (range 1-290). Six developed isolated local/regional recurrence and were managed with total laryngectomy (n = 1), tracheal resection (n = 1), cervical lymphadenectomy (n = 1), or repeat radiotherapy (n = 3). All six patients remain free of disease at a mean follow-up of 5 years. Of those who underwent initial laryngotracheal resection, four remain free of disease at a mean follow-up of 5 years. The rates of 10-year disease-free survival and overall survival for all patients were 47.9% (95% confidence interval [CI] 24.8, 71.0) and 83.9% (95% CI 70.3, 97.5), respectively. CONCLUSIONS: These data suggest that adequate management of thyroid cancer with laryngotracheal invasion can be achieved with a more conservative surgical approach and adjuvant radiotherapy, reserving more radical resections for extensive primary lesions or locally recurrent disease. 相似文献
992.
For the original article see ibid., vol. 33, p. 1748-49 (1997). This comment relates to the aforementioned Letter which presents a floating inductance simulation circuit. The proposed circuit uses four plus-type second-generation current-conveyors (CCII+), two floating resistors and one grounded capacitor. It is shown here that such a realisation is a special case of three already published circuits for floating inductance realisation 相似文献
993.
In Saccharomyces cerevisiae, alpha-factor is internalized by receptor-mediated endocytosis and transported via vesicular intermediates to the vacuole where the pheromone is degraded. Using beta-tubulin and actin mutant strains, we showed that actin plays a direct role in receptor-mediated internalization of alpha-factor, but is not necessary for transport from the endocytic intermediates to the vacuole. beta-tubulin mutant strains showed no defect in these processes. In addition, cells lacking the actin-binding protein, Sac6p, which is the yeast fimbrin homologue, are defective for internalization of alpha-factor suggesting that actin filament bundling might be required for this step. The actin dependence of endocytosis shows some interesting similarities to endocytosis from the apical membrane in polarized mammalian cells. 相似文献
994.
Under serum-free conditions the beta-glucan receptor of mouse macrophages mediates phagocytosis of beta-1,3-D-glucan-coated microbeads (diameter 2 microns). IFN-gamma increases the phagocytic function of the beta-glucan receptor in a dose-dependent manner, giving the plateau level at 100 U/ml. Maximum activity appears 9 h after addition of IFN-gamma to the cells. The effect disappears within 24 h. The effect of IFN-gamma may be a result of augmented receptor synthesis since treatment with cycloheximide reduces the phagocytosis. IL-1 also increases the phagocytic function of the beta-glucan receptor giving a dose-dependent response and with the plateau level reached at 10 U/ml. Maximum activity is found 4 h after addition of IL-1 to macrophages. The effect disappears within 24 h. TNF does not alter the phagocytic function of the beta-glucan receptor, but TNF together with IL-1 prolongs the effect of IL-1. PGE2 reduces the phagocytic function of the beta-glucan receptor. Maximum reduction is achieved with 8 ng/ml. Time-course studies show the lowest phagocytic activity 9 h after addition of PGE2 to the cells. 相似文献
995.
996.
997.
998.
Deale O.C. Ng K.T. Kim E.J. Lerman B.B. 《IEEE transactions on bio-medical engineering》1995,42(12):1208-1211
A high common mode voltage (Vcm) relative to earth ground is produced on the myocardium during the delivery of a defibrillator pulse and can generate a differential error signal when potential gradients are recorded with bipolar electrodes and isolation amplifiers. The error signal is proportional to Vcm, and therefore, a reduction in Vcm improves the accuracy of the potential gradient data. Experiments were conducted on 5 dogs to determine whether Vcm can be controlled using a bridge circuit. The bridge circuit consisted of a 5 kΩ power rheostat in parallel with the transthoracic resistance of the dog. The variable contact of the rheostat was connected to earth ground, and by adjusting the rheostat, Vcm on the myocardium could be varied. In each dog, 20 A shocks were delivered through stainless steel transthoracic electrodes. Point contact electrodes sutured to the epicardium were used to measure Vcm. It was determined that Vcm could be reduced to approximately zero at a given electrode on the heart. In addition, for the 5 dogs studied, the maximum measured Vcm on the heart was only 10% of the transthoracic voltage when the bridge circuit was balanced for an interior point in the heart 相似文献
999.
Persistence of the hypoglossal artery is an unusual congenital abnormality of the carotid arterial system, and the simultaneous occurrence of atheromatous disease in the internal carotid artery and persistent hypoglossal artery is even more uncommon. Carotid surgery in this situation is challenging, and the surgeon must be aware of potential inherent pitfalls. A 74-year-old woman with asymptomatic stenosis of both internal carotid and hypoglossal arteries associated with occlusion of the contralateral internal carotid artery underwent successful revascularization. The anatomy of this unusual lesion and the surgical strategies, which included cranial nerve dissection and mandibular subluxation, are reviewed. 相似文献
1000.
Guha A. Pavan A. Liu J. Rastogi A. Steeves T. 《Selected Areas in Communications, IEEE Journal on》1995,13(4):749-763
This paper describes the distributed system, network and software architecture, the application development environment, the performance, and the early lessons learned on the ATM LAN testbed Mercuri established at the Honeywell Technology Center, to develop distributed multimedia technologies for real-time control applications. We have developed a client-server-based software architecture on Sun Sparcstation-2s connected by a Fore Systems' ASX-100 ATM switch, with video processing handled by Parallax's X Video cards. The architecture enables network-transparent applications and provides simple primitives for multimedia capture, display, transmission, storage, and retrieval. A real-time multimedia-in-the-loop control application was developed as the vehicle for testing the capabilities and performance of the network. Our test measurements focus on the end-user-level performance metrics such as message throughput and round-trip delay as well as video-frame jitter under no-load and load conditions. Our results show that the maximum burst throughput that can be supported at the user level is 48 Mb/s using AAL 5, while round-trip delays for 4-kbyte messages are about 3 ms. Our experience reveals a number of performance bottlenecks and open issues in using commercial ATM switches for practical applications. Our conclusions are outlined 相似文献