首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   423165篇
  免费   3628篇
  国内免费   882篇
电工技术   7754篇
综合类   210篇
化学工业   62415篇
金属工艺   21100篇
机械仪表   14758篇
建筑科学   7888篇
矿业工程   4233篇
能源动力   8197篇
轻工业   22962篇
水利工程   5539篇
石油天然气   14422篇
武器工业   35篇
无线电   45201篇
一般工业技术   94594篇
冶金工业   74447篇
原子能技术   13802篇
自动化技术   30118篇
  2021年   3765篇
  2019年   3745篇
  2018年   7032篇
  2017年   7284篇
  2016年   7673篇
  2015年   4285篇
  2014年   7442篇
  2013年   17091篇
  2012年   11024篇
  2011年   14159篇
  2010年   11505篇
  2009年   13060篇
  2008年   13542篇
  2007年   13225篇
  2006年   11325篇
  2005年   10286篇
  2004年   10178篇
  2003年   9841篇
  2002年   9554篇
  2001年   9721篇
  2000年   9362篇
  1999年   9244篇
  1998年   22150篇
  1997年   15569篇
  1996年   11911篇
  1995年   9087篇
  1994年   8121篇
  1993年   8273篇
  1992年   6271篇
  1991年   6226篇
  1990年   6325篇
  1989年   6042篇
  1988年   5679篇
  1987年   5157篇
  1986年   5128篇
  1985年   5570篇
  1984年   5227篇
  1983年   4882篇
  1982年   4602篇
  1981年   4781篇
  1980年   4561篇
  1979年   4657篇
  1978年   4845篇
  1977年   5157篇
  1976年   6329篇
  1975年   4346篇
  1974年   4379篇
  1973年   4384篇
  1972年   3849篇
  1971年   3481篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
942.
The concept of a new system of emf and dc voltage measurements is and methods of its implementation capable to satisfy the predicted demands of the Russian economy for 2003–2010 are proposed as a matter of discussion. Translated from Izmeritel'naya Tekhnika, No. 10, pp. 34–37, October, 1998.  相似文献   
943.
Segmental zoster paresis (SZP) is the focal, asymmetrical neurogenic weakness which may occur in a limb affected by cutaneous zoster. We have summarized the features of this syndrome, based on a retrospective review of 8 personal and 96 published cases. Limb SZP becomes apparent in at least 3-5% of patients with cutaneous zoster, who are usually over the age of sixty and weak proximally (C5,6,7 or L2,3,4 innervated muscles). Functional motor recovery occurs in about 75% of cases, generally by 1-2 years. Limb weakness is probably due to a lesion of the ventral nerve root, in close proximity to the initiating dorsal ganglionitis. The electrodiagnostic findings, scarce in the literature, typically consist of absent compound sensory nerve action potentials in the involved limb, with less frequent reduction or loss of compound muscle action potentials. Fibrillations and positive sharp waves become detectable within 1-4 months in limb and related paraspinal muscles, decreasing or disappearing later. In addition to this radiculopathy, peripheral nerves may also occasionally become involved, manifest as mononeuropathies of the median, ulnar, long thoracic, recurrent laryngeal, and phrenic nerves. The zoster infection or consequent inflammatory response appears able to affect motor axons distally as well as proximally.  相似文献   
944.
Functional magnetic resonance imaging (fMRI) is capable of detecting task-induced blood oxygenation changes using susceptibility sensitive pulse sequences such as gradient-recalled echo-planar imaging (EPI). The local signal increases seen in the time course are believed to be due to an increase in oxygen delivery that is incommensurate with oxygen demands. To help isolate the sources of functional signal changes, the authors have incorporated various forms of diffusion weighting into EPI pulse sequences to characterize the apparent mobility of the functionally modulated protons. Results suggest that the majority of the functional signal at 1.5 T arises from protons that have apparent diffusion coefficients that are approximately four or five times higher than that of brain tissue. This implies that significant functional signal sources are either protons within the vascular space or protons from the perivascular space that is occupied by cerebrospinal fluid.  相似文献   
945.
In neonatally allylestrenol treated animals in adult age a single benzpyrene treatment significantly decreases the female and significantly increases the male rat's sexual activity. Three month old females display the negative sexual behavioral effect of neonatal allylestrenol treatment less than the six month old ones. The benzpyrene treatment in adult age decreases the sexual activity of male rats. The experiments call the attention to the modifying effect of perinatal steroid treatments to similar exposure in adult age.  相似文献   
946.
The properties of glasses of the lithium-aluminoborosilicate system were investigated, namely, the density, spreadability, thermal expansion, and nature of crystallized phases at various temperatures. A crystal-optical analysis was conducted. The glasses were used to prepare abrasive compositions. Their strength properties were studied as a function of the composition of the glass binder and the regime of heat treatment.Translated from Steklo i Keramika, No. 3, pp. 27–30, March, 1996.  相似文献   
947.
Translated from Kibernetika i Sistemnyi Analiz, No. 3, pp. 71–86, May–June, 1995.  相似文献   
948.
A 6H-SiC thyristor has been fabricated and characterized. A forward breakover voltage close to 100 V and a pulse switched current density of 5200 A/cm2 have been demonstrated. The thyristor is shown to operate under pulse gate triggering for turn-on and turn-off, with a rise time of 43 ns and a fall time of less than 100 ns. The forward breakover voltage is found to decrease by only 4% when the operating temperature is increased from room temperature to 300°C. It is found that anode ohmic contact resistance dominates the device forward drop at high current densities  相似文献   
949.
950.
The effect on gastric contractility following bilateral microinjection of thyrotropin-releasing hormone (TRH) analog, RX 77368, into the central nucleus of the amygdala was examined in fasted, urethane-anesthetized rats. Extraluminal force transducers were used to measure gastric corpus contractility. Bilateral microinjection of RX 77368 (0.5 microgram, 1.0 microgram, n = 6 each) stimulated gastric contractility for up to 120 min post-injection, P < 0.05. Gastric contractility was not significantly stimulated by microinjection of 0.1 microgram RX 77368, 0.1% bovine serum albumin (BSA) into the central nucleus or RX 77368 (0.5 microgram, 1.0 microgram) into sites adjacent to the central nucleus. Peak responses (1.0 microgram) occurred 40 min post-injection and represented a 16-26-fold increase over basal values. The frequency of gastric contraction waves was attenuated for 0-90 min in rats receiving central amygdaloid microinjection of RX 77368 (0.1, 0.5 or 1.0 microgram) versus rats microinjected with the vehicle or RX 77368 into sites adjacent to the central nuclei. The stimulatory effect of RX 77368 (1.0 microgram) on gastric contractility was abolished by subdiaphragmatic vagotomy. These results indicate that the TRH analog, RX 77368, acts within the central amygdala to vagally stimulate gastric contractility.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号