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   934篇
  免费   60篇
  国内免费   2篇
电工技术   15篇
化学工业   269篇
金属工艺   13篇
机械仪表   28篇
建筑科学   20篇
能源动力   26篇
轻工业   80篇
水利工程   10篇
石油天然气   3篇
无线电   100篇
一般工业技术   150篇
冶金工业   89篇
原子能技术   3篇
自动化技术   190篇
  2023年   11篇
  2022年   39篇
  2021年   64篇
  2020年   31篇
  2019年   17篇
  2018年   42篇
  2017年   30篇
  2016年   27篇
  2015年   27篇
  2014年   44篇
  2013年   68篇
  2012年   65篇
  2011年   67篇
  2010年   41篇
  2009年   31篇
  2008年   43篇
  2007年   40篇
  2006年   36篇
  2005年   19篇
  2004年   21篇
  2003年   16篇
  2002年   15篇
  2001年   14篇
  2000年   9篇
  1999年   21篇
  1998年   22篇
  1997年   17篇
  1996年   18篇
  1995年   5篇
  1994年   10篇
  1993年   13篇
  1992年   5篇
  1991年   5篇
  1990年   3篇
  1989年   5篇
  1987年   5篇
  1985年   5篇
  1984年   4篇
  1983年   5篇
  1982年   2篇
  1981年   4篇
  1977年   8篇
  1976年   3篇
  1975年   3篇
  1974年   2篇
  1968年   1篇
  1967年   1篇
  1966年   2篇
  1961年   1篇
  1957年   1篇
排序方式: 共有996条查询结果,搜索用时 500 毫秒
91.
BACKGROUND: The medical treatment of advanced medullary thyroid carcinoma (MTC) is still questionable. Results of chemotherapy are disappointing with almost no curative responses, few partial responses, and many side-effects. A recent report has suggested the activity of combination recombinant interferon alpha-2b (rIFN-alpha-2b) and octreotide, a somatostatin analogue, in the treatment of a metastatic carcinoid tumor. This new therapeutic schedule may be used in other neuroendocrine tumors. In this study we evaluated the therapeutic effectiveness of octreotide and rIFN-alpha-2b in patients with advanced MTC. METHODS: Eight patients affected by advanced MTC received octreotide at a daily dose of 150 micrograms for 6 months and subsequently at a daily dose of 300 micrograms for another 6 months, subcutaneously, and rIFN-alpha-2b at a daily dose of 5.000.000 IU intramuscularly 3 times a week for 12 months. Plasma calcitonin, carcinoembryonic antigenic levels, and morphologic staging were evaluated at 0, 1, 3, 6, and 12 months. RESULTS: The therapy was stopped in two patients because of diarrhea and toxicity of drugs used. Pre-existing diarrhea in four patients and flushing in one significantly improved during treatment. A maximum decrease of calcitonin was reached after 1 month in 2 patients and after 3 months in 4. In all of the patients carcinoembryonic antigen levels decreased during treatment. No significant changes of size of metastases were observed. CONCLUSIONS: The combination of octreotide and interferon is well tolerated and can be recommended for the treatment of advanced MTC.  相似文献   
92.
A new scheme to alleviate contention in optical burst switching networks is proposed. It consists of preventively reserving resources in a node, to be used if resources are busy on the next hop node. The burst is sent back to the preceding node and then resent forward. Simulations are carried out to assess the feasibility of the proposed scheme. Its performance is compared with that of contention resolution based on deflection routing.  相似文献   
93.
To determine whether a metastatic phenotype may be corelated with a characteristic lipid pattern, we compared the lipid composition of low metastasizing Balb/c 3T3 cells transformed by the B77 strain of Rous sarcoma virus (B77-3T3 cells) with that of a subclone isolated by growth in 0.6% agar, the B77-AA6 cells, which exhibit a high capacity for spontaneous metastasis. B77-3T3 cells revealed characteristics in their lipid composition common to other systems of transformed cells, i.e., an accumulation of ether-linked lipids, a reduction of the more complex gangliosides, an increase of oleic acid (18∶1) and a decrease of arachidonic (20∶4) and C22 polyunsaturated fatty acids in phospholipids. High metastatic B77-AA6 cells showed: a) an even more marked decrease of complex gangliosides; b) a more pronounced increase of 18∶1 and decrease of 20∶4 and 22 polyunsaturated fatty acids in certain phospholipid classes; and c) a higher percentage of alkyl-acyl subfractions in both phosphatidylcholine and phosphatidylethanolamine than B77-3T3 cells. Comparing the data for other systems of metastatic cells with those of lipid studies of spontaneously metastasizing B77-AA6 cell system leads us to conclude that the metastatic phenotype is characterized by a change in ether-linked lipids, rather than in fatty acids.  相似文献   
94.
95.
In global navigation satellite systems (GNSS) navigation the receiver and satellite clocks play a key role. The receivers are usually equipped with inaccurate quartz clocks, which experiment large drift relative to system time and consequently offset growing very fast; receiver manufactures bound the magnitude of the receiver clock offset to prevent it becomes too large and the actual bounding procedures vary from one manufacturer to another. The most common approach consists of introducing discrete jumps when the offset exceeds a threshold (usually 1 ms). This method is common in low-cost GNSS receivers and influences several applications as differential positioning, cycle-slip detection, precise point positioning technique, absolute positioning with Kalman filter. In this work some techniques to detect and account for millisecond clock jump, suitable for code positioning of a single receiver with Kalman filter, are proposed. Two deterministic algorithms to detect receiver clock jumps are shown: in measurement and parameter domain. The technique in measurement domain uses current pseudorange measurements compared with pseudorange and Doppler measurements at previous epoch; the technique in parameter domain compares current and previous least squares estimations of receiver clock bias, considering the clock drift. Two different approaches are described to account for the clock jumps, once detected, a deterministic one, consisting of fixing the pseudorange discontinuities, and a statistic one, consisting of suitably varying the Kalman filter settings. A static GNSS data set is processed with and without the proposed algorithms to demonstrate their efficiency.  相似文献   
96.
97.
98.
We discuss the origin of an additional dip other than the charge neutrality point observed in the transfer characteristics of graphene-based field-effect transistors with a Si/SiO2 substrate used as the back-gate. The double dip is proved to arise from charge transfer between the graphene and the metal electrodes, while charge storage at the graphene/SiO2 interface can make it more evident. Considering a different Fermi energy from the neutrality point along the channel and partial charge pinning at the contacts, we propose a model which explains all the features observed in the gate voltage loops. We finally show that the double dip enhanced hysteresis in the transfer characteristics can be exploited to realize graphene-based memory devices.  相似文献   
99.
Several experimental investigations in the past few years have highlighted the fact that the compressive strength of glass was significantly higher than its tensile strength, allowing new applications of glass in compression members. However, due to the high slenderness of structural glass elements made of thin glass panels, they tend to fail in a brittle manner. A substantial amount of fundamental research has been carried out in the past few years to investigate the stability behaviour of structural glass elements. However, although buckling of glass panels has been quite well studied, a very poor amount of research has been addressed to glass columns, which by contrast represent the most interesting case due to their direct application in buildings. In this paper, the results of ten compressive tests on glass panels and columns are presented and discussed. The main variables considered were slenderness of panels and the shape of the cross-section for columns. The results of six bending tests on monolithic and laminated glass panels are also shown, and the level of connection between the glass sheets was evaluated. A review of the theoretical background is provided and the results achievable with existing analytical models are compared.  相似文献   
100.
Network survivability requires the provisioning of backup resources in order to protect active traffic against any failure scenario. Backup resources, however, can remain unused most of the time while the network is not in failure condition, inducing high power consumption wastage, if fully powered on. In this paper, we highlight the power consumption wastage of the additional resources for survivability in IP/multi-protocol label switching (MPLS) over dense wavelength division multiplexing multi-layer optical networks. We assume MPLS protection switching as the failure recovery mechanism in the network, a solution interesting for current network operators to ensure fast recovery as well as fine-grained recovery treatment per label switched path. Next, we quantitatively show how elastic optical technologies can effectively reduce such a power consumption by dynamically adjusting the data rate of the transponders to the carried amount of traffic.  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