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   1421篇
  免费   12篇
  国内免费   2篇
电工技术   118篇
综合类   3篇
化学工业   267篇
金属工艺   27篇
机械仪表   20篇
建筑科学   16篇
能源动力   36篇
轻工业   116篇
水利工程   3篇
石油天然气   2篇
无线电   229篇
一般工业技术   185篇
冶金工业   251篇
原子能技术   18篇
自动化技术   144篇
  2024年   5篇
  2023年   5篇
  2022年   22篇
  2021年   26篇
  2020年   11篇
  2019年   20篇
  2018年   11篇
  2017年   11篇
  2016年   27篇
  2015年   22篇
  2014年   35篇
  2013年   57篇
  2012年   46篇
  2011年   72篇
  2010年   46篇
  2009年   57篇
  2008年   55篇
  2007年   56篇
  2006年   56篇
  2005年   37篇
  2004年   46篇
  2003年   41篇
  2002年   34篇
  2001年   31篇
  2000年   32篇
  1999年   33篇
  1998年   127篇
  1997年   69篇
  1996年   45篇
  1995年   41篇
  1994年   21篇
  1993年   30篇
  1992年   12篇
  1991年   18篇
  1990年   16篇
  1989年   15篇
  1988年   11篇
  1987年   9篇
  1986年   18篇
  1985年   14篇
  1984年   13篇
  1983年   10篇
  1982年   11篇
  1981年   8篇
  1980年   6篇
  1979年   4篇
  1978年   6篇
  1977年   12篇
  1976年   13篇
  1975年   3篇
排序方式: 共有1435条查询结果,搜索用时 15 毫秒
71.
The aim of this study was to determine whether chemo-endocrine therapy after the resection of liver metastasis from colorectal cancer would prevent recurrence in the remnant liver and prolong survival. Eleven colorectal cancer patients underwent hepatic resection for liver metastasis. Subsequently, they were administered Proglumide gastrin antagonist 1,200 mg/day + 5'-DFUR 800 mg/day for 2 years. In seven of them, MMC 6-10 mg and ADM 20 mg were infused intra-arterially every two weeks alternately for one year. In four of them, 5-FU 250 mg/day was infused for seven days continuously intra-arterially every two weeks for one year. Recurrence in the remnant liver occurred in four of 11 patients. All of these patients underwent repeated hepatectomy. The mean disease-free survival in the remnant liver was 37 months and the five-year survival rate was 91%. These results indicate that intra-arterial chemotherapy with gastrin receptor antagonist might be effective for adjuvant therapy in patients with resectable liver metastasis from colorectal cancer.  相似文献   
72.
OBJECTIVE: The accuracy of the PyloriTek test (a 1-h rapid urease test) used after eradication therapy of Helicobacter pylori (H. pylori) has not been well clarified. This study was done to evaluate the accuracy of the PyloriTek test results for cases with and without eradication therapy, using culture and histology as gold standard methods, and to establish the suitable timing of the PyloriTek test after eradication treatment. METHODS: One hundred sixty-three patients undergoing upper endoscopy were randomly selected; 100 patients had not received eradication therapy and 63 had. Three biopsy specimens each were obtained from the gastric antrum and the body for examination by PyloriTek, culture, and histology. The absence of H. pylori was established with negative results from both culture and histology. RESULTS: In cases without eradication therapy, PyloriTek, correctly identified 66 of 67 H. pylori-positive cases and 30 of 33 H. pylori-negative cases, yielding 98.5% sensitivity and 90.9% specificity. In cases with eradication therapy, PyloriTek gave correct diagnoses in 10 of 17 H. pylori-positive cases and in 45 of 46 H. pylori-negative cases, for 58.8% sensitivity and 97.8% specificity. However, when PyloriTek was used more than 4 months after the end of eradication therapy, both the sensitivity and the specificity increased to 100%. CONCLUSION: Considering time and cost, the use of PyloriTek alone may be satisfactory for detecting H. pylori infection in cases without eradication therapy. When patients are examined more than 4 months after intervention, the use of PyloriTek alone may be sufficient for correctly diagnosing H. pylori infections.  相似文献   
73.
Integral benchmark experiments with DT neutrons are not always sufficient for nuclear data benchmarking in the MeV region, below 10 MeV. A neutron spectrum shifter, which will be placed between a sample and a DT neutron source, is effective to moderate DT neutrons incident to the sample. In order to estimate effects of the spectrum shifter, the ratio of the contribution of 14 MeV neutrons in the leakage neutron and gamma-ray spectra was calculated with MCNP-4C for an experimental configuration at FNS of JAEA, Japan. The calculations were carried out for a Li2TiO3 sample with a Be, D2O, or 7LiD spectrum shifter. It was found out that the Be shifter was superior to others and the Be shifter was effective to decrease the contribution of 14 MeV neutrons especially for secondary gamma-ray spectrum measurements.  相似文献   
74.
An end-to-end packet delay in the Internet is an important performance parameter, because it heavily affects the quality of real-time applications. In the current Internet, however, because the packet transmission qualities (e.g., transmission delays, jitters, packet losses) may vary dynamically, it is not easy to handle a real-time traffic. In UDP-based real-time applications, a smoothing buffer (playout buffer) is typically used at a client host to compensate for variable delays. The issue of playout control has been studied by some previous works, and several algorithms controlling the playout buffer have been proposed. These studies have controlled the network parameters (e.g., packet loss ratio and playout delay), not considered the quality perceived by users. In this paper, we first clarify the relationship between Mean Opinion Score (MOS) of played audio and network parameters (e.g., packet loss, packet transmission delay, transmission rate). Next, utilizing the MOS function, we propose a new playout buffer algorithm considering user's perceived quality of real-time applications. Our simulation and implementation tests show that it can enhance the perceived quality, compared with existing algorithms.  相似文献   
75.
High-power aging tests on 1.3 ?m double-channel planar buried-heterostructure (DC-PBH) lasers with a reflective coated mirror have been performed. Stable operation for over 6000 h has been demonstrated under constant power conditions of 20 and 30 mW from the front facet at 50°C.  相似文献   
76.
In this work three mathematical models for methane steam reforming in membrane reactors were developed. The first one is a steady state, non isothermal, non isobaric and one dimensional model derived from material and energy balances and validated using experimental data from the literature. It is referred as full model. The influence of two different intrinsic kinetics available, as well as, the influence of five important parameters on methane conversion (XCH4_{mathrm{CH}_{4}}) and hydrogen recovery (YH2_{mathrm{H}_{2}}) were parametrically evaluated through simulations. The second model, referred as meta-model, was obtained though the response surface technique. This meta-model was included into a constrained optimization problem solved using NPSOL. The third model, referred as a simplified model, takes into account only mass balances from the full model. Using this model, a gradient based method (DIRCOL) was used to perform the optimization of the sum of methane conversion and hydrogen recovery. High methane conversions and hydrogen recoveries were reached through these methodologies.  相似文献   
77.
This paper describes a novel dynamic flip-flop (FF) circuit that can operate 30% faster than conventional clocked inverter-type FFs. A new wideband clock buffer is introduced to cover the FF operation range. An 8- to 24-Gb/s decision circuit and a 9- to 26-GHz 1/2 frequency divider were developed utilizing production-level 0.2-μm GaAs MESFET technology  相似文献   
78.
79.
1.55 ?m-band distributed-feedback laser diodes with double-channel planar buried heterostructure (DFB-DC-PBH LDs) have been developed. As well as low threshold current, 19 mA at room temperature, stable CW single-longitudinal-mode operation up to the high power level of 23 mW and the high temperature of 108°C has been obtained.  相似文献   
80.
One of the most promising approaches for high speed networks for integrated service applications is fast packet switching, or ATM (asynchronous transfer mode). ATM can be characterized by very high speed transmission links and simple, hard-wired protocols within a network. To match the transmission speed of the network links, and to minimize the overhead due to the processing of network protocols, the switching of cells is done in hardware switching fabrics in ATM networks. A number of designs have been proposed for implementing ATM switches. Although many differences exist among the proposals, the vast majority of them are based on self-routeing multistage interconnection networks. This is because of the desirable features of multi-stage interconnection networks such as self-routeing capability and suitability for VLSI implementation. Existing ATM switch architectures can be classified into two major classes: blocking switches, where blockings of cells may occur within a switch when more than one cell contends for the same internal link, and non-blocking switches, where no internal blocking occurs. A large number of techniques have also been proposed to improve the performance of blocking and non-blocking switches. In this paper, we present an extensive survey of the existing proposals for ATM switch architectures, focusing on their performance issues.  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