全文获取类型
收费全文 | 679篇 |
免费 | 19篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 48篇 |
化学工业 | 146篇 |
金属工艺 | 5篇 |
机械仪表 | 7篇 |
建筑科学 | 13篇 |
能源动力 | 13篇 |
轻工业 | 63篇 |
水利工程 | 3篇 |
无线电 | 105篇 |
一般工业技术 | 87篇 |
冶金工业 | 177篇 |
原子能技术 | 11篇 |
自动化技术 | 29篇 |
出版年
2023年 | 3篇 |
2022年 | 9篇 |
2021年 | 12篇 |
2020年 | 1篇 |
2019年 | 4篇 |
2018年 | 5篇 |
2017年 | 5篇 |
2016年 | 8篇 |
2015年 | 10篇 |
2014年 | 6篇 |
2013年 | 32篇 |
2012年 | 19篇 |
2011年 | 25篇 |
2010年 | 22篇 |
2009年 | 29篇 |
2008年 | 22篇 |
2007年 | 24篇 |
2006年 | 31篇 |
2005年 | 24篇 |
2004年 | 18篇 |
2003年 | 20篇 |
2002年 | 14篇 |
2001年 | 9篇 |
2000年 | 8篇 |
1999年 | 12篇 |
1998年 | 62篇 |
1997年 | 47篇 |
1996年 | 33篇 |
1995年 | 24篇 |
1994年 | 13篇 |
1993年 | 37篇 |
1992年 | 7篇 |
1991年 | 14篇 |
1990年 | 13篇 |
1989年 | 4篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 14篇 |
1985年 | 12篇 |
1984年 | 2篇 |
1983年 | 6篇 |
1982年 | 9篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1976年 | 5篇 |
1975年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有707条查询结果,搜索用时 15 毫秒
51.
High spectral efficiency combined with power efficiency, is a requirement for high speed digital broadcast satellite systems. The effect of the recovered carrier phase noise and the nonlinearity on the performance of 16-QAM (quadrature amplitude modulation) and staggered 16-QAM is investigated and compared. It is found that for the phase noise, 16-QAM is more degraded for a roll-off factor of less than 0.4. For roll-off factor of more than 0.8, staggered 16-QAM has superior performance. For the nonlinearity staggered 16-QAM is more sensitive for a roll-off factor of less than 0.4. It is concluded that coincident 16-QAM is suitable for spectrally efficient digital broadcast systems 相似文献
52.
Raynoo Thanan Shinji Oikawa Yusuke Hiraku Shiho Ohnishi Ning Ma Somchai Pinlaor Puangrat Yongvanit Shosuke Kawanishi Mariko Murata 《International journal of molecular sciences》2015,16(1):193-217
Reactive oxygen and nitrogen species have been implicated in diverse pathophysiological conditions, including inflammation, neurodegenerative diseases and cancer. Accumulating evidence indicates that oxidative damage to biomolecules including lipids, proteins and DNA, contributes to these diseases. Previous studies suggest roles of lipid peroxidation and oxysterols in the development of neurodegenerative diseases and inflammation-related cancer. Our recent studies identifying and characterizing carbonylated proteins reveal oxidative damage to heat shock proteins in neurodegenerative disease models and inflammation-related cancer, suggesting dysfunction in their antioxidative properties. In neurodegenerative diseases, DNA damage may not only play a role in the induction of apoptosis, but also may inhibit cellular division via telomere shortening. Immunohistochemical analyses showed co-localization of oxidative/nitrative DNA lesions and stemness markers in the cells of inflammation-related cancers. Here, we review oxidative stress and its significant roles in neurodegenerative diseases and cancer. 相似文献
53.
Guoqing Guan Marion Teshima Chie Sato Sung Mo Son Muhammad Faisal Irfan Katsuki Kusakabe Norihiro Ikeda Tsao‐Jin Lin 《American Institute of Chemical Engineers》2010,56(5):1383-1390
Flow patterns in the course of transesterification of waste cooking oil (WCO), sunflower oil (SFO) with water and/or oleic acid as a model of WCO, and pure SFO in the presence of a KOH catalyst in microtubes were investigated. FAME yield for the transesterification of WCO reached more than 89% in the microtube reactors with a residence time of 252 s at 333 K. The flow patterns when using WCO were changed from a liquid–liquid slug flow at the inlet region to a parallel flow at the middle region, and then to a homogeneous liquid flow at the outlet region as the reaction proceeded at 333 K. Fine droplets containing glycerol and methanol generally formed in oil slugs when using pure SFO, but were almost unobservable when using WCO. The soap produced from free fatty acids was considered to be the main factor affecting the flow patterns of WCO and SFO. © 2009 American Institute of Chemical Engineers AIChE J, 2010 相似文献
54.
This paper proposes some basic methods of content search yielding high user utility or user's satisfaction from numerous information sources scattered over large‐scale networks. In these methods, the search policy is decided by the estimated user utility gain and/or current user utility for each search action, and the most favorable combination of information sources and search content items is selected so as to enlarge the total user utility of the entire search activity. In addition, we evaluate the efficiency of the methods by computer simulations, in which we specify the network topology, user utility functions, probabilities of existence of the search content items in each information source, and so on, apply the proposed methods and other methods for comparison, and compare their aggregate utility gains as an estimation index. The proposed methods are found to achieve good performance in general and an index value about 2.45 times that of ordinary search is observed in an extreme simulation scenario. We discuss the pros and cons of the proposed methods for all the simulation scenarios. 相似文献
55.
Partially fluorinated metal oxides were studied for manufacturing dichloropentafluoropropanes (CF3CF2CHCl2 and CCl2FCF2CHClF) and controlling the selectivity of their isomers. When activated by elemental fluorine or dichlorodifluoromethane, metal oxides such as TiO2, HfO2, Al2O3, and ZrO2, exhibited catalytic activity in the reaction of dichlorofluoromethane with tetrafluoroethylene. In the case of the TiO2 catalyst, the more fluorine incorporated, the higher the selectivity was for the CCl2FCF2CHClF formation. The fluorine-activated TiO2 catalyst was identified by XRD and XPS as a mixture of TiO2 and partially fluorinated TiO2 including TiOF2. 相似文献
56.
In practice, water pricing is the main economic instrument used to discourage the wasteful use of residential water. Owing to considerations of affordability, residential water is systematically underpriced because water is essential for life. Such a low price results in water being used inefficiently. This paper proposes a system that supplements the existing price system with a cap-and-trade measure to reconcile conflicts among the goals of residential water use. It forces all people (independent of income) to be faced with reasonable price signals and to use water efficiently. The poor could, however, gain from trade and afford water. By taking advantage of the agent-based model, a simulation of this system applied to Taipei, Taiwan shows that those with lower income per capita are better off under this system even though the equilibrium price of residential water is higher. The simulated average price elasticity of market demand is ?0.449. 相似文献
57.
58.
H Matsumoto S Hayashi H Shioura T Ohtsubo R Kitai K Ohnishi N Hayashi T Ohnishi E Kano 《Canadian Metallurgical Quarterly》1998,41(4):915-920
To confirm whether or not the alar cartilage of the unilateral cleft lip nose is primarily hypoplastic as compared with the noncleft side, 35 unilateral cleft lip nasal patients who had no previous nasal surgery underwent direct measurement of the lateral crus of alar cartilage on both sides during their nasal tip plasties. Both lower lateral cartilages were dissected freely, and the thickness was measured at the intercrural, middle, and distal portions. The width was measured at the widest portion, and the length was measured from the intercrural point to the distal end. Two-mm-punch biopsies were obtained from each cartilage for histologic study. The lateral crus of the cleft side was no smaller than that of the noncleft side. Histologically, no difference was ascertained. In conclusion, we think the lateral crus of the alar cartilage of the cleft side is not hypoplastic. Therefore, external factors such as soft-tissue defect or external abnormal vector force are more attributable than intrinsic factors to the development of cleft lip nasal deformity. 相似文献
59.
Y Harima K Harima N Shikata A Oka T Ohnishi Y Tanaka 《Canadian Metallurgical Quarterly》1998,124(9):503-510
PURPOSE: The ratio of Bcl-2 to Bax expression determines survival or death following an apoptotic stimulus. In order to establish a new predictor of the outcome of treatment for human cervical carcinoma, we investigated the relationship between the expressions of the Bax and Bcl-2 proteins and the response to radiotherapy after the administration of 10.8 Gy. METHODS: A total of 44 patients with histologically proven carcinoma of the uterine cervix, including three with recurrent cervical stump carcinomas, were treated with definitive radiotherapy. The presence of mutations in exons 5-8 of the p53 gene was analyzed by a single-strand conformation polymorphism analysis and DNA sequencing. RESULTS: Forty patients were found to have wild-type p53, and the remaining four had mutant p53. The Bax and Bcl-2 protein expressions prior to radiotherapy did not correlate with response and survival. However, the Bax and Bcl-2 protein expressions after radiotherapy correlated with both response and survival. Bax-positive tumors showed significantly better responses than the Bax-negative tumors after 10.8 Gy radiation (P = 0.0002). In contrast, the Bcl-2-positive tumors showed significantly poorer responses than the Bcl-2-negative tumors after radiation (P = 0.002). Increased Bax expression after the 10.8 Gy radiotherapy was found to be correlated with good survival (P = 0.04). In contrast, increased Bcl-2 expression after such radiotherapy was correlated with poor survival (P = 0.002). CONCLUSION: The levels of Bax and Bcl-2 expression after 10.8 Gy radiotherapy are useful prognostic markers in patients with human cervical carcinoma. 相似文献
60.
K Harada T Sugahara T Ohnishi Y Ozaki Y Obiya S Miki T Miki M Imamura Y Kobayashi H Watanabe M Akashi Y Furusawa N Mizuma H Yamanaka E Ohashi C Yamaoka M Yajima M Fukui T Nakano S Takahashi T Amano K Sekikawa K Yanagawa S Nagaoka 《Canadian Metallurgical Quarterly》1998,1(5):817-822
OBJECTIVE: To explore whether there are different disease patterns of rheumatoid arthritis (RA) in women and men. METHODS: We studied 55 male case patients and 110 female control patients who developed RA between 1970 and 1985 and who resided and received medical care in Olmsted County, Minnesota, for at least 10 years after the diagnosis of RA. Case and control patients were matched for the date of first diagnosis. The pattern and extent of joint involvement, the frequency of joint surgeries, and the presence and type of extraarticular manifestations were determined by retrospective chart review. RESULTS: Incidence rates in women were variable and age dependent, whereas the risk in men older than 36 years was constant over their lifetime. Erosive disease was more frequent in men than in women (72% versus 55%, respectively; P < 0.05) and tended to occur earlier (47% versus 31% for erosive disease within the first 4 years of RA). Although male sex was correlated with a higher risk of bony erosions and an accelerated course of RA, structural consequences of joint destruction were more pronounced in women. Joint surgery was performed more frequently in women (50%) than in men (27%) (P = 0.01). In particular, the frequencies of arthroplasties and arthrodeses of hand and foot joints were different (34 procedures in women versus 1 procedure in men; P < 0.001). Sex influenced the risk as well as the pattern of organ involvement in RA. Nodules and rheumatoid lung disease were typical manifestations in men (P = 0.001 and P < 0.001, respectively), whereas women typically developed sicca syndrome (P = 0.05). Despite differences in disease aggressiveness and disease pattern, there was little difference in the medical therapy in the men compared with the women. CONCLUSION: RA is a heterogeneous disease with variations in phenotype. Sex-associated factors influence disease severity as well as disease pattern. Because sex-related effects influence treatment goals, treatment responses, and side effects, they should be considered in clinical study design and analysis as well as in the treatment decisions for individual patients with RA. 相似文献