全文获取类型
收费全文 | 43734篇 |
免费 | 5011篇 |
国内免费 | 3341篇 |
专业分类
电工技术 | 3524篇 |
技术理论 | 1篇 |
综合类 | 3853篇 |
化学工业 | 5956篇 |
金属工艺 | 2857篇 |
机械仪表 | 2894篇 |
建筑科学 | 3069篇 |
矿业工程 | 1260篇 |
能源动力 | 1310篇 |
轻工业 | 4663篇 |
水利工程 | 1345篇 |
石油天然气 | 1383篇 |
武器工业 | 422篇 |
无线电 | 4887篇 |
一般工业技术 | 4580篇 |
冶金工业 | 2703篇 |
原子能技术 | 628篇 |
自动化技术 | 6751篇 |
出版年
2024年 | 251篇 |
2023年 | 697篇 |
2022年 | 1821篇 |
2021年 | 2264篇 |
2020年 | 1583篇 |
2019年 | 1199篇 |
2018年 | 1256篇 |
2017年 | 1534篇 |
2016年 | 1283篇 |
2015年 | 1865篇 |
2014年 | 2447篇 |
2013年 | 2886篇 |
2012年 | 3358篇 |
2011年 | 3483篇 |
2010年 | 3280篇 |
2009年 | 3147篇 |
2008年 | 3239篇 |
2007年 | 3127篇 |
2006年 | 2699篇 |
2005年 | 2175篇 |
2004年 | 1613篇 |
2003年 | 1099篇 |
2002年 | 1084篇 |
2001年 | 997篇 |
2000年 | 830篇 |
1999年 | 422篇 |
1998年 | 552篇 |
1997年 | 413篇 |
1996年 | 300篇 |
1995年 | 186篇 |
1994年 | 155篇 |
1993年 | 149篇 |
1992年 | 73篇 |
1991年 | 54篇 |
1990年 | 66篇 |
1989年 | 54篇 |
1988年 | 37篇 |
1987年 | 39篇 |
1986年 | 26篇 |
1985年 | 32篇 |
1984年 | 27篇 |
1983年 | 20篇 |
1982年 | 23篇 |
1981年 | 50篇 |
1980年 | 33篇 |
1979年 | 21篇 |
1978年 | 13篇 |
1977年 | 28篇 |
1976年 | 32篇 |
1975年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
82.
Giuseppe Gradenigo (1859-1926) was an important figure in the development of Otology. Within this paper the authors consider his background and his particular contributions to the development of various aspects of audiology. 相似文献
83.
AM Luciani S Di Capua L Guidoni R Ragona A Rosi V Viti 《Canadian Metallurgical Quarterly》1996,41(3):509-521
NMR relaxation times T1 and T2 of agarose and Fricke agarose gels have been measured in the range 17-51 MHz. The analysis of the spin echo curves indicates a multiexponential behaviour, characterized by three components, at all the examined frequencies. The relative T2 values, ranging from a few to a hundred milliseconds, can be attributed to different species of water molecules present in the gel. Two of these components are characterized by relaxation rates R2a and R2b, more sensitive than R1 to gamma irradiation, the sensitivity S being S(R1) = 0.066 s-1 Gy-1, S(R2a) = 0.088 s-1 Gy-1, S(R2b) = 0.17 s-1 Gy-1. The three T2 values decrease as a function of frequency, but no gain in dose sensitivity is obtained by changing the working frequency in the examined range. The relaxivity of agarose gels containing ferrous or ferric ions has also been measured and found to be different from those of the corresponding solutions in the absence of agarose. Thus it was possible to estimate the irradiation yield from three independent parameters, R1, R2a and R2b. No effect of the dose rate or of the source energy has been observed for any of these parameters. 相似文献
84.
G Barbaro G Barbarini W Calderon B Grisorio P Alcini G Di Lorenzo 《Canadian Metallurgical Quarterly》1996,111(5):1169-1177
BACKGROUNDS & AIMS: Contrasting opinions exist about the pharmacological treatment of esophageal candidiasis in patients with acquired immunodeficiency syndrome (AIDS). The aim of this study was to assess the long-term efficacy of fluconazole and itraconazole treatment. METHODS: This study evaluated 2213 human immunodeficiency virus-positive patients at first episode of esophageal candidiasis diagnosed by endoscopy; 1105 received fluconazole and 1108 received itraconazole. The endoscopic and clinical response to treatment was assessed periodically until the end of the follow-up period (1 year). RESULTS: At week 2, endoscopic cure occurred in 81.2% of patients treated with fluconazole and in 65.6% of patients treated with itraconazole (P < 0.001). Clinical cure was observed in 81.5% of patients treated with fluconazole and in 75.2% of patients treated with itraconazole (P < 0.001). At the end of the follow-up period, endoscopic and clinical cure were observed in 96% of patients treated with fluconazole and in 95.6% of patients treated with itraconazole (P = 0.788), with similar differences by intention-to-treat analysis (93.6% vs. 93.3%; P = 0.853). Treatment failure was observed in 22.3% of fluconazole-treated patients and in 26.6% of itraconazole-treated patients (P = 0.022). CONCLUSIONS: Fluconazole and itraconazole are provided with good long-term therapeutic efficacy in the treatment of Candida esophagitis in patients with AIDS. Fluconazole is associated with a higher rate of cure than itraconazole in short-term treatment. 相似文献
85.
单轴-平面W型复合锶铁氧体的制备及其吸波特性研究 总被引:3,自引:0,他引:3
用草酸盐共沉淀和微量掺杂法研制六角晶系W型Ni,Zn,Co,Al多元复合锶铁氧体,通过调节Ni2W同Co2W的摩尔比例,可使该种铁氧体易磁化方向从C单轴型向垂于C轴的平面型转化,控制置换锶铁氧体中部分Fe3 的微量掺杂Al3 ,可以调整4πMs值,提高磁晶各向异性场,测试分析了5种不同含Co量的W型复合锶铁氧体粉料涂层的吸波特性,发现其自然共振吸收峰随Co含量增加向低频方向偏移,最高吸收峰可达32.8dB,是适用于电子隐形技术的高品位的微波吸收剂。 相似文献
86.
87.
利用Sobolev插值不等式和关于时间t的先验估计,研究了一类广义耦合的具有周期初值问题的KdV方程,得到了整体解和整体吸引子的存在性。 相似文献
88.
基于可寻址分支分配器的CATV收费系统 总被引:2,自引:1,他引:1
给出了一种基于可寻址分支分配器的CATV收费管理系统设计方案,并着重介绍了系统的工作原理及可寻址分支分配器的设计。 相似文献
89.
A broadly cross-protective monoclonal antibody binding to Escherichia coli and Salmonella lipopolysaccharides 总被引:1,自引:0,他引:1
FE Di Padova H Brade GR Barclay IR Poxton E Liehl E Schuetze HP Kocher G Ramsay MH Schreier DB McClelland 《Canadian Metallurgical Quarterly》1993,61(9):3863-3872
During the last decade, episodes of sepsis have increased and Escherichia coli has remained the most frequent clinical isolate. Lipopolysaccharides (LPS; endotoxin) are the major toxic and antigenic components of gram-negative bacteria and qualify as targets for therapeutic interventions. Molecules that neutralize the toxic effects of LPS are actively investigated. In this paper, we describe a murine monoclonal antibody (MAb; WN1 222-5), broadly cross-reactive and cross-protective for smooth (S)-form and rough (R)-form LPS. As shown in enzyme-linked immunosorbent assay and the passive hemolysis assay, WN1 222-5 binds to the five known E. coli core chemotypes, to Salmonella core, and to S-form LPS having these core structures. In immunoblots, it is shown to react with both the nonsubstituted core LPS and with LPS carrying O-side chains, indicating the exposure of the epitope in both S-form and R-form LPS. This MAb of the immunoglobulin G2a class is not lipid A reactive but binds to E. coli J5, an RcP+ mutant which carries an inner core structure common to many members of the family Enterobacteriaceae. Phosphate groups present in the inner core contribute to the epitope but are not essential for the binding of WN1 222-5 to complete core LPS. Cross-reactivity for clinical bacterial isolates is broad. WN1 222-5 binds to all E. coli clinical isolates tested so far (79 blood isolates, 80 urinary isolates, and 21 fecal isolates) and to some Citrobacter, Enterobacter, and Klebsiella isolates. This pattern of reactivity indicates that its binding epitope is widespread among members of the Enterobacteriaceae. WN1 222-5 exhibits biologically relevant activities. In vitro, it inhibits the Limulus amoebocyte lysate assay activity of S-form and R-form LPS in a dose-dependent manner and it neutralizes the LPS-induced release of clinically relevant monokines (interleukin 6 and tumor necrosis factor). In vivo, WN1 222-5 blocks endotoxin-induced pyrogenicity in rabbits and lethality in galactosamine-sensitized mice. The discovery of WN1 222-5 settles the long-lasting controversy over the existence of anti-core LPS MAbs with both cross-reactive and cross-protective activity, opening new possibilities for the immunotherapy of sepsis caused by gram-negative bacteria. 相似文献
90.
VM Coiro AL Segre A Di Nola M Paci A Grottesi G Veglia A Ballio 《Canadian Metallurgical Quarterly》1998,257(2):449-456
Pseudomycin A is a cyclic lipodepsinonapeptide phytotoxin produced by a strain of the plant pathogenic bacterium Pseudomonas syringae. Like other members of this family of bacterial metabolites, it is characterised by a fatty acylated cyclic peptide with mixed chirality and lactonic closure. Several biological activities of Pseudomycin A are lower than those found for some of its congeners, a difference which might depend on the diverse number and distribution of charged residues in the peptide moiety. Hence, it was of interest to investigate its conformation in solution. After the complete interpretation of the two-dimensional NMR spectra, NOE data were obtained and the structure was determined by computer simulations, applying distance geometry and molecular dynamics procedures. The conformation of the large ring of Pseudomycin A in solution includes three rigid structural regions interrupted by three short flexible regions that act as hinges. The overall three-dimensional structure of the cyclic moiety is similar to that of previously studied bioactive lipodepsinonapeptides produced by other pseudomonads. 相似文献