全文获取类型
收费全文 | 3682篇 |
免费 | 220篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 40篇 |
化学工业 | 862篇 |
金属工艺 | 44篇 |
机械仪表 | 85篇 |
建筑科学 | 141篇 |
矿业工程 | 5篇 |
能源动力 | 126篇 |
轻工业 | 579篇 |
水利工程 | 27篇 |
石油天然气 | 18篇 |
无线电 | 259篇 |
一般工业技术 | 536篇 |
冶金工业 | 562篇 |
原子能技术 | 23篇 |
自动化技术 | 600篇 |
出版年
2023年 | 19篇 |
2022年 | 22篇 |
2021年 | 152篇 |
2020年 | 72篇 |
2019年 | 82篇 |
2018年 | 106篇 |
2017年 | 103篇 |
2016年 | 128篇 |
2015年 | 114篇 |
2014年 | 155篇 |
2013年 | 218篇 |
2012年 | 178篇 |
2011年 | 273篇 |
2010年 | 151篇 |
2009年 | 186篇 |
2008年 | 169篇 |
2007年 | 155篇 |
2006年 | 138篇 |
2005年 | 94篇 |
2004年 | 104篇 |
2003年 | 113篇 |
2002年 | 93篇 |
2001年 | 57篇 |
2000年 | 69篇 |
1999年 | 70篇 |
1998年 | 202篇 |
1997年 | 130篇 |
1996年 | 97篇 |
1995年 | 72篇 |
1994年 | 54篇 |
1993年 | 45篇 |
1992年 | 22篇 |
1991年 | 23篇 |
1990年 | 16篇 |
1989年 | 19篇 |
1988年 | 12篇 |
1987年 | 13篇 |
1986年 | 17篇 |
1985年 | 17篇 |
1984年 | 17篇 |
1983年 | 13篇 |
1982年 | 13篇 |
1981年 | 16篇 |
1980年 | 11篇 |
1979年 | 8篇 |
1978年 | 9篇 |
1977年 | 15篇 |
1976年 | 17篇 |
1973年 | 4篇 |
1965年 | 4篇 |
排序方式: 共有3907条查询结果,搜索用时 187 毫秒
41.
Claudio Agostinelli 《Computational statistics & data analysis》2007,51(12):5867-5875
The problems arising when there are outliers in a data set that follow a circular distribution are considered. A robust estimation of the unknown parameters is obtained using the methods of weighted likelihood and minimum disparity, each of which is defined for a general parametric family of circular data. The class of power divergence and the related residual adjustment function is investigated in order to improve the performance of the two methods which are studied for the Von Mises (circular normal) and the Wrapped Normal distributions. The techniques are illustrated via two examples based on a real data set and a Monte Carlo study, which also enables the discussion of various computational aspects. 相似文献
42.
Edoardo Ballico Claudio Fontanari 《Applicable Algebra in Engineering, Communication and Computing》2006,17(2):135-139
Here we apply the so-called Horace method for zero-dimensional schemes to error-correcting codes on complete intersections. In particular, we obtain sharper estimates on the minimum distance. 相似文献
43.
44.
A novel mosquitocidal bacterium, Bacillus thuringiensis subsp. jegathesan, and one of its toxins, Cry11B, in a recombinant B. thuringiensis strain were evaluated for cross-resistance with strains of the mosquito Culex quinquefasciatus that are resistant to single and multiple toxins of Bacillus thuringiensis subsp. israelensis. The levels of cross-resistance (resistance ratios [RR]) at concentrations which caused 95% mortality (LC95) between B. thuringiensis subsp. jegathesan and the different B. thuringiensis subsp. israelensis-resistant mosquito strains were low, ranging from 2.3 to 5.1. However, the levels of cross-resistance to Cry11B were much higher and were directly related to the complexity of the B. thuringiensis subsp. israelensis Cry toxin mixtures used to select the resistant mosquito strains. The LC95 RR obtained with the mosquito strains were as follows: 53.1 against Cq4D, which was resistant to Cry11A; 80.7 against Cq4AB, which was resistant to Cry4A plus Cry4B; and 347 against Cq4ABD, which was resistant to Cry4A plus Cry4B plus Cry11A. Combining Cyt1A with Cry11B at a 1:3 ratio had little effect on suppressing Cry11A resistance in Cq4D but resulted in synergism factors of 4.8 and 11.2 against strains Cq4AB and Cq4ABD, respectively; this procedure eliminated cross-resistance in the former mosquito strain and reduced it markedly in the latter strain. The high levels of activity of B. thuringiensis subsp. jegathesan and B. thuringiensis subsp. israelensis, both of which contain a complex mixture of Cry and Cyt proteins, against Cry4- and Cry11-resistant mosquitoes suggest that novel bacterial strains with multiple Cry and Cyt proteins may be useful in managing resistance to bacterial insecticides in mosquito populations. 相似文献
45.
One week after a single administration of 3,4-methylenedioxymethamphetamine (MDMA HCI, 30 mg/kg i.p.), 5-HT1A receptor density was significantly increased by approximately 25-30% in the frontal cortex and hypothalamus of rats. The increased density correlated with the potentiation of the hypothermic response to the 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT, 1 mg/kg s.c.). Hypothalamic 5-HT7 receptors, which also bind 8-OH-DPAT, were not changed, however, by MDMA. Fluoxetine (5 mg/kg s.c.), ketanserin (5 mg/kg s.c.) or haloperidol (2 mg/kg i.p.), given 15 min prior to MDMA, prevented the depletion of 5-hydroxytryptamine (5-HT) induced by MDMA and also blocked the effects of this neurotoxin on 5-HT1A receptor density and on 8-OH-DPAT-induced hypothermia. The protection afforded by drugs against 5-HT loss did not correlate, however, with the antagonism of the acute hyperthermic effect of MDMA. The present results indicate that drugs able to prevent or to attenuate MDMA-induced 5-HT loss also prevent the changes in 5-HT1A receptor density as well as the enhanced hypothermic response to the 5-HT1A receptor agonist 8-OH-DPAT in MDMA-treated rats. 相似文献
46.
47.
D Del Bufalo C Cucco C Leonetti G Citro I D'Agnano M Benassi T Geiser G Zon B Calabretta G Zupi 《Canadian Metallurgical Quarterly》1996,74(3):387-393
We investigated the effect of c-myb antisense phosphorothioate oligodeoxynucleotides [(S)ODNs] and cisplatin (CDDP) combination on the human colon carcinoma cell line LoVo Dx both in vitro and in nude mice bearing LoVo Dx solid tumour. We show that antisense (S)ODN treatment decreases c-myb mRNA and protein expression, induces growth arrest in the G1 phase of the cell cycle, and inhibits cell proliferation. In vivo treatment with c-myb antisense (S)ODNs results in a reduction in tumour growth. A greater inhibition of cell proliferation in vitro and a higher increase of tumour growth inhibition and growth delay in vivo were obtained with the combination of (S)ODNs and CDDP than when the two agents were administered separately. This comparative study, using the same tumour cell line in vitro and in vivo, suggests that c-myb antisense (S)ODNs might be useful in the therapy of colon cancer in combination with antineoplastic drugs. 相似文献
48.
B Kaschten A Stevenaert B Sadzot M Deprez C Degueldre G Del Fiore A Luxen M Reznik 《Canadian Metallurgical Quarterly》1998,39(5):778-785
This study evaluates the usefulness of PET for the preoperative evaluation of brain gliomas and methods of quantification of PET results. METHODS: Fifty-four patients with brain gliomas were studied by PET with 18F-fluorodeoxyglucose (FDG) (n = 45) and/or 11C-methionine (MET) (n = 41) before any treatment. Results of visual analysis, calculation of glucose consumption and five tumor-to-normal brain ratios for both tracers were correlated with two histologic grading systems and with follow-up. RESULTS: Visual analysis (for FDG) and tumor-to-mean cortical uptake (T/MCU) ratio proved to be the best tools for the evaluation of PET results. Methionine was proven to be better than FDG at delineating low-grade gliomas. Tumor-to-mean cortical uptake ratios for FDG and MET were clearly correlated (r = 0.78), leading to the equation T/MCU(FDG) = 0.4 x T/MCU(MET). We showed a good correlation between FDG PET and histologic grading. MET uptake could not differentiate between low-grade and anaplastic astrocytomas but was significantly increased in glioblastomas. Low-grade oligodendrogliomas exhibited high uptake of FDG and MET, probably depending more on oligodendroglial cellular differentiation than on proliferative potential. Uptake was decreased in anaplastic oligodendrogliomas, probably due to dedifferentiation. Care must be taken with peculiar histologic subgroups, i.e., juvenile pilocytic astrocytomas and oligodendrogliomas, because of a discrepancy between high PET metabolism and low proliferative potential (good prognosis). Both tracers proved useful for the prediction of survival prognosis. Methionine proved slightly superior to FDG for predicting the histologic grade and prognosis of gliomas, despite the impossibility of differentiation between Grades II and III astrocytomas with MET. This superiority of MET could be explained by patient sampling (low number of Grade III gliomas submitted to examination with both tracers). The combination of both tracers improved the overall results compared to each tracer alone. CONCLUSION: Both tracers are useful for the prediction of the histologic grade and prognosis. The apparent superiority of MET over FDG could be due to the small number of Grade III gliomas studied with both tracers. 相似文献
49.
Microstructural characteristics of (Pb, Ca)TiO3 piezoelectric ceramic particles have been deduced from computer analysis of their images and the corresponding statistical treatment of the data obtained. It is intended that this study should be used as a nexus, or link, between the geometrical parameters of these particles and some of their physical properties. 相似文献
50.