全文获取类型
收费全文 | 4929篇 |
免费 | 12篇 |
专业分类
电工技术 | 10篇 |
化学工业 | 66篇 |
金属工艺 | 7篇 |
机械仪表 | 6篇 |
建筑科学 | 32篇 |
能源动力 | 13篇 |
轻工业 | 29篇 |
水利工程 | 4篇 |
石油天然气 | 4篇 |
无线电 | 75篇 |
一般工业技术 | 75篇 |
冶金工业 | 4490篇 |
原子能技术 | 13篇 |
自动化技术 | 117篇 |
出版年
2020年 | 7篇 |
2016年 | 5篇 |
2015年 | 6篇 |
2013年 | 27篇 |
2012年 | 21篇 |
2011年 | 12篇 |
2010年 | 18篇 |
2009年 | 12篇 |
2008年 | 17篇 |
2007年 | 20篇 |
2006年 | 28篇 |
2005年 | 18篇 |
2004年 | 15篇 |
2003年 | 23篇 |
2002年 | 12篇 |
2001年 | 14篇 |
2000年 | 15篇 |
1999年 | 139篇 |
1998年 | 1297篇 |
1997年 | 778篇 |
1996年 | 504篇 |
1995年 | 251篇 |
1994年 | 251篇 |
1993年 | 257篇 |
1992年 | 33篇 |
1991年 | 61篇 |
1990年 | 56篇 |
1989年 | 60篇 |
1988年 | 44篇 |
1987年 | 55篇 |
1986年 | 72篇 |
1985年 | 58篇 |
1984年 | 13篇 |
1983年 | 34篇 |
1982年 | 28篇 |
1981年 | 38篇 |
1980年 | 63篇 |
1979年 | 10篇 |
1978年 | 15篇 |
1977年 | 139篇 |
1976年 | 292篇 |
1975年 | 18篇 |
1974年 | 15篇 |
1973年 | 17篇 |
1972年 | 7篇 |
1971年 | 7篇 |
1970年 | 7篇 |
1969年 | 7篇 |
1966年 | 5篇 |
1955年 | 6篇 |
排序方式: 共有4941条查询结果,搜索用时 15 毫秒
41.
A Fernandez Rodríguez M Arrabal Martín JF Domínguez Molinero JL Mijan Ortiz J Sánchez Tamayo A Zuluaga Gómez 《Canadian Metallurgical Quarterly》1995,19(8):620-626
A prospective study was conducted on 374 patients with urinary lithiasis, aiming to analyze the participation of oxalate in the lithogenesis and composition of the calcium oxalate calculi, alone or associated to other factors. METHODOLOGY: Metabolic urinary study of the patient and analysis of calculi with infrared spectrography and optical microscopy. RESULTS: 26.3% patients had hyperoxaluria and 77.5% of the calculi contain calcium oxalate; these are 167 cases of calcium oxalate, 110 of oxalate and calcium phosphate and 13 cases of mixed calcium oxalate and uric acid lithiasis. 43.4% patients with pure monohydrate calcium oxalate calculi have hypercalciuria, 22.6% hyperoxaluria and 19% hyperuricosuria. Dihydrated calcium oxalate calculi are related to high hypercalciuria in 65% cases and to significant hyperoxaluria in 35% cases. 45% patients present a single lithogenic factor, either hypercalciuria (49.6%), hyperoxaluria (20.6%), hyperuricosuria (13.74%), hypocitraturia (9%), urinary infection (1.5%), A.T.R. (2.25%) or acid oliguria (3%). 相似文献
42.
RA Pollock JF Rosenbaum A Marrs BS Miller J Biederman 《Canadian Metallurgical Quarterly》1995,18(4):745-766
Although the exact path of acquisition remains incompletely understood, research supports the association between anxiety disorders in children and psychopathologic conditions in adults. This article addresses this relationship; reviews findings on the temperamental profile and behavioral inhibition, which may be an early identifiable childhood predictor of later anxiety disorders; and discusses the importance of early intervention. 相似文献
43.
44.
45.
Several factors promote the progression of renal disease, including glomerular hypertension and hypertrophy, molecular factors such as cytokines and growth hormones, proteinuria, acidosis, and hyperlipidemia. Regardless of the underlying etiology, many patients with chronic renal insufficiency will ultimately require kidney replacement therapy. Your goal is to delay the progression of renal failure, mainly through aggressive control of blood pressure. Other possible interventions include protein restriction, bicarbonate therapy, and lipid-lowering drugs. 相似文献
46.
Well-differentiated thyroid cancer (i.e. papillary microcarcinoma) may be revealed by a clinically palpable cervical node, especially in young patients. Primary tumor specificity (small-sized, superior location, invasion, multifocality) and characteristics of cervical node involvement (with synchronous central and lateral multiple node spread) require appropriate treatment by a skilled surgeon. Contrary to the primary tumor treatment (total thyroidectomy), surgical management of the cervical node basins remains controversial. Only a special knowledge of the specificity of this disease and cervical lymphatic anatomy will ensure a good prognosis for the patient. 相似文献
47.
LS Melchers M Apotheker-de Groot JA van der Knaap AS Ponstein MB Sela-Buurlage JF Bol BJ Cornelissen PJ van den Elzen HJ Linthorst 《Canadian Metallurgical Quarterly》1994,5(4):469-480
A novel chitinase gene of tobacco was isolated and characterized by DNA sequence analysis of a genomic clone and a cDNA clone. Comparative sequence analysis of both clones showed an identity of 94%. The proteins encoded by these sequences do not correspond to any of the previously characterized plant chitinases of classes I-IV and are designated as class V chitinases. Comparison of the chitinase class V peptide sequence with sequences in the Swiss Protein databank revealed significant sequence similarity with bacterial exo-chitinases from Bacillus circulans, Serratia marcescens and Streptomyces plicatus. It was demonstrated that class V chitinase gene expression is induced after treatment of tobacco with different forms of stress, like TMV-infection, ethylene treatment, wounding or ultraviolet irradiation. Two related chitinase class V proteins of 41 and 43 kDa were purified from Samsun NN tobacco leaves inoculated with tobacco mosaic virus. The proteins were purified by Chelating Superose chromatography and gel filtration. In vitro assays demonstrated that class V chitinases have endo-chitinase activity and exhibit antifungal activity toward Trichoderma viride and Alternaria radicina. In addition, it was shown that class V chitinase acts synergistically with tobacco class I beta-1,3-glucanase against Fusarium solani germlings. 相似文献
48.
The verification and recognition of peak-shaped signals in analytical data are ubiquitous scientific problems. Experimental data contain overlapping signals and noise, which make sensitive and reliable peak recognition difficult. A peak detection system based on a class of neural networks known as "multilayered perceptrons" has been created. The network was trained and evaluated with use of vapor-phase infrared spectral data. The results of varying the network architecture on system training and prediction performance along with refinement of the form of the input pattern are presented. 相似文献
49.
Aliphatic polybenzoxazoles, polybenzothiazoles, and polybenzimidazoles have been prepared by three methods: in poly(phosphoric acid), by the polyamide precursor, and by melt polymerization. The melt polymerization method was found to be the most satisfactory. All of the aliphatic heterocyclic polymers had excellent thermal stability, resistance to alkaline hydrolysis, high glass transition temperatures, and a high degree of flexibility. The only class of polymer found having any degree of solubility, however, was the polybenzimidazoles. Aliphatic polybenzimidazole films were prepared by solution casting. These films were found to be extremely flexible at ambient and cryogenic temperatures. The films were unaffected by alkaline hydrolysis, even in an oxidizing medium. A molding prepared from the aliphatic polybenzimidazole had excellent physical properties at both cryogenic and room temperature. 相似文献
50.
The canonical monomers (approximately 170 bp) of an abundant (1.9 x 10(6) copies per diploid genome) satellite DNA sequence family in the genome of Cyprinodon variegatus, a "pupfish" that ranges along the Atlantic coast from Cape Cod to central Mexico, are divergent in base sequence in 10 of 12 samples collected from natural populations. The divergence involves substitutions, deletions, and insertions, is marked in scope (mean pairwise sequence similarity = 61.6%; range = 35-95.9%), is largely confined to the 3' half of the monomer, and is not correlated with the distance among collecting sites. Repetitive cloning and direct genomic sequencing experiments failed to detect intrapopulation and intraindividual variation, suggesting high levels of sequence homogeneity within populations. The satellite sequence has therefore undergone "concerted evolution," at the level of the local population. Concerted evolution has previously almost always been discussed in terms of the divergence of species or higher taxa; its intraspecific occurrence apparently has not been reported previously. The generality of the observation is difficult to evaluate, for although satellite DNAs from a large number of organisms have been studied in detail, there appear to be little or no other data on their sequence variation in natural populations. The relationship (if any) between concerted, population level, satellite DNA divergence and the extent of gene flow/genetic isolation among conspecific natural populations remains to be established. 相似文献