全文获取类型
收费全文 | 412777篇 |
免费 | 6276篇 |
国内免费 | 1385篇 |
专业分类
电工技术 | 7715篇 |
综合类 | 350篇 |
化学工业 | 62114篇 |
金属工艺 | 14295篇 |
机械仪表 | 11877篇 |
建筑科学 | 11654篇 |
矿业工程 | 869篇 |
能源动力 | 11131篇 |
轻工业 | 43864篇 |
水利工程 | 3318篇 |
石油天然气 | 1839篇 |
武器工业 | 13篇 |
无线电 | 55416篇 |
一般工业技术 | 76681篇 |
冶金工业 | 75062篇 |
原子能技术 | 5568篇 |
自动化技术 | 38672篇 |
出版年
2021年 | 2680篇 |
2019年 | 2448篇 |
2018年 | 3858篇 |
2017年 | 3923篇 |
2016年 | 4166篇 |
2015年 | 3442篇 |
2014年 | 5738篇 |
2013年 | 19299篇 |
2012年 | 10221篇 |
2011年 | 14702篇 |
2010年 | 11304篇 |
2009年 | 12904篇 |
2008年 | 13935篇 |
2007年 | 14303篇 |
2006年 | 12797篇 |
2005年 | 11969篇 |
2004年 | 11590篇 |
2003年 | 11291篇 |
2002年 | 10921篇 |
2001年 | 11142篇 |
2000年 | 10274篇 |
1999年 | 10778篇 |
1998年 | 24042篇 |
1997年 | 17609篇 |
1996年 | 13915篇 |
1995年 | 10985篇 |
1994年 | 9776篇 |
1993年 | 9364篇 |
1992年 | 7121篇 |
1991年 | 6792篇 |
1990年 | 6400篇 |
1989年 | 6112篇 |
1988年 | 5861篇 |
1987年 | 4888篇 |
1986年 | 4834篇 |
1985年 | 5979篇 |
1984年 | 5599篇 |
1983年 | 4835篇 |
1982年 | 4498篇 |
1981年 | 4447篇 |
1980年 | 4211篇 |
1979年 | 4081篇 |
1978年 | 3771篇 |
1977年 | 4549篇 |
1976年 | 6104篇 |
1975年 | 3115篇 |
1974年 | 3011篇 |
1973年 | 2890篇 |
1972年 | 2318篇 |
1971年 | 2003篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
A random sample of patients (n = 43) had been investigated to detect any difference in response of bright light therapy in lithium-treated inpatients (n = 18) suffering from depression. Only 27% of the lithium-based inpatients respond to bright light therapy, but 73% of patients respond who were not treated with lithium. We conclude that lithium therapy reduces the chance of achieving t remission of depression by bright light therapy. 相似文献
993.
JN Vauthey RJ Tomczak T Helmberger P Gertsch C Forsmark J Caridi A Reed MR Langham GY Lauwers P Goffette J Lerut 《Canadian Metallurgical Quarterly》1997,113(4):1390-1401
BACKGROUND & AIMS: Arterioportal fistulas (APFs) are rare vascular disorders of the mesenteric circulation. The aim of this study was to determine the etiology, anatomical location, and main symptom at presentation of APFs, and analyze the various modes of treatment. METHODS: The etiology, clinical presentation, radiographs, and treatment of 12 patients with APFs are reported in detail, and another 76 cases published since 1980 are reviewed. RESULTS: APFs result from trauma (n = 25, 28%), iatrogenic procedures (n = 14, 16%), congenital vascular malformations (n = 13, 15%), tumor (n = 13, 15%), aneurysm (n = 12, 14%), and other causes (n = 11, 12%). The origin of APFs is the hepatic artery in the majority of patients (n = 56, 65%). The main symptoms at presentation are lower or upper gastrointestinal bleeding (n = 29, 33%), ascites (n = 23, 26%), heart failure (n = 4.5%), or diarrhea (n = 4.5%). Radiological intervention provides definitive treatment in 42% (n = 33) of patients, whereas the remainder are treated by surgery alone (n = 27, 31%) or a combination of radiological intervention and surgery (n = 8, 9%). CONCLUSIONS: APFs result in a protean syndrome variously combining portal hypertension and other hemodynamic imbalances (heart failure, intestinal ischemia). Single or multiple interventional radiological procedures using arterial and/or venous approaches allow definitive treatment of most APFs. With increasing technological advances, it is anticipated that surgery will only be indicated in rare instances after failure of radiological intervention(s). 相似文献
994.
A detection error mechanism termed delay ambiguity is identified as one of the main causes of the irreducible bit error rate observed for data detection over fast fading communication channels. A periodic sequence of phase rotations applied to the phase shift keyed (PSK) transmit data symbols is proposed to prevent this type of detection error 相似文献
995.
A chromosomally integrated Bradyrhizobium japonicum hoxA mutant is unable to oxidize hydrogen in free-living conditions. Derepressing conditions that induce hydrogenase activity in free-living, wild-type B. japonicum cells cannot induce expression of the hydrogenase structural genes in the hoxA mutant. The DNA-binding capacity of HoxA at the hup promoter region was studied by means of gel retardation. Both heterotrophically growing cells and cells induced to express hydrogenase activity contain a protein that specifically binds to the hup promoter region. Crude protein extracts isolated from a B. japonicum hoxA mutant do not contain this binding compound. The HoxA protein was overexpressed in E. coli and isolated in the form of a maltose-binding protein (MBP)-HoxA fusion. The MBP-HoxA hybrid protein specifically bound to a 50 bp region of the hupSL promoter known to be important for regulation of hupSL expression. 相似文献
996.
J Weber P Majer J Litera J Urban M Soucek J Vondrásek J Konvalinka P Novek J Sedlácek P Strop HG Kr?usslich I Pichová 《Canadian Metallurgical Quarterly》1997,341(1):62-69
The results of investigation of haptoglobin (Hp) types in 596 donor blood samples in some towns of Ukraine (Dnepropetrovsk, Kharkov, Odessa, Kiev, Uzhgorod, Zhitomir) are presented. Three normal Hp types (Hp1-1, Hp2-1 and Hp2-2) have been found. The reliable interpopulation differences in the Hp types frequency were not found. On the whole the Hp types frequency in the type Hp1-1 comprised 12.7%. In the type Hp2-1-48.1% and in the type Hp2-2-36.5%. The frequency of the gene Hp1 is 0.38. The frequency of the Hp types and of the gene Hpl in Ukraine is similar to that in population of Eastern Europe and European Part of Russia. 相似文献
997.
S. Vaynman R. S. Guico M. E. Fine S. J. Manganello 《Metallurgical and Materials Transactions A》1997,28(5):1274-1276
998.
Wernicke encephalopathy is considered a complication of dialytic therapy, but there are few reports of this complication. We report a 57 years old man and a 45 years old woman, with grade IV renal failure, who after acute peritoneodialysis and chronic hemodialysis respectively, had a confusional syndrome that responded to the administration of thiamine. CT scans in both patients discarded abnormal blood collections or new cerebrovascular episodes. The man bad two previous cerebrovascular episodes, a severe anemia that was corrected, angina and an episode of arrhythmia during the dialytic procedure previous to the confusional episode. The woman had an acute uremic syndrome and a concomitant urinary tract infection during the confusional episode. Wernicke encephalopathy must be suspected in patients in dialysis with confusional episodes. 相似文献
999.
J.-M DURAND J OLIVIER-FOURCADE J.-C JUMAS M WOMES P PARENT 《Journal of Materials Science》1997,32(17):4679-4686
The local environment of arsenic atoms in vitreous samples of the system Sb2S3–As2S3–Tl2S has been studied by EXAFS at the AsK-edge. The crystalline compound Tl5.6As15S25.3 situated within the zone of glass formation of the Sb2S3–As2S3–Tl2S phase diagram was used as reference compound in order to derive appropriate phase and amplitude functions. The structure
parameters determined were the number of first neighbours N
As–S, the arsenic-sulphur distance, R
As–S, and the Debye-Waller factor, σAs–S. The influence of the glass-forming antimony sulphide Sb2S3 and the glass-modifying thallium sulphide Tl2S on the As2S3 host matrix has been shown.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
1000.
J Müller-Ehmsen K Brixius C Schulze RH Schwinger 《Canadian Metallurgical Quarterly》1997,355(6):727-732
Insect cell lines in culture are used for a variety of studies. In this laboratory imaginal disc cell lines have been established from primary cultures from third instar larvae, and used for a number of experiments. The effect of ageing on the morphology and physiology of Drosophila cell lines has received very little attention, although problems of genotypic or phenotypic changes in cell lines with age are recognized in other areas of animal cell culture. We tested our cell line Cl8+ for any difference in growth, morphology and response to 20-hydroxyecdysone (20HE) at different ages (passage numbers). The cells were found to multiply faster, adhere less firmly to the substrate and to lose the tendency to aggregate at higher passages. The response to 20HE in terms of cell numbers and induction of beta-galactosidase was similar at all passage numbers but morphological changes in hormone-treated cells were less obvious in the higher passages. Cell lines are likely to vary in the extent of ageing effects but workers are advised to be aware of the possibilities. We suggest the effects of age on cell lines should be established, and passage numbers noted in experimental reports. 相似文献