全文获取类型
收费全文 | 388043篇 |
免费 | 4273篇 |
国内免费 | 1664篇 |
专业分类
电工技术 | 7182篇 |
综合类 | 2588篇 |
化学工业 | 53791篇 |
金属工艺 | 20364篇 |
机械仪表 | 15746篇 |
建筑科学 | 9478篇 |
矿业工程 | 1753篇 |
能源动力 | 7988篇 |
轻工业 | 28642篇 |
水利工程 | 3869篇 |
石油天然气 | 3169篇 |
武器工业 | 7篇 |
无线电 | 45827篇 |
一般工业技术 | 76569篇 |
冶金工业 | 60559篇 |
原子能技术 | 5177篇 |
自动化技术 | 51271篇 |
出版年
2021年 | 1669篇 |
2019年 | 1521篇 |
2018年 | 22348篇 |
2017年 | 21973篇 |
2016年 | 15130篇 |
2015年 | 2997篇 |
2014年 | 3565篇 |
2013年 | 11388篇 |
2012年 | 10534篇 |
2011年 | 23466篇 |
2010年 | 20547篇 |
2009年 | 18235篇 |
2008年 | 19249篇 |
2007年 | 21937篇 |
2006年 | 7490篇 |
2005年 | 11215篇 |
2004年 | 9123篇 |
2003年 | 8831篇 |
2002年 | 7428篇 |
2001年 | 6666篇 |
2000年 | 6196篇 |
1999年 | 6672篇 |
1998年 | 17299篇 |
1997年 | 12087篇 |
1996年 | 9398篇 |
1995年 | 6995篇 |
1994年 | 6177篇 |
1993年 | 5991篇 |
1992年 | 4174篇 |
1991年 | 4146篇 |
1990年 | 3698篇 |
1989年 | 3630篇 |
1988年 | 3569篇 |
1987年 | 3030篇 |
1986年 | 2934篇 |
1985年 | 3527篇 |
1984年 | 3139篇 |
1983年 | 2837篇 |
1982年 | 2617篇 |
1981年 | 2655篇 |
1980年 | 2492篇 |
1979年 | 2340篇 |
1978年 | 2293篇 |
1977年 | 2911篇 |
1976年 | 4356篇 |
1975年 | 1961篇 |
1974年 | 1856篇 |
1973年 | 1837篇 |
1972年 | 1514篇 |
1971年 | 1354篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
This concerns a patient with compression myelopathy following passive hyperextension of the cervical spine during a dental procedure. Although he had been asymptomatic prior to the procedure, subsequent cervical spinal imaging revealed advanced spondylosis and spinal stenosis. Spinal stenosis is often asymptomatic for a long time. However, when radiculomyelopathy occurs after minor trauma to the head or neck, the patient is often found to have spinal stenosis. Specifically, hyperextension of a cervical spine with spondylotic changes can lead to compression myelopathy. Acquired spinal stenosis correlates positively with aging. As the size of the elderly population continues to increase the prevalence of cervical spondylotic radiculo-myelopathy will likely increase as well. Since appropriate precautions against potential neurologic damage can be undertaken, we suggest radiographic screening for pre-existing spinal stenosis prior to a procedure requiring hyperextension of the neck. Preventive measures for individuals with asymptomatic spondylotic changes and education of all health-care professionals to avoid abrupt or prolonged hyperextension of the cervical spine is emphasized. 相似文献
992.
The contribution of chloride to the haemodynamic changes of salt-dependent deoxycorticosterone (DOC) hypertension was studied in young Wistar rats subjected to dietary loading with sodium chloride (NaCl) or sodium bicarbonate (NaHCO3). Mean arterial pressure (MAP), cardiac output, systemic resistance (TPR) and arterial rigidity (estimated from pulse pressure/stroke volume ratio, PP/SV) were determined in conscious chronically cannulated rats. DOC-induced increase of MAP and TPR appeared earlier in NaCl-loaded than in NaHCO3-loaded rats. After 4-6 weeks of hypertensive treatment MAP, TPR and PP/SV ratio were higher in DOC-treated rats fed NaCl diet than in those fed NaHCO3 diet. In contrast, after a long-term hypertensive regimen (lasting for 7-9 weeks) there was no significant difference in either MAP or TPR between rats loaded with NaCl or NaHCO3. On the other hand, DOC hypertension induced by a long-term feeding of NaHCO3 diet was not associated with an increase of arterial rigidity which was characteristic for DOC-NaCl hypertensive rats. Thus, a sufficiently long selective dietary sodium loading is capable to increase the systemic resistance but not to alter the arterial rigidity. This was also confirmed by a comparison of blood pressure-matched DOC hypertensive rats fed NaCl or NaHCO3 diets. These animals did not differ in the degree of systemic resistance elevation but the arterial rigidity was increased only in NaCl-loaded rats. 相似文献
993.
994.
H Kazunaga H Suwaki K Ameno H Kinoshita I Ijiri 《Canadian Metallurgical Quarterly》1994,29(5):429-437
We report here the comparison of urinary dolichols/creatine (D/Cr) concentration ratios in male non-drinkers, moderate-drinkers and heavy drinkers at admission and during hospitalization, and also discuss its usefulness as a biological marker for alcohol abuse. Urine samples were collected from the following four experimental groups: non-(male and female) and moderate-drinker (male) volunteers, and alcoholic heavy-drinking patients (male) at admission for psychiatric treatment and after 9-15 days hospitalization (informed consent was obtained). Urinary dolichols were determined by high performance liquid chromatography after BondElutC18 (500 mg) extraction. Due to significant differences in urinary D/Cr concentrations between male and female groups in non-drinkers and because the heavy-drinkers available for this study were exclusively male, comparison of the value of urinary D/Cr concentration ratios was subsequently limited to male only. There were no statistical differences in urinary D/Cr concentrations in the male among non-drinkers, moderate-drinkers and heavy-drinkers at admission. The accuracy of urinary D/Cr as a biological marker for alcohol abuse, calculated using the mean +/- 2 s.d. in non- and moderate-drinkers as the normal range, is only 33.3% in heavy-drinkers at admission, while their value of gamma-GTP in serum was 88.3%.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
995.
Y Tomigahara M Mori K Shiba N Isobe H Kaneko I Nakatsuka H Yamada 《Canadian Metallurgical Quarterly》1994,24(12):1205-1214
1. To examine the metabolic fate of (1RS, trans)- or (1RS, cis)-tetramethrin [3, 4, 5, 6-tetrahydrophthalimidomethyl (1RS, trans)- or (1RS, cis)-chrysanthemate], rat was administered a single oral dose of trans- or cis-[alcohol-14C]tetramethrin at dose levels of 2 or 250 mg/kg. 2. The radiocarbon was almost completely eliminated from rat within 7 days after administration in all groups. 14C-recoveries (expressed as percentages relative to the dosed 14C) in faeces and urine were 38-58 and 42-58% respectively in rat administrated trans-[alcohol-14C]tetramethrin, and in faeces and urine were 66-91 and 9-31% respectively in rat administered cis-[alcohol-14C]tetramethrin. 3. Fourteen metabolites found in excreta were purified by using several chromatographic techniques and identified by spectroanalyses (nmr and MS). Five sulphonate derivatives and three dicarboxylic acid derivatives were found. 4. The main metabolites were sulphonate derivatives in the faeces, and in the urine, alcohols, dicarboxylic acid and reduced metabolites derived from the 3,4,5,6-tetrahydrophthalimide moiety. 相似文献
996.
H Iai S Goto M Yamagata T Tamaki H Moriya K Takahashi M Mimura 《Canadian Metallurgical Quarterly》1994,19(3):272-276
Rheumatoid arthritis frequently contributes to instability of the upper cervical spine. Rotational instability of the upper cervical spine was evaluated in rheumatoid arthritis patients using biplanar x-ray photogrammetry. Three-dimensional cervical motion and the instantaneous axis of rotation of the atlas relative to the axis were evaluated in normal and rheumatoid arthritis patients during axial rotation in the horizontal plane. Anterior atlantoaxial subluxation did not increase during axial head rotation in either the atlantoaxial subluxation or the vertical subluxation groups, while the instantaneous axes of rotation were distributed posteriorly in the dens in the RA-normal group, but were widely scattered in the atlantoaxial subluxation group. 相似文献
997.
998.
Dr.-Ing. H. G. Ittstein 《Electrical Engineering (Archiv fur Elektrotechnik)》1992,75(5):311-319
Übersicht Mittels der Feldtheorie wird das Luftspaltfeld eines zweipoligen dauermagneterregten Gleichstrommotors unter Berücksichtigung des Läuferfeldes bestimmt. Das Anzugsmoment ergibt sich durch Integration der Tangentialkomponente der Maxwellschen Spannung über eine frei gewählte kreiszylindrische Luftspaltfläche, die den Läufer vollständig einschließt.Die numerische Auswertung zeigt den Einfluß des Polbedekkungswinkels und der Magnetisierungsart der betrachteten Magneterregersysteme auf das Anzugsmoment.
Influence of the kind of magnetisation and pole are extension on the starting torques in permanent magnet excited dc motors
Contents The field in the air gap of a two-pole permanent magnet excited dc motor is determined by means of field theory. The starting torque is obtained by integrating the tangential component of the Maxwell Stresses along an arbitrarily selected circular-cylindrical air gap surface which surrounds the rotor completely.The numerical evaluation shows the influence of pole arc extension and the kind of magnetisation of the considered magnetic field systems on the starting torque.相似文献
999.
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
1000.
K Saitoh N Sugae N Koike Y Akiyama Y Iwamura H Kimura 《Canadian Metallurgical Quarterly》1993,46(8):773-775
A case of BK virus cystitis in a 5 year old boy is reported. This patient, who was not immunocompromised, had had acute cystitis for two weeks. Many intracytoplasmic inclusions were observed in urinary sediment smears stained by the Papanicolaou method. Electron microscopic examination showed virus particles, presumed to be human polyomavirus, in the nuclei of the degenerated urothelial cells. A DNA sequence of the BK virus was detected in 200-300 urothelial cells in Papanicolaou stained smears by the polymerase chain reaction. BK virus is an unusual cause of symptomatic cystitis in a healthy child. 相似文献