全文获取类型
收费全文 | 31788篇 |
免费 | 1409篇 |
国内免费 | 113篇 |
专业分类
电工技术 | 429篇 |
综合类 | 232篇 |
化学工业 | 5848篇 |
金属工艺 | 703篇 |
机械仪表 | 676篇 |
建筑科学 | 1062篇 |
矿业工程 | 96篇 |
能源动力 | 1037篇 |
轻工业 | 4403篇 |
水利工程 | 271篇 |
石油天然气 | 162篇 |
武器工业 | 6篇 |
无线电 | 2421篇 |
一般工业技术 | 4611篇 |
冶金工业 | 6929篇 |
原子能技术 | 258篇 |
自动化技术 | 4166篇 |
出版年
2023年 | 168篇 |
2022年 | 555篇 |
2021年 | 860篇 |
2020年 | 587篇 |
2019年 | 679篇 |
2018年 | 784篇 |
2017年 | 853篇 |
2016年 | 822篇 |
2015年 | 628篇 |
2014年 | 948篇 |
2013年 | 1650篇 |
2012年 | 1450篇 |
2011年 | 1770篇 |
2010年 | 1308篇 |
2009年 | 1370篇 |
2008年 | 1242篇 |
2007年 | 1102篇 |
2006年 | 877篇 |
2005年 | 909篇 |
2004年 | 956篇 |
2003年 | 882篇 |
2002年 | 857篇 |
2001年 | 752篇 |
2000年 | 584篇 |
1999年 | 582篇 |
1998年 | 2207篇 |
1997年 | 1457篇 |
1996年 | 1019篇 |
1995年 | 656篇 |
1994年 | 536篇 |
1993年 | 590篇 |
1992年 | 254篇 |
1991年 | 302篇 |
1990年 | 241篇 |
1989年 | 216篇 |
1988年 | 231篇 |
1987年 | 177篇 |
1986年 | 178篇 |
1985年 | 198篇 |
1984年 | 149篇 |
1983年 | 107篇 |
1982年 | 134篇 |
1981年 | 138篇 |
1980年 | 131篇 |
1979年 | 104篇 |
1978年 | 90篇 |
1977年 | 163篇 |
1976年 | 278篇 |
1975年 | 96篇 |
1973年 | 62篇 |
排序方式: 共有10000条查询结果,搜索用时 17 毫秒
111.
112.
113.
114.
Exhaled air condensate provides a noninvasive means of obtaining samples from the lower respiratory tract. Hydrogen peroxide (H2O2) in exhaled air has been proposed as a marker of airway inflammation. We hypothesized that in stable asthmatic children the H2O2 concentration in exhaled air condensate may be elevated as a result of airway inflammation. In a cross-sectional study, 66 allergic asthmatic children (of whom, 41 were treated with inhaled steroids) and 21 healthy controls exhaled through a cold trap. The resulting condensate was examined fluorimetrically for the presence of H2O2. All subjects were clinically stable, nonsmokers, without infection. The median H2O2 level in the exhaled air condensate of the asthmatic patients was significantly higher than in healthy controls (0.60 and 0.15 micromol, respectively; p<0.05), largely because of high values in the stable asthmatic children who did not use anti-inflammatory treatment (0.8 micromol; p<0.01 compared to controls). We conclude that hydrogen peroxide is elevated in exhaled air condensate of children with stable asthma, and may reflect airway inflammation. 相似文献
115.
M Ramirez-Salomon R Soler-Bientz R de la Garza-González CM Palacios-Garza 《Canadian Metallurgical Quarterly》1997,23(9):586-587
It is important for endodontic instruments to have a low fracture rate. If a fracture does occur, it would be desirable to have the ability to bypass the broken segment and complete the root canal treatment. One hundred sixty-two root canals in 52 maxillary and mandibular first molars were cleaned and shaped with Lightspeed instruments by three endodontists in their private practices. The canals were instrumented using the technique recommended by the manufacturer. All canals were instrumented to at least a size 45 at the working length. Six instruments separated during treatment. All six had been used more times than recommended by the manufacturer. Five of the six were easily bypassed and treatment completed. 相似文献
116.
Gyrotron coaxial resonators with a longitudinally slotted inner cylinder are examined analytically using a surface impedance model, from which expressions for the electromagnetic field, ohmic quality (Q) factor, and characteristic equation of the transverse eigenvalues χ m,p are obtained. The major attributes of such resonators are expressed by the dependence of χm,p on the parameter C-defined as the ratio of the outer to inner radii of the coaxial structure. In that connection, the effect of the corrugation parameters on χm,p is particularly investigated on the basis of an expression derived for the slope function dχm,p,p/dC. It is shown that the χm,p(C) curve may either exhibit oscillatory behavior or present a flat portion over a wide range of C depending on the corrugation parameters chosen. The theory is checked against experiment in which resonant frequencies and total Q factors were measured for TE modes operating in the range of 8-16 GHz in a coaxial cavity with 40 slots. Good agreement is found in that the magnitude of the relative error in frequency is less than 0.5%. Corrugated coaxial resonators prove to be relevant to megawatt gyrotrons where highly selective cavities are required to ensure high conversion efficiency 相似文献
117.
P Fransen GP Pizzolato P Otten A Reverdin R Lagier N de Tribolet 《Canadian Metallurgical Quarterly》1997,86(6):1027-1030
A case of cystic degeneration of the transverse ligament located posteriorly to the dens and causing compression to the lower medulla and upper cervical spinal cord is reported. The clinical, pathological, and radiological findings are described and compared to the literature to characterize this syndrome more fully. The advantages of a posterolateral surgical approach are stressed. 相似文献
118.
PE Verweij A Voss JP Donnelly BE de Pauw JF Meis 《Canadian Metallurgical Quarterly》1997,35(9):2422-2423
Wooden sticks used to suspend feces obtained for surveillance cultures were found to be the source of Rhizopus microsporus var. rhizopodiformis causing a pseudo-outbreak among 17 immunocompromised patients cared for in three different wards. Nonsterile wooden products should therefore not be used for collecting, handling, and processing specimens for microbiological examination. 相似文献
119.
LA Pérula de Torres J Martínez de la Iglesia J Espejo Espejo MV Rubio Cuadrado I Enciso Berge FJ Fonseca del Pozo JM Aranda Lara 《Canadian Metallurgical Quarterly》1997,20(8):425-434
OBJECTIVE: To describe the health status of a population over 60 years and to study their relationship with several socio-demographic variables. DESIGN: A cross-sectional study, population based. SETTINGS: A community. PARTICIPANTS: A randomized sample of 1,103 non institutionalized people over 60 years living in the city of Cordoba (Spain). MEASUREMENTS AND MAIN RESULTS: By mean of a personal interview at home we used the OARS-MFAQ-VE questionnaire. Low self-rated health was associated with the age, to be female sex, a low cultural background, and a low income. Only 5.2% of the study people do not suffered any illness and 56% state that their health problems are major problems for doing their current activities. 4.9% declared to have some degree of physical incapacity. 3.7% of elderly population has an important cognitive deficit. CONCLUSIONS: The majority of elderly people has good health. Age is related with a poor health. Women have more health problems than men. 相似文献
120.
D Cullinan F Johnson AP Grollman M Eisenberg C de los Santos 《Canadian Metallurgical Quarterly》1997,36(39):11933-11943
Vinyl chloride reacts with cellular DNA producing 3,N4-etheno-2'-deoxycytidine (epsilonC) along with other exocyclic adducts. The solution structure of an oligodeoxynucleotide duplex containing an epsilonC.dG base pair was determined by high-resolution NMR spectroscopy and molecular dynamics simulations. NMR data indicated that the duplex adopts a right-handed helical structure having all residues in anti orientation around the glycosylic torsion angle. The epsilonC adduct has a sugar pucker in the C3'-endo/C4'-exo region while the rest of the residues are in the C2'-endo/C3'-exo range. NOE interactions established Watson-Crick alignments for canonical base pairs of the duplex. The imino proton of the lesion-containing base pair resonated as a sharp signal that was resistant to water exchange, suggesting hydrogen bonding. Restrained molecular dynamics simulations generated three-dimensional models in excellent agreement with the spectroscopic data. The refined structures are slightly bent at the lesion site without major perturbations of the sugar-phosphate backbone. The adduct is displaced and shifted toward the major groove of the helix while its partner on the complementary strand remains stacked. The epsilonC(anti).dG(anti) base pair alignment is sheared and stabilized by the formation of hydrogen bonds. The biological implications of structures of epsilonC-containing DNA duplexes are discussed. 相似文献