全文获取类型
收费全文 | 4949篇 |
免费 | 18篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 12篇 |
化学工业 | 165篇 |
金属工艺 | 30篇 |
机械仪表 | 32篇 |
建筑科学 | 23篇 |
矿业工程 | 2篇 |
能源动力 | 15篇 |
轻工业 | 92篇 |
水利工程 | 4篇 |
石油天然气 | 6篇 |
无线电 | 71篇 |
一般工业技术 | 113篇 |
冶金工业 | 4271篇 |
原子能技术 | 10篇 |
自动化技术 | 123篇 |
出版年
2022年 | 8篇 |
2021年 | 10篇 |
2018年 | 7篇 |
2017年 | 8篇 |
2016年 | 17篇 |
2015年 | 10篇 |
2014年 | 18篇 |
2013年 | 37篇 |
2012年 | 25篇 |
2011年 | 21篇 |
2010年 | 30篇 |
2009年 | 20篇 |
2008年 | 39篇 |
2007年 | 33篇 |
2006年 | 27篇 |
2005年 | 25篇 |
2004年 | 38篇 |
2003年 | 36篇 |
2002年 | 22篇 |
2001年 | 33篇 |
2000年 | 21篇 |
1999年 | 141篇 |
1998年 | 1241篇 |
1997年 | 761篇 |
1996年 | 497篇 |
1995年 | 253篇 |
1994年 | 243篇 |
1993年 | 245篇 |
1992年 | 47篇 |
1991年 | 61篇 |
1990年 | 49篇 |
1989年 | 61篇 |
1988年 | 45篇 |
1987年 | 60篇 |
1986年 | 68篇 |
1985年 | 48篇 |
1984年 | 11篇 |
1983年 | 22篇 |
1982年 | 27篇 |
1981年 | 30篇 |
1980年 | 62篇 |
1979年 | 11篇 |
1978年 | 20篇 |
1977年 | 122篇 |
1976年 | 278篇 |
1975年 | 15篇 |
1974年 | 7篇 |
1973年 | 5篇 |
1969年 | 5篇 |
1955年 | 5篇 |
排序方式: 共有4969条查询结果,搜索用时 0 毫秒
71.
Following a survey in 19 European countries of the habits, attitudes and knowledge of medical students regarding tobacco, World Health Organisation European Office and the International Union against Tuberculosis and Lung Disease jointly circulated to the Deans of all European medical schools a summary of the results, including figures for mortality for smoking-related diseases in their countries and a brief questionnaire concerning faculty action on the tobacco problem. The response rate was just over 50%, higher in Northern Europe (66%) than in Southern (35%) or Eastern (38%). Only 8% of faculties had a specific teaching module on tobacco. In most it was either systematically (35%) or unsystematically (55%) integrated in other teaching. Teaching hospitals, teaching areas and faculty meetings were said to be smokefree by over 90%; figures were lower for other areas. Seventy-seven per cent of Deans intended to discuss our approach with their teaching staff; 72% gave the name of a staff member with a particular tobacco interest. 相似文献
72.
The in vitro activities of the N,N-dimethylglycyl-amino derivative of minocycline (DMG-MINO) and 6-dimethyl-6-dexoxytetracycline (DMG-DMDOT), members of a new generation of tetracyclines, were evaluated by an agar dilution method and were compared with those of tetracycline and minocycline against 224 tetracycline-resistant and 73 tetracycline-susceptible recent clinical isolates of gram-positive cocci, including multiple-antibiotic-resistant methicillin-resistant Staphylococcus aureus and penicillin-resistant Streptococcus pneumoniae. The MICs of DMG-MINO and DMG-DMDOT were up to 500- to 2,000-fold lower than those of tetracycline against methicillin-resistant S. aureus and Streptococcus pneumoniae (MIC for 50% of strains tested [MIC50], < 0.06 microgram/ml). Against Streptococcus groups A, B, C, and G and Enterococcus faecalis, the MIC50 was 0.5 microgram/ml. MIC50s were greater only for coagulase-negative staphylococci (2 micrograms/ml). These data indicate that DMG-MINO and DMG-DMDOT are very potent drugs, and further in vitro and in vivo studies are warranted. 相似文献
73.
JF McCarthy DJ Cook MG Massad Y Sano KJ O''Malley NR Ratliff RW Stewart NG Smedira RC Starling JB Young PM McCarthy 《Canadian Metallurgical Quarterly》1998,14(2):197-200
28 isolates of canine parvovirus type-2 (CPV-2) were obtained from dogs with hemorrhagic gastroenteritis in Italy. The antigenic structure of CPV-2 isolates was characterized, using four discriminating monoclonal antibodies. In addition, four vaccinal strains were examined. Similar to reports from Australia and the United Kingdom, a much higher prevalence of CPV-2a (25/28 isolates) was observed than the other variant type, CPV-2b (3/28 isolates). DNA fragments (2.2 kbp) of representative strains of CPV-2, CPV-2a and CPV-2b were amplified by the polymerase chain reaction (PCR) and the products were digested by the restriction enzymes (RE) RsaI, HpaII, HindIII and PvuII. The RvaI enzyme allows the differentiation of CPV-2 from CPV-2a and CPV-2b. 相似文献
74.
JY Scoazec JF Flejou A D'Errico M Fiorentino A Zamparelli AF Bringuier G Feldmann WF Grigioni 《Canadian Metallurgical Quarterly》1996,24(5):1128-1136
We have analyzed the composition of the tumor stroma and the expression of cell-matrix and cell-cell adhesion molecules in 11 cases of fibrolamellar carcinoma of the liver (FLC), in comparison with 34 cases of hepatocellular carcinoma and 8 cases of focal nodular hyperplasia. Fibrolamellar carcinoma was characterized by the presence of large amounts of tenascin in tumor stroma and by the scarce expression of basement membrane components at the contact of neoplastic clusters. Like normal hepatocytes, neoplastic cells constantly expressed the alpha1 integrin chain, lacked the beta4 integrin chain, and coexpressed E-cadherin and the hepatocyte N-related cadherin. Abnormalities in the expression of cell adhesion molecules, including altered cadherin expression, alphaV integrin chain induction, and CD44 expression, were detected in the majority of cases. The composition of the tumor stroma and the pattern of expression of cell adhesion molecules in fibrolamellar carcinoma were reminiscent of those observed in grade III and grade IV hepatocellular carcinomas. Our results therefore show that, despite its slow local growth and good prognosis, fibrolamellar carcinoma expresses many characteristics usually associated with clinically aggressive malignancies. Further studies are needed to identify the factors responsible for the apparent dissociation between clinical behavior and biological characteristics in this tumor. 相似文献
75.
76.
77.
78.
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
79.
80.
Understanding information sharing is an important challenge to modern organizations, and is likely to be increasingly considered when IT investment decisions are made world-wide. Our research study investigated the influence of cultural factors on information sharing in China. It was postulated that social network structures such as guanxi, Confucian dynamism, and collectivism could explain the degree to which information sharing took place between people in China. It was found that guanxi, Confucian dynamism, and collectivism all had a significant influence on information sharing. 相似文献