全文获取类型
收费全文 | 59392篇 |
免费 | 7172篇 |
国内免费 | 5047篇 |
专业分类
电工技术 | 5291篇 |
综合类 | 6389篇 |
化学工业 | 7053篇 |
金属工艺 | 3950篇 |
机械仪表 | 4249篇 |
建筑科学 | 4815篇 |
矿业工程 | 2505篇 |
能源动力 | 1571篇 |
轻工业 | 6672篇 |
水利工程 | 2028篇 |
石油天然气 | 1999篇 |
武器工业 | 935篇 |
无线电 | 6194篇 |
一般工业技术 | 4614篇 |
冶金工业 | 3171篇 |
原子能技术 | 1023篇 |
自动化技术 | 9152篇 |
出版年
2024年 | 255篇 |
2023年 | 915篇 |
2022年 | 2415篇 |
2021年 | 2936篇 |
2020年 | 2102篇 |
2019年 | 1447篇 |
2018年 | 1560篇 |
2017年 | 1723篇 |
2016年 | 1530篇 |
2015年 | 2545篇 |
2014年 | 3128篇 |
2013年 | 3746篇 |
2012年 | 5017篇 |
2011年 | 4981篇 |
2010年 | 4877篇 |
2009年 | 4719篇 |
2008年 | 4921篇 |
2007年 | 4612篇 |
2006年 | 4090篇 |
2005年 | 3478篇 |
2004年 | 2502篇 |
2003年 | 1600篇 |
2002年 | 1546篇 |
2001年 | 1458篇 |
2000年 | 1218篇 |
1999年 | 437篇 |
1998年 | 462篇 |
1997年 | 279篇 |
1996年 | 214篇 |
1995年 | 98篇 |
1994年 | 104篇 |
1993年 | 114篇 |
1992年 | 46篇 |
1991年 | 60篇 |
1990年 | 54篇 |
1989年 | 52篇 |
1988年 | 36篇 |
1987年 | 29篇 |
1986年 | 29篇 |
1985年 | 17篇 |
1984年 | 12篇 |
1983年 | 14篇 |
1982年 | 15篇 |
1981年 | 12篇 |
1980年 | 31篇 |
1979年 | 15篇 |
1977年 | 38篇 |
1976年 | 97篇 |
1959年 | 8篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
81.
Interleukin-2 (IL-2) therapy often causes gastrointestinal side effects and at least 8 cases of bowel perforation have been reported. The patient reported here developed a colosplenic fistula, diagnosed by CT, with no neoplastic involvement of these organs. Awareness of these complications of IL-2 can help lead to earlier diagnosis. 相似文献
82.
Hepatitis B virus (HBV) infection is a major health problem in the United States; in 1995, approximately 128,000 cases occurred. Transmission of HBV occurs primarily by blood exchange (eg, by shared needles during injection drug use) and by sexual contact. Persons infected early in life are much more likely to become chronically infected than those infected during adulthood: as many as 90% of infants infected perinatally develop chronic infection and up to 25% will die of HBV-related chronic liver disease as adults. Clinical signs of acute hepatitis occur in about 50% of infected adults but in only 5% of infected preschool-aged children. In the United States, hepatitis B vaccine is currently made by recombinant DNA technology using baker's yeast. Preexposure vaccination results in protective antibody levels in almost all infants and children (> 95%) and healthy adults younger than 40 years of age (> 90%). The most common adverse event following administration of hepatitis B vaccine is pain at the injection site, which occurs in 13% to 29% of adult and 3% to 9% of children. A comprehensive hepatitis B vaccination policy is now recommended that includes (1) routine infant vaccination; (2) catch-up vaccination of 11- to 12-year-olds who were not previously vaccinated; (3) catch-up vaccination of young children at high risk for infection; (4) vaccination of adolescents and adults based on lifestyle or environmental, medical, and occupational situations that place them at risk; and (5) prevention of perinatal HBV infection. 相似文献
83.
84.
E Pittenauer ER Schmid G Allmaier B Pfanzagl W L?ffelhardt CQ Fernández MA de Pedro W Stanek 《Canadian Metallurgical Quarterly》1993,22(9):524-536
A strategy for the structural characterization of the four major NaBH4-reduced peptidoglycan monomers derived from muramidase-digested peptidoglycan from the cyanelles of the flagellate Cyanophora paradoxa Korschikoff is described. Initial molecular weight determination of these glycopeptides was performed by positive and negative ion plasma desorption mass spectrometry. Due to the presence of two pairs of disaccharide tripeptide and disaccharide tetrapeptide monomers differing in mass by 112 units, respectively, an as yet unknown peptidoglycan modification either at the carbohydrate or at the peptide moiety was assumed. beta-Elimination of the disaccharide unit from the unreduced peptidoglycan monomers yielded the corresponding (modified) N1-lactyltripeptides and -tetrapeptides, respectively. These peptides, N-terminally blocked with lactic acid, unambiguously showed the modification to be located on the peptide moiety. By positive ion fast atom bombardment/hybrid tandem mass spectrometry of the reduced peptidoglycan monomers as well as of the corresponding deglycosylated monomers (= N1-lactylpeptides) the modification was determined to be linked to the glutamic acid moiety. Based on combined data from plasma desorption mass spectrometry, tandem mass spectrometry, accurate mass measurement and amino acid analysis of the acid hydrolysate after derivatization with o-phthaldialdehyde by high-performance liquid chromatography we could establish the structure of the modification as N-acetylputrescine. Finally, the confirmation of the linkage of the glutamic acid to diaminopimelic acid via the gamma-COOH was based on the presence of a-type peptide backbone fragment ions in the positive ion plasma desorption mass spectra of the modified N1-lactylpeptides. 相似文献
85.
Y Ohe ER Podack KJ Olsen Y Miyahara K Miura H Saito Y Koishihara Y Ohsugi T Ohira K Nishio 《Canadian Metallurgical Quarterly》1993,67(5):939-944
HuIL-6 cDNA, cloned into a neomycin resistant conferring expression vector, BMGNeo, was transfected into Lewis Lung Carcinoma (LLC) cells. LLC cells (5 x 10(6) ml-1) transfected with IL-6 cDNA (LLC-IL6) secreted IL-6 into the culture supernatant at a concentration of 9.9 ng ml-1 within 48 h. When 1,000,000 of untransfected LLC, BMGNeo vector transfected LLC (LLC-Neo) or LLC-IL6 cells were transplanted into C57BL/6 mice subcutaneously, the mean +/- s.d. of survival times of these mice were 33.3 +/- 9.7, 34.3 +/- 7.1 and 17.0 +/- 3.1 days, respectively. The survival time of LLC-IL6 cells transplanted mice was significantly shorter than that of LLC (P < 0.01) or LLC-Neo (P < 0.01) cells transplanted mice without a measurable difference of tumour size. Plasma concentration of IL-6 steadily increased in LLC-IL6 transplanted mice. Body weight and serum albumin were significantly lower in LLC-IL6 transplanted mice than in LLC transplanted mice. Mouse IL-1 alpha and mouse TNF-alpha were not detected in the plasma of LLC-IL6 transplanted mice. These data suggested that secretion of IL-6 from LLC cells was unable to alter net tumour growth rate but rather caused a state similar to cachexia without detectable increase of IL-1 alpha and TNF-alpha in the plasma. This state may be responsible for the shortened survival of LLC-IL6 tumour-bearing mice. 相似文献
86.
施志康 《电子产品可靠性与环境试验》2002,(5):27-30
阐述了试行产中产品质量和可靠性的主要保证方法,由于这些做法来自于工厂的生产实践,所以,对承制方,订购方等各级,各类人员都有借鉴意义。同时对理论工作者也有一定的参考价值。 相似文献
87.
88.
辐射技术在食品加工中的应用 总被引:9,自引:0,他引:9
综述了食品辐射加工的原理及其作用效果,以及该技术在欧美的应用现状及存在的发展障碍。 相似文献
89.
线性时变系统的区间稳定性与鲁棒稳定性 总被引:7,自引:0,他引:7
本文应用向量比较定理研究线性时变系统的区间稳定性和具非线性时变摄动的线性时变系统的鲁棒稳定性,所得的新结果包含文献的一些主要结果作为特例,本文的研究方法说明向量比较方法是分析区间稳定性和鲁棒稳定性的一种自然而有力的工具。 相似文献
90.
提高脲醛树脂胶质量的途径 总被引:1,自引:0,他引:1
根据生产实践,论述了原料和工艺条件等对提高脲醛树脂胶质量的影响。其中原料以尿素、甲醛、各种改性剂为主,工艺条件包括反应物配比、反应温度、介质pH值、终点控制方法等。 相似文献