全文获取类型
收费全文 | 7338篇 |
免费 | 59篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 37篇 |
综合类 | 2篇 |
化学工业 | 464篇 |
金属工艺 | 111篇 |
机械仪表 | 57篇 |
建筑科学 | 141篇 |
矿业工程 | 8篇 |
能源动力 | 50篇 |
轻工业 | 294篇 |
水利工程 | 18篇 |
石油天然气 | 7篇 |
无线电 | 254篇 |
一般工业技术 | 405篇 |
冶金工业 | 5157篇 |
原子能技术 | 27篇 |
自动化技术 | 368篇 |
出版年
2021年 | 15篇 |
2020年 | 17篇 |
2019年 | 22篇 |
2018年 | 24篇 |
2017年 | 36篇 |
2016年 | 27篇 |
2015年 | 19篇 |
2014年 | 33篇 |
2013年 | 128篇 |
2012年 | 57篇 |
2011年 | 103篇 |
2010年 | 77篇 |
2009年 | 84篇 |
2008年 | 103篇 |
2007年 | 101篇 |
2006年 | 88篇 |
2005年 | 98篇 |
2004年 | 77篇 |
2003年 | 78篇 |
2002年 | 86篇 |
2001年 | 60篇 |
2000年 | 62篇 |
1999年 | 215篇 |
1998年 | 1467篇 |
1997年 | 903篇 |
1996年 | 585篇 |
1995年 | 317篇 |
1994年 | 328篇 |
1993年 | 317篇 |
1992年 | 73篇 |
1991年 | 90篇 |
1990年 | 90篇 |
1989年 | 93篇 |
1988年 | 79篇 |
1987年 | 87篇 |
1986年 | 103篇 |
1985年 | 108篇 |
1984年 | 67篇 |
1983年 | 53篇 |
1982年 | 52篇 |
1981年 | 70篇 |
1980年 | 79篇 |
1979年 | 35篇 |
1978年 | 41篇 |
1977年 | 159篇 |
1976年 | 335篇 |
1975年 | 33篇 |
1974年 | 26篇 |
1973年 | 18篇 |
1972年 | 21篇 |
排序方式: 共有7400条查询结果,搜索用时 15 毫秒
1.
The aim of this study was to assess the association between the length of maternity leave and the quality of mother-infant interactions; 198 employed mothers of 4-month-old infants were interviewed and videotaped in their homes during a feeding time. Hierarchical multiple regression analyses indicated a direct association between shorter length of leave and more negative affect and behavior in maternal interactions with their infants. Infant and mother stressor/protective variables added significantly in predicting the quality of the mother-infant relationship. There were also significant interaction effects between the length of leave and these variables. Mothers who either reported more depressive symptoms or who perceived their infant as having a more difficult temperament and who had shorter leaves, compared with mothers who had longer leaves, were observed to express less positive affect, sensitivity, and responsiveness in interactions with their infants. The public policy implications of the relation between length of maternity leave, maternal and infant individual differences, and the quality of mother-infant interactions are discussed. 相似文献
2.
JF Favarel-Garrigues F Sztark ME Petitjean M Thico?pé P Lassié P Dabadie 《Canadian Metallurgical Quarterly》1996,82(2):312-316
Protective immunity against infection with Mycobacterium tuberculosis is imparted by T cells rather than antibodies, but B cells can play a role as antigen-presenting cells and in granuloma formation. We re-evaluated the role of B cells in the course of tuberculous infection in mu-chain knock-out (Ig-) mice. Surprisingly, the organs of M. tuberculosis-infected Ig- mice were found to have three- to eight-fold elevated counts of viable bacilli compared with normal littermates at 3-6 weeks post-infection. Splenic interferon-gamma responses to whole antigen were unimpaired, whilst proliferation to certain mycobacterial peptides was found to be diminished. However, bacille Calmette-Guérin (BCG) vaccination significantly reduced the infection in Ig- mice. The mechanisms by which B cells can influence primary tuberculous infection need further study. 相似文献
3.
SG Rijpkema RG Herbes N Verbeek-De Kruif JF Schellekens 《Canadian Metallurgical Quarterly》1996,117(3):563-566
Epiglottic disruption is an uncommon injury usually associated with significant supraglottic trauma. This injury may be overlooked because of the difficulty in examining the larynx or other associated severe injuries. We present two cases of clinically unsuspected epiglottic disruption that were first seen on MR images of the neck. 相似文献
4.
JA van Dorst CJ van Heusden JM Tikkanen JP Kamerling JF Vliegenthart 《Canadian Metallurgical Quarterly》1997,297(3):209-227
Seven analogues of the trisaccharide beta-D-Galp-(1-->4)-beta-D-GlcpNAc-(1-->2)-alpha-D-Manp-(1-->O)(CH 2)7CH3 have been synthesized as potential substrates for glycosyltransferases involved in the chain-termination of N-acetyllactosamine-type N-glycans. These compounds include: 3-O-methyl-beta-D-Galp-(1-->4)-beta-D-GlcpNAc-(1-->2)-alpha-D-Manp -(1-->O) (CH2)7CH3, 3-deoxy-beta-D-Galp-(1-->4)-beta-D-GlcpNAc-(1-->2)-alpha-D-Manp-(1 -->O) (CH2)7CH3, 3-deoxy-3-fluoro-beta-D-Galp-(1-->4)-beta-D-GlcpNAc-(1-->2)-alpha-D-M anp- (1-->O)(CH2)7Ch3, 3-amino-3-deoxy-beta-D-Galp-(1-->4)-beta-D-GlcpNAc-(1-->2)-alpha-D-Ma np- (1-->O)(CH2)7CH3, beta-D-Gulp-(1-->4)-beta-D-GlcpNAc-(1-->2)-alpha-D-Manp-(1-- >O)(CH2)7CH3, beta-L-Galp-(1-->4)-beta-D-GlcpNAc-(1-->2)-alpha-D-Manp-(1-->O)(CH 2)7CH3, and alpha-L-Altp-(1-->4)-beta-D-GlcpNAc-(1-->2)-alpha-D-Manp-(1- ->O) (CH2)7CH3. All trisaccharides were obtained by condensation of suitably modified glycosyl donors based on imidates or thioglycosides with the same disaccharide acceptor, octyl 3,4,6-tri-O-benzyl-2-O-(3,6-di-O-benzyl-2-deoxy-2-phthalimido-beta-D- glucopyranosyl)-alpha-D-mannopyranoside, followed by deprotection. 相似文献
5.
N Delanty MP Reilly D Pratico JA Lawson JF McCarthy AE Wood ST Ohnishi DJ Fitzgerald GA FitzGerald 《Canadian Metallurgical Quarterly》1997,95(11):2492-2499
BACKGROUND: Myocardial reperfusion is believed to be associated with free radical injury. However, indexes of oxidative stress in vivo have been limited by their poor specificity and sensitivity. Isoprostanes are stable products of arachidonic acid formed in a nonenzymatic, free radical-catalyzed manner. We have developed a sensitive and specific assay for one of these compounds, 8-epi prostaglandin (PG) F2 alpha. METHODS AND RESULTS: To address its utility as an index of oxidative stress during coronary reperfusion, we measured urinary levels by gas chromatography/mass spectrometry in a canine model of coronary thrombolysis, in patients with acute myocardial infarction treated with thrombolytic therapy, and in patients after elective coronary artery bypass surgery. Urinary 8-epi PGF2 alpha was unchanged after circumflex artery occlusion in a canine model of coronary thrombolysis (n = 13; 437.2 +/- 56.4 versus 432.7 +/- 55.2 pmol/mmol creatinine) but increased significantly (P < .05) immediately after reperfusion (553.8 +/- 64.7 pmol/mmol). Urinary levels were increased (P < .001) in patients (n = 12) with acute myocardial infarction given lytic therapy (265.8 +/- 40.8 pmol/mmol) compared with age-matched control subjects (n = 20; 91.5 +/- 11.8 pmol/mmol) and patients with stable coronary disease (n = 20; 95.7 +/- 6.3 pmol/mmol). Preoperative levels rose from 113.2 +/- 11.8 to 248.2 +/- 86.3 pmol/mmol at 30 minutes into revascularization to 332.2 +/- 82.6 pmol/mmol by 15 minutes after global myocardial reperfusion (P < .05) and dropped to 181.2 +/- 50.4 pmol/mmol at 30 minutes and 120.2 +/- 9.9 pmol/mmol at 24 hours after bypass surgery (n = 5). Corresponding changes in spin adduct formation, found with electron paramagnetic resonance, were noted in 2 patients. CONCLUSIONS: These data support the hypothesis that free radical generation occurs during myocardial reperfusion. Measurement of isoprostane production may serve as a noninvasive index of oxidative stress. 相似文献
6.
BS Kendrick BS Chang T Arakawa B Peterson TW Randolph MC Manning JF Carpenter 《Canadian Metallurgical Quarterly》1997,94(22):11917-11922
Understanding the mechanism for sucrose-induced protein stabilization is important in many diverse fields, ranging from biochemistry and environmental physiology to pharmaceutical science. Timasheff and Lee [Lee, J. C. & Timasheff, S. N. (1981) J. Biol. Chem. 256, 7193-7201] have established that thermodynamic stabilization of proteins by sucrose is due to preferential exclusion of the sugar from the protein's surface, which increases protein chemical potential. The current study measures the preferential exclusion of 1 M sucrose from a protein drug, recombinant interleukin 1 receptor antagonist (rhIL-1ra). It is proposed that the degree of preferential exclusion and increase in chemical potential are directly proportional to the protein surface area and that, hence, the system will favor the protein state with the smallest surface area. This mechanism explains the observed sucrose-induced restriction of rhIL-1ra conformational fluctuations, which were studied by hydrogen-deuterium exchange and cysteine reactivity measurements. Furthermore, infrared spectroscopy of rhlL-1ra suggested that a more ordered native conformation is induced by sucrose. Electron paramagnetic resonance spectroscopy demonstrated that in the presence of sucrose, spin-labeled cysteine 116 becomes more buried in the protein's interior and that the hydrodynamic diameter of the protein is reduced. The preferential exclusion of sucrose from the protein and the resulting shift in the equilibrium between protein states toward the most compact conformation account for sucrose-induced effects on rhIL-1ra. 相似文献
7.
8.
9.
10.