全文获取类型
收费全文 | 4811篇 |
免费 | 334篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 55篇 |
综合类 | 3篇 |
化学工业 | 1049篇 |
金属工艺 | 93篇 |
机械仪表 | 131篇 |
建筑科学 | 116篇 |
矿业工程 | 6篇 |
能源动力 | 166篇 |
轻工业 | 896篇 |
水利工程 | 24篇 |
石油天然气 | 30篇 |
无线电 | 168篇 |
一般工业技术 | 572篇 |
冶金工业 | 1326篇 |
原子能技术 | 27篇 |
自动化技术 | 489篇 |
出版年
2024年 | 22篇 |
2023年 | 43篇 |
2022年 | 149篇 |
2021年 | 189篇 |
2020年 | 131篇 |
2019年 | 169篇 |
2018年 | 190篇 |
2017年 | 185篇 |
2016年 | 183篇 |
2015年 | 114篇 |
2014年 | 166篇 |
2013年 | 323篇 |
2012年 | 265篇 |
2011年 | 256篇 |
2010年 | 215篇 |
2009年 | 240篇 |
2008年 | 173篇 |
2007年 | 142篇 |
2006年 | 113篇 |
2005年 | 79篇 |
2004年 | 67篇 |
2003年 | 62篇 |
2002年 | 61篇 |
2001年 | 46篇 |
2000年 | 36篇 |
1999年 | 61篇 |
1998年 | 394篇 |
1997年 | 263篇 |
1996年 | 180篇 |
1995年 | 111篇 |
1994年 | 82篇 |
1993年 | 80篇 |
1992年 | 25篇 |
1991年 | 33篇 |
1990年 | 22篇 |
1989年 | 30篇 |
1988年 | 27篇 |
1987年 | 22篇 |
1986年 | 18篇 |
1985年 | 16篇 |
1984年 | 5篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 13篇 |
1980年 | 11篇 |
1978年 | 14篇 |
1977年 | 31篇 |
1976年 | 65篇 |
1975年 | 4篇 |
1972年 | 4篇 |
排序方式: 共有5151条查询结果,搜索用时 17 毫秒
61.
MB Iarustovski? RG Grigor'iants VS Timokhov MV Abramian IL Mikha?lova SS Volkova IaV Banketov II Golenishchev II Iakovleva 《Canadian Metallurgical Quarterly》1997,(6):40-46
The efficacy of continuous methods of renal substitute therapy (RST) in patients with multiple organ failure is assessed. The patients were divided in 2 groups administered different types of PST. Group 1 were 16 patients subjected to RST by peritoneal dialysis, in group 2 (n = 16) GP and/or GDP were used. Hemodynamics, hematological and biochemical values, and clearance of inflammation mediators were monitored and hemohydrobalance and complications of therapy assessed in the course of RST. Both RST methods proved to be highly effective. The possibility of differentiated use of peritoneal dialysis and GP/GDP permits an individual approach to treatment, and equally high efficacy of both methods solves the problem of treating total renal insufficiency in the majority of patients with multiple organ failure following cardiovascular surgery. 相似文献
62.
The functional significance of the developmental transition from slow skeletal troponin I (ssTnI) to cardiac TnI (cTnI) isoform expression in cardiac myocytes remains unclear. We show here the effects of adenovirus-mediated ssTnI gene transfer on myofilament structure and function in adult cardiac myocytes in primary culture. Gene transfer resulted in the rapid, uniform, and nearly complete replacement of endogenous cTnI with the ssTnI isoform with no detected changes in sarcomeric ultrastructure, or in the isoforms and stoichiometry of other myofilament proteins compared with control myocytes over 7 days in primary culture. In functional studies on permeabilized single cardiac myocytes, the threshold for Ca2+-activated contraction was significantly lowered in adult cardiac myocytes expressing ssTnI relative to control values. The tension-Ca2+ relationship was unchanged from controls in primary cultures of cardiac myocytes treated with adenovirus containing the adult cardiac troponin T (TnT) or cTnI cDNAs. These results indicate that changes in Ca2+ activation of tension in ssTnI-expressing cardiac myocytes were isoform-specific, and not due to nonspecific functional changes resulting from overexpression of a myofilament protein. Further, Ca2+-activated tension development was enhanced in cardiac myocytes expressing ssTnI compared with control values under conditions mimicking the acidosis found during myocardial ischemia. These results show that ssTnI enhances contractile sensitivity to Ca2+ activation under physiological and acidic pH conditions in adult rat cardiac myocytes, and demonstrate the utility of adenovirus vectors for rapid and efficient genetic modification of the cardiac myofilament for structure/function studies in cardiac myocytes. 相似文献
63.
The Fas receptor is a member of a family of cell death receptors, including tumor necrosis factor receptor I (TNFR I), death receptor 3 and 4 (DR3 and DR4), and cytopathic avian receptor 1 (CAR1). The Fas receptor is composed of several discrete domains, including three cysteine-rich domains (CRDs), a transmembrane domain, and an intracellular domain responsible for transmitting an apoptotic signal. While the mechanism of Fas-mediated cell death has become elucidated, the requirements for Fas ligand binding to the receptor have not been fully defined. Using a series of chimeric Fc-receptor fusion proteins between the human Fas receptor and TNFR I, each cysteine-rich domain of Fas was found to be required for interaction with the Fas ligand. Interestingly, TNFR I CRD1 could partially substitute for the Fas CRD1. The importance of this domain was underscored by the analysis of a Fas extracellular mutation (C66R), which resulted in a complete loss of ligand binding. This mutation was cloned from a human patient suffering from Canale-Smith syndrome, which is characterized by autoimmunity resembling that observed in the lpr and lprcg mice. The localization of essential ligand binding domains in the Fas receptor correlated exactly with the ability of the Fas receptor fusion proteins to prevent cell death mediated by the Fas ligand. 相似文献
64.
65.
Pursuing optimal solutions for large scale transmission network planning problems is a formidable task due to their combinatorial nature and also due to the nonconvexities involved. Successful approaches using hierarchical Benders decomposition incur in a high computational cost mainly due to the need to solve a large integer program (the investment sub-problem) for every Benders iteration. In this work the authors propose to use heuristics within the decomposition framework, therefore avoiding to solve to optimality each integer sub-problem. The global computational effort is substantially reduced, and allows coping with large problems that would be intractable using classical combinatorial techniques. Case studies with the 6 bus Garver test system and a reduced Southeastern Brazilian power network are presented and discussed 相似文献
66.
Taking into consideration a study published 10 years ago on sexual disturbances of students at the University of S?o Paulo, the importance of the subject is discussed, along with the creation in 1993 of the Sexuality Project at the university hospital of the University of S?o Paulo School of Medicine. In its first year, this multidisciplinary project attended 140 patients with sexual dysfunctions (associated or not to other clinical manifestations); the majority were younger than 60 years-old, and 80 percent were male. 相似文献
67.
Chestnuts were dehydrated by using a combined method of osmotic dehydration followed by air drying. Samples were osmotically pretreated with sucrose (60% w/w) and glucose (56% w/w) for 8 h, air-dried at temperatures of 45, 55, and 65°C, at a relative humidity of 30% and at a velocity of 2.7 m·s-1 and the experimental data of the drying kinetics were obtained. Whole samples were dried with different peelings: (a) removal of endocarp and pericarp (peeled) and (b) additionally the internal rough surface (cut). In all cases, cut chestnuts show greater drying rates than peeled samples, indicating that a significant mass transfer resistance in the layer nearest to the surface takes place. Peeled samples pretreated with sucrose solutions behave in a similar way to untreated samples. For the rest of the samples, the cut samples osmotically treated with sucrose solutions and all the samples treated with the glucose solution, the drying rates decrease during drying. Drying kinetics are successfully modeled by employing a diffusional model that takes the shrinkage into account. The effective coefficient of water diffusion was evaluated and correlated with temperature. The quality of the final product was monitored by color change. In spite of the fact that the total color difference is not modified by the osmotic treatment, the L*, a*, and b* color coordinates of cut samples treated with sucrose and glucose solutions do undergo changes; the L* and a* coordinates change less than the b*. 相似文献
68.
Subalpine fir (Abies lasiocarpa Hook) lumber containing wetpockets (wetwood) was used for the measurements of gas permeability and the results were then compared to the gas permeability of normal wood, which was free of the wetpockets. The impacts of pretreatment methods were also investigated, including steaming at green condition, steaming at fiber saturation point (FSP), microwave treatment, and radio-frequency treatment. Results from this study demonstrated that both the transverse and the longitudinal gas permeability of subalpine fir wetwood are greater than that of normal wood. There is no significant change in the permeability after 4-h steaming pretreatment at green condition and at FSP. The impacts of microwave and radio-frequency pretreatments were not significant, but the findings cannot be generalized because they may depend on the power intensity applied. 相似文献
69.
Presynaptic paired-pulse facilitation (PPF) rate decreased in most CA1 pyramidal neurones following the long-term potantiation (LTP) induction. The decrease correlated with the LTP magnitude as well as with the initial (pretetanic) PPF rate. The data obtained suggests an involvement of presynaptic mechanisms in maintaining the early and the delayed LTPs. 相似文献
70.
Cerebellar granule cells isolated from postnatal day 7 mice, and cultured in minimal medium containing only insulin-like growth factor-I (IGF-I), both survive and differentiate. This differentiation is marked by neurite growth and expression of genes associated with terminal differentiation, the myocyte-specific enhancer factor 2A (MEF2A) and the alpha 6 subunit of the gamma-aminobutyric acidA receptor (GABAA alpha 6). Percoll gradient purified granule cells maintained without IGF-I, in minimal medium alone or in medium containing the antioxidant N-acetylcysteine (NAC), also express MEF2A and GABAA alpha 6. Thus, cultured granule neurons can differentiate to some extent cell-autonomously and IGF-I may not be a critical factor for this process. 相似文献