全文获取类型
收费全文 | 2656篇 |
免费 | 11篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 2篇 |
综合类 | 1篇 |
化学工业 | 67篇 |
金属工艺 | 8篇 |
机械仪表 | 3篇 |
建筑科学 | 7篇 |
能源动力 | 7篇 |
轻工业 | 48篇 |
无线电 | 37篇 |
一般工业技术 | 55篇 |
冶金工业 | 2395篇 |
原子能技术 | 2篇 |
自动化技术 | 38篇 |
出版年
2023年 | 4篇 |
2022年 | 4篇 |
2021年 | 14篇 |
2019年 | 7篇 |
2018年 | 7篇 |
2017年 | 5篇 |
2016年 | 9篇 |
2015年 | 6篇 |
2014年 | 5篇 |
2013年 | 13篇 |
2012年 | 16篇 |
2011年 | 26篇 |
2010年 | 15篇 |
2009年 | 10篇 |
2008年 | 14篇 |
2007年 | 8篇 |
2006年 | 12篇 |
2005年 | 14篇 |
2004年 | 8篇 |
2003年 | 11篇 |
2002年 | 8篇 |
2001年 | 7篇 |
2000年 | 3篇 |
1999年 | 90篇 |
1998年 | 747篇 |
1997年 | 459篇 |
1996年 | 285篇 |
1995年 | 166篇 |
1994年 | 117篇 |
1993年 | 165篇 |
1992年 | 23篇 |
1991年 | 18篇 |
1990年 | 26篇 |
1989年 | 20篇 |
1988年 | 15篇 |
1987年 | 18篇 |
1986年 | 23篇 |
1985年 | 16篇 |
1983年 | 11篇 |
1982年 | 12篇 |
1981年 | 12篇 |
1980年 | 22篇 |
1978年 | 6篇 |
1977年 | 53篇 |
1976年 | 119篇 |
1975年 | 2篇 |
1972年 | 3篇 |
1970年 | 4篇 |
1969年 | 2篇 |
1955年 | 4篇 |
排序方式: 共有2670条查询结果,搜索用时 15 毫秒
61.
62.
Essential role of beta-adrenergic receptor kinase 1 in cardiac development and function 总被引:1,自引:0,他引:1
63.
Age differences in processing resources seem salient to age-related declines in secondary (or "recent") memory. Community-dwelling adults (N = 90, ages 30-80) completed 4 memory tests: Wechsler Memory Scale-Revised (WMS-R) Logical Memory (LM), Cowboy Story (CS), WMS-R Visual Reproductions (VR), and Extended Complex Figure Test (ECFT; Fastenau, in press). Two space-capacity measures (WMS-R Digit Span and Visual Memory Span) and 4 processing speed measures (cancellation and mental-tracking tasks) assessed processing resources. A statistical control procedure was used to isolate retrieval efficiency and measures contributions of age and processing resources to retrieval. A negative relationship between age and retrieval efficiency emerged on all measures (p < .05). The age effect was reduced 60% on LM and CS when processing resources were controlled, eliminated for VR, and unchanged on ECFT. It is possible that visual-spatial retrieval requires fewer processing resources than does verbal retrieval. 相似文献
64.
65.
Quorum sensing in Escherichia coli, Salmonella typhimurium, and Vibrio harveyi: a new family of genes responsible for autoinducer production 总被引:1,自引:0,他引:1
In bacteria, the regulation of gene expression in response to changes in cell density is called quorum sensing. Quorum-sensing bacteria produce, release, and respond to hormone-like molecules (autoinducers) that accumulate in the external environment as the cell population grows. In the marine bacterium Vibrio harveyi two parallel quorum-sensing systems exist, and each is composed of a sensor-autoinducer pair. V. harveyi reporter strains capable of detecting only autoinducer 1 (AI-1) or autoinducer 2 (AI-2) have been constructed and used to show that many species of bacteria, including Escherichia coli MG1655, E. coli O157:H7, Salmonella typhimurium 14028, and S. typhimurium LT2 produce autoinducers similar or identical to the V. harveyi system 2 autoinducer AI-2. However, the domesticated laboratory strain E. coli DH5alpha does not produce this signal molecule. Here we report the identification and analysis of the gene responsible for AI-2 production in V. harveyi, S. typhimurium, and E. coli. The genes, which we have named luxSV.h., luxSS.t., and luxSE.c. respectively, are highly homologous to one another but not to any other identified gene. E. coli DH5alpha can be complemented to AI-2 production by the introduction of the luxS gene from V. harveyi or E. coli O157:H7. Analysis of the E. coli DH5alpha luxSE.c. gene shows that it contains a frameshift mutation resulting in premature truncation of the LuxSE.c. protein. Our results indicate that the luxS genes define a new family of autoinducer-production genes. 相似文献
66.
67.
Elisa Boschetti Leonardo Caporali Roberto DAngelo Carolina Malagelada Anna Accarino Maria Teresa Dotti Roberta Costa Giovanna Cenacchi Loris Pironi Rita Rinaldi Vincenzo Stanghellini Stefano Ratti Lucia Manzoli Valerio Carelli Roberto De Giorgio 《International journal of molecular sciences》2022,23(15)
mitochondrial neuro-gastrointestinal encephalomyopathy (MNGIE) is a rare genetic disorder characterized by thymidine phosphorylase (TP) enzyme defect. The absence of TP activity induces the imbalance of mitochondrial nucleotide pool, leading to impaired mitochondrial DNA (mtDNA) replication and depletion. Since mtDNA is required to ensure oxidative phosphorylation, metabolically active tissues may not achieve sufficient energy production. The only effective life-saving approach in MNGIE has been the permanent replacement of TP via allogeneic hematopoietic stem cell or liver transplantation. However, the follow-up of transplanted patients showed that gut tissue changes do not revert and fatal complications, such as massive gastrointestinal bleeding, can occur. The purpose of this study was to clarify whether the reintroduction of TP after transplant can recover mtDNA copy number in a normal range. Using laser capture microdissection and droplet-digital-PCR, we assessed the mtDNA copy number in each layer of full-thickness ileal samples of a naive MNGIE cohort vs. controls and in a patient pre- and post-TP replacement. The treatment led to a significant recovery of gut tissue mtDNA amount, thus showing its efficacy. Our results indicate that a timely TP replacement is needed to maximize therapeutic success before irreversible degenerative tissue changes occur in MNGIE. 相似文献
68.
Lorenzo Scalise Daniele Rinaldi Fabrizio DavìNicola Paone 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2011,654(1):122-126
Scintillating crystals are employed in high energy physics, in medical imaging, diagnostic and security. Two mechanical properties of lutetium-yttrium oxyorthosilicate cerium-doped Lu2(1−x)Y2xSiO5:Ce with x=0.1 (LYSO) crystals have been measured: the ultimate tensile stress (σUTS) and the Young elastic modulus (E). Measurements are made by means of a 4-points loading device and the experimental results account for an elastic-brittle stress-strain relation, which depends heavily on the specimen preparation and the material defects. σUTS along the [0 1 0] tensile direction ranges within 68.14 and 115.61 MPa, which, in the lowest case, is more than twice with respect to those measured for PbWO4 (PWO), exhibiting a marked difference between the annealed and the not-annealed samples. The mean elastic modulus (E), along the same direction, is E=1.80×1011 (±2.15×1010) N/m2, with lower dispersion respect to UTS data. This type of analysis and study can be included into quality control procedures of crystals, based on samples taken out of production; such procedures can be established for industrial processing of crystals aimed to the high energy physics (calorimeters) and medical imaging (PET, etc.) applications. 相似文献
69.
Anna Vallverdú-Queralt José Fernando Rinaldi de Alvarenga Ramon Estruch Rosa M. Lamuela-Raventos 《Food chemistry》2013
Sofrito is a key component of the Mediterranean diet, a diet that is strongly associated with a reduced risk of cardiovascular events. In this study, different Mediterranean sofritos were analysed for their content of polyphenols and carotenoids after a suitable work-up extraction procedure using liquid chromatography/electrospray ionisation-linear ion trap quadrupole-Orbitrap-mass spectrometry (LC/ESI-LTQ-Orbitrap-MS) and liquid chromatography/electrospray ionisation tandem triple quadrupole mass spectrometry (LC/ESI-MS-MS). In this way, 40 polyphenols (simple phenolic and hydroxycinnamoylquinic acids, and flavone, flavonol and dihydrochalcone derivatives) were identified with very good mass accuracy (<2 mDa), and confirmed by accurate mass measurements in MS and MS2 modes. The high-resolution MS analyses revealed the presence of polyphenols never previously reported in Mediterranean sofrito. The quantification levels of phenolic and carotenoid compounds led to the distinction of features among different Mediterranean sofritos according to the type of vegetables (garlic and onions) or olive oil added for their production. 相似文献
70.
Gabriel Birck Antoniox Rinaldi Ignacio Iturrioz 《Fatigue & Fracture of Engineering Materials & Structures》2019,42(12):2709-2724
The damage process in quasi‐brittle materials is characterized by the evolution of a micro‐crack field, followed by the joining of micro‐cracks, stress localization and crack instability. In network models, masses are lumped at nodal points which are interconnected by one‐dimensional elements with a bilinear constitutive relation, considering the energy consistency during the simulated process. In order to replicate the material imperfections, to render a realistic behaviour in damage localization, the model has not only random elastic and rupture properties, but also a geometric perturbation. In the present paper 2D plates with different levels of brittleness are simulated. The numerical results are presented in terms of global stress vs strain diagram, final network configuration, energy balance during the process and as geometric damage evolution. Therefore, the predictive potential of the lattice discrete element model to capture fracture processes in quasi‐brittle materials is demonstrated. 相似文献