全文获取类型
收费全文 | 1771篇 |
免费 | 123篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 15篇 |
综合类 | 4篇 |
化学工业 | 436篇 |
金属工艺 | 25篇 |
机械仪表 | 22篇 |
建筑科学 | 60篇 |
矿业工程 | 5篇 |
能源动力 | 44篇 |
轻工业 | 340篇 |
水利工程 | 7篇 |
石油天然气 | 6篇 |
无线电 | 67篇 |
一般工业技术 | 308篇 |
冶金工业 | 322篇 |
原子能技术 | 5篇 |
自动化技术 | 232篇 |
出版年
2024年 | 5篇 |
2023年 | 20篇 |
2022年 | 48篇 |
2021年 | 77篇 |
2020年 | 40篇 |
2019年 | 48篇 |
2018年 | 60篇 |
2017年 | 62篇 |
2016年 | 69篇 |
2015年 | 48篇 |
2014年 | 67篇 |
2013年 | 158篇 |
2012年 | 108篇 |
2011年 | 134篇 |
2010年 | 89篇 |
2009年 | 89篇 |
2008年 | 71篇 |
2007年 | 63篇 |
2006年 | 67篇 |
2005年 | 44篇 |
2004年 | 47篇 |
2003年 | 49篇 |
2002年 | 24篇 |
2001年 | 27篇 |
2000年 | 29篇 |
1999年 | 29篇 |
1998年 | 74篇 |
1997年 | 52篇 |
1996年 | 35篇 |
1995年 | 27篇 |
1994年 | 16篇 |
1993年 | 23篇 |
1992年 | 7篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 9篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 8篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 9篇 |
1981年 | 5篇 |
1979年 | 4篇 |
1976年 | 5篇 |
1974年 | 2篇 |
1971年 | 2篇 |
1969年 | 2篇 |
1968年 | 2篇 |
排序方式: 共有1898条查询结果,搜索用时 31 毫秒
21.
皮光远 《北京机械工业学院学报》1996,11(1):95-105
本文用近代物理学有关理论讨论了大爆炸宇宙学模型的一些主要观测事实,如哈勃定律,宇宙微波背景辐射、氦的丰度等问题,尝试对大爆炸宇宙学模型双观测事实到理论作一个初步地描述。 相似文献
22.
Esther Brown 《Information & Communications Technology Law》1995,4(1):79-94
This paper outlines the development considerations which led to the construction of a prototype “expert law tutor”. This is a system which models the competencies of the trained law teacher and is intended primarily for use as an interactive student‐directed multidimensional learning tool. The aim is to computerize those activities which might be encountered in a real‐life tutorial exercise—research, reasoning, problem solving and advising, testing, diagnosis and feedback. The paper takes a liberal view of what constitutes an expert system. The terminology expert system is retained but is defined broadly, perhaps contrary to convention, to encompass not only an advisory component or a diagnostic tool but other tutorial functions. To highlight this difference reference is made to an “expert law tutor”. It is the “expertise” of the human law tutor which is called upon. For this reason the system includes a hypertext library or information component and an multiple choice assessment component as well as a legal adviser. Providing “expert” tutor feedback is a key element in the dialogue between system and student. The prototype system was developed using (inter alia) a rule‐based expert system shell and an object‐oriented hypertext tool, and the paper comments on the features of these development tools. 相似文献
23.
The exploration of social dilemmas is being considered a major foundation for encountering the enforced necessities of cooperation in self-organizing environments. Such environments are characterized by self-interested parties and the absence of trusted third parties. Recent approaches apply evolutionary socio-inspired games to formally prove the existence and further prolongation of cooperation patterns within communities. For instance, the Prisoner’s Dilemma game has thus provided a rich opportunity to examine self-interested behaviors in pure peer-to-peer networks. However, assuming a total absence of coalitions, incentives and punishment mechanisms, several works argue against a durable maintenance of cooperation neither at single-shot nor repeated-scenarios. In this article, we formally and experimentally demonstrate a counterexample for the latter by applying evolutionary game theory and a particular instance of the Rock–Scissors–Paper game. Our framework proves that the cyclic dominance of certain type of nodes within a P2P system has an impact and introduces a strategic aspect to the evolution of the overall community. 相似文献
24.
The perovskite-type oxide PrCoO3 has been studied by means of X-ray photoelectron spectroscopy (XPS), reduction in H2 and X-ray diffraction. Two types of oxygen were detected: lattice oxygen (binding energy = 528.4 eV) and adsorbed oxygen (binding energy = 530.9 eV). The increase in relative intensity of the peak corresponding to the latter species after reduction of PrCo03 to 3e– per molecule is assigned to the formation of hydroxyl groups. Temperature-programmed reduction (TPR) results showed two reduction steps: to 1 e– per molecule (Co3.1 Co2+) at 475 to 635 K, and to 3e– per molecule (Co21 Co0) at 725 to 815 K. Reduction in the first and second steps occurs according to the contracting sphere model and the nucleation mechanism, respectively. Reduction of Co3+ to Co2+ causes minimal structural changes in the perovskite. Reduction to 3e– per molecule yielded Pr2O3 and metallic cobalt. After this reduction and reoxidation at 973 K, the perovskite structure was regained. By XPS and TPR it was shown that PrCo03 is more easily reducible than LaCo03. It is concluded that the cation in the A position of the structure plays a significant role in the bulk and surface properties of LnCo03 (Ln, lanthanide elements) oxides. 相似文献
25.
Victor Sosa J. A. Azamar-Barrios J. L. Peña L. Francisco Garfias A. I. Oliva P. Quintana 《Journal of Materials Science》1992,27(22):6131-6133
Synthesis of ceramic YBa2Cu3O7– by solid-state reaction was performed under different conditions. Different values of cooling rate and oxygen flow were used, and no significant influence on superconducting characteristics of the samples was observed. A major influence on their mechanical properties was found. 相似文献
26.
Lejla Medzikovic Hylja Heese Pieter B. van Loenen Cindy P. A. A. van Roomen Ingeborg B. Hooijkaas Vincent M. Christoffels Esther E. Creemers Carlie J. M. de Vries Vivian de Waard 《International journal of molecular sciences》2021,22(4)
Fibrosis is a hallmark of adverse cardiac remodeling, which promotes heart failure, but it is also an essential repair mechanism to prevent cardiac rupture, signifying the importance of appropriate regulation of this process. In the remodeling heart, cardiac fibroblasts (CFs) differentiate into myofibroblasts (MyoFB), which are the key mediators of the fibrotic response. Additionally, cardiomyocytes are involved by providing pro-fibrotic cues. Nuclear receptor Nur77 is known to reduce cardiac hypertrophy and associated fibrosis; however, the exact function of Nur77 in the fibrotic response is yet unknown. Here, we show that Nur77-deficient mice exhibit severe myocardial wall thinning, rupture and reduced collagen fiber density after myocardial infarction and chronic isoproterenol (ISO) infusion. Upon Nur77 knockdown in cultured rat CFs, expression of MyoFB markers and extracellular matrix proteins is reduced after stimulation with ISO or transforming growth factor–β (TGF-β). Accordingly, Nur77-depleted CFs produce less collagen and exhibit diminished proliferation and wound closure capacity. Interestingly, Nur77 knockdown in neonatal rat cardiomyocytes results in increased paracrine induction of MyoFB differentiation, which was blocked by TGF-β receptor antagonism. Taken together, Nur77-mediated regulation involves CF-intrinsic promotion of CF-to-MyoFB transition and inhibition of cardiomyocyte-driven paracrine TGF-β-mediated MyoFB differentiation. As such, Nur77 provides distinct, cell-specific regulation of cardiac fibrosis. 相似文献
27.
María del Mar Noblejas-Lpez Mariona Baliu-Piqu Cristina Nieto-Jimnez Francisco J. Cimas Esther C. Morafraile Atanasio Pandiella ngel L. Corbi Balzs Gyrffy Alberto Ocaa 《International journal of molecular sciences》2021,22(8)
Targeting the innate immune system has attracted attention with the development of anti- CD47 antibodies. Anti-CD47 antibodies block the inhibition of the phagocytic activity of macrophages caused by the up-regulation of CD47 on tumor cells. In this study, public genomic data was used to identify genes highly expressed in breast tumors with elevated CD47 expression and analyzed the association between the presence of tumor immune infiltrates and the expression of the selected genes. We found that 142 genes positively correlated with CD47, of which 83 predicted favorable and 32 detrimental relapse-free survival (RFS). From those associated with favorable RFS, we selected the genes with immunologic biological functions and defined a CD47-immune signature composed of PTPRC, HLA-E, TGFBR2, PTGER4, ETS1, and OPTN. In the basal-like and HER2+ breast cancer subtypes, the expression of the CD47-immune signature predicted favorable outcome, correlated with the presence of tumor immune infiltrates, and with gene expression signatures of T cell activation. Moreover, CD47 up-regulated genes associated with favorable survival correlated with pro-tumoral macrophages. In summary, we described a CD47-immune gene signature composed of 6 genes associated with favorable prognosis, T cell activation, and pro-tumoral macrophages in breast cancer tumors expressing high levels of CD47. 相似文献
28.
Goren Saenz-Pipaon Esther Martinez-Aguilar Josune Orbe Arantxa Gonzlez Miqueo Leopoldo Fernandez-Alonso Jose Antonio Paramo Carmen Roncal 《International journal of molecular sciences》2021,22(7)
Peripheral arterial disease (PAD) of the lower extremities is a chronic illness predominantly of atherosclerotic aetiology, associated to traditional cardiovascular (CV) risk factors. It is one of the most prevalent CV conditions worldwide in subjects >65 years, estimated to increase greatly with the aging of the population, becoming a severe socioeconomic problem in the future. The narrowing and thrombotic occlusion of the lower limb arteries impairs the walking function as the disease progresses, increasing the risk of CV events (myocardial infarction and stroke), amputation and death. Despite its poor prognosis, PAD patients are scarcely identified until the disease is advanced, highlighting the need for reliable biomarkers for PAD patient stratification, that might also contribute to define more personalized medical treatments. In this review, we will discuss the usefulness of inflammatory molecules, matrix metalloproteinases (MMPs), and cardiac damage markers, as well as novel components of the liquid biopsy, extracellular vesicles (EVs), and non-coding RNAs for lower limb PAD identification, stratification, and outcome assessment. We will also explore the potential of machine learning methods to build prediction models to refine PAD assessment. In this line, the usefulness of multimarker approaches to evaluate this complex multifactorial disease will be also discussed. 相似文献
29.
Pablo Bonilla Joaquim Hernandez Esther Giraldo Miguel A. Gonzlez-Prez Ana Alastrue-Agudo Hoda Elkhenany María J. Vicent Xavier Navarro Michael Edel Victoria Moreno-Manzano 《International journal of molecular sciences》2021,22(11)
We currently lack effective treatments for the devastating loss of neural function associated with spinal cord injury (SCI). In this study, we evaluated a combination therapy comprising human neural stem cells derived from induced pluripotent stem cells (iPSC-NSC), human mesenchymal stem cells (MSC), and a pH-responsive polyacetal–curcumin nanoconjugate (PA-C) that allows the sustained release of curcumin. In vitro analysis demonstrated that PA-C treatment protected iPSC-NSC from oxidative damage in vitro, while MSC co-culture prevented lipopolysaccharide-induced activation of nuclear factor-κB (NF-κB) in iPSC-NSC. Then, we evaluated the combination of PA-C delivery into the intrathecal space in a rat model of contusive SCI with stem cell transplantation. While we failed to observe significant improvements in locomotor function (BBB scale) in treated animals, histological analysis revealed that PA-C-treated or PA-C and iPSC-NSC + MSC-treated animals displayed significantly smaller scars, while PA-C and iPSC-NSC + MSC treatment induced the preservation of β-III Tubulin-positive axons. iPSC-NSC + MSC transplantation fostered the preservation of motoneurons and myelinated tracts, while PA-C treatment polarized microglia into an anti-inflammatory phenotype. Overall, the combination of stem cell transplantation and PA-C treatment confers higher neuroprotective effects compared to individual treatments. 相似文献
30.
Summary Three copolymers of ethylene and 1-decene, covering a wide range of compositions, have been synthesized with a MgCl2-supported Ziegler-Natta catalyst. The analysis by DSC and X-ray shows a great degree of heterogeneity in these copolymers and appreciable levels of crystallinity, corresponding to the orthorhombic lattice of polyethylene, are present even for very high 1-decene contents. 相似文献