首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1750篇
  免费   18篇
电工技术   6篇
化学工业   103篇
金属工艺   3篇
机械仪表   3篇
建筑科学   13篇
矿业工程   3篇
能源动力   16篇
轻工业   1471篇
水利工程   3篇
无线电   12篇
一般工业技术   59篇
冶金工业   48篇
原子能技术   2篇
自动化技术   26篇
  2022年   12篇
  2021年   12篇
  2020年   6篇
  2019年   8篇
  2017年   13篇
  2016年   12篇
  2015年   10篇
  2014年   16篇
  2013年   10篇
  2012年   11篇
  2011年   20篇
  2010年   13篇
  2009年   12篇
  2008年   15篇
  2007年   16篇
  2005年   6篇
  2004年   5篇
  2003年   5篇
  2001年   5篇
  1998年   15篇
  1997年   6篇
  1996年   10篇
  1993年   5篇
  1979年   8篇
  1976年   7篇
  1968年   8篇
  1924年   15篇
  1923年   10篇
  1922年   13篇
  1921年   35篇
  1920年   20篇
  1919年   33篇
  1918年   31篇
  1917年   83篇
  1916年   87篇
  1915年   47篇
  1914年   24篇
  1913年   38篇
  1912年   104篇
  1911年   103篇
  1910年   90篇
  1909年   114篇
  1908年   112篇
  1907年   112篇
  1906年   97篇
  1905年   72篇
  1904年   69篇
  1903年   47篇
  1902年   25篇
  1901年   39篇
排序方式: 共有1768条查询结果,搜索用时 15 毫秒
1.
While experimenting with the growth of metal-containing amorphous carbon (a-c:Me) thin films using two different growth processes, self-assembled multilayered structures were observed. One of the processes is a reactive magnetron sputter deposition process. The other process is a mass selective ion beam deposition process. Despite of the differences in the growth method and the growth condition, self-assembled multilayered thin films, consisting of alternating dark layer and bright layer, were obtained in both processes. Based on the consideration of energy for atomic diffusion in the thin films, the growth mechanism is discussed.  相似文献   
2.
Humoral hypercalcemia refers to the elevated blood calcium levels caused by neoplasms which release a bone resorptive substance into the circulation. Previously reported infants with malignant and benign solid tumors causing humoral hypercalcemia have presented with large abdominal masses. The case we describe, a hypercalcemic infant due to an occult parathyroid hormone-related protein-containing metanephric adenoma of the kidney, shows that radionuclide bone scanning can be a useful test to identify humoral hypercalcemia. Humoral hypercalcemia stemming from a soft tissue neoplasm should be ruled out, even in the absence of clinical signs of a tumor, if bone scans show generalized uptake in the absence of hypervitaminosis D or radiological signs of bone lesions, and serum parathyroid hormone is low.  相似文献   
3.
The effect of a cellular prion protein (PrPc) deficiency on neuroenergetics was primarily analyzed via surveying the expression of genes specifically involved in lactate/pyruvate metabolism, such as monocarboxylate transporters (MCT1, MCT2, MCT4). The aim of the present study was to elucidate a potential involvement of PrPc in the regulation of energy metabolism in different brain regions. By using quantitative real-time polymerase chain reaction (qRT-PCR), we observed a marked reduction in MCT1 mRNA expression in the cortex of symptomatic Zürich I Prnp−/− mice, as compared to their wild-type (WT) counterparts. MCT1 downregulation in the cortex was accompanied with significantly decreased expression of the MCT1 functional interplayer, the Na+/K+ ATPase α2 subunit. Conversely, the MCT1 mRNA level was significantly raised in the cerebellum of Prnp−/− vs. WT control group, without a substantial change in the Na+/K+ ATPase α2 subunit expression. To validate the observed mRNA findings, we confirmed the observed change in MCT1 mRNA expression level in the cortex at the protein level. MCT4, highly expressed in tissues that rely on glycolysis as an energy source, exhibited a significant reduction in the hippocampus of Prnp−/− vs. WT mice. The present study demonstrates that a lack of PrPc leads to altered MCT1 and MCT4 mRNA/protein expression in different brain regions of Prnp−/− vs. WT mice. Our findings provide evidence that PrPc might affect the monocarboxylate intercellular transport, which needs to be confirmed in further studies.  相似文献   
4.
(1) Background: The unusual accumulation of Na,K-ATPase complexes in the brush border membrane of choroid plexus epithelial cells have intrigued researchers for decades. However, the full range of the expressed Na,K-ATPase subunits and their relation to the microvillus cytoskeleton remains unknown. (2) Methods: RT-PCR analysis, co-immunoprecipitation, native PAGE, mass spectrometry, and differential centrifugation were combined with high-resolution immunofluorescence histochemistry, proximity ligase assays, and stimulated emission depletion (STED) microscopy on mouse choroid plexus cells or tissues in order to resolve these issues. (3) Results: The choroid plexus epithelium expresses Na,K-ATPase subunits α1, α2, β1, β2, β3, and phospholemman. The α1, α2, β1, and β2, subunits are all localized to the brush border membrane, where they appear to form a complex. The ATPase complexes may stabilize in the brush border membrane via anchoring to microvillar actin indirectly through ankyrin-3 or directly via other co-precipitated proteins. Aquaporin 1 (AQP1) may form part of the proposed multi-protein complexes in contrast to another membrane protein, the Na-K-2Cl cotransporter 1 (NKCC1). NKCC1 expression seems necessary for full brush border membrane accumulation of the Na,K-ATPase in the choroid plexus. (4) Conclusion: A multitude of Na,K-ATPase subunits form molecular complexes in the choroid plexus brush border, which may bind to the cytoskeleton by various alternative actin binding proteins.  相似文献   
5.
Social medias have changed and challenge the way we interact with each other. Social medias, such as Facebook, open up new possibilities for presentation of self and of managing the self you present to others. Is this process different for those that have grown up with social medias (The Net Generation) [Tapscott (Growing up digital: the rise of the net generation. Mcgraw-Hill, NY, 1998)] from how an older group of social media users would do it? What is their primary use of Facebook and how does this differ between generations? Such questions are discussed through engaging a group of Facebook users, with clear ideas of why and how they use Facebook, in joint reflections. The participants represent two generations of internet users; Those who was introduced to internet and social medias, such as Facebook, as adults (i.e. 40 years and older) and those who have grown up with the technology (i.e. under 25 years old, also called “The Net Generation”). The discussion indicate that there are differences in how these two groups relate to social medias, such as Facebook and for what they use Facebook. Further research is necessary to pursue those differences.  相似文献   
6.
Dawody  Jazaer  Tönnies  Inga  Fridell  Erik  Skoglundh  Magnus 《Topics in Catalysis》2007,42(1-4):183-187
Transient experiments were performed to study sulfur deactivation and regeneration of Pt/BaO/Al2O3 and Pt/SrO/Al2O3 NO x storage catalysts. It was found that the strontium-based catalysts are more easily regenerated than the barium-based catalysts and that a higher fraction of the NO x storage sites are regenerated when H2 is used in combination with CO2 compared to H2 only.  相似文献   
7.
Today technology design can no longer be understood as a design process on a green site. Design and implementation of new technology are always dependent on existing technology and the way it is used by people. In this respect Software-Engineering has also changed to the characteristics of normal technology design taking into account existing computer systems. Experiences show that the conditions and needs of such Software-Reengineering projects are highly complex and differ in their special characteristics ranging from aspects of quality of existing system documentation to organizational structures of the computer departments concerned. The Task-Artifact Cycle presented here gives a suitable reengineering approach emphasizing both analysis and design in Software-Reengineering.  相似文献   
8.
Diffusion tensor imaging is of high value in neurosurgery, providing information about the location of white matter tracts in the human brain. For their reconstruction, streamline techniques commonly referred to as fiber tracking model the underlying fiber structures and have therefore gained interest. To meet the requirements of surgical planning and to overcome the visual limitations of line representations, a new real-time visualization approach of high visual quality is introduced. For this purpose, textured triangle strips and point sprites are combined in a hybrid strategy employing GPU programming. The triangle strips follow the fiber streamlines and are textured to obtain a tube-like appearance. A vertex program is used to orient the triangle strips towards the camera. In order to avoid triangle flipping in case of fiber segments where the viewing and segment direction are parallel, a correct visual representation is achieved in these areas by chains of point sprites. As a result, a high quality visualization similar to tubes is provided allowing for interactive multimodal inspection. Overall, the presented approach is faster than existing techniques of similar visualization quality and at the same time allows for real-time rendering of dense bundles encompassing a high number of fibers, which is of high importance for diagnosis and surgical planning.  相似文献   
9.
Polymeric substrate materials like polystyrene (PS), polycarbonate (PC) or cyclic olefins (COC) are getting more attention besides silica, glass and ceramic for the preparation of reaction vessels, optical slides, microfluidic components or microtiterplates in applications like medical diagnostics and pharmaceutical drug screening. Actually, the market of transparent polymeric chips is demanding the availability of modified surfaces with well defined arrays of wettable areas or special chemical functionalities. The modified areas are starting point to graft bioactive molecules, for instance proteins or DNA‐oligomers. Another application is pretreatment of adhesive bonded joints. Presently surface modifications are performed chemically and physically by plasma surface interaction. IWS has developed a new technique for dry chemical structuring of polymeric surfaces based on the principle of excimer laser irradiation in reactive gas atmosphere. This technique is characterized by a high resolution and a negligible amount of chemicals. The procedure consists of only a few processing steps, in contrast to conventional lithographic structuring methods. Also wetting problems do not play a role as they do in printing techniques. The technology provides the possibility of tailoring the chemical and topographical surface properties from ultrahydrophobic to hydrophilic or to functionalize areas of choice in the μm range with a chemical group of defined density. Using an excimer‐laser to induce reactions, mask imaging can be applied for microstructuring the surface with new properties, e. g. for microarrays. In addition, the laser allows defined amount of energy into the elementary reaction, according to the wavelength applied, which opens the possibility of replacing atoms in the polymer molecules by other atoms or molecules taken from an agent in the environment, in a selective way. The precondition is that both the polymer and the agent absorb the same wavelength. For instance 193 nm radiation (ArF excimer laser) is absorbed by polyolefines and by ammonia allowing an exchange of H atoms for amino groups by which the surface is changed to starting point to graft bioactive molecules. Chemical microstructures for instance amino group arrays have been realized on a variety of polymeric materials like cyclic olefin foil. This array of monofunctionality is the starting point for the preparation of parallel microreactors. These samples of topographical and chemical microstructures are the first step for biochemical preparations in medical diagnostic kits, DNA‐, protein‐ or cell biochips. The upscaling of the laser modification process in a multi‐chamber reactor offers the semicontinuous functionalization of polymers in pilot scale or in batch processing. On this basis the surface modification step can be adapted into a mass production line of “Lab‐on‐a‐chip” systems.  相似文献   
10.
Maternal obesity predisposes for hepato-metabolic disorders early in life. However, the underlying mechanisms causing early onset dysfunction of the liver and metabolism remain elusive. Since obesity is associated with subacute chronic inflammation and accelerated aging, we test the hypothesis whether maternal obesity induces aging processes in the developing liver and determines thereby hepatic growth. To this end, maternal obesity was induced with high-fat diet (HFD) in C57BL/6N mice and male offspring were studied at the end of the lactation [postnatal day 21 (P21)]. Maternal obesity induced an obese body composition with metabolic inflammation and a marked hepatic growth restriction in the male offspring at P21. Proteomic and molecular analyses revealed three interrelated mechanisms that might account for the impaired hepatic growth pattern, indicating prematurely induced aging processes: (1) Increased DNA damage response (γH2AX), (2) significant upregulation of hepatocellular senescence markers (Cdnk1a, Cdkn2a); and (3) inhibition of hepatic insulin/insulin-like growth factor (IGF)-1-AKT-p38-FoxO1 signaling with an insufficient proliferative growth response. In conclusion, our murine data demonstrate that perinatal obesity induces an obese body composition in male offspring with hepatic growth restriction through a possible premature hepatic aging that is indicated by a pathologic sequence of inflammation, DNA damage, senescence, and signs of a possibly insufficient regenerative capacity.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号