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   843篇
  免费   65篇
电工技术   12篇
综合类   5篇
化学工业   247篇
金属工艺   16篇
机械仪表   5篇
建筑科学   49篇
矿业工程   2篇
能源动力   39篇
轻工业   29篇
水利工程   2篇
石油天然气   1篇
无线电   107篇
一般工业技术   156篇
冶金工业   67篇
原子能技术   1篇
自动化技术   170篇
  2024年   4篇
  2023年   34篇
  2022年   37篇
  2021年   73篇
  2020年   46篇
  2019年   26篇
  2018年   41篇
  2017年   32篇
  2016年   46篇
  2015年   30篇
  2014年   60篇
  2013年   61篇
  2012年   46篇
  2011年   62篇
  2010年   33篇
  2009年   34篇
  2008年   31篇
  2007年   31篇
  2006年   12篇
  2005年   12篇
  2004年   17篇
  2003年   8篇
  2002年   8篇
  2001年   5篇
  2000年   3篇
  1999年   7篇
  1998年   21篇
  1997年   9篇
  1996年   7篇
  1995年   4篇
  1994年   4篇
  1991年   2篇
  1990年   4篇
  1988年   2篇
  1987年   3篇
  1986年   6篇
  1985年   3篇
  1984年   3篇
  1983年   4篇
  1982年   4篇
  1981年   3篇
  1980年   3篇
  1979年   3篇
  1978年   4篇
  1976年   3篇
  1975年   3篇
  1973年   2篇
  1971年   2篇
  1925年   1篇
  1919年   1篇
排序方式: 共有908条查询结果,搜索用时 15 毫秒
51.
52.
Between 20 to 25% of Crohn’s disease (CD) patients suffer from perianal fistulas, a marker of disease severity. Seton drainage combined with anti-TNFα can result in closure of the fistula in 70 to 75% of patients. For the remaining 25% of patients there is room for in situ injection of autologous or allogenic mesenchymal stem cells such as adipose-derived stem/stromal cells (ADSCs). ADSCs exert their effects on tissues and effector cells through paracrine phenomena, including the secretome and extracellular vesicles. They display anti-inflammatory, anti-apoptotic, pro-angiogenic, proliferative, and immunomodulatory properties, and a homing within the damaged tissue. They also have immuno-evasive properties allowing a clinical allogeneic approach. Numerous clinical trials have been conducted that demonstrate a complete cure rate of anoperineal fistulas in CD ranging from 46 to 90% of cases after in situ injection of autologous or allogenic ADSCs. A pivotal phase III-controlled trial using allogenic ADSCs (Alofisel®) demonstrated that prolonged clinical and radiological remission can be obtained in nearly 60% of cases with a good safety profile. Future studies should be conducted for a better knowledge of the local effect of ADSCs as well as for a standardization in terms of the number of injections and associated procedures.  相似文献   
53.
ABSTRACT

Studies have been performed with the purpose of determining the optimal solvent composition of a Chalmers grouped actinide extraction (CHALMEX) solvent for the selective co-extraction of transuranic elements in a novel Grouped ActiNide EXtraction (GANEX) process. The solvent is composed of 6,6’-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-benzo-[1,2,4]-triazin-3-yl)-[2,2’]-bipyridine (CyMe4-BTBP) and tri-n-butyl phosphate (TBP) in phenyl trifluoromethyl sulfone (FS-13). The performance of the system has been shown to significantly depend on the ratios of the two extracting agents and the diluent to one another. Furthermore, the performance of the determined optimal solvent (10 mM CyMe4-BTBP in 30% v/v TBP and 70% v/v FS-13) on various simulated PUREX raffinate solutions was tested. It was found that the solvent extracts all transuranic elements with high efficiency and good selectivity with regard to most other elements (fission products/activation products) present in the simulated PUREX raffinate solutions. Moreover, the solvent was found to extract a significant amount of acid. Palladium, silver, and cadmium were co-extracted along with the TRU-radionuclides, which has also been observed in other similar CHALMEX systems. The extraction of plutonium and uranium was preserved for all tested simulated PUREX raffinate solutions compared to experiments using trace amounts.  相似文献   
54.
N‐4‐Fluorobut‐2‐yn‐1‐yl‐2β‐carbomethoxy‐3β‐phenyltropane (PR04.MZ) has been developed as dopamine transporter (DAT) ligand for molecular imaging. It contains a terminally fluorinated, conformationally constrained nitrogen substituent that is well suited for the introduction of fluorine‐18. The present report describes the pharmacological characterisation of [18F]PR04.MZ. The ligand shows an IC50 value of 2 nM against human DAT, whereas the IC50 value against human serotonin transporter and human noradrenalin transporter are lower (110 nM and 22 nM , respectively). Furthermore, its ex vivo organ distribution, its binding profile in the rat brain and reversibility of binding were examined. A μPET study illuminates a fast kinetic profile and specific binding to rat DAT.  相似文献   
55.
An implementation of locally adaptive penalized spline smoothing using a class of heavy-tailed shrinkage priors for the estimation of functional forms with highly varying curvature or discontinuities is presented. These priors utilize scale mixtures of normals with locally varying exponential-gamma distributed variances for the differences of the P-spline coefficients. A fully Bayesian hierarchical structure is derived with inference about the posterior being based on Markov Chain Monte Carlo techniques. Three increasingly flexible and automatic approaches are introduced to estimate the spatially varying structure of the variances. An extensive simulation study for Gaussian, Poisson, and Binomial responses shows that the performance of this approach on a number of benchmark functions is competitive to that of previous approaches. Results from applications with Gaussian and Poisson responses support the simulation results.  相似文献   
56.
The analysis of complex networks is of major interest in various fields of science. In many applications we face the challenge that the exact topology of a network is unknown but we are instead given information about distances within this network. The theoretical approaches to this problem have so far been focusing on the reconstruction of graphs from shortest path distance matrices. Often, however, movements in networks do not follow shortest paths but occur in a random fashion. In these cases an appropriate distance measure can be defined as the mean length of a random walk between two nodes — a quantity known as the mean first hitting time.In this contribution we investigate whether a graph can be reconstructed from its mean first hitting time matrix and put forward an algorithm for solving this problem. A heuristic method to reduce the computational effort is described and analyzed. In the case of trees we can even give an algorithm for reconstructing graphs from incomplete random walk distance matrices.  相似文献   
57.

Background  

Using an in vitro triple cell co-culture model consisting of human epithelial cells (16HBE14o-), monocyte-derived macrophages and dendritic cells, it was recently demonstrated that macrophages and dendritic cells create a transepithelial network between the epithelial cells to capture antigens without disrupting the epithelial tightness. The expression of the different tight junction proteins in macrophages and dendritic cells, and the formation of tight junction-like structures with epithelial cells has been demonstrated. Immunofluorescent methods combined with laser scanning microscopy and quantitative real-time polymerase chain reaction were used to investigate if exposure to diesel exhaust particles (DEP) (0.5, 5, 50, 125 μg/ml), for 24 h, can modulate the expression of the tight junction mRNA/protein of occludin, in all three cell types.  相似文献   
58.
59.
The processes of constructing meaning in digital database environments entail a paradigm shift from previous models of audio-visual communication. Media emerging from the Electro-mechanical era (film/TV/video) present fixed spatio-temporal linearity and material conditions which objectify and render passive viewer and process. The problematic aspects of cinematic communication were addressed by Latin American filmmakers of the Third Cinema movement. Their concerns and approach presaged and assisted an understanding of the radical redefinition of audio-visual communication possible with digital databases. The conceptual and aesthetic aspirations of Third Cinema artists such as Julio Garcia Espinosa and Fernando Solanas were ultimately contradictory to linear media and find their fitting medium in digital modular construction. The materiality of database expression lacks an intrinsic temporal or spatial state and permits a more dynamic and multidirectional set of power relationships between author/s, piece, viewer/s. Other important referents for contextualising database art are modern art practitioners that rejected linear representational space and fractured the centrality of authorship. The author's own work, ...two, three, many Guevaras, an exploratory database environment, embraces the redefinition of process as artistic expression, the empowerment of interacting generative forces, and serves to illustrate the revolutionary potential of the new media.  相似文献   
60.
The aim of the study was to assess the biomechanical strains on the hand-wrist system during grapevine pruning with newly designed pruning shears. Surface electromyography of the finger flexor muscle and wrist postures were analyzed in four vineyard workers during actual work with the new and reference hand-powered pruning shears. Due to the large inter-individual differences in biomechanical data observed with both pruning shears, no systematic effect of the new pruning shears on "extreme" flexion/extension (F/E) and ulnar/radial (U/R) wrist deviations was demonstrated. However, the use of the new pruning shears was associated with a higher frequency of "neutral and moderate" U/R deviations (U/R < 20%(max)) and, to a lesser extent, of "neutral and moderate" F/E deviations (F/E < 20%(max)). Due to the small sample of workers, this result must be confirmed in a larger population of vineyard workers.  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