首页 | 官方网站   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   3118篇
  免费   194篇
  国内免费   10篇
工业技术   3322篇
  2023年   34篇
  2022年   32篇
  2021年   165篇
  2020年   90篇
  2019年   95篇
  2018年   109篇
  2017年   113篇
  2016年   130篇
  2015年   90篇
  2014年   141篇
  2013年   256篇
  2012年   211篇
  2011年   221篇
  2010年   152篇
  2009年   145篇
  2008年   166篇
  2007年   143篇
  2006年   119篇
  2005年   100篇
  2004年   89篇
  2003年   88篇
  2002年   75篇
  2001年   50篇
  2000年   26篇
  1999年   35篇
  1998年   37篇
  1997年   31篇
  1996年   30篇
  1995年   34篇
  1994年   25篇
  1993年   29篇
  1992年   17篇
  1991年   17篇
  1990年   15篇
  1989年   17篇
  1988年   15篇
  1987年   21篇
  1986年   13篇
  1985年   8篇
  1984年   12篇
  1983年   13篇
  1982年   12篇
  1981年   11篇
  1980年   10篇
  1979年   15篇
  1978年   9篇
  1977年   6篇
  1975年   5篇
  1974年   11篇
  1973年   9篇
排序方式: 共有3322条查询结果,搜索用时 15 毫秒
991.
This work describes the influence of aloe vera gel on Pluronic F127 triblock copolymer (F127) micellization behavior. Aloe vera gel was obtained from aloe vera mucilage found in leaf pulp. F127 (20% w/w) gel and the aloe vera/F127 blend gel were obtained by using the cold method. Fourier transform infrared spectroscopy and X‐ray diffraction analyses of lyophilized samples did not show any important copolymer interaction between aloe vera gel and F127. However, in aqueous medium, the dynamic light scattering data showed that there was an important reduction in micelle size with increasing temperature of the aloe vera/F127 blend hydrogel. The differential scanning calorimetry results indicate that the aloe vera/F127 blend has a higher micellization temperature, affected by the lower dehydrating effect of the poly(propylene oxide) blocks during the micelle formation in comparison to F127 gel. The texture analyses (hardness and adhesiveness) showed that the addition of aloe vera gel did not change the Pluronic F127 gel texture properties. The photosensitizer zinc phthalocyanine (ZnPC) was incorporated into the aloe vera/F127 blend, and the results suggest that this formulation is suitable as a ZnPC delivery system for photodynamic therapy. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46191.  相似文献   
992.
Tuan Le  Mario Gerla 《电信纪事》2018,73(9-10):549-558
Delay-tolerant networks (DTNs) are sparse mobile ad hoc networks, in which there is typically no complete path between the source and destination. Anycast is an important group communication paradigm for numerous DTN applications such as resource discovery and information exchange in emergency or crisis situations. Unlike unicast and multicast, which have been studied extensively in DTNs, few prior works have addressed the DTN anycast routing problem. Furthermore, they often ignore the time constraint and assume long contact durations in formulating the relay selection strategy. In this paper, we study a single-copy time-constrained anycast (TCA) routing under short contact duration. We address two key issues: (1) to which next hop relay node should messages be forwarded and (2) in which order should messages be forwarded. To reduce the transmission cost, we select relay nodes from both current and past contacts based on the one-hop and two-hop delivery probabilities, respectively. We derive the delivery probability from the distribution of inter-contact time and contact duration time. We address the case of exponential and Pareto distribution, which are the most popular assumptions in literature. For the message scheduling, messages with the highest delivery probability are prioritized to be transmitted first. Extensive simulation results based on Cabspotting and MIT Reality traces show that our scheme can achieve up to 29% higher delivery rate, 24% lower delay, and 36% lower transmission cost compared to other anycast routing strategies.  相似文献   
993.
The El Plomo mummy was a pre‐Columbian Incan child who was found mummified in the Andes Mountains above an altitude of 17,700 feet. In the environment, natural mummification occurred due to low temperatures and strong winds. Dating measurements (relative dating) by experts from the National Museum of Natural History of Chile established that the mummified body corresponds the Inca period (1,450 to 1,500 AD). In 2003, the body was transferred to the University of Chile Medical School for exhaustive medical examination. Tissue samples from the right quadriceps muscle were extracted and fixed in glutaraldehyde and postfixed in osmium tetroxide to obtain ultrathin sections to be observed by transmission electron microscope. Images were recorded on photographic paper, digitalized and analyzed by experts on morphology. Results showed a preservation of cell boundaries in striated muscle cells, but specific subcellular organelles or contractile sarcomeric units (actin and myosin) were unable to be recognized. However, the classical ultrastructural morphology of the polypeptide collagen type I was preserved intact both in primary and secondary organization. Therefore, we concluded that the process of natural mummification by freezing and strong winds is capable of damaging the ultrastructure of muscle cells and preserving collagen type I intact.  相似文献   
994.
提出了一种混合式的路由协议AODV-DFR,它不仅具有先验式及反应式路由协议的特点,而且还融入了某些具有地理位置辅助的路由协议的特性。在路由失败的情况下,AODV-DFR能在断点立刻进行方向转发,快速找到合适的下一跳节点,建立新的路由。大量的仿真实验证明AODV-DFR路由协议对网络性能有较大的提高。  相似文献   
995.
The interaction and crosstalk of Toll-like receptors (TLRs) is an established pathway in which the innate immune system recognises and fights pathogens. In a single nucleotide polymorphisms (SNP) analysis of an Indian cohort, we found evidence for both TLR4-399T and TRL8-1A conveying increased susceptibility towards tuberculosis (TB) in an interdependent manner, even though there is no established TLR4 ligand present in Mycobacterium tuberculosis (Mtb), which is the causative pathogen of TB. Docking studies revealed that TLR4 and TLR8 can build a heterodimer, allowing interaction with TLR8 ligands. The conformational change of TLR4-399T might impair this interaction. With immunoprecipitation and mass spectrometry, we precipitated TLR4 with TLR8-targeted antibodies, indicating heterodimerisation. Confocal microscopy confirmed a high co-localisation frequency of TLR4 and TLR8 that further increased upon TLR8 stimulation. The heterodimerisation of TLR4 and TLR8 led to an induction of IL12p40, NF-κB, and IRF3. TLR4-399T in interaction with TLR8 induced an increased NF-κB response as compared to TLR4-399C, which was potentially caused by an alteration of subsequent immunological pathways involving type I IFNs. In summary, we present evidence that the heterodimerisation of TLR4 and TLR8 at the endosome is involved in Mtb recognition via TLR8 ligands, such as microbial RNA, which induces a Th1 response. These findings may lead to novel targets for therapeutic interventions and vaccine development regarding TB.  相似文献   
996.
997.
998.
Photocatalytic degradation of acetonitrile was carried out in gas–solid regime by using two commercial TiO2 samples (Merck and Degussa P25) irradiated in two continuous annular photoreactors. The inlet gas flow consisted of oxygen, nitrogen, acetonitrile and water vapours. The influence on the photodegradation rate of gas flow rate, acetonitrile, oxygen and water concentrations and photon flux was investigated. The degradation products of acetonitrile were carbon dioxide and hydrogen cyanide. The photocatalysts performance was not affected by the presence or absence of water vapour in the reacting mixture. The Langmuir–Hinshelwood model describes adequately the photoreactivity results and provides the values of kinetic and equilibrium adsorption constants. FT-IR spectroscopy was used to investigate the adsorption patterns and photo-oxidation intermediates of acetonitrile on fully hydrated surface of TiO2 powders. Acetonitrile was adsorbed on Ti4+ surface ions and hydroxyl groups for both types of TiO2. In the absence of UV light this interaction was completely reversible for Merck catalyst whereas for Degussa P25 part of adsorbed acetonitrile molecules reacted to form acetamide-like species.  相似文献   
999.
One of the most important goals of the European energy policy involves the implementation of energy-efficiency measures in large scale so as to promote sustainable development in the European Union (EU) level. The multidimensional character of energy end-use efficiency (EEE) necessitates the collection of a number of related data, apart from the performance and system parameters data, such as socio-economic (e.g., employment, turnover) and Research and Development (R&D) expenditures. Moreover, improved co-ordination of EEE programmes and policies of the community and the member states so as a unified acceptable system to be developed for the monitoring of the EEE data with respect to the existing targets is of significant importance. Even though data-gathering efforts have been implemented, a lot of fragmented data and deduced findings are currently available, which sometimes lack consistency and verification. In this context, the main aim of the paper is to present a sustainable reference methodology for validating EEE data in EU, through the review of existing approaches and methods, defining of most relevant inconsistencies and gaps and provision of recommendations for improvements in EEE data aggregation and statistical interpretation, taking into consideration the related analysis of statisticians, energy technology experts and energy socio-economists.  相似文献   
1000.
We investigate, within the PAC learning model, the problem of learning nonoverlapping perceptron networks (also known as read-once formulas over a weighted threshold basis). These are loop-free neural nets in which each node has only one outgoing weight. We give a polynomial time algorithm that PAC learns any nonoverlapping perceptron network using examples and membership queries. The algorithm is able to identify both the architecture and the weight values necessary to represent the function to be learned. Our results shed some light on the effect of the overlap on the complexity of learning in neural networks.  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-23

京公网安备 11010802026262号