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   9765篇
  免费   722篇
  国内免费   99篇
电工技术   128篇
综合类   30篇
化学工业   2130篇
金属工艺   189篇
机械仪表   368篇
建筑科学   209篇
矿业工程   36篇
能源动力   568篇
轻工业   1024篇
水利工程   107篇
石油天然气   71篇
武器工业   1篇
无线电   1207篇
一般工业技术   2218篇
冶金工业   617篇
原子能技术   111篇
自动化技术   1572篇
  2024年   47篇
  2023年   267篇
  2022年   602篇
  2021年   1005篇
  2020年   614篇
  2019年   685篇
  2018年   687篇
  2017年   577篇
  2016年   568篇
  2015年   377篇
  2014年   463篇
  2013年   761篇
  2012年   451篇
  2011年   531篇
  2010年   331篇
  2009年   283篇
  2008年   235篇
  2007年   214篇
  2006年   146篇
  2005年   105篇
  2004年   97篇
  2003年   104篇
  2002年   77篇
  2001年   59篇
  2000年   58篇
  1999年   75篇
  1998年   170篇
  1997年   137篇
  1996年   109篇
  1995年   89篇
  1994年   67篇
  1993年   65篇
  1992年   44篇
  1991年   49篇
  1990年   36篇
  1989年   36篇
  1988年   29篇
  1987年   34篇
  1986年   34篇
  1985年   36篇
  1984年   29篇
  1983年   31篇
  1982年   16篇
  1981年   16篇
  1980年   12篇
  1979年   11篇
  1978年   18篇
  1977年   20篇
  1976年   23篇
  1972年   8篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Autonomous mapping of HL7 RIM and relational database schema   总被引:1,自引:0,他引:1  
Healthcare systems need to share information within and across the boundaries in order to provide better care to the patients. For this purpose, they take advantage of the full potential of current state of the art in healthcare standards providing interoperable solutions. HL7 V3 specification is an international message exchange and interoperability standard. HL7 V3 messages exchanged between healthcare applications are ultimately recorded into local healthcare databases, mostly in relational databases. In order to bring these relational databases in compliance with HL7, mappings between HL7 RIM (Reference Information Model) and relational database schema are required. Currently, RIM and database mapping is largely performed manually, therefore it is tedious, time consuming, error prone and expensive process. It is a challenging task to determine all correspondences between RIM and schema automatically because of extreme heterogeneity issues in healthcare databases. To reduce the amount of manual efforts as much as possible, autonomous mapping approaches are required. This paper proposes a technique that addresses the aforementioned mapping issue and aligns healthcare databases to HL7 V3 RIM specifications. Furthermore, the proposed technique has been implemented as a working application and tested on real world healthcare systems. The application loads the target healthcare schema and then identifies the most appropriate match for tables and the associated fields in the schema by using domain knowledge and the matching rules defined in the Mapping Knowledge Repository. These rules are designed to handle the complexity of semantics found in healthcare databases. The GUI allows users to view and edit/re-map the correspondences. Once all the mappings are defined, the application generates Mapping Specification, which contains all the mapping information i.e. database tables and fields with associated RIM classes and attributes. In order to enable the transactions, the application is facilitated with the autonomous code generation from the Mapping Specification. The Code Generator component focuses primarily on generating custom classes and hibernate mapping files against the runtime system to retrieve and parse the data from the data source—thus allows bi-directional HL7 to database communication, with minimum programming required. Our experimental results show 35–65% accuracy on real laboratory systems, thus demonstrating the promise of the approach. The proposed scheme is an effective step in bringing the clinical databases in compliance with RIM, providing ease and flexibility.  相似文献   
102.
A mobile ad hoc network (MANET) is dynamic in nature and is composed of wirelessly connected nodes that perform hop-by-hop routing without the help of any fixed infrastructure. One of the important requirements of a MANET is the efficiency of energy, which increases the lifetime of the network. Several techniques have been proposed by researchers to achieve this goal and one of them is clustering in MANETs that can help in providing an energy-efficient solution. Clustering involves the selection of cluster-heads (CHs) for each cluster and fewer CHs result in greater energy efficiency as these nodes drain more power than noncluster-heads. In the literature, several techniques are available for clustering by using optimization and evolutionary techniques that provide a single solution at a time. In this paper, we propose a multi-objective solution by using multi-objective particle swarm optimization (MOPSO) algorithm to optimize the number of clusters in an ad hoc network as well as energy dissipation in nodes in order to provide an energy-efficient solution and reduce the network traffic. In the proposed solution, inter-cluster and intra-cluster traffic is managed by the cluster-heads. The proposed algorithm takes into consideration the degree of nodes, transmission power, and battery power consumption of the mobile nodes. The main advantage of this method is that it provides a set of solutions at a time. These solutions are achieved through optimal Pareto front. We compare the results of the proposed approach with two other well-known clustering techniques; WCA and CLPSO-based clustering by using different performance metrics. We perform extensive simulations to show that the proposed approach is an effective approach for clustering in mobile ad hoc networks environment and performs better than the other two approaches.  相似文献   
103.
This paper presents a method of transferring voice using short messaging service in satellite communication system. The method is especially applicable in a situation where signal strength is low and voice call is not possible. In a tunnel, basement or environment with bad climate conditions, signal strength usually gets weak which make voice call difficult but SMS works in such situation. An application has been developed using J2ME language in order to test the proposed method. For experimentation, Thuraya SG-2520 satellite phone has been used.  相似文献   
104.
The electrical and optical properties of binary semiconducting oxide glasses containing 45 mol % V2O5 and 55 mol % GeO2 fused and equilibrated at various temperatures (T ) in air were measured.T was varied over the range from 1000 to 1350° C. Their electrical and optical properties are shown to be sensitive to microstructure and melt temperature. We suggest that the change inT caused progressive microstructure changes of these glasses, which dramatically affected the electronic conductivity and the activation enthalpy for conduction.  相似文献   
105.
A.c. susceptibility measurements were carried out on the disordered spinel system Co2–x Zn x TiO4 (0<x<1) between 10 and 80 K. Our measurements show three peaks in the versus T curve for Co2TiO4 and CoZnTiO4 compounds. In both compounds two peaks are very close to each other, indicating that the Néel and semi-spin glass temperatures are very close. A third peak indicates the presence of the semi-spin glass to spin glass transition. In Co1.5Zn0.5TiO4 only one peak is observed which indicates spin glass ordering at 26 K. Furthermore, the A-site canting present in Co2TiO4 and CoZnTiO4 has a collinear and magnetic structure, indicating strong A-B coupling. X-ray analysis indicated that compounds of the system Co2ZnxTiO4 synthesized with cubic symmetry. From transport properties it was found that the activation energy and thermoelectric coefficient decrease with increasing concentration of Zn in the system. The mobility of the system calculated from infrared measurements is typically of the order of 10–9cm2V–1s–1.  相似文献   
106.
The optical properties of vanadium-phosphate glasses containing various amounts of (V2O5)50(P2O5)50–x (VCl3) x , wherex = 0.05, 0.06, 0.08 and 0.1, were measured as a function of VCl3 content. It is found that by adding VCl3 to the melt when the glass is formed, the added chlorine which acts as an oxidizing agent alters the ratio of concentration of vanadium ions and thus the absorption coefficient. Data on absorption in this study show that the power law,() =B() –E 0) n / is best followed forn = 3, and the absorption is solely due to vanadium oxide. Furthermore, the infrared absorption spectra of this system were investigated in the wave number range 400 to 4600cm–1. The addition of VCl3 to the vanadium-phosphate glasses does not seem to introduce any new absorption band in this range as compared with the spectrum of a pure vanadium-phosphate glass. Furthermore, no significant difference in the absorption spectra was observed by annealing the V2O5-P2O5 glasses up to 200° C.  相似文献   
107.
Adhesion to skin     
The failure energy of an adhesive bond can be factorized into two terms, one of which is a dimensionless loss function and the other, the true interfacial bonding energy, 0. Experimental techniques have been developed to effect a separation of these two terms and thus measure 0, but they are unsuitable for the pressure-sensitive adhesives used in surgical tapes and dressings. This is because these adhesives flow readily under load. This paper describes an extrapolation technique by which this problem can be resolved. Adhesive peel data are extrapolated both to zero peel velocity and zero load, to give a true threshold value for peeling energy which is independent of temperature. Values of 0 are given for a natural-rubber based adhesive and substrates of glass and human skinin vivo. For glass 0 = 28J m–2 and for normal skin 0 14J m-2.  相似文献   
108.
Neo-tetraploid rice with high fertility is a useful germplasm for polyploid rice breeding, which was developed from the crossing of different autotetraploid rice lines. However, little information is available on the molecular mechanism underlying the fertility of neo-tetraploid rice. Here, two contrasting populations of tetraploid rice, including one with high fertility (hereafter referred to as JG) and another with low fertility (hereafter referred to as JD), were generated by crossing Huaduo 3 (H3), a high fertility neo-tetraploid rice that was developed by crossing Jackson-4x with 96025-4x, and Huajingxian74-4x (T452), a low fertility autotetraploid rice parent. Cytological, global genome sequencing-based bulked-segregant (BSA-seq) and CRISPR/Cas9 technology were employed to study the genes associated with pollen fertility in neo-tetraploid rice. The embryo sacs of JG and JD lines were normal; however, pollen fertility was low in JD, which led to scarce fertilization and low seed setting. Cytological observations displayed low pollen fertility (25.1%) and approximately 31.3 and 27.2% chromosome lagging at metaphase I and II, and 28.8 and 24.8% chromosome straggling at anaphase I and II in JD, respectively. BSA-seq of F2–3 generations and RNA-seq of F4 generation detected a common fragment, i.e., 18,915,234–19,500,000, at chromosome 7, which was comprised of 78 genes associated with fertility. Among 78 genes, 9 genes had been known to be involved in meiosis and pollen development. Two mutants ny1 (LOC_Os07g32406) and ny2 (LOC_Os07g32040) were generated by CRISPR/Cas9 knockout in neo-tetraploid rice, and which exhibited low pollen fertility and abnormal chromosome behavior. Our study revealed that two unknown genes, LOC_Os07g32406 (NY1) and LOC_Os07g32040 (NY2) play an important role in pollen development of neo-tetraploid rice and provides a new perspective about the genetic mechanisms of fertility in polyploid rice.  相似文献   
109.
Surface functionalization of blast furnace slag with sulfamic acid(a zwitterion) was performed for the removal of Cr~(3+) and methylene blue dye(MB) from water samples. The slag functionalization process was optimized using Response Surface Methodology Design. Statistical analysis of the parameters that include the sulfamic acid amount(A), reaction time(B), and temperature(C) revealed that(A) increase had a negative effect on the adsorption of both pollutants by the zwitterion slag, whereas(B) and(C)increase presented a positive impact. At the optimum condition of 2 g sulfamic acid amount, 50 min reaction time and 37 °C temperature, the prepared slag showed a removal efficiency of more than 90% for both Cr~(3+) and MB. Surface characterization by SEM/EDS, FTIR, XPS and surface area analyser, showed an improvement in surface properties and the incorporation of zwitterionic NH_2~+ and S@O groups of sulfamic acid. Adsorption isotherm and kinetic studies conducted with the zwitterion slag showed the adsorption process was suited to Freundlich isotherm model and pseudo-second-order kinetic model.The thermodynamic study conducted revealed the spontaneity of the process based on the calculated negative DG(Gibb's free energy) values. The prepared zwitterion slag offered easy regeneration with dilute HCl solution and showed a considerable removal(Cr3+: 65% and MB: 80%) for both pollutants even after 3 cycles of usage.  相似文献   
110.
In this work,a degradable polyurethane composed of caprolactone(CL)and L-Lactide(LLA)as soft seg-ments,and 4,4'-methylenebis(cyclohexyl isocyanate)(H12MDI)and polytetramethylene ether glycol(PTMEG)as hard segments,was prepared.Hydrolytic degradation experiment revealed that the degrad-able polyurethane(PU)could be degraded in artificial seawater.It also showed that caprolactone-co-polyurethane(CL-PU)copolymer with higher crystallinity degraded much slower in artificial seawater.However,the introduction of LLA resulted in an increase in the hydrophilicity and reduction in the crys-tallinity of degradable PU,as demonstrated by the contact angle analysis.The result of the scanning elec-tron microscope showed that the surface of degradable PU renewed under static condition.Moreover,degradable PU was able to be used as a carrier,and it controlled the release rate of 4,5-dichloro-2-octyl-isothiazolone(DCOIT).The anti-diatom(Navicula incerta)test demonstrated that the(caprolactone-co-L-lactide)-co-polyurethane 4(CL/LAx-PU4)with DCOIT contents prevented the adhe-sion of diatom Navicula incerta(88.37%reduction)due to their self-polishing and the release of antifou-lants.Therefore,the degradable PU consisted of CL,LLA,and DCOIT could be a durable resin with good antifouling activity for the application in the marine anti-biofouling field.  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