全文获取类型
收费全文 | 1803篇 |
免费 | 23篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 4篇 |
化学工业 | 84篇 |
金属工艺 | 10篇 |
机械仪表 | 31篇 |
建筑科学 | 23篇 |
矿业工程 | 3篇 |
能源动力 | 31篇 |
轻工业 | 59篇 |
水利工程 | 4篇 |
石油天然气 | 6篇 |
无线电 | 60篇 |
一般工业技术 | 91篇 |
冶金工业 | 1359篇 |
原子能技术 | 3篇 |
自动化技术 | 61篇 |
出版年
2023年 | 4篇 |
2022年 | 6篇 |
2021年 | 12篇 |
2020年 | 7篇 |
2019年 | 12篇 |
2018年 | 22篇 |
2017年 | 12篇 |
2016年 | 21篇 |
2015年 | 16篇 |
2014年 | 15篇 |
2013年 | 41篇 |
2012年 | 19篇 |
2011年 | 21篇 |
2010年 | 21篇 |
2009年 | 24篇 |
2008年 | 27篇 |
2007年 | 20篇 |
2006年 | 16篇 |
2005年 | 17篇 |
2004年 | 16篇 |
2003年 | 13篇 |
2002年 | 10篇 |
2000年 | 10篇 |
1999年 | 34篇 |
1998年 | 354篇 |
1997年 | 237篇 |
1996年 | 168篇 |
1995年 | 122篇 |
1994年 | 69篇 |
1993年 | 91篇 |
1992年 | 16篇 |
1991年 | 28篇 |
1990年 | 10篇 |
1989年 | 14篇 |
1988年 | 12篇 |
1987年 | 11篇 |
1986年 | 9篇 |
1985年 | 10篇 |
1984年 | 3篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1981年 | 16篇 |
1980年 | 19篇 |
1978年 | 13篇 |
1977年 | 55篇 |
1976年 | 101篇 |
1974年 | 4篇 |
1972年 | 3篇 |
1967年 | 3篇 |
1957年 | 3篇 |
排序方式: 共有1829条查询结果,搜索用时 15 毫秒
11.
12.
VM Ponomarenko 《Canadian Metallurgical Quarterly》1995,(5-6):12-15
An assessment is submitted of morbidity rates and physical development of children aged under 14, residing in the territories being monitored after the Chernobyl Power Plant accident. A high level of disharmony in physical development of the children examined was recordable, as was an excess in morbidity of both general and separate classes of disease entities among the pediatric population having been victims of the Chernobyl accident, as compared to that in relatively "clean" areas and in Ukraine as a whole. 相似文献
13.
When initiating monotherapy for the treatment of essential hypertension, multiple determinants factor into the decision. The goal of treatment is to lower blood pressure and lessen the likelihood of progression to target organ failure. Physicians frequently prioritize these determinants and make decisions to initiate monotherapy based on the race of an individual. All too often, however, the black/white issue is overstated and given too much consideration. The overall goal of this review is to suggest the appropriate "role" for racial profiling in the initial selection of an antihypertensive agent. 相似文献
14.
Personal clinical observations during the recent years allow the authors to confirm the indisputable value of surgical experience got during the Great Patriotic War (1941-1945) and in particular, the "fourfold" scheme proposed by V. I. Voiachek for the diagnosis and treatment of blind gunshot wounds to the skull base. Computed tomography considerably increases the probability of detection of the exact localization of foreign bodies in complex anatomical structures of the skull and thus facilitates choosing the most rational surgical management. The use of the electro-optical transducer for the extraction of foreign bodies from almost inaccessible areas of the skull base decreases the risk of operation. 相似文献
15.
This paper contextualises, describes and discusses a student project which takes a particular exploratory approach to using
mathematical surface definition as a language and vehicle for co-rational design co-authorship for architecture and engineering.
The project has two authors, one from an architectural and one from an engineering educational background. It investigates
the metaphorical and operational role of mathematics in the design process and outcomes. 相似文献
16.
Abdullah Saad Abdullah Ibrahim El Tantawy El Sayed Abdel Moneim A. El-Torgoman Abul Kalam S. Wageh Maher A. Kamel 《International journal of molecular sciences》2022,23(10)
Background: Silymarin (SIL) has long been utilized to treat a variety of liver illnesses, but due to its poor water solubility and low membrane permeability, it has a low oral bioavailability, limiting its therapeutic potential. Aim: Design and evaluate hepatic-targeted delivery of safe biocompatible formulated SIL-loaded chitosan nanoparticles (SCNPs) to enhance SIL’s anti-fibrotic effectiveness in rats with CCl4-induced liver fibrosis. Methods: The SCNPs and chitosan nanoparticles (CNPs) were prepared by ionotropic gelation technique and are characterized by physicochemical parameters such as particle size, morphology, zeta potential, and in vitro release studies. The therapeutic efficacy of successfully formulated SCNPs and CNPs were subjected to in vivo evaluation studies. Rats were daily administered SIL, SCNPs, and CNPs orally for 30 days. Results: The in vivo study revealed that the synthesized SCNPs demonstrated a significant antifibrotic therapeutic action against CCl4-induced hepatic injury in rats when compared to treated groups of SIL and CNPs. SCNP-treated rats had a healthy body weight, with normal values for liver weight and liver index, as well as significant improvements in liver functions, inflammatory indicators, antioxidant pathway activation, and lipid peroxidation reduction. The antifibrotic activities of SCNPs were mediated by suppressing the expression of the main fibrosis mediators TGFβR1, COL3A1, and TGFβR2 by boosting the hepatic expression of protective miRNAs; miR-22, miR-29c, and miR-219a, respectively. The anti-fibrotic effects of SCNPs were supported by histopathology and immunohistochemistry (IHC) study. Conclusions: According to the above results, SCNPs might be the best suitable carrier to target liver cells in the treatment of liver fibrosis. 相似文献
17.
The technique of scanning transmission electron microscopy (STEM) has been employed usefully in studies of amorphous materials, and the theory of image formation and interpretation in this case has been well developed. Less attention has been given to the practical and theoretical problems associated with the use of STEM for the examination of crystalline materials. In this case the contrast mechanisms are dominated by Bragg diffraction and so they are quite different from those occurring in amorphous substances. In this paper practical techniques for the observation and interpretation of contrast from defects in crystalline materials are discussed. It is shown that whilst images of defects are obtained readily under all typical STEM operating conditions, the form of the image and the information it contains varies with the angle subtended at the specimen by the detector. If this angle is too large significant image modifications relative to the "conventional" transmission electron microscope case may occur and the resolution of the image may degrade. If this angle is too small, then signal to noise considerations make an interpretation of the image difficult. In this paper we indicate how the detector angle may be chosen correctly, and also present techniques for setting up a STEM instrument for imaging a crystalline material containing lattice defects. 相似文献
18.
In this paper, we introduce the splitter placement problem in wavelength-routed networks (SP-WRN). Given a network topology, a set of multicast sessions, and a fixed number of multicast-capable cross-connects, the SP-WRN problem entails the placement of the multicast-capable cross-connects so that the blocking probability is minimized. The SP-WRN problem is NP-complete as it includes as a subproblem the routing and wavelength assignment problem which is NP-complete. To gain a deeper insight into the computational complexity of the SP-WRN problem, we define a graph-theoretic version of the splitter placement problem (SPG), and show that even SPG is NP-complete. We develop three heuristics for the SP-WRN problem with different degrees of trade-off between computation time and quality of solution. The first heuristic uses the CPLEX general solver to solve an integer-linear program (ILP) of the problem. The second heuristic is based on a greedy approach and is called most-saturated node first (MSNF). The third heuristic employs simulated annealing (SA) with route-coordination. Through numerical examples on a wide variety of network topologies we demonstrate that: (1) no more than 50% of the cross-connects need to be multicast-capable, (2) the proposed SA heuristic provides fast near-optimal solutions, and (3) it is not practical to use general solvers such as CPLEX for solving the SP-WRN problem. 相似文献
19.
Maher Arar Abbas Yongacoglu 《Communications Letters, IEEE》2006,10(12):819-821
We propose an efficient 2Ntimes2N MIMO detection algorithm where the transmit signals are grouped in pairs and separately coded using the standard Alamouti space-time code. At the receiver, one or more QR decompositions are performed and the upper triangular property of the R matrices so obtained is exploited in order to successively decode the transmitted symbols starting with those interference-free symbols corresponding to the last two rows and columns of R. Bit-error-rate simulation results, for a 4times4 MIMO system and a bandwidth efficiency of 8 bits/s/Hz, show that the proposed technique, while less complex than ordered MMSE V-BLAST, outperforms the latter by 2-6 dB at a BER of 10-4 相似文献
20.
This paper addresses the problem of routing and wavelength assignment of bit-rate-differentiated optical services in a hybrid network. Hybrid optical networks are composed of resources, such as fiber links and photonic/electronic switches, that vary in their capabilities and transmission qualities. These networks are also responsible for the realization of optical services with varying quality-of-service (QoS) guarantees. In such networks, it is required to have a cost-effective assignment of the optical and electronic resources to these services in order to maximize the revenue of the network operator. This paper deals with optical services that are defined according to their tolerance to transmission impairments. We first divide the provisioning problem into two phases: (1) routing and (2) wavelength assignment and regeneration reservation. In the routing phase, a set of k-routes are generated to select from in the second phase, where each route optimizes a specific aspect of the problem (e.g., number of hops, maximum accumulated noise, etc.). The second phase, using the information about the resources along each route, attempts at finding the best wavelength allocation on that route such that the signal quality meets the service-level agreement (SLA). The second phase also uses the minimum number of regenerator ports on intermediate nodes for the purpose of wavelength translation and signal clean-up. Comparisons of the above scheme with a probing-based method, reveal substantial enhancements to the blocking performance with a maximum running time increase of 60%. In addition, the use of multiple routes provides higher reduction in the blocking probability over single-routing schemes. Moreover, the proposed, non-pessimistic, provisioning approach has a major impact on reducing the regeneration budget of the network. 相似文献