全文获取类型
收费全文 | 613201篇 |
免费 | 7968篇 |
国内免费 | 2062篇 |
专业分类
电工技术 | 11481篇 |
综合类 | 525篇 |
化学工业 | 91271篇 |
金属工艺 | 21894篇 |
机械仪表 | 17723篇 |
建筑科学 | 16498篇 |
矿业工程 | 1667篇 |
能源动力 | 16966篇 |
轻工业 | 58453篇 |
水利工程 | 5083篇 |
石油天然气 | 4880篇 |
武器工业 | 27篇 |
无线电 | 80763篇 |
一般工业技术 | 115914篇 |
冶金工业 | 115605篇 |
原子能技术 | 9733篇 |
自动化技术 | 54748篇 |
出版年
2021年 | 4503篇 |
2020年 | 3188篇 |
2019年 | 4045篇 |
2018年 | 6575篇 |
2017年 | 6673篇 |
2016年 | 7081篇 |
2015年 | 5286篇 |
2014年 | 8891篇 |
2013年 | 28583篇 |
2012年 | 15056篇 |
2011年 | 21358篇 |
2010年 | 16726篇 |
2009年 | 19048篇 |
2008年 | 20359篇 |
2007年 | 20577篇 |
2006年 | 18348篇 |
2005年 | 16774篇 |
2004年 | 16293篇 |
2003年 | 16178篇 |
2002年 | 15431篇 |
2001年 | 15873篇 |
2000年 | 14713篇 |
1999年 | 15612篇 |
1998年 | 37308篇 |
1997年 | 26690篇 |
1996年 | 20839篇 |
1995年 | 16063篇 |
1994年 | 14413篇 |
1993年 | 13946篇 |
1992年 | 10300篇 |
1991年 | 9860篇 |
1990年 | 9404篇 |
1989年 | 8942篇 |
1988年 | 8694篇 |
1987年 | 7335篇 |
1986年 | 7239篇 |
1985年 | 8532篇 |
1984年 | 7956篇 |
1983年 | 7136篇 |
1982年 | 6665篇 |
1981年 | 6565篇 |
1980年 | 6222篇 |
1979年 | 5963篇 |
1978年 | 5528篇 |
1977年 | 6752篇 |
1976年 | 9132篇 |
1975年 | 4608篇 |
1974年 | 4455篇 |
1973年 | 4282篇 |
1972年 | 3587篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
Few studies have prospectively examined the characteristics associated with worksite adoption of tobacco-control initiatives. Data were collected as part of the Community Intervention Trial (COMMIT) for Smoking Cessation, which conducted interventions in 11 communities. This smoking cessation intervention was based on community organization principles and delivered through multiple community channels, including worksites, health care providers, the media, and cessation resources. This article reports results from telephone interviews of intervention community worksites having 50 or more employees, conducted at baseline and the end of the intervention period. Among worksites that responded to both baseline and final surveys, 83% had not adopted a smoke-free policy at baseline, and 61% did not offer any cessation aid or quitting resources at baseline. By the final survey, 34% of those with no smoking ban at baseline had become smoke-free, and 36% of those offering no cessation assistance at baseline were offering cessation resources at the follow-up. The prevalence of policy adoption was higher among worksites employing more female employees and offering other health-promotion activities; manufacturing businesses were significantly less likely than businesses other than service and wholesale/retail businesses to adopt policies. Adoption of cessation programs was significantly more likely among worksites employing 100 to 249 workers, compared with those employing 50 to 99 workers; those predominantly employing men; those offering other types of health-promotion activities; and those with a higher rate of turnover. These results provide important information about the characteristics of worksites likely to engage in tobacco-control efforts. Health educators and others may choose to target those worksites most ready for adoption of tobacco control policies and programs, as indicated by these findings. 相似文献
962.
963.
The response of P. falciparum to chloroquine and pyrimethamine-sulfadoxine in vivo and chloroquine and amodiaquine in vitro was investigated in parasitaemic school children from six locations. Mean parasite sensitivity to chloroquine at day 7 was 74% (range 61-97) with parasite clearance rates between 2-3 days and complete defervescence in 85% of febrile children. Sensitivity declined in the four sites followed up to day 14 to 45% (range 37-53). Parasites were significantly more sensitive to pyrimethamine/sulfadoxine at 5/6 sites (100% day 7) but 5% of subjects became parasitaemic by day 14. In vitro isolates were significantly less sensitive to chloroquine than to amodiaquine with a mean 99% effective concentration of 348 mumol/L compared to 6.44 mumol/L. Clearly the role of chloroquine as the primary therapy for uncomplicated P. falciparum malaria should be reconsidered especially in the light of increasing disease severity and resurgence. Amodiaquine may be suitable alternative with pyrimethamine/sulfadoxine as second line and for more severe malaria prior to referral. The cost of alternative antimalarials and the dynamic and deteriorating pattern of resistance are powerful arguments for more objective slide diagnosis to minimise drug pressure and a regular drug sensitivity surveillance system. We believe that the latter should concentrate on measuring clinical drug efficacy in symptomatic outpatients rather than in asymptomatic children while the former needs more pragmatic and economical strategies possibly centred on seasonality and risk. 相似文献
964.
Business process redesign (BPR) has been widely touted as a means for leveraging the power of information technology to change business processes radically, resulting in substantial improvements in organizational effectiveness and efficiency. This study represents an early attempt at examining the strategic nature of the phenomenon. Because BPR is radical change and has the ability to alter both the competitive and operational nature of the corporation, it is critical that BPR be coordinated with corporate strategy. Through a survey of information system executives, the relationships between corporate competitive strategy and three types of BPR – intrafunctional, interfunctional and interorganizational – were examined. It was found that organizations following a cost strategy tended to do more BPR projects on interfunctional processes. Furthermore, the positive effect of a cost strategy on interfunctional BPR was found to be strengthened by the degree of integration of IS and business planning. It was also found that while interorganizational BPR was not related to a specific strategy, it was strongly related directly with IS–business planning integration. 相似文献
965.
F Foussadier P Menard R Zaza J Pillet JC Bertrand 《Canadian Metallurgical Quarterly》1993,94(5):312-317
The use of osseointegrated implants to provide support for auricle prosthesis as been carried out by Tjellstrom. This method has provided the maxillofacial surgeon with another approach to the treatment of defect of the auricle. The principles and concepts of extra-oral osseointegrated implants are the same as those of the intra-oral application developed by Branemark 26 years ago. This simple and reliable method allow the attachment to splint bar fixated to three or two mastoid osseointegrated implants. This method represent an interesting possibility for the management of auricle defects. We report on our experience of 11 cases. 相似文献
966.
967.
J. M. Kremer A. A. Shabana G. E. O. Widera 《International journal for numerical methods in engineering》1993,36(1):17-42
This investigation concerns itself with the computer implementation of the dynamic formulation of thin laminated composite plates consisting of layers of orthotropic laminae that undergo large arbitrary rigid body displacements and small elastic deformations. A finite element preprocessor computer program is developed to automatically generate the invariants of the laminae, which may have arbitrary orientations. The laminae invariants are then used to obtain the invariants of the elements and the composite laminated plate. The consistent and lumped mass formulations of the invariants of motion of composite plates are compared and it is concluded that the two methods are comparable, if a fine enough finite element mesh is used. The structure of the dynamic equations of motion, based on the formulation presented in Part I of this paper, is examined. Non-linear centrifugal and Coriolis forces arising as the result of the finite rotations of the laminae are defined, and the solution schemes of the resulting non-linear differential equations of motion are discussed. Numerical examples illustrating the differences between homogeneous isotropic and laminated composite plates are presented. An RSSR (Revolute-Spherical-Spherical-Revolute) mechanism is used in the numerical examples, with the coupler modelled as a laminated plate flexible body. It is found that the inertia of the plate contributed greatly to the transverse deformation. The effects of laminae orientation is also investigated. 相似文献
968.
969.
It is shown that the applicability of memory-polarized distance relay mho elements to the protection of MOV (metal oxide varistor) protected series-compensated lines is dependent on the system configuration, line loading, the location of the potential source, and the magnitude of memory polarization. For a configuration with compensation at one end of a line, the results indicate certain advantages in using the potential from the line side of the capacitor, and the use of a relatively large magnitude of memory polarization. The presence of a conducting MOV enhances the performance of the mho element both in terms of security on reverse faults and dependability on forward faults. The results obtained pertain to the proposed application in the Ontario Hydro system of a relatively large amount of compensation at one terminal in each circuit of a double-circuit line 相似文献
970.
Munish Agarwal Ali K. Kamrani Hamid R. Parsaei 《Journal of Intelligent Manufacturing》1994,5(4):235-249
The philosophy of group technology (GT) is an important concept in the design of flexible manufacturing systems and manufacturing cells. Group technology is a manufacturing philosophy that identifies similar parts and groups them into families. Beside assigning unique codes to these parts, group technology developers intend to take advantage of part similarities during design and manufacturing processes. GT is not the answer to all manufacturing problems, but it is a good management technique with which to standardize efforts and eliminate duplication. Group technology classifies parts by assigning them to different families based on their similarities in: (1) design attributes (physical shape and size), and/or (2) manufacturing attributes (processing sequence). The manufacturing industry today is process focused; departments and sub units are no longer independent but are interdependent. If the product development process is to be optimized, engineering and manufacturing cannot remain independent any more: they must be coordinated. Each sub-system is a critical component within an integrated manufacturing framework. The coding and classification system is the basis of CAPP and the functioning and reliability of CAPP depends on the robustness of the coding system. The proposed coding system is considered superior to the previously proposed coding systems, in that it has the capability to migrate into multiple manufacturing environments. This article presents the design of a coding and classification system and the supporting database for manufacturing processes based on both design and manufacturing attributes of parts. An interface with the spreadsheet will calculate the machine operation costs for various processes. This menu-driven interactive package is implemented using dBASE-IV. Part Family formation is achieved using a KAMCELL package developed in TURBO Pascal. 相似文献