全文获取类型
收费全文 | 3428篇 |
免费 | 17篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 15篇 |
化学工业 | 160篇 |
金属工艺 | 33篇 |
机械仪表 | 25篇 |
建筑科学 | 25篇 |
能源动力 | 15篇 |
轻工业 | 120篇 |
水利工程 | 31篇 |
石油天然气 | 4篇 |
无线电 | 84篇 |
一般工业技术 | 137篇 |
冶金工业 | 2637篇 |
原子能技术 | 22篇 |
自动化技术 | 138篇 |
出版年
2021年 | 13篇 |
2019年 | 8篇 |
2018年 | 19篇 |
2017年 | 10篇 |
2016年 | 21篇 |
2015年 | 7篇 |
2014年 | 30篇 |
2013年 | 51篇 |
2012年 | 31篇 |
2011年 | 40篇 |
2010年 | 32篇 |
2009年 | 23篇 |
2008年 | 32篇 |
2007年 | 43篇 |
2006年 | 43篇 |
2005年 | 36篇 |
2004年 | 35篇 |
2003年 | 27篇 |
2002年 | 35篇 |
2001年 | 25篇 |
2000年 | 28篇 |
1999年 | 90篇 |
1998年 | 703篇 |
1997年 | 443篇 |
1996年 | 281篇 |
1995年 | 148篇 |
1994年 | 142篇 |
1993年 | 167篇 |
1992年 | 31篇 |
1991年 | 37篇 |
1990年 | 37篇 |
1989年 | 50篇 |
1988年 | 43篇 |
1987年 | 44篇 |
1986年 | 41篇 |
1985年 | 40篇 |
1984年 | 9篇 |
1983年 | 17篇 |
1982年 | 28篇 |
1981年 | 29篇 |
1980年 | 36篇 |
1979年 | 11篇 |
1978年 | 15篇 |
1977年 | 93篇 |
1976年 | 207篇 |
1975年 | 23篇 |
1974年 | 13篇 |
1973年 | 7篇 |
1972年 | 8篇 |
1970年 | 7篇 |
排序方式: 共有3446条查询结果,搜索用时 0 毫秒
991.
992.
993.
Mediating the intersections of organizational routines during the introduction of a health IT system
Public interest in the quality and safety of health care has spurred examination of specific organizational routines believed to yield risk in health care work. Medication administration routines, in particular, have been the subject of numerous improvement projects involving information technology development, and other forms of research and regulation. This study draws from ethnographic observation to examine how the common routine of medication administration intersects with other organizational routines, and why understanding such intersections is important. We present three cases describing intersections between medication administration and other routines, including a pharmacy routine, medication administration on the next shift and management reporting. We found that each intersection had ostensive and performative dimensions; and furthermore, that IT-enabled changes to one routine led to unintended consequences in its intersection with others, resulting in misalignment of ostensive and performative aspects of the intersection. Our analysis focused on the activities of a group of nurses who provide technology use mediation (TUM) before and after the rollout of a new health IT system. This research offers new insights on the intersection of organizational routines, demonstrates the value of analyzing TUM activities to better understand the relationship between IT introduction and changes in routines, and has practical implications for the implementation of technology in complex practice settings. 相似文献
994.
The preservation of crimped wheat grains by three bacterial inoculants or a chemical additive was compared. Crimped wheat grain [56.8 g dry matter (DM)/kg] was conserved in 1.75-kg plastic bag, mini-silos without treatment, with 4L/tonne of Crimpstore (CS; an additive containing a mixture of ammonium formate, propionate, ethyl benzoate, and benzoate, SAS Kelvin Cave, Ltd., UK) or 1 x 10(5) cfu/g of each of three inoculant additives containing Lactobacillus fermentum (A), Leuconostoc mesenteroides (B), and Lactobacillus buchneri (C). Six replicates were conserved per treatment. Ensiling DM losses, chemical composition, fermentation characteristics, and aerobic stability were measured in the silages after 68 d of ensiling. All the silages were well fermented and remained stable for 84 h after aeration. Subsequently, the rate of deterioration was slowest in crimped grains treated with CS treatment, followed by those treated with inoculant C, while those treated with inoculant A deteriorated most rapidly. Residual water-soluble carbohydrate concentration was higher in crimped grains treated with CS than those treated with the inoculants. Ammonia nitrogen concentrations were lowest in CS-treated crimped grains, followed by inoculants C and A. DM losses were greater in CS-treated crimped grains than in crimped grains treated with inoculants A and C. In vivo digestibility was also measured in Texel-cross lambs fed a grass silage basal diet supplemented with the additive-treated crimped grains or a conventional, lamb finisher concentrate. Dry matter intake and digestibility were unaffected by treatment. In conclusion, bacterial inoculants containing L. buchneri are promising preservatives for crimped wheat grains. 相似文献
995.
The H+(aq) concentration in Wilmington, NC, precipitation has decreased by approximately 50% during the preceding two decades, similar to trends seen nationwide. The decrease in acidity is important because solution pH plays a key role in atmospheric reactions, and because the change is so large. This study presents the first long-range study of dissolved organic carbon (DOC) levels in precipitation which demonstrates that DOC concentrations have decreased by approximately half in Wilmington, NC, precipitation. The concentrations of H+(aq) and DOC are highly correlated primarily because small organic acids contribute to both DOC and H+(aq) in precipitation. Ammonium ion concentrations in precipitation have increased due to increased agricultural activities, and this also affects precipitation pH. The reduction of SO2 emissions in 1995 imposed by the Clean Air Act Amendment, better control of emissions of volatile organic compounds, and the increase in ammonia emissions all contribute to the decreasing H+(aq) in precipitation nationwide. These compositional changes in precipitation have many environmental implications, such as decreased acid deposition to lakes, changing speciation for trace metals in precipitation, increased ammonium deposition to coastal waters, and decreased DOC transport to the open ocean. 相似文献
996.
Caleb S. Brooks Basar Ozar Takashi Hibiki Mamoru Ishii 《International Journal of Heat and Mass Transfer》2012,55(21-22):6121-6129
The two-group two-fluid model with interfacial area transport equation has been developed to improve the prediction of void fraction and heat transfer characteristics in two-phase systems. In the one-dimensional formulation, a closure relation is required for the group-1 and group-2 area-average local relative velocity. Furthermore, in the case of the modified two-fluid model with the gas-mixture momentum equation, the group-1 and group-2 void weighted gas velocities must be calculated with additional closure relations. The drift-flux general expression is extended to two bubble groups in order to describe the group-1 and group-2 void weighted gas velocities and area-averaged local relative velocities. Correlations for group-1 and group-2 distribution parameters and drift velocities are proposed and evaluated with a two-group boiling dataset taken in an internally heated annulus. The proposed distribution parameters show an average agreement within ±5%. The overall estimation of group-1 and group-2 void weighted gas velocities calculated with the newly proposed two-group drift-flux general expression shows an average agreement within ±16% of the measured value. The equations obtained for area-averaged relative velocity of group-1 and group-2 bubbles were simplified by neglecting covariance in void fraction. This assumption was compared with the experimental database and resulted in an average error within ±13%. 相似文献
997.
Tanner BD Brooks JP Haas CN Gerba CP Pepper IL 《Environmental science & technology》2005,39(6):1584-1590
This study investigated bioaerosol emission rates and plume characteristics of bioaerosols generated during land application of liquid Class B biosolids. In addition, it compared the rate of aerosolization of coliphages and total coliform bacteria during land application of liquid Class B biosolids to the rate of aerosolization during land application of groundwater inoculated with similar concentrations of Escherichia coli and coliphage MS2. Air samples were taken immediately downwind of a spray applicator as it applied liquid (approximately 8% solids) biosolids to farmland near Tucson, Arizona. Air samples were also collected immediately downwind of groundwater seeded with MS2 and E. coli applied to land in an identical manner. Air samples, collected with liquid impingers, were taken in horizontal and vertical alignment with respect to the passing spray applicator. Vertical and horizontal sample arrays made it possible to calculate the flux of microorganisms through a virtual plane of air samplers, located 2 m downwind of the passing spray applicator. Neither coliphages nor coliform bacteria were detected in air downwind of spray application of liquid Class B biosolids. Based on limits of detection for the methodology, the rate of aerosolization during land application of liquid biosolids was calculated to be less than 33 plaque forming units (PFU) of coliphage and 10 colony forming units (CFU) of coliform bacteria per meter traveled by the spray applicator. The rate of aerosolization during land application of seeded groundwater was found to be, on average, 2.02 x 10(3) CFU E. coli and 3.86 x 10(3) PFU MS2 aerosolized per meter traveled by the spray applicator. This is greater aerosolization than was observed during land application of biosolids. Because concentrations of coliphages and coliforms were similar in the liquid biosolids and the seeded water, itwas concluded that some property of biosolids reduces aerosolization of microorganisms relative to groundwater. Additional experiments utilizing a novel air sampling protocol showed that the duration of bioaerosol exposure immediately (2 m) downwind of biosolids spray application is brief and the plume of bioaerosols generated is discrete. Additional air samples showed that aerosolization of coliphages and coliform bacteria after liquid biosolids have been applied to land does not occur at detectable levels. 相似文献
998.
Aquatic ecological risk assessment is primarily focused on aqueous exposure, but many hydrophobic contaminants bind to particulate material and accumulate in sediments. The risk posed by such contaminants is partially dependent on the importance of dietary exposure. Here, we describe the bioaccumulation of a highly hydrophobic compound (dioctadecyl-dimethyl ammonium chloride (DODMAC)) to four freshwater macroinvertebrates (i.e., Asellus aquaticus, Chironomus riparius, Gammarus pulex, Lumbriculus variegatus) and investigate the mechanistic basis for observed interspecific variation in bioaccumulation. Although more than 99.99% of DODMAC was sediment-bound, it was bioavailable to all four species via dietary exposure. Interspecific variation in bioaccumulation was apparent despite the lack of selective feeding and biotransformation potential and after normalization for body size and lipid content. Chironomus riparius had the highest lipid-normalized DODMAC concentration and L. variegatus had the lowest. Study species differed in factors affecting uptake (i.e., feeding rate) and absorption efficiency (i.e., gut passage time and gut surfactancy). Feeding rate did not explain interspecific variation in bioaccumulation, but bioaccumulation was enhanced by either high surfactancy and short gut passage time (e.g., G. pulex) or low surfactancy and long gut passage time (e.g., C. riparius). Risk assessment of hydrophobic contaminants should consider dietary exposure and the potential food chain effects of interspecific variation in bioaccumulation. 相似文献
999.
K. A. Brooks 《纺织学会志》2013,104(3):285-290
An investigation is reported in which a panel of judges, using visual and tactile skills, assessed a series of milled and wet-raised fabrics for smoothness, softness, and stiffness. It was found that fabric smoothness and softness were clearly related to the amount or raise given to the fabrics. 相似文献
1000.