全文获取类型
收费全文 | 2930篇 |
免费 | 69篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 38篇 |
综合类 | 1篇 |
化学工业 | 387篇 |
金属工艺 | 53篇 |
机械仪表 | 47篇 |
建筑科学 | 89篇 |
矿业工程 | 7篇 |
能源动力 | 39篇 |
轻工业 | 322篇 |
水利工程 | 16篇 |
石油天然气 | 6篇 |
无线电 | 200篇 |
一般工业技术 | 360篇 |
冶金工业 | 1022篇 |
原子能技术 | 17篇 |
自动化技术 | 398篇 |
出版年
2022年 | 18篇 |
2021年 | 31篇 |
2020年 | 32篇 |
2019年 | 35篇 |
2018年 | 37篇 |
2017年 | 36篇 |
2016年 | 33篇 |
2015年 | 32篇 |
2014年 | 47篇 |
2013年 | 122篇 |
2012年 | 79篇 |
2011年 | 111篇 |
2010年 | 88篇 |
2009年 | 77篇 |
2008年 | 102篇 |
2007年 | 110篇 |
2006年 | 94篇 |
2005年 | 66篇 |
2004年 | 67篇 |
2003年 | 67篇 |
2002年 | 68篇 |
2001年 | 45篇 |
2000年 | 54篇 |
1999年 | 70篇 |
1998年 | 243篇 |
1997年 | 156篇 |
1996年 | 107篇 |
1995年 | 71篇 |
1994年 | 67篇 |
1993年 | 74篇 |
1992年 | 38篇 |
1991年 | 30篇 |
1990年 | 29篇 |
1989年 | 37篇 |
1988年 | 27篇 |
1987年 | 25篇 |
1986年 | 28篇 |
1985年 | 39篇 |
1984年 | 26篇 |
1983年 | 30篇 |
1982年 | 39篇 |
1981年 | 30篇 |
1980年 | 36篇 |
1979年 | 25篇 |
1978年 | 22篇 |
1977年 | 24篇 |
1976年 | 46篇 |
1975年 | 23篇 |
1972年 | 12篇 |
1963年 | 13篇 |
排序方式: 共有3002条查询结果,搜索用时 0 毫秒
91.
Governments use incentive programmes to attract new businesses. Due to limited resources, there are questions about which incentives are most effective. Using establishment data from California, and data on the location of disbursements through two federal programmes, we consider the effectiveness of different programmes in attracting new businesses. We find that the amount of funding through the New Markets Tax Credit programme has a significant impact on business activity but find no evidence of an effect from the Community Development Financial Institutions programme. Our results suggest that the effectiveness of these programmes depends on how they provide assistance. 相似文献
92.
93.
94.
Predictive microbiology: providing a knowledge-based framework for change management 总被引:7,自引:0,他引:7
This contribution considers predictive microbiology in the context of the Food Micro 2002 theme, "Microbial adaptation to changing environments". To provide a reference point, the state of food microbiology knowledge in the mid-1970s is selected and from that time, the impact of social and demographic changes on microbial food safety is traced. A short chronology of the history of predictive microbiology provides context to discuss its relation to and interactions with hazard analysis critical control point (HACCP) and risk assessment. The need to take account of the implications of microbial adaptability and variable population responses is couched in terms of the dichotomy between classical versus quantal microbiology introduced by Bridson and Gould [Lett. Appl. Microbiol. 30 (2000) 95]. The role of population response patterns and models as guides to underlying physiological processes draws attention to the value of predictive models in development of novel methods of food preservation. It also draws attention to the paradox facing today's food industry that is required to balance the "clean, green" aspirations of consumers with the risk, to safety or shelf life, of removing traditional barriers to microbial development. This part of the discussion is dominated by consideration of models and responses that lead to stasis and inactivation of microbial populations. This highlights the consequence of change on predictive modelling where the need is now to develop interface and non-thermal death models to deal with pathogens that have low infective doses for general and/or susceptible populations in the context of minimal preservation treatments. The challenge is to demonstrate the validity of such models and to develop applications of benefit to the food industry and consumers as was achieved with growth models to predict shelf life and the hygienic equivalence of food processing operations. 相似文献
95.
Anjela Manandhar Mona H. Haron Samir A. Ross Michael L. Klein Khaled M. Elokely 《International journal of molecular sciences》2022,23(8)
Vitamin E acetate, which is used as a diluent of tetrahydrocannabinol (THC), has been reported as the primary causative agent of e-cigarette, or vaping, product use-associated lung injury (EVALI). Here, we employ in vitro assays, docking, and molecular dynamics (MD) computer simulations to investigate the interaction of vitamin E with the membrane-bound cannabinoid 2 receptor (CB2R), and its role in modulating the binding affinity of THC to CB2R. From the MD simulations, we determined that vitamin E interacts with both CB2R and membrane phospholipids. Notably, the synchronized effect of these interactions likely facilitates vitamin E acting as a lipid modulator for the cannabinoid system. Furthermore, MD simulation and trajectory analysis show that when THC binds to CB2R in the presence of vitamin E, the binding cavity widens, facilitating the entry of water molecules into it, leading to a reduced interaction of THC with CB2R. Additionally, the interaction between THC and vitamin E in solution is stabilized by several H bonds, which can directly limit the interaction of free THCs with CB2R. Overall, both the MD simulations and the in vitro dissociation assay results indicate that THC binding to CB2R is reduced in the presence of vitamin E. Our study discusses the role of vitamin E in limiting the effect of THCs and its implications on the reported pathology of EVALI. 相似文献
96.
Insertion sequence (IS) elements were found to be associated with the truncation of predicted cellobiose transport, acetaldehyde dehydrogenase and diacetyl reductase genes in the genome of Lactobacillus helveticus DPC 4571. The conservation of the IS elements in these different genomic locations among L. helveticus cheese isolates was determined by amplification with gene-specific and IS element-specific primers. The presence of two of the IS elements was found to follow a genotypic profile of the strains generated by randomly amplified polymorphic DNA (RAPD)-PCR and strains that clustered by RAPD-PCR tended to have the IS element in the same position. However, the IS element that interrupted the cellobiose transport gene was found to be common to all strains tested. This conserved genotype suggests the insertion event occurred early in the evolution of L. helveticus as a separate species. 相似文献
97.
The porosity of a typical activated carbon is investigated with small angle neutron scattering (SANS), using the contrast matching technique, by changing the hydrogen/deuterium content of the absorbed liquid (toluene) to extract the carbon density at different scattering vector (Q) values and by measuring the p/p0 dependence of the SANS, using fully deuterated toluene. The contrast matching data shows that the apparent density is Q-dependent, either because of pores opening near the carbon surface during the activation processor or changes in D-toluene density in nanoscale pores. For each p/p0 value, evaluation of the Porod Invariant yields the fraction of empty pores. Hence, comparison with the adsorption isotherm, shows that the fully dry powder undergoes densification when liquid is added. An algebraic function is developed to fit the SANS signal at each p/p0 value hence yielding the effective Kelvin radii of the liquid surfaces as a function of p/p0. These values, when compared with the Kelvin equation, show that the resultant surface tension value is accurate for the larger pores but tends to increase for small (nanoscale) pores. The resultant pore size distribution is less model-dependent than for the traditional methods of analyzing the adsorption isotherms. 相似文献
98.
S.W. Fessenden T.J. Hackmann D.A. Ross E. Block A. Foskolos M.E. Van Amburgh 《Journal of dairy science》2019,102(4):3036-3052
The objective of this study was to evaluate the effect of a fermentation by-product on rumen function, microbial yield, and composition and flows of nutrients from the rumen in high-producing lactating dairy cattle. Eight ruminally cannulated multiparous Holstein cows averaging (mean ± standard deviation) 60 ± 10 d in milk and 637 ± 38 kg of body weight were randomly assigned to 1 of 2 treatment sequences in a switchback design. Treatment diets contained (dry matter basis) 44% corn silage, 13% alfalfa silage, 12% ground corn, and 31% protein premix, containing either a control mix of urea and wheat middlings (CON) or a commercial fermentation by-product meal (Fermenten, Arm and Hammer Animal Nutrition, Princeton, NJ) at 3% diet inclusion rate (EXP). The trial consisted of three 28-d experimental periods, where each period consisted of 21 d of diet adaptation and 7 d of data and sample collection. A triple-marker technique and double-labeled 15N15N-urea were used to were used to measure protozoal, bacterial, and nonmicrobial omasal flow of AA. Rumen pool sizes and omasal flows were used to determine digestion parameters, including fractional rates of carbohydrate digestion, microbial growth, and yield of microbial biomass per gram of degraded substrate. Fermentation by-product inclusion in EXP diets increased microbial N and amino acid N content in microbes relative to microbes from CON cows fed the urea control. Microbial AA profile did not differ between diets. Daily omasal flows of AA were increased in EXP cows as a result of decreased degradation of feed protein. The inclusion of the fermentation by-product increased nonmicrobial AA flow in cows fed EXP versus CON. Average protozoal contribution to microbial N flow was 16.8%, yet protozoa accounted for 21% of the microbial AA flow, with a range of 8 to 46% for individual AA. Cows in this study maintained an average rumen pool size of 320 g of microbial N, and bacterial and protozoal pools were estimated at 4 different theoretical levels of selective protozoa retention. Fractional growth rate of all microbes was estimated to be 0.069 h?1, with a yield of 0.44 g of microbial biomass per gram of carbohydrate degraded. Results indicated that fermentation by-product can increase omasal flow of AA while maintaining adequate rumen N available for microbial growth and protein synthesis. Simulations from a developmental version of the Cornell Net Carbohydrate and Protein System indicated strong agreement between predicted and observed values, with some areas key for improvement in AA flow and bacterial versus protozoal N partitioning. 相似文献
99.
Andrew D. Kligerman Garret B. Nelson Jeffrey A. Ross Gregory L. Erexson 《Polycyclic Aromatic Compounds》2013,33(3-4):841-851
Experiments were designed to investigate how the route of exposure to polycyclic aromatic hydrocarbons (PAHs) in mice and rats affects the induction of cytogenetic end points and DNA adduction. Both mice and rats were exposed to 100 mg/kg of benz[ a ]anthracene (B[ a ]A), benzo[ b ]fluoranthene (B[ b ]F), benzo[ a ]pyrene (B[ a ]P), or chrysene (Chr) by gavage or by intraperitoneal injection (i.p.). Peripheral blood was removed by cardiac puncture 7 days after PAH administration. Blood samples were analyzed in parallel for sister chromatid exchange (SCE) frequency, the frequency of micronuclei in cytochalasin B-induced binucleate cells (MN bn ), and DNA adduction using 32P-postlabeling. The i.p. route of exposure produced both the highest levels of cytogenetic damage and DNA adducts for each PAH. The mouse was more sensitive than the rat to PAH exposure as measured by SCE induction and the total amount of DNA adducts/ w g DNA. 相似文献
100.