全文获取类型
收费全文 | 311570篇 |
免费 | 4780篇 |
国内免费 | 1340篇 |
专业分类
电工技术 | 5056篇 |
综合类 | 547篇 |
化学工业 | 47314篇 |
金属工艺 | 11746篇 |
机械仪表 | 9152篇 |
建筑科学 | 7432篇 |
矿业工程 | 1654篇 |
能源动力 | 7663篇 |
轻工业 | 27807篇 |
水利工程 | 3318篇 |
石油天然气 | 5907篇 |
武器工业 | 49篇 |
无线电 | 34861篇 |
一般工业技术 | 61970篇 |
冶金工业 | 57874篇 |
原子能技术 | 7632篇 |
自动化技术 | 27708篇 |
出版年
2021年 | 3018篇 |
2020年 | 2327篇 |
2019年 | 2854篇 |
2018年 | 4941篇 |
2017年 | 4968篇 |
2016年 | 5298篇 |
2015年 | 3556篇 |
2014年 | 5639篇 |
2013年 | 14617篇 |
2012年 | 9010篇 |
2011年 | 11617篇 |
2010年 | 9050篇 |
2009年 | 10126篇 |
2008年 | 10401篇 |
2007年 | 10317篇 |
2006年 | 8658篇 |
2005年 | 7982篇 |
2004年 | 7833篇 |
2003年 | 7601篇 |
2002年 | 7322篇 |
2001年 | 7258篇 |
2000年 | 6858篇 |
1999年 | 7171篇 |
1998年 | 18289篇 |
1997年 | 12967篇 |
1996年 | 9789篇 |
1995年 | 7398篇 |
1994年 | 6427篇 |
1993年 | 6555篇 |
1992年 | 4581篇 |
1991年 | 4370篇 |
1990年 | 4224篇 |
1989年 | 4210篇 |
1988年 | 3899篇 |
1987年 | 3525篇 |
1986年 | 3514篇 |
1985年 | 3891篇 |
1984年 | 3582篇 |
1983年 | 3317篇 |
1982年 | 3143篇 |
1981年 | 3189篇 |
1980年 | 3186篇 |
1979年 | 2919篇 |
1978年 | 2952篇 |
1977年 | 3397篇 |
1976年 | 4682篇 |
1975年 | 2468篇 |
1974年 | 2427篇 |
1973年 | 2463篇 |
1972年 | 2048篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
A Lander R Redkar G Nicholls A Lawson SR Choudhury JJ Corkery P Gornall RG Buick IW Booth 《Canadian Metallurgical Quarterly》1997,77(2):F119-F122
AIM: To assess the efficacy of cisapride in reducing ileus persisting to the tenth postoperative day after neonatal abdominal surgery. METHODS: A prospective, randomised, double blind trial comparing rectal cisapride (1.4-2.3 mg/kg/day) with placebo over seven days was undertaken in 33 neonates. RESULTS: Seven of 12 (58%) patients receiving placebo and eight of 11 (73%) receiving cisapride achieved a first sustained feed during treatment. Of those receiving cisapride, the first sustained feed occurred at 2.3 days (SEM 0.6) compared with 4.7 days (SEM 0.8) with placebo. By the seventh day the mean daily net enteral balance was 69 (SEM 18) ml/kg in the cisapride subgroup and 17 (SEM 8) ml/kg for those receiving placebo. Stool was passed on 6.3 (SEM 0.4) treatment days in the cisapride subgroup compared with 4.1 (SEM 1.0) treatment days in the placebo subgroup. CONCLUSION: Cisapride is effective in neonates with a prolonged ileus after abdominal surgery. 相似文献
972.
973.
A method for imposing the gauge condition on the 3-D magnetic vector potential magnetostatic field computation using nodal finite elements is presented. In this method, the gauge A .w =0 is applied in the part of the problem that is not situated in the neighborhood of the materials interfaces that are tangential to w . This results in a formulation which maintains the discontinuous properties of the magnetic induction tangential components, reduces the number of unknowns, and improves the system matrix conditioning. The proposed formulation is compared with the Coulomb-gauge and ungauged formulations, showing that it results in better precision and worse conditioning than the Coulomb-gauge and has the same precision with a better conditioning than the ungauged formulation 相似文献
974.
975.
M. C. Julienne M. J. Alonso J. L. G
Mez Amoza J. P. Benoit 《Drug development and industrial pharmacy》1992,18(10):1063-1077
This study investigates the use of the solvent evaporation method for preparing acid and glycolic acid-based copolymer nanoparticles. Initially, appropriate technological and formulation factors for elaboration of polymeric particles were selected by screening. Most favourable results were obtained using polyvinyl alcohol as a dispersing agent and a high pressure homogenizer to reduce the droplet size of the emulsion initially formed. On the basis of the conclusion thus drawn, a composite rotational experimental design was employed to evaluate the joint influence of three formulation variables (phase volume ratio of the emulsion formed, polymer concentration and homogenization pressure) on the micromeritic properties of the suspension finally obtained (mean particle size, coefficient of variation and polydispersity of the particle size distribution). Analysis of variance corresponding to the experimental design, showed a significant influence of the volume phase ratio and the polymer concentration on the mean particle size and the coefficient of variation, whereas the polydispersity is also affected by the homogenization pressure. Considering this information, a 32 experimental factorial design was then selected to investigate the possible interaction between the phase volume ratio and the concentration of polyvinyl alcohol in the aqueous phase. Analysis of variance and subsequent sequencial regression analysis evidenced last hypothesis providing the way to determine the experimental conditions required to achieve a specific particle size distribution. 相似文献
976.
A stochastic damage mechanics failure model of composites This paper focuses on the theoretical simulation of strength and failure of specimens with nonlocal damage. A concept is proposed for quantitative interpretation and prediction of nonlinear. nominal stress-strain curves of damaged materials like fine ceramics or intermetallic alloys. For that reason methods of damage mechanics and of probability theory are combined. 相似文献
977.
Ivasashin O. M. Markovskii P. E. Dneprenko V. N. Boguslaev V. A. Nalimov Yu. S. Gerasimchuk O. N. 《Strength of Materials》1992,24(6):391-397
The influence of the structure and crystallographic texture of VT3-1 alloy formed by thermomechanical processing of a forging and also of the production factors of subsequent production of a gas turbine engine blade from the forging on the fatigue resistance characteristics was investigated. It was established that the reason for the reduction in fatigue limit and the significant spread in test data is nonuniformity of the structure and texture, both in different forgings and within the same forging, caused by variations in such parameters of thermomechanical processing as the temperature and degree of deformation. The nonuniformity plays a determining role in the reduction in fatigue limit as the result of hydrogen absorption during chemical etching. It was shown that such an effect may be eliminated by degassing vacuum annealing and the general level of fatigue resistance characteristics may be increased as the result of thermomechanical processing of forgings with strict observance of the specified forging temperature.Translated from Problemy Prochnosti, No. 6, pp. 12–19, June, 1992. 相似文献
978.
Air cleaning as a means of mitigating the risks arising from exposure to indoor radon progeny has been evaluated in a single-family house in the north eastem US. using an automated, semi-continuous activity-weighted size distribution measurement system. The measurements included radon concentration, condensation nuclei count, and activity-weighted size distribution of radon decay products. Measurements were made in the house with and without an operating air filtration system and with various particle sources common to normal indoor activities operating. Aerosols were generated by running water in a shower, candle burning, cigarette smoking, vacuuming, opening doors, and cooking. Using a room model, the changes in attachment rates, average attachment diameters, and deposition rates of the unattached fraction with and without the air cleaning system were calculated. In the presence of active aerosol sources, the air filtration unit typically reduced the concentration of particles within the hour following the end of particle generation. After candle burning, cigarette smoking, and vacuuming in the bedroom, the reductions of PAEC by air filtration are about 60% with the air filtration system operating in the bedroom. During cooking in the kitchen, the reductions of PAEC in the bedroom with the air filtration system were about 40%. However, for all cases the dose reductions were smaller than the particle and PAEC reductions. For those particles that were generated within the bedroom, there was a 20% to 50% reduction in dose. In the case of cooking where the door was open and particles infiltrated from the rest of the house, the dose reduction was only 5% on average and appears to be insignificant. Thus, the dose reductions were h e r than the reductions in activity concentration, but there were no cases where the estimated dose actually increased. 相似文献
979.
The long-term corrosion rate of passive iron in anaerobic alcaline solutions Gas generation is an important issue in safety assessments of low and intermediate level radioactive repositories. In this connection the hydrogen production from corrosion of passive iron in saturated calcium hydroxide, in dilute alkali hydroxide and cement porewater solutions has been determined. The measurements were performed manometrically using fusion sealed glass cells, the measurement periods being between 275 and 560 days. In 0.1 M and 0.04 M alkali hydroxide solutions the initial hydrogen generation rate was 12 mmol/m2yr corresponding to a linear corrosion rate of 64 nm/yr. The reaction rate decreases with time. The smallest value obtained after 330 days is 0.3 mmol/m2yr corresponding to 1.5 nm/yr. The influence on iron of the saturated calcium hydroxide solution and the calcic porewater solutions differs from that of the alkali hydroxide solutions. At pH 12.5 the hydrogen generation rate remains practically constant up to breaking off the experiment, the value being about 1 mmol/m2yr corresponding to 5 nm/yr. 相似文献
980.
S. F. Krivoi A. P. Krikovlyuk I. G. Moroz-Podvorchan F. I. Mushka E. M. Pik 《Cybernetics and Systems Analysis》1992,28(3):445-450
A trajectory problem of pursuit and evasion on a plane is considered for the case of equal absolute velocities of the players. Exact solutions are obtained for fixed initial conditions.Translated from Kibernetika i Sistemnyi Analiz, No. 3, pp. 138–143, May–June, 1992. 相似文献