全文获取类型
收费全文 | 432844篇 |
免费 | 11422篇 |
国内免费 | 5490篇 |
专业分类
电工技术 | 11397篇 |
技术理论 | 14篇 |
综合类 | 5935篇 |
化学工业 | 65856篇 |
金属工艺 | 19329篇 |
机械仪表 | 15473篇 |
建筑科学 | 15229篇 |
矿业工程 | 3791篇 |
能源动力 | 10429篇 |
轻工业 | 35479篇 |
水利工程 | 4903篇 |
石油天然气 | 10998篇 |
武器工业 | 745篇 |
无线电 | 51569篇 |
一般工业技术 | 77291篇 |
冶金工业 | 75252篇 |
原子能技术 | 7547篇 |
自动化技术 | 38519篇 |
出版年
2022年 | 4091篇 |
2021年 | 6106篇 |
2020年 | 4399篇 |
2019年 | 4642篇 |
2018年 | 6450篇 |
2017年 | 6698篇 |
2016年 | 6907篇 |
2015年 | 6396篇 |
2014年 | 9649篇 |
2013年 | 20014篇 |
2012年 | 14744篇 |
2011年 | 18459篇 |
2010年 | 15345篇 |
2009年 | 16218篇 |
2008年 | 16851篇 |
2007年 | 17068篇 |
2006年 | 15931篇 |
2005年 | 14164篇 |
2004年 | 11923篇 |
2003年 | 11124篇 |
2002年 | 10506篇 |
2001年 | 10762篇 |
2000年 | 10403篇 |
1999年 | 11062篇 |
1998年 | 23835篇 |
1997年 | 17000篇 |
1996年 | 13321篇 |
1995年 | 9790篇 |
1994年 | 8788篇 |
1993年 | 8289篇 |
1992年 | 6006篇 |
1991年 | 5682篇 |
1990年 | 5564篇 |
1989年 | 5322篇 |
1988年 | 4882篇 |
1987年 | 3975篇 |
1986年 | 4033篇 |
1985年 | 4350篇 |
1984年 | 4146篇 |
1983年 | 3771篇 |
1982年 | 3377篇 |
1981年 | 3572篇 |
1980年 | 3184篇 |
1979年 | 3288篇 |
1978年 | 3125篇 |
1977年 | 3368篇 |
1976年 | 4630篇 |
1975年 | 2743篇 |
1974年 | 2547篇 |
1973年 | 2557篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
W Guo RS Lovell YH Zhang BL Huang TP Burris WJ Craigen ER McCabe 《Canadian Metallurgical Quarterly》1996,178(1-2):31-34
We cloned the murine full-length cDNA encoding Ahch, the mouse homologue of DAX1 (DSS-AHC Region on Human X Chromosome, Gene1) which is the gene responsible for human X-linked adrenal hypoplasia congenita (AHC) and hypogonadotropic hypogonadism (HH). Sequence analysis revealed that the murine and human cDNAs have 65% aa identity and 75% aa similarity overall. The cysteine residues in the putative DNA binding domain, which may interact with Zn2+ ions to form zinc fingers, are 100% conserved between the two species, indicating that the novel zinc-finger structures in DAX1 may be functional. In addition, mouse interspecific backcrosses show that the Ahch gene is closely linked to the glycerol kinase locus, GyK, on the mouse X chromosome, indicating that the order of the loci is conserved in this syntenic region between mouse and human. 相似文献
992.
龙潭拱坝坝高90m,砼上坝运输是砼施工过程中的中间环节,控制进度的关键,必须因时因地制宜地选择适当的运输机械和运输方案,使砼运输能做到保质、保量、及时和经济,通过论证比较,结合本工程现实情况,砼上坝运输不采用缆机而采用门机方案. 相似文献
993.
994.
This article examines the mathematical aspects of a method developed for frequency-time correction of distortions of radiation
patterns recorded in a closed range with partial echo suppression. The efficiency of the method is analyzed with allowance
for the dimensions of the range and the bandwidth of the test antenna.
Translated from Izmeritel'naya Tekhnika, No. 12, pp. 44–46, December, 1996. 相似文献
995.
K. Goracinova Lj Klisarova A. Simov E. Fredro-kumbaradzi L. Petrusevska-tozi 《Drug development and industrial pharmacy》1996,22(3):255-262
Verapamil hydrochloride solid dispersion granules were prepared using solvent evaporation technique. Ethyl cellulose, hydroxypropyl cellulose, Eudragit L or Eudragit S were used as polymers for controlling the dissolution rate of the drug substance, and to avoid the continuous decrease of drug dissolution rate at higher pH values. By incorporating Eudragit L in ethyl cellulose network it is possible to prepare controlled-release formulation with increased release rate of active substance (weak base) at higher pH values without causing abrupt drug release at lower pH values. The release rate at low pH values was not highly influenced by Eudragit L content. The behavior of Eudragit L and Eudragit S in coprecipitates was different relating to the solubilization effect and the release of active substance. In order to understand the drug release mechanism better, the release data were tested assuming Higuchi model and first-order kinetic model. Since the calculated correlation coeflcients were very close for both kinetics, to distinguish between the mechanisms the differential forms of first-order and square root of time equation were used. The differential test showed that diffusion-controlled release was operative in solid dispersions, except for series with higher content of Eudragit S. X-ray powder difSraction method, IR spectroscopy studies, and differential thermal analysis were used for physical characterization of coprecipitates and drugpolymer interaction evaluation. After 24 months of real time stability studies, the prepared coprecipitates were still x-ray amorphous, with no changes in their IR spectra and DTA studies. Ehe dissolution rates of the tested formulations showed no significant changes during the stability studies, reflecting the stability of x-ray amorphous drug phase. 相似文献
996.
Spreading depression (SD) is known to be involved in the N-methyl-D-aspartate receptor-mediated neuronal damage. In urethane-anesthetized rats, we examined the release of adenosine and glutamate during SD induced by microdialysis of high K+ perfusate through the hippocampal CA1 area. The effects of endogenous adenosine upon SD were studied by applying an adenosine antagonist, theophylline (1 mM) and by a simultaneous application of adenosine uptake blockers, dipyridamole (DPR) (100 microM) and nitrobenzylthioinosine (NBI) (50 microM). The dialysates were sampled every 5 or 10 min and analyzed by HPLC. SD was identified by flattening of background EEg and disappearance of population spikes recorded from the pyramidal cell layer of CA1 area by a glass microelectrode. Adenosine and glutamate release was enhanced significantly in association with the occurrence of SD. Theophylline increased the release of glutamate and the incidence of SD and decreased the latency of the SD occurrence. DPR+NBI decreased the release of glutamate and the occurrence of SD, but increased extracellular adenosine concentration. The effects of DPR+NBI were blocked by application of a selective antagonist of adenosine A1 receptor, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 0.1 microM). These findings suggest that endogenous adenosine exerts inhibitory influences upon the development of SD and the glutamate release through the A1 receptor in rat hippocampus. 相似文献
997.
To provide insight into the stream of Medicare payments over time, a sixteen-year longitudinal study examines three age cohorts of beneficiaries, looking separately at beneficiaries who died during the study period and those who survived. The common wisdom that a small minority of the population accounts for a large majority of health care expenditures is tempered when health care use is examined over an extended period of time. By putting high average costs in the final years of life in the context of a cohort's total lifetime experience, the study shows a leveling of spending over time, resulting in a lower concentration of health care resources on a small fraction of the population. 相似文献
998.
999.
Calculation methods for comparing the performance of pure and mixed working fluids in heat pump applications 总被引:2,自引:0,他引:2
Three methods for comparing cycle performance of working fluids, pure as well as non-azeotropic mixtures, are investigated for two applications and for two mixture pairs, HCFC22-CFC114 and HCFC22-HCFC142b, and their pure components. The methods differ in the way of calculating the heat exchange processes. They assume, respectively, equal minimum approach temperatures, equal mean temperature differences and equal heat transfer areas. Changes of coefficient of performance (COP) with composition are explained for all methods. It is shown that transport properties must be taken into account when making rigorous comparisons between working fluids. To predict the relations between fluids with high accuracy, one must use the method with equal heat transfer areas. By the method with equal mean temperature differences, the COP can be estimated with the same accuracy for mixtures as for pure fluids, and can be used for rough estimations of the COP level with different fluids. The method of equal minimum approach temperatures should be avoided for non-azeotropic mixtures. 相似文献
1000.
Research in object-oriented manufacturing simulations:an assessment of the state of the art 总被引:1,自引:0,他引:1
S. Narayanan D.A. Bodner T. Govindaraj L.F. Mcginnis C.M. Mitchell U. Sreekanth 《IIE Transactions》1998,30(9):795-810
Object-oriented programming (OOP) has been revolutionizing software development and maintenance. When applied to simulation of manufacturing systems, OOP also provides an opportunity for developing new ways of thinking and modeling. In this paper, we identify existing large-scale, persistent OOP-based research efforts focusing on manufacturing system simulation, and present an integrating framework for discussing the associated modeling abstractions, implementation strategies, common themes, and distinctive features. The goal is to identify the fundamental research and application issues, assess the current state of the art, and identify key research needs. 相似文献