全文获取类型
收费全文 | 506308篇 |
免费 | 8824篇 |
国内免费 | 3164篇 |
专业分类
电工技术 | 10297篇 |
技术理论 | 2篇 |
综合类 | 2609篇 |
化学工业 | 74772篇 |
金属工艺 | 18510篇 |
机械仪表 | 15847篇 |
建筑科学 | 14856篇 |
矿业工程 | 2299篇 |
能源动力 | 14196篇 |
轻工业 | 47934篇 |
水利工程 | 4521篇 |
石油天然气 | 7564篇 |
武器工业 | 221篇 |
无线电 | 65997篇 |
一般工业技术 | 93055篇 |
冶金工业 | 92371篇 |
原子能技术 | 8238篇 |
自动化技术 | 45007篇 |
出版年
2022年 | 3255篇 |
2021年 | 5106篇 |
2020年 | 3795篇 |
2019年 | 4197篇 |
2018年 | 6412篇 |
2017年 | 6646篇 |
2016年 | 6899篇 |
2015年 | 5432篇 |
2014年 | 8760篇 |
2013年 | 24003篇 |
2012年 | 14077篇 |
2011年 | 19185篇 |
2010年 | 15431篇 |
2009年 | 17018篇 |
2008年 | 17857篇 |
2007年 | 17693篇 |
2006年 | 16233篇 |
2005年 | 14507篇 |
2004年 | 13535篇 |
2003年 | 13503篇 |
2002年 | 12488篇 |
2001年 | 13132篇 |
2000年 | 12122篇 |
1999年 | 13234篇 |
1998年 | 31741篇 |
1997年 | 22145篇 |
1996年 | 16974篇 |
1995年 | 12852篇 |
1994年 | 11318篇 |
1993年 | 11022篇 |
1992年 | 7831篇 |
1991年 | 7414篇 |
1990年 | 7074篇 |
1989年 | 6694篇 |
1988年 | 6509篇 |
1987年 | 5356篇 |
1986年 | 5195篇 |
1985年 | 6016篇 |
1984年 | 5414篇 |
1983年 | 5132篇 |
1982年 | 4709篇 |
1981年 | 4697篇 |
1980年 | 4449篇 |
1979年 | 4110篇 |
1978年 | 3794篇 |
1977年 | 4556篇 |
1976年 | 6079篇 |
1975年 | 3178篇 |
1974年 | 3062篇 |
1973年 | 3074篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Studied the effects of variations in base rate (BR) information and temporal context on predictions of violence and hindsight bias (HB). 270 undergraduates estimated the likelihood of violent offenders committing another violent offense based upon fictitious case history information. Ss were given 1 of 2 population BRs of the likelihood of reoffending (30% or 70%) and a recidivism estimation question that was phrased either predictively, predictively with a given outcome of either recidivism or no recidivism, or postdictively. Although different offenders were perceived as differentially likely to reoffend, estimated likelihood of recidivism was affected by neither BR nor temporal phrasing of the estimation task. A 2nd study of 182 undergraduates, using shorter case histories, also found no BR effect. HB effects were weak and inconsistent in both studies. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
992.
993.
994.
Hepatocyte growth factor (HGF) is known to induce the dispersion of epithelial cells, as scatter factor. On the other hand, cadherins play a crucial role in connecting cells together. Two groups of cadherins are involved in epithelial cell adhesion, those locating in adherens junctions (AJ) and in desmosomes. Here, we examined the effect of HGF on the function of these cadherins in keratinocyte cell lines F and 308R, which expressed E- and P-cadherin in AJ (referred to as AJ cadherins) and desmoplakin in desmosomes. In the presence of HGF, these cells spread more extensively than in control cultures and their associations apparently loosened. However, they maintained cell-cell contacts where cadherins and desmoplakin concentrated, although the level of the concentration was reduced by HGF treatment. When antibodies to E- and P-cadherins were added to cultures of these cells without HGF, AJ cadherins were redistributed into non-junctional areas of the cells, but desmoplakin still localized at cell-cell boundaries. When HGF was added together with anti-AJ cadherin antibodies to the cultures, cell-cell contacts were now disrupted. In these cultures, not only AJ cadherins but also desmoplakin were lost at cell-cell contact sites, indicating that HGF can disrupt desmosomal cell-cell adhesion when AJ cadherins are inactive. These results suggest that, although HGF cannot block cadherin-mediated cell-cell adhesion when the entire cadherin system is intact, it might modulate the activities of cadherins, especially, of desmosomal cadherins. 相似文献
995.
996.
C Nieto 《Archivos latinoamericanos de nutrición》1991,41(2):213-221
An analysis of tuber roots yield and nutritional characteristics for 10 lines of jícama (Polymnia sonchifolia Poepp et Endl.) was carried out under the environmental conditions of Santa Catalina Experimental Station (12 degrees C of temperature and 3,100 m above sea level). The following average mean values were obtained: A fresh tuber root's yield from 29,755 to 73,558 kg/ha with 41,547 kg/ha of average, while the yield of the useful part (roots without skin) was from 24,309 to 60,097 kg/ha with 33,944 kg/ha of average. On the other hand, average mean values of 3.7% of protein, 3.5% ashes, 1.5% fat, 3.4% fiber, 2.2% potassium, 0.12% phosphorus, 96 micrograms/100 g iron, and 390 micrograms/100 g zinc, were obtained from the edible root samples. Besides, we obtained average values of 2.47, 2.12, 1.63 and 2.51 g/100 g of fructose, alfa glucose, beta glucose and saccharose, respectively, on edible root samples with skin, for the 10 lines studied. All these analyses were reported on a dry basis. 相似文献
997.
Inbreeding coefficients were computed for 910,444 animals of the Swiss Braunvieh population. Of the animals born in 1984, 71.5% were inbred with 67.9, 3.4, and .2% having inbreeding coefficients between greater than 0 and 5%, greater than 5 to 10%, and greater than 10%, respectively. The average inbreeding coefficient was 1.14% but, for animals with both parents and at least one grandparent known, it was 1.67%. Breeding values for total milk, fat, and protein yields and for fat and protein percentages were predicted using a repeatability animal model including a regression on the inbreeding coefficient. Phenotypic performance was sizeably depressed for milk yield only (-26 kg/% of inbreeding or 2.4% of the phenotypic standard deviation). Adjusting for inbreeding increased the estimated genetic trend slightly. Inbreeding is only partially accounted for when it is ignored in the construction of the inverse of the numerator relationship matrix. This effect was investigated by comparing predicted breeding values from a model including the complete matrix with predicted breeding values from a model including a matrix constructed with inbreeding ignored. Only .8% of all predicted breeding values were affected by more than +/- 5.5 kg. The maximum difference observed was 55.3 kg. The observed average absolute differences between the breeding values of offspring predicted with the two models increased with inbreeding of parents. 相似文献
998.
C. Guminski 《Journal of Phase Equilibria》1992,13(6):657-663
An erratum to this article is available at . 相似文献
999.
Anjana Bhattacharya Jagannath Das Swapan Mitra Sisir K. Roy 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1992,54(4):399-407
Silicoaluminophosphate (SAPO-5) molecular sieves have been synthesised from reaction mixtures having a molar composition of: 0.7–1.0 Al2O3:0.7–1.0 P2O5:0.01–2.0 SiO2:xR:40 H2O (where R = (C2H3)3N or (C2H3)4NOH and x = 1.5–2.5 for (C2H5)5N and 0.5 for (C2H5)4NOH, at 473 K using various sources of alumina and silica. The effects of (i) varying the crystallinity of the alumina source (boehmite) and (ii) the use of different silica sources such as freshly prepared silica either from sodium silicate or paddy husk extract, silica gel from commercial water-glass, and tetraethyl orthosilicate have been studied. The crystallinity of boehmite has been found to have a strong effect on its reactivity towards the formation of SAPO-5. The activity of boehmite for SAPO-5 formation increased with a decrease in its crystallinity (or with increase in its moisture content). Any silica source devoid of sodium ions could be employed for the synthesis of SAPO-5. The process of crystallisation started as early as within 1.5 h of reaction and incorporation of silicon into the AlPO4 framework has been noted at this stage. Formation of some tridymite phase as impurity has been observed under conditions such as (i) SiO2 concentration > 1.7 mole and (ii) x > 2.0 when R = (C2H5)3N. 相似文献
1000.
K. Scott 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1992,54(3):257-266
This paper presents a relatively straightforward approach to the modelling of electrochemical reactors operated in batch or continuous modes. The models are based on ideal flow assumptions of either well-mixed or plug flow and incorporate reaction rate models based on electrochemical kinetics and mass transport at one electrode. General characteristics of the reactor models are described, particularly with regard to the need for good mass transport in metal recovery applications. An example is given on the use of the model in the recovery of a heavy metal (Cd2+) from an acidified solution containing Cd(II) and Fe(III) ions. The reaction rate model is based on experimental data. 相似文献