全文获取类型
收费全文 | 2349篇 |
免费 | 9篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 35篇 |
综合类 | 4篇 |
化学工业 | 80篇 |
金属工艺 | 8篇 |
机械仪表 | 14篇 |
建筑科学 | 20篇 |
能源动力 | 19篇 |
轻工业 | 22篇 |
水利工程 | 10篇 |
石油天然气 | 4篇 |
无线电 | 46篇 |
一般工业技术 | 93篇 |
冶金工业 | 1909篇 |
原子能技术 | 15篇 |
自动化技术 | 82篇 |
出版年
2021年 | 8篇 |
2018年 | 6篇 |
2017年 | 7篇 |
2016年 | 4篇 |
2014年 | 10篇 |
2013年 | 40篇 |
2012年 | 15篇 |
2011年 | 13篇 |
2010年 | 9篇 |
2009年 | 17篇 |
2008年 | 16篇 |
2007年 | 21篇 |
2006年 | 29篇 |
2005年 | 23篇 |
2004年 | 25篇 |
2003年 | 20篇 |
2002年 | 21篇 |
2001年 | 16篇 |
2000年 | 19篇 |
1999年 | 69篇 |
1998年 | 654篇 |
1997年 | 337篇 |
1996年 | 200篇 |
1995年 | 111篇 |
1994年 | 93篇 |
1993年 | 118篇 |
1992年 | 29篇 |
1991年 | 24篇 |
1990年 | 32篇 |
1989年 | 34篇 |
1988年 | 25篇 |
1987年 | 20篇 |
1986年 | 32篇 |
1985年 | 13篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 12篇 |
1981年 | 20篇 |
1980年 | 21篇 |
1979年 | 5篇 |
1978年 | 12篇 |
1977年 | 35篇 |
1976年 | 84篇 |
1975年 | 6篇 |
1974年 | 7篇 |
1967年 | 2篇 |
1965年 | 2篇 |
1923年 | 3篇 |
1922年 | 3篇 |
1921年 | 3篇 |
排序方式: 共有2361条查询结果,搜索用时 296 毫秒
21.
22.
The chondro-osseous junction has been the subject of considerable scrutiny, especially in terms of the fate and role of the terminally differentiated chondrocyte. Although it has been proposed that these cells change their phenotype and survive in the epiphysis, possibly as osteoblasts, evidence from a number of other studies suggests that chondrocytes may undergo apoptosis or programmed cell death. A useful test for programmed cell death is to end label DNA in cryosections using the commercial reagent ApopTag and detect antibody binding to fragmented DNA by epifluorescence; more direct assessments include examination of the nucleus for condensation of chromatin evaluating fragmentation through alkaline and pulsed field agarose gel electrophoresis of DNA, and measuring apoptosis by flow cytometry. We found that we could label cells in the proliferative and the hypertrophic region of the proximal tibial growth plate of the chick with ApopTag. Most of the chondrocytes in the hypertrophic region were labeled by the reagent; in contrast, few proliferative chondrocytes were stained by the end-labeling procedure. Both agarose and pulsed field electrophoresis were used to confirm that there was fragmentation of chondrocyte DNA. Alkaline gel electrophoresis indicated that there was more fragmentation of DNA from hypertrophic cells than from proliferative chondrocytes. Further evidence in support of apoptosis was provided by electron microscopic observation of cells in the hypertrophic region of the growth plate. We noted that many of the cells in this region of the growth plate appeared to be undergoing programmed cell death since their nuclei contained condensed chromatin. Finally, we used flow cytometry to analyze chondrocytes isolated from the proliferating and hypertrophic regions of the growth plate for apoptosis. Dual parameteric flow cytometric contour plots of Hoechst and 7-amino-actinomycin D fluorescence showed that abut 8% of cells in the plate were apoptotic. Most of these cells were in hypertrophic cartilage. In summary, the results of this investigation indicate that chondrocytes terminate their life history by apoptosis. While it is possible that the terminal labeling studies may overestimate the number of cells undergoing this event, the data lend credence to the view that cells are removed from the epiphysis through apoptosis. If this is the case, then chondrocytes probably enter the terminal phase of their life as fully functioning cells and genomic, and/or local environmental conditions provide termination signals that initiate events that lead to programmed cell death. 相似文献
23.
KK Doak CE Haas KJ Dunnigan RA Reiss JR Reiser J Huntress JL Altavela 《Canadian Metallurgical Quarterly》1998,18(3):637-645
In the absence of E1B, the 289-amino acid product of human adenovirus type 5 13S E1A induces p53-independent apoptosis by a mechanism that requires viral E4 gene products (Marcellus, R.C., J.C. Teodoro, T. Wu, D.E. Brough, G. Ketner, G.C. Shore, and P.E. Branton. 1996. J. Virol. 70:6207-6215) and involves a mechanism that includes activation of caspases (Boulakia, C.A., G. Chen, F.W. Ng, J. G. Teodoro, P.E. Branton, D.W. Nicholson, G.G. Poirier, and G.C. Shore. 1996. Oncogene. 12:529-535). Here, we show that one of the E4 products, E4orf4, is highly toxic upon expression in rodent cells regardless of the p53 status, and that this cytotoxicity is significantly overcome by coexpression with either Bcl-2 or Bcl-XL. Conditional expression of E4orf4 induces a cell death process that is characterized by apoptotic hallmark features, such as externalization of phosphatidylserine, loss of mitochondrial membrane potential, cytoplasmic vacuolation, condensation of chromatin, and internucleosomal DNA degradation. However, the wide-spectrum inhibitor of caspases, tetrapeptide zVAD-fmk, does not affect any of these apoptogenic manifestations, and does not alter the kinetics of E4orf4-induced cell death. Moreover, E4orf4 expression does not result in activation of the downstream effector caspase common to most apoptosis-inducing events, caspase-3 (CPP32). We conclude, therefore, that in the absence of E1A, E4orf4 is sufficient by itself to trigger a p53-independent apoptosis pathway that may operate independently of the known zVAD-inhibitable caspases, and that may involve an as yet uncharacterized mechanism. 相似文献
24.
Hepatic and pancreatic effects of polyenoylphosphatidylcholine in rats with alloxan-induced diabetes
V Buko O Lukivskaya V Nikitin Y Tarasov L Zavodnik A Borodinsky B Gorenshtein B Janz KJ Gundermann R Schumacher 《Canadian Metallurgical Quarterly》1996,14(2):131-137
In neonatally allylestrenol treated animals in adult age a single benzpyrene treatment significantly decreases the female and significantly increases the male rat's sexual activity. Three month old females display the negative sexual behavioral effect of neonatal allylestrenol treatment less than the six month old ones. The benzpyrene treatment in adult age decreases the sexual activity of male rats. The experiments call the attention to the modifying effect of perinatal steroid treatments to similar exposure in adult age. 相似文献
25.
N Iyer MS Reagan KJ Wu B Canagarajah EC Friedberg 《Canadian Metallurgical Quarterly》1996,35(7):2157-2167
26.
Selhi H. Christopoulos C. Howe A.F. Hui S.Y.R. 《Energy Conversion, IEEE Transaction on》1996,11(2):287-297
The simulation of a complete induction motor drive is presented. The entire network is modelled using the transmission-line modelling (TLM) technique. The network is split into three sections which are solved independently and are joined together by link transmission-line models. Advantages of this approach are the explicit nature of the algorithm which remains unaltered irrespective of the network topology, unconditional stability, and straightforward modelling of switching elements. Results are presented for a complete drive which illustrate the capabilities and flexibility of the simulation technique 相似文献
27.
28.
29.
30.
Human peripheral blood monocytes were examined for migration across an endothelial cell monolayer in an in vitro vessel wall construct. Few monocytes invaded in the absence of a chemotactic gradient, despite significant adhesion to the endothelial monolayer. However, the addition of zymosan-activated human plasma to the lower compartment, to create a chemotactic gradient across the vessel wall, resulted in significantly enhanced monocyte migration. Pretreatment of the monocytes with monoclonal antibodies to thrombospondin (TSP) dramatically inhibited monocyte diapedesis into the vessel wall. The same treatment inhibited monocyte adhesion to endothelial cells in two-dimensional monolayer cultures as well as in vessel wall constructs (no chemotactic gradient). Of interest, however, the monoclonal antibodies had no inhibitory effect on monocyte migration into collagen gels devoid of endothelial cells in response to the same chemotactic gradient, suggesting the importance of TSP in monocyte-endothelial cell interactions. Monoclonal antibodies to fibronectin and normal mouse immunoglobulin G did not inhibit migration in this model of a vessel wall. Furthermore, monoclonal antibodies to TSP showed no inhibition of human peripheral blood neutrophil migration. Previous studies have shown that monocytes synthesize TSP and express this moiety on their surface. The present data suggest that monocytes may utilize TSP to interact with endothelial cells lining the vessel wall during diapedesis. 相似文献