全文获取类型
收费全文 | 1404篇 |
免费 | 22篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 27篇 |
化学工业 | 194篇 |
金属工艺 | 21篇 |
机械仪表 | 26篇 |
建筑科学 | 56篇 |
矿业工程 | 3篇 |
能源动力 | 42篇 |
轻工业 | 121篇 |
水利工程 | 9篇 |
石油天然气 | 2篇 |
无线电 | 180篇 |
一般工业技术 | 230篇 |
冶金工业 | 385篇 |
原子能技术 | 19篇 |
自动化技术 | 113篇 |
出版年
2023年 | 6篇 |
2022年 | 10篇 |
2021年 | 16篇 |
2020年 | 6篇 |
2019年 | 14篇 |
2018年 | 14篇 |
2017年 | 13篇 |
2016年 | 17篇 |
2015年 | 17篇 |
2014年 | 26篇 |
2013年 | 54篇 |
2012年 | 37篇 |
2011年 | 46篇 |
2010年 | 34篇 |
2009年 | 40篇 |
2008年 | 53篇 |
2007年 | 67篇 |
2006年 | 61篇 |
2005年 | 44篇 |
2004年 | 58篇 |
2003年 | 40篇 |
2002年 | 39篇 |
2001年 | 28篇 |
2000年 | 27篇 |
1999年 | 37篇 |
1998年 | 129篇 |
1997年 | 76篇 |
1996年 | 69篇 |
1995年 | 42篇 |
1994年 | 36篇 |
1993年 | 48篇 |
1992年 | 24篇 |
1991年 | 16篇 |
1990年 | 16篇 |
1989年 | 18篇 |
1988年 | 11篇 |
1987年 | 8篇 |
1986年 | 10篇 |
1985年 | 13篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 11篇 |
1979年 | 8篇 |
1978年 | 12篇 |
1977年 | 16篇 |
1976年 | 18篇 |
1975年 | 3篇 |
1972年 | 5篇 |
排序方式: 共有1428条查询结果,搜索用时 10 毫秒
11.
A Ehrnberg J De Pablos G Martinez-Lotti A Kreicbergs O Nilsson 《Canadian Metallurgical Quarterly》1993,11(3):438-447
The bone inductive capability of the Urist and Ilizarov procedures was compared in the repair of large diaphyseal defects in sheep. In 30 animals, a 4 cm segmental defect was created in the middle portion of the right femur and was stabilized with an external fixator. The sheep were divided into four groups according to the type of reconstruction of the defect. In group 1, a demineralized allogeneic bone matrix (DABM) cylinder was used; in group 2, DABM chips; and in group 3, gradual transport of a piece of bone detached from the proximal femoral fragment was used to fill the defect. Group 4 served as a control (the defect was left empty). New bone formation was assessed by serial radiographs until the time of death at 2 or 4 months. Postmortem specimens were analyzed with respect to bone mineral content, uptake of isotopes (45Ca and 3H-proline), and histology. The first signs of new bone formation were radiographically evident at 4 weeks. In the two groups in which reconstruction involved DABM (Urist procedures), new bone failed to form in eight of the 13 animals. Full bridging of the defect was observed at 8 weeks in one animal with a DABM cylinder and two with DABM chips. No decisive difference in bone yield could be demonstrated between the two Urist procedures. In the group treated with the Ilizarov procedure, new bone formation consistently occurred at a high rate; full bridging of the defect was observed in seven of the eight animals. Bone mineral scanning and histologic analysis essentially confirmed the radiographic results. Uptake of isotopes was selectively analyzed in two sheep from each experimental group in which new bone formation was exhibited in the defect; new bone formation was increased compared with that in the contralateral femur but was equal among the three experimental groups. Our study shows that gradual transport of a detached piece of autogeneic bone (Ilizarov procedure) is more effective than implantation of DABM (Urist procedure) in eliciting new bone formation in large diaphyseal defects in sheep. The variable bone induction by DABM may be explained by differences in host immune responses to the implants. 相似文献
12.
Various aspects on probabilistic modelling of cleavage fracture are discussed. The investigation involves consideration of
a unit cell with an explicitly modelled void. The results from this model are compared with results for the case when the
void content is accounted for in the sense of a Gurson-Tvergaard law. It is found that explicit modelling of the void can
give substantially different results for the fracture probability. The effect depends on the exponent in the assumed Weibull
distribution, the threshold stress, the constraint conditions and the hardening of the material.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
13.
David Lloyd Suzie Morrell Helle N. Carlsen Hans Degn Phillip E. James Christopher C. Rowlands 《Yeast (Chichester, England)》1993,9(8):825-833
Saccharomyces cerevisiae HSc was grown with ethanol at concentrations up to 10% (v/v). The immediate effects of additions of externally added ethanol on CO2 production and O2 consumption of washed organisms were studied by stopped-flow membrane inlet quadrupole mass spectrometry. Fermentative activities of organisms grown with ethanol (0–5% v/v) showed similar sensitivities to inhibition by ethanol, whereas those grown with 10% (v/v) ethanol had become protected and were markedly less sensitive. The fluidity of subcellular membrane fractions was measured by determination of the temperature dependence of the rotational order parameter of the spin label 5-doxyl stearic acid (free radical) by electron spin resonance. Mitochondria prepared from yeasts grown with 0, 7 and 9% (v/v) ethanol showed similar overall fluidity, although differences in temperature-dependent behaviour indicate altered lipid composition or lateral phase separations. On the other hand the microsomal fraction from organisms grown with 9% ethanol showed a remarkable increase in fluidity. These data suggest that the protective effects of growth with ethanol near the limit of tolerance on fermentative activities may arise from altered plasma membrane fluidity properties. 相似文献
14.
15.
16.
Oberg M. Rigole P.-J. Nilsson S. Klinga T. Backbom L. Streubel K. Wallin J. Kjellberg T. 《Lightwave Technology, Journal of》1995,13(9):1892-1898
The spectral characteristics of a widely tunable super structure grating distributed Bragg reflector (SSG-DBR) laser are investigated and the design considerations of the grating reflectors are given. By systematically adjusting the control currents of the two reflector sections and the phase section it is experimentally shown that every wavelength in an interval of 40 nm can be reached with a side-mode suppression usually better than 30 dB 相似文献
17.
S Thisted Lambertz A Ballagi-Pordány A Nilsson P Norberg ML Danielsson-Tham 《Canadian Metallurgical Quarterly》1996,81(3):303-308
The beige mutation is a murine autosomal recessive disorder, resulting in hypopigmentation, bleeding and immune cell dysfunction. The gene defective in beige is thought to be a homologue of the gene for the human disorder Chediak-Higashi syndrome. We have identified the murine beige gene by in vitro complementation and positional cloning, and confirmed its identification by defining mutations in two independent mutant alleles. The sequence of the beige gene message shows strong nucleotide homology to multiple human ESTs, one or more of which may be associated with the Chediak-Higashi syndrome gene. The amino acid sequence of the Beige protein revealed a novel protein with significant amino acid homology to orphan proteins identified in Saccharomyces cerevisiae, Caenorhabditis elegans and humans. 相似文献
18.
19.
Social media plays an increasingly prominent role in the interaction between impact assessments and society. Impact assessment is thus becoming part of social networks that are claimed to be able to improve interaction between actors in impact assessment processes. By investigating the use of social media in impact assessment and planning processes of national linear infrastructure development, we explore how social media impinge on participatory practices and how the potential of social media is realized in the current use related to public participation processes. The study focuses on experiences among national developers working in road, rail, electricity, gas, and metro infrastructures in Denmark. The article shows that the current use of social media in public participatory practices is limited to branding and on-way communication and that the increasing use of social media in linear infrastructure planning gives rise to a variety of concerns among developers that are related to especially organizational cultures, perception of the target groups, and prioritization of resources. 相似文献
20.
GB Hagberg F Blomstrand M Nilsson H Tamir E Hansson 《Canadian Metallurgical Quarterly》1998,32(2):153-162
A two-step exocytosis/endocytosis protocol was used in rat pancreatic acini to study membrane trafficking events at the apical plasma membrane (APM) as a function of extracellular pH. Exocytosis, as measured by cholecystokinin (CCK)-8-induced release of amylase into the incubation medium, was relatively insensitive to changes in extracellular pH from 5.5 to 9.0. In contrast, endocytosis, as measured by temperature-dependent uptake of horseradish peroxidase (HRP), was robust at pH values between 6.5 and 8.3 but abolished at acidic pH values of 5.5 to 6.0. Energy metabolism and cell viability were maintained during pH 6-induced cessation of HRP uptake, and the vesicular block could be reversed upon raising the luminal pH to 7.4. Histochemical and morphometric studies of HRP uptake examined by electron microscopy indicated that extracellular pH regulates endocytosis at the apical plasma membrane. At pH 6.0 in prestimulated cells, HRP uptake at the APM was abolished, and acinar lumen membranes remained markedly dilated with decreased density of microvilli and "arrested" exocytic images. At pH 7.4, HRP was taken up into endolysosomal structures within the Golgi complex, and acinar lumen membranes were contracted. Cleavage of GP2, a glycosyl phosphatidylinositol-anchored protein, was associated with the pH-dependent activation of HRP uptake. These studies demonstrate that acinar lumen pH regulates endocytic but not exocytic activity at the APM and suggest that alkalinization of the acinar lumen by duct cells is required for retrieval of exocytic membranes into the acinar cell via vesicular uptake mechanisms. The role of acid-base interactions within the acinar lumen provides a novel basis for understanding the cellular and luminal defects observed within the exocrine pancreas in cystic fibrosis. 相似文献