全文获取类型
收费全文 | 16958篇 |
免费 | 565篇 |
国内免费 | 29篇 |
专业分类
电工技术 | 211篇 |
综合类 | 14篇 |
化学工业 | 3621篇 |
金属工艺 | 323篇 |
机械仪表 | 360篇 |
建筑科学 | 703篇 |
矿业工程 | 98篇 |
能源动力 | 458篇 |
轻工业 | 1204篇 |
水利工程 | 196篇 |
石油天然气 | 120篇 |
无线电 | 1023篇 |
一般工业技术 | 2854篇 |
冶金工业 | 3476篇 |
原子能技术 | 147篇 |
自动化技术 | 2744篇 |
出版年
2023年 | 104篇 |
2022年 | 180篇 |
2021年 | 259篇 |
2020年 | 204篇 |
2019年 | 209篇 |
2018年 | 300篇 |
2017年 | 278篇 |
2016年 | 317篇 |
2015年 | 301篇 |
2014年 | 435篇 |
2013年 | 1125篇 |
2012年 | 718篇 |
2011年 | 894篇 |
2010年 | 655篇 |
2009年 | 657篇 |
2008年 | 804篇 |
2007年 | 749篇 |
2006年 | 689篇 |
2005年 | 610篇 |
2004年 | 544篇 |
2003年 | 465篇 |
2002年 | 471篇 |
2001年 | 313篇 |
2000年 | 278篇 |
1999年 | 301篇 |
1998年 | 346篇 |
1997年 | 314篇 |
1996年 | 294篇 |
1995年 | 248篇 |
1994年 | 270篇 |
1993年 | 236篇 |
1992年 | 242篇 |
1991年 | 164篇 |
1990年 | 211篇 |
1989年 | 221篇 |
1988年 | 173篇 |
1987年 | 208篇 |
1986年 | 179篇 |
1985年 | 207篇 |
1984年 | 218篇 |
1983年 | 181篇 |
1982年 | 177篇 |
1981年 | 142篇 |
1980年 | 134篇 |
1979年 | 144篇 |
1978年 | 119篇 |
1977年 | 145篇 |
1976年 | 126篇 |
1975年 | 120篇 |
1974年 | 109篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
A George J Gui NA Jenkins DJ Gilbert NG Copeland A Veis 《Canadian Metallurgical Quarterly》1994,42(12):1527-1531
Dentinogenesis is being used as a model for understanding the biomineralization process. The odontoblasts synthesize a structural matrix comprised of Type I collagen fibrils which define the basic architecture of the tissue. The odontoblasts also synthesize and deliver a number of dentin-specific acidic macromolecules into the extracellular compartment. These acidic macromolecules may be involved in regulating the ordered deposition of hydroxyapatite crystals within the matrix. AG1 is the first tooth-specific acidic macromolecule to have been cloned and sequenced. To identify which cells of the rat incisor pulp/odontoblast complex were responsible for synthesis of AG1, in situ hybridization was used. Digoxigenin labeled sense and anti-sense AG1 riboprobes were prepared. The AG1 mRNA was found to be expressed in the mature secretory odontoblasts. Neither pulp cells nor pre-odontoblasts showed any staining with the anti-sense probes. Chromosomal localization studies placed the AG1 gene on mouse chromosome 5q21, in tight linkage with Fgf5. AG1 has been renamed Dmp1 (dentin matrix protein 1) in accordance with present chromosomal nomenclature. Mouse 5q21 corresponds to the 4q21 locus in humans. This is the locus for the human tooth mineralization disorder dentinogenesis imperfecta Type II (DI-II). These data suggest that the Dmp1 gene is involved in mineralization and is a candidate gene for DI-II. 相似文献
182.
183.
H Reznik-Wolf TA Treves M Davidson J Aharon-Peretz PH St George Hyslop J Chapman AD Korczyn B Goldman E Friedman 《Canadian Metallurgical Quarterly》1996,98(6):700-702
Germline mutations in the presenilin 1 (PS1) gene apparently account for the majority of early-onset, familial Alzheimer's disease (AD). Using a mutation-screening strategy (denaturing gradient gel electrophoresis; DGGE), we analyzed a large family with early onset AD and seizures. The patients in this family showed a novel missense mutation in exon 5 of the PS1 gene (A to T change in codon 120, altering glutamine to aspartic acid). This novel mutation is located within the second hydrophilic domain of the molecule, a region not particularly involved in previously described germline mutations, and is of unknown biological significance. These results also demonstrate that DGGE can be used effectively to screen for mutations within this gene. 相似文献
184.
Chung-In Um Jae-Rok Kahng Kyu-Hwang Yeon Thomas F. George 《Journal of Low Temperature Physics》1996,102(3-4):307-324
Using the variational density matrix method, we obtain a temperature-dependent elementary excitation spectrum for two-dimensional liquid4He. For more precise results, we use a Jastrow-Feenberg-type trial wave function and include the contribution of elementary diagrams within the hypernetted chain approximation. The behavior of the excitation spectrum as a function of the temperature and density in two dimensions is similar to that of the bulk system, but has a smaller roton minimum. The roton minimum of the excitation spectrum decreases with increasing temperature and increases with increasing density at low densities but decreases at large densities. The results agree well with Monte Carlo calculations and are closer than pevious theories to experimental measurements of4He film adsorbed on substrates. 相似文献
185.
Bonanno George A.; Moskowitz Judith Tedlie; Papa Anthony; Folkman Susan 《Canadian Metallurgical Quarterly》2005,88(5):827
Recent research has indicated that many people faced with highly aversive events suffer only minor, transient disruptions in functioning and retain a capacity for positive affect and experiences. This article reports 2 studies that replicate and extend these findings among bereaved parents, spouses, and caregivers of a chronically ill life partner using a range of self-report and objective measures of adjustment. Resilience was evidenced in half of each bereaved sample when compared with matched, nonbereaved counterparts and 36% of the caregiver sample in a more conservative, repeated-measures ipsative comparison. Resilient individuals were not distinguished by the quality of their relationship with spouse/partner or caregiver burden but were rated more positively and as better adjusted by close friends. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
186.
187.
Exfoliation and related microstructures in 2024 aluminum body skins on aging aircraft 总被引:3,自引:0,他引:3
Maria Posada L. E. Murr C. -S. Niou D. Roberson D. Little Roy Arrowood Debra George 《Materials Characterization》1997,38(4-5):259-272
Exfoliation, a directional attack along elongated grain boundaries, has been examined in some detail in rolled 2024 aluminum sheet and plate for KC-135 aging aircraft body skin samples utilizing optical (light) metallography, scanning electron microscopy, and transmission electron microscopy. A detailed analysis and comparison of precipitates within the grains and in the grain boundaries were performed, as well as an examination of elemental depletion profiles across grain boundaries. These observations suggest that corrosion-related anodic sites play a far less significant role in the propagation of exfoliation than do the hard corrosion products creating wedging stresses within the elongated grain boundaries, which seem to demonstrate unique and unusual structural or energetic features or both. 相似文献
188.
Steven Spier 《The Journal of Architecture》1998,3(2):135-146
William Forsythe's research into ways of engendering and organising movement has led him to pursue counterpoint, proprioperception, entrainment, and authenticity for organisational principles that also allow improvisation. Artistic director and choreographer of the Ballett Frankfurt, and himself trained in ballet, Forsythe shows an appreciation of and often a critical engagement with classical dance, transforming and revitalising it. When he works collaboratively, Forsythe challenges the traditional distinction between choreographer and dancer, thus questioning hierarchy, authorship, and disciplinary boundaries. 相似文献
189.
190.
Vulcanization of latex products are usually carried out at lower temperatures compared to dry rubber products. It has been suggested that, in latex vulcanization systems where thiourea is used as a secondary accelerator, it acts as a nucleophilic reagent facilitating the cleavage of the sulfur bonds in the primary accelerator like TMTD or CBS at lower temperature. But no conclusive proof is given to such a postulate. In the present study 1-phenyl-2,4-thiobiuret (DTB II) and 1,5-diphenyl-2,4-dithiobiuret (DTB III), which are more nucleophilic than thiourea and which vary in their nucleophilic reactivity, were studied as secondary accelerators along with tetramethyl thiuram disulphide (TMTD) and N-cyclohexylbenzothiazyl sulphenamide (CBS) in the vulcanization of natural rubber latex. These binary systems were found to be very effective in reducing the optimum vulcanization time. Also it was noted that 1-phenyl-2,4-dithiobiuret, which is more nucleophilic, is more reactive (as observed from the reduction in optimum cure time) as a secondary accelerator, indicating a nucleophilic reaction mechanism in the vulcanization reactions under review. The optimum dosages of the secondary accelerators required were derived. Physical properties like tensile strength, 300% modulus, and elongation at break of the latex vulcanizates were also studied. There is a definite advantage with respect to many of these properties for dithiobiuret systems compared to the systems containing TMTD alone or TMTD/thiourea. DTB III gives higher values in many of these physical properties than DTB II. Chemical characterization of the vulcanizates was also carried out to correlate the physical properties with the type of chemical crosslinks formed. © 1993 John Wiley & Sons, Inc. 相似文献