全文获取类型
收费全文 | 109961篇 |
免费 | 1551篇 |
国内免费 | 1232篇 |
专业分类
电工技术 | 2114篇 |
综合类 | 158篇 |
化学工业 | 12128篇 |
金属工艺 | 5603篇 |
机械仪表 | 3586篇 |
建筑科学 | 2167篇 |
矿业工程 | 233篇 |
能源动力 | 2998篇 |
轻工业 | 6366篇 |
水利工程 | 752篇 |
石油天然气 | 682篇 |
武器工业 | 15篇 |
无线电 | 16307篇 |
一般工业技术 | 23561篇 |
冶金工业 | 25610篇 |
原子能技术 | 1399篇 |
自动化技术 | 9065篇 |
出版年
2022年 | 407篇 |
2021年 | 695篇 |
2020年 | 522篇 |
2019年 | 678篇 |
2018年 | 1787篇 |
2017年 | 1779篇 |
2016年 | 1673篇 |
2015年 | 1136篇 |
2014年 | 1586篇 |
2013年 | 4709篇 |
2012年 | 2854篇 |
2011年 | 4233篇 |
2010年 | 3134篇 |
2009年 | 3780篇 |
2008年 | 3962篇 |
2007年 | 4165篇 |
2006年 | 3724篇 |
2005年 | 5359篇 |
2004年 | 4372篇 |
2003年 | 3841篇 |
2002年 | 2769篇 |
2001年 | 2980篇 |
2000年 | 2728篇 |
1999年 | 3077篇 |
1998年 | 9439篇 |
1997年 | 6155篇 |
1996年 | 4764篇 |
1995年 | 3162篇 |
1994年 | 2787篇 |
1993年 | 2726篇 |
1992年 | 1629篇 |
1991年 | 1593篇 |
1990年 | 1518篇 |
1989年 | 1325篇 |
1988年 | 1171篇 |
1987年 | 864篇 |
1986年 | 886篇 |
1985年 | 917篇 |
1984年 | 804篇 |
1983年 | 699篇 |
1982年 | 700篇 |
1981年 | 681篇 |
1980年 | 567篇 |
1979年 | 477篇 |
1978年 | 414篇 |
1977年 | 533篇 |
1976年 | 959篇 |
1975年 | 300篇 |
1974年 | 277篇 |
1973年 | 256篇 |
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
131.
Yoshitomi T. Saito M. Ohguro T. One M. Momose H.S. Morifuji E. Morimoto T. Katsumata Y. Iwai H. 《Electron Devices, IEEE Transactions on》1998,45(6):1295-1299
A silicided silicon-sidewall source and drain (S4D) structure is proposed for sub-0.1-μm devices. The merit of the S4D structure is that the series resistance of the source and drain is significantly reduced since the silicide layer is attached very close to the gate electrode and the silicon sidewall can be doped very highly. Thus, very high drain current drive can be expected, Another advantage of this structure is that the source and drain extensions are produced by the solid-phase diffusion of boron from the highly doped silicon-sidewall. Thus, shallow extensions with very high doping can be realized. A 75-nm gate length pMOSFET fabricated with this structure is shown to exhibit excellent electrical characteristics 相似文献
132.
133.
Zona-free mouse eggs at the pronucleus stage were infected with a replication-defective adenovirus vector containing a nuclear-targeted lacZ gene. Exogenous beta-galactosidase activity was detected in almost all eggs at the two-cell stage. Of 27 mice that developed from infected eggs, three carried the integrated exogenous gene mediated by the adenovirus. Two of the three expressed the lacZ gene, and all three mice transmitted the adenovirus-mediated transgene to F1 progeny Southern blot analysis was consistent with single copy integration. This finding should accelerate the development of new strategies for transgenesis and assist studies on the function of cloned genes in vivo. 相似文献
134.
N Manabe Y Imai H Ohno Y Takahagi M Sugimoto H Miyamoto 《Canadian Metallurgical Quarterly》1996,52(7):647-651
The porcine antral follicles, 3-6 mm in diameter, were dissected from the ovaries of mature pigs, and then granulosa and cumulus cells were isolated from each follicle. In atretic follicles, high activity of neutral Ca2+/Mg2+-dependent endonuclease and DNA ladder formation, estimated by electrophoresis, were noted in granulosa cells but not in cumulus cells. Extremely low activity of the endonuclease and no DNA ladder formation were observed in both types of cells obtained from healthy follicles. Moreover, apoptotic cells were observed histochemically among granulosa cells only. A good correlation (r = 0.987) between the endonuclease activity of granulosa cells and the progesterone/estradiol ratio of follicular fluid in each follicle was found. These results suggest that apoptosis occurs in granulosa cells but not cumulus cells in the atretic antral follicles in pigs. 相似文献
135.
The objective is to have uniformly distributed tangential stresses on the transition profile of a stepped bar subjected to tensile and torsional loading using an axisymmetric boundary element formulation. The transition curve is represented by the Langragian interpolation polynomial with progressive degrees to avoid shape distortion during the optimization procedure. The calculated result is compared with that obtained by fluid dynamics given in the literature. It is seen that the transition curve obtained in this paper is reasonable. 相似文献
136.
137.
D Galasko T Saitoh Y Xia LJ Thal R Katzman LR Hill L Hansen 《Canadian Metallurgical Quarterly》1994,44(10):1950-1951
We determined apolipoprotein E (ApoE) genotypes in 122 autopsied demented patients. The frequency of the ApoE epsilon 4 allele was 39.6% in Alzheimer's disease (AD), 29.0% in the Lewy body variant of AD (LBV), and 6.25% in diffuse Lewy body disease. For AD and LBV patients, the epsilon 4 frequency was significantly higher than that reported in nondemented controls (10 to 15%). Therefore, LBV and AD share ApoE epsilon 4 as a genetic risk factor, providing further evidence that these conditions overlap. 相似文献
138.
139.
T Seya M Nomura Y Murakami NA Begum M Matsumoto S Nagasawa 《Canadian Metallurgical Quarterly》1998,1(5):809-816
OBJECT: In this retrospective study, the authors analyzed the frequency, anatomical distribution, and appearance of traumatic brain lesions in 42 patients in a posttraumatic persistent vegetative state. METHODS: Cerebral magnetic resonance (MR) imaging was used to detect the number of lesions, which ranged from as few as five to as many as 19, with a mean of 11 lesions. In all 42 cases there was evidence on MR imaging of diffuse axonal injury, and injury to the corpus callosum was detected in all patients. The second most common area of diffuse axonal injury involved the dorsolateral aspect of the rostral brainstem (74% of patients). In addition, 65% of these patients exhibited white matter injury in the corona radiata and the frontal and temporal lobes. Lesions to the basal ganglia or thalamus were seen in 52% and 40% of patients, respectively. Magnetic resonance imaging showed some evidence of cortical contusion in 48% of patients in this study; the frontal and temporal lobes were most frequently involved. Injury to the parahippocampal gyrus was detected in 45% of patients; in this subgroup there was an 80% incidence of contralateral peduncular lesions in the midbrain. The most common pattern of injury (74% in this series) was the combination of focal lesions of the corpus callosum and the dorsolateral brainstem. In patients with no evidence of diffuse axonal injury in the upper brainstem (26% in this series), callosal lesions were most often associated with basal ganglia lesions. Lesions of the corona radiata and lobar white matter were equally distributed in patients with or without dorsolateral brainstem injury. Moreover, cortical contusions and thalamic, parahippocampal, and cerebral peduncular lesions were also similarly distributed in both groups. CONCLUSIONS: The data indicate that diffuse axonal injury may be the major form of primary brain damage in the posttraumatic persistent vegetative state. In addition, the authors demonstrated in this study that MR imaging, in conjunction with a precise clinical correlation, may provide useful supportive information for the accurate diagnosis of a persistent vegetative state after traumatic brain injury. 相似文献
140.
The Frizzled genes encode receptors for WNTs, secreted glycoproteins implicated in development as well as in carcinogenesis. In this paper, we report molecular cloning of Hfz6, the human homologue of Mfz6. Nucleotide sequence analysis showed that the Hfz6 gene encodes the 706 amino-acid protein with seven transmembrane domains, a cystein-rich domain in the N-terminal extracellular region, two N-linked glycosylation sites, and two cystein residues in the second and third extracellular loops. Hfz6 mRNA 4.4-kb in size was detected in various normal adult and fetal tissues, and a larger amount of Hfz6 mRNA was detected in both fetal lung and fetal kidney. The Hfz6 gene has been mapped to human chromosome 8q22.3-q23.1. In conclusion, we have cloned Hfz6, which encodes a seven-transmembrane receptor with the cystein-rich domain in the N-terminal extracellular region, but without the Ser/Thr-X-Val motif in the C-terminus. 相似文献