全文获取类型
收费全文 | 2554篇 |
免费 | 9篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 2篇 |
化学工业 | 36篇 |
金属工艺 | 7篇 |
机械仪表 | 25篇 |
建筑科学 | 15篇 |
矿业工程 | 1篇 |
轻工业 | 152篇 |
无线电 | 9篇 |
一般工业技术 | 27篇 |
冶金工业 | 2253篇 |
原子能技术 | 2篇 |
自动化技术 | 35篇 |
出版年
2021年 | 4篇 |
2019年 | 4篇 |
2016年 | 2篇 |
2013年 | 53篇 |
2012年 | 5篇 |
2011年 | 3篇 |
2010年 | 3篇 |
2009年 | 7篇 |
2008年 | 4篇 |
2007年 | 11篇 |
2006年 | 6篇 |
2005年 | 3篇 |
2004年 | 3篇 |
2003年 | 5篇 |
2002年 | 7篇 |
2001年 | 3篇 |
2000年 | 7篇 |
1999年 | 73篇 |
1998年 | 742篇 |
1997年 | 383篇 |
1996年 | 274篇 |
1995年 | 137篇 |
1994年 | 122篇 |
1993年 | 127篇 |
1992年 | 23篇 |
1991年 | 33篇 |
1990年 | 23篇 |
1989年 | 26篇 |
1988年 | 25篇 |
1987年 | 26篇 |
1986年 | 26篇 |
1985年 | 22篇 |
1984年 | 8篇 |
1983年 | 14篇 |
1982年 | 17篇 |
1981年 | 25篇 |
1980年 | 22篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 69篇 |
1976年 | 160篇 |
1975年 | 3篇 |
1973年 | 2篇 |
1968年 | 3篇 |
1967年 | 7篇 |
1966年 | 4篇 |
1964年 | 3篇 |
1958年 | 2篇 |
1955年 | 5篇 |
1947年 | 3篇 |
排序方式: 共有2564条查询结果,搜索用时 15 毫秒
1.
Phospholamban (PLN) was expressed in Escherichia coli as a protein fusion with glutathione S-transferase (GST). GST-PLN was mostly present in the insoluble protein fraction and accounted for approximately 50% of total insoluble protein. Attempts to suppress inclusion body formation or to use GST as an affinity-purification tag failed. A successful purification method is based on preparative SDS/PAGE and electrodialysis. From 1 g cells we typically purified 13.5 mg fusion protein with a PLN content of 2.8 mg. We genetically inserted an enterokinase (EK) protease site just in front of the PLN sequence and demonstrated the proteolytical liberation of PLN from the carrier protein. The approach described represents a substantial advancement in PLN expression and purification. 相似文献
2.
BACKGROUND: The effect of topical corticosteroids after excimer laser photorefractive keratectomy (PRK) remains a matter of some controversy. Refractive effects may be different according to the amount of myopia and timing of instillation. METHODS: Two groups of patients were studied: Study A consisted of 215 eyes (128 patients) with PRK (mean baseline myopia, -6.53 +/- 2.22 D) that received no corticosteroids (No Corticosteroid Group) unless significant regression or corneal haze appeared (Delayed Corticosteroid Group), and in Study B, we randomly assigned eyes to the Initial Corticosteroid Group (mean baseline myopia, -6.39 +/- 1.84 D) or the No/delayed Corticosteroid Group (mean baseline myopia -5.78 +/- 2.02 D). Clinical results after PRK for low-to-moderate and high myopia were compared. RESULTS: In the first group, 70.9% (73 eyes) of moderately myopic eyes (mean, -4.56 +/- 1.10 D) belonged to the No Corticosteroid Group that had a mean refraction of -5.39 +/- 1.77 D. Delayed Corticosteroid Group eyes were more myopic (mean, -7.52 +/- 2.10 D), and showed more severe haze than those in the No Corticosteroid Group. In study B, only in high myopes with more than -6.00 D (mean, -7.76 +/- 1.15 D) did refraction and corneal haze outcomes show significant difference between the Initial Corticosteroid Group and the No/delayed Corticosteroid Group. CONCLUSIONS: The effects of topical corticosteroids after PRK were less in moderate myopes compared to high myopes. Delayed instillation of corticosteroids did not reverse the regression or haze whereas initial instillation showed a beneficial effect on high myopes but not on moderate myopes. 相似文献
3.
5.
Stress in Leached Phase-Separated Glass 总被引:2,自引:0,他引:2
When a phase-separated glass is leached, stresses develop because of release of thermal stresses, creation of surface area, ion exchange, and hydration. Analyses are presented for the thermal stresses, including the portion that develops on cooling from the heat-treatment temperature to the setting temperature of the less viscous phase. During leaching, the interfacial energy of the residual phase increases, so that phase tends to contract. A more important effect is the contraction caused by removal of alkali and B2 O3 from the residual phase during leaching. The extent of removal of B2 O2 decreases with heat-treatment time, tH , because the scale of the microstructure increases as t1/3 H . The change in residual B2 O2 content with tH is shown to be consistent with diffusion-controlled ion exchange. The dependence of stress on tH in partially leached glasses, measured by Drexhage and Gupta, results principally from the change in extent of ion exchange; the reduction in surface area with increasing tH also has a significant effect on the stresses. 相似文献
6.
Larynx-associated lymphoid tissue (LALT) in young children 总被引:1,自引:0,他引:1
A Kracke AS Hiller T Tschernig M Kasper WJ Kleemann HD Tr?ger R Pabst 《Canadian Metallurgical Quarterly》1997,248(3):413-420
BACKGROUND: Mucosa-associated lymphoid tissue (MALT) plays a central role in mucosal immunity. Whereas the characteristics and function of MALT in the intestine are well established, almost nothing is known about MALT in the larynx. METHODS: In this study we examined the morphology and the lymphocyte subset composition of MALT in the larynges of children who had died of sudden infant death or various defined traumatic or nontraumatic causes. RESULTS: Organized lymphoid tissue was found in the supraglottic parts of the larynx in nearly 80% of the children in both groups. This lymphoid tissue showed all morphological signs of MALT, such as typical lymphoid follicles with germinal centers, infiltration of the overlying epithelium by lymphocytes, and high endothelial venules (HEV). Thus we will use the term LALT (larynx-associated lymphoid tissue) to refer to this tissue. The lymphoid follicles of LALT contained mainly B lymphocytes with some CD4+ lymphocytes in the germinal centers. Remarkably, T lymphocytes of both subset types and B lymphocytes were observed in comparable numbers in the parafollicular area. CONCLUSIONS: We assume that LALT is a physiological structure of the larynx in young children. The morphology and the distribution of lymphocyte subsets are similar to those of MALT in the human gut. LALT may be a regular part of the mucosal immune system in young children with the role of respiratory inductive site for mucosal immunity. 相似文献
7.
Recordings from the central branches of single identified dactyl sensory afferent (DSA) neurons in a crayfish in vitro preparation were performed to study modifications of the sensory message occurring before the first central synapse. These afferents comprised hairs and force-sensitive mechanoreceptors with phasic and phasotonic response characteristics in the terminal segment (dactyl) of the crayfish leg. More than one afferent spike size was often observed in intracellular recordings from these afferents, thus indicating the presence of electrical coupling between the central processes of DSA fibers. Additionally, in identified DSA fibers with large spike sizes, primary afferent depolarizations (PADs) of up to 15 mV were observed, which sometimes triggered antidromic spikes in the afferent. Nevertheless, PADs were clearly inhibitory, because they shunted the afferent spikes. They exhibited the following properties. First, each PAD was preceded by an afferent spike from a neighboring hair, indicating that the PADs had a sensory rather than central origin. Second, PADs could follow high frequencies of afferent discharges without failure, a property suggestive of monosynaptic connections, but because PAD latencies varied by +/-0.5 ms it is more likely that they were mediated by a disynaptic pathway. Third, although PADs were evoked in an extremely reliable manner, their amplitude varied in a quantal manner. Most unitary PADs were the result of the release of < 12 quanta, the mean quantal content lying between 4 and 5; quantal size was large, approximately 1 mV. Fourth, PADs showed facilitation in some fibers, whereas in others they became much smaller when occurring at brief intervals. We suggest that PADs may be an efficient and parsimonious way to limit sensory inflow in space and time, allowing the crayfish to identify precisely both weak and strong mechanical stimuli. 相似文献
8.
WJ Lebkowski 《Canadian Metallurgical Quarterly》1997,2(8):111-112
The studies aimed to estimate an incidence of the low back pain (LBP) in the youngsters and teenagers and correlating it with risk factors. A groups of 2,346 secondary school pupils (1,704 girls and 642 boys) of a mean age 17 +/- 1 yrs, and 970 high-school students (532 women and 438 men) of a mean age 24 +/- 2 yrs have been examined. Low back pain has been seen in 1,416 out of 2,346 secondary school pupils (60%), and in 32% of the examined students. Statistical analysis with chi 2 test has confirmed a correlation between LBP and such risk factors as the incorrect sedentary position (p < .001 for pupils, and p < .02 for students), and smoking (p < .001 for students and p < .02 for pupils). 相似文献
9.
10.
Human B-cell glucokinase displays sigmoidal kinetics towards D-glucose or D-mannose, but fails to do so towards D-fructose. Yet, D-glucose, D-mannose and 2-deoxy-D-glucose confer to the enzyme positive cooperativity towards D-fructose. For instance, in the presence of 5 mM D-[U-14C]fructose, its rate of phosphorylation is increased to 214.3 +/- 11.0%, 134.0 +/- 4.3% and 116.5 +/- 3.0% of paired control value by D-glucose, D-mannose and 2-deoxy-D-glucose (each 6 mM), respectively. D-glucose and, to a lesser extent, D-mannose also display reciprocal kinetic cooperativity. D-fructose, however, fails to affect D-glucose or D-mannose phosphorylation under conditions in which positive cooperativity is otherwise observed. These findings are relevant to the reciprocal effects of distinct hexoses upon their phosphorylation by B-cell glucokinase and, as such, to the metabolic and functional response evoked in pancreatic islet B-cells by these sugars, when tested either separately or in combination. 相似文献