全文获取类型
收费全文 | 2577篇 |
免费 | 13篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 42篇 |
化学工业 | 243篇 |
金属工艺 | 106篇 |
机械仪表 | 123篇 |
建筑科学 | 44篇 |
矿业工程 | 10篇 |
能源动力 | 11篇 |
轻工业 | 67篇 |
水利工程 | 18篇 |
石油天然气 | 34篇 |
无线电 | 83篇 |
一般工业技术 | 282篇 |
冶金工业 | 1396篇 |
原子能技术 | 30篇 |
自动化技术 | 104篇 |
出版年
2022年 | 25篇 |
2021年 | 43篇 |
2020年 | 21篇 |
2019年 | 30篇 |
2018年 | 59篇 |
2017年 | 59篇 |
2016年 | 65篇 |
2015年 | 37篇 |
2014年 | 57篇 |
2013年 | 83篇 |
2012年 | 66篇 |
2011年 | 107篇 |
2010年 | 77篇 |
2009年 | 91篇 |
2008年 | 96篇 |
2007年 | 92篇 |
2006年 | 69篇 |
2005年 | 31篇 |
2004年 | 18篇 |
2003年 | 7篇 |
2002年 | 9篇 |
2001年 | 8篇 |
2000年 | 27篇 |
1999年 | 51篇 |
1998年 | 355篇 |
1997年 | 256篇 |
1996年 | 168篇 |
1995年 | 118篇 |
1994年 | 64篇 |
1993年 | 77篇 |
1992年 | 10篇 |
1991年 | 28篇 |
1990年 | 13篇 |
1989年 | 10篇 |
1988年 | 7篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1985年 | 13篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 9篇 |
1981年 | 17篇 |
1980年 | 17篇 |
1978年 | 8篇 |
1977年 | 51篇 |
1976年 | 108篇 |
1975年 | 5篇 |
1973年 | 4篇 |
1972年 | 2篇 |
1966年 | 2篇 |
排序方式: 共有2593条查询结果,搜索用时 8 毫秒
131.
NW Chong VM Cassone M Bernard DC Klein PM Iuvone 《Canadian Metallurgical Quarterly》1998,61(1-2):243-250
Many aspects of retinal physiology are controlled by a circadian clock located within the eye. This clock controls the rhythmic synthesis of melatonin, which results in elevated levels during the night and low levels during the day. The rate-limiting enzyme in melatonin biosynthesis in retina appears to be tryptophan hydroxylase (TPH)[G.M. Cahill and J.C. Besharse, Circadian regulation of melatonin in the retina of Xenopus laevis: Limitation by serotonin availability, J. Neurochem. 54 (1990) 716-719]. In this report, we found that TPH mRNA is strongly expressed in the photoreceptor layer and the vitread portion of the inner nuclear layer; the message is also expressed, but to a lesser extent, in the ganglion cell layer. The abundance of retinal TPH mRNA exhibits a circadian rhythm which persists in constant light or constant darkness. The phase of the rhythm can be reversed by reversing the light:dark cycle. In parallel experiments we found a similar pattern of expression in the chicken pineal gland. However, whereas a pulse of light at midnight suppressed retinal TPH mRNA by 25%, it did not alter pineal TPH mRNA, suggesting that there are tissue-specific differences in photic regulation of TPH mRNA. In retinas treated with kainic acid to destroy serotonin-containing amacrine and bipolar cells, a high amplitude rhythm of TPH mRNA was observed indicating that melatonin-synthesizing photoreceptors are the primary source of the rhythmic message. These observations provide the first evidence that chick retinal TPH mRNA is under control of a circadian clock. 相似文献
132.
A Seth I Ourmanov MJ Kuroda JE Schmitz MW Carroll LS Wyatt B Moss MA Forman VM Hirsch NL Letvin 《Canadian Metallurgical Quarterly》1998,95(17):10112-10116
The utility of modified vaccinia virus Ankara (MVA) as a vector for eliciting AIDS virus-specific cytotoxic T lymphocytes (CTL) was explored in the simian immunodeficiency virus (SIV)/rhesus monkey model. After two intramuscular immunizations with recombinant MVA-SIVSM gag pol, the monkeys developed a Gag epitope-specific CTL response readily detected in peripheral blood lymphocytes by using a functional killing assay. Moreover, those immunizations also elicited a population of CD8+ T lymphocytes in the peripheral blood that bound a specific major histocompatibility complex class I/peptide tetramer. These Gag epitope-specific CD8+ T lymphocytes also were demonstrated by using both functional and tetramer-binding assays in lymph nodes of the immunized monkeys. These observations suggest that MVA may prove a useful vector for an HIV-1 vaccine. They also suggest that tetramer staining may be a useful technology for monitoring CTL generation in vaccine trials in nonhuman primates and in humans. 相似文献
133.
134.
135.
AA Zargarov II Senin AM Alekseev SV Shul''ga-Morsko? PP Filippov VM Lipkin 《Canadian Metallurgical Quarterly》1996,22(7):483-488
Numerous data strongly suggest the involvement of cytokines and the matrix metalloproteinase collagenase (MMP-1) in the pathogenesis of periodontitis. Recently, we have demonstrated that, upon culturing under the influence of IL-1 alpha + EGF, a large amount of inactive procollagenase (MMP-1) is stored in the extracellular matrix of periosteal tissue. We now show that this endogenous reservoir of proenzyme can be operative after activation with plasmin and is able to induce a rapid and almost complete breakdown of the collagenous extracellular matrix. The level of collagen degradation following activation showed a strong correlation with the amount of proenzyme that was incorporated in the tissue. The highest level of degradation (70% of the total amount of collagenous proteins) was found with the IL-1 alpha + EGF-treated explants, followed by those treated with IL-1 alpha alone (35%). Explants cultured with EGF or in the absence of cytokines, containing only small amounts of procollagenase, showed little collagen breakdown following plasmin activation (7%). Inhibition of metalloproteinases by EDTA, or blockage of plasmin by PMSF, prevented the degradation in all explants irrespective of the amount of proenzyme present in the tissue. Our findings demonstrate that endogenous proenzyme stored in a native connective tissue matrix can be activated at a later time interval which results in a massive breakdown of the tissue. This study shows a possible pathway of collagenase-induced breakdown without recent de novo synthesis of the enzyme. Such a sequence may be operative in chronic inflammatory diseases, such as periodontitis, where production of procollagenase under the influence of cytokines spans a longer time period, whereas breakdown is often characterized by a cyclic behaviour. 相似文献
136.
H Ramirez-Gil E Feldberg VM Almeida-Val AL Val 《Canadian Metallurgical Quarterly》1998,31(11):1449-1458
Karyological characteristics, i.e., diploid number, chromosome morphology and nucleolus organizer regions (NORs), biochemical characteristics, i.e., electrophoretic analysis of blood hemoglobin and the tissue enzymes lactate dehydrogenase (LDH), malate dehydrogenase (MDH), alcohol dehydrogenase (ADH), and phosphoglucose isomerase (PGI), and physiological characteristics, i.e., relative concentration of hemoglobin and intraerythrocytic concentrations of organic phosphates were analyzed for the species Callophysus macropterus collected from Marchantaria Island (white water system--Solim?es River) and Anavilhanas Archipelago (black water system--Negro River). Karyological and biochemical data did not reveal significant differences between specimens collected at the two sites. However, the relative distribution of hemoglobin bands I and III (I = 16.33 +/- 1.05 and III = 37.20 +/- 1.32 for Marchantaria specimens and I = 6.33 +/- 1.32 and III = 48.05 +/- 1.55 for Anavilhanas specimens) and levels of intraerythrocytic GTP (1.32 +/- 0.16 and 2.76 +/- 0.18 for Marchantaria and Anavilhanas specimens, respectively), but not ATP or total phosphate, were significantly different, indicating a physiological adaptation to the environmental conditions of these habitats. It is suggested that C. macropterus specimens from the two collecting sites belong to a single population, and that they adjusted some physiological characteristics to adapt to local environmental conditions. 相似文献
137.
138.
139.
140.