全文获取类型
收费全文 | 54816篇 |
免费 | 5210篇 |
国内免费 | 2650篇 |
专业分类
电工技术 | 3495篇 |
技术理论 | 4篇 |
综合类 | 3639篇 |
化学工业 | 8716篇 |
金属工艺 | 3274篇 |
机械仪表 | 3704篇 |
建筑科学 | 4173篇 |
矿业工程 | 1750篇 |
能源动力 | 1686篇 |
轻工业 | 3854篇 |
水利工程 | 1157篇 |
石油天然气 | 2830篇 |
武器工业 | 553篇 |
无线电 | 6155篇 |
一般工业技术 | 6499篇 |
冶金工业 | 2988篇 |
原子能技术 | 795篇 |
自动化技术 | 7404篇 |
出版年
2024年 | 267篇 |
2023年 | 963篇 |
2022年 | 1690篇 |
2021年 | 2350篇 |
2020年 | 1784篇 |
2019年 | 1564篇 |
2018年 | 1751篇 |
2017年 | 1876篇 |
2016年 | 1752篇 |
2015年 | 2328篇 |
2014年 | 2904篇 |
2013年 | 3373篇 |
2012年 | 3898篇 |
2011年 | 4076篇 |
2010年 | 3562篇 |
2009年 | 3421篇 |
2008年 | 3232篇 |
2007年 | 3030篇 |
2006年 | 2857篇 |
2005年 | 2405篇 |
2004年 | 1806篇 |
2003年 | 1644篇 |
2002年 | 1715篇 |
2001年 | 1501篇 |
2000年 | 1201篇 |
1999年 | 1168篇 |
1998年 | 917篇 |
1997年 | 712篇 |
1996年 | 630篇 |
1995年 | 542篇 |
1994年 | 393篇 |
1993年 | 330篇 |
1992年 | 245篇 |
1991年 | 177篇 |
1990年 | 141篇 |
1989年 | 93篇 |
1988年 | 107篇 |
1987年 | 51篇 |
1986年 | 63篇 |
1985年 | 28篇 |
1984年 | 24篇 |
1983年 | 16篇 |
1982年 | 14篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 10篇 |
1977年 | 12篇 |
1976年 | 15篇 |
1975年 | 5篇 |
1970年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
23.
Converting cysteine 543 to tyrosine in the influenza virus hemagglutinin (HA) introduces both a basolateral sorting signal and an internalization signal into the HA cytoplasmic domain. Another HA mutant, HA+8, contains eight additional amino acids at the end of the cytoplasmic domain that include a powerful internalization signal. HA+8 was also sorted efficiently to the basolateral surface of Madin-Darby canine kidney cells. The simplest explanation for the observation that multiple sorting phenotypes depend upon the same small amino acid sequence is that certain tyrosine-based internalization signals might also function as basolateral sorting signals. To test this hypothesis, second-site mutations were introduced into HA C543Y or HA+8 to determine if the internalization and basolateral sorting functions can be separated. For HA C543Y, the same sequence positions were important for both basolateral sorting and internalization, but the two functions responded differently to individual amino acid replacements, indicating that they were distinct. For HA+8, the basolateral sorting signal required the same tyrosine as the internalization signal, but did not share any other characteristics. Thus, even when basolateral sorting signals that depend on tyrosine overlap or are co-linear with internalizations signals, the two sorting processes are sensitive to different characteristics of the sequence. 相似文献
24.
OBJECTIVE: To evaluate the therapeutical mechanism of Bushen Shengxue Paste (BSSXP) on anemia. METHODS: Chronic renal failure induced anemia patients were treated with BSSXP, clinical manifestation, anemia and renal function as indicators were observed in patients. The erythropoietin (EPO) and inhibition of colony-forming unit-erythrocyte (CFU-E) in patients' serum were determined by CFU-E in vitro. RESULTS: The patients' symptoms, renal function and anemia were improved after administration with BSSXP 1-2 course. EPO in serum was slightly increased. The inhibition of CFU-E in patient's serum was significantly decreased. CONCLUSIONS: BSSXP could improve the anemia degree, its mechanism might be through clearing the inhibitor of CFU-E in serum. 相似文献
25.
For the first time, the surface metal on nonalloyed ohmic electrodes is found to significantly change the profiles of gate grooves, when resist openings are employed to monitor drain current during wet-chemical gate recess for sub-micron InAlAs/lnGaAs heterojunction field-effect transistors (HFETs). The surface metal of Ni enhances the etching rate in comparison with that in the absence of electrodes by a factor of 4 and 10, laterally and vertically, which is favorable to fabricate deep gate grooves with small side etching. The Pt surface metal, however, leads to preferential etching of InGaAs over InAlAs, which can be useful to realize large side etching. The existence of an electrochemistry-related etching component, which arises when the ohmic electrodes are present during recess etching, is considered to be responsible for these behaviors 相似文献
26.
Q Hu M Trevisan Y Xu W Dong SA Berger SD Lyman MD Minden 《Canadian Metallurgical Quarterly》1995,95(6):2530-2538
The growth of human leukemic cells in culture and in vivo is dependent upon the presence of hematopoietic growth factors. Most populations of human leukemic acute myeloblastic leukemia (AML) cells express c-Kit on their surface and respond to Kit ligand (KL) in culture. To determine if this interaction was of potential significance in vivo we used a mouse model system. 32D cells, a murine IL-3-dependent myeloid cell line, were rendered KL responsive by transfection of the murine c-Kit. After injection of 32D or 32D-Kit cells into syngeneic hosts, animals bearing 32D-Kit cells, but not 32D cells, became moribund and were killed. These animals had circulating leukemic blast cells, infiltration of bone marrow, spleen, brain, liver, lung, and kidney. Cells recovered from some of the animals continued to be dependent upon IL-3 or KL for growth while in other cases the cells were factor independent. This model illustrates that the constitutive expression of c-Kit enhances the leukemic potential of 32D cells. The model will be useful for studying the progression of leukemia in vivo and testing whether interruption of the interaction of Kit and KL can affect the growth of leukemic cells. 相似文献
27.
Kwang Soo Lee In Soo Park & Dong Sun Lee 《International Journal of Food Science & Technology》1996,31(1):7-13
The aim of this study was to design a modified atmosphere package for a mixed vegetable salad consisting of 75 g of cut carrot, 55 g of cut cucumber, 20 g of sliced garlic and 50 g of whole green pepper. Respiration data of all the components were combined with film permeability data to predict package atmospheres and design optimal packages for experimental testing for improved shelf-life of the produce. The optimal package avoided minimum O2 and maximum CO2 tolerance limits, and chilling injury temperatures for any component. A pouch form package made of 27 mm low density polyethylene developed a modified atmosphere of 2.0–2.1% O2 and 5.5–5.7% CO2 , which was beneficial for all components and provided better quality retention than other test packages. 相似文献
28.
29.
30.