全文获取类型
收费全文 | 30176篇 |
免费 | 1725篇 |
国内免费 | 1247篇 |
专业分类
电工技术 | 1212篇 |
技术理论 | 3篇 |
综合类 | 1177篇 |
化学工业 | 4524篇 |
金属工艺 | 2131篇 |
机械仪表 | 1435篇 |
建筑科学 | 1831篇 |
矿业工程 | 476篇 |
能源动力 | 1014篇 |
轻工业 | 1588篇 |
水利工程 | 378篇 |
石油天然气 | 1245篇 |
武器工业 | 110篇 |
无线电 | 3825篇 |
一般工业技术 | 6190篇 |
冶金工业 | 2466篇 |
原子能技术 | 355篇 |
自动化技术 | 3188篇 |
出版年
2024年 | 65篇 |
2023年 | 329篇 |
2022年 | 524篇 |
2021年 | 809篇 |
2020年 | 549篇 |
2019年 | 590篇 |
2018年 | 733篇 |
2017年 | 723篇 |
2016年 | 730篇 |
2015年 | 822篇 |
2014年 | 1085篇 |
2013年 | 1765篇 |
2012年 | 1571篇 |
2011年 | 1902篇 |
2010年 | 1595篇 |
2009年 | 1811篇 |
2008年 | 1665篇 |
2007年 | 1630篇 |
2006年 | 1617篇 |
2005年 | 1333篇 |
2004年 | 1098篇 |
2003年 | 948篇 |
2002年 | 869篇 |
2001年 | 822篇 |
2000年 | 844篇 |
1999年 | 845篇 |
1998年 | 1104篇 |
1997年 | 881篇 |
1996年 | 782篇 |
1995年 | 614篇 |
1994年 | 462篇 |
1993年 | 368篇 |
1992年 | 288篇 |
1991年 | 226篇 |
1990年 | 212篇 |
1989年 | 201篇 |
1988年 | 142篇 |
1987年 | 82篇 |
1986年 | 81篇 |
1985年 | 61篇 |
1984年 | 58篇 |
1983年 | 45篇 |
1982年 | 42篇 |
1981年 | 25篇 |
1980年 | 28篇 |
1979年 | 19篇 |
1978年 | 21篇 |
1977年 | 17篇 |
1974年 | 13篇 |
1970年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
921.
922.
β-木糖苷酶在完全快速降解木聚糖类半纤维素为木糖的过程中起重要作用.海栖热袍菌(Thermotoga maritima)是一个极端嗜高温厌氧细菌,所产耐热酶类具有非常可观的工业应用前景,但这类酶在大肠杆菌中的表达很低.采用基因重组技术将源自海栖热袍菌的具有阿拉伯糖苷酶活性的耐热β-木糖苷酶基因克隆至表达载体pET-28a,与组氨酸标签融合表达构建重组质粒pET-28a-xyl,然后转化不同大肠杆菌宿主,结果在大肠杆菌BL21-CodonPlus(DE3)-RIL中获得高效表达;重组酶蛋白经诱导表达、破胞和热处理后纯度在90%以上,经Ni2 亲和层析后达电泳纯;用HPLC和TLC检测酶解产物,β-木糖苷酶和木聚糖酶联合水解后,酶解产物主要为木糖,外加阿拉伯糖苷酶后能使其酶解产物中木糖含量明显提高.因此,具有阿拉伯糖苷酶活性的耐热β-木糖苷酶在木糖制备中具有重要的工业应用价值. 相似文献
923.
本文就当前社会人们对建筑安全水平和质量要求不断提高的背景下,对回弹检测法检测混凝土强度的相关问题进行探讨,并以此推动回弹法检测混凝土强度行业标准的规范化发展进程,希望能够给从事相关行业的工作者提供帮助。 相似文献
924.
925.
The physicochemical properties and in vitro digestibility of selected cereals,tubers and legumes grown in China 总被引:1,自引:0,他引:1
Digestibility, gelatinization, retrogradation and pasting properties of starch in various cereal, tuber and legume flours were determined. Rapidly and slowly digestible starch and resistant starch were present in 11 selected flours. In general, cereal starches were more digestible than legume starches and tuber starches contained a high amount of resistant starch. Thermal and rheological properties of flours were different depending on the crop source. 相似文献
926.
The impacts of aspartic acid and glutamine used as nitrogen supplements for alcoholic fermentations conducted by Saccharomyces were studied. Synthetic grape juice media and commercially prepared grape juices were supplemented with diammonium phosphate, aspartic acid, or glutamine to increase yeast-assimilable nitrogen concentrations to 250 mg N/L prior to fermentation. Two yeast strains, UCD522 and EC1118, were inoculated at 105 CFU/mL and fermentations were monitored for soluble solids, hydrogen sulfide (H2S), and residual amino acids. In general, unsupplemented media/juices fermented slower than supplemented ones, produced more H2S, and contained lower concentrations of amino acids after fermentation. Among the supplemented treatments, fermentation rates, H2S production, and amino acid utilization varied depending on the nitrogen source and yeast strain. Those fermentations supplemented with aspartic acid were generally slower and sometimes did not achieve dryness. In contrast, glutamine additions yielded fermentation rates and H2S production equivalent or better than other supplemented treatments. Based on these results, the use of glutamine appears promising as an alternative nitrogen supplement for wine production. 相似文献
927.
Yixing Wang Liheng Dai Kai Qu Lu Qin Linzhou Zhuang Hu Yang Zhi Xu 《Frontiers of Chemical Science and Engineering》2021,15(4):892-901
Photocatalytic membranes have received increasing attention due to their excellent separation and photodegradation of organic contaminants in wastewater. Herein, we bound Ag-AgBr nanoparticles onto a synthesized polyacrylonitrile-ethanolamine (PAN-ETA) membrane with the aid of a chitosan (CS)-TiO2 layer via vacuum filtration and in-situ partial reduction. The introduction of the CS-TiO2 layer improved surface hydrophilicity and provided attachment sites for the Ag-AgBr nanoparticles. The PAN-ETA/CS-TiO2/Ag-AgBr photocatalytic membranes showed a relatively high water permeation flux (~ 47 L·m–2·h–1·bar–1) and dyes rejection (methyl orange: 88.22%; congo red: 95%; methyl blue: 97.41%; rose bengal: 99.98%). Additionally, the composite membranes exhibited potential long-term stability for dye/salt separation (dye rejection: ~97%; salt rejection: ~6.5%). Moreover, the methylene blue and rhodamine B solutions (20 mL, 10 mg·L−1) were degraded approximately 90.75% and 96.81% in batch mode via the synthesized photocatalytic membranes under visible light irradiation for 30 min. This study provides a feasible method for the combination of polymeric membranes and inorganic catalytic materials. 相似文献
928.
Ye Ding Xiaoqian Dai Yanfei Jiang Zhaofeng Zhang Lei Bao Yujie Li Feng Zhang Xiaotao Ma Xiaxia Cai Lulu Jing Jiaojiao Gu Yong Li 《Molecular nutrition & food research》2013,57(2):365-369
Although ER stress in pancreas, liver, and adipose tissue was reported to be a novel event linked to the pathogenesis of type 2 diabetes mellitus, there is much less information on this event in skeletal muscle. Some studies indicated that treatment with antioxidants had beneficial effects on ER stress and diabetes. This study focuses on the effects of a strong antioxidant, grape seed proanthocyanidin extracts (GSPE), on skeletal muscle in diabetic rats induced with low dose streptozotocin‐ and a high‐carbohydrate/high‐fat diet. After 16 wk of GSPE treatment, diabetic rats showed decreased plasma glucose levels and insulin resistance. The efficacious effect of GSPE was manifested by the amelioration of muscular damage and dysfunction, as observed by histological examination and periodic acid Schiff staining. Concurrently, calcium overload and the abnormal activities of antioxidant enzymes and ATPases in diabetic muscles were partially reversed by GSPE treatment. GSPE also increased the activity of protein kinase B (a mediator of insulin's metabolic action) and partially alleviated severe ER stress. These findings suggest that GSPE may have auxiliary therapeutic potential for type 2 diabetes mellitus by decreasing oxidative stress and ER stress in skeletal muscle. 相似文献
929.
Effects of Bacillus subtilis natto on performance and immune function of preweaning calves 总被引:3,自引:0,他引:3
The effects of Bacillus subtilis natto on performance and immune function of dairy calves during the preweaning phase were investigated in this study. Twelve Holstein male calves 7 ± 1 d of age were randomly allotted to 2 treatments of 6 calves. The Bacillus subtilis natto was mixed with milk and fed directly to the calves. The calves were weaned when their starter intake reached 2% of their weight. Blood was collected and IgA, IgE, IgG, IgM, and cytokine levels in the serum of all the calves were determined. The results showed that Bacillus subtilis natto increased general performance by improving the average daily gain and feed efficiency and advanced the weaning age of the calves. No difference was observed in serum IgE, IgA, and IgM, whereas serum IgG was higher in the Bacillus subtilis natto-supplemented calves than in the control calves. Furthermore, calves fed with Bacillus subtilis natto were found to secrete more IFN-γ, but tended to produce less IL-4 than did the control calves, although serum IL-6 and IL-10 were not affected. This study demonstrated that Bacillus subtilis natto did not stimulate IgE-mediated allergic reactions, but increased serum IgG and IFN-γ levels in the probiotic-fed calves. We propose that the viable probiotic characteristics of Bacillus subtilis natto benefit calf immune function. 相似文献
930.