全文获取类型
收费全文 | 101333篇 |
免费 | 10857篇 |
国内免费 | 7077篇 |
专业分类
电工技术 | 7772篇 |
技术理论 | 2篇 |
综合类 | 8708篇 |
化学工业 | 14599篇 |
金属工艺 | 6293篇 |
机械仪表 | 7242篇 |
建筑科学 | 8448篇 |
矿业工程 | 3250篇 |
能源动力 | 2912篇 |
轻工业 | 8901篇 |
水利工程 | 2785篇 |
石油天然气 | 4210篇 |
武器工业 | 1243篇 |
无线电 | 12168篇 |
一般工业技术 | 10508篇 |
冶金工业 | 4062篇 |
原子能技术 | 1472篇 |
自动化技术 | 14692篇 |
出版年
2024年 | 522篇 |
2023年 | 1735篇 |
2022年 | 3646篇 |
2021年 | 4878篇 |
2020年 | 3582篇 |
2019年 | 2613篇 |
2018年 | 2796篇 |
2017年 | 3347篇 |
2016年 | 2970篇 |
2015年 | 4595篇 |
2014年 | 5555篇 |
2013年 | 6655篇 |
2012年 | 7765篇 |
2011年 | 8294篇 |
2010年 | 7660篇 |
2009年 | 7357篇 |
2008年 | 7443篇 |
2007年 | 6995篇 |
2006年 | 6458篇 |
2005年 | 5194篇 |
2004年 | 3613篇 |
2003年 | 2613篇 |
2002年 | 2470篇 |
2001年 | 2246篇 |
2000年 | 1823篇 |
1999年 | 1299篇 |
1998年 | 885篇 |
1997年 | 732篇 |
1996年 | 669篇 |
1995年 | 606篇 |
1994年 | 477篇 |
1993年 | 408篇 |
1992年 | 282篇 |
1991年 | 254篇 |
1990年 | 172篇 |
1989年 | 144篇 |
1988年 | 107篇 |
1987年 | 73篇 |
1986年 | 63篇 |
1985年 | 39篇 |
1984年 | 32篇 |
1983年 | 44篇 |
1982年 | 25篇 |
1981年 | 23篇 |
1980年 | 31篇 |
1979年 | 17篇 |
1976年 | 4篇 |
1965年 | 6篇 |
1959年 | 11篇 |
1951年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
42.
43.
SC Liang TR Schoeb JK Davis JW Simecka GH Cassell JR Lindsey 《Canadian Metallurgical Quarterly》1995,32(6):661-667
In several chronic diseases, lesions are more severe in LEW rats than in F344 rats. To determine whether or not acute viral diseases also are more severe in LEW rats than in F344 rats, we inoculated 6-7-week-old LEW and F344 rats with 10(7.2) cell culture infective units of sialodacryoadenitis virus or 10(4.7) infective units of Sendai virus. Twenty-four rats of each strain were given each virus. Lesions in nasal passages, tracheas, intrapulmonary airways, and pulmonary alveoli in 6 or 12 rats inoculated with each virus were assessed by scoring 5, 10, and 14 days after inoculation. Both viruses caused typical patchy necrotizing rhinitis, tracheitis, bronchitis, and bronchiolitis, with multifocal pneumonitis, in rats of both strains. Mean lesion indices for LEW rats given sialodacryoadenitis virus were significantly different from those for F344 rats for nasal passages on days 10 (0.999 vs. 0.680) and 14 (0.736 vs. 0.278), bronchi on day 5 (0.479 vs. 0.361), and alveoli on day 5 (0.677 vs. 0.275). Lesion indices for LEW rats given Sendai virus were significantly different from those for F344 rats for nasal passages on days 10 (1.000 vs. 0.611) and 14 (0.778 vs. 0.583); trachea on day 10 (0.625 vs. 0.028); bronchi on days 5 (0.476 vs. 0.331), 10 (0.123 vs. 0.013), and 14 (0.038 vs. 0); and alveoli on days 5 (0.413 vs. 0.114) and 10 (0.185 vs. 0.020). Thus, at the tested doses, both viruses caused more severe respiratory tract lesions in LEW rats than in F344 rats. 相似文献
44.
45.
该文介绍一种简单、可靠、小巧的转速传感器。它的特点是在强振环境下仍具有很高的可靠,可用于坦克底盘、重型工程机械,燃气轮机组等机械作为转速监测。 相似文献
46.
The solubilities of ethyl palmitate, ethyl oleate, ethyl eicosapentaenoate (EPA) and ethyl docosahexaenoate (DHA) in supercritical
carbon dioxide were determined by a continuous flow method. The solubilities of fatty acid ethyl esters increased with pressure
and decreased as the temperature was increased. An empirical equation, similar to Chrastil's equation, was used to describe
the relationship between solute solubility and the density of carbon dioxide. The empirical equation was further used to qualitatively
estimate the separation efficiency of isolating EPA and DHA ethyl esters from fatty acid esters. The operating conditions
yielding high solubility gave fast extraction rate but resulted in low separation efficiency. Experiments were conducted to
separate ethyl EPA and ethyl DHA from a model mixture containing four fatty acid ethyl esters and from esterified squid visceral
oil. The experimental data compared closely with the calculated values. 相似文献
47.
The in vitro effect of citric acid application on periodontally involved root surfaces was investigated using scanning electron microscopy. Teeth were selected following specific criteria. The specimens were prepared for observation, and the features of the root surface were studied. The results demonstrated that a 3-minute application of citric acid (pH = 1.0) to the root surface after scaling and root planing demineralized the outer root surface, opened the dentinal tubules, and exposed collagen fibers. Scaling and root planing alone left the surface with a smear layer, scattered islands of cementum, and no collagen fibers or exposed dentinal tubules. 相似文献
48.
Four monoalkyl esters of isoalkylphosphonic acids have been studied for the chromatographic separation ofrare earths (RE).The relationship between distribution ratios and acid concentration of the eluants forsamarium and ytterbium has been explored.The characteristics of these extractants loaded onto macroreticularpoly (methyl methacrylate) resin beads for the separation of lanthanum,cerium,praseodymium and neodymiumhave been compared.Among the extractants studied,mono(1-methylheptyl) ester of isooctylphosphonic acidwas found to be the best for RE separation.The acidity for separation is lower than any known P-containingextractants for the same purpose.For instance,with 1.73 mol·L~(-1) nitric acid as eluent,thulium,ytterbium andlutetium can be separated quantitatively.The extractant-loaded resins possess high column efficiency with goodkinetic characteristics.The extraction mechanism was also explored. 相似文献
49.
本文对氨基酸营养条件下植物体内硝酸盐含量变化及其机理,土施植物激素前体色氨酸和蛋氨酸对高等植物生长和化学组成的影响。氨基酸和氨基酸肥料对植物产量和品质的影响作了综述。 相似文献
50.
介绍柳钢35t转炉方坯连铸机系统优化措施,通过优化使生产稳定性提高,铸坯质量得到改善,提高各项经济技术指标。 相似文献