全文获取类型
收费全文 | 19956篇 |
免费 | 2233篇 |
国内免费 | 1036篇 |
专业分类
电工技术 | 1271篇 |
技术理论 | 1篇 |
综合类 | 1363篇 |
化学工业 | 3097篇 |
金属工艺 | 1348篇 |
机械仪表 | 1459篇 |
建筑科学 | 1542篇 |
矿业工程 | 632篇 |
能源动力 | 534篇 |
轻工业 | 1356篇 |
水利工程 | 457篇 |
石油天然气 | 1136篇 |
武器工业 | 219篇 |
无线电 | 2284篇 |
一般工业技术 | 2368篇 |
冶金工业 | 1047篇 |
原子能技术 | 345篇 |
自动化技术 | 2766篇 |
出版年
2024年 | 82篇 |
2023年 | 388篇 |
2022年 | 686篇 |
2021年 | 964篇 |
2020年 | 780篇 |
2019年 | 670篇 |
2018年 | 689篇 |
2017年 | 780篇 |
2016年 | 700篇 |
2015年 | 1076篇 |
2014年 | 1308篇 |
2013年 | 1460篇 |
2012年 | 1556篇 |
2011年 | 1424篇 |
2010年 | 1293篇 |
2009年 | 1161篇 |
2008年 | 1091篇 |
2007年 | 1066篇 |
2006年 | 1018篇 |
2005年 | 816篇 |
2004年 | 539篇 |
2003年 | 470篇 |
2002年 | 475篇 |
2001年 | 411篇 |
2000年 | 346篇 |
1999年 | 312篇 |
1998年 | 243篇 |
1997年 | 200篇 |
1996年 | 204篇 |
1995年 | 165篇 |
1994年 | 133篇 |
1993年 | 90篇 |
1992年 | 95篇 |
1991年 | 67篇 |
1990年 | 52篇 |
1989年 | 38篇 |
1988年 | 42篇 |
1987年 | 24篇 |
1986年 | 37篇 |
1985年 | 18篇 |
1984年 | 17篇 |
1983年 | 12篇 |
1982年 | 13篇 |
1981年 | 17篇 |
1980年 | 11篇 |
1979年 | 10篇 |
1977年 | 10篇 |
1976年 | 23篇 |
1975年 | 10篇 |
1974年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
121.
不平坦的三角洲前缘席状砂--来自露头和地下的证据 总被引:1,自引:0,他引:1
延长剖面发育的三叠系延长统三角洲前缘席状砂.平面上呈席状,垂向上表现为砂泥岩互层,剖面上可见不同规模的水下分流河道砂岩透镜体。大庆油田三角洲前缘席状砂解剖发现.即使在外前缘相带.席状砂仍然具明显的水道特征。由于湖盆三角洲受波浪和潮汐的作用较小,受河漉作用较强,分流河道向前延伸直至三角洲的前端,貌似平坦的席状砂前缘实际上分布着大大小小的分流河道,河道的迁移就形成了由多个宽厚比极大的对称或不对称的透镜状单元叠加而成的三角洲前缘席状砂。三角洲前缘席状砂的建筑结构分析表明,貌似平坦简单的席状砂实际上是一个复杂的非均质体.储层物性的非均质变化受砂体建筑结构的控制具有明显的层次性规律。 相似文献
122.
123.
本文通过实验并运用未确知数学的方法确定气体常数R,此法不仅给出R所在的区间,而且可根据可信度密度确定最可靠的R值 相似文献
124.
Lee Y. Wangi Jung-Sheng Wu Sheng-Mao Tseng Chang-Shu Kuo Kuo-Huang Hsieh Wen-Bin Liau Long Y. Chiang 《Journal of Polymer Research》1996,3(1):1-10
Utilization of polyhydroxylated C60 (fullerenols) in a condensation reaction with diisocyanated oligo(tetramethylene oxide) led to the successful fabrication of elastomeric poly (urethane-ether) networks. These polymer networks exhibit interesting thermal behavior at low temperatures, improved tensile strength and elongation at ambient temperatures, and enhanced thermal mechanical stability at high temperatures, as compared with those of the parent linear polyurethane analogues; or with the conventional oligo (tetramethylene oxide)-derived polyurethane elastomers cross-linked by trihydroxylated reagents (1,I,1-trismethylol propane) or tetrahydroxylated reagents (pentaerythritol). The presence of a limited quantity of water molecules in the condensation reaction of fullerenols with diisocyanated prepolymers modified the physical properties of the resulting elastomeric products with a notable increase in tensile strength, modulus, and Ts over those of elasotmers prepared under anhydrous conditions. These water molecules contributed effectively to the increase of the number of cross-linking centers during the reaction. 相似文献
125.
Protoporphyria is a genetic disorder in which patients may develop severe protoporphyrin-induced liver damage and require transplantation. Because unique problems occur in the perioperative period and because excess production of protoporphyrin by the bone marrow continues after liver transplantation, the efficacy of this procedure for protoporphyric liver disease is uncertain. We present follow-up of nine patients who underwent liver transplantation. Two patients died within 2 months of transplantation, one from complications of abdominal bleeding and the other from sepsis after bowel perforations. The remaining seven patients had follow-up at 14 months to 8 years after transplantation (mean, 3.8 years). Two of the seven had suffered skin burns from exposure to operating room lights, which healed without scarring. Three had axonal neuropathies in the postoperative period requiring prolonged mechanical ventilation, and motor defects persisted in two. Five patients had normal liver chemistries at follow-up (mean, 3.5 years), with liver biopsy results normal or showing mild portal triad abnormalities, but erythrocyte protoporphyrin levels remained significantly elevated (1,765 +/- 365 mcg/dL; normal, < 65). The other two patients, both of whom had rejection, cytomegalovirus infection, and biliary tract obstruction requiring endoscopic therapy, had a recurrence of protoporphyric liver disease as indicated by liver biopsy features. One died 5 years after transplantation from complications of the liver disease. The other was stable 3.3 years after transplantation and was being monitored for possible retransplantation. Thus, liver transplantation can be performed successfully in patients with protoporphyric liver disease, with intermediate survival rates comparable to the general transplant population. However, disease may recur in the graft, particularly if there are complications that cause cholestasis. 相似文献
126.
127.
Yih-Loong Lai Wen-Yi Chiou Long Y. Chiang 《Fullerenes, Nanotubes and Carbon Nanostructures》1997,5(7):1337-1345
The intratracheal instillation of xanthine-xanthine oxidase caused a marked decrease in dynamic respiratory compliance, indicating airway constriction. The constriction was significantly attenuated by fullerenol-1, but not by other agents or receptor antagonists. 相似文献
128.
SC Bowden B Dodds G Whelan C Long P Dudgeon A Ritter C Clifford 《Canadian Metallurgical Quarterly》1997,19(5):755-762
Previous analyses of the Wechsler Memory Scale-Revised (WMS-R; Wechsler, 1987) have reported one-, two-, and three-factor solutions and raised questions about the validity of the visual memory subtests. These various findings may stem in part from different methods of analysis, and from the study of different participant samples. To address these issues, we analysed data from the WMS-R and a spatial maze test administered to 154 participants with a history of alcohol dependence. Results from confirmatory factor analysis supported the interpretation of three factors underlying the WMS-R subtests and the spatial maze score in this sample, namely, attention-concentration, immediate memory, and delayed recall. This result held despite the inclusion of the maze score which is a well-validated measure of visuo-spatial memory. 相似文献
129.
D. E. Long 《Journal of the Institute of Brewing》1985,91(1):41-42
Commercial brewing trials with Zenith hops from the 1982 and 1983 crops have shown that these hops are suitable for producing both ales and lager beers. 相似文献
130.
针对污水排放特征,将污染源分为连续排放型污染源和间隙排放型污染源。对连续排放型污染源,采用确定性方法定义污染源强;而对于间隙排放型污染源,运用不确定性理论,根据其排放污染源的随机统计特征,对污染源进行随机概化。将不确定性理论应用于多污染源随机排污对环境水体的水质影响分析,给出了基于不确定性理论的水质影响预测方法,建立了二维随机水质数学模型。并将该方法应用于某市水源地水质影响的随机分析,得到了在多污染源随机排放协同影响下水质浓度随机变化的统计特征。 相似文献