首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   39609篇
  免费   1624篇
  国内免费   325篇
电工技术   792篇
技术理论   1篇
综合类   720篇
化学工业   6538篇
金属工艺   937篇
机械仪表   978篇
建筑科学   1471篇
矿业工程   304篇
能源动力   1198篇
轻工业   4629篇
水利工程   373篇
石油天然气   606篇
武器工业   58篇
无线电   2953篇
一般工业技术   5076篇
冶金工业   9891篇
原子能技术   287篇
自动化技术   4746篇
  2024年   79篇
  2023年   263篇
  2022年   712篇
  2021年   1095篇
  2020年   746篇
  2019年   801篇
  2018年   925篇
  2017年   1024篇
  2016年   951篇
  2015年   836篇
  2014年   1238篇
  2013年   1915篇
  2012年   1745篇
  2011年   2151篇
  2010年   1613篇
  2009年   1636篇
  2008年   1521篇
  2007年   1374篇
  2006年   1206篇
  2005年   1164篇
  2004年   1152篇
  2003年   1044篇
  2002年   989篇
  2001年   903篇
  2000年   711篇
  1999年   817篇
  1998年   3264篇
  1997年   2074篇
  1996年   1413篇
  1995年   881篇
  1994年   740篇
  1993年   767篇
  1992年   278篇
  1991年   322篇
  1990年   266篇
  1989年   234篇
  1988年   255篇
  1987年   191篇
  1986年   190篇
  1985年   203篇
  1984年   133篇
  1983年   106篇
  1982年   149篇
  1981年   139篇
  1980年   139篇
  1979年   96篇
  1978年   85篇
  1977年   234篇
  1976年   395篇
  1975年   87篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
83.
84.
We evaluated the acute and chronic experimental toxicity of a water extract of saponins from Argania spinosa following oral and intraperitoneal (i.p.) administration in mice (Iops Ofa) and rats (Wistar). The DL50 obtained were 79 mg/kg for the i.p. route and 1,300 mg/kg for the oral route. For the chronic toxicity studies, we administred 100 and 200 mg/kg orally once a day during a 3 month period. There was a decrease in blood sugar in the third month of each therapy. Blood creatinine levels increased, thus evoking a renal pathology. A slight increase in transaminases levels was not significatif. Hematologic parameters were unchanged during the treatment and the histopathologic study showed hepatic glycogen decrease and a focal renal tube deterioration.  相似文献   
85.
Flavobacterium aurantiacum NRRL B-184 possesses the ability to degrade aflatoxin B1 in solution and in several food items. Aflatoxin B1 is a potent carcinogen that causes significant economic losses to the agricultural and food industry. The role of trace metal ions (Cu2+, Mn2+, Zn2+, and Co2+) were studied in an effort to understand the enzymatic system involved in aflatoxin B1 degradation by F aurantiacum. The effect of divalent chelators (EDTA and 1,10-phenanthroline [OPT]) in the presence of the trace metal ions was studied as well. Aflatoxin B1 (10 microg/ml) was added to 72-h cultures of F aurantiacum that had been washed and resuspended in phosphate buffer (pH 7.0). HPLC was used to determine aflatoxin B1 concentration in these cultures. Incubating cells at 30 degrees C with 1 and 10 mM Cu2+, Mn2+, and Zn2+ significantly decreased aflatoxin B degradation after 4 and 24 h (P < 0.05). Decreased degradation was also observed with 1 and 10 mM Cu2+ and Zn2+ after 48 h and with 0.1 mM Cu2+ after 24 and 48 h. Co2+ did not have a significant effect on aflatoxin B1 degradation. EDTA and OPT did not counter the inhibition in the presence of Cu2+. The addition of 1 mM EDTA countered the inhibition by 1 mM Mn2+ after 4 and 24 h, but 1 mM OPT did not counter the inhibition by 10 mM Mn2+ after 4 and 24 h. OPT countered the inhibition by 1 mM Zn2+ after 4 and 48 h. These trace elements inhibit aflatoxin B1 degradation by F aurantiacum. In addition, their presence necessitates higher concentrations (>1 mM) of EDTA and OPT for the removal of their inhibitory effect.  相似文献   
86.
Allogeneic blood stem cell transplantation is associated with multiple complications. We report a case of pneumoperitoneum without peritonitis associated with colonic pneumatosis in a patient who had undergone an allogeneic peripheral blood cell transplant  相似文献   
87.
88.
This study was designed to: (a) identify the perceptions of retirees about changes in their life patterns during retirement; (b) investigate the kinds of adjustment problems occurring in retirement as a basis for developing prevention oriented pre-retirement programs; and (c) identify extant factors which could demonstrate underlying themes relating to retirement adjustment. A 72-item, multiple response questionnaire was used to gather demographic data, information on use of time, pre-retirement planning, health problems, changing life patterns, and adjustment to retirement. It is the latter which is reported in these findings. The population included 1565 retirees from a designated company living in the south-eastern United States of America, with a response of 764 subjects (48.82%). Findings suggest the respondents were generally healthy and well adjusted; however, numerous adjustment problem areas were identified within the six life patterns. Additional factor analysis (principal components) demonstrated four factors of particular importance: satisfaction with retirement, retirement concerns, spousal relationships, and pre-retirement preparation outcomes.  相似文献   
89.
Hybrid cam mechanisms   总被引:10,自引:0,他引:10  
This paper investigates the problem of driving a machine with several reciprocating heavy inertias. The drive should also realize some programmable flexibility of the motion, so that the operation of the machine, e,g., synchronization between different motions and duration of standstills, can easily be modified. The use of a single servomotor for every motion is not the best solution, since it does not allow for energy recuperation. This means that the installed servomotor power will be much higher than the required net peak power for the machine as a whole. The presented solution, however, reduces the servomotor peak torque and power by one order of magnitude, and makes energy transfer between the motions possible. The hybrid cam mechanism consists of a hybrid drive, which is a combination of a servomotor, a constant velocity motor and a cam follower mechanism. The operation principle exploits the nonlinear characteristics of the cam to add flexibility at low cost of energy. The hybrid solution is particularly successful for motions involving high peak acceleration. In addition, the concept can be used to reject disturbances. Simulations show the performance of the hybrid cam mechanism.  相似文献   
90.
The Journal of Supercomputing - In this paper, we propose a parallel source separation system designed to extract heart and lung sounds from single-channel mixtures. The proposed system is based on...  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号