全文获取类型
收费全文 | 414247篇 |
免费 | 2015篇 |
国内免费 | 1547篇 |
专业分类
电工技术 | 7525篇 |
综合类 | 735篇 |
化学工业 | 61920篇 |
金属工艺 | 16170篇 |
机械仪表 | 12510篇 |
建筑科学 | 10248篇 |
矿业工程 | 1924篇 |
能源动力 | 10517篇 |
轻工业 | 37346篇 |
水利工程 | 4135篇 |
石油天然气 | 6631篇 |
武器工业 | 49篇 |
无线电 | 50522篇 |
一般工业技术 | 81180篇 |
冶金工业 | 72103篇 |
原子能技术 | 9811篇 |
自动化技术 | 34483篇 |
出版年
2021年 | 2931篇 |
2019年 | 3073篇 |
2018年 | 4516篇 |
2017年 | 4626篇 |
2016年 | 5114篇 |
2015年 | 3465篇 |
2014年 | 5909篇 |
2013年 | 17719篇 |
2012年 | 9766篇 |
2011年 | 13668篇 |
2010年 | 10592篇 |
2009年 | 12261篇 |
2008年 | 13031篇 |
2007年 | 13262篇 |
2006年 | 11460篇 |
2005年 | 10697篇 |
2004年 | 10565篇 |
2003年 | 10264篇 |
2002年 | 10117篇 |
2001年 | 10178篇 |
2000年 | 9613篇 |
1999年 | 9892篇 |
1998年 | 21943篇 |
1997年 | 16103篇 |
1996年 | 12670篇 |
1995年 | 9987篇 |
1994年 | 8943篇 |
1993年 | 8798篇 |
1992年 | 6755篇 |
1991年 | 6487篇 |
1990年 | 6342篇 |
1989年 | 6320篇 |
1988年 | 5890篇 |
1987年 | 5319篇 |
1986年 | 5286篇 |
1985年 | 5980篇 |
1984年 | 5499篇 |
1983年 | 5136篇 |
1982年 | 4875篇 |
1981年 | 4812篇 |
1980年 | 4709篇 |
1979年 | 4506篇 |
1978年 | 4444篇 |
1977年 | 5024篇 |
1976年 | 6441篇 |
1975年 | 3838篇 |
1974年 | 3665篇 |
1973年 | 3708篇 |
1972年 | 3084篇 |
1971年 | 2784篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Spontaneously hypertensive rats (SHR) of 3 to 12 months of age learned and retrieved less information than normotensive Wistar-Kyoto rats (WKY), although no difference was found with animals from 18 and 24 months of age. The combined influence of hypertension and aging had an additive detrimental effect on cognitive functions. Notwithstanding these deficiencies in learning and memory, SHR have seldom been used as a model in the screening of drugs with therapeutic potential for treatment of disorders of cognitive processes. Moreover, the calcium channel blocker nimodipine has beneficial effects on learning in both aged and hypertensive animals and humans. However, no attempt has been made to investigate whether nimodipine can reverse the additive deleterious effects of aging and hypertension in the same subject. We recently reported that deteriorated animals (middle-aged and/or hypertensive) chronically treated with nimodipine (via osmotic minipumps) exhibit higher learning scores. This information indicates that nimodipine can reverse the impairing effects of either aging or hypertension on learning; the presence of the two conditions, however, produces a severe impairment that can be partially reversed by this drug. Therefore, we propose that mature and middle-aged SHR represent a model for the screening of potentially useful drugs in the treatment of learning disorders, probably associated with hypertension and/or aging. Nevertheless, it must be remembered that the SHR is a genetic model and the appearance of neural disturbances could be a parallel genetic phenomenon and not necessarily or exclusively related to hypertension per se. 相似文献
992.
993.
994.
P Dobkowski K Mlosek P Zydlewski G Aderek L Królicki 《Canadian Metallurgical Quarterly》1998,4(19):10-11
The aim of our study was to show the results of the Magnetic Resonance Angiography of pelvis and lower extremities. 21 patients with clinical signs of venous thrombosis were examined. The obtained results show the MRA is very useful in evaluation of venous flow. 相似文献
995.
996.
Maurice E. Monnom G. Ostrowsky D.B. Baxter G.W. 《Lightwave Technology, Journal of》1995,13(7):1349-1353
We propose a sensor based on the temperature dependant behavior of the two lines of green emission of the erbium ion. The ratio of the intensities of these two lines presents a very low dependance on pump wavelength and pump power fluctuations. The sensitivity of the ratio is 0.013/°C between room temperature and 600°C. In addition, the measurement is self-calibrated 相似文献
997.
Oberg M. Rigole P.-J. Nilsson S. Klinga T. Backbom L. Streubel K. Wallin J. Kjellberg T. 《Lightwave Technology, Journal of》1995,13(9):1892-1898
The spectral characteristics of a widely tunable super structure grating distributed Bragg reflector (SSG-DBR) laser are investigated and the design considerations of the grating reflectors are given. By systematically adjusting the control currents of the two reflector sections and the phase section it is experimentally shown that every wavelength in an interval of 40 nm can be reached with a side-mode suppression usually better than 30 dB 相似文献
998.
Demartini G. Granelli G.P. Marannino P. Montagna M. Ricci M. 《Power Systems, IEEE Transactions on》1996,11(4):1785-1791
The paper deals with the problem of improving co-ordination between the online economic dispatch (ED) function and the very short-term advance dispatch (AD). Both procedures are formulated as optimal dispatching problems, but while a static model is used for the ED function, a dynamic model is employed in AD. The need to account for ramp-rate limits of thermal power generation even in the ED phase is satisfied by adding suitable penalty terms to the objective function of the classical ED problem. These penalties are proportional to the Lagrange multipliers associated with ramp-rate limits that are active at the AD solution. An efficient updating procedure is used to correct the penalization by taking the load forecast errors into account. The proposed co-ordination procedure can provide the snapshot ED with the long range perspective of AD without resorting to heuristic approaches. The procedure is validated by extensive testing carried out both on a small CIGRE test case and on a medium-large scale network representative of the Italian EHV system. Moreover, test results show that the CPU time requirements of the modified ED procedure are still suited to online applications 相似文献
999.
1000.