全文获取类型
收费全文 | 54751篇 |
免费 | 4481篇 |
国内免费 | 2692篇 |
专业分类
电工技术 | 3525篇 |
技术理论 | 3篇 |
综合类 | 4984篇 |
化学工业 | 7629篇 |
金属工艺 | 3360篇 |
机械仪表 | 4086篇 |
建筑科学 | 4287篇 |
矿业工程 | 1608篇 |
能源动力 | 1463篇 |
轻工业 | 5347篇 |
水利工程 | 1250篇 |
石油天然气 | 2142篇 |
武器工业 | 659篇 |
无线电 | 5604篇 |
一般工业技术 | 4558篇 |
冶金工业 | 2589篇 |
原子能技术 | 596篇 |
自动化技术 | 8234篇 |
出版年
2024年 | 104篇 |
2023年 | 402篇 |
2022年 | 1202篇 |
2021年 | 1681篇 |
2020年 | 1362篇 |
2019年 | 966篇 |
2018年 | 1112篇 |
2017年 | 1413篇 |
2016年 | 1352篇 |
2015年 | 2253篇 |
2014年 | 3011篇 |
2013年 | 3653篇 |
2012年 | 4514篇 |
2011年 | 4879篇 |
2010年 | 4594篇 |
2009年 | 4493篇 |
2008年 | 4341篇 |
2007年 | 4079篇 |
2006年 | 3603篇 |
2005年 | 2747篇 |
2004年 | 1991篇 |
2003年 | 1442篇 |
2002年 | 1346篇 |
2001年 | 1196篇 |
2000年 | 802篇 |
1999年 | 668篇 |
1998年 | 563篇 |
1997年 | 457篇 |
1996年 | 377篇 |
1995年 | 269篇 |
1994年 | 227篇 |
1993年 | 186篇 |
1992年 | 115篇 |
1991年 | 108篇 |
1990年 | 63篇 |
1989年 | 63篇 |
1988年 | 49篇 |
1987年 | 25篇 |
1986年 | 18篇 |
1985年 | 20篇 |
1984年 | 6篇 |
1983年 | 11篇 |
1982年 | 8篇 |
1981年 | 11篇 |
1980年 | 17篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 33篇 |
1976年 | 76篇 |
1958年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
71.
阐述了东江水库基本情况,通过对库区及周围的地质构造特点、诱发地震监测,总结出东江水库地震的活动特征和诱发地震活动趋势。 相似文献
72.
After considering the stabilization of a specific class of stochastic nonlinear systems in a companion paper, in this second part, we address the classical question of when is a stabilizing (in probability) controller optimal and show that for every system with a stochastic control Lyapunov function it is possible to construct a controller which is optimal with respect to a meaningful cost functional. Then we return to the problem from Part I and design an optimal backstepping controller whose cost functional includes penalty on control effort and which has an infinite gain margin. 相似文献
73.
Because a so-called mandibular whiplash injury requires the absence of short-latency jaw-closing reflexes in order to explain the postulated mechanism of injury (excessive jaw opening); the authors studied the presence and absence and more importantly, the kinematics (duration, displacement, velocity, acceleration) of monosynaptic and possibly, polysynaptic myotatic (stretch) reflexes in the jaw elevator muscles. In six healthy adults jaw jerk maneuvers were elicited through a brisk tap on the chin, and surface electromyography identified elevator reflexes while translational electrognathography identified the kinematics of the reflexes. The maneuvers were done while maintaining the rest position (3% MVC) and moderate clenching of the teeth (30% MVC). Electromyography was also used to identify phasic elevator excitations during a passive brisk neck extension maneuver. A sudden and unexpected elongation of the jaw elevators released autogenic reflex responses that, in conjunction with augmented tissue elasticity (stiffness), elevated the mandible into centric occlusion within approximately 150 milliseconds. In 86% of trials, the responses occurred regardless of the prevailing resting and clenching contractile activities. There was no evidence of a depressor force that consistently would and could anchor the mandible in a position of extreme or moderate depression, the theoretical linchpin of the mandibular whiplash injury. It was concluded that the mandibular locomotor system is very efficient in maintaining the rest and intercuspal positions of the mandible. This study found no evidence corroborating the mechanism claimed to release a so-called mandibular whiplash injury. 相似文献
74.
SV Varha OH Reznikov IS Turchyn VM Demchenko OP Potikha PV Sinitsyn LV Tarasenko LV Cha?kovs'ka 《Canadian Metallurgical Quarterly》1994,40(5-6):105-109
The effect exerted by transplantation of the 5 day culture of testicles from newly born piglets on the hypogonadal state of mature X-ray irradiated (3 Gy) rats was studied. It has been found that a month after transplantation (two months after irradiation) the hypogonadal state disappeared for a while, which is confirmed by normalization of the weight of seminal vesicles, content of testosterone and biologically active lutropine, restoration of the reproductive function of rats. No significant changes in steroidogenesis activity have been found, which proves a substituent character of transplantation. The effect disappears three months later but certain restoration of the content of nucleic acids in the testicles is observed. 相似文献
75.
76.
77.
LV Osadchuk 《Canadian Metallurgical Quarterly》1997,33(11):1534-1538
The level of cortisol in serum and adrenals and its production by adrenals in vitro was studied by the radioimmune method in male and female silver fox embryos, starting from day 30 of pregnancy every five days. Pregnant females from a commercial population and an experimental population, which had been selected for domestic behavior, was used. It was shown that, at the end of the prenatal developmental stage, all investigated parameters of the glucocorticoid function of adrenals were significantly lower in embryos from selected mothers as compared to the unselected control group. The addition of adrenocorticotropic hormone into the incubation medium increased cortisol biosynthesis at all embryogenesis stages, but in the selected population the increase was less than that in the control group. 相似文献
78.
C/O测井响应随源距变化的理论研究 总被引:17,自引:7,他引:10
针对井内介质分别为水、油,地层分别为35%孔隙度饱和水砂和油砂的4种情况,采用蒙特卡罗方法模拟外径φ89碳氧比测井仪不同源距处的非弹性散射伽马能谱。通过分析地层或井内介质不同时的C/O差值随源距变化的关系,为设计仪器推荐源距参数。 相似文献
79.
PVDF中空纤维滤膜的形态结构 总被引:3,自引:0,他引:3
用L-S相转换法制备了聚偏氟乙烯(PVDF)中空纤维不对称滤膜。铸膜液由聚合物、溶剂和添加剂组成。用电子显微镜(SEM)考察了聚合物浓度、添加剂用量及种类对膜形态结构的影响。实验结果表明,聚合物浓度对膜形态结构有显著影响,当铸膜液中聚合物浓度较低时,无论用什么种类添加剂,都能形成大、且多的孔,但孔的形状随添加剂不同而异。当恒定聚合物浓度时,添加剂的用量对膜形态结构有很大的影响,但孔的大小及多少与添加剂含量的多少不成正比。 相似文献
80.
Ming Dai Yu Zhang Yiman Hua Wansun Ni Gonghuan Du 《Electronics letters》1998,34(10):951-953
By active-passive-decomposition synchronisation, the application of the one-way coupled ring map lattice hyperchaotic system in secure digital speech communication is demonstrated. Synchronisation guarantees strong security and recovery without error 相似文献