全文获取类型
收费全文 | 486655篇 |
免费 | 6908篇 |
国内免费 | 2745篇 |
专业分类
电工技术 | 8891篇 |
技术理论 | 5篇 |
综合类 | 3535篇 |
化学工业 | 75715篇 |
金属工艺 | 21808篇 |
机械仪表 | 14900篇 |
建筑科学 | 12423篇 |
矿业工程 | 2974篇 |
能源动力 | 10613篇 |
轻工业 | 41996篇 |
水利工程 | 5466篇 |
石油天然气 | 8857篇 |
武器工业 | 245篇 |
无线电 | 52923篇 |
一般工业技术 | 91578篇 |
冶金工业 | 77933篇 |
原子能技术 | 9222篇 |
自动化技术 | 57224篇 |
出版年
2021年 | 3534篇 |
2019年 | 3111篇 |
2018年 | 18944篇 |
2017年 | 17821篇 |
2016年 | 15035篇 |
2015年 | 4671篇 |
2014年 | 6929篇 |
2013年 | 17970篇 |
2012年 | 14279篇 |
2011年 | 24191篇 |
2010年 | 20029篇 |
2009年 | 18657篇 |
2008年 | 20536篇 |
2007年 | 21649篇 |
2006年 | 12556篇 |
2005年 | 12254篇 |
2004年 | 11282篇 |
2003年 | 10685篇 |
2002年 | 10098篇 |
2001年 | 9751篇 |
2000年 | 9308篇 |
1999年 | 9278篇 |
1998年 | 21598篇 |
1997年 | 15758篇 |
1996年 | 12098篇 |
1995年 | 9174篇 |
1994年 | 8138篇 |
1993年 | 7966篇 |
1992年 | 6126篇 |
1991年 | 5907篇 |
1990年 | 5842篇 |
1989年 | 5837篇 |
1988年 | 5527篇 |
1987年 | 4835篇 |
1986年 | 4776篇 |
1985年 | 5442篇 |
1984年 | 5143篇 |
1983年 | 4791篇 |
1982年 | 4291篇 |
1981年 | 4548篇 |
1980年 | 4166篇 |
1979年 | 4346篇 |
1978年 | 4224篇 |
1977年 | 4650篇 |
1976年 | 6015篇 |
1975年 | 3758篇 |
1974年 | 3575篇 |
1973年 | 3675篇 |
1972年 | 3108篇 |
1971年 | 2832篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
52.
OL Lopez RP Brenner JT Becker RF Ulrich F Boller ST DeKosky 《Canadian Metallurgical Quarterly》1997,48(6):1521-1525
We examined whether either psychotic features (e.g., delusions and hallucinations) or EEG abnormalities are associated with more rapid progression of Alzheimer's disease (AD). AD patients with psychosis have exhibited more EEG abnormalities than those without psychosis, and both abnormal EEG and psychosis have been noted to be predictors of functional and cognitive decline in AD. Ninety-five probable AD patients participating in a longitudinal study of dementia had an EEG and a semistructured psychiatric interview at baseline. Using EEG spectral analysis, we classified records as normal/abnormal based on the parasagittal mean frequency. Patients with abnormal EEGs were more functionally (e.g., Blessed Rating Scale for activities of daily living) and cognitively (e.g., Mini-Mental State) impaired than patients with normal EEG. AD patients with psychosis were only more functionally impaired than patients without psychosis. A two-factor analysis showed no interaction between abnormal EEG and psychosis. In addition, using a Cox proportional hazard model adjusted for age and education, the presence of an abnormal EEG or psychotic symptom at study entry was associated with higher risk of reaching severe cognitive and functional impairment during follow-up. Neither abnormal EEG nor the presence of psychosis predicted death. These results indicate that both abnormal EEG and psychosis are independent predictors of disease progression but not of physical survival. 相似文献
53.
The ultradian clocks of eukaryotic microbes: timekeeping devices displaying a homeostasis of the period 总被引:1,自引:0,他引:1
F Kippert 《Canadian Metallurgical Quarterly》1997,14(5):469-479
Ultra-high-sensitivity, biopolymer sequencing is a goal in many fields of molecular biology, and collisionally activated decomposition electrospray mass spectrometry (CAD ES MS/MS) using a triple quadrupole mass spectrometer has become a method of choice for work in the high- to mid-femtomole range. However, when the detection of ions becomes statistical, as it may in that range, the mass assignment of fragment ions is inaccurate and either sequencing becomes impossible or ambiguities result due, for example, to the closeness in amino acid residue masses (I/L, N or K/Q, E). Some ambiguities may be resolved by synthesizing possible sequences, but this is unsatisfactory. In considering the limitations of triple quadrupole MS/MS with respect to scanning ion detection, resolution, transmission, and mass accuracy, we reasoned that a novel geometry quadrupole orthogonal acceleration time-of-flight (Q-TOF) instrument would have special merit for ultra-high-sensitivity MS/MS sequencing, and suggested its construction for this purpose some three years ago. A prototype Q-TOF has now been built by Micromass [Morris et al. (1996), Rapid Commun. Mass Spectrom. 10, 889-896], and in the first research on the instrument, including MHC antigen and filarial nematode glycoprotein studies, we demonstrate low-femtomole- and attomole-range sequencing with mass accuracy of better than 0.1 Da throughout the daughter-ion spectrum, thus removing sequencing ambiguities in some of the most challenging work demanding the highest sensitivity. 相似文献
54.
A high prevalence of epilepsy (up to 1.3%) was observed in an area hyperendemic for onchocerciasis in the province of Bururi, Burundi. Following this observation, epileptics and controls were examined in 2 communes (administrative units) with different endemicity for onchocerciasis. Altogether, onchocerciasis was more frequent in epileptics (81.8%) than in controls from the same households (68.3%; P < 0.05). This difference was more marked in the hyperendemic area. Other possible causes of epilepsy, including cysticercosis, were infrequent (18 possible cases among 110 epileptics). During this survey, 9 epileptics with growth retardation were seen. They showed most characteristics of Nakalanga syndrome, which was described from Uganda. All 9 such cases were suffering from onchocerciasis. These findings give more evidence of a possible association between onchocerciasis and epilepsy, and between onchocerciasis and Nakalanga syndrome. 相似文献
55.
56.
Using the fear-potentiated startle paradigm in rats, 4 experiments examined whether the inhibitory effect of a feature is evident after its offset following serial feature-negative discrimination training (A+ and X-->A-). When startle probes were presented shortly after the offset of X on X-->A test trials, the inhibitory properties of X were observed immediately after its offset. Furthermore, trace reinforcement of X (X-->+), but not delay reinforcement (X+), disrupted the ability of X to inhibit fear-potentiated startle on X-->A trials. Trace conditioning to X was also retarded after A+ and X-->A- training. These results suggest that the inhibitory properties of the serially trained feature are present after its offset and raise the possibility that either temporal information regarding nonreinforcement or poststimulus attributes of X acquire inhibitory properties. 相似文献
57.
B Amblard C Assaiante JC Fabre L Mouchnino J Massion 《Canadian Metallurgical Quarterly》1997,114(2):214-225
The ability voluntarily to stabilize the head in space during lateral rhythmic oscillations (0.59+/-0.09 Hz) of the trunk has been investigated during microgravity (microG) and normal gravity (nG) conditions (parabolic flights). Five healthy young subjects, who gave informed consent, were examined. The movements were performed with eyes open or eyes closed, during phases of either microG or nG. The main result was that head orientation with respect to vertical may be stabilized about the roll axis under microG with, as well as without vision, despite the reduction in vestibular afferent and muscle proprioceptive inputs. Moreover, the absence of head stabilization about the yaw axis confirms that the degrees of freedom of the neck can be independently controlled, as was previously reported. These results seem to indicate that voluntary head stabilization does not depend crucially upon static vestibular afferents. Head stabilization in space may in fact be organized on the basis of either dynamic vestibular afferents or a short-term memorized postural body schema. 相似文献
58.
59.
N. Mitchell A. Alekseev R. Gallix D. Holland R. Meyder A. Panin M. Shimada F. Wong E. Zapretelina 《Journal of Fusion Energy》1997,16(1-2):25-35
The ITER magnet system consists of structurally linked sets of toroidal (TF) and poloidal (PF) field coils, central solenoid (CS), and various support structures. The coils are superconducting, force flow Helium cooled with a Kapton-Glass-Epoxy multilayer insulation system. The stored magnetic energy is about 100GJ in the TF system and 20GJ in the PF-CS. Coils and structure are maintained at 4 K by enclosing them in a vacuum cryostat. The cryostat, comprising an outer envelope to the magnets, forms most of the second radioactivity confinement barrier. The inner primary barrier is formed by the vacuum vessel, its ports and their extensions. To keep the machine size within acceptable bounds, it is essential that the magnets are in close proximity to both of the nuclear confinement barriers. The objective of the magnet design is that, although local damage to one of the barriers may occur in very exceptional circumstances, large scale magnet structural or thermal failure leading to simultaneous breaching of both barriers is not credible. Magnet accidents fall into three categories: thermal (which includes arcing arising from insulation failure and local overheating due to discharge failure in the event of a superconductor quench), structural (which includes component mechanical failure arising from material inadequacies, design errors and exceptional force patterns arising from coil shorts or control failures), and fluid (Helium release due to cooling line failure). After a preliminary survey to select initial faults conceivable within the present design, these faults are systematically analyzed to provide an assessment of the damage potential. The results of this damage assessment together with an assessment of the reliability of the monitoring and protective systems, shows that the magnets can operate with the required safety condition. 相似文献
60.
This paper presents a new self-routing packet network called the plane interconnected parallel network (PIPN). In the proposed design, the traffic arriving at the network is shaped and routed through two banyan network based interconnected planes. The interconnections between the planes distribute the incoming load more homogeneously over the network. The throughput of the network under uniform and heterogeneous traffic requirements is studied analytically and by simulation. The results are compared with the results of the baseline network and another banyan network based parallel interconnection network. It is shown that, for the proposed design, a higher degree of heterogeneity results in better performance 相似文献