全文获取类型
收费全文 | 3750篇 |
免费 | 58篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 30篇 |
化学工业 | 436篇 |
金属工艺 | 35篇 |
机械仪表 | 78篇 |
建筑科学 | 119篇 |
矿业工程 | 5篇 |
能源动力 | 66篇 |
轻工业 | 182篇 |
水利工程 | 19篇 |
石油天然气 | 9篇 |
无线电 | 236篇 |
一般工业技术 | 405篇 |
冶金工业 | 1860篇 |
原子能技术 | 46篇 |
自动化技术 | 285篇 |
出版年
2021年 | 23篇 |
2020年 | 19篇 |
2019年 | 22篇 |
2018年 | 31篇 |
2017年 | 24篇 |
2016年 | 29篇 |
2015年 | 37篇 |
2014年 | 33篇 |
2013年 | 105篇 |
2012年 | 64篇 |
2011年 | 82篇 |
2010年 | 73篇 |
2009年 | 68篇 |
2008年 | 95篇 |
2007年 | 97篇 |
2006年 | 70篇 |
2005年 | 69篇 |
2004年 | 67篇 |
2003年 | 61篇 |
2002年 | 61篇 |
2001年 | 58篇 |
2000年 | 62篇 |
1999年 | 93篇 |
1998年 | 512篇 |
1997年 | 325篇 |
1996年 | 214篇 |
1995年 | 117篇 |
1994年 | 124篇 |
1993年 | 120篇 |
1992年 | 48篇 |
1991年 | 46篇 |
1990年 | 46篇 |
1989年 | 51篇 |
1988年 | 50篇 |
1987年 | 36篇 |
1986年 | 32篇 |
1985年 | 47篇 |
1984年 | 42篇 |
1983年 | 36篇 |
1982年 | 36篇 |
1981年 | 56篇 |
1980年 | 33篇 |
1979年 | 29篇 |
1978年 | 33篇 |
1977年 | 88篇 |
1976年 | 142篇 |
1975年 | 32篇 |
1974年 | 18篇 |
1973年 | 31篇 |
1972年 | 20篇 |
排序方式: 共有3811条查询结果,搜索用时 46 毫秒
1.
D Galasko T Saitoh Y Xia LJ Thal R Katzman LR Hill L Hansen 《Canadian Metallurgical Quarterly》1994,44(10):1950-1951
We determined apolipoprotein E (ApoE) genotypes in 122 autopsied demented patients. The frequency of the ApoE epsilon 4 allele was 39.6% in Alzheimer's disease (AD), 29.0% in the Lewy body variant of AD (LBV), and 6.25% in diffuse Lewy body disease. For AD and LBV patients, the epsilon 4 frequency was significantly higher than that reported in nondemented controls (10 to 15%). Therefore, LBV and AD share ApoE epsilon 4 as a genetic risk factor, providing further evidence that these conditions overlap. 相似文献
2.
3.
Sensory activity mediates regulation of tyrosine hydroxylase (TH), the first enzyme in the dopamine biosynthetic pathway, in the rodent olfactory bulb. The current studies established for the first time primary cultures of neonatal mouse olfactory bulb expressing TH and tested whether L-type calcium channels mediate the activity-dependent regulation of the dopamine phenotype. After 1 d in vitro (DIV), a small population of TH-immunostained neurons that lacked extensive processes could be demonstrated. After an additional 2 DIV in serum-free medium, the number of TH neurons had doubled, and they exhibited long interdigitating processes. Membrane depolarization for 48 hr with 50 mM KCl produced a further 2.4-fold increase in the number of TH-immunoreactive neurons compared with control cultures. Increased TH neuron number required at least 36 hr of exposure to KCl. Forskolin, which increases intracellular cAMP levels, induced a 1.5- to 1.6-fold increase in the number of TH-immunostained neurons. Combined treatment with KCl and forskolin was not additive. Nifedipine, an L-type calcium channel blocker, completely prevented the depolarization-mediated increase in TH expression but did not block the response to forskolin. Treatment with Bay K8644, an L-type calcium channel agonist, also significantly increased the number of TH-expressing neurons. Depolarization also induced alterations in neuritic outgrowth, resulting in a stellate versus an elongate morphology that, in contrast, was not prevented by nifedipine. These results are the first demonstration that in vitro, as in vivo, depolarization increases TH expression in olfactory bulb and that L-type calcium channels mediate this activity-dependent regulation of the dopamine phenotype. 相似文献
4.
5.
Structural engineers use design codes formulated to consider uncertainty for both reinforced concrete and structural steel
design. For a simple one-bay structural steel frame, we survey typical uncertainties and compute an interval solution for
displacements and forces. The naive solutions have large over-estimations, so we explore the Mullen-Muhanna assembly strategy,
scaling, and constraint propagation to achieve tight enclosures of the true ranges for displacements and forces in a fraction
of the CPU time typically used for simulations. That we compute tight enclosures, even for large parameter uncertainties used
in practice, suggests the promise of interval methods for much larger structures. 相似文献
6.
Norris Fran H.; Murphy Arthur D.; Baker Charlene K.; Perilla Julia L.; Rodriguez Francisco Gutiérrez; Rodriguez José de Jesús Gutiérrez 《Canadian Metallurgical Quarterly》2003,112(4):646
Prevalence rates of trauma and posttraumatic stress disorder (PTSD) were estimated from a probability sample of 2,509 adults from 4 cities in Mexico. PTSD was assessed according to Diagnostic and Statistical Manual of Mental Disorders (American Psychiatric Association, 1994) criteria using the Composite International Diagnostic Interview (CIDI; WHO, 1997). Lifetime prevalence of exposure and PTSD were 76% and 11.2%, respectively. Risk for PTSD was highest in Oaxaca (the poorest city), persons of lower socioeconomic status, and women. Conditional risk for PTSD was highest following sexual violence, but nonsexual violence and traumatic bereavement had greater overall impact because of their frequency. Of lifetime cases, 62% became chronic; only 42% received medical or professional care. The research demonstrates the importance of expanding the epidemiologic research base on trauma to include developing countries around the world. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
7.
M. A. Amer D. B. Kupranycz B. E. Baker 《Journal of the American Oil Chemists' Society》1985,62(11):1551-1557
Both summer and winter butterfats were fractionated using a laboratory procedure which was designed to simulate a commercial
fractionation process. The process is based on a slow, controlled cooling of the melted fat, a short stabilization time at
the fractionation temperature, and separation of the crystals from the liquid oil by vacuum filtration using a stainless steel
perforated disc. Fractionation temperatures of 29, 26, 23 and 19 C for winter butterfat and 29 and 19 C for summer butterfat
were used to obtain solid and liquid fractions at each temperature. Three replications at each temperature showed good reproducibility
of results. The fractions were characterized by their fatty acid and triglyceride compositions, melting and crystallization
behavior, iodine value, peroxide value and melting point.
Presented at the AOCS meeting in Philadelphia in May 1985. 相似文献
8.
The performance of netted radar is evaluated in terms of a netted version of the radar equation and the ambiguity function. A software simulation has been developed to allow assessment of netted radar sensitivity and ambiguity properties in both two-and three-dimensional space. Simulation results demonstrate that coherent netted radar sensitivity depends not only on the radar parameters, but also on the numbers, locations and specification of transmit and receive nodes. The netted radar ambiguity function is affected by a combination of many factors. In addition to those that determine the form of the monostatic ambiguity function, the locations of transmit and receive nodes as well as the position and velocity of the target all are shown to play an important role in evaluating system performance. As a result of these dependencies, it is shown that there is severe degradation of range and Doppler resolution when a target crosses sufficiently close to a transmit-receive baseline. 相似文献
9.
10.
SA Cook RT Bronson LR Donahue N Ben-Arie MT Davisson 《Canadian Metallurgical Quarterly》1997,8(2):108-112
OBJECTIVE: To discuss the case of an 8-yr-old boy with an aneurysmal bone cyst of the right proximal humerus, including the features imaged on plain film radiography, computed tomography (CT), magnetic resonance imaging (MRI), including spin echo and fast field echo imaging. CLINICAL FEATURES: The patient suffered for 1 yr from intermittent but progressive pain in his right upper arm and shoulder area. There was no history of trauma or known systemic disease. There was decreased range of motion in abduction of the glenohumeral joint and pain on focal pressure along the deltoid muscle. A complete imaging evaluation consisting of plain film radiography, CT and MRI was performed, which revealed the classical imaging features of an aneurysmal bone cyst. An additional cystic lesion was detected by the MRI that was not appreciated on the plain films or CT. INTERVENTION AND OUTCOME: The patient was referred for biopsy to confirm the preliminary diagnosis of aneurysmal bone cyst. No treatment was instituted. CONCLUSION: Evaluation of aneurysmal bone cyst may be completed with CT scanning and more specifically with MRI MRI coronal T2, weighted images are advantageous for visualization of the main cystic lesion and any additional cysts. Fast field echo images show a better contrast between the cyst and bone marrow with extension of the cyst into the epiphysis as evident in this case. Follow-up studies revealed complete healing of the cyst with only residual densities in the humeral metaphyseal area. 相似文献