全文获取类型
收费全文 | 4557篇 |
免费 | 53篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 23篇 |
综合类 | 2篇 |
化学工业 | 293篇 |
金属工艺 | 40篇 |
机械仪表 | 38篇 |
建筑科学 | 79篇 |
矿业工程 | 6篇 |
能源动力 | 62篇 |
轻工业 | 263篇 |
水利工程 | 20篇 |
石油天然气 | 2篇 |
无线电 | 233篇 |
一般工业技术 | 283篇 |
冶金工业 | 3039篇 |
原子能技术 | 23篇 |
自动化技术 | 206篇 |
出版年
2023年 | 12篇 |
2022年 | 16篇 |
2021年 | 21篇 |
2020年 | 11篇 |
2019年 | 16篇 |
2018年 | 25篇 |
2017年 | 25篇 |
2016年 | 37篇 |
2015年 | 29篇 |
2014年 | 24篇 |
2013年 | 83篇 |
2012年 | 54篇 |
2011年 | 100篇 |
2010年 | 63篇 |
2009年 | 68篇 |
2008年 | 90篇 |
2007年 | 92篇 |
2006年 | 97篇 |
2005年 | 77篇 |
2004年 | 55篇 |
2003年 | 58篇 |
2002年 | 68篇 |
2001年 | 61篇 |
2000年 | 37篇 |
1999年 | 151篇 |
1998年 | 926篇 |
1997年 | 520篇 |
1996年 | 356篇 |
1995年 | 202篇 |
1994年 | 181篇 |
1993年 | 204篇 |
1992年 | 52篇 |
1991年 | 55篇 |
1990年 | 58篇 |
1989年 | 57篇 |
1988年 | 50篇 |
1987年 | 37篇 |
1986年 | 34篇 |
1985年 | 38篇 |
1984年 | 26篇 |
1983年 | 26篇 |
1982年 | 31篇 |
1981年 | 17篇 |
1980年 | 37篇 |
1979年 | 13篇 |
1978年 | 18篇 |
1977年 | 72篇 |
1976年 | 155篇 |
1975年 | 12篇 |
1973年 | 11篇 |
排序方式: 共有4612条查询结果,搜索用时 15 毫秒
51.
ML McLaws C Murphy P Taylor M Ferson J Gold R Donnellan D Dalton 《Canadian Metallurgical Quarterly》1997,18(11):778-780
The rate of nosocomial respiratory syncytial virus (RSV) infection was measured in a large pediatric hospital using an incidence density method. The at-risk days for nosocomial RSV were summed during a defined winter period in which there were 54 admissions with community-acquired RSV infection giving a rate of 2.9 cases per 1,000 at-risk days (95% confidence interval, 0.3-5.4 per 1,000). 相似文献
52.
53.
54.
The ingestion of I-131 by pregnant women can have consequences for the developing foetus, in particular brain function. As the foetal thyroid accumulates iodine from the twelfth week of gestation onwards, the determination of foetal brain dose resulting from such I-131 accumulation is essential. Normal dosimetric methods fail to treat the case of foetus. Using an approximation method based on the MIRD approach, a foetal dose estimation scheme is developed to allow the determination of foetal brain dose from foetal thyroid irradiation. Dose values are obtained for the foetus based on the maternal intake of I-131. It was found that the choice of biokinetic model for the mother/foetus has a large impact on the determined dose estimate. 相似文献
55.
Over a period of 4.5 years, 14 patients with frontoethmoidal meningoencephaloceles were treated. Most patients came from Northern Namibia. Precise delineation of all cranial abnormalities was obtained by modern imaging techniques, and specific patterns of cerebral abnormality were found. The malformation was corrected in a single stage, and significant modifications have been developed to render the procedure simpler and safer. Information from our series favors delayed neural tube closure as the primary pathogenesis of the defect and suggests a common teratogen as the most probable etiological agent. Our experience leads us to advocate early correction of even small defects. 相似文献
56.
The authors of [Remarks on the LUC public key system, see ibid., vol. 30, p. 123, 1994] consider the Lucas function on which the public cryptosystem LUC proposed by Smith and Lennon [1993] is based. For a finite field G with m∈G, the Lucas function Vn(m) is defined by the second order linear recurrence relation Vn(m)=mVn-1(m)-Vn-2(m) where Vo (m)=2, V1(m)=m. The characteristic polynomial f of the Lucas function is f(x)=x2-mx+1, and Vx(m)=α x+α-x where α is a root of f. We now consider some of the results of and give concise proofs 相似文献
57.
When the phenotype of neurons in pre- and paravertebral sympathetic ganglia are compared, there are marked differences in NGF dependence, neuropeptide content, connectivity and electrophysiological properties. The trophic interactions that induce these differences are currently poorly understood. One explanation is that prevertebral neurons receive a second neurotrophic signal, other than NGF, from their target of innervation. If this is the case, neurons in the prevertebral ganglia should express another neurotrophin receptor, in addition to the NGF receptor (trkA). To test this prediction, the level of expression of three neurotrophin receptors, trkA, trkB and trkC, were examined in one paravertebral sympathetic ganglia, the SCG, and two prevertebral ganglia, the celiac and superior mesenteric ganglia. It was found that mRNA encoding the full-length form of the trkB receptor was barely expressed in the SCG. Significantly higher levels of full-length trkB mRNA expression were found in the prevertebral ganglia. Ligands of the trkB receptor may, therefore, contribute to the differentiation and/or survival of some prevertebral sympathetic neurons. 相似文献
58.
PURPOSE: To measure the effect of silicon diode detectors used for in vivo dosimetry on beam characteristics and determine whether this effect is clinically significant. METHODS AND MATERIALS: Commercially available photon and electron diodes were placed on the central axis of photon and electron beams. The beam characteristics were measured for 6- and 10-MV photon and 6-20-MeV electron energies from a Varian Clinac 1800 medical linear accelerator. Water was used for the medium, and measurements were made for various clinically common field sizes and depths. RESULTS: Beam attenuations along the central axis were 10 and 7.5% for 6- and 10-MV photons, respectively. Electron beam dose reductions were between 13 and 25% for 20-6-MeV electrons. Photon beam flatness varied up to 7% at different depths, but the symmetry was not affected much. Electron beam flatness and symmetry were significantly changed to as much as 18 and 6%, respectively. CONCLUSION: Use of diode detectors on central axis of photon and electron beams for in vivo dosimetry causes significant attenuation and alteration of the beam characteristics. The percentage of the volume affected is significant (e.g., 23% of the volume in a 4 x 4 field gets 10% less dose for a 6-MV photon beam), especially if these diodes are used for in vivo dosimetry on the central axis every day for every treatment, as is done in some clinics. Other beam parameters such as penumbra and skin dose are also affected. It is therefore recommended that the diodes be used only as needed. 相似文献
59.
Recently, it has been shown that EDM wires undergo thermal buckling at low axial transport speeds and a series of transport instabilities at high axial transport speeds. Hence, only intermediate speeds ensure the straight wire configuration, which is needed for high-accuracy cutting. These conclusions are based on the assumption that the convective heat transfer coefficient remains piecewise constant along the length of the wire. However, a recent study on convection from a vibrating, flexible body shows that the convection coefficient becomes modal. The present study re-examines the wire stability problem with this modal effect in mind. It is shown that at low axial transport speeds, the straight wire configuration may be stable. Its stability hinges on vibration—large amplitude motion implies increased convection and increased stability from thermal buckling. At high transport speeds, the system still undergoes the reported transport instabilities. This work shows that the well-defined intermediate speed range is not so well-defined in the presence of wire vibrations. 相似文献
60.
Murphy Philip N.; Bentall Richard P.; Ryley Lisa D.; Ralley Richard 《Canadian Metallurgical Quarterly》2003,17(2):167
Admission scores from a model comprising 3 motivation factors concerning the cessation of heroin use and a confidence scale concerning postdischarge abstinence were tested for their ability to predict postdischarge outcomes in patients beginning inpatient opiate detoxification. Statistically significant prediction of abstinence from heroin 30 days after discharge and the number of heroin-free days in the 3 months following admission was based on the confidence scale and a factor concerned with externally imposed constraints on continued heroin use. The single-scale confidence measure made the largest contribution to each prediction, indicating that such scales may be potentially useful outcome predictors for postdischarge abstinence. External constraints on heroin use may not provide a basis for success in this treatment modality. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献