全文获取类型
收费全文 | 7278篇 |
免费 | 144篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 68篇 |
综合类 | 3篇 |
化学工业 | 817篇 |
金属工艺 | 118篇 |
机械仪表 | 124篇 |
建筑科学 | 184篇 |
矿业工程 | 11篇 |
能源动力 | 100篇 |
轻工业 | 532篇 |
水利工程 | 42篇 |
石油天然气 | 20篇 |
无线电 | 652篇 |
一般工业技术 | 796篇 |
冶金工业 | 3392篇 |
原子能技术 | 64篇 |
自动化技术 | 502篇 |
出版年
2022年 | 27篇 |
2021年 | 41篇 |
2020年 | 45篇 |
2019年 | 51篇 |
2018年 | 59篇 |
2017年 | 62篇 |
2016年 | 78篇 |
2015年 | 49篇 |
2014年 | 65篇 |
2013年 | 248篇 |
2012年 | 108篇 |
2011年 | 173篇 |
2010年 | 122篇 |
2009年 | 133篇 |
2008年 | 159篇 |
2007年 | 150篇 |
2006年 | 137篇 |
2005年 | 119篇 |
2004年 | 157篇 |
2003年 | 151篇 |
2002年 | 125篇 |
2001年 | 125篇 |
2000年 | 113篇 |
1999年 | 192篇 |
1998年 | 980篇 |
1997年 | 582篇 |
1996年 | 402篇 |
1995年 | 260篇 |
1994年 | 243篇 |
1993年 | 252篇 |
1992年 | 108篇 |
1991年 | 105篇 |
1990年 | 112篇 |
1989年 | 106篇 |
1988年 | 92篇 |
1987年 | 97篇 |
1986年 | 91篇 |
1985年 | 98篇 |
1984年 | 65篇 |
1983年 | 73篇 |
1982年 | 79篇 |
1981年 | 83篇 |
1980年 | 74篇 |
1979年 | 57篇 |
1978年 | 61篇 |
1977年 | 118篇 |
1976年 | 244篇 |
1975年 | 49篇 |
1974年 | 42篇 |
1973年 | 36篇 |
排序方式: 共有7425条查询结果,搜索用时 18 毫秒
81.
KJ Clark AB Sarr PG Grant TD Phillips GN Woode 《Canadian Metallurgical Quarterly》1998,63(2-4):137-146
Rotaviruses are the leading cause and coronaviruses are the major contributors of acute gastroenteritis in the young of various mammalian and avian species. Despite numerous trials and decades of research, vaccines have limited efficacy particularly for calves. As an alternative method of controlling infection, we have investigated broad spectrum antiviral agents that are not discriminatory among various viruses. This report involves testing a variety of adsorbent agents including charcoal, clay, and clay minerals to adsorb rotavirus and coronavirus in vitro. Results revealed that all the adsorbent agents had good to excellent capability of adsorbing rotavirus and excellent capability of adsorbing coronavirus. Percent adsorptions ranged from 78.74% to 99.89% for rotavirus and 99.99% for coronavirus; while sand (negative control) was < 0.01%. A high affinity binding was present as determined by a low percent desorption (0.06-3.09%). However, the adsorbent bound virus complex retained, and may have actually enhanced, infectivity. 相似文献
82.
J Chesney C Metz AB Stavitsky M Bacher R Bucala 《Canadian Metallurgical Quarterly》1998,160(1):419-425
We recently described a novel population of blood-borne cells, termed fibrocytes, that display a distinct cell surface phenotype (collagen+/CD13+/CD34+/CD45+), rapidly enter sites of tissue injury, and contribute to scar formation. To further characterize the role of these cells in vivo, we examined the expression of type I collagen and cytokine mRNAs by cells isolated from wound chambers implanted into mice. Five days after chamber implantation, CD34+ fibrocytes but not CD14+ monocytes or CD90+ T cells expressed mRNA for type I collagen. Fibrocytes purified from wound chambers also were found to express mRNA for IL-1beta, IL-10, TNF-alpha, JE/MCP, MIP-1alpha, MIP-1beta, MIP-2, PDGF-A, TGF-beta1, and M-CSF. The addition of IL-1beta (1-100 ng/ml), a critical mediator in wound healing, to fibrocytes isolated from human peripheral blood induced the secretion of chemokines (MIP-1alpha, MIP-1beta, MCP-1, IL-8, and GRO alpha), hemopoietic growth factors (IL-6, IL-10, and macrophage-CSF), and the fibrogenic cytokine TNF-alpha. By contrast, IL-1beta decreased the constitutive secretion of type I collagen as measured by ELISA. Additional evidence for a role for fibrocytes in collagen production in vivo was obtained in studies of livers obtained from Schistosoma japonicum-infected mice. Mouse fibrocytes localized to areas of granuloma formation and connective matrix deposition. We conclude that fibrocytes are an important source of cytokines and type I collagen during both the inflammatory and the repair phase of the wound healing response. Furthermore, IL-1beta may act on fibrocytes to effect a phenotypic transition between a repair/remodeling and a proinflammatory mode. 相似文献
83.
SW Qian JK Burmester PD Sun A Huang DJ Ohlsen L Suardet KC Flanders D Davies AB Roberts MB Sporn 《Canadian Metallurgical Quarterly》1994,33(40):12298-12304
Transforming growth factor-beta (TGF-beta) is a potent regulator of cell growth and differentiation. On the basis of the crystal structure of TGF-beta 2, we have designed and synthesized two mutant TGF-beta s, TGF-beta 1 (71 Trp) and TGF-beta 1 (delta 69-73). Although both of these molecules inhibited the growth of Mv1Lu mink lung epithelial cells and LS1034 colorectal cancer cells, which are affected equally by TGF-beta 1 and TGF-beta 2, TGF-beta 1 (delta 69-73) was much less potent than TGF-beta 1 or TGF-beta 1 (71 Trp) at inhibiting the growth of LS513 colorectal cancer cells which are growth-inhibited by TGF-beta 1 but not TGF-beta 2. Both TGF-beta 1 (71 Trp) and TGF-beta 1 (delta 69-73) increased levels of mRNAs for fibronectin and plasminogen activator inhibitor with Mv1Lu cells, whereas only TGF-beta 1 (71 Trp) and not TGF-beta 1 (delta 69-73) up-regulated the mRNA level of carcinoembryonic antigen in LS513 cells. The expression level of carcinoembryonic antigen mRNA in LS1034 cells was not altered by either wild-type or mutant TGF-beta s. Receptor labeling experiments demonstrated that TGF-beta 1 (71 Trp) bound with high affinity to the cell-surface receptors of Mv1Lu, LS1034, and LS513 cells while TGF-beta 1 (delta 69-73) bound effectively to the receptors of Mv1Lu and LS1034 cells but much less to the receptors on LS513 cells.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
84.
85.
A study of eight deaths involving the benzodiazepine flunitrazepam was performed to assess the contribution of this drug to the fatalities. Coronial deaths in Victoria in the 2-year period to mid-1991 were selected in which either flunitrazepam or flunitrazepam and ethanol were the principal toxicological findings. All bodies were subject to a full autopsy by forensic pathologists, and a full toxicological examination. No significant pathology was found at autopsy in any case. Very high concentrations of 7-aminoflunitrazepam, a metabolite of flunitrazepam, were present in all cases. In four cases no other significant drug was detected, whereas in the other four cases there were significant concentrations of ethanol (mean 1.6 g/L). In these two groups of cases the concentrations of 7-aminoflunitrazepam were 0.45 mg/L and 0.16 mg/L, respectively. Only moderate levels of flunitrazepam were detected, suggesting that 7-aminoflunitrazepam is produced postmortem and may be an important marker of flunitrazepam usage. The causes of death in these eight cases were probably either flunitrazepam toxicity or a combination of flunitrazepam and ethanol toxicity. Only one case appeared likely to have been a suicide. Our observations in these cases suggest that flunitrazepam may cause death in the absence of other drugs or significant disease. The presence of ethanol reduces the amount of flunitrazepam needed to cause death. 相似文献
86.
SD Walter SE Birnie LD Marrett SM Taylor D Reynolds J Davies JJ Drake M Hayes 《Canadian Metallurgical Quarterly》1994,84(3):367-376
OBJECTIVES: Our objectives were (1) to describe an analysis of the spatial pattern of cancer incidence in Ontario and (2) to discuss the quality of data in the Ontario Cancer Registry with respect to the accuracy of local cancer rates. METHODS: Cancer incidence rates were calculated for 22 cancer sites in 49 counties of Ontario during 1976 to 1986. Capture-recapture methods were used to estimate completeness of case registration, and completeness of residence information was also assessed. Spatial autocorrelation was used in measuring the geographic pattern of incidence rates. Comparisons were also made between sexes and with earlier data from 1966 to 1975. RESULTS: The quality of the geographic data in the registry appeared good, and corrections for incomplete or inaccurate registration had little impact. About one third of the sex-site combinations showed some evidence of spatial patterning in the cancer rate. Particularly strong regional variation was noted for cancers of the stomach, lung, uterus, and prostate. CONCLUSIONS: The analysis revealed a number of cancers with significant spatial patterning of risk. Further work is needed to relate the cancer data to other information on potential life-style and environmental factors. 相似文献
87.
This paper analyses the HIPERLAN channel access mechanism. Both a purely mathematical and a simulation model are built in order to evaluate the two successive phases of the contention scheme. Several optimisations, based on the choice of parametric values, are proposed, evaluated and compared. 相似文献
88.
P Verkade LH Schrama AJ Verkleij WH Gispen AB Oestreicher 《Canadian Metallurgical Quarterly》1997,79(4):1207-1218
Calmodulin and de-phosphorylated B-50/growth-associated protein-43 (GAP-43) have been shown to bind in vitro in a molecular complex, but evidence for an in situ association in the nervous system does not exist. Previously, we have reported that, in the model of the regenerating rat sciatic nerve, the B-50/GAP-43 immunoreactivity is increased and concentrated at the axolemma of unmyelinated axons located proximal to the site of injury and axon outgrowth. To explore a putative function of B-50/GAP-43, namely, the capacity of binding calmodulin to the plasma membrane, we examined the ultrastructural distribution of calmodulin in the proximal unmyelinated axon shafts of this model, using double immunolabelling and detection by fluorescent or gold probes conjugated to second antibodies. Immunofluorescence showed that seven days post-sciatic nerve crush the calmodulin immunoreactivity, similar to B-50/GAP-43 immunoreactivity, was intense in unmyelinated axon shafts located proximal to the site of injury of the regenerating nerve. Ultrastructurally, calmodulin was located at the axolemma of these regenerating unmyelinated axon shafts and inside the axoplasm, where it was associated with vesicles and microtubules. The plasma membrane labelling (approximately 69%) was significantly higher than the axoplasmic labelling. Over 60% of the plasma membrane-associated calmodulin co-localized with B-50/GAP-43 in a non-random distribution. Since normally calmodulin is largely present in the cytoplasm, these data suggest that calmodulin has been concentrated at the plasma membrane of unmyelinated axons, most probably by B-50/GAP-43. If the concentrating effect is due to B-50/GAP-43, then there is a possibility that these proteins may be present as a molecular complex in situ. The physiological significance could be that this association regulates the local availability of both B-50/GAP-43 and calmodulin for other interactions. 相似文献
89.
Spectrally stable Er-fiber laser for application in phase-sensitive optical time-domain reflectometry 总被引:3,自引:0,他引:3
Kyoo Nam Choi H.F. Taylor 《Photonics Technology Letters, IEEE》2003,15(3):386-388
A high degree of frequency stability in an Er-fiber laser with the Fabry-Perot configuration was achieved using a long (25-km) optical-feedback loop. The frequency-drift rate was determined to be <1 MHz/min by observing temporal fringes in an unbalanced Mach-Zehnder interferometer. Instantaneous linewidth measured with a delayed self-heterodyne interferometer was less than the 3-kHz resolution limit. The laser was utilized in an optical time-domain reflectometry experiment to detect and locate a time-varying phase perturbation applied to an optical fiber. 相似文献
90.
NE Taylor RN Rosenthal B Chabus S Levine AS Hoffman J Reynolds L Santos I Willets P Friedman 《Canadian Metallurgical Quarterly》1993,15(1):36-40
Cryptococcal meningitis has a high mortality rate of central nervous infection. The patients usually die of the disease itself, or complications from increased intracranial pressure. Early diagnosis and treatment, including surgical drainage, will improve the results. In this series, twenty-one patients with high intracranial pressure (ICP > 300 mmH2 O) are presented. Fourteen received implantation of Ommaya reservoir to aspirate cerebrospinal fluid (CSF) for relief of symptoms of ICP. Meanwhile 4 of these 14 patients also received intraventricular injection of amphotericin B because of poor response to systemic drugs. Another seven patient received systemic drug therapy only. Survival during therapy occurred in 11 of 14 patients in the surgical group, compared with only 1 of 7 patients treated by drug therapy alone (P = 0.019). In the 14 patients who received implantation of an Ommaya reservoir, there was one complication of CSF leakage when the reservoir ruptured because of repeated aspiration. For patients with cryptococcal meningitis with high ICP, early implantation of an Ommaya reservoir will improve the survival rate. 相似文献