全文获取类型
收费全文 | 1158篇 |
免费 | 28篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 4篇 |
综合类 | 2篇 |
化学工业 | 101篇 |
金属工艺 | 16篇 |
机械仪表 | 35篇 |
建筑科学 | 4篇 |
矿业工程 | 2篇 |
能源动力 | 13篇 |
轻工业 | 25篇 |
水利工程 | 1篇 |
石油天然气 | 1篇 |
无线电 | 107篇 |
一般工业技术 | 82篇 |
冶金工业 | 740篇 |
原子能技术 | 7篇 |
自动化技术 | 47篇 |
出版年
2023年 | 6篇 |
2022年 | 7篇 |
2021年 | 8篇 |
2020年 | 9篇 |
2019年 | 10篇 |
2018年 | 17篇 |
2017年 | 6篇 |
2016年 | 23篇 |
2015年 | 14篇 |
2014年 | 17篇 |
2013年 | 20篇 |
2012年 | 27篇 |
2011年 | 39篇 |
2010年 | 19篇 |
2009年 | 28篇 |
2008年 | 24篇 |
2007年 | 23篇 |
2006年 | 20篇 |
2005年 | 14篇 |
2004年 | 15篇 |
2003年 | 16篇 |
2002年 | 13篇 |
2001年 | 14篇 |
2000年 | 10篇 |
1999年 | 36篇 |
1998年 | 223篇 |
1997年 | 125篇 |
1996年 | 75篇 |
1995年 | 37篇 |
1994年 | 49篇 |
1993年 | 35篇 |
1992年 | 9篇 |
1991年 | 11篇 |
1990年 | 8篇 |
1989年 | 14篇 |
1988年 | 15篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1983年 | 6篇 |
1982年 | 2篇 |
1981年 | 6篇 |
1980年 | 16篇 |
1979年 | 2篇 |
1978年 | 5篇 |
1977年 | 29篇 |
1976年 | 67篇 |
1975年 | 2篇 |
1966年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有1187条查询结果,搜索用时 15 毫秒
101.
HB Benestad T S?rensen KM Iranpour K Liest?l K Yogesan I Str?m-Gundersen X Wang D L?vhaug 《Canadian Metallurgical Quarterly》1998,26(10):936-941
A system for automatic analysis of in vitro hematopoietic colonies is described and evaluated. With the standard resolution provided by video cameras, the improvement in visualization obtained using features other than size and darkness when classifying potential colonies appears to be limited. We confirmed this by comparing results obtained with the test system with those obtained with a commercial one. However, for some applications it may be useful to supplement the system with specific methods, e.g., to separate merged colonies. Digital image analyses provide new possibilities, for instance of measuring the total cellularity of the dish or analyzing colonies according to the size and cell density of each colony. Examples provided are time course studies of colony development, cellularity feedback effects on colony sizes, and bell-shaped dose-response curves for the growth stimulation obtained by certain conditioned media on a subpopulation of progenitor cells that gives rise to large colonies. 相似文献
102.
Autonomic dysfunction has been demonstrated in various conditions associated with peripheral neuropathy such as acute intermittent porphyria, amyloidosis, and Guillain-Barré syndrome (GBS). In the latter, hypertension is an associated complication that typically occurs after neurological signs are already present. We report a case of a patient with autonomic dysfunction as the presenting feature who was admitted to the coronary unit with chest pain and hypertension. Subsequently, he developed progressive symmetric muscle, weakness, sensory changes, and areflexia. GBS was then diagnosed based on the clinical picture, albuminocytologic dissociation in the cerebrospinal fluid, and electrodiagnostic abnormalities suggestive of demyelinative polyneuropathy with conduction block. Few cases in the literature have reported autonomic dysfunction as the presenting feature of GBS, such as in this case. In a previously asymptomatic patient, acute onset of autonomic dysfunction should alert the physician to the possibility of an acute polyneuropathy, such as GBS. 相似文献
103.
The genetic analysis of human papillomavirus (HPV) functions during the vegetative viral life cycle is dependent upon the ability to generate human keratinocyte cell lines which maintain episomal copies of transfected viral genomes. We have previously demonstrated that lipofection of normal human foreskin keratinocytes with recircularized cloned HPV-31 genomic sequences resulted in a high frequency of cell lines which maintained viral genomes as extrachromosomal elements (M.G. Frattini, H. Lim, and L.A. Laimins, Proc. Natl. Acad. Sci. USA 93:3062-3067, 1996). Following the growth of these cell lines in organotypic (raft) cultures, the differentiation-dependent expression of viral late genes, the amplification of viral genomes, and virion biosynthesis were observed. In the present study, we demonstrate that these methodologies are not restricted to HPV-31 but are applicable to other HPV types, including the oncogenic HPV-18. HPV-18 genomes were purified from bacterial vector sequences, religated, and transfected into normal human foreskin keratinocytes together with a neomycin-selectable marker. Following drug selection, resistant cells were expanded and examined for the state of the viral DNA. All cell lines examined were found to contain approximately 100 to 200 episomal copies of HPV-18 DNA per cell. Growth of these cell lines in raft cultures resulted in the differentiation-dependent expression of the E1 [symbol: see text] E4 and L1 capsid genes. In addition, viral genome amplification was observed in suprabasal cells following DNA in situ hybridization analysis of differentiated raft cultures. The induction of these late viral functions has previously been shown to be directly associated with differentiation-dependent virion biosynthesis. Our studies indicate the ability to perform a detailed genetic analysis of the various phases of the viral life cycle, including control of the differentiation-dependent late viral functions, using a second oncogenic HPV type. 相似文献
104.
After i.v. injection into adult rats, human insulin-like growth factor-binding protein-3 (hIGFBP-3) forms 150-kDa complexes with excess endogenous rat acid-labile subunit (ALS) within 2 min (Lewitt et al., 1993, Endocrinology 133:1797). Because their previous in vitro studies indicated that hIGFBP-3 only bound to ALS in the presence of IGF-I, and because little free IGF-I is present in plasma, the authors postulated that IGF-I had been mobilized to the circulation to saturate the 150-kDa hIGFBP-3 complexes. We examined this hypothesis by determining whether the hIGFBP-3 that appears in 150-kDa complexes 2 min after i.v. injection is accompanied by an increase in IGF-I. Within 2 min, some of the injected hIGFBP-3 (approximately 30% as much as endogenous intact rat IGFBP-3) is present in complexes that are cleared slowly from the circulation and presumed to be 150-kDa complexes. Gel filtration and immunoprecipitation studies performed on blood collected 2 min after injection confirmed that the injected hIGFBP-3 (46-82% as much as rat IGFBP-3) was associated with ALS in 150-kDa complexes. The formation of 150-kDa complexes containing hIGFBP-3 was not accompanied by a corresponding change in the IGF-I content (determined by RIA) of whole serum or 150-kDa serum fractions, suggesting that the hIGFBP-3 had rapidly associated with rALS in vivo without mobilizing IGF-I. Surprisingly, however, hIGFBP-3 was cleared much more rapidly from 150-kDa complexes formed after injection of hIGFBP-3 than after injection of hIGFBP-3:IGF-I complexes, suggesting that the complexes observed after hIGFBP-3 injection might not have formed in vivo. In fact, 150-kDa complexes formed to a similar extent when hIGFBP-3 was added ex vivo to blood collected from rats that had not received hIGFBP-3. We conclude that hIGFBP-3 can rapidly associate with rALS to form 150-kDa complexes in vivo without the mobilization of IGF-I. Because 150-kDa complexes also are formed ex vivo, however, we are unable to resolve whether the complexes that formed in vivo formed as binary or ternary complexes. 相似文献
105.
The purpose of this exploratory investigation was to evaluate the heuristic potential of 31P magnetic resonance spectroscopy (MRS) in elucidating a neurobiologic component of the liability for a substance use disorder (SUD). We investigated 31P MRS spectra employing chemical shift imaging (CSI) derived from four distinct anatomic brain locations (i.e. frontal, occipital, right parietal, left parietal) in three groups of peripubertal children who are hypothesized to be at increasing levels of familial SUD risk. Specifically, we studied children with a positive paternal family history of SUD and a disruptive behavior disorder (DBD) diagnosis (SUD+/DBD+; n = 10), in contrast, to those with a positive paternal SUD history in the absence of other psychopathology (SUD+/DBD-; n = 13) and matched control children from normal families (SUD-/DBD-; n = 13). In addition, we examined neurocognitive tests of our subjects to determine any associations between cognitive capacities with regional 31P MRS spectra. The highest-risk sample (SUD+/DBD+) demonstrated a diminished proportion of phosphodiesters confined to the right parietal voxel. This right parietal phosphodiester proportion correlated only with the Information Scale score on a standard intelligence test for children. This suggested a relationship between general learning ability and motivation for academic achievement and right parietal physiology in the highest-risk sample. Variations in synaptic pruning could account for this observation. 相似文献
106.
Earlier investigations of the oxidation of 3,5,3',5'-tetramethylbenzidine (TMB) using horseradish peroxidase and prostaglandin H-synthase have shown the formation of a cation free radical of TMB in equilibrium with a charge-transfer complex, consistent with either a two- or a one-electron initial oxidation. In this work, we exploited the distinct spectroscopic properties of myeloperoxidase and its oxidized intermediates, compounds I and II, to establish two successive one-electron oxidations of TMB. By employing stopped-flow techniques under transient-state and steady-state conditions, we also determined the rate constants for the elementary steps of the myeloperoxidase-catalyzed oxidation of TMB at pH 5.4 and 20 degrees C. The second-order rate constant for compound I formation from the reaction of native enzyme with H2O2 is 2.6 x 10(7) M-1 s-1. Compound I undergoes a one-electron reduction to compound II in the presence of TMB, and the rate constant for this reaction was determined to be (3.6 +/- 0.1) x 10(6) M-1 s-1. The spectral scans show that compound II accumulates in the steady state. The rate constant for compound II reduction to native enzyme by TMB obtained under steady-state conditions is (9.4 +/- 0.6) x 10(5) M-1 s-1. The results are applied to a new, more accurate assay for myeloperoxidase based upon the formation of the charge-transfer complex between TMB and its diimine final product. 相似文献
107.
108.
109.
J Ulrich G Johannson-Locher WO Seiler HB St?helin 《Canadian Metallurgical Quarterly》1997,94(5):450-454
The objective of this report is to investigate whether smoking exerts any influence on the number of senile plaques and Alzheimer neurofibrillary tangles. A retrospective study was based on unselected consecutive autopsy findings on the brains of 301 patients aged 65 years or older examined at the Institute of Pathology, Basel. Brains were investigated according to a fixed protocol. Histological examination was performed on 15 paraffin-embedded tissue blocks per brain using staining with silver impregnation specific for Alzheimer neurofibrillary tangles and for senile plaques, and Alzheimer-type changes were quantified. Retrospective assessment of smoking history was also based on a fixed protocol. Statistical analysis of the relationship between the smoking habits and the amount of Alzheimer-type changes was performed and included analysis of 72 age- and sex-matched smoker-nonsmoker pairs from within the total of 301 cases to compensate for variations in these changes due to age/sex alone. The influence of smoking on the total of 301 cases cannot be proven statistically. But a protective action against senile plaque formation could be demonstrated in 28 age matched pairs of smoking-nonsmoking women. Furthermore a positive correlation between the amount of smoking and the neurofibrillary changes as expressed in Braak stages in smokers of both sexes was present. Thus, there seems to be an influence of nicotine on the structural alterations of Alzheimer's disease which can exert itself in opposite directions. 相似文献
110.
F Umlauft DT Wong PA Underhill PJ Oefner L Jin M Urbanek K Gruenewald HB Greenberg 《Canadian Metallurgical Quarterly》1997,92(11):1986-1991
OBJECTIVE: To characterize the nature of hepatitis G virus (HGV) infections in hemodialysis patients and to determine the responsiveness of HGV to antiviral therapy in these patients. METHODS: HGV, a recently identified flavivirus, is associated with non-A-E viral hepatitis infections. We studied HGV infections in hepatitis C virus (HCV)-infected hemodialysis patients over a 1-yr period, using two independent PCR assays and nucleic acid sequencing. Thirty-four of 63 study patients were treated with interferon. RESULTS: We observed a 27% prevalence (17/63 patients) and a 4% annual incidence of HGV infections in the study population. HGV was not detected in any of the 10 HGV-infected patients immediately after interferon therapy. Although seven of these 10 patients developed HGV relapses, three had long-term responses. The interferon responsiveness of HGV and HCV appeared to be unrelated. In contrast, all seven untreated HGV-infected patients remained viremic. Sequence analyses of the different HGV isolates revealed only very limited genetic variability in the polymerase chain reaction-amplified regions of HGV during 1 yr of observation. CONCLUSIONS: Our data suggest that HCV-infected hemodialysis patients are at substantial risk of acquiring HGV infection and that HGV infections are prevalent in this population. In addition, HGV infections become chronic but are responsive to interferon treatment. 相似文献