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Genetic variation among malaria parasites has important consequences with regard to drug resistance, pathogenicity, immunity, transmission, and speciation. In this regard, malaria parasites have been shown to display a high degree of inter- and intra-species genetic divergence. The nuclear genomes of Plasmodium falciparum, Plasmodium yoelii, and Plasmodium gallinaceum are vastly divergent yet share a similar codon usage and total A/T content of approximately 82%. This is in contrast to other primate-specific species including P. vivax which have an A/T content of approximately 67%. To assess the effects of this evolutionary divergence on the conservation of gene content, organization, and codon usage in the mitochondrial DNA (mtDNA) of malaria parasites, we have cloned and sequenced the mitochondrial genome of Plasmodium vivax, and compared it with the mtDNAs of P. falciparum, P. yoelii, and P. gallinaceum. The P. vivax mitochondrial genome was found to be 5990 base pairs in length, and displayed a gene organization identical to that of P. falciparum, P. yoelii, and P. gallinaceum. Furthermore, there was a remarkable 90% conservation of sequence identity between the mitochondrial genomes of all four species. As an example of intra-species conservation, comparison of mtDNAs from two independently cloned P. falciparum isolates, Malay Camp and C10, revealed only a single nucleotide substitution. A/T content of the P. vivax mitochondrial genome was found to be identical to other species of Plasmodium, hence, we have postulated that the mitochondrial genomes of malaria parasites were refractory to the evolutionary shifts in nucleotide content seen among the nuclear genomes of malaria parasites. Among different Plasmodium species, the second position of mitochondrial codons were found to be the least prone to substitutions and displayed a significant bias in pyrimidines. These aspects of mitochondrial codon usage were distinct from the nuclear genome and may reflect functional aspects of decoding by the mitochondrial translational system. 相似文献
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BACKGROUND: The effect of the human immunodeficiency virus (HIV) epidemic on tuberculosis (TB) has been evaluated for certain countries in sub-Saharan Africa. However, no multi-country comparisons have been performed of the magnitude of the changes in TB case rates and the roles of the HIV epidemic and national TB control program (NTP) quality in these changes. METHODS: We examined trends in TB case rates after 1985 for 20 sub-Saharan African countries, and also from 1975-1984 for 10 of these countries (core countries). Average annual changes in TB case rates after 1985 were stratified by 1992 urban low-risk HIV seroprevalence and by NTP quality, as determined by a survey of international TB experts. RESULTS: Case rates in the core countries decreased by an average of -1.6% per year prior to 1985, but increased by an average of +7.0% per year after 1985 (+7.7% per year after 1985 in all 20 countries). Average annual case rates after 1985 increased approximately twice as fast in countries with high vs low or intermediate HIV seroprevalence ratings. In both the core countries and all 20 countries, the average annual rate of rise in case rates after 1985 decreased as NTP quality rating increased. This relationship persisted even after stratification by HIV seroprevalence rating. CONCLUSIONS: TB case rates have increased in sub-Saharan Africa since 1985. These increases were relatively greater as HIV seroprevalence increased, and relatively lower as NTP quality increased. Improving NTP quality is essential to mitigate the resurgence of TB in the HIV era. 相似文献
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This report covers hyperplastic and neoplastic lesions of the human vermiform appendix that, although unusual, are likely to be encountered by general surgical pathologists. Topics include epithelial neoplasms, hyperplastic polyps, diffuse epithelial hyperplasia, pseudomyxoma peritonei, goblet cell and tubular carcinoid tumors, neuroma, and neurogenous hyperplasia. We discuss recent advances in the prognosis and management of appendiceal carcinoma, current controversies regarding the relationship between ovarian and appendiceal epithelial neoplasms, the concept of the mucinous tumor of uncertain malignant potential (UMP), and practical aspects of reporting pseudomyxoma peritonei. Classical carcinoid tumors are beyond the scope of this article, and primary neoplasms that are so rare they occur in the literature only as isolated case reports are not covered. 相似文献
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AIM: The study of clinical running of gastric or duodenal ulcer in associated coronary heart disease (CHD). MATERIALS AND METHODS: 209 CHD patients with gastric ulcer (GU) or duodenal ulcer (DU) were examined clinically plus histological examination of gastric or duodenal mucosa biopsies was made. RESULTS: In CHD patients GU occurred more frequently (56%) than DU. The lesions involved more frequently lesser curvature of the stomach and pyloric part of the stomach. Males developed ulcers 3.5 times more frequently than females. Ulcers tended to a painless course without season exacerbations. The disease manifested first with gastric bleeding in 52% of the patients. GU and DU ran with frequent recurrences and long-term exacerbations (76% of patients) which coincided in time with CHD exacerbations. 68% of patients developed exacerbations within 10 days after myocardial infarction or aortocoronary bypass operation. Helicobacter pylori was present as a resolving factor in arising ulcer in 26% of patients. Microcirculatory disorders, reduced blood flow speed in gastric or duodenal mucosa, hypocoagulation syndrome, dyslipidemia provoked exacerbations in 62% of patients. Examinations of biopsies from gastric and duodenal mucosa showed marked dystrophic changes in the mucosa, its connective tissue basis in the vessels in the presence of mild inflammation at ulcer site. CONCLUSION: The onset of ulcers and erosions in the mucosa of the gastrointestinal tract in CHD may be due to circulatory disorders in gastric mucosa. The main factors of aggression are hypoxia, hypoxia-induced trophic defects in gastric and duodenal mucosa, circulatory disorders. 相似文献
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NJ Siegel RA Feldman B Lytton JP Hayslett M Kashgarian 《Canadian Metallurgical Quarterly》1977,40(4):379-384
To examine the role of intrarenal hemodynamics in in obstructive nephropathy, we determined cortical blood flow distribution (CBFD) in rats with bilateral ureteral occlusion (BUO) and unilateral ureteral occlusion (UUO) during and after release of obstruction. Prior to release of obstruction of 24 hours' duration, we found that outer cortical perfusion decreased by 20+/-5% in both BUO and UUO rats. Furthermore, one hour after release of BUO, there was rapid normalization of CBFD associated with a modest return of glomerular filtration rate (GFR), an almost complete return of renal blood flow (RBF), and a marked postobstructive diuresis. In contrast, after release of UUO, we observed that outer cortical perfusion remained decreased by 21+/-31%, both GFR and RBF remained markedly depressed, and no diuresis occurred. These data demonstrate (1) marked ischemia of the outer cortex in both BUO and UUO during obstruction, (2) a rapid return of CBFD to a normal pattern after release of BUO, but (3) persistent outer cortical ischemia following release of UUO. 相似文献
18.
Complex traits are generally taken to be under the influence of multiple genes, which may interact with each other to confer susceptibility to disease. Statistical methods in current use for localizing such genes essentially work under single-gene models, either implicitly or explicitly. In genomic screens for complex disease genes, some of the marker loci must be in tight linkage with disease susceptibility genes. We developed a general multi-locus approach to identify sets of such marker loci. Our approach focuses on affected sib pair data and employs a nonparametric pattern recognition technique using artificial neural networks. This technique analyzes all markers simultaneously in order to detect patterns of locus interactions. When applied to previously published sib pair data on type I diabetes, our approach finds the same genes as in the published report in addition to some new loci. For a specific two-locus model of inheritance, the power of our approach is higher than that of the currently used analysis standard. 相似文献
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