全文获取类型
收费全文 | 3847篇 |
免费 | 3篇 |
专业分类
化学工业 | 12篇 |
轻工业 | 9篇 |
石油天然气 | 2篇 |
无线电 | 2篇 |
一般工业技术 | 1篇 |
冶金工业 | 3822篇 |
自动化技术 | 2篇 |
出版年
2023年 | 2篇 |
2018年 | 1篇 |
2016年 | 1篇 |
2014年 | 1篇 |
2013年 | 1篇 |
2010年 | 1篇 |
2007年 | 1篇 |
2006年 | 2篇 |
2005年 | 3篇 |
2004年 | 4篇 |
2003年 | 8篇 |
2000年 | 1篇 |
1999年 | 117篇 |
1998年 | 1254篇 |
1997年 | 729篇 |
1996年 | 474篇 |
1995年 | 241篇 |
1994年 | 167篇 |
1993年 | 220篇 |
1992年 | 19篇 |
1991年 | 45篇 |
1990年 | 42篇 |
1989年 | 41篇 |
1988年 | 47篇 |
1987年 | 30篇 |
1986年 | 35篇 |
1985年 | 31篇 |
1983年 | 6篇 |
1982年 | 11篇 |
1981年 | 13篇 |
1980年 | 29篇 |
1979年 | 3篇 |
1978年 | 6篇 |
1977年 | 76篇 |
1976年 | 179篇 |
1975年 | 3篇 |
1966年 | 1篇 |
1964年 | 1篇 |
1955年 | 4篇 |
排序方式: 共有3850条查询结果,搜索用时 15 毫秒
961.
RD Burwell ML Shapiro MT O'Malley H Eichenbaum 《Canadian Metallurgical Quarterly》1998,9(13):3013-3018
Neuronal activity in the perirhinal cortex was recorded while rats performed a spatial task on a four arm radial maze. The maze was defined by proximal multisensory cues on the arm surfaces and distal complex visual cues at the surround. During each recording session, rats were run in three conditions: baseline, a condition in which proximal and distal cues were manipulated, and a second baseline. Compared with the activity of hippocampal neurons in the same paradigm, a much smaller proportion of perirhinal neurons exhibited spatial selectivity and perirhinal place fields were larger than hippocampal place fields. Although perirhinal place fields exhibited a high degree of spatial tuning and reliability within a condition, they were not stable across conditions. 相似文献
962.
Interpopulation variation in the diet of the wood mouse, Apodemus sylvaticus, is well documented. In this study, we examined the gut morphology and apparent absorption efficiencies of two populations of wood mice whose diet in the field was known to differ. One population inhabited sand dunes, where food availability was relatively low and the diet was dominated by invertebrates. The other population lived in deciduous woodland, with greater food availability and a diet consisting primarily of seeds. Wood mice from the woodland had longer small intestines and total digestive tract lengths than mice from the sand dunes. However, these differences had no effect on the apparent absorption efficiencies of dry mass or energy when the mice were fed mealworms, wheat grain, or All-Bran diets (apparent energy absorption efficiencies of 88%, 89%, and 65%, respectively). The population differences in gut morphometry may be linked to different resource availabilities at the two field sites. 相似文献
963.
HJ Kaplan TH Tezel AS Berger ML Wolf LV Del Priore 《Canadian Metallurgical Quarterly》1997,115(9):1168-1172
OBJECTIVE: To establish the technical feasibility and safety of photoreceptor transplantation in retinitis pigmentosa. METHODS: A sheet of human photoreceptor cells was harvested from 2 human cadaveric eyes with a vibratome and transplanted into the subretinal spaces of 2 patients with advanced retinitis pigmentosa and visual acuity of no light perception by means of submacular surgery techniques. Preoperative and postoperative electrophysiologic testing, fundus photography, fluorescein angiography, and scanning laser ophthalmoscopy were performed. RESULTS: Twelve months after photoreceptor transplantation, the visual acuity of each patient remained no light perception. The temporal edge of the retinotomy in 1 patient was folded but was not associated with a retinal detachment. The patients were not immunosuppressed, and there was no evidence of rejection of the allogeneic transplant. Cystoid macular edema, uveitis, and macular pucker were not observed. CONCLUSION: A sheet of adult human photoreceptor cells can be harvested from human cadaveric eyes and safely transplanted to the subretinal spaces of patients with retinitis pigmentosa without systemic immunosuppression. 相似文献
964.
ML Macknin M Piedmonte C Calendine J Janosky E Wald 《Canadian Metallurgical Quarterly》1998,279(24):1962-1967
CONTEXT: The common cold is one of the most frequently occurring illnesses and is responsible for substantial morbidity and economic loss. Biochemical evidence suggests that zinc may be an effective treatment, and zinc gluconate glycine (ZGG) lozenges have been shown to reduce the duration of cold symptoms in adults. OBJECTIVE: To determine the efficacy of ZGG treatment of colds in children and adolescents. DESIGN: A randomized, double-masked, placebo-controlled study. SETTING: Two suburban school districts in Cleveland, Ohio. PATIENTS: A total of 249 students in grades 1 through 12 were enrolled within the first 24 hours of experiencing at least 2 of 9 symptoms of the common cold. INTERVENTION: Zinc lozenges, 10 mg, orally dissolved, 5 times a day (in grades 1-6) or 6 times a day (in grades 7-12). MAIN OUTCOME MEASURES: Time to resolution of cold symptoms based on subjective daily symptom scores for cough, headache, hoarseness, muscle ache, nasal congestion, nasal drainage, scratchy throat, sore throat, and sneezing. RESULTS: Time to resolution of all cold symptoms did not differ significantly between students receiving zinc (n = 124) and those receiving placebo (n = 125) (median, 9 days; 95% confidence interval [CI], 8-9 days; median, 9 days, 95% CI, 7-10 days, respectively; P=.71). There were no significant differences in the time to resolution of any of the 9 symptoms studied. Compared with controls, more students in the zinc group reported adverse effects (88.6% vs 79.8%; P=.06); bad taste (60.2% vs 37.9%; P=.001); nausea (29.3% vs 16.1%; P=.01); mouth, tongue, or throat discomfort (36.6% vs 24.2%; P=.03); and diarrhea (10.6% vs 4.0%; P=.05). CONCLUSIONS: In this community-based, randomized controlled trial, ZGG lozenges were not effective in treating cold symptoms in children and adolescents. Further studies with virologic testing are needed to clarify what role, if any, zinc may play in treating cold symptoms. 相似文献
965.
F Drago E Ranieri F Malaguti ML Battifoglio E Losi A Rebora 《Canadian Metallurgical Quarterly》1997,195(4):374-378
BACKGROUND: Clinical evidence suggests a viral etiology for pityriasis rosea (PR). OBJECTIVE: To evaluate human herpesvirus (HHV)-6 and HHV-7 as candidates for the etiology of PR. METHODS: Blood and skin tissue from 12 patients with acute PR, and 12 patients with other dermatoses were studied, as well as blood samples from 25 healthy persons. Serum interferon (IFN)-alpha and IFN-gamma were analyzed by ELISA. Analysis of morphological changes in cocultured peripheral blood mononuclear cells (PBMC) and electron microscopy (EM) to identify viral particles were performed. Polymerase chain reaction (PCR) with specific primers for HHV-6 and HHV-7 DNA sequences was performed on the plasma and PBMC of patients and healthy controls and on the skin of patients with PR and other skin diseases. RESULTS: PR plasma contained detectable IFN-alpha and IFN-gamma, whereas plasma from controls did not. PBMC from PR patients showed ballooning cells and syncytia after 7 days in culture whereas PBMC from controls and recovered PR patients did not. This cytopathic effect was also documented in a PR patient who relapsed and in Sup-T1 cell cultures inoculated with the cell-free supernatant from centrifuged cultured PBMC; in this supernatant, herpesvirus, virions were detected by EM, PCR identified HHV-7 DNA in PBMC, plasma and skin from all patients with active PR and in the PBMC only of 5 patients tested 10-14 months later. Weaker signals of HHV-7 DNA were detected in PBMC of 11 controls, but not in their plasma. Skin was negative for HHV-7 in all control specimens. CONCLUSIONS: Although the detection of HHV-7 DNA in PBMC and tissues does not prove directly a causal role, HHV-7 DNA in cell-free plasma corresponds to active replication which supports a causal relationship. We propose that PR is a clinical presentation of HHV-7 reactivation. 相似文献
966.
967.
The relationship of the extent and composition of coronary lesions and the degree of cardiac hypertrophy to anthropometric indicators of abdominal fatness and the amount of intra-abdominal fat was investigated in a group of 32 forensic autopsy cases that consisted of sudden deaths from violent causes of previously healthy men under 40 years of age. Body height and weight, waist and hip circumferences, and the thickness of the subscapular and abdominal subcutaneous fat were measured; the body mass index (BMI) and waist-to-hip ratio (WHR) were calculated; and omental, mesenteric, and perirenal fat deposits and the heart were weighed. The degree of coronary narrowing was determined visually, and the extent of coronary lesions was measured by planimetry. The thickness of the intima and intima-media was measured by computerized image analysis. Intimal macrophage foam cells and smooth muscle cells were detected by immunohistochemistry. Significant positive correlations were found between WHR and the overall degree of coronary narrowing and the intima-media thicknesses of the left anterior descending artery and right coronary artery when adjusted for age. Intima-media thickness was also related to tertiles of WHR. Heart weight indexed to height showed a significant positive correlation with BMI, waist circumference, WHR, and the size of intra-abdominal fat deposits, of which WHR was the best predictor of mild cardiac hypertrophy. The results indicate that the severity of clinically silent lesions in the atherosclerosis-prone regions of the coronary arteries is associated with WHR in young male individuals who also have mild myocardial hypertrophy associated with abdominal fatness and an accumulation of intra-abdominal fat. These associations between fat distribution and early cardiovascular changes point to a powerful need for preventive action with respect to weight gain in young men to alleviate progression of the lesions. 相似文献
968.
O Lang E Liebermeister J Liesegang ML Sautter-Bihl 《Canadian Metallurgical Quarterly》1998,174(12):629-632
PURPOSE: With regard to the poor prognosis of patients with glioblastoma multiforme, the aspect of life quality with a minimal treatment time becomes essential. The purpose of the present study is to evaluate whether the results of a radiotherapy schedule using increased single fractions applied over a shortened treatment time is feasible without compromising treatment efficiency or providing more side effects than a conventionally fractionated treatment. PATIENTS AND METHODS: A total of 38 patients (f = 21, m = 17, mean age 58 years) with histologically proven glioblastoma multiforme were irradiated after (partial) resection (n = 29) or stereotactic surgery (n = 9) with single doses of 3.5 Gy (ICRU) 5 fractions a week up to a total dose of 42 Gy following individual treatment planning. RESULTS: Median survival was 45.7 weeks, survival rate after 6 months was 80.9% and decreased to 34.2% after 12 months. Radiotherapy was tolerated without any important acute toxicity or any late side effects during the follow-up period. CONCLUSIONS: The increase of the dose per fraction using a fraction size of 3.5 Gy enhanced neither acute nor late toxicity. The survival rate compared well to those described in the literature. Thus the shortened treatment schedule seems as efficient as conventional radiotherapy. Moreover, it seems preferable with regard to quality of life. 相似文献
969.
C Roncero JJ Ventura A Sánchez B Bois-Joyeux ML Mesa H Thomassin JL Danan M Benito I Fabregat 《Canadian Metallurgical Quarterly》1998,1402(2):151-164
The mammalian spermatozoon undergoes continuous modifications during spermatogenesis, maturation in the epididymis, and capacitation in the female reproductive tract. Only the capacitated spermatozoa are capable of binding the zona-intact egg and undergoing the acrosome reaction. The fertilization process is a net result of multiple molecular events which enable ejaculated spermatozoa to recognize and bind to the egg's extracellular coat, the zona pellucida (ZP). Sperm-egg interaction is a species-specific event which is initiated by the recognition and binding of complementary molecule(s) present on sperm plasma membrane (receptor) and the surface of the ZP (ligand). This is a carbohydrate-mediated event which initiates a signal transduction cascade resulting in the exocytosis of acrosomal contents. This step is believed to be a prerequisite which enables the acrosome reacted spermatozoa to penetrate the ZP and fertilize the egg. This review focuses on the formation and contents of the sperm acrosome as well as the mechanisms underlying the induction of the acrosome reaction. Special emphasis has been laid on the synthesis, processing, substrate specificity, and mechanism of action of the acid glycohydrolases present within the acrosome. The hydrolytic action of glycohydrolases and proteases released at the site of sperm-zona binding, along with the enhanced thrust generated by the hyperactivated beat pattern of the bound spermatozoon, are important factors regulating the penetration of ZP. We have discussed the most recent studies which have attempted to explain signal transduction pathways leading to the acrosomal exocytosis. 相似文献
970.
CR Engwerda ML Murphy SE Cotterell SC Smelt PM Kaye 《Canadian Metallurgical Quarterly》1998,28(2):669-680
Aspergillus nidulans grows by apical extension of multinucleate cells called hyphae that are subdivided by the insertion of crosswalls called septa. Apical cells vary in length and number of nuclei, whereas subapical cells are typically 40 microm long with three to four nuclei. Apical cells have active mitotic cycles, whereas subapical cells are arrested for growth and mitosis until branch formation reinitiates tip growth and nuclear divisions. This multicellular growth pattern requires coordination between localized growth, nuclear division, and septation. We searched a temperature-sensitive mutant collection for strains with conditional defects in growth patterning and identified six mutants (designated hyp for hypercellular). The identified hyp mutations are nonlethal, recessive defects in five unlinked genes (hypA-hypE). Phenotypic analyses showed that these hyp mutants have aberrant patterns of septation and show defects in polarity establishment and tip growth, but they have normal nuclear division cycles and can complete the asexual growth cycle at restrictive temperature. Temperature shift analysis revealed that hypD and hypE play general roles in hyphal morphogenesis, since inactivation of these genes resulted in a general widening of apical and subapical cells. Interestingly, loss of hypA or hypB function lead to a cessation of apical cell growth but activated isotropic growth and mitosis in subapical cells. The inferred functions of hypA and hypB suggest a mechanism for coordinating apical growth, subapical cell arrest, and mitosis in A. nidulans. 相似文献