全文获取类型
收费全文 | 12420篇 |
免费 | 153篇 |
国内免费 | 10篇 |
专业分类
电工技术 | 90篇 |
综合类 | 4篇 |
化学工业 | 1236篇 |
金属工艺 | 162篇 |
机械仪表 | 227篇 |
建筑科学 | 282篇 |
矿业工程 | 55篇 |
能源动力 | 164篇 |
轻工业 | 695篇 |
水利工程 | 70篇 |
石油天然气 | 19篇 |
武器工业 | 1篇 |
无线电 | 748篇 |
一般工业技术 | 1341篇 |
冶金工业 | 6642篇 |
原子能技术 | 81篇 |
自动化技术 | 766篇 |
出版年
2022年 | 48篇 |
2021年 | 54篇 |
2020年 | 40篇 |
2019年 | 56篇 |
2018年 | 78篇 |
2017年 | 72篇 |
2016年 | 84篇 |
2015年 | 78篇 |
2014年 | 99篇 |
2013年 | 354篇 |
2012年 | 193篇 |
2011年 | 251篇 |
2010年 | 252篇 |
2009年 | 237篇 |
2008年 | 255篇 |
2007年 | 250篇 |
2006年 | 214篇 |
2005年 | 239篇 |
2004年 | 177篇 |
2003年 | 196篇 |
2002年 | 189篇 |
2001年 | 159篇 |
2000年 | 172篇 |
1999年 | 284篇 |
1998年 | 2052篇 |
1997年 | 1262篇 |
1996年 | 854篇 |
1995年 | 531篇 |
1994年 | 465篇 |
1993年 | 492篇 |
1992年 | 142篇 |
1991年 | 142篇 |
1990年 | 150篇 |
1989年 | 168篇 |
1988年 | 160篇 |
1987年 | 112篇 |
1986年 | 101篇 |
1985年 | 129篇 |
1984年 | 116篇 |
1983年 | 95篇 |
1982年 | 84篇 |
1981年 | 87篇 |
1980年 | 117篇 |
1979年 | 79篇 |
1978年 | 92篇 |
1977年 | 207篇 |
1976年 | 395篇 |
1975年 | 66篇 |
1974年 | 63篇 |
1973年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
991.
992.
The present investigation simulated a group conversation in which participants asked (inquirer) and answered (responder) questions, as well as listened to others exchange information. Source (inquirer; responder) identification accuracy was evaluated immediately or after 1 week. Older adults were less adept at source identification, although this difference was reduced with personal (Experiment 2) rather than categorical (Experiment 1) topics. The age difference was independent of explicit memory (cued recall and recognition), suggesting that memory for source and information are separable. Older adults were comparable to younger adults in responder identification but worse at inquirer identification. Responder identification was better than inquirer identification, with the latter dropping to chance at 1 week. Source identification was most accurate when participants were in the responder role; there was little difference between the inquirer and listener roles. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
993.
JS Kang PJ Mulieri C Miller DA Sassoon RS Krauss 《Canadian Metallurgical Quarterly》1998,143(2):403-413
Cauliflower mosaic virus (CaMV) uses a specialised translation mechanism to bypass the long leader sequence of the 35S RNA. The effect of the CaMV 35S RNA leader sequence on the expression of a downstream beta-glucuronidase (GUS) reporter gene was studied in transgenic tobacco plants. Enzymatic GUS assays of these transgenic plants show that a shunt mechanism of translation indeed occurs in planta with an average efficiency of 5% compared with the leaderless construct. Histological GUS analyses indicate that the shunt mechanism occurs throughout the whole plant and at all developmental stages. 相似文献
994.
MA Pfaller RN Jones GV Doern HS Sader RJ Hollis SA Messer 《Canadian Metallurgical Quarterly》1998,36(7):1886-1889
An international program of surveillance of bloodstream infections (BSIs) in the United States, Canada, and South America between January and December 1997 detected 306 episodes of candidemia in 34 medical centers (22 in the United States, 6 in Canada, and 6 in South America). Eighty percent of the BSIs were nosocomial and 50% occurred in patients hospitalized in an intensive care unit. Overall, 53.3% of the BSIs were due to Candida albicans, 15.7% were due to C. parapsilosis, 15.0% were due to C. glabrata, 7.8% were due to C. tropicalis, 2.0% were due to C. krusei, 0.7% were due to C. guilliermondii, and 5.8% were due to Candida spp. However, the distribution of species varied markedly by country. In the United States, 43.8% of BSIs were due to non-C. albicans species. C. glabrata was the most common non-C. albicans species in the United States. The proportion of non-C. albicans BSIs was slightly higher in Canada (47.5%), where C. parapsilosis, not C. glabrata, was the most common non-C. albicans species. C. albicans accounted for 40.5% of all BSIs in South America, followed by C. parapsilosis (38.1%) and C. tropicalis (11.9%). Only one BSI due to C. glabrata was observed in South American hospitals. Among the different species of Candida, resistance to fluconazole (MIC, > or = 64 microg/ml) and itraconazole (MIC, > or = 1.0 microg/ml) was observed with C. glabrata and C. krusei and was observed more rarely among other species. Isolates of C. albicans, C. parapsilosis, C. tropicalis, and C. guilliermondii were all highly susceptible to both fluconazole (99.4 to 100% susceptibility) and itraconazole (95.8 to 100% susceptibility). In contrast, 8.7% of C. glabrata isolates (MIC at which 90% of isolates are inhibited [MIC90], 32 microg/ml) and 100% of C. krusei isolates were resistant to fluconazole, and 36.9% of C. glabrata isolates (MIC90, 2.0 microg/ml) and 66.6% of C. krusei isolates were resistant to itraconazole. Within each species there were no geographic differences in susceptibility to fluconazole or itraconazole. 相似文献
995.
HP Selker JR Beshansky JL Griffith TP Aufderheide DS Ballin SA Bernard SG Crespo JA Feldman SS Fish WB Gibler DA Kiez RA McNutt AW Moulton JP Ornato PJ Podrid JH Pope DN Salem MR Sayre RH Woolard 《Canadian Metallurgical Quarterly》1998,129(11):845-855
BACKGROUND: Approximately 6 million U.S. patients present to emergency departments annually with symptoms suggesting acute cardiac ischemia. Triage decisions for these patients are important but remain difficult. OBJECTIVE: To test whether computerized prediction of the probability of acute ischemia, used with electrocardiography, improves the accuracy of triage decisions. DESIGN: Controlled clinical trial. SETTING: 10 hospital emergency departments in the midwestern, southeastern, and northeastern United States. PATIENTS: 10689 patients with chest pain or other symptoms suggestive of acute cardiac ischemia. INTERVENTION: The probability of acute ischemia predicted by the acute cardiac ischemia time-insensitive predictive instrument (ACI-TIPI), either automatically printed or not printed on patients' electrocardiograms. MEASUREMENTS: Emergency department triage to a coronary care unit (CCU), telemetry unit, ward, or home. Other measurements were the bed capacity of the CCU relative to that of the telemetry unit; training or supervision status of the triaging physician; and patient diagnoses and outcomes based on clinical, electrocardiographic, and creatine kinase data. RESULTS: For patients without cardiac ischemia, in hospitals with high-capacity CCUs and relatively low-capacity cardiac telemetry units, use of ACI-TIPI was associated with a reduction in CCU admissions from 15% to 12%, a change of -16% (95% CI, -30% to 0%), and an increase in emergency department discharges to home from 49% to 52%, a change of 6% (CI, 0% to 14%; overall P=0.09). Across all hospitals, for patients evaluated by unsupervised residents, use of ACI-TIPI was associated with a reduction in CCU admissions from 14% to 10%, a change of -32% (CI, -55% to 3%); a reduction in telemetry unit admissions from 39% to 31%, a change of -20% (CI, -34% to -2%); and an increase in discharges to home from 45% to 56%, a change of 25% (CI, 8% to 45%; overall P=0.008). Among patients with stable angina, in hospitals with high-capacity CCUs, use of ACI-TIPI was associated with a reduction in CCU admissions from 26% to 13%, a change of -50% (CI, -70% to -17%), and an increase in discharges to home from 20% to 22%, a change of 10% (CI, -29% to 71%; overall P=0.02). At hospitals with high-capacity telemetry units, use of ACI-TIPI was associated with a reduction in telemetry unit admissions from 68% to 59%, a change of -14% (CI, -27% to 1%), and an increase in emergency department discharges to home from 10% to 21%, a change of 100% (CI, 22% to 230%; overall P=0.02). Among patients with acute myocardial infarction or unstable angina, use of ACI-TIPI did not change appropriate admission (96%) to the CCU or telemetry unit at hospitals with high-capacity CCUs or telemetry units. CONCLUSIONS: Use of ACI-TIPI was associated with reduced hospitalization among emergency department patients without acute cardiac ischemia. This result varied as expected according to the CCU and cardiac telemetry unit capacities and physician supervision at individual hospitals. Appropriate admission for unstable angina or acute infarction was not affected. If ACI-TIPI is used widely in the United States, its potential incremental impact may be more than 200000 fewer unnecessary hospitalizations and more than 100000 fewer unnecessary CCU admissions. 相似文献
996.
997.
PJ Franaszczuk GK Bergey PJ Durka HM Eisenberg 《Canadian Metallurgical Quarterly》1998,106(6):513-521
A Spanish-language questionnaire designed for measuring the impact of asthma on quality of life in adults was developed. It was derived, by the application of a rigorous translation protocol, from a previously validated, English-language Asthma Quality of Life (AQL) questionnaire which had been developed in Australia. The aim of this study was to evaluate the psychometric properties of the Spanish AQL questionnaire using a cross-sectional and longitudinal design. Two hundred ninety-four clinically stable subjects with asthma (168 women, mean baseline forced expiratory volume in 1 sec [FEV1] = 85% predicted), aged 17-70, attended for the initial baseline assessment. All subjects completed the AQL questionnaire and a full history and physical examination were performed. The clinical assessment of severity was based on the classification recommended by the Global Initiative on Asthma (GINA). One week after the initial assessment subjects completed the AQL questionnaire for a second time. Six months later, subjects were assessed clinically and completed all the assessment measures at baseline. Principal components analysis of the AQL questionnaire responses at the baseline visit revealed a structure that was almost identical to that seen in the original English-language questionnaire. The questionnaire was shown to be internally consistent (Cronbach's alpha 0.91 for total score and 0.80-0.86 for the four subscales) and repeatable (intraclass correlation coefficient 0.91 for the total scale and 0.78-0.92 for the subscales). The finding of expected strong correlations with the subject's global assessment of severity (p = 0.70) and dyspnea (p = 0.63), a weak inverse correlation with FEV1 (p = -0.17), and good discrimination among the four GINA severity categories (F3,291 = 37.16, p < 0.0001) supports the construct validity of the questionnaire. AQL scores increased with age (p = 0.31) and were higher in women (p < 0.005). The AQL was responsive to both improvement (mean change 1.02, p < 0.0001) and deterioration (mean change -1.13, p < 0.001) in the severity of asthma over a 6-month period. This disease-specific, Spanish-language AQL questionnaire was shown to have sound psychometric properties which make it suitable for use in cross-sectional or longitudinal studies where it is appropriate to assess the impact of asthma on the quality of life of individual patients. 相似文献
998.
Understanding how the regulation of growth factor pathways alters during prostate cancer (PC) progression may enable researchers to develop targeted therapeutic strategies for advanced disease. PC progression involves the shifting of cells from androgen-dependent growth to an androgen-independent state, sometimes with the loss or mutation of the androgen receptors in PC cells. Both autocrine and paracrine pathways are up-regulated in androgen-independent tumors and may replace androgens as primary growth stimulatory factors in cancer progression. Our discussion focuses on growth factor families that maintain homeostasis between epithelial and stromal cells in the normal prostate and that undergo changes as PC progresses, often making stromal cells redundant. These growth factors include fibroblast growth factor, insulin-like growth factors, epidermal growth factor, transforming growth factor alpha, retinoic acid, vitamin D3, and the transforming growth factor beta families. We review their role in normal prostate development and in cancer progression, using evidence from clinical specimens and models of PC cell growth. 相似文献
999.
PJ Cagnoni Y Nieto EJ Shpall SI Bearman AE Barón M Ross S Matthes SE Dunbar RB Jones 《Canadian Metallurgical Quarterly》1998,16(5):1661-1668
PURPOSE: To evaluate the feasibility of high-dose chemotherapy (HDC) with autologous hematopoietic progenitor-cell support (AHPCS) as part of combined modality therapy (CMT) in patients with inflammatory breast cancer (IBC). PATIENTS AND METHODS: From April 1993 to March 1997, 30 patients with IBC were treated at our program. Twenty-three patients received neoadjuvant chemotherapy (NAC) before HDC; 18 patients also received adjuvant chemotherapy following surgery, but before HDC. All patients received HDC with high-dose cyclophosphamide, cisplatin, and carmustine (BCNU) with AHPCS. Every patient underwent surgery either before (27 patients) or after (three patients) HDC. Patients received radiotherapy after HDC in addition to tamoxifen if their tumors were estrogen receptor-positive. RESULTS: Thirteen patients experienced grade 3 or 4 nonhematologic noninfectious toxicities. In 12 patients (40%), this represented drug-induced lung injury, which in all cases responded to a 10-week course of corticosteroids. The only treatment-related death was secondary to hemolytic-uremic syndrome (HUS). Another patient suffered grade 4 CNS toxicity, which was completely reversible. All patients engrafted promptly. Eight patients relapsed, five of whom had a poor pathologic response to NAC. Relapses were local (five patients), local plus systemic (one), or systemic only (two). Median follow-up time from diagnosis and HDC is 23.5 (range, 7 to 49) and 19 (range, 4 to 44) months, respectively. Twenty-one patients (70%; 95% confidence interval [CI], 51% to 86%) remain alive and free of disease 4 to 44 months after HDC. Median disease-free survival (DFS) and overall survival have not yet been reached. CONCLUSION: HDC as part of CMT is feasible in patients with IBC. The toxicity of this treatment program is significant, but tolerable. Despite the short follow-up duration, the promising DFS observed in this group of patients warrants randomized studies that include a HDC-containing arm in patients with IBC. 相似文献
1000.
JL Mankowski DL Carter JP Spelman ML Nealen KR Maughan LM Kirstein PJ Didier RJ Adams M Murphey-Corb MC Zink 《Canadian Metallurgical Quarterly》1998,153(4):1123-1130
We investigated the effects of dietary factors on the pH and the ammonia emission from slurry of growing-finishing pigs. Sixteen male hybrid pigs (80 to 90 kg BW) were allotted to one of four diets based on barley-wheat, tapioca, barley-tapioca, and sugar beet pulp. Diets were formulated to have similar NE and CP contents and a similar lysine:NE ratio. Diets differed in nonstarch polysaccharide content (NSP) and dietary electrolyte balance (dEB). Urine and feces were daily collected quantitatively in metabolism cages and mixed as a slurry at the end of the collection period. After mixing, the pH and the ammonia emission from the slurry were measured daily in a laboratory setup for 7 d at 20 degrees C. The type of diet affected the pH of the slurry and the ammonia emission (P < .001). The pH of the slurry from pigs fed the sugar beet pulp-based diet was .8 unit lower and ammonia emission was 52 to 53% lower than that of the other three diets. The low dEB and high NPS sugar beet pulp-based diet increased the VFA concentration and reduced the pH and ammonia emission from the slurry. We conclude that dietary NSP and dEB influence the pH and ammonia emission from slurry of growing-finishing pigs. 相似文献