全文获取类型
收费全文 | 1887篇 |
免费 | 7篇 |
专业分类
电工技术 | 1篇 |
化学工业 | 123篇 |
金属工艺 | 16篇 |
机械仪表 | 1篇 |
建筑科学 | 11篇 |
能源动力 | 17篇 |
轻工业 | 12篇 |
石油天然气 | 4篇 |
无线电 | 28篇 |
一般工业技术 | 72篇 |
冶金工业 | 1486篇 |
原子能技术 | 8篇 |
自动化技术 | 115篇 |
出版年
2018年 | 4篇 |
2016年 | 5篇 |
2015年 | 7篇 |
2014年 | 9篇 |
2013年 | 17篇 |
2012年 | 13篇 |
2011年 | 14篇 |
2010年 | 25篇 |
2009年 | 14篇 |
2008年 | 14篇 |
2007年 | 20篇 |
2006年 | 12篇 |
2005年 | 17篇 |
2004年 | 21篇 |
2003年 | 17篇 |
2002年 | 9篇 |
2001年 | 10篇 |
2000年 | 14篇 |
1999年 | 52篇 |
1998年 | 393篇 |
1997年 | 260篇 |
1996年 | 158篇 |
1995年 | 73篇 |
1994年 | 91篇 |
1993年 | 85篇 |
1992年 | 34篇 |
1991年 | 18篇 |
1990年 | 34篇 |
1989年 | 35篇 |
1988年 | 36篇 |
1987年 | 32篇 |
1986年 | 23篇 |
1985年 | 27篇 |
1984年 | 13篇 |
1983年 | 14篇 |
1982年 | 12篇 |
1981年 | 12篇 |
1980年 | 16篇 |
1979年 | 15篇 |
1978年 | 23篇 |
1977年 | 37篇 |
1976年 | 91篇 |
1975年 | 8篇 |
1974年 | 8篇 |
1973年 | 7篇 |
1972年 | 3篇 |
1971年 | 4篇 |
1970年 | 5篇 |
1964年 | 4篇 |
1963年 | 3篇 |
排序方式: 共有1894条查询结果,搜索用时 21 毫秒
71.
Discordance of databases designed for claims payment versus clinical information systems. Implications for outcomes research 总被引:6,自引:0,他引:6
JG Jollis M Ancukiewicz ER DeLong DB Pryor LH Muhlbaier DB Mark 《Canadian Metallurgical Quarterly》1993,119(8):844-850
OBJECTIVE: To determine the suitability of insurance claims information for use in clinical outcomes research in ischemic heart disease. DESIGN: Concordance study of two databases. SETTING: Tertiary care referral center. PATIENTS: A total of 12,937 consecutive patients hospitalized for cardiac catheterization for suspected ischemic heart disease between July 1985 and May 1990. INTERVENTIONS: Two-by-two tables were used to compute overall and kappa measures of agreement comparing clinical versus claims data for 12 important predictors of prognosis in patients with ischemic heart disease. MEASUREMENTS: Kappa statistics (agreement adjusted for chance agreement) were used to quantify agreement rates. RESULTS: Agreement rates between the clinical and claims databases ranged from 0.83 for the diagnosis of diabetes to 0.09 for the diagnosis of unstable angina (kappa values). Claims data failed to identify more than one half of the patients with prognostically important conditions, including mitral insufficiency, congestive heart failure, peripheral vascular disease, old myocardial infarction, hyperlipidemia, cerebrovascular disease, tobacco use, angina, and unstable angina, when compared with the clinical information system. CONCLUSIONS: Our results suggest that insurance claims data lack important diagnostic and prognostic information when compared with concurrently collected clinical data in the study of ischemic heart disease. Thus, insurance claims data are not as useful as clinical data for identifying clinically relevant patient groups and for adjusting for risk in outcome studies, such as analyses of hospital mortality. 相似文献
72.
73.
EM Manno DR Gress LH Schwamm MN Diringer CS Ogilvy 《Canadian Metallurgical Quarterly》1998,29(2):422-428
BACKGROUND AND PURPOSE: Transcranial doppler ultrasound (TCD) is used after subarachnoid hemorrhage to detect cerebral vasospasm and is often treated with induced hypertension. Cerebral autoregulation, however, may be disturbed in this population, raising the possibility that TCD velocities may be elevated by induced hypertension. To study this possibility, we performed continuous TCD monitoring of the middle cerebral artery during the induction and withdrawal of induced hypertension in patients after subarachnoid hemorrhage. METHODS: Twenty-eight patients were studied during the induction and withdrawal of hypertension using primarily phenylephrine. Continuous monitoring was performed on the middle cerebral artery with the highest flow velocity. Treatment was based on rising TCD velocities or clinical evidence for cerebral vasospasm. Mean arterial pressure and mean TCD velocities were recorded every minute. A change of > 15% from starting TCD values was considered significant. Cerebral autoregulation was calculated as a percentage of intact autoregulation. Patients were subsequently divided into groups of disturbed and intact autoregulation. RESULTS: In 10 of 19 patients (53%), TCD velocities changed by > 15% and paralleled changes in mean arterial pressure. This directly altered the TCD interpretation of the grade of vasospasm in 7 of 19 patients (36%). Three additional patients had smaller absolute changes in TCD velocities. No clinical difference could be identified between patients with disturbed and intact autoregulation. CONCLUSIONS: In patients with disturbed autoregulation after subarachnoid hemorrhage, induced hypertension can alter cerebral blood flow velocities. The level of autoregulation needs to be considered when interpreting TCD velocities in patients after subarachnoid hemorrhage. 相似文献
74.
OBJECTIVE: To study type IV collagen of skin and serum in patients with ALS. BACKGROUND: Collagen abnormalities of skin have been reported in ALS patients. However, little is known concerning type IV collagen in ALS. METHODS: We studied type IV collagen immunoreactivity of skin and measured serum levels of the 7S fragment of the N-terminal domain of type IV collagen (7S collagen) in patients with ALS and control subjects. RESULTS: The basement membrane as well as blood vessels of skin in ALS patients was weakly positive for type IV collagen as compared with those of diseased control subjects. This weak immunostaining became more pronounced as ALS progressed. The optical density for type IV collagen immunoreactivity in ALS patients was significantly lower (p < 0.001) than in diseased control subjects and was significantly decreased with duration of illness (r = -0.85, p < 0.01). Serum 7S collagen levels in patients with ALS were significantly decreased (p < 0.01) as compared with those in diseased and healthy control subjects and were negatively and significantly associated with duration of illness (r = -0.81, p < 0.001). There was an appreciable positive correlation between concentrations of serum 7S collagen and the density for type IV collagen immunoreactivity in ALS patients (r = 0.81, p < 0.02). CONCLUSIONS: These data suggest that a metabolic alteration of type IV collagen may take place in the skin of ALS patients and that the decreased levels of serum 7S collagen may reflect a decreased type IV collagen immunoreactivity of skin in patients with ALS. 相似文献
75.
76.
77.
This report describes differences in humoral immune response of acute and chronic phases of human Chagas disease. The reactivities of IgG, IgM, and IgA anti-Trypanosoma cruzi antibodies in serum samples from both groups of patients were compared by enzyme-linked immunosorbent assay (ELISA) employing either one of four antigenic fractions: mouse laminin (LAM), which reacts through Gal alpha 1-3Gal epitopes expressed on trypomastigote surface: whole intact trypomastigotes (TCT); trypomastigotes excreted/secreted antigens (TESA); and epimastigote alkaline extract (EAE). The selection of T. cruzi antigen preparations was based on their relative content of surface and internal antigens found in trypomastigote forms. The proportion of IgG reactive to carbohydrate epitopes was assessed through the decay of IgG reactivity from acute and chronic sera after m-periodate oxidation of solid-phase bound antigens. Trypomastigote and TESA antigens recognized by IgG from acute and chronic sera were also compared by immunoblotting. ELISA and immunoblotting data showed that: (1) the proportion of IgG directed to trypomastigote surface antigens was higher in acute than in chronic sera, whereas the opposite was found for internal antigens, (2) acute sera contained a higher percentage of IgG reactive to trypomastigote carbohydrate epitopes than chronic sera, and (3) anti-T. cruzi IgA was found exclusively in acute sera and led to 100% positivity when LAM, TCT, and TESA were employed as antigens. IgA ELISA with these antigens and IgG immunoblotting pattern with TESA could be useful as serological markers for the acute phase of human Chagas disease. 相似文献
78.
LH Lim 《Canadian Metallurgical Quarterly》1998,28(10):1495-1515
The diversity of monogeneans from Southeast Asia was examined using information from the literature to show their diversity at different taxonomic (subclass, family, genera, species) levels. Knowledge of monogeneans is still incomplete in Southeast Asia and the present numbers of monogeneans are likely an underestimate of what is present on/in aquatic organisms in the region, since so few hosts have been examined. An estimate of the possible numbers of monogeneans that could be present on/in fishes and turtles in Peninsular Malaysia indicates that only 8% of the monogeneans are presently known. Analysis of the available data on monogenean diversity (or species richness) at different taxonomic levels will provide useful information on their distribution patterns. There is an uneven distribution of investigations on this topic and Malayan fauna is considered to be representative of the Southeast Asian fauna. Southeast Asian (Sundaland) monogeneans are related (at the generic level) to the monogenean fauna of South China, India and Africa. 相似文献
79.
80.
Ninety-two patients with Dukes' class C colonic carcinoma, divided equally into those who survived 5 years or more and those surviving less than 5 years after resection for cure, underwent evaluation of multiple histopathologic characteristics of the primary tumor and the uninvolved regional lymph nodes. These characteristics were analyzed by the chi-square test for correlation with survival. A statistically significant correlation (P less than 0.05) in the group who survived 5 years or more was observed for Broders' grades 1 and 2, tumor not involving serosa, and a pushing tumor margin. Of the 14 patients who had a pushing tumor margin and tumor not involving serosa, 12 (86%) survived 5 years or more. Seven patients had an infiltrating tumor margin and peritumor venous invasion, and of this group, only one (14%) survived 5 years or more. Histopathologic characteristics of host immune reaction at the tumor or in the uninvolved regional lymph nodes did not correlate with survival. 相似文献