全文获取类型
收费全文 | 8469篇 |
免费 | 176篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 26篇 |
综合类 | 4篇 |
化学工业 | 784篇 |
金属工艺 | 82篇 |
机械仪表 | 54篇 |
建筑科学 | 123篇 |
矿业工程 | 14篇 |
能源动力 | 64篇 |
轻工业 | 280篇 |
水利工程 | 14篇 |
石油天然气 | 7篇 |
武器工业 | 3篇 |
无线电 | 181篇 |
一般工业技术 | 543篇 |
冶金工业 | 6077篇 |
原子能技术 | 10篇 |
自动化技术 | 388篇 |
出版年
2023年 | 30篇 |
2022年 | 94篇 |
2021年 | 96篇 |
2020年 | 66篇 |
2019年 | 71篇 |
2018年 | 80篇 |
2017年 | 88篇 |
2016年 | 112篇 |
2015年 | 92篇 |
2014年 | 108篇 |
2013年 | 200篇 |
2012年 | 168篇 |
2011年 | 146篇 |
2010年 | 158篇 |
2009年 | 118篇 |
2008年 | 136篇 |
2007年 | 126篇 |
2006年 | 97篇 |
2005年 | 75篇 |
2004年 | 63篇 |
2003年 | 58篇 |
2002年 | 48篇 |
2001年 | 37篇 |
2000年 | 45篇 |
1999年 | 205篇 |
1998年 | 1982篇 |
1997年 | 1130篇 |
1996年 | 748篇 |
1995年 | 411篇 |
1994年 | 299篇 |
1993年 | 379篇 |
1992年 | 55篇 |
1991年 | 48篇 |
1990年 | 62篇 |
1989年 | 58篇 |
1988年 | 47篇 |
1987年 | 50篇 |
1986年 | 48篇 |
1985年 | 55篇 |
1984年 | 17篇 |
1983年 | 27篇 |
1982年 | 31篇 |
1981年 | 53篇 |
1980年 | 70篇 |
1978年 | 21篇 |
1977年 | 140篇 |
1976年 | 301篇 |
1975年 | 23篇 |
1974年 | 15篇 |
1973年 | 12篇 |
排序方式: 共有8654条查询结果,搜索用时 15 毫秒
21.
22.
The data of nine children with post-traumatic intramural haematoma of the duodenum treated in Aghia Sophia Children's Hospital of Athens from 1967 to 1980 were retrospectively analysed. Diagnosis was preoperative in all but two children, in whom diagnosis was made during laparotomy. All but one were managed by operative intervention which consisted of simple evacuation of the haematoma and closure of the serosal incision in two out of eight children. Six out of eight children operated on were followed up for 15 years, during which they were free of symptoms. Hypotonic duodenography performed in the above patients was negative for deformity or stricture of the duodenum. 相似文献
23.
IuP Spizhenko AV Biliaiev AM Zaremba IV Nahorny? AP Tkachenko 《Canadian Metallurgical Quarterly》1997,43(5-6):42-48
Investigated all links of oxygen homeostasis of patients in early period afterwards surgical stoppage gastro-intestinal bleeding and urgent intravascular volume replacement. Macrodelivery of oxygen (DO2) was reduced in two and more time in comparison with norm predominant in connection with anemia. In spite of the infringement of transport of oxygen through alveolar-capillary membrane (especially in patients with complications and death in early postoperative period), little affected of degree of hemoglobin saturation by oxygen. Despite decrease of erythrocyte zeta-potential, largely expressed in cases of lethal outcome, considerable infringement of passage through microcirculation vessels is fixed was not. The increase of degree of morbidity and anaerobic metabolism in early postoperative period was accompanied of hyperdynamic hemodynamic reaction. The increase of degree of morbidity was accompanied of increase oxygen deficit owing to infringement of oxidoreduction in fabries also. 相似文献
24.
AM Luciani S Di Capua L Guidoni R Ragona A Rosi V Viti 《Canadian Metallurgical Quarterly》1996,41(3):509-521
NMR relaxation times T1 and T2 of agarose and Fricke agarose gels have been measured in the range 17-51 MHz. The analysis of the spin echo curves indicates a multiexponential behaviour, characterized by three components, at all the examined frequencies. The relative T2 values, ranging from a few to a hundred milliseconds, can be attributed to different species of water molecules present in the gel. Two of these components are characterized by relaxation rates R2a and R2b, more sensitive than R1 to gamma irradiation, the sensitivity S being S(R1) = 0.066 s-1 Gy-1, S(R2a) = 0.088 s-1 Gy-1, S(R2b) = 0.17 s-1 Gy-1. The three T2 values decrease as a function of frequency, but no gain in dose sensitivity is obtained by changing the working frequency in the examined range. The relaxivity of agarose gels containing ferrous or ferric ions has also been measured and found to be different from those of the corresponding solutions in the absence of agarose. Thus it was possible to estimate the irradiation yield from three independent parameters, R1, R2a and R2b. No effect of the dose rate or of the source energy has been observed for any of these parameters. 相似文献
25.
AM De Mattos MA Head J Everett J Hosenpud R Hershberger A Cobanoglu G Ott R Ratkovec DJ Norman 《Canadian Metallurgical Quarterly》1994,57(4):626-630
To determine if cardiac allograft outcome is improved among patients with fewer HLA-DR mismatches with their donors, we studied 132 recipients of a primary cardiac allograft who were transplanted between December 1985 and December 1991. These recipients and their donors all had high-confidence-level serological HLA-DR typing, previously shown to correlate highly with DNA DR typing. Patients were divided in two groups based on the HLA-DR mismatch with their donors. Group I consisted of 78 patients with 1 or zero DR mismatch and group II of 54 patients with 2 DR mismatches. Allograft outcome measurements included incidence of moderate rejection, incidence of allograft vasculopathy at 12 months, cardiac function measured as left ventricular ejection fraction (LVEF) and cardiac index (CI), and actuarial graft survival up to 7 years. Groups I and group II were not different with regard to recipient age, donor age, ischemia time, pulmonary vascular resistance, sex, or PRA greater than 0%. Group II had a higher incidence of moderate rejection on the first-week biopsy (47% vs. 25%, P = 0.019), and during the first month (84% vs. 58%, P = 0.006), but no difference was found in frequency of rejection from months 2 to 12. LVEF was not different in the groups at any point. CI was better in group I at 12 months (2.76 vs. 2.5, P = 0.03). No statistically significant difference was found in incidence of allograft vasculopathy (17% vs. 26%, P = 0.204). Actual graft survival at 1 year was better for group I (91% vs. 74%, P = 0.008), and actuarial graft survival at 6 years also favored group I (76% vs. 56%, P = 0.04). Using high-confidence-level serological HLA-DR typing assignments we demonstrated that HLA-DR mismatching correlates highly with cardiac allograft outcome. Implications are that heart transplant survival could be improved if prospective matching were feasible and prioritized or if immunosuppression were tailored to the HLA-DR match. 相似文献
26.
27.
OBJECTIVE: To review epidemiological studies dealing with the temporal and geographic variability in the occurrence of rheumatoid arthritis (RA) and clinical studies that address the variability of severity and manifestations among populations. METHODS: An extensive search of the literature, including a Medline search, was completed. Studies addressing the origin, history, and trends in the occurrence of RA were reviewed first. Next, studies of the prevalence and incidence of RA in different populations were reviewed, and occurrence rates compared. Standardization was attempted by tabulating adult prevalence rates of studies using equivalent sets of criteria. Studies comparing RA patients from two populations were sought next. Finally, studies dealing with explanations of the presumed variability were reviewed. RESULTS: Temporal variability is indicated by paleopathological evidence that RA has existed in the New World since 4000 BC, whereas there is no evidence that it occurred in Europe before the 17th century, or in Africa before the 20th century. Epidemiological studies show a possible trend of decreasing incidence of RA in the United States and Western Europe, whereas reports from Africa note a rising incidence. In white populations of Europe and America, prevalence is approximately 1%, and incidence is 0.03%. Significantly higher rates are found in some North American Indians, and significantly lower rates in some Asian and African populations, even when the different population structures are taken into account. In the latter populations, different patterns of occurrence from those observed in whites emerge, such as greater female preponderance and a much younger peak age at onset. Direct standardized comparisons of two diverse populations of RA patients showed some differences in expression, severity, or manifestations of RA between populations. CONCLUSION: The occurrence and manifestations of RA are temporally and geographically variable. 相似文献
28.
29.
F F?ndrich AM Waaga J Schr?der E Schweizer A Schmid S Jacob HH Wacker P Schroeder 《Canadian Metallurgical Quarterly》1995,27(2):1553-1554
30.
JH Winstanley SJ Leinster TG Cooke BR Westley AM Platt-Higgins PS Rudland 《Canadian Metallurgical Quarterly》1993,67(4):767-772
The expression of the protease cathepsin-D has been evaluated using an immunohistochemical technique with a polyclonal antibody in paraffin-embedded tissue from 359 patients treated between the years 1975-1981 for Stage I and II breast cancer. One hundred and twenty seven patients (35%) have strongly positive, granular staining, 138 (38%) are intermediately stained in the cytoplasm, and in 94 (26%) no staining is observed. There is a strong positive association between expression of cathepsin-D and the presence of tumour in axillary lymph nodes (P < 0.006). Expression of the protease is associated with significantly poorer survival of patients in univariate analysis (P = 0.025); however, this is not independent of other tumour variables. 相似文献