全文获取类型
收费全文 | 59262篇 |
免费 | 4719篇 |
国内免费 | 2581篇 |
专业分类
电工技术 | 3590篇 |
技术理论 | 3篇 |
综合类 | 3956篇 |
化学工业 | 9611篇 |
金属工艺 | 3342篇 |
机械仪表 | 3835篇 |
建筑科学 | 4560篇 |
矿业工程 | 1824篇 |
能源动力 | 1680篇 |
轻工业 | 3794篇 |
水利工程 | 1041篇 |
石油天然气 | 3933篇 |
武器工业 | 524篇 |
无线电 | 6275篇 |
一般工业技术 | 6954篇 |
冶金工业 | 3845篇 |
原子能技术 | 582篇 |
自动化技术 | 7213篇 |
出版年
2024年 | 262篇 |
2023年 | 1041篇 |
2022年 | 1770篇 |
2021年 | 2428篇 |
2020年 | 1945篇 |
2019年 | 1574篇 |
2018年 | 1736篇 |
2017年 | 1929篇 |
2016年 | 1668篇 |
2015年 | 2285篇 |
2014年 | 2963篇 |
2013年 | 3303篇 |
2012年 | 3590篇 |
2011年 | 4044篇 |
2010年 | 3501篇 |
2009年 | 3278篇 |
2008年 | 3215篇 |
2007年 | 2975篇 |
2006年 | 3071篇 |
2005年 | 2561篇 |
2004年 | 1840篇 |
2003年 | 1629篇 |
2002年 | 1608篇 |
2001年 | 1390篇 |
2000年 | 1293篇 |
1999年 | 1568篇 |
1998年 | 1684篇 |
1997年 | 1319篇 |
1996年 | 1147篇 |
1995年 | 907篇 |
1994年 | 718篇 |
1993年 | 557篇 |
1992年 | 425篇 |
1991年 | 280篇 |
1990年 | 230篇 |
1989年 | 177篇 |
1988年 | 145篇 |
1987年 | 97篇 |
1986年 | 81篇 |
1985年 | 52篇 |
1984年 | 35篇 |
1983年 | 34篇 |
1982年 | 37篇 |
1981年 | 29篇 |
1980年 | 29篇 |
1979年 | 7篇 |
1978年 | 7篇 |
1977年 | 23篇 |
1976年 | 59篇 |
1940年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
12.
BACKGROUND: In the Minnesota Colon Cancer Control Study, annual fecal occult blood testing reduced mortality from colorectal cancer by at least 33.4%. Some attribute a large part of this reduction to chance detection of cancers by colonoscopies; rehydration of guaiac test slides greatly increased positivity and consequently the number of colonoscopies performed. This study was conducted to determine how much of the reduction resulted from chance detection. METHODS: We used a mathematical model developed by Lang and Ransohoff to estimate the proportion of the 33.4% mortality attainable by chance alone. Applying the model requires the specification of five parameters: duration of follow-up, rate of compliance with fecal occult blood testing, rate of compliance with colonoscopy, positivity rate, and efficacy of colonoscopy in reducing colorectal cancer mortality. We took values for four of the five parameters directly from the Minnesota study. For the fifth parameter, efficacy of colonoscopy, we selected a value of 60%, based on the conclusions of another study. Whereas the Lang-Ransohoff model selects persons for colonoscopy by chance alone, those with bleeding cancers would also be selected by sensitive fecal occult blood testing. We therefore adjusted the result of the Lang-Ransohoff model for this dual detectability. RESULTS: We found that 16%-25% of the reduction in colorectal cancer deaths effected by fecal occult blood testing in the Minnesota study was due to chance detection; the remainder was due to sensitive detection. CONCLUSION: Chance played a minor role in the detection of colorectal cancers by fecal occult blood testing in the Minnesota study. 相似文献
13.
OBJECTIVE: To identify the influence of the increased level of serum cholyglycine (CG) on lipid metabolism and hemorrheology in patients with intrahepatic cholestasis during pregnancy (ICP). METHODS: The concentrations of serum CG, total cholesterol (CH), triglycerides (TG), high density lipoprotein-cholesterol (HDL-C), low density lipoprotein-cholesterol (LDL-C), high shear and low shear of blood specific viscosity (HS and LS), plasma specific viscosity (PV) and hematocrit (HCT) were measured in 68 cases of primiparas with single pregnancy and 30 healthy nonpregnant women respectively. The group of ICP was composed of 35 cases with CG > 6 mumol/L, the group of normal pregnancy, 33 cases with CG < 6 mumol/L. RESULTS: The means of CG and the lipidic parameters in the two pregnant groups were significantly higher than those in the non-pregnancy group (P < 0.02-0.001) except the means of HDL-C between the groups of ICP and non-pregnancy. The levels of LDL-C, LDL-C/HDL-C, LS, PV and HCT in the ICP were significantly higher than those in the normal pregnancy group (P < 0.02-0.001). CONCLUSIONS: There are significant changes of lipid metabolism and hemorrheology in patients with ICP. However, these changes could be corrected after pregnancy termination, when the level of serum CG returned to normal. The results suggest that the pathophysiologic changes of ICP are associated with increased level of serum CG. 相似文献
14.
The narrow pore-size distribution of activated carbon fibres (ACF) limits their application in the fields concerning larger
molecules, such as liquid adsorption and catalyst support. On the addition of carbon particles and organic materials to polyacrylonitrile
fibres, and after stabilizing and activating, the mesoporosity in the resultant ACF has been obviously increased. Among these
additives, carbon black gives the best effect. With 1 wt% carbon black I in precursor and on activating at 880°C for 30 min,
a mesoporosity of 48.2% (total pore volume 0.704 ml g-1, mesopore volume 0.340 ml g-1) has been obtained. The mechanism of
mesopore formation is also discussed.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
15.
ED Schneiderman SM Willis CJ Kowalski TR Ten have 《Canadian Metallurgical Quarterly》1993,32(1):35-43
Sixty-five patients initially seropositive for IgM anti-phenolic glycolipid-I (PGL-I) antibodies were tested for antibody levels to PGL-I, lipoarabinomannan (LAM), and the 35-kDa protein of Mycobacterium leprae at regular intervals for up to 30 months following the commencement of multidrug therapy (MDT). There was a steady decline in IgM anti-PGL-I and anti-35-kDa antibody levels to a mean of 17% and 14%, respectively, of the starting level at 24 months. The development of type 1 and type 2 reactions or the presence of drug-resistant organisms in a small number of patients had no significant influence on the changes in antibody level. The rate of decline was similar in different disease categories, but a higher proportion of lepromatous patients remained seropositive at the end of 2 years of treatment than borderline tuberculoid patients. By contrast, the mean IgG anti-LAM antibody levels remained stable or increased. Again the occurrence of type 1 or type 2 reactions had no significant effect on antibody level over 2 years. Falls in the IgM anti-PGL-I antibody levels mirrored the falls in the bacterial index in individual patients and provide an additional parameter for monitoring the response to chemotherapy. 相似文献
16.
17.
There is great interest today in massively parallel analytical strategies as a way to accelerate the rate of discovery in biological research; among them being 'biochips' and 'laboratories-on-a-chip'. The concept in the 'chip' approach is that minaturization will allow large numbers of operations to be performed in parallel in a small space, as in electronics. Proceeding with the semiconductor analogy, this paper demonstrates that in situ micromachining can be used to simultaneously fabricate millions of micrometer size, particle like structures in multiple liquid chromatography columns on a single wafer. Reduction of this widely used bioanalytical tool to the nanoliter volume, parallel processing, chip format is a significant step toward laboratories-on-a-chip. 相似文献
18.
19.
高温炉内的辐射传热是工业生产中常遇到的问题。过去,人们在应用热流法计算辐射传热时遇到了一定的困难,使计算结果与实际有一定的偏差。本文运用文献[1]中给出的新热流数学模型,开发出由新热流方程与能量方程相耦合的计算机程序,其中的比热流参数由线加热热源情况下计算得到。用该程序计算了实验室用马弗炉内的温度场,并且用热电偶实测了炉内的一些温度值,理论计算与实测值符合很好。 相似文献