全文获取类型
收费全文 | 4261篇 |
免费 | 94篇 |
国内免费 | 10篇 |
专业分类
电工技术 | 39篇 |
综合类 | 3篇 |
化学工业 | 639篇 |
金属工艺 | 124篇 |
机械仪表 | 103篇 |
建筑科学 | 121篇 |
矿业工程 | 14篇 |
能源动力 | 73篇 |
轻工业 | 293篇 |
水利工程 | 21篇 |
石油天然气 | 9篇 |
无线电 | 544篇 |
一般工业技术 | 722篇 |
冶金工业 | 1259篇 |
原子能技术 | 33篇 |
自动化技术 | 368篇 |
出版年
2021年 | 35篇 |
2019年 | 27篇 |
2018年 | 44篇 |
2017年 | 29篇 |
2016年 | 40篇 |
2015年 | 31篇 |
2014年 | 57篇 |
2013年 | 232篇 |
2012年 | 97篇 |
2011年 | 99篇 |
2010年 | 101篇 |
2009年 | 120篇 |
2008年 | 128篇 |
2007年 | 117篇 |
2006年 | 103篇 |
2005年 | 99篇 |
2004年 | 88篇 |
2003年 | 99篇 |
2002年 | 77篇 |
2001年 | 91篇 |
2000年 | 114篇 |
1999年 | 110篇 |
1998年 | 356篇 |
1997年 | 241篇 |
1996年 | 165篇 |
1995年 | 135篇 |
1994年 | 101篇 |
1993年 | 108篇 |
1992年 | 57篇 |
1991年 | 62篇 |
1990年 | 80篇 |
1989年 | 75篇 |
1988年 | 51篇 |
1987年 | 59篇 |
1986年 | 43篇 |
1985年 | 60篇 |
1984年 | 68篇 |
1983年 | 61篇 |
1982年 | 46篇 |
1981年 | 61篇 |
1980年 | 45篇 |
1979年 | 43篇 |
1978年 | 26篇 |
1977年 | 67篇 |
1976年 | 72篇 |
1975年 | 36篇 |
1974年 | 36篇 |
1973年 | 45篇 |
1972年 | 23篇 |
1970年 | 24篇 |
排序方式: 共有4365条查询结果,搜索用时 15 毫秒
941.
942.
943.
The role of interior design elements in mitigating the negative relationship between residential crowding and psychological health was investigated. Residents of crowded homes with greater architectural depth (the number of spaces one must pass through to get from one room in the house to another) are less likely to socially withdraw or to be psychologically distressed than residents in crowded homes with relatively low depth. Additional analyses suggest that greater depth buffers the association between residential crowding and psychological distress because it reduces social withdrawal among residents of crowded homes. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
944.
RW Evans SS Sankey BA Hauth K Sutton-Tyrrell MI Kamboh LH Kuller 《Canadian Metallurgical Quarterly》1996,31(11):1197-1203
This study evaluated the effect of storage on the quantitation of lipoprotein (Lp)(a) in 25 serum samples. Aliquots of serum were stored for up to three years at either -20 degrees C or -70 degrees C and Lp(a) subsequently analyzed using an enzyme-linked immunosorbent assay kit. Concentrations of Lp(a) declined during storage, and the temperatures employed elicited significantly different (P < 0.05) values within 12 mon which further diverged during three years of storage. Compared to baseline values, significant decreases (P < 0.05) in Lp(a) levels were evident after six months of storage at -20 degrees C with apparent losses (geometric mean) reaching 36.9% (95% confidence interval: 30.9%, 42.9%) after three years. Similarly, significantly lower (P < 0.05) Lp(a) values were recorded after six months of storage at -70 degrees C and at three years the decrease (geometric mean) was 19.1% (95% confidence interval: 14.3%, 24.0%). The losses, after three years, in terms of the arithmetic mean were 53.5 and 26.2% at -20 and -70 degrees C, respectively. Phenotype analysis suggested that large isoforms are more susceptible to degradation than smaller moieties. This may be related to the observation that apparent losses are reduced in samples containing over 8 mg/dL Lp(a). Nevertheless, Lp(a) levels in stored samples retained a strong correlation with the baseline values. These results must be considered specific for the storage conditions and analytical procedures employed. 相似文献
945.
SA Evans SM Turner BJ Bosch CC Hardy MA Woodhead 《Canadian Metallurgical Quarterly》1996,9(8):1601-1604
Sputum isolation of Pseudomonas aeruginosa (PA) is associated with extensive disease in bronchiectasis. It is not known, however, whether infection with P. aeruginosa is the result or the cause of severe disease. We compared spirometry in patients with bronchiectasis before and after infection with P. aeruginosa, with that of patients infected by other organisms. All patients (n=12) with chronic colonization by P. aeruginosa (PA group) were studied. These were compared with other patients with bronchiectasis with no isolations of P. aeruginosa (n=37, non-PA group). In the PA group, forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) were lower than in the non-PA group. The PA group, however, also had lower values at the time of initial colonization with P. aeruginosa than the current values for the non-PA group. Change in FEV1 and FVC over time was faster in the PA group than in the non-PA group. Reduction of FEV1 and FVC over time in the PA group prior to P. aeruginosa colonization was intermediate, not being statistically different from either value above. Our results confirm the association of chronic P. aeruginosa colonization with poor lung function, but conclude that patients with bronchiectasis who become colonized by P. aeruginosa have poorer lung function when first colonized than those colonized by other organisms. Decline in lung function is faster in those chronically colonized by P. aeruginosa than in those colonized by other organisms. It is not clear whether chronic P. aeruginosa colonization causes an accelerated decline in lung function or whether it is simply a marker of those whose lung function is already declining rapidly. 相似文献
946.
947.
The problem of offset elimination in adaptive control systems is considered. The key idea is to constrain the estimator in order to ensure that the DC gain of the feedforward reference model and the feedback polynomial of the adaptive controller are always equal, thus allowing the loop integrator to work properly 相似文献
948.
M Shabahang RR Buras F Davoodi LM Schumaker RJ Nauta SR Evans 《Canadian Metallurgical Quarterly》1993,53(16):3712-3718
The antiproliferative action of 1,25-dihydroxyvitamin D3 in osteosarcoma, breast carcinoma, and colon carcinoma cell lines has been described. In this study, the level of vitamin D receptor was analyzed in a panel of colon adenoma and adenocarcinoma cell lines and the receptor level was correlated with the response to treatment with 1,25-dihydroxyvitamin D3. Ribonuclease protection and ligand-binding assays quantitated the level of vitamin D receptor mRNA expression and the level of functional receptors, respectively. The more well-differentiated cell lines, such as VACO 330, showed higher levels of vitamin D receptor than less-differentiated cell lines, such as SW620. Proliferation assay, clonogenic assay, and growth curve study in HT29 and SW620 cell lines assessed the antiproliferative effect of 1,25-dihydroxyvitamin D3 at concentrations ranging from 10(-11) to 10(-6) M. HT29 showed significant (P < 0.05) growth inhibition at 10(-9) to 10(-6) M concentrations, but growth of SW620 remained unchanged. The amount of vitamin D receptor in 12 malignant colonic tumors was compared with that of adjacent normal tissue, and in 9 cases, the tumor expressed a lower vitamin D receptor level. Our results suggest that the level of vitamin D receptor correlates with the degree of differentiation in human colon cancer cell lines and may serve as a useful biological marker in predicting clinical outcome in patients. 相似文献
949.
950.