全文获取类型
收费全文 | 3885篇 |
免费 | 3篇 |
专业分类
电工技术 | 1篇 |
综合类 | 2篇 |
化学工业 | 57篇 |
金属工艺 | 11篇 |
机械仪表 | 6篇 |
建筑科学 | 21篇 |
能源动力 | 6篇 |
轻工业 | 9篇 |
水利工程 | 6篇 |
石油天然气 | 3篇 |
无线电 | 18篇 |
一般工业技术 | 31篇 |
冶金工业 | 3669篇 |
原子能技术 | 3篇 |
自动化技术 | 45篇 |
出版年
2022年 | 3篇 |
2021年 | 2篇 |
2020年 | 2篇 |
2017年 | 4篇 |
2016年 | 3篇 |
2015年 | 3篇 |
2014年 | 6篇 |
2013年 | 18篇 |
2012年 | 7篇 |
2011年 | 8篇 |
2010年 | 7篇 |
2009年 | 4篇 |
2008年 | 8篇 |
2007年 | 14篇 |
2006年 | 5篇 |
2005年 | 7篇 |
2004年 | 8篇 |
2003年 | 9篇 |
2002年 | 5篇 |
2001年 | 3篇 |
2000年 | 5篇 |
1999年 | 131篇 |
1998年 | 1258篇 |
1997年 | 679篇 |
1996年 | 403篇 |
1995年 | 250篇 |
1994年 | 197篇 |
1993年 | 244篇 |
1992年 | 42篇 |
1991年 | 53篇 |
1990年 | 45篇 |
1989年 | 39篇 |
1988年 | 28篇 |
1987年 | 48篇 |
1986年 | 29篇 |
1985年 | 27篇 |
1984年 | 4篇 |
1983年 | 8篇 |
1982年 | 15篇 |
1981年 | 21篇 |
1980年 | 21篇 |
1978年 | 6篇 |
1977年 | 70篇 |
1976年 | 119篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1965年 | 2篇 |
1943年 | 1篇 |
排序方式: 共有3888条查询结果,搜索用时 15 毫秒
61.
RS Wallis P Nsubuga C Whalen RD Mugerwa A Okwera D Oette JB Jackson JL Johnson JJ Ellner 《Canadian Metallurgical Quarterly》1996,174(4):727-733
Macrophage activation and tumor necrosis factor-alpha (TNF-alpha) production are critical in tuberculosis immunity but may result in increased human immunodeficiency virus (HIV) expression and accelerated HIV disease progression in HIV-infected persons. Pentoxifylline inhibits expression of TNF-alpha and HIV. A double-blind, placebo-controlled study of adjunctive therapy with pentoxifylline (1800 mg/day) as a timed-release formulation was done in Ugandan HIV-infected patients with pulmonary tuberculosis. Subjects had early HIV disease (mean CD4 cell count, 380/microL) and did not receive other antiretroviral drugs. Pentoxifylline resulted in decreased plasma HIV RNA and serum beta 2-microglobulin and, in a subset of moderately anemic patients, improved blood hemoglobin levels. Trends were noted toward reduced TNF-alpha production in vitro and improved performance scores, but these did not reach statistical significance. No effect was noted on body mass, CD4 cell count, or survival. Additional studies of more potent TNF-alpha inhibitors in HIV-positive subjects with tuberculosis are warranted. 相似文献
62.
63.
64.
65.
SJ Phillips 《Canadian Metallurgical Quarterly》1993,55(5):1281-1282
66.
American Academy of Pediatrics (AAP) fellows responded to a questionnaire measuring knowledge of 1991 Centers for Disease Control and Prevention (CDC) guidelines. Generalists' scores on a knowledge scale were positively correlated with reporting CDC and AAP documents as knowledge sources, and negatively correlated with private practice, medical school as a knowledge source, and age. However, private practitioners who read AAP documents scored well. 相似文献
67.
68.
69.
Real-time ultrasonic measurements of 10th-rib backfat (BF10) and loin muscle area (LMA) were made by a single technician at four mean BW (67.4, 80.3, 93.4, and 104.9 kg) on live hogs to assess the accuracy of predicting carcass measurements before and at slaughter weight. Records were evaluated on 655 purebred barrows and 472 purebred gilts in two tests. Residual correlations-accounting for test, sex, and breed effects, among and between scans and carcass measurements--were moderate to high for BF10 (r=.69 to .82) and LMA (r=.57 to .68), with the largest correlations at 104.9 kg of live weight. Ultrasonic BF10 and LMA were within +/-4 mm and +/-6.45 cm2, respectively, of the corresponding carcass measurement 75.9 and 89.8% of the time. Sex differences for LMA bias were significant (P < .001); ultrasonic LMA was overestimated in barrows by .75 cm2 and underestimated in gilts by .91 cm2. Breed differences were significant (P < .001) for BF10 and LMA bias. Standard errors of prediction (SEP) for BF10 and LMA across the two tests were 3.46 mm and 4.04 cm2, respectively. The SEP for BF10 were 3.60 mm for barrows and 3.19 mm for gilts. The SEP for LMA were 3.77 cm2 for barrows and 4.22 cm2 for gilts. The SEP for BF10 within breeds ranged from 3.25 to 3.72 mm, and for LMA, ranged from 2.98 cm2 to 4.90 cm2. Ultrasound measurements overestimated the carcass measurement by .57 mm for carcasses measuring < 24.1 mm and underestimated by 2.81 mm carcasses with BF10 > 30.3 mm. Ultrasonic LMA overestimated the carcass by 2.35 cm2 in carcasses measuring < 32.5 cm2 and underestimated by 2.29 cm2 in carcasses measuring greater than 37.9 cm2. Results indicate that the magnitude of the carcass measurement affects bias and accuracy of prediction for real-time ultrasonic measurements of BF10 and LMA. The SEP statistic is more consistent in evaluating accuracy of ultrasonic measurement than bias, absolute deviations, and percentage of absolute deviation. 相似文献
70.
The mechanism of decline in viremia following acute infection with HIV is unknown. To characterize this process virologically, the expression of viral RNAs was analyzed in samples of peripheral blood mononuclear cells (PBMCs) from a patient who experienced a 100-fold decline in plasma viremia over a 13-day period prior to the initiation of antiretroviral therapy. Cell-associated viral RNA declined in association with the decline in plasma virus. During the initial 7 days of observation, plasma viremia declined more than 10-fold with no change in the ratio of unspliced to multiply spliced mRNAs. The efficiency of viral gene expression did not decline during the study period and varied from 380 to 2800 unspliced RNA copies per productively infected cell. Together, these data indicate no change in the relative proportion of cells in late- and early-stage gene expression during the initial decline and provide evidence against shortening of the viral replication cycle by immune surveillance. However, the prevalence of productively infected cells declined markedly during the 13 days of observation, from 1 in 250 to 1 in 25,000 PBMCs. These data are compatible with depletion of available target cells during the initial decline in viremia. As the level of plasma virus stabilized after 8 days of observation, the ratio of unspliced to multiply spliced mRNAs rose; this rise was due to a relatively greater decline in multiply spliced mRNA. These data suggest the possible onset of a blockade to new infection events (for example, by neutralizing antibody or chemokines), causing an increase in the relative proportion of cells in late-stage gene expression. They may also be explained, however, by the persistence of cell-associated virions together with the near disappearance of productively infected cells from the circulation. 相似文献