全文获取类型
收费全文 | 676637篇 |
免费 | 9842篇 |
国内免费 | 2332篇 |
专业分类
电工技术 | 11965篇 |
综合类 | 2732篇 |
化学工业 | 100579篇 |
金属工艺 | 30901篇 |
机械仪表 | 24096篇 |
建筑科学 | 15361篇 |
矿业工程 | 3893篇 |
能源动力 | 17021篇 |
轻工业 | 48913篇 |
水利工程 | 7367篇 |
石油天然气 | 11340篇 |
武器工业 | 24篇 |
无线电 | 76656篇 |
一般工业技术 | 135890篇 |
冶金工业 | 112308篇 |
原子能技术 | 13017篇 |
自动化技术 | 76748篇 |
出版年
2022年 | 3470篇 |
2021年 | 5490篇 |
2020年 | 4174篇 |
2019年 | 5353篇 |
2018年 | 25677篇 |
2017年 | 25060篇 |
2016年 | 20486篇 |
2015年 | 7087篇 |
2014年 | 10251篇 |
2013年 | 28221篇 |
2012年 | 20130篇 |
2011年 | 33752篇 |
2010年 | 28451篇 |
2009年 | 27750篇 |
2008年 | 28799篇 |
2007年 | 30415篇 |
2006年 | 16822篇 |
2005年 | 18358篇 |
2004年 | 16396篇 |
2003年 | 15869篇 |
2002年 | 14270篇 |
2001年 | 13248篇 |
2000年 | 12623篇 |
1999年 | 13043篇 |
1998年 | 34004篇 |
1997年 | 23583篇 |
1996年 | 18006篇 |
1995年 | 13346篇 |
1994年 | 11608篇 |
1993年 | 11689篇 |
1992年 | 8303篇 |
1991年 | 7901篇 |
1990年 | 7743篇 |
1989年 | 7412篇 |
1988年 | 7077篇 |
1987年 | 6287篇 |
1986年 | 6076篇 |
1985年 | 6853篇 |
1984年 | 6343篇 |
1983年 | 5744篇 |
1982年 | 5338篇 |
1981年 | 5494篇 |
1980年 | 5040篇 |
1979年 | 4892篇 |
1978年 | 4878篇 |
1977年 | 5708篇 |
1976年 | 7666篇 |
1975年 | 4179篇 |
1974年 | 3988篇 |
1973年 | 4118篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
951.
952.
953.
S Mahanty CL King V Kumaraswami J Regunathan A Maya K Jayaraman JS Abrams EA Ottesen TB Nutman 《Canadian Metallurgical Quarterly》1993,151(7):3704-3711
Helminth infections in humans and animals are associated with strong T helper 2 (Th2) responses. To determine whether parasite-derived Ag preferentially expand a Th2-like cell population, a filter immunoplaque assay was used to enumerate the frequencies (F0) of PBMC and CD4(+)-enriched PBMC from individuals with helminth infections secreting selected cytokines in response to parasite-derived (PAg) and nonparasite antigens (NPAg). In 20 individuals with lymphatic filariasis, frequency analysis of PBMC secreting IL-4 and IFN-gamma indicated that the F0 of PAg-specific IL-4-secreting cells (geometric mean F0 (GM): 1/12,100) was 57-fold higher than the corresponding F0 of NPAg-reactive cells (GM: 1/692,000; p < 0.02). In marked contrast, the F0 of IFN-gamma-secreting cells responding to PAg (GM: 1/2,700) did not differ from those of cells specific for NAPg (GM: 1/3,400; p = 0.83). In another group of helminth-infected individuals, the F0 of highly enriched CD4+ cells secreting IL-4 and IL-5 in response to PAg (GMs: 1/2,600 and 1/5,600 CD4+ cells, respectively) were also found to be significantly higher than those specific for NPAg (GMs: 1/291,000 and 1/303,000 CD4+; p < 0.05 and p < 0.01, respectively), whereas the corresponding F0 of IFN-gamma- and granulocyte-macrophage-CSF-secreting cells were equivalent for PAg and NPag. Furthermore, the proportion of PAg-specific IL-4- and IL-5-secreting CD4+ cells relative to all cells secreting the given cytokine were approximately 29-fold higher than the proportion of NPAg-specific cells secreting these cytokines. Again, the corresponding proportions of Ag-specific IFN-gamma-and GM-CSF-secreting CD4+ cells were equivalent for PAg and NPAg. Thus, in this ex vivo system, a circulating population of IL-4- and IL-5-secreting (Th2-like) cells has been shown to exist in humans; PAg appears to expand these cells preferentially. 相似文献
954.
N Pasetto V Petrozza C Ticconi A Zicari F Carpino E Piccione M Melis 《Canadian Metallurgical Quarterly》1993,35(2):99-102
Ten patients with biopsy verified chronic hepatitis C virus (HCV) infection were treated with oral ribavirin at a dose of 1,000-1,200 mg per day in two divided doses for 12 weeks. Serum alanine aminotransferase (ALT) levels and hepatitis C viral ribonucleic acid (RNA) levels in serum were followed prior to, during, and 12 weeks posttreatment. ALT levels decreased significantly in all patients during therapy from a mean level of 3.21 mukat/l (range 1.22 to 7.79) before, to 1.25 mukat/l (range 0.78 to 2.04) at the end of treatment (P < 0.005). Hereafter, relapse to pretreatment levels was seen within 12 weeks after treatment stop. The hepatitis C viral RNA levels decreased from a mean 10 log titer of 4.1 (range 1-6) before treatment to 3.4 (range 1-5) at treatment stop. Five patients did not change their HCV RNA titers during treatment. Twelve weeks posttreatment only 3 patients had lower titers than prior to treatment. We conclude that oral ribavirin seems to reduce the viral load, at least temporarily, in some patients with chronic viremic HCV infection. Further studies are needed to evaluate fully the effect of oral ribavirin on chronic HCV infection. 相似文献
955.
SF Breniere MF Bosseno C Barnabe S Urdaneta-Morales M Tibayrenc 《Canadian Metallurgical Quarterly》1993,88(1):163-165
Detection of a nondistended pyriform sinus on cross-sectional imaging studies represents a diagnostic dilemma. The finding may be an inconstant physiologic phenomenon without clinical significance, or it may be due to tissue thickening and lack of pliability related to neoplasia or inflammation. Rescanning during respiratory maneuvers may clarify the anatomy, but full patient cooperation is needed. We demonstrate a method (turning the patient's head away from the side of the nondistended sinus) that induces distention of the pyriform sinus but does not require active patient participation. 相似文献
956.
957.
958.
959.
F Jónsson P Madsen LG J?rgensen M Lunding NH Secher 《Canadian Metallurgical Quarterly》1996,158(44):6256-6259
Indices of fluid balance were evaluated during and after aortic surgery in 16 consecutive patients. Thoracic electrical impedance (TI), heart rate (HR), central venous (CVP), pulmonary artery mean (PAMP), pulmonary wedge (PWP) and mean arterial (MAP) pressures as well as fourteen arterial and venous blood gas variables were followed. Consistent with a reduction of TI during the operation, fluid balance was in excess, and it remained elevated on the first postoperative morning. The HR, MAP and PWP remained stable, while CVP and PAMP decreased. Of the determined variables only TI revealed a meaningful correlation to fluid balance (rho = -0.41; p < 0.01). The results indicate that while central venous and pulmonary artery mean pressures gave the impression of a volume deficit, the positive fluid balance was mirrored by thoracic electrical impedance. 相似文献
960.