首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1154篇
  免费   25篇
  国内免费   12篇
电工技术   8篇
综合类   12篇
化学工业   39篇
金属工艺   18篇
机械仪表   24篇
建筑科学   8篇
矿业工程   7篇
能源动力   3篇
轻工业   17篇
水利工程   6篇
石油天然气   15篇
武器工业   1篇
无线电   15篇
一般工业技术   25篇
冶金工业   965篇
原子能技术   3篇
自动化技术   25篇
  2023年   5篇
  2022年   3篇
  2021年   19篇
  2020年   6篇
  2019年   5篇
  2018年   8篇
  2016年   5篇
  2015年   7篇
  2014年   8篇
  2013年   18篇
  2012年   13篇
  2011年   17篇
  2010年   10篇
  2009年   6篇
  2008年   11篇
  2007年   8篇
  2006年   5篇
  2005年   6篇
  2004年   6篇
  2003年   5篇
  2002年   3篇
  2001年   3篇
  1999年   26篇
  1998年   262篇
  1997年   157篇
  1996年   111篇
  1995年   77篇
  1994年   62篇
  1993年   55篇
  1992年   10篇
  1991年   18篇
  1990年   21篇
  1989年   13篇
  1988年   10篇
  1987年   6篇
  1986年   9篇
  1985年   3篇
  1983年   3篇
  1982年   4篇
  1981年   8篇
  1980年   8篇
  1979年   7篇
  1978年   4篇
  1977年   39篇
  1976年   79篇
  1969年   2篇
  1965年   2篇
  1962年   2篇
  1958年   2篇
  1957年   2篇
排序方式: 共有1191条查询结果,搜索用时 31 毫秒
111.
112.
113.
The application of potent combinations of antiretroviral drugs ('highly active antiretroviral therapy' (HAART)) makes effective therapy of HIV infection feasible. Consequently, the pattern of opportunistic infections and other secondary complications has changed. The incidence of infections and mortality due to aids has declined significantly. Further, the occurrence of other infections and syndromes, till now unknown in patients with aids, has been observed. It is thought that these are caused by HAART-induced inflammation, a phenomenon due to immune enhancement following HAART. An important issue is whether primary and secondary prophylaxis against opportunistic infections can be discontinued after improvement of the immune system: indeed, there are reports that discontinuation is safe in patients with persistent CD4+ cell counts above the critical level for that particular infection while CD4+ cell counts are monitored carefully.  相似文献   
114.
Dot-immunoblotting assay (DIA) using five monoclonal antibodies (MAbs) to infectious bronchitis virus (IBV) was used to detect and classify the viruses propagated in embryonated chicken eggs. Using a group-specific MAb 3F5, 10 reference strains and 12 Korean isolates of IBV were successfully detected by DIA, and the lowest virus titer of IBV detected by DIA was approximately less than 10(3.8) mean embryo infective dose/ml. For evaluating the diagnostic efficiency, DIA was compared with the conventional infectious bronchitis (IB) diagnostic method. IBV antigens in allantoic fluid from embryonated eggs inoculated with IB-suspected field samples were specifically detected by DIA within only one or two egg passages, whereas the conventional embryonated egg inoculation method required four to seven egg passages for confirming IBV infection. These results indicated that DIA could significantly reduce time and cost for IB diagnosis. For examining the possibility of classifying IBV by DIA, four strain-specific MAbs, 3A4, 2A3, 6F7, and 2C6, were used. According to the MAb reacting patterns to the IBV antigens, the 10 IBV reference strains were classified into six groups; seven strains belonged to three different groups, and the other three strains each belonged to an individual group. In the case of 12 Korean isolates of IBV, they were classified in six groups. Among the six groups, the MAb reacting patterns of three groups matched those of the IBV reference strains, but the others did not. These data suggest that at least three variant serotypes of IBV exist in Korea.  相似文献   
115.
We have investigated the regulatory role of nitric oxide (NO) in corticotropin-releasing hormone (CRH) release from the human perfused placental lobule in vitro. The effects of the NO donor sodium nitroprusside, the NO synthase inhibitor N omega-nitro-L-arginine, and the NO substrate L-arginine on human (h) placental CRH secretion have been studied. Single lobules of term placentae were bilaterally perfused with Krebs solution (5 mL/min; 95% O2-5% CO2; 37 C; pH 7.3). Fetal and maternal perfusates were collected at 4 C every 30 min for 3 h. CRH immunoreactivity (CRH-IR) in perfusates was measured by RIA using the 41-residue synthetic CRH as standard, 125I-labeled Tyr-hCRH as tracer, and a rabbit anti-CRH antibody Y2BO. The sensitivity of the assay was 0.13 pmol/L. Under basal conditions, human perfused placentae in vitro continuously secreted CRH-IR, which diluted in parallel to a synthetic hCRH-(1-41) standard curve. Size-exclusion chromatography of placental perfusates using a Sephadex G-50 column indicated that placental CRH-IR predominately coeluted with hCRH-(1-41) standard. Basal maternal perfusate CRH-IR levels (27 +/- 4 pmol/L) released from perfused placental lobules were nearly 10-fold greater than fetal perfusate CRH-IR levels (3.4 +/- 0.7 pmol/L; P < 0.05). Infusion of sodium nitroprusside (30-100 mumol/L) into the maternal and fetal placental circulations inhibited CRH-IR release into maternal perfusate in a concentration-dependent manner, but did not inhibit CRH-IR release into the fetal perfusate. N omega-nitro-L-arginine (100 mumol/L) increased placental CRH-IR secretion into fetal perfusate, and this effect was reversed by the infusion of L-arginine (100 mumol/L), which also reduced release below basal levels. In contrast, maternal perfusate CRH-IR levels were not affected by N omega-nitro-L-arginine or L-arginine. These results indicate that the human perfused placenta in vitro releases a substance of similar mol wt and hCRH-IR. Moreover, modulators of the NO signaling pathway differentially affect placental secretion of CRH-IR into the maternal and fetal perfusates. These data are consistent with the involvement of NO in the regulation of placental CRH release during pregnancy.  相似文献   
116.
The necessity is substantiated for use of apiphytoproducts in patients with duodenal ulcer who had become victims of Chernobyl accident. Apiphytoproducts were found out to accelerate the natural elimination of cesium radionuclides from the body, to normalize the indices for lipid peroxidation; they can be used on a monotherapy basis or combined with antisecretory or anti-Helicobacter drug preparations.  相似文献   
117.
Such important, yet basic, questions as the percentage chance that an individual will over the course of his or her life be in need of or actually undergo a groin herniorrhaphy or the absolute number and type of hernias that exist in a given society on any particular day continue to be statistically undefined. A review of epidemiologic data provides come preliminary answers. Recent studies from the National Center for Health Statistics show that approximately 750,000 groin herniorrhaphies are completed annually in the United States. More than 80% of these operations involve the use of mesh prosthesis and are performed on an outpatient basis. Despite the large number of hernioplasties completed, the public's understanding of hernias and their management remains unsophisticated.  相似文献   
118.
Exposure to infection information is important for estimating vaccine efficacy, but it is difficult to collect and inherently prone to missingness and mismeasurement. It is, therefore, generally not feasible to collect good exposure information on all participants in a large vaccine trial. We discuss study designs that collect detailed exposure information for only a small subset of trial participants, while collecting crude exposure information on all participants, and treat estimation of vaccine efficacy in the missing data/measurement error framework. We demonstrate with the example of an HIV vaccine trial the improvements in bias and efficiency when we combine the different levels of exposure information to estimate vaccine efficacy for reducing both susceptibility and infectiousness. We compare the performance of recently developed semi-parametric missing data methods of Pepe and Fleming and Carroll and Wand, Robins, Hsieh and Newey, and Reilly and Pepe.  相似文献   
119.
120.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号