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   1517篇
  免费   5篇
电工技术   5篇
化学工业   45篇
金属工艺   4篇
机械仪表   6篇
建筑科学   19篇
能源动力   14篇
轻工业   17篇
水利工程   3篇
无线电   36篇
一般工业技术   83篇
冶金工业   1181篇
原子能技术   6篇
自动化技术   103篇
  2021年   4篇
  2019年   6篇
  2017年   5篇
  2015年   6篇
  2014年   4篇
  2013年   13篇
  2012年   8篇
  2011年   14篇
  2010年   15篇
  2009年   16篇
  2008年   18篇
  2007年   14篇
  2006年   16篇
  2005年   11篇
  2004年   16篇
  2003年   17篇
  2002年   7篇
  2001年   9篇
  2000年   9篇
  1999年   48篇
  1998年   335篇
  1997年   172篇
  1996年   154篇
  1995年   82篇
  1994年   66篇
  1993年   74篇
  1992年   13篇
  1991年   10篇
  1990年   13篇
  1989年   20篇
  1988年   20篇
  1987年   26篇
  1986年   19篇
  1985年   19篇
  1984年   6篇
  1983年   20篇
  1981年   13篇
  1980年   13篇
  1979年   13篇
  1978年   3篇
  1977年   31篇
  1976年   84篇
  1975年   4篇
  1974年   4篇
  1973年   9篇
  1972年   5篇
  1970年   7篇
  1969年   7篇
  1968年   4篇
  1964年   3篇
排序方式: 共有1522条查询结果,搜索用时 15 毫秒
81.
82.
83.
84.
PURPOSE: To determine if lucanthone crossed the blood-brain barrier in experimental animals; and to determine accelerated tumor regression of human brain metastases treated jointly with lucanthone and whole brain radiation. METHODS AND MATERIALS: The organ distribution of 3H lucanthone in mice and 125I lucanthone in rats was determined to learn if lucanthone crossed the blood-brain barrier. Size determinations were made of patients' brain metastases from magnetic resonance images or by computed tomography before and after treatment with 30 Gy whole brain radiation alone or with lucanthone. RESULTS: The time course of lucanthone's distribution in brain was identical to that in muscle and heart after intraperitoneal or intravenous administration in experimental animals. Lucanthone, therefore, readily crossed the blood-brain barrier in experimental animals. CONCLUSION: Compared with radiation alone, the tumor regression in patients with brain metastases treated with lucanthone and radiation was accelerated, approaching significance using a permutation test at p = 0.0536.  相似文献   
85.
Laser-based diagnostic methods can measure the absolute concentrations of various atoms and molecules, even at low concentrations. They can also measure temperature with high accuracy. One very important advantage of these methods is the ability to make measurements without affecting the studied process, for example flame. Laser-based spectroscopy can thus provide important information for the validation of chemical mechanisms in well-defined, low-pressure flat flames. This paper reviews several methods: laser-induced fluorescence, cavity ring-down spectroscopy, intracavity laser absorption spectroscopy, and polarization spectroscopy. All four are sufficiently sensitive to measure the concentrations of trace species in low-pressure flat flames. The complementarity of the methods for combustion diagnostics is also discussed.  相似文献   
86.
87.
BACKGROUND: Chronic myelogenous leukemia (CML) is an indolent but ultimately fatal disease. Because the natural history of CML varies and quality of life with CML may be excellent until shortly before death, deciding whether and when to pursue unrelated donor bone marrow transplantation is often difficult. OBJECTIVE: To compare early transplantation, delayed transplantation, and no transplantation for patients with chronic-phase CML on the basis of discounted, quality-adjusted life expectancy. DESIGN: A markov model comparing different strategies was constructed. This model considers patient age, quality of life, risk aversion, and the competing risks for CML progression and transplant toxicity. SETTING: Therapeutic decision at the time of diagnosis of CML. PATIENTS: The base case is a 35-year-old patient with intermediate-prognosis CML. Younger and older patients with better and worse prognoses are also evaluated. INTERVENTION: Early transplantation, delayed transplantation, and no transplantation. MEASUREMENTS: Quality-adjusted, discounted life expectancy. RESULTS: For patients with newly diagnosed CML, transplantation within the first year provides the greatest quality-adjusted expected survival, although this benefit decreases with increasing patient age. For a 35-year-old patient with intermediate-prognosis CML, transplantation within the first year results in 53 more discounted, quality-adjusted years of life expectancy than does no transplantation. This finding is robust even with varying baseline assumptions. CONCLUSIONS: These results support the use of early unrelated donor bone marrow transplantation for most patients with CML.  相似文献   
88.
IAPs comprise a family of inhibitors of apoptosis found in viruses and animals. In vivo binding studies demonstrated that both baculovirus and Drosophila IAPs physically interact with an apoptosis-inducing protein of Drosophila, Reaper (RPR), through their baculovirus IAP repeat (BIR) region. Expression of IAPs blocked RPR-induced apoptosis and resulted in the accumulation of RPR in punctate perinuclear locations which coincided with IAP localization. When expressed alone, RPR rapidly disappeared from the cells undergoing RPR-induced apoptosis. Expression of P35, a caspase inhibitor, also blocked RPR-induced apoptosis and delayed RPR decline, but RPR remained cytoplasmic in its location. Mutational analysis of RPR demonstrated that caspases were not directly responsible for RPR disappearance. The physical interaction of IAPs with RPR provides a molecular mechanism for IAP inhibition of RPR's apoptotic activity.  相似文献   
89.
Increasing the contrast of just one eye's image degrades stereothresholds; this phenomenon is referred to as the stereo contrast paradox. In experiment one, this paradox was found to be absent in dynamic random-element stereograms; thresholds were simply limited by the lower of the two eyes' contrasts. In experiment two, in which narrowband Gabor targets were used, the paradox was found to be strongest at relatively low spatial frequencies (1 cycle deg-1). As spatial frequency was increased, the paradox gradually disappeared. At relatively high spatial frequencies (5 cycles deg-1), thresholds were generally limited by the lower of the two eyes' contrasts, as was found for the dynamic noise targets. These results demonstrate the interactions of spatial frequency and contrast in binocular image combination and yield clues as to the different roles which high and low spatial frequencies may play in stereopsis.  相似文献   
90.
OBJECTIVES: Our objectives were to (1) expand and strengthen the women's health curriculum at the University of California, San Francisco, and (2) evaluate the responses of both medical students and faculty to this curriculum. STUDY DESIGN: A written evaluation of the curriculum in women's health was completed by both students and faculty. Variables studied included mean scores of cases, the overall course score, and the preferences of medical students for faculty specialty in teaching the small groups. RESULTS: The overall course evaluation score was 7.81 (range 1 to 10). For those students who had both faculty from internal medicine or family medicine and obstetrics and gynecology, there was a strong preference that obstetrician-gynecologists teach the majority of the cases. CONCLUSIONS: The new case-based curriculum in women's health was enthusiastically received by both medical students and faculty.  相似文献   
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