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   2578篇
  免费   5篇
电工技术   15篇
化学工业   100篇
金属工艺   5篇
机械仪表   12篇
建筑科学   30篇
矿业工程   4篇
能源动力   13篇
轻工业   26篇
水利工程   6篇
石油天然气   1篇
无线电   73篇
一般工业技术   92篇
冶金工业   2135篇
原子能技术   8篇
自动化技术   63篇
  2021年   4篇
  2020年   8篇
  2019年   5篇
  2018年   9篇
  2017年   4篇
  2016年   7篇
  2014年   6篇
  2013年   33篇
  2012年   12篇
  2011年   22篇
  2010年   5篇
  2009年   10篇
  2008年   17篇
  2007年   15篇
  2006年   11篇
  2005年   8篇
  2004年   12篇
  2003年   13篇
  2002年   3篇
  2001年   3篇
  2000年   11篇
  1999年   77篇
  1998年   618篇
  1997年   388篇
  1996年   253篇
  1995年   141篇
  1994年   109篇
  1993年   134篇
  1992年   24篇
  1991年   39篇
  1990年   27篇
  1989年   41篇
  1988年   35篇
  1987年   32篇
  1986年   32篇
  1985年   30篇
  1984年   14篇
  1983年   11篇
  1982年   18篇
  1981年   24篇
  1980年   24篇
  1979年   14篇
  1978年   11篇
  1977年   68篇
  1976年   137篇
  1975年   12篇
  1974年   7篇
  1973年   6篇
  1972年   6篇
  1965年   6篇
排序方式: 共有2583条查询结果,搜索用时 0 毫秒
61.
62.
63.
OBJECTIVE: To estimate the potential direct cost of making triple combination antiretroviral therapy widely available to HIV-positive adults and children living in countries throughout the world. METHODS: For each country, antiretroviral costs were obtained by multiplying the annual cost of triple antiretroviral therapy by the estimated number of HIV-positive persons accessing therapy. Per capita antiretroviral costs were computed by dividing the antiretroviral costs by the country's total population. The potential economic burden was calculated by dividing per capita antiretroviral costs by the gross national product (GNP) per capita. All values are expressed in 1997 US dollars. RESULTS: The potential cost of making triple combination antiretroviral therapy available to HIV-positive individuals throughout the world was estimated to be over US$ 65.8 billion. By far the greatest financial burden was on sub-Saharan Africa. The highest per capita drug cost in this region would be incurred in the subregions of Southern Africa (US$ 149) followed by East Africa (US$ 116), Middle Africa (US$ 44), and West Africa (US$ 42). In the Americas, subregional data indicated the highest per capita drug cost would be in the Latin Caribbean (US$ 22), followed by the Caribbean (US$ 17), Andean Area (US$ 7), the Southern Cone (US$ 6), North America (US$ 6), and Central American Isthmus (US$ 5). In Asia and Europe the percentage of the GNP necessary to finance drug therapy was less than 1% in most countries examined. CONCLUSION: Our results demonstrate that the cost of making combination antiretroviral therapy available worldwide would be exceedingly high, especially in countries with limited financial resources.  相似文献   
64.
Raman and infrared spectra were examined for guanosine 5'-diphosphate (GDP) and guanosine 5'-triphosphate (GTP) in aqueous solution. The vibrational modes were assigned on the basis of isotopic frequency shifts and relative intensities in the Raman and infrared spectra. The observed frequency shifts on 18O isotope labeling made it possible to identify the bands from each phosphate group (alpha, beta, gamma). Frequency shifts were observed as Mg2+ complexes with GDP and GTP. The results suggested that Mg2+ binds to GDP in a bidentate manner to the alpha, beta P[symbol: see text]O bonds and in a tridentate manner to the alpha, beta and gamma P[symbol: see text]O bonds of Mg.GTP. The results indicate that structure of Mg2+ coordinated to GTP in aqueous solution differs somewhat to that found for Mg.ATP.  相似文献   
65.
This report describes a case of systemic anaphylaxis to bacitracin zinc ointment in a 24-year-old man who was injured in a motorcycle accident. Extensive abrasions on the patient's extremities were cleaned with Shurclens before application of viscous Xylocaine and bacitracin zinc ointment. Five minutes later, the patient exhibited symptoms of severe anaphylaxis and required the administration of epinephrine, antihistamines, intravenous fluids, and corticosteroids. Two weeks later, he underwent prick/puncture skin testing to Shurclens and bacitracin zinc ointment as well as prick/puncture, intracutaneous, and subcutaneous challenge with Xylocaine. Only the result of the prick test to bacitracin zinc ointment was positive. Although bacitracin is considered to be a safe topical antibiotic, physicians should be aware of the potential not only for delayed hypersensitivity but also for acute IgE-mediated allergic reactions and life-threatening anaphylaxis.  相似文献   
66.
The molecular structure of free radicals formed in gamma-irradiated orthorhombic single crystals of hydrated testosterone was investigated by Electron Nuclear Double Resonance (ENDOR) spectroscopy. Only one kind of radical was observed, which is formed by addition of hydrogen atom to oxygen atom O(3). We observed interaction of the unpaired electron, which is delocalized on the carbons C(3), C(4) and C(5), with one alpha-proton in position 4 and with four unequivalent beta-protons connected with the carbon atoms C(2) and C(6). The matrices of the hyperfine couplings and the g-factor of the radical are given.  相似文献   
67.
The objectives of the study were (a) to investigate the characteristics of drug abuse treatment clients who return to treatment and (b) among those with readmissions, to describe changes over time in risk behavior for human immunodeficiency virus (HIV) infection and to identify factors associated with behavior change. Data were derived from a multisite HIV surveillance program in a single community; the program used a unique identifier to link HIV test results and behavioral information from multiple contacts. During a 30-month period, 1994 clients were admitted to three satellite facilities of a single treatment agency: detoxification, long-term residential, and outpatient. Of these clients, 574 (29%) had one or more readmissions to the same or a different facility during the 24 months following the index admission. Drug injectors, those tested for HIV, and those living in the community were more likely to be readmitted to treatment. There was little overall change in HIV risk behavior between the index admission and the readmission furthest in time from the index admission. Clients whose index visit was at the residential facility were more likely to reduce their injection risk behavior than those admitted to the other facilities. Clients readmitted to either the residential or the outpatient facility were more likely to have reduced their injection risk behavior than those readmitted to detoxification. Treatment facility was not associated with sexual risk behavior change. Men were more likely than women to reduce their high-risk sexual behaviors. The results underscore the need for treatment programs to make HIV testing readily available to their clients and to make special efforts to assist female clients to reduce their HIV risk.  相似文献   
68.
The natural mouse pathogen polyoma virus is highly oncogenic in H-2k mice carrying the endogenous superantigen encoded by the mouse mammary tumor provirus Mtv-7. This superantigen results in deletion of Vbeta6 TCR-expressing polyoma-specific CD8+ CTL, which appear to be critical effectors against polyoma tumorigenesis. Here we have isolated cloned lines of CD8+ T cells from resistant (i.e., Mtv-7-) H-2k mice that specifically lyse syngeneic polyoma virus-infected cells and polyoma tumor cells. Nearly all these CTL clones express Vbeta6 and are restricted in their recognition of virus-infected cells by H-2Dk. Screening a panel of synthetic peptides predicted to bind to Dk, for which no consensus peptide binding motif is known, we identified a peptide corresponding to a nine-amino acid sequence in the carboxyl-terminus of the middle T (MT) protein (amino acids 389-397) that was recognized by all the Vbeta6+ CD8+ CTL clones. The inability of MT(389-397)-reactive CTL to recognize cells infected with a mutant polyoma virus encoding a MT truncated just proximal to this sequence indicates that MT(389-397) is a naturally processed peptide. The frequencies of precursor CTL specific for polyoma virus and MT(389-397) peptide were similar, indicating that MT(389-397) is the immunodominant epitope in H-2k mice. In addition, polyoma-infected resistant mice possess a 10- to 20-fold higher MT(389-397)-specific precursor CTL frequency than susceptible mice. This highly focused CTL response to polyoma virus provides a valuable animal model to investigate the in vivo activity of CTL against virus-induced neoplasia.  相似文献   
69.
70.
The feasibility of improving myocardial/blood pool contrast in MR cine images through use of an intravascular contrast agent (Ferumoxtran, Advanced Magnetics, Inc., Cambridge, MA) was tested in four subjects. The contrast-to-noise ratio (CNR) demonstrated a trend toward improvement in the short axis and improved significantly in the long axis cine by an average of 128% (P < .05). Image intensity gradients at the myocardial/blood pool interface increased significantly in both the short and long axis (P < .01). It is expected that larger image intensity gradients at the endocardial border should improve the capabilities of automated segmentation algorithms, reducing the uncertainty and need for manual editing.  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