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   4706篇
  免费   96篇
  国内免费   4篇
电工技术   29篇
综合类   6篇
化学工业   427篇
金属工艺   61篇
机械仪表   66篇
建筑科学   62篇
矿业工程   13篇
能源动力   45篇
轻工业   394篇
水利工程   46篇
石油天然气   7篇
无线电   213篇
一般工业技术   399篇
冶金工业   2685篇
原子能技术   38篇
自动化技术   315篇
  2022年   28篇
  2021年   38篇
  2020年   29篇
  2019年   33篇
  2018年   27篇
  2017年   36篇
  2016年   55篇
  2015年   47篇
  2014年   62篇
  2013年   86篇
  2012年   59篇
  2011年   97篇
  2010年   89篇
  2009年   78篇
  2008年   94篇
  2007年   91篇
  2006年   60篇
  2005年   84篇
  2004年   58篇
  2003年   68篇
  2002年   73篇
  2001年   57篇
  2000年   52篇
  1999年   127篇
  1998年   805篇
  1997年   503篇
  1996年   333篇
  1995年   192篇
  1994年   154篇
  1993年   171篇
  1992年   54篇
  1991年   49篇
  1990年   46篇
  1989年   50篇
  1988年   53篇
  1987年   42篇
  1986年   46篇
  1985年   54篇
  1984年   29篇
  1983年   20篇
  1982年   25篇
  1981年   27篇
  1980年   34篇
  1978年   24篇
  1977年   84篇
  1976年   141篇
  1975年   26篇
  1972年   28篇
  1971年   20篇
  1970年   25篇
排序方式: 共有4806条查询结果,搜索用时 0 毫秒
51.
Taking into consideration a study published 10 years ago on sexual disturbances of students at the University of S?o Paulo, the importance of the subject is discussed, along with the creation in 1993 of the Sexuality Project at the university hospital of the University of S?o Paulo School of Medicine. In its first year, this multidisciplinary project attended 140 patients with sexual dysfunctions (associated or not to other clinical manifestations); the majority were younger than 60 years-old, and 80 percent were male.  相似文献   
52.
This review reports the different genetic factors that have been identified either as risk factor for Alzheimer's disease (AD) or directly causing the disease. First are reviewed epidemiological data and biological mechanisms about the apoplipoprotein E gene allele epsilon 4 that is a major risk factor for Alzheimer's disease. The second part describes the mutations responsible for early-onset autosomal dominant AD found in three different genes. The gene located on chromosome 21 encodes the amyloid precusor protein (APP). The presenilin 1 and presenilin 2 genes, located on chromosome 14 and 1 respectively, encode not yet known membrane proteins.  相似文献   
53.
The kinetics of silver chloride cluster formation in a sodium borate glass heat treated isothermally at different temperatures above the glass transition temperature has been studied with small-angle X-ray scattering (SAXS). It is established that the size distributions of particle number and particle volume have bimodal shapes, i.e. the system of AgCl droplets consists of two populations with significantly different mean radii. The bimodality of the size distribution functions is confirmed by results of transmission electron microscopy (TEM) even if different techniques of sample preparation are used. The resolution limits of the TEM techniques applied amount to 2 nm and are comparable with the smallest particle diameters detectable by the SAXS method. The evolution of the size distributions is discussed in the framework of the theories of nucleation, growth and Ostwald ripening.  相似文献   
54.
Ws/Ws rats are deficient in both mucosal- and connective tissue-type mast cells. To study the role of mast cells in active anaphylaxis, changes in vascular permeability in the trachea upon intravenous antigen challenge with Evans blue dye were examined in Ws/Ws, heterogenic Ws/+, and normal +/ + rats sensitized with the nematode Nippostrongylus brasiliensis. Antigen challenge resulted in fatal anaphylactic shock in some +/+ and Ws/+ rats, but not in Ws/Ws rats. Marked dye leakage developed within 30 min in the trachea of +/+ and Ws/+ rats, while Ws/Ws rats showed no substantial increases in the levels of vascular permeability. Ex vivo stimulation of sensitized lung fragments from +/+ animals with specific antigen induced significant releases of histamine and leukotriene (LT) C4, while sensitized Ws/Ws rat-lung fragments did not. In Ws/Ws rats, levels of nematode-specific IgE, IgG1 and IgG2a antibodies as well as levels of lung eosinophilia were not significantly different from those in +/+ rats. These results show that mast cell-deficient Ws/Ws rats fail to develop active anaphylaxis, and this is mediated probably by the lack of mast cell-derived mediators required for initiation of the reaction.  相似文献   
55.
A major problem in the intensive care unit nowadays is the development of multiple organ dysfunction syndrome (MODS), a cumulative sequence of progressive deterioration of organ functions. While the pathogenic pathways of MODS remain to be elucidated, it is assumed that cells of the host defence system, especially the macrophages, are altered in their function. During the development of MODS it is assumed that macrophages are overactivated and that an exaggerated inflammatory response may contribute to its pathogenesis. In order to gain insight into the alterations of the functional status of the macrophage during the development of MODS, a series of macrophage functions was measured in the subsequent phases of zymosan induced generalized inflammation in mice. Male C57BL/6 mice received a single dose of zymosan intraperitoneally and groups of animals were killed after 2, 5, 8, and 12 days. Peritoneal macrophages were collected for in vitro assessment of the ADCC, the production of superoxide (O2-) and nitric oxide (NO), and complement mediated phagocytosis and intracellular killing of Staphylococcus aureus. A single intraperitoneal injection with zymosan resulted in a three-phase illness. During the third phase the animals developed MODS-like symptoms. Peritoneal cells from control animals produced very low to non-detectable amounts of O2- and NO, and the cytotoxic activity was also low. During the development of MODS, from day 7 onwards, the ability to produce O2- and NO2- became strongly elevated, as did the cytotoxic activity. These findings are in parallel with the development of MODS whereas the phagocytic and killing capacity remained essentially unaltered. The changes found could be detrimental for the organism, thus possibly contributing to the onset and development of MODS.  相似文献   
56.
57.
The response people have to vaccination varies because their immune systems differ and vaccine failures occur. Here we consider the effect that a random response, independent for each vaccinee, has on the vaccination coverage required to prevent epidemics in a large community. For a community of uniformly mixing individuals an explicit expression is found for the critical vaccination coverage (CVC) and the effect of the vaccine response is determined entirely by the mean E(AB), where A and B, respectively, reflect the infectivity and susceptibility of a vaccinated individual. This result shows that the usual concept of vaccine efficacy, which focuses on the amount of protection the vaccine provides the vaccinee against infection, is not adequate to describe the requirements for preventing epidemics when vaccination affect infectivity. The estimation of E(AB) poses a problem because A and B refer to the vaccine response of the same individual. Similar results are found when there are different types of individual, but now the mean E(AB) may differ between types. However, for a community made up of households it is shown that the CVC also depends on other characteristics of the vaccine response distribution. In practice this means that estimating a single measure of vaccine effectiveness is generally not enough to determine the CVC. For a specific community of households it is found that the vaccination coverage required to prevent epidemics decreases as the variation in the vaccine response increases.  相似文献   
58.
AIMS: To evaluate the effectiveness of oral vancomycin in the prophylaxis of necrotising enterocolitis in preterm, very low birthweight infants. METHODS: A prospective, double blind, randomised, placebo controlled study in a tertiary referral centre of a university teaching hospital was conducted on 140 very low birthweight infants consecutively admitted to the neonatal unit. The babies were randomly allocated to receive oral vancomycin (15 mg/kg every 8 hours for 7 days) or an equivalent volume of placebo solution. Prophylaxis was started 24 hours before the start of oral feeds. All suspected cases of necrotising enterocolitis were investigated with a full sepsis screen and serial abdominal radiographs. Necrotising enterocolitis was diagnosed and staged according to modified Bell's criteria. RESULTS: Nine of 71 infants receiving oral vancomycin and 19 of 69 infants receiving the placebo solution developed necrotising enterocolitis (p = 0.035). Infants with necrotising enterocolitis were associated with a significant increase in mortality (p = 0.026) and longer duration of hospital stay (p = 0.002). CONCLUSIONS: Prophylactic oral vancomycin conferred protection against necrotising enterocolitis in preterm, very low birthweight infants and was associated with a 50% reduction in the incidence. However, widespread implementation of this preventive measure is not recommended, as it would only be effective in necrotising enterocolitis caused by Gram positive organisms and could increase the danger of the emergence of vancomycin resistant or dependent organisms. Its use should be restricted to a high prevalence nursery for a short and well defined period in a selected group of high risk patients.  相似文献   
59.
60.
The MPC105 peripheral component interconnection bridge/memory controller provides a platform-specification-compliant bridge between Power PC microprocessors and the PCI bus. With it, designers can create systems using peripherals already designed for a variety of standard PC interfaces. This bridge chip also integrates a secondary cache controller and high-performance memory controller that supports DRAM or synchronous DRAM and ROM or flash ROM  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