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   31474篇
  免费   82篇
  国内免费   121篇
系统科学   304篇
丛书文集   563篇
教育与普及   98篇
理论与方法论   98篇
现状及发展   14755篇
研究方法   1155篇
综合类   14404篇
自然研究   300篇
  2012年   367篇
  2011年   697篇
  2009年   187篇
  2008年   508篇
  2007年   566篇
  2006年   503篇
  2005年   533篇
  2004年   552篇
  2003年   565篇
  2002年   505篇
  2001年   920篇
  2000年   958篇
  1999年   576篇
  1994年   366篇
  1992年   537篇
  1991年   426篇
  1990年   514篇
  1989年   476篇
  1988年   476篇
  1987年   494篇
  1986年   519篇
  1985年   622篇
  1984年   434篇
  1983年   430篇
  1982年   383篇
  1981年   411篇
  1980年   470篇
  1979年   993篇
  1978年   819篇
  1977年   794篇
  1976年   620篇
  1975年   701篇
  1974年   969篇
  1973年   828篇
  1972年   800篇
  1971年   1025篇
  1970年   1186篇
  1969年   1028篇
  1968年   941篇
  1967年   915篇
  1966年   793篇
  1965年   592篇
  1964年   209篇
  1959年   342篇
  1958年   575篇
  1957年   423篇
  1956年   349篇
  1955年   354篇
  1954年   338篇
  1948年   235篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
93.
This paper introduces the conception of open complex giant system and the methodology for dealing with the system, with stress on its profound significance in development of science and technology. The authors conclude that the reductionism underlying the exact science is not suitable to open complex giant system, and the only feasible alternative is the meta-synthetic engineering from the qualitative to the quantitative.  相似文献   
94.
95.
During the past few years, several methods have been developed for the detection of specific nucleic acid sequences by in situ hybridization using non-radioactive labels such as fluorochromes, cytochemically detectable enzymes and electron-dense markers. These methods are preferable to autoradiography in terms of speed of performance and topological resolution. Their limited sensitivity, however, has so far restricted their use to the detection of repeated sequences. Here we report single gene detection with a procedure using 2-acetylaminofluorene (AAF)-modified probes, immunoperoxidase cytochemistry and reflection-contrast microscopy. We confirmed the autoradiographic data on the localization of the human thyroglobulin (Tg) gene to the distal end of the long arm of chromosome 8. A mixture of cosmid cHT2-derived subclones of the 3' part of the Tg gene, 22.3 kilobase pairs (kbp) in total, was used as a hybridization probe. This procedure can be used to map other unique sequences, if genomic clones are available from which clones with an appropriate amount of inserts can be isolated.  相似文献   
96.
On going trend of miniaturization in electronic rel at ed parts, which is an average of two times in every 5~7 years introduce grindin g challenges. In grinding process, the surface waviness control of thin parts is an ardent task due to its warpage, induced by the high specific grinding energy (2~10 J/mm 3). Therefore, coolant is often used to avoid thermal damage, obtai n better surface integrity and to prolong wheel life. However coolant, the incomp ressibility media introduce high forces at the gri...  相似文献   
97.
Acquired immunity and epidemiology of Schistosoma haematobium   总被引:1,自引:0,他引:1  
Human immune responses to schistosome infection have been characterized in detail. But there has been controversy over the relative importance of ecological factors (variation in exposure to infection) and immunological factors (acquired immunity) in determining the relationships between levels of infection and age typically found in areas where infection is endemic. Independent effects of exposure and age on the rates of reinfection with Schistosoma haematobium after chemotherapy have been demonstrated in the Gambia and Zimbabwe. This age effect could be the result of acquired immunity to infection. Indeed, allowing for variation in exposure and age, low rates of reinfection in the Gambia are correlated with high amounts of specific IgE antibodies--human IgE can kill S. mansoni schistosomulae in vitro. Further, animals can acquire immunologically mediated resistance to S. mansoni infection, although nonimmunological factors could also be involved. Acquisition of this immunity seems to be related to the cumulative effects of repeated infection and provides only partial protection. These characteristics are consistent with immuno-epidemiological data for both S. mansoni and S. haematobium infections of humans. We have now analysed age-prevalence data for human infection with S. haematobium, and find patterns of variation that are indeed consistent with the epidemiological effects of acquired immunity predicted by mathematical models.  相似文献   
98.
99.
研究以水泥处理固体有机物时,有机物对水泥水化的影响。以膜流模式说明水份在水泥浆体内传输的现象。水膜存在半干之水泥浆体,其厚度小于100nm,膜流由离分压所驱动,而离分压来自分子间作用力。膜拟结果发现,水泥浆体内局部位置可用以进行水化之水量为Q=-Aslv/6vπ。当有机物添加在水泥浆体内时,会影响Hamaker常数,Aslv因此可能使膜流不稳定或完全抑制膜流,因而使水泥浆体内局部缺水,影响水化进行,造成成品强度降低,影响品质。  相似文献   
100.
T Matsuda  Y Yabushita  T Doi  H Iwata 《Experientia》1985,41(7):924-925
The highest specific activity of thiamin pyrophosphokinase was found in the cerebellum, and lower activity in cerebral cortex and midbrain. The regional difference in the enzyme activity was similar to that in thiamin content and the influx rate in rat brain, suggesting that the enzyme is involved in the thiamin transport.  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