全文获取类型
收费全文 | 42003篇 |
免费 | 178篇 |
国内免费 | 375篇 |
专业分类
系统科学 | 517篇 |
丛书文集 | 834篇 |
教育与普及 | 111篇 |
理论与方法论 | 150篇 |
现状及发展 | 17839篇 |
研究方法 | 1593篇 |
综合类 | 20668篇 |
自然研究 | 844篇 |
出版年
2014年 | 234篇 |
2013年 | 531篇 |
2012年 | 782篇 |
2011年 | 1640篇 |
2010年 | 495篇 |
2009年 | 446篇 |
2008年 | 925篇 |
2007年 | 1078篇 |
2006年 | 1075篇 |
2005年 | 975篇 |
2004年 | 831篇 |
2003年 | 719篇 |
2002年 | 720篇 |
2001年 | 1227篇 |
2000年 | 1226篇 |
1999年 | 839篇 |
1992年 | 759篇 |
1991年 | 581篇 |
1990年 | 627篇 |
1989年 | 604篇 |
1988年 | 582篇 |
1987年 | 667篇 |
1986年 | 603篇 |
1985年 | 743篇 |
1984年 | 609篇 |
1983年 | 469篇 |
1982年 | 458篇 |
1981年 | 477篇 |
1980年 | 590篇 |
1979年 | 1198篇 |
1978年 | 976篇 |
1977年 | 980篇 |
1976年 | 800篇 |
1975年 | 858篇 |
1974年 | 1176篇 |
1973年 | 1023篇 |
1972年 | 1032篇 |
1971年 | 1152篇 |
1970年 | 1435篇 |
1969年 | 1138篇 |
1968年 | 1124篇 |
1967年 | 1126篇 |
1966年 | 970篇 |
1965年 | 704篇 |
1959年 | 383篇 |
1958年 | 635篇 |
1957年 | 437篇 |
1956年 | 373篇 |
1955年 | 366篇 |
1954年 | 352篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
The gas-liquid-liquid reactive extraction system for preparing hydrogen peroxide via anthraquinone was investigated. The oxidation reaction of hydrogenated working solution was combined with the extraction of hydrogen peroxide from working solution in a sieve plate column. The reaction of 2-ethylanthrahydroquionone with oxygen and the liquid-liquid extraction of hydrogen peroxide take place simultaneously. The oxygen was introduced with hydrogenated working solution through a nozzle in the bottom of the column, which worked as agitated air as well as oxidation reagent. The results showed the oxidation and extraction do not hamper each other, on the contrary, the presence of oxidation gas in the column can promote the transfer of hydrogen peroxide from organic phase to aqueous phase, thus the reaction efficiency and extraction efficiency increased with increasing gas superficial velocity. Furthermore, the oxidation efficiency is almost 100% and the extraction efficiency is higher than 90% in this process. 相似文献
102.
李惠玲 《玉林师范学院学报》2004,25(2):115-118
从高校非中文专业学生知识结构的现状出发,阐述加强人文素质教育的重要性;“中国古典文学鉴赏”课的课程特点及其在人文素质教育中所起的作用决定了在高校非中文专业学生中开设这门课程的必要性和可行性。 相似文献
103.
We investigated the sound communication associated with mating inNezara viridula (L.) to clarify conflicting reports on the medium through which acoustic signals are borne. Recordings made from virgin pairs ofN. viridula during precopulatory and compulatory behaviour have revealed that signals transmitted as vibrations through the substrate are a more likely means of communication than signals transmitted by a radiation of sound pressure waves through the air (at least in Australian populations). We present evidence (additional to that already in the literature) that air-borne acoustics are an unlikely mechanism of sexual communication in this species. Specifically, the recorded pulse train patterns showed no consistency or repeatability in relation to different stages of mating behaviour. In contrast, frequency spectrograms of substrate-borne signals reveal repeatable patterns that do correspond with the stage of mating behaviour. 相似文献
104.
105.
Aspirin-like drugs may block pain independently of prostaglandin synthesis inhibition 总被引:2,自引:0,他引:2
K. Brune W. S. Beck G. Geisslinger S. Menzel-Soglowek B. M. Peskar B. A. Peskar 《Cellular and molecular life sciences : CMLS》1991,47(3):257-261
Summary Using flurbiprofen, a chiral anti-inflammatory and analgesic 2-arylpropionic acid derivative, the enantiomers of which are not converted to each other (less than 5%) in rats or man, we obtained evidence that prostaglandin synthesis inhibition is primarily mediating the anti-inflammatory activity but prostaglandin synthesis independent mechanisms contribute to the analgesic effects. Thus, the S-form inhibited prostaglandin synthesis, inflammation and nociception in rats. The R-form had much less effect on prostaglandin synthesis and did not affect inflammation. It did, however, block nociception in rats almost as potently as the S-form. S-flurbiprofen, in contrast to the R-form, was clearly ulcerogenic in the gastrointestinal mucosa. These results indicate additional molecular mechanisms of analgesia and suggest the use of R-arylpropionic acids as analgesics. 相似文献
106.
107.
史济群 《华中科技大学学报(自然科学版)》1994,(3)
报道一种新颖的激光开槽、埋槽电极硅太阳电池的结构、工艺流程及其研制结果。在AM1.5,25℃,100mW/cm2的条件下,以面积为45cm3的36片硅片研制的硅太阳电池的输出参数的平均值为JSC=36.1mA/cm2,V∞=633mV,F.F.=0.798,η=18.23%,最后分析了种高性能硅太阳电池的设计特点。 相似文献
108.
M. Ishibashi M. Tsuda Y. Ohizumi T. Sasaki J. Kobayashi 《Cellular and molecular life sciences : CMLS》1991,47(3):299-300
Summary A new bromotyrosine-derived alkaloid with antileukemic activity, purealidin A (5), has been isolated from the Okinawan marine spongePsammaplysilla purea and its chemical structure elucidated on the basis of the spectroscopic data. 相似文献
109.
Memories become stabilized through a time-dependent process that requires gene expression and is commonly known as consolidation. During this time, memories are labile and can be disrupted by a number of interfering events, including electroconvulsive shock, trauma and other learning or the transient effect of drugs such as protein synthesis inhibitors. Once consolidated, memories are insensitive to these disruptions. However, they can again become fragile if recalled or reactivated. Reactivation creates another time-dependent process, known as reconsolidation, during which the memory is restabilized. Here we discuss some of the questions currently debated in the field of memory consolidation and reconsolidation, the molecular and anatomical requirements for both processes and, finally, their functional relationship. 相似文献
110.
Selenium is an essential trace element. In cattle, selenium deficiency causes dysfunction of various organs, including skeletal
and cardiac muscles. In humans as well, lack of selenium is associated with many disorders, but despite accumulation of clinical
reports, muscle diseases are not generally considered on the list. The goal of this review is to establish the connection
between clinical observations and the most recent advances obtained in selenium biology. Recent results about a possible role
of selenium-containing proteins in muscle formation and repair have been collected. Selenoprotein N is the first selenoprotein
linked to genetic disorders consisting of different forms of congenital muscular dystrophies. Understanding the muscle disorders
associated with selenium deficiency or selenoprotein N dysfunction is an essential step in defining the causes of the disease
and obtaining a better comprehension of the mechanisms involved in muscle formation and maintenance.
Received 13 July 2005; received after revision 9 September 2005; accepted 4 October 2005 相似文献