全文获取类型
收费全文 | 37138篇 |
免费 | 105篇 |
国内免费 | 180篇 |
专业分类
系统科学 | 209篇 |
丛书文集 | 523篇 |
教育与普及 | 77篇 |
理论与方法论 | 174篇 |
现状及发展 | 16778篇 |
研究方法 | 1491篇 |
综合类 | 17534篇 |
自然研究 | 637篇 |
出版年
2013年 | 314篇 |
2012年 | 522篇 |
2011年 | 1185篇 |
2010年 | 222篇 |
2008年 | 654篇 |
2007年 | 715篇 |
2006年 | 725篇 |
2005年 | 694篇 |
2004年 | 744篇 |
2003年 | 666篇 |
2002年 | 658篇 |
2001年 | 1085篇 |
2000年 | 1047篇 |
1999年 | 715篇 |
1992年 | 716篇 |
1991年 | 517篇 |
1990年 | 593篇 |
1989年 | 602篇 |
1988年 | 564篇 |
1987年 | 658篇 |
1986年 | 588篇 |
1985年 | 752篇 |
1984年 | 603篇 |
1983年 | 469篇 |
1982年 | 435篇 |
1981年 | 447篇 |
1980年 | 551篇 |
1979年 | 1136篇 |
1978年 | 953篇 |
1977年 | 921篇 |
1976年 | 773篇 |
1975年 | 817篇 |
1974年 | 1075篇 |
1973年 | 967篇 |
1972年 | 962篇 |
1971年 | 1115篇 |
1970年 | 1443篇 |
1969年 | 1066篇 |
1968年 | 1066篇 |
1967年 | 1049篇 |
1966年 | 959篇 |
1965年 | 667篇 |
1964年 | 235篇 |
1959年 | 347篇 |
1958年 | 609篇 |
1957年 | 390篇 |
1956年 | 369篇 |
1955年 | 335篇 |
1954年 | 313篇 |
1948年 | 266篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
A diffusion chamber technique based on time-lag analysis for the estimation of effective diffusion coefficients of radiolabelled macromolecules of varying molecular weights through native mucus gel is reported. For all solutes studied, a reduction in effective diffusion coefficients was observed with a retardation of solute flux in both aqueous and mucus layers. Over the molecular weight range of solutes investigated (126-186,000 Daltons), a consistent effect of molecular weight was evident with regard to the retarding effect of mucus. No apparent or absolute molecular weight cut-off for macromolecular transfer was exhibited. However, at high molecular weights (greater than 30,000 Daltons) the retardation was greatly enhanced. The results confirm that mucus can be regarded as a gel with finite pores, but that it does not constitute an absolute barrier to even high molecular weight solutes. 相似文献
102.
103.
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
104.
105.
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
106.
卢武星 《北京师范大学学报(自然科学版)》1994,(4)
1.0MeV208Pb离子在非晶Si中的投影射程RP和射程偏差ΔRP作为注量和温度二者的函数用背散射法进行测定.注量的变化范围为5×1013~7×1014cm-2.注入是在室温和t=-120℃下完成的.由由实验所确定的投影射程,射程偏差与注量或温度无关,并且分别等于295和72.2nm.与TRIM86的计算结果相比较,发现RP的偏离为18%,而ΔRP的偏离为36%.RP和ΔRP二者与注量及温度的无关性,排除了所观察到的与TRIM的矛盾是由于注入期间辐射增强扩散或离子束混合效应而引起的解释。 相似文献
107.
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
108.
109.
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
110.
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