全文获取类型
收费全文 | 693578篇 |
免费 | 73785篇 |
国内免费 | 541篇 |
专业分类
767904篇 |
出版年
2018年 | 6325篇 |
2016年 | 8407篇 |
2015年 | 11885篇 |
2014年 | 13344篇 |
2013年 | 19256篇 |
2012年 | 21322篇 |
2011年 | 21022篇 |
2010年 | 13993篇 |
2009年 | 12595篇 |
2008年 | 18542篇 |
2007年 | 18821篇 |
2006年 | 18171篇 |
2005年 | 17226篇 |
2004年 | 17074篇 |
2003年 | 16209篇 |
2002年 | 15812篇 |
2001年 | 29066篇 |
2000年 | 29531篇 |
1999年 | 23409篇 |
1998年 | 8238篇 |
1997年 | 8565篇 |
1996年 | 8176篇 |
1995年 | 7556篇 |
1994年 | 7427篇 |
1993年 | 7449篇 |
1992年 | 19090篇 |
1991年 | 18551篇 |
1990年 | 18046篇 |
1989年 | 17720篇 |
1988年 | 16486篇 |
1987年 | 15880篇 |
1986年 | 14875篇 |
1985年 | 15097篇 |
1984年 | 12530篇 |
1983年 | 10787篇 |
1982年 | 8573篇 |
1981年 | 7946篇 |
1980年 | 7331篇 |
1979年 | 12296篇 |
1978年 | 9765篇 |
1977年 | 9163篇 |
1976年 | 8583篇 |
1975年 | 9607篇 |
1974年 | 10641篇 |
1973年 | 10478篇 |
1972年 | 9581篇 |
1971年 | 8808篇 |
1970年 | 7833篇 |
1969年 | 7728篇 |
1968年 | 7094篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
Georg Steinhauser Johannes H. Sterba Karin Poljanc Max Bichler Karl Buchtela 《Journal of trace elements in medicine and biology》2006,20(3):119-153
In this study, 18 partly commercially available samples of rock salt from Austria, Germany, Pakistan, Poland, Switzerland, and Ukraine were investigated with respect to their content of trace elements using instrumental neutron activation analysis. Elements detected were Al, Ba, Br, Ca, Ce, Cl, Co, Cr, Cs, Eu, Fe, Hf, La, Mn, Na, Rb, Sb, Sc, Sm, Sr, Ta, Tb, Th, and Zn, some of them only in individual cases. An estimation of the bioavailability of these trace elements was performed by dissolving an equivalent of the sodium chloride samples in diluted hydrochloric acid (simulating stomach acid), filtering off the insoluble components, and analyzing the evaporated filtrate. It could be shown that in most cases bioactive trace elements like Fe can be found in rock salt in the form of almost insoluble compounds and are therefore not significantly bioavailable, whereas thorium, for example, was partly bioavailable in two cases. A significant contribution to the recommended daily intake of metal trace elements by using rock salt for nutrition can be excluded. 相似文献
932.
933.
934.
Jan Suchá?ek Petr Sed’a Václav Friedrich Renata Wachowiak-Smolíková Mark P. Wachowiak 《PloS one》2016,11(11)
Media, and particularly TV media, have a great impact on the general public. In recent years, spatial patterns of information and the relevance of intangible geographies have become increasingly important. Gatekeeping plays a critical role in the selection of information that is transformed into media. Therefore, gatekeeping, through national media, also co-forms the generation of mental maps. In this paper, correspondence analysis (a statistical method) combined with cloud lines (a new visual analytics technique) is used to analyze how individual major regional events in one of the post-communist countries, the Czech Republic, penetrate into the media on a national scale. Although national news should minimize distortions about regions, this assumption has not been verified by our research. Impressions presented by the media of selected regions that were markedly influenced by one or several events in those regions demonstrate that gatekeepers, especially news reporters, functioned as a filter by selecting only a few specific, and in many cases, unusual events for dissemination. 相似文献
935.
The epididymis of buffalo is differentiated into 6 regions. The head represents the first 3 regions, the body the 4th region and the tail the 5th and 6th region. At 3-30 weeks, the epithelium is simple high columnar with few basal cells in region I, simple low columnar with few basal cells in region II, pseudostratified low columnar in regions III, IV, V, and pseudostratified low columar in region VI. As age advances, the epithelium increases in height and shows a tendency toward advanced pseudostratification. The basal cells are greater in number in regions III, IV and V than in the other regions of the epididymis. The epithelial cells contain stereocilia in region I at 3 weeks and regions III, IV and V at 30 weeks, whereas they are absent in regions II and VI. The tubules in region I are the smallest in diameter while the tubules in region VI have the largest diameter. 相似文献
936.
A method for separation and visualization of the different apolipoprotein B species using 0.2% sodium dodecyl sulfate-1.5% agarose gel electrophoresis and immunoblotting is described. The method is capable of demonstrating the different forms of apolipoprotein B (apo B) in plasma volumes of 10-50 microliters without prior ultracentrifugation. After ultracentrifugation of samples, estimation of the ratio between apo B 48 and apo B 100 is possible by scanning of Coomassie-stained gels or immunoblots. 相似文献
937.
938.
The refractory period in light-induced reproductive development of golden-crowned sparrows 总被引:1,自引:0,他引:1
MILLER AH 《The Journal of experimental zoology》1948,109(1):1-11
939.
940.
Synthesis of lysogangliosides 总被引:6,自引:0,他引:6
The synthesis of gangliosides GM3, GM2, GM1, and GD1a solely lacking the fatty acid moiety, and thus called lysogangliosides in analogy to lysophospholipids, is described. Since a selective elimination of the fatty acid residue has not been achieved as yet, the gangliosides were first subjected to alkaline hydrolysis. By this procedure the fatty acyl as well as the acetyl groups of the sialic acid residue(s) were completely removed. The acetamido group of the N-acetylgalactosamine moiety of the gangliosides GM2, GM1, and GD1a was very little (congruent to 10%) hydrolyzed. In a two-phase system composed of water and ether, the selective protection of the sphingoid amino group was accomplished with a hydrophobic protective group (9-fluorenylmethoxycarbonyl). Lysogangliosides were obtained after re-N-acetylation of the sialooligosaccharide amino group(s) followed by removal of the protecting group. The overall yield was about 30%. The structures of the lysogangliosides were confirmed by chemical analysis as well as negative ion FAB mass spectrometry and 1H NMR spectroscopy. By simple re-N-acylation of lysogangliosides with any labeled fatty acid, labeled gangliosides are now obtainable that are identical with their parent gangliosides except for their labeled fatty acid residue. This has been demonstrated by the synthesis of GM1 with a [1-13C]palmitic acid moiety in its ceramide portion. If desired, double-labeled gangliosides may be obtained by use of labeled acetic anhydride in the synthesis of the lysogangliosides. 相似文献