全文获取类型
收费全文 | 431541篇 |
免费 | 44700篇 |
国内免费 | 203篇 |
专业分类
476444篇 |
出版年
2016年 | 4903篇 |
2015年 | 6520篇 |
2014年 | 7734篇 |
2013年 | 11335篇 |
2012年 | 12430篇 |
2011年 | 12875篇 |
2010年 | 8713篇 |
2009年 | 7989篇 |
2008年 | 11398篇 |
2007年 | 11972篇 |
2006年 | 11322篇 |
2005年 | 10693篇 |
2004年 | 10783篇 |
2003年 | 10511篇 |
2002年 | 10229篇 |
2001年 | 17491篇 |
2000年 | 17512篇 |
1999年 | 14184篇 |
1998年 | 5074篇 |
1997年 | 5353篇 |
1996年 | 5061篇 |
1995年 | 4783篇 |
1994年 | 4696篇 |
1993年 | 4695篇 |
1992年 | 12347篇 |
1991年 | 12130篇 |
1990年 | 12143篇 |
1989年 | 11917篇 |
1988年 | 11207篇 |
1987年 | 10559篇 |
1986年 | 9880篇 |
1985年 | 10309篇 |
1984年 | 8498篇 |
1983年 | 7329篇 |
1982年 | 5655篇 |
1981年 | 5057篇 |
1980年 | 4744篇 |
1979年 | 8140篇 |
1978年 | 6328篇 |
1977年 | 5979篇 |
1976年 | 5707篇 |
1975年 | 6168篇 |
1974年 | 6733篇 |
1973年 | 6592篇 |
1972年 | 6150篇 |
1971年 | 5557篇 |
1970年 | 4783篇 |
1969年 | 4791篇 |
1968年 | 4467篇 |
1967年 | 3818篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
881.
Jeroen M. G. Stevens Hilde Vervaecke Han de Vries Linda van Elsacker 《International journal of primatology》2007,28(6):1417-1430
Bonobos have a reputation as a female-dominated and egalitarian species. We examined the 2 aspects of dominance in 6 captive
bonobo groups. Females do not consistently evoke submission from all males in all contexts. Though females occupy the highest-ranking
positions in the dominance hierarchy, there are in each group males that obtain rather high ranks and are able to dominate
≥1 female. Thus female dominance is not complete and hierarchies can be better described as nonexclusive female dominance.
We studied egalitarianism by measuring linearity and steepness of dominance hierarchies. The hierarchies of all groups are
highly linear. Hierarchies among males are steeper than among females. On average, male bonobos are more despotic than females,
but females too can have despotic relations, both with other females and with males. Hence one can call bonobos in captivity
semidespotic rather than egalitarian. 相似文献
882.
883.
Inhibition of prostaglandin F 2a or LH induced luteolysis in the pseudopregnant rabbit by 17 -estradiol 总被引:1,自引:0,他引:1
884.
885.
E Shistik T Keren-Raifman G H Idelson Y Blumenstein N Dascal T Ivanina 《The Journal of biological chemistry》1999,274(44):31145-31149
The first 46 amino acids (aa) of the N terminus of the rabbit heart (RH) L-type cardiac Ca(2+) channel alpha(1C) subunit are crucial for the stimulating action of protein kinase C (PKC) and also hinder channel gating (Shistik, E., Ivanina, T., Blumenstein, Y., and Dascal, N. (1998) J. Biol. Chem. 273, 17901-17909). The mechanism of PKC action and the location of the PKC target site are not known. Moreover, uncertainties in the genomic sequence of the N-terminal region of alpha(1C) leave open the question of the presence of RH-type N terminus in L-type channels in mammalian tissues. Here, we demonstrate the presence of alpha(1C) protein containing an RH-type initial N-terminal segment in rat heart and brain by using a newly prepared polyclonal antibody. Using deletion mutants of alpha(1C) expressed in Xenopus oocytes, we further narrowed down the part of the N terminus crucial for both inhibitory gating and for PKC effect to the first 20 amino acid residues, and we identify the first 5 aa as an important determinant of PKC action and of N-terminal effect on gating. The absence of serines and threonines in the first 5 aa and the absence of phosphorylation by PKC of a glutathione S-transferase-fusion protein containing the initial segment suggest that the effect of PKC does not arise through a direct phosphorylation of this segment. We propose that PKC acts by attenuating the inhibitory action of the N terminus via phosphorylation of a remote site, in the channel or in an auxiliary protein, that interacts with the initial segment of the N terminus. 相似文献
886.
887.
H. Wiksell V. Ekstrand C. Wadström G. Auer 《Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Association of Biomedical Physics (AIFB)》2009,25(3):128-132
A large and increasing number of women in the western world will at some point during their life be investigated morphologically for some type of breast lesion. Fine Needle Aspiration (FNA) is one morphological method which is considered to be the fastest, cheapest and the most patient-friendly approach. However, the frequency of conclusive samples using this method varies and is often too low, especially when performed by unexperienced operators. In this study we have developed and tested a new semi-automated instrument (“CytoTest”) designed for FNA which is intended to improve the efficacy of the technique by increasing the percentage of conclusive samples. A total of 443 consecutive aspiration procedures on palpable breast lesions were performed to compare this new “CytoTest” equipment with the standard protocol using the same type of needles. We conclude that by increasing the extent and frequency of the reciprocatory motions used by an experienced sampling operator as well as enhancing the ejection pressure, the cellular yield can be increased almost three folded compared to the standard protocol. For cases with high amounts of non-diagnostic material (such as blood or cystic fluid) which were discarded, up to four times more sample could be obtained. Furthermore, the frequency of sparse samples under 1 mg was halved with use of the “CytoTest”. 相似文献
888.
A number of motile strains of Azospirillum brasilense, A. lipoferum, and A. irakense, were found to possess tyrosinase activity both on the surface of and inside the cells. A. brasilense Sp245, Sp7, and A. irakense KBC-1 each possessed two forms of tyrosinase of different molecular masses; A. lipoferum 43, A. lipoferum 59b, and A. irakense KA-3 each had a single tyrosinase form of approximately the same molecular mass; and A. brasilense Sp107 possessed a single form of tyrosinase different from all the other forms. 相似文献
889.
M G Netsky 《BMJ (Clinical research ed.)》1986,293(6562):1670-1672
890.
Effect of carbon source on lysine-mediated inhibition of postexponential growth of Saccharomyces cerevisiae 总被引:1,自引:0,他引:1 下载免费PDF全文
T G Watson 《Journal of bacteriology》1983,154(2):1013-1014
Lysine-mediated inhibition of postexponential growth in Saccharomyces cerevisiae occurred when glucose, fructose, or maltose, but not lactate, pyruvate, or ethanol, was used as the carbon source. Arginine starvation is not responsible for the inhibitory effect, since neither the intracellular pool of glucose-grown (inhibited) cells nor that of lactate-grown (noninhibited) cells contained arginine. 相似文献