全文获取类型
收费全文 | 4737篇 |
免费 | 347篇 |
国内免费 | 1篇 |
专业分类
5085篇 |
出版年
2023年 | 25篇 |
2022年 | 51篇 |
2021年 | 94篇 |
2020年 | 59篇 |
2019年 | 68篇 |
2018年 | 96篇 |
2017年 | 90篇 |
2016年 | 160篇 |
2015年 | 208篇 |
2014年 | 226篇 |
2013年 | 318篇 |
2012年 | 382篇 |
2011年 | 360篇 |
2010年 | 227篇 |
2009年 | 196篇 |
2008年 | 297篇 |
2007年 | 304篇 |
2006年 | 276篇 |
2005年 | 258篇 |
2004年 | 222篇 |
2003年 | 201篇 |
2002年 | 204篇 |
2001年 | 47篇 |
2000年 | 28篇 |
1999年 | 44篇 |
1998年 | 61篇 |
1997年 | 27篇 |
1996年 | 39篇 |
1995年 | 45篇 |
1994年 | 24篇 |
1993年 | 40篇 |
1992年 | 33篇 |
1991年 | 25篇 |
1990年 | 18篇 |
1989年 | 13篇 |
1988年 | 14篇 |
1987年 | 23篇 |
1986年 | 17篇 |
1985年 | 19篇 |
1984年 | 15篇 |
1983年 | 16篇 |
1982年 | 15篇 |
1981年 | 17篇 |
1980年 | 17篇 |
1979年 | 14篇 |
1976年 | 12篇 |
1975年 | 18篇 |
1974年 | 12篇 |
1973年 | 12篇 |
1972年 | 14篇 |
排序方式: 共有5085条查询结果,搜索用时 0 毫秒
1.
2.
3.
4.
Fátima H. Vaz Patrícia M. Machado Rita D. Brand?o Cátia T. Laranjeira Joana S. Eugénio Aires H. Fernandes Saudade P. André 《The journal of histochemistry and cytochemistry》2007,55(11):1105-1113
Only 20-25% of families screened for BRCA1/2 mutations are found positive. Because only a positive result is informative, we studied the role of BRCA1/2 immunohistochemistry as an additional method for patient selection. From 53 high-risk-affected probands, 18 (34%) had available paraffin blocks of their tumors and were selected for this study. Mutation screening was done by conformation-sensitive gel electrophoresis and multiplex ligation-dependent probe amplification. For immunohistochemistry, 21 neoplastic specimens (15 breast carcinomas, 5 ovary neoplasms, and 1 rectal adenocarcinoma) were analyzed with BRCA1 (monoclonal antibody, Ab-1, oncogene) and BRCA2 (polyclonal antibody, Ab-2, oncogene) antibodies. Absence of the BRCA1 protein was confirmed in negative tumors by Western blotting. Seven patients were positive for BRCA1/2 mutations: 5 for BRCA1 and 2 for BRCA2. Four out of five positive patients had tumors negative for BRCA1 immunostaining, and the remaining 13 BRCA1-negative patients had positive BRCA1 immunostaining in all tumor samples. Sensitivity to predict for BRCA1 mutation carriers was 80%, and specificity was 100%, with a positive predictive value of 100% and a negative predictive value of 93%. This correlation was statistically significant (p=0.001). No correlation was observed for BRCA2. If larger studies confirm these results, high-risk patients with BRCA1-negative tumors should be screened first for this gene. 相似文献
5.
Partial inactivation of tau-dinitrophenylhistidine-200 human carbonic anhydrase B, induced by visible light, followed first order kinetics (k(app) = 6.05 times 10-2 min-1). After 50 min the tau-dinitrophenylhistidine (tau-DNP-histidine) content decreased to a negligible level, but the illuminated enzyme retained, at pH 7.6, approximately 9.2 percent of the esterase activity of the native enzyme. The following lines of evidence suggest that the loss of activity results from the destruction of tau-DNP-histidine-200. (1) No significant loss of amino acid other than tau-DNP-histidine was detected after illumination. (2) The rate of loss of activity correlated well with the loss of tau-DNP-histidine. (3) In the photooxidized enzyme the DNP moiety was retained but had lost the characteristic sensitivity of tau-DNP-histidine to nucleophilic attack. Titration of the illuminated enzyme with acetazolamide indicated that the residual activity is an intrinsic property of the modified enzyme. The chromatographically purified photooxidized enzyme migrated as a single band on isoelectrofocusing in polyacylamide gel, and at pH 7.6 possessed 7.5 percent esterase activity relative to the native enzyme. By establishing effective destruction of histidine-200, it can be concluded that neither the pi N nor, as previously shown, the tau N of histidine-200 is critical for the catalysis. 相似文献
6.
The nerve growth factor thirty-five years later 总被引:1,自引:0,他引:1
Rita Levi-Montalcini 《In vitro cellular & developmental biology. Plant》1987,23(4):227-238
7.
8.
9.
To study the effect of protein synthesis inhibition on long-term sensitization of the gill- and siphon-withdrawal reflex of Aplysia, we have developed an isolated reflex preparation in which we could expose the inhibitor to only that part of the central nervous system involved in mediating the reflex and not to the other parts of the animal's central nervous system, thus minimizing the possible systemic side effects. We have found that long-term sensitization can be obtained in the isolated gill reflex, and that this long-term process, but not the short-term process, is blocked selectively by anisomycin, a reversible inhibitor of protein synthesis. Moreover, to obtain this blockade of long-term sensitization, this drug need only be applied during the training procedure. 相似文献
10.
Veronique Blanchard Rita Raisman-Vozari Marc Savasta Etienne Hirsch France Javoy-Agid Claude Feuerstein Yves Agid 《Journal of neurochemistry》1993,61(2):617-626
Abstract: We developed a rapid and sensitive radioimmunohistochemical method for the quantification of tyrosine hydroxylase (TH) at both the anatomical and cellular level. Coronal tissue sections from fresh-frozen rat brains were incubated in the presence of a TH monoclonal antibody. The reaction was revealed with a 35 S-labeled secondary antibody. TH content was quantified in catecholaminergic brain areas by measuring optical density on autoradiographic films or silver grain density on autoradiographic emulsion-coated sections. Regional TH concentrations determined in the locus ceruleus (LC), substantia nigra pars compacta (SNC), and ventral tegmental area (VTA) were significantly increased by 45% after reserpine treatment in the LC but unchanged in the SNC and VTA. Microscopic examination of TH radioimmunolabeling showed a heavy accumulation of silver grains over catecholaminergic cell bodies. In the LC, grain density per cell was heterogeneous and higher in the ventral than in the dorsal part of the structure. After reserpine treatment, TH levels were significantly increased (57%) in the neurons of the LC but not in those of the SNC or VTA. The data support the validity of this radioimmunohistochemical method as a tool for quantifying TH protein at the cellular level and they confirm that TH protein content is differentially regulated in noradrenergic and dopaminergic neurons in response to reserpine. 相似文献