全文获取类型
收费全文 | 9072篇 |
免费 | 711篇 |
国内免费 | 694篇 |
专业分类
10477篇 |
出版年
2024年 | 44篇 |
2023年 | 190篇 |
2022年 | 280篇 |
2021年 | 426篇 |
2020年 | 463篇 |
2019年 | 774篇 |
2018年 | 444篇 |
2017年 | 290篇 |
2016年 | 277篇 |
2015年 | 343篇 |
2014年 | 603篇 |
2013年 | 774篇 |
2012年 | 396篇 |
2011年 | 515篇 |
2010年 | 314篇 |
2009年 | 312篇 |
2008年 | 378篇 |
2007年 | 388篇 |
2006年 | 346篇 |
2005年 | 328篇 |
2004年 | 263篇 |
2003年 | 266篇 |
2002年 | 254篇 |
2001年 | 195篇 |
2000年 | 152篇 |
1999年 | 142篇 |
1998年 | 131篇 |
1997年 | 136篇 |
1996年 | 102篇 |
1995年 | 97篇 |
1994年 | 88篇 |
1993年 | 86篇 |
1992年 | 81篇 |
1991年 | 92篇 |
1990年 | 39篇 |
1989年 | 72篇 |
1988年 | 53篇 |
1987年 | 47篇 |
1986年 | 33篇 |
1985年 | 33篇 |
1984年 | 35篇 |
1983年 | 34篇 |
1982年 | 33篇 |
1981年 | 28篇 |
1980年 | 21篇 |
1979年 | 25篇 |
1978年 | 20篇 |
1977年 | 11篇 |
1976年 | 12篇 |
1974年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
When the conditions for detecting proteins by ammoniacal silver staining (B. R. Oakley, D. R. Kirsch, and N. R. Morris (1980) Anal. Biochem. 105, 361-363.) following gel electrophoresis were varied, it was noted that glutaraldehyde pretreatment was necessary for maximal staining, which could not be explained simply as the result of "fixation." Further studies indicated that glutaraldehyde enhancement of protein staining with this silver reagent was probably due to oxidation of the aldehyde groups by silver ions, resulting in metallic silver depositions within the gel which act as nucleation sites for additional metallic silver localization in the protein bands upon the addition of formaldehyde developer. This proposed mechanism is consistent with the Tollen's reaction, as well as some aspects of the photographic process. Consistent with this notion, silver-staining intensities are directly related to mole percentage lysine of various standard proteins. 相似文献
52.
53.
Ichiro Kimura Yae Gotoh Eijiro Ozawa 《In vitro cellular & developmental biology. Plant》1989,25(3):236-242
Summary A mitogenic factor which promotes quail myoblast proliferation has been purified some 105-fold from chick embryo extract by a combination of cation-exchange chromatography and heparin-affinity chromatography. The
factor is eluted from heparin-Sepharose with 2M NaCl and is a single-chain polypeptide with an apparent molecular weight of 15000 to 17000. It is active at subnanogram level
in triggering the proliferation and thereby delaying temporarily fusion of myoblasts. It also stimulates the proliferation
of quail fibroblasts in a similar effective concentration range. For both myoblasts and fibroblasts the dose-response to the
factor is quantitatively and qualitatively comparable with that of bovine pituitary fibroblast growth factor. These observations
strongly suggest that the factor very probably corresponds to chicken fibroblast growth factor or to a closely related molecule(s)
and that it is possibly involved in the regulation of myogenesis.
This work was partly supported by a grant from the National Center of Neurology and Psychiatry (NCNP grant 86-01) of the Ministry
of Health and Welfare, Japan. 相似文献
54.
55.
Growth factor modulation of melanoma growth stimulatory activity mRNA expression in human malignant melanoma cells correlates with cell growth 总被引:2,自引:0,他引:2
This report demonstrates that the expression of melanoma growth stimulatory activity (MGSA) mRNA can be modulated in a positive fashion in the Hs294T human melanoma cell line by PDGF and MGSA. There is close correlation between MGSA expression and the pattern of cell growth in Hs294T cells. 相似文献
56.
Hisashi Miyazaki Masatoshi Iida Yoshimasa Matsunaga Toshihiko Fujii Keiko Nambu Hideki Amejima Yoshinori Oh-e Hideo Furukawa Yukiharu Matsui Yasunobu Sohmura Masahisa Hashimoto 《Biotherapy》1989,1(1-2):47-57
The mode of antitumor action of rHu-TNF was elucidated in BALB/c mice bearing Meth A fibrosarcoma 7 days after transplantation with respect to time course, dose-response relationships and selectivity of the effects. The maximal cytotoxic effect on tumor cells revealed by inhibition of DNA synthesis and maximal lesional effect on tumor vasculature revealed by change in blood pool-size in the tissue were detected at 30 min and I h after administration of rHu-TNF, respectively. The dose-response relationship between cytotoxic and tumoricidal effects of rHu-TNF was irrespective of administration route. ED50s of these antitumor effects afteri.v. administration of rHu-TNF were about 50 times as high as ED50s afteri.t. administration. ED50 ofi.t. given rHu-TNF for vascular effect was about 20 times as high as that for cytotoxicity while ED50 ofi.v. rHu-TNF for vascular effect was only 2–3 times as high as that for cytotoxicity. The whole body autoradiographies with [125I] HSA giveni.v. to see the blood influx into tumor tissue and [14C]thymidine given i.v. to see DNA synthesis in the whole body after administration of rHu-TNF revealed that the distribution of radioactivity was markedly changed in the tumor alone without any detectable change in other whole body tissues.In conclusion, thein vivo antitumor effect of rHu-TNF giveni.t. ori.v., appears to be exerted through the direct action on Meth A sarcoma rather than indirectly on tumor vasculature. Under present conditions, the effect of rHu-TNF in the whole body tissues seems rather selective on cells and vasculature of the tumor. 相似文献
57.
Myogenic cells were isolated from adult rat skeletal muscles and cultured in vitro. Cell proliferation was analyzed between days 1 and 14. The cell cycle phases were determined by examining Feulgen-stained cultures with a cell image processor. The nuclei were automatically analyzed by calculating 18 parameters relating to the texture and densitometry of chromatin and the shape of each nucleus. Cell cycle phases were characterized (Moustafa and Brugal, 1984). The recognition methods made it possible to analyse the nuclei of the myogenic cell populations which were either involved in each phase of the mitotic cycle, or left out of the cycle after fusion into myotubes.After 3 hr of culture 10% of the cell population was involved in the cell cycle. In the presence of foetal calf serum, this percentage increased until day 3 after plating. At that time, the DNA content of 28.2% of the cell population was higher than 3C, whereas it is 2C in G1 or G0 nuclei; image analysis showed that 42% of these cells were in S or G2 phase. From day 4, the proliferation rate gradually slowed down until day 8. After day 8, when numerous myotubes differentiated, the percentage of S and G2 phase cells had diminished to between 3 and 8%. The percentage of nuclei in G0 increased when the first myotubes differentiated around day 5. Myotube nuclei were largely in G0. When horse serum was added to the culture medium on day 4 to enhance myotube differentiation, significant cell proliferation was observed before cell fusion.These methods of analysis give the first daily pattern of myogenic cell proliferation and fusion in a cell population isolated from adult muscles. 相似文献
58.
Olwin BB 《Cytotechnology》1989,2(4):351-365
Heparin-binding growth factors modulate diverse biological activities including cellular proliferation, cellular differentiation, morphogenesis, and angiogenesis. Biochemical characterization for two members of the heparin-binding growth factor family, acidic and basic fibroblast growth factors, is extensive, while characterization of the remaining five members is forthcoming. Cell surface receptors have been identified for acidic and basic fibroblast growth factors, but little is known concerning their sites of action in vivo or the mechanisms involved in transducing the energy of growth factor binding to a biological response. An understanding of the biological basis for the diversity of the heparin binding growth factor family and the in vivo actions of these factors will prove a major challenge to future research efforts. 相似文献
59.
Flemming Jessen Bruce D. Cherksey Thomas Zeuthen Else K. Hoffmann 《The Journal of membrane biology》1989,108(2):139-151
Summary Furosemide-binding proteins were isolated from cholate-solubilized membranes of Ehrlich ascites tumor cells by affinity chromatography, using furosemide as ligand. Solubilized proteins retarded by the affinity material were eluted by furosemide. In reducing and denaturing gels, the major proteins eluted by furosemide were 100 and 45 kDa. In nonreducing, nondenaturing gels, homodimers of both polypeptides were found, whereas no oligomeric proteins containing both polypeptides were seen. It is concluded that the furosemide gel binds two distinct dimeric proteins. The isolated proteins were reconstituted into phospholipid vesicles and the K+ transport activity of these vesicles was assayed by measurement of86Rb+ uptake against a large opposing K+ gradient. The reconstituted system was found to contain a K+ transporting protein, which is sensitive to Ba2+ like the K+ channel previously demonstrated to be activated in intact cells after cell swelling. 相似文献
60.
小鼠骨髓细胞经7d培养后进行细胞形态学观察,可见不同发育阶段的巨核细胞及不同大小的巨核细胞集落。通过计数每个集落中的细胞数,可确定相应祖细胞的有丝分裂能力。结果表明,具有不同有丝分裂能力的祖细胞的体外增殖动力学有所不同。祖细胞的数量与其有丝分裂次数呈负相关(r=-0.986)。进行0、1、2和3次有丝分裂的祖细胞的阿糖胞苷自杀率分别为48.9,58.7,48.0和41.2%;放射敏感性的D_O值(Gy)分别为1.71,1.24,1.03和0.77,D_O值的大小与有丝分裂次数呈负相关(r=-0.958)。经3Gy全身照射后CFU-Meg与CFU-GM的恢复动态过程具有不同特点。 相似文献