全文获取类型
收费全文 | 2469篇 |
免费 | 227篇 |
出版年
2023年 | 14篇 |
2022年 | 25篇 |
2021年 | 51篇 |
2020年 | 38篇 |
2019年 | 35篇 |
2018年 | 66篇 |
2017年 | 48篇 |
2016年 | 64篇 |
2015年 | 106篇 |
2014年 | 118篇 |
2013年 | 122篇 |
2012年 | 165篇 |
2011年 | 188篇 |
2010年 | 97篇 |
2009年 | 86篇 |
2008年 | 131篇 |
2007年 | 127篇 |
2006年 | 127篇 |
2005年 | 94篇 |
2004年 | 93篇 |
2003年 | 93篇 |
2002年 | 81篇 |
2001年 | 60篇 |
2000年 | 58篇 |
1999年 | 46篇 |
1998年 | 33篇 |
1997年 | 14篇 |
1996年 | 20篇 |
1995年 | 22篇 |
1994年 | 16篇 |
1993年 | 22篇 |
1992年 | 38篇 |
1991年 | 22篇 |
1990年 | 34篇 |
1989年 | 24篇 |
1988年 | 20篇 |
1987年 | 22篇 |
1986年 | 20篇 |
1985年 | 30篇 |
1984年 | 13篇 |
1982年 | 13篇 |
1980年 | 16篇 |
1979年 | 20篇 |
1978年 | 17篇 |
1977年 | 13篇 |
1975年 | 13篇 |
1974年 | 12篇 |
1972年 | 17篇 |
1971年 | 12篇 |
1970年 | 11篇 |
排序方式: 共有2696条查询结果,搜索用时 203 毫秒
21.
Mathias Sprinzl Karl-Heinz Scheit Hans Sternbach Friedrich von der Haar Friedrich Cramer 《Biochemical and biophysical research communications》1973,51(4):881-887
2′-Deoxyadenosine and 3′-deoxyadenosine (cordycepin) can be incorporated into the 3′-terminal position of tRNAPhe by tRNA nucleotidyl transferase. tRNAPhe-C-C-2′dA and tRNAPhe-C-C-3′dA, missing the cis-diol group at the 3′-terminal end are resistant to periodate oxidation and are not able to form borate complexes. In aminoacylation experiments only the tRNAPhe-C-C-3′dA proved to be chargeable. 相似文献
22.
23.
24.
25.
26.
27.
A. A. J. J. L. Rutten B. G. A. G. G. Béquet-Passelecq H. B. W. M. Koëter 《In vitro cellular & developmental biology. Plant》1990,26(4):353-360
Summary A new method was developed for rabbit skin organ culture. In a two-compartment model, skin discs were cultured on a Millicell-HA
insert unit with a microporous membrane which allows transport of culture medium via the dermis into the epidermis, whereas
the epidermal side remains free of direct contact with culture medium. In this relatively simple two-compartment organ culture
model, rabbit skin could be cultured for 7 d in RPMI 1640 medium supplemented with fetal bovine serum, or for 2 d in RPMI
1640 medium supplemented with cofactors. The histomorphology and ultrastructure of 7-d cultured rabbit skin discs was essentially
similar to that of freshly isolated rabbit skin. Keratinocytes in the stratum basale continued to divide during organ culture.
The terminal differentiation of the epidermis continued in vitro as was found by the presence of keratohyalin granules, the
intact stratum corneum, and keratin expression. Furthermore, glucose consumption continued until culture Day 7, but thereafter
it declined rapidly. Concomitantly, degenerative changes were found. At the end of the 7-d culture period the distance between
single dermal collagen fibrils had increased as compared to noncultured skin. This model of skin organ cultures can be used
to study biological processes, dermal toxicity, and penetration and metabolism of xenobiotics in intact skin. Furthermore,
within certain limits, processes responsible for repair and regeneration of damaged skin can also be studied in this model
because the rabbit skin can be cultured for 7 d.
The present study was financially supported by grants of Duphar B. V. (Weesp, Netherlands), the European Community, and the
Dutch animal welfare organizations Samenwerkingsverband van de Nederlandse Vereniging tot Bescherming van Dieren en de Nederlandse
Bond tot Bestrijding van de Vivisectie, Anti-Vivisectie Stichting en Stichting Schoonheid Zonder Wreedheid. 相似文献
28.
Receptor (CD46) modulation and complement-mediated lysis of uninfected cells after contact with measles virus-infected cells. 总被引:4,自引:4,他引:0 下载免费PDF全文
J Schneider-Schaulies J J Schnorr J Schlender L M Dunster S Schneider-Schaulies V ter Meulen 《Journal of virology》1996,70(1):255-263
Recently, it has been observed that the infection of human target cells with certain measles virus (MV) strains leads to the downregulation of the major MV receptor CD46. Here we report that CD46 downregulation can be rapidly induced in uninfected cells after surface contact with MV particles or MV-infected cells. Receptor modulation is detectable after 30 min of cocultivation of uninfected cells with MV-infected cells and is complete after 2 to 4 h, a time after which newly synthesized MV hemagglutinin (MV-H) cannot be detected in freshly infected target cells. This contact-mediated receptor modulation is also induced by recombinant MV-H expressed by vaccinia virus and is inhibitable with antibodies against CD46 and MV-H. By titrating the effect with MV Edmonston strain-infected cells, a significant contact-mediated CD46 modulation was detectable up to a ratio of 1 infected to 64 uninfected cells. As a result of CD46 downregulation, an increased susceptibility of uninfected cells for complement-mediated lysis was observed. This phenomenon, however, is MV strain dependent, as observed for the downregulation of CD46 after MV infection. These data suggest that in acute measles or following measles vaccination, uninfected cells might also be destroyed by complement after contacting an MV-infected cell. 相似文献
29.
Spectral and kinetic characteristics of fluorescence from isolated reaction centers of photosynthetic purple bacteria Rhodobacter sphaeroides and Rhodobacter capsulatus were measured at room temperature under rectangular shape of excitation at 810 nm. The kinetics of fluorescence at 915 nm reflected redox changes due to light and dark reactions in the donor and acceptor quinone complex of the reaction center as identified by absorption changes at 865 nm (bacteriochlorophyll dimer) and 450 nm (quinones) measured simultaneously with the fluorescence. Based on redox titration and gradual bleaching of the dimer, the yield of fluorescence from reaction centers could be separated into a time-dependent (originating from the dimer) and a constant part (coming from contaminating pigment (detached bacteriochlorin)). The origin was also confirmed by the corresponding excitation spectra of the 915 nm fluorescence. The ratio of yields of constant fluorescence over variable fluorescence was much smaller in Rhodobacter sphaeroides (0.15±0.1) than in Rhodobacter capsulatus (1.2±0.3). It was shown that the changes in fluorescence yield reflected the disappearance of the dimer and the quenching by the oxidized primary quinone. The redox changes of the secondary quinone did not have any influence on the yield but excess quinone in the solution quenched the (constant part of) fluorescence. The relative yields of fluorescence in different redox states of the reaction center were tabulated. The fluorescence of the dimer can be used as an effective tool in studies of redox reactions in reaction centers, an alternative to the measurements of absorption kinetics.Abbreviations Bchl
bacteriochlorophyll
- Bpheo
bacteriopheophytin
- D
electron donor to P+
- P
bacteriochlorophyll dimer
- Q
quinone acceptor
- QA
primary quinone acceptor
- QB
secondary quinone acceptor
- RC
reaction center protein
- UQ6
ubiquinone-30 相似文献
30.
R Sadoul P A Fernandez A L Quiquerez I Martinou M Maki M Schr?ter J D Becherer M Irmler J Tschopp J C Martinou 《The EMBO journal》1996,15(15):3845-3852
Sympathetic neurons undergo programmed cell death (PCD) upon deprivation of nerve growth factor (NGF). PCD of neurons is blocked by inhibitors of the interleukin-1beta converting enzyme (ICE)/Ced-3-like cysteine protease, indicating involvement of this class of proteases in the cell death programme. Here we demonstrate that the proteolytic activities of the proteasome are also essential in PCD of neurons. Nanomolar concentrations of several proteasome inhibitors, including the highly selective inhibitor lactacystin, not only prolonged survival of NGF-deprived neurons but also prevented processing of poly(ADP-ribose) polymerase which is known to be cleaved by an ICE/Ced-3 family member during PCD. These results demonstrate that the proteasome is a key regulator of neuronal PCD and that, within this process, it is involved upstream of proteases of the ICE/Ced-3 family. This order of events was confirmed in macrophages where lactacystin inhibited the proteolytic activation of precursor ICE and the subsequent generation of active interleukin-1beta. 相似文献