全文获取类型
收费全文 | 6978篇 |
免费 | 692篇 |
国内免费 | 1篇 |
出版年
2021年 | 150篇 |
2020年 | 83篇 |
2019年 | 111篇 |
2018年 | 127篇 |
2017年 | 108篇 |
2016年 | 204篇 |
2015年 | 285篇 |
2014年 | 315篇 |
2013年 | 405篇 |
2012年 | 446篇 |
2011年 | 454篇 |
2010年 | 291篇 |
2009年 | 228篇 |
2008年 | 363篇 |
2007年 | 349篇 |
2006年 | 335篇 |
2005年 | 278篇 |
2004年 | 269篇 |
2003年 | 235篇 |
2002年 | 219篇 |
2001年 | 111篇 |
2000年 | 118篇 |
1999年 | 99篇 |
1998年 | 72篇 |
1997年 | 63篇 |
1996年 | 52篇 |
1995年 | 63篇 |
1994年 | 54篇 |
1993年 | 60篇 |
1992年 | 85篇 |
1991年 | 76篇 |
1990年 | 86篇 |
1989年 | 82篇 |
1988年 | 85篇 |
1987年 | 66篇 |
1986年 | 56篇 |
1985年 | 59篇 |
1984年 | 55篇 |
1983年 | 46篇 |
1982年 | 52篇 |
1981年 | 51篇 |
1980年 | 33篇 |
1979年 | 56篇 |
1978年 | 45篇 |
1977年 | 32篇 |
1976年 | 50篇 |
1975年 | 52篇 |
1974年 | 59篇 |
1973年 | 77篇 |
1972年 | 54篇 |
排序方式: 共有7671条查询结果,搜索用时 15 毫秒
81.
Binding properties and biological potencies of insulin-like growth factors in L6 myoblasts. 总被引:8,自引:4,他引:4 下载免费PDF全文
F J Ballard L C Read G L Francis C J Bagley J C Wallace 《The Biochemical journal》1986,233(1):223-230
Protein synthesis in rat L6 myoblasts is stimulated and protein breakdown inhibited in a co-ordinate manner by insulin-like growth factors (IGF) or insulin. For both processes, bovine IGF-1 was somewhat more potent than human IGF-1, which was effective at a tenth the concentration of insulin, rat IGF-2 or human IGF-2. A similar order of potency is noted when DNA synthesis or protein accumulation is monitored over a 24 h period, but between 20- and 50-fold higher concentrations of each growth factor are required than those needed to produce effects in the 4 h protein-synthesis or -breakdown measurements. Binding experiments with labelled human or bovine IGF-1 as ligand demonstrated competition at concentrations of IGF-2, especially human IGF-2, lower than that of either IGF-1 preparation. This pattern was much more pronounced when the radioligand was either human IGF-2 or rat IGF-2. Insulin competed 10-15% for the binding of labelled IGF-1, but not at all with labelled IGF-2. Ligand-receptor cross-linking experiments showed that labelled bovine IGF-1 bound approximately equally to the type 1 IGF receptor (Mr 130000 after reduction) and to the type 2 IGF receptor (Mr 270000 after reduction), and that unlabelled IGF-1 competed equally with radioligand binding to both receptors. On the other hand, rat IGF-2 competed more effectively for binding to the type-2 receptor, and insulin competed only for binding to the type-1 receptor. Further cross-linking experiments with rat IGF-2 as radioligand demonstrated binding only to the type-2 receptor and to proteins with Mr values after reduction of 230000 and 200000. This binding was prevented by high rat IGF-2 concentrations, less effectively by bovine IGF-1 and not at all by insulin. The apparently conflicting biological potencies and receptor binding of the different growth factors can be explained if all the biological actions are mediated via the type-1 IGF receptor, rather than through the abundant type-2 receptor. 相似文献
82.
Changes in teleost yolk proteins during oocyte maturation: correlation of yolk proteolysis with oocyte hydration 总被引:3,自引:0,他引:3
M S Greeley D R Calder R A Wallace 《Comparative biochemistry and physiology. B, Comparative biochemistry》1986,84(1):1-9
Yolk proteins of prematuration occytes and postmaturation eggs were compared by SDS gel electrophoresis in several teleosts, including freshwater species that produce demersal eggs, estuarine and marine species with demersal eggs, and marine species with pelagic eggs. In certain teleosts distinct changes in yolk protein banding patterns during oocyte maturation are suggestive of extensive secondary proteolysis of yolk proteins at this time; proteolysis is most pronounced in marine fishes with pelagic eggs. In many teleosts the oocyte swells by hydration during maturation; this hydration is also most pronounced in marine fishes with pelagic eggs. The extent of yolk proteolysis is well correlated with the extent of oocyte hydration during maturation. 相似文献
83.
Compartmentation of fatty acid oxidation in liver cells 总被引:1,自引:0,他引:1
84.
Clearance rates of three sessile and four free-swimming rotifer species from a small acid bog-pond were measured using in situ techniques. Three radioactively labeled cell types, an alga (Chlamydomonas), a bacterium (Enterobacter = Aerobacter), and a yeast (Rhodotorula) were used as tracers. Clearance rates (using yeast) ranged from <1.0 to >250 µl · animal?1 · h?1 depending on species. Ptygura crystallina, Ptygura pilula, Floscularia conifera, and an unidentified bdelloid ingested all three foods with substantial variation in clearance rates among species and cell type. There was an insignificant error (<0.3%) in clearance rate associated with non-ingestive uptake of radioactivity. Among the free-swimming taxa, Lecane sp. had a clearance rate of <0.5 µl · animal?1 · h?1 on yeast, while another Lecane sp. and Trichotria tetractis did not ingest that cell type. 相似文献
85.
Breakdown of Diazotized Proteins and Synthetic Substrates by Rumen Bacterial Proteases 总被引:4,自引:3,他引:1 下载免费PDF全文
Several different kinds of substrate were used to investigate the proteolytic activity of rumen bacteria and of proteases released from rumen bacteria by blending (“coat proteases”). These substrates included diazotized feed proteins and diazotized soluble and insoluble pure proteins. It was concluded that, while solubility was an important factor, the secondary and tertiary structure of a protein had a major influence on its rate of digestion. The resistance of elastin congo red to digestion indicated that similar fibrous proteins in plant material might resist proteolytic attack by rumen bacteria. Coat proteases had a broad specificity, including several exo- and endopeptidase activities, as determined by using synthetic peptide substrates. 相似文献
86.
The semisynthesis of analogues of cytochrome c. Modifications of arginine residues 38 and 91. 总被引:5,自引:4,他引:1 下载免费PDF全文
The arginine residues at positions 38 and 91 of horse cytochrome c are absolutely conserved throughout eukaryotic evolution. For studies of the functional roles of these residues, we have prepared, by semisynthetic techniques, analogues of cytochrome c in which one or the other of the arginine residues has been modified. The products of modification by adduct formation with pentane-2,4-dione were purified and extensively characterized. In biological tests, the arginine-91-modified cytochrome c showed little difference in behaviour from native horse cytochrome c. Modification of arginine-38, however, led to extensive changes in biological and chemical properties. We also prepared and tested adducts with cyclohexane-1,2-dione and camphorquinone-10-sulphonic acid. The same effects on biological properties were noted irrespective of the nature of the modifying group. We suggest reasons for the differences in sensitivity of the two sites. 相似文献
87.
Studies on Nondefective Adenovirus-Simian Virus 40 Hybrid Viruses I. A Newly Characterized Simian Virus 40 Antigen Induced by the Ad2+ND1 Virus 总被引:50,自引:39,他引:11 下载免费PDF全文
The nondefective adenovirus 2 (Ad2)-simian virus 40 (SV40) hybrid virus, Ad2(+)ND(1), does not induce heat-labile SV40 T antigen but does induce a previously uncharacterized heat-stable SV40 antigen-the SV40 "U" antigen. This antigen is detectable by both immunofluorescence and complement fixation by using sera from hamsters with SV40 tumors. Sera from hamsters bearing SV40 tumors can be divided into two groups, those that react with both SV40 T and U antigens (T(+)U(+) sera) and those that react with SV40 T antigen only (T(+)U(-) sera). SV40 U-specific sera from monkeys immunized with Ad2(+)ND(1)-infected cells do not react with SV40 T antigen by immunofluorescence but do react with an antigen in the nucleus of SV40-transformed cells and with an early, cytosine arabinoside-resistant antigen present in the nucleus of SV40-infected cells. A heat-stable SV40 antigen detectable by complement fixation with T(+)U(+) hamster sera is present in extracts of SV40-induced hamster tumors and in cell packs of SV40-infected or -transformed cells. SV40 U-antigen synthesis by Ad2(+)ND(1) virus is partially sensitive to inhibitors of deoxyribonucleic acid synthesis, whereas U-antigen synthesis by SV40 virus is an early cytosine arabinoside-resistant event. As an early SV40 antigen differing from SV40 T antigen, U antigen may play a role in malignant transformation mediated by SV40. 相似文献
88.
Arthur Wallace 《Plant and Soil》1971,34(1):121-131
Summary When nonexchangeable absorption of Rb86, Na22, and Cs137 by bush bean (Phaseolus vulgaris L. var. Improved Tendergreen) was determined at different root temperatures and with and without Ca additions or pretreatments,
a strong interaction between temperature and Ca was observed. Ca inhibited Rb86 absorption markedly at low temperatures but had less effect on Cs137. Absorption of Na22 was inhibited by Ca at both low and high temperatures. Little effect for Ca with sometimes a Viets effect was observed at
high temperature for Rb but not for Cs or Na. Ratio pairs of Rb, Ca, and Na were used as an index of similarity of absorption
mechanisms. Cs and Rb, and Na and Rb appeared to be absorbed by different mechanisms at 10−3
M as indicated by temperature and Ca responses. Nitrate-N stimulated uptake of Rb only at high temperature with or without
Ca but not at low temperature. Ca in the pretreatment tended to result in greater long distance transport to shoots of Rb86 and Cs137 for the high temperature but Ca in the test solution slightly decreased the long distance transport. The data are discussed
in terms of the Viets effect and of a possible role of Ca in synthesis of transport proteins. 相似文献
89.
Ultraviolet Mutagenesis and Its Repair in an ESCHERICHIA COLI Strain Containing a Nonsense Codon 总被引:2,自引:1,他引:1 下载免费PDF全文
Stanley Person John Allen McCloskey Wallace Snipes Richard C. Bockrath 《Genetics》1974,78(4):1035-1049
Ultraviolet mutagenesis and its repair were studied mainly in WU36-10-89, a uvr(-) strain of Escherichia coli containing a UAG mutation in a gene for leucine biosynthesis. Following ultraviolet (UV) irradiation revertants appearing with or without direct photoreactivation (PR) were classified according to the presence and type of suppressor they contained. We find UV mutation production to be quite specific. An analysis of revertants produced by UV indicates they are formed mainly from GC --> AT and that the miscoding is due to a cytosine residue at the site of mutation in a cytosine-thymine (CT) dimer. We propose that the dimer serves as template during some aspects of repair replication and at the time of replication the C in the dimer directs the insertion of A in the complementary strand. We also note that C --> A and T -->G changes caused by a CT dimer occur much less frequently. 相似文献
90.