全文获取类型
收费全文 | 1171篇 |
免费 | 7篇 |
出版年
2013年 | 22篇 |
2012年 | 16篇 |
2011年 | 24篇 |
2010年 | 42篇 |
2009年 | 52篇 |
2008年 | 48篇 |
2007年 | 58篇 |
2006年 | 39篇 |
2005年 | 35篇 |
2004年 | 24篇 |
2003年 | 9篇 |
2002年 | 7篇 |
1999年 | 9篇 |
1998年 | 19篇 |
1997年 | 20篇 |
1996年 | 25篇 |
1995年 | 8篇 |
1994年 | 12篇 |
1993年 | 14篇 |
1992年 | 21篇 |
1991年 | 25篇 |
1990年 | 12篇 |
1989年 | 28篇 |
1988年 | 24篇 |
1987年 | 25篇 |
1986年 | 18篇 |
1985年 | 22篇 |
1984年 | 22篇 |
1983年 | 22篇 |
1982年 | 11篇 |
1981年 | 20篇 |
1980年 | 7篇 |
1979年 | 24篇 |
1978年 | 26篇 |
1977年 | 21篇 |
1976年 | 13篇 |
1975年 | 25篇 |
1974年 | 26篇 |
1973年 | 29篇 |
1972年 | 45篇 |
1971年 | 47篇 |
1970年 | 9篇 |
1969年 | 16篇 |
1968年 | 14篇 |
1967年 | 12篇 |
1966年 | 12篇 |
1965年 | 10篇 |
1959年 | 11篇 |
1958年 | 7篇 |
1954年 | 9篇 |
排序方式: 共有1178条查询结果,搜索用时 15 毫秒
101.
102.
103.
GEORGE WILLIAM SALT 《The Journal of eukaryotic microbiology》1968,15(2):275-280
SYNOPSIS. Density of prey (Paramecium aurelia) and predator (Amoeba proteus) were varied while volume of inorganic medium was kept constant. Variations in density of prey had little effect on the rates of feeding and reproduction of the amoebae; but with increasing predator density the amoebae captured the paramecia less rapidly and ingested fewer before dividing, altho division size did not change appreciably. Therefore, amoebae of a low density population with a constant food supply carry more nutritional reserves from generation to generation than do those in a denser population. 相似文献
104.
NANCY S. LAMONTAGNE DAVID F. JOHNSON WILLIAM B. JAKOBY CHESTER E. HOLMLUND 《The Journal of eukaryotic microbiology》1982,29(3):401-405
ABSTRACT. Dehydrogenase activity with hydroxysteroids has been observed in Tetrahymena furgasoni (formerly T. pyriformis strain W), and the enzyme responsible has been isolated from this organism. The purified dehydrogenase is active with a variety of steroid alcohols at apparent Km values ranging from 0.2 to 4.0 mM. The C-3 hydroxyl of ring A of the steroid nucleus is the preferred position of oxidation. However, a variety of other secondary alcohols are also substrates, with apparent Km values for 2-butanol, 2-pentanol, and cyclohexanol of 880, 1000. and 150 mM, respectively. With both steroidal and nonsteroidal alcohols. NAD is the preferred co-substrate, although low activity with NADP is observed. Evidence is presented that the activity with secondary alcohols, whether steroidal or not, is the property of a single protein species. 相似文献
105.
106.
SAMIR R. AKRUK WALTER J. HUMPHREYS WILLIAM L. WILLIAMS 《Differentiation; research in biological diversity》1979,13(2):125-131
Prior to fertilization mammalian spermatozoa undergo physiological changes in the female reproductive tract. These changes are collectively known as capacitation. In essence capacitation is a further differentiation that the sperm cell must acquire beyond the maturational changes that it undergoes in the epididymis. Although capacitation in vitro has been easily achieved in rodents, its accomplishment in the rabbit is inconsistent and difficult. We report here successful in vitro capacitation of ejaculated rabbit sperm, assessed by in vitro and in vivo fertilization of rabbit ova. Sperm were used from pooled ejaculates collected from bucks of proven fertility since sperm collected from individual bucks resulted in significant differences in fertilization levels. Conditions favoring in vitro capacitation were: (1) extended incubation time of 12 h, (2) addition of 20% heated rabbit serum to incubation medium, and (3) an atmosphere of 5% CO2, 8% O2, and 87% N2 during incubation. In vitro capacitation of sperm under these conditions resulted in 67% fertilization compared to 89% for control sperm capacitated for 13 h in the uterus. 相似文献
107.
SYNOPSIS. Autoradiographic technics with tritium-labeled thymidine have been used to determine G1, S, G2 and D for the kinetoplast and the nucleus of Crithidia fasciculata at 15, 25 and 32 C. The kinetoplast completes division before the nucleus at all 3 temperatures. The S phases of both organelles occur in approximate synchrony and are approximately equal in length but the nucleus begins and completes S before the kinetoplast at the 2 lower temperatures. This relationship is reversed at 32 C. Most of the effect of temperature on generation time is due to its effect on the length of S. The results are compared with similar studies on C. luciliae, Trypanosoma mega, other protozoa and tissue cells in culture. The role of the approximate synchrony of nuclear and kinetoplastic cycles in maintenance of the kinetoplastic condition is discussed and the hypothesis is proposed that this synchrony results from the sharing by nucleus and kinetoplast of the same mechanism for the production of the deoxyribonucleotides used in replication of their respective DNAs. 相似文献
108.
WILLIAM A. ROTTSCHAEFER 《Biology & philosophy》1997,12(3):369-384
In his recent The Temptation of Evolutionary Ethics, Paul Farber has given a negative assessment of the last one hundred years of attempts in Anglo-American philosophy, beginning with Darwin, to develop an evolutionary ethics. Farber identifies some version of the naturalistic fallacy as one of the central sources for the failures of evolutionary ethics. For this reason, and others, Farber urges that though it has its attraction, evolutionary ethics is a temptation to be resisted. In this discussion I identify three major, historically relevant forms of the naturalistic fallacy, the (1) the deductive, (2) genetic, and (3) open question forms and argue that none of them pose an intrinsic problem for evolutionary ethics. I conclude that on this score at least there is no reason to resist temptation. 相似文献
109.
110.