全文获取类型
收费全文 | 763篇 |
免费 | 57篇 |
出版年
2013年 | 12篇 |
2012年 | 14篇 |
2011年 | 14篇 |
2010年 | 22篇 |
2009年 | 22篇 |
2008年 | 17篇 |
2007年 | 21篇 |
2006年 | 16篇 |
2005年 | 13篇 |
2004年 | 9篇 |
2003年 | 7篇 |
2002年 | 7篇 |
2000年 | 7篇 |
1998年 | 8篇 |
1997年 | 17篇 |
1995年 | 12篇 |
1994年 | 6篇 |
1993年 | 14篇 |
1992年 | 13篇 |
1991年 | 12篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 12篇 |
1985年 | 10篇 |
1983年 | 9篇 |
1982年 | 12篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 11篇 |
1977年 | 8篇 |
1976年 | 13篇 |
1975年 | 8篇 |
1974年 | 6篇 |
1972年 | 9篇 |
1971年 | 8篇 |
1959年 | 19篇 |
1958年 | 41篇 |
1957年 | 40篇 |
1956年 | 36篇 |
1955年 | 38篇 |
1954年 | 28篇 |
1953年 | 27篇 |
1952年 | 23篇 |
1951年 | 29篇 |
1950年 | 22篇 |
1949年 | 20篇 |
1948年 | 16篇 |
1946年 | 6篇 |
排序方式: 共有820条查询结果,搜索用时 15 毫秒
91.
92.
Under the conditions employed, the rate of clearing of washed cell suspensions of Micrococcus lysodeikticus, measured photometrically, is nearly proportional to enzyme concentration and nearly inversely proportional to the initial concentration of cells. With a given amount of lysozyme (usually 1.5 μg./ml.) the density of a cell suspension decreases exponentially with time, until it is reduced to between 20 and 40% of that at the start, followed by a decreasing rate of clearing. Under increased hydrostatic pressures of 4000 and 8000 p.s.i., respectively, the rate of clearing is faster than at normal pressure at various pH's between 5.65 and 8.70, at 35 °C. 相似文献
93.
94.
Temperature Dependence of Plant and Crop Process 总被引:16,自引:2,他引:14
The quantitative effects of temperature on plant and crop processesare discussed and related to the underlying theory, by meansof a critical and expository essay which aims to provide a conceptualbasis for the consideration of these problems. The topics consideredinclude the Arrhenius equation and Q10; the collision and transition-statetheories of the rate constant; models with a temperature optimum;models without a temperature optimum; phase changes; diffusion,viscosity and translocation; hybrid systems (biochemistry plustransport); photosynsthesis; respiration; and development withthe day-degree hypothesis. Temperature, model, plants, crops 相似文献
95.
Evidence that Enzyme Polymorphisms are not Selectively Neutral 总被引:2,自引:0,他引:2
GEORGE B. JOHNSON 《Nature: New biology》1972,237(75):170-171
THE discovery of large amounts of electrophoretically-detectable genetic variation within natural populations has aroused considerable interest in the factors maintaining so much polymorphism. It has been proposed that these allozyme polymorphisms reflect the action of random processes1–6, the polymorphic variation being of little or no selective significance. Alternative hypotheses have suggested that these polymorphisms may be maintained by a balance of selective forces7–10. 相似文献
96.
A Model of the Partitioning of Growth between the Shoots and Roots of Vegetative Plants 总被引:5,自引:2,他引:3
A model of the partitioning of new growth between the shootsand roots of vegetative plants is presented. There are two partitioningfunctions, involving one partitioning parameter, which describethe priorities for new growth in both the shoots and roots.The dynamic responses, to changes in the environment and toshoot defoliation, of shoot and root specific growth rates,shoot: root ratio, and carbon and nitrogen substrate levels,are examined; realistic behaviour is observed. Balanced exponentialgrowth solutions are also examined and it is concluded thatrelationships between some derived plant growth quantities maybe non-unique, thus emphasizing the need for a critical understandingof the underlying physiological processes involved in plantgrowth. Mathematical model, partitioning of assimilates, shoot: root ratio, specific growth rate, carbon and nitrogen substrate levels 相似文献
97.
ELIZABETH JOHNSON 《Mammal Review》1972,1(7-8):198-208
Moulting in mammals is a cyclic phenomenon which often occurs in a wave–like pattern. The moult cycle depends upon an inherent rhythm of activity in the hair follicles, which may be modified by systemic factors. In laboratory rodents a number of hormones affect the timing of the moult, as well as affecting the amount of hair produced and the loss of club hairs.
In Microtus agrestis a seasonal moult results in a sparse coat with coarse hairs in summer and a dense coat with fine hairs in winter. The moult appears to be adjusted to the environment by way of the endocrine system, with adrenal and thyroid hormones, as well as sex hormones, involved in the regulation. The importance of such adaptive coat changes are discussed. 相似文献
In Microtus agrestis a seasonal moult results in a sparse coat with coarse hairs in summer and a dense coat with fine hairs in winter. The moult appears to be adjusted to the environment by way of the endocrine system, with adrenal and thyroid hormones, as well as sex hormones, involved in the regulation. The importance of such adaptive coat changes are discussed. 相似文献
98.
99.
100.