全文获取类型
收费全文 | 1601956篇 |
免费 | 146577篇 |
国内免费 | 1429篇 |
出版年
2021年 | 18196篇 |
2019年 | 16185篇 |
2018年 | 19489篇 |
2017年 | 18316篇 |
2016年 | 29204篇 |
2015年 | 42737篇 |
2014年 | 50841篇 |
2013年 | 76934篇 |
2012年 | 46248篇 |
2011年 | 37603篇 |
2010年 | 47378篇 |
2009年 | 47561篇 |
2008年 | 34535篇 |
2007年 | 33698篇 |
2006年 | 36422篇 |
2005年 | 37765篇 |
2004年 | 36592篇 |
2003年 | 33946篇 |
2002年 | 31901篇 |
2001年 | 47774篇 |
2000年 | 45178篇 |
1999年 | 41867篇 |
1998年 | 27120篇 |
1997年 | 26831篇 |
1996年 | 26135篇 |
1995年 | 24285篇 |
1994年 | 23911篇 |
1993年 | 23189篇 |
1992年 | 35464篇 |
1991年 | 34070篇 |
1990年 | 32600篇 |
1989年 | 33040篇 |
1988年 | 30216篇 |
1987年 | 29001篇 |
1986年 | 27308篇 |
1985年 | 28804篇 |
1984年 | 27074篇 |
1983年 | 23927篇 |
1982年 | 22680篇 |
1981年 | 21681篇 |
1980年 | 20275篇 |
1979年 | 23222篇 |
1978年 | 20915篇 |
1977年 | 19645篇 |
1976年 | 18915篇 |
1975年 | 19012篇 |
1974年 | 19856篇 |
1973年 | 20109篇 |
1972年 | 17352篇 |
1971年 | 15764篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
L A Chouinard 《Journal of cell science》1970,6(1):73-85
942.
Evidence has been presented for the formation of an intermediate compound in the metabolism of 3-hydroxyanthranilic acid to quinolinic acid by 3-hydroxyanthranilase from rat liver preparations. The production of the intermediate was demonstrated by spectrophotometric analyses and quinolinic acid measurements of incubation mixtures in which small amounts of acetone powder extracts of rat liver were used as the enzyme source. The calculated extinction coefficient of the compound was more than double that of the substrate or of the final product, quinolinic acid.The intermediate was shown to be an oxidation product of 3-hydroxyanthranilate as indicated by Thunberg experiments. The data obtained indicate that the intermediate may be a quinone-type compound. 相似文献
943.
VICTOR G. BRUCE 《The Journal of eukaryotic microbiology》1970,17(2):328-334
SYNOPSIS. Chlamydomonas reinhardi has a biological clock regulating phototaxis in dividing and non-dividing cultures; it also can exert some control on growth of continuous cultures. The period length is ∼ 24 hr; it is temperature-compensated and not dependent on the average growth rate. The rhythm can be entrained or phased by light-dark conditions. In dividing cultures a periodic fluctuation in cell number and total protein persists in continuous light. 相似文献
944.
945.
Summary The iliofibularis muscle ofXenopus laevis is reported to contain five types of fibres which have different force—velocity relationships. Ten fibres of each type were selected on the basis of succinate dehydrogenase activity, cross-sectional area and location in the muscle, in order to assess the validity of the fibre type classification.Maximum calcium-stimulated myofibrillar ATPase activity (V
max) and apparent Michaelis constant (K
m) for ATP were determined for these 50 fibres from serial sections. The values obtained varied according to the type of fibre. Type 1 had the highest and type 5 the lowest values forK
m andV
max.In a separate experiment, single freeze-dried fibres were used to determine the relationship between their ATP content and apparentK
m for ATP. There was a tendency for high ATP concentrations in fibres with highK
m values.When myofibrillar ATPase activity was related to the maximum velocity of shortening of the five fibre types, a significant correlation was found. It is concluded that calcium-stimulated myofibrillar ATPase histochemistry allows an estimate of the maximum shortening velocity of muscle fibres fromXenopus laevis. 相似文献
946.
Zusammenfassung Mit Untersuchungen über die Abhängigkeit des Zellvolumens vom osmotischen Wert und über die Konzentration der Zellinhaltsstoffe wird versucht, zur Kenntnis der Ursachen der Osmotoleranz bei Hefen beizutragen. In konzentrierten Lösungen verringern alle untersuchten Hefen ihr Volumen, die osmotoleranten Hefen aber weniger als die nichtosmotoleranten. Der Beginn einer meßbaren Volumenverringerung tritt bei osmotoleranten Hefen bei höheren Konzentrationen ein als bei nichtosmotoleranten. Eine Abhängigkeit der Zellgröße vom osmotischen Wert kann nur in einem bestimmten Konzentrationsbereich (zwischen 0,7–2% und 10% NaCl) festgestellt werden. Darunter fehlt eine osmotische Reaktion, und darüber bleibt die Zellgröße gleich. In Nährlösungen mit erhöhtem osmotischen Wert vermehren sich Zellen beider Typen in ihrer normalen Größe. Der osmotische Wert ihres Zellinhaltes ist annähernd gleich groß. Eine veränderte Struktur des Zellplasmas bzw. ein dadurch bedingter höherer Gehalt an fest gebundenem Hydratationswasser wird als Ursache der Osmotoleranz bei Hefen angesehen.
(Prof. Dr. S. Windisch) 相似文献
About the causes of osmotolerance in yeasts
Summary The question, if the yeast cell volume depends on the osmotic pressure and on the solutes of the cell, has been investigated. In concentrated solutions all yeasts investigated reduced their volume. A smaller reduction was found in osmotolerant yeasts. Osmotolerant yeasts begin to reduce their volume at higher osmotic pressures than non-osmotolerant ones. In concentrated nutrient media the cells of osmotolerant and non-osmotolerant yeasts grow in their normal size. The cell size depends only in the range between 0.7 to 2% and 10% NaCl approximately on the osmotic pressure of the surrounding medium. Beneath 2% there is no osmotic reaction and above 10% the cell size remains unchanged. The osmotic value in the cells of both yeast types is about the same. Causes of osmotolerance in yeasts may be a modified structure of cytoplasm and an increased content of bound water.
(Prof. Dr. S. Windisch) 相似文献
947.
We used self‐reported data from United Methodist clergy to assess the prevalence of obesity and having ever been told certain chronic disease diagnoses. Of all actively serving United Methodist clergy in North Carolina (NC) 95% (n = 1726) completed self‐report height and weight items and diagnosis questions from the Behavioral Risk Factor Surveillance Survey (BRFSS). We calculated BMI categories and diagnosis prevalence rates for the clergy and compared them to the NC population using BRFSS data. The obesity rate among clergy aged 35–64 years was 39.7%, 10.3% (95% CI = 8.5%, 12.1%) higher than their NC counterparts. Clergy also reported significantly higher rates of having ever been given diagnoses of diabetes, arthritis, high blood pressure, angina, and asthma compared to their NC peers. Health interventions that address obesity and chronic disease among clergy are urgently needed. 相似文献
948.
949.
950.