全文获取类型
收费全文 | 20029篇 |
免费 | 1651篇 |
国内免费 | 5篇 |
专业分类
21685篇 |
出版年
2023年 | 88篇 |
2022年 | 232篇 |
2021年 | 433篇 |
2020年 | 233篇 |
2019年 | 306篇 |
2018年 | 423篇 |
2017年 | 353篇 |
2016年 | 637篇 |
2015年 | 1034篇 |
2014年 | 1169篇 |
2013年 | 1410篇 |
2012年 | 1748篇 |
2011年 | 1651篇 |
2010年 | 1062篇 |
2009年 | 936篇 |
2008年 | 1264篇 |
2007年 | 1291篇 |
2006年 | 1105篇 |
2005年 | 1060篇 |
2004年 | 1034篇 |
2003年 | 937篇 |
2002年 | 892篇 |
2001年 | 205篇 |
2000年 | 145篇 |
1999年 | 153篇 |
1998年 | 233篇 |
1997年 | 149篇 |
1996年 | 136篇 |
1995年 | 125篇 |
1994年 | 113篇 |
1993年 | 101篇 |
1992年 | 81篇 |
1991年 | 65篇 |
1990年 | 67篇 |
1989年 | 61篇 |
1988年 | 50篇 |
1987年 | 55篇 |
1986年 | 42篇 |
1985年 | 46篇 |
1984年 | 43篇 |
1983年 | 63篇 |
1982年 | 37篇 |
1981年 | 33篇 |
1980年 | 36篇 |
1979年 | 28篇 |
1978年 | 43篇 |
1977年 | 35篇 |
1976年 | 32篇 |
1975年 | 25篇 |
1974年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
Zusammenfassung 1. Respirometrische Messungen der spezifisch-dynamischen Wirkung (SDW) bei körnerfressenden Singvögeln zeigen, daß die SDW mit sinkenden Umgebungstemperaturen relativ kleiner wird. 2. Der Existenzstoffwechsel körnerfressender Singvögel weist nahrungsspezifische Unterschiede auf. Diese Unterschiede sind durch den unterschiedlichen SDW-Effekt verschiedener Nährstoffzusammensetzungen verursacht und sind von der Umgebungstemperatur abhängig: Sinken die Umgebungstemperaturen, werden die Unterschiede relativ kleiner. Diese Ergebnisse weisen darauf hin, daß körnerfressende Singvögel in der Lage sind, mit der SDW die Thermoregulation zu unterstützen.
Can the specific dynamic action (SDA) contribute to the thermoregulation of granivorous song birds?
Summary 1. Respirometric measurements of the specific dynamic action (SDA) of granivorous song birds show that the SDA decreases relatively with dropping temperatures. 2. The existence metabolic rates of granivorous song birds show diet-related differences. These differences are caused by the SDA of different food types and are depend on the ambient temperature: With dropping ambient temperature differences become relatively smaller. These results indicate that granivorous song birds are able to use the SDA in thermoregulation.相似文献
132.
Christian Brochmann 《Nordic Journal of Botany》1992,12(6):657-673
Pollen and seed morphology were examined in 54 diploid and allopolyploid populations representing 15 Nordic species of the taxonomically complex genus Draba. The pollen size was strongly correlated with chromosome number, but it was unreliable for inferring the exact ploidal level of individual populations. Five main pollen types were recognized based on sculpturing of the exine. Two populations of D. lactea had conspicuously different exine sculpturing, supporting a previous hypothesis based on molecular data that this hexaploid is polyphyletic and has been derived from various combinations of diploid species. The pollen morphological data are also consistent with the hypotheses that the 16-ploid D. corymbosa is an intersectional allopolyploid derived from the sections Draba and Chrysodraba , that the hexaploid D. cinerea is a progenitor of the decaploid D. arctica , and that D. crassifolia and D. adamsii represent isolated allopolyploid lineages. The seed size and weight were only weakly correlated with chromosome number, but showed a close relationship to habitat ecology. The largest seeds were observed in species typical of closed habitats, in which seedling establishment probably is limited by competition with mosses. The seed coat surface had a characteristic verrucate reticulum, but the differentiation among species was vague or absent. The seed size and colour, however, distinguish some species, e.g., in the D. alpina complex, which otherwise are morphologically very similar. 相似文献
133.
Almuth-Sigrun Jandel Helmut Hustedt Christian Wandrey 《Applied microbiology and biotechnology》1982,15(2):59-63
Summary L-alanine was produced continuously from fumaric acid by means of soluble aspartase and L-aspartate--decarboxylase. The two reaction steps were carried out in two membrane reactors in series at different pH and temperature. The retention of the soluble enzymes within the reactor vessels was achieved by means of ultrafiltration membranes. 相似文献
134.
The only representatives ofRubiaceae-Rubieae in Madagascar are five species ofGalium. G. thunbergianum andG. chloroionanthum are essentially afromontane species, ± widely distributed in both the African mainland and Madagascar. The new speciesG. andringitrense andG. ankaratrense are endemic to Madagascar but show close affinities to two afromontane—afroalpine groups from the African mainland, theG. simense—G. ruwenzoriense andG. glaciale complex respectively.G. polyacanthum (new combination) exhibits certain primitive morphological traits and appears to be an old Madagascan endemic without close allies. New chromosome counts for populations from the African mainland demonstrate thatG. chloroionanthum andG. simense are 4x (x=11). Distribution patterns and origins of theGalium species in Madagascar and their relationships with African taxa are discussed. 相似文献
135.
Surface Changes in Mild Steel Coupons from the Action of Corrosion-Causing Bacteria 总被引:7,自引:4,他引:3 下载免费PDF全文
Christian O. Obuekwe Donald W. S. Westlake Fred D. Cook J. William Costerton 《Applied microbiology》1981,41(3):766-774
Changes which occur on the surface of mild steel coupons submerged in cultures of an Fe(III)-reducing bacterium, isolated from corroded pipe systems carrying crude oil, were studied microscopically to investigate the interaction between the corrosion-causing bacterium and the corroding mild steel coupon. Under micro-aerobic conditions and in the absence of the bacteria, a dense, crystalline, amorphous coat formed on the surface of the steel coupons. In the presence of bacteria the surface coat was extensively removed, exposing the bare metal to the environment. After about 2 weeks of exposure, the removal of the surface coating was followed by colonization of the metal surface by the bacteria. Colonization was mediated by fibrous, exopolysaccharidic material formed by the bacteria. Extension of studies to other bacteria isolated from crude oil and corroded pipes reveals that the formation of exopolysaccharide fibers and possession of adherent properties are common characteristics of bacteria from crude oil systems. 相似文献
136.
137.
Elisabeth Tillberg Christian Dons May Haugstad Stein Nilsen 《Physiologia plantarum》1981,52(4):401-406
The effects of abscisic acid (ABA) on photosynthesis, dark respiration, and photorespiration were studied in Lemna gibba L. plants. The initial concentration of ABA in the nutrient solution was 10−7 M and in a few experiments, 10−6 M. The cultures were grown in the same solution for time periods ranging from one hour to 12 days. Net photosynthesis, measured as CO2 uptake by infrared gas analyser technique, was inhibited after four hours of ABA treatment and reached a minimum after four to seven days depending on the time of the year. After 12 days a substantial recovery of photosynthesis was observed. Dark respiration was significantly stimulated after two to seven days of ABA treatment but then returned to the control level. The transient effects of ABA on photosynthesis and dark respiration corresponded to the previously measured time course of [14 C]-ABA uptake by Lemna . Photorespiration measured as oxygen inhibition of photosynthesis was not affected by ABA. 相似文献
138.
Louis Piovetti Christian Francisco Ginette Pauly Otmane Benchabane Colette Bernard-Dagan Anne Diara 《Phytochemistry》1981,20(6):1299-1302
Analysis of wood essential oil of Cupressus dupreziana revealed 26 components: 13 monoterpenes and 13 sesquiterpenes. The main components were carv 相似文献
139.
Christian Gaillard 《Geobios》1980,13(3):465-471
A new trace fossil corresponding to a spiral burrow is described in the Upper Valanginian of the Ardèche area (France). It seems to be restricted to marine hemipelagic facies (outer shelf and upper slope). 相似文献
140.
Monique Boloukhre Christian Thomas Viviane Heilporn-Pohl Franoise Hanocq J. Brachet 《Experimental cell research》1980,130(2):291-295
This study shows, by means of autoradiography, that RNA polymerase I activity is present in some of the nuclei isolated from Xenopus blastulae. This activity is localized in one or two nucleoli which have a diameter of at least 1.5 μm. The ratio between nucleolar and total nuclear grain counts allows a quantitative estimation of RNA polymerase I activity relative to total RNA polymerase activity at the blastula stage. 相似文献