首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   722篇
  免费   68篇
  2023年   7篇
  2022年   12篇
  2021年   15篇
  2020年   9篇
  2019年   8篇
  2018年   19篇
  2017年   12篇
  2016年   19篇
  2015年   29篇
  2014年   46篇
  2013年   54篇
  2012年   53篇
  2011年   58篇
  2010年   35篇
  2009年   29篇
  2008年   33篇
  2007年   49篇
  2006年   36篇
  2005年   42篇
  2004年   34篇
  2003年   34篇
  2002年   26篇
  2001年   6篇
  2000年   8篇
  1999年   10篇
  1998年   5篇
  1996年   3篇
  1994年   5篇
  1993年   5篇
  1992年   5篇
  1991年   6篇
  1990年   4篇
  1989年   3篇
  1988年   4篇
  1987年   3篇
  1985年   2篇
  1983年   4篇
  1982年   2篇
  1981年   5篇
  1977年   2篇
  1974年   3篇
  1973年   4篇
  1972年   5篇
  1971年   5篇
  1970年   5篇
  1969年   2篇
  1967年   2篇
  1963年   2篇
  1956年   2篇
  1954年   3篇
排序方式: 共有790条查询结果,搜索用时 31 毫秒
1.
2.
A simple procedure for obtaining useful narrow-pH-range ampholytes from inexpensive laboratory-synthesized ampholytes by preparative isoelectric focusing in Pevikon is described. The narrow range ampholytes prepared in this way are comparable to commercial ampholyte preparation as judged by conductivity, buffer capacity, pH gradient formation, and resolving power. These inexpensive narrow-range ampholytes are particularly well suited to preparative isoelectric focusing applications requiring large quantities of ampholytes.  相似文献   
3.
Zusammenfassung Mit Hilfe von autoradiographischen und elektrophoretischen Methoden wurde die Dottereinlagerung in den wachsenden Oocyten vonMusca domestica untersucht. Sie beginnt nach 30 min im Autoradiogramm sichtbar zu werden. Durch ihre Färbbarkeit und Markierung konnte die Dotterfraktion im Pherogramm von Ovar und Hämolymphe eines mittleren Wachstumsstadiums (Stadium 3) nachgewiesen werden. Nach Abschlu\ der Vitellogenese tritt sie in der Hämolymphe nicht mehr auf. Die Einlagerung der Dotterproteine wird durch Actinomycin gestört, dagegen läuft ihre Synthese nahezu unbeeinflu\t weiter. Die Transporthemmung kann als bisher unbekannter Nebeneffekt des Actinomycins gedeutet werden.
Synthesis of haemolymph proteine and the uptake of the yolk fraction in the oocyte during Actinomycin-treatment. (Studies onMusca domestica)
Summary By means of radioautographic and electrophoretic techniques yolk protein uptake in the growing oocytes ofMusca domestica was investigated. After 30 min yolk protein becomes visible in the radioautograms. By stainability and labeling the yolk fraction could be demonstrated in the pherogram of ovary and haemolymph in an intermediate developmental stage (stage 3). After the end of vitellogenesis it does not appear in the haemolymph. The yolk protein uptake is inhibited by Actinomycin, but the synthesis goes on nearly as normal. This inhibition can be interpretated as a new accessory effect of Actinomycin.
  相似文献   
4.
Bier  Karlheinz 《Chromosoma》1965,16(1):58-69
Summary The influence of O2-deprivation and reduction of temperature on the incorporation of the RNA-precursors 3H-uridine und 3H-cytidine is investigated in various tissues of the larvae and in the ovaries of adults of the housefly Musca domestica L. While RNA-synthesis in most of the tissues is strongly reduced under anaerobic conditions, synthesis continues in a moderate extent in muscle cell nuclei and nurse cell nuclei. The RNA-macromolecules (mRNA and rRNA), however, do not migrate into the cytoplasma. RNA-synthesis within the cell nucleus is less affected by a sudden reduction of temperature than the passage of RNA through the nuclear membrane which is reduced to a very low rate. The macromolecular RNA, therefore, does not diffuse into the cytoplasma but is transported actively through the nuclear envelope. The malformations caused by anaerobiosis during embryogenesis are brought in connexion with the active RNA-transport through the nuclear envelope and the separation of transport and synthesis.

Herrn Professor Dr. Hans Bauer zum 60. Geburtstag gewidmet.

Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.  相似文献   
5.
Zusammenfassung Arbeiterinnen vonMyrmica ruginodis Nyl. werden im weisellosen Zustand fertil. Sie legen aber keine Eier, wenn sie mehr als 3 Larven je Arbeiterin zu versorgen haben (Mamsch, 1965). Arbeiterinnengruppen wurden mit und ohne Larven von der Königin abgetrennt. In den eierlegenden Gruppen wurde die erneut zugesetzte eigene Königin entweder nicht beachtet oder angegriffen. In den Gruppen, in denen die Arbeiterinnen durch Larvenpflege unfruchtbar blieben, wurde die Königin intensiv beleckt und in das engere Nest eingetragen. Isolierte eierlegende Arbeitergruppen zeigten im Gegensatz zu Arbeiterinnen mit inaktiven Ovarien keine Tendenz, sich mit der Königingruppe zu vereinigen. Das veränderte Verhalten der Arbeiterinnen gegenüber der Königin ist demnach nicht vom Zeitraum der Weisellosigkeit abhängig. Es wurde nur bei eierlegenden Arbeiterinnen beobachtet.
Summary Workers ofMyrmica ruginodis Nyl. start laying eggs after being separated from their queen. No deposition of eggs occurs in groups in which each worker has to feed 3 or more larvae (Mamsch, 1965). Worker groups rearing larvae and those without brood were separated from the queen.When the queen was put again into an egg-laying worker group, either no attention was paid to her or she was attacked. In groups of workers sterile due to rearing larvae the queen was licked intensively and carried into the nest cavity. Fertile worker groups showed no tendency to join the queen group. The change in the workers' behaviour does not depend on the time of the separation from the queen. It only occurs in groups of fertile workers.

Résumé Des ouvrières deMyrmica ruginodis Nyl. deviennent fertiles après avoir été séparées de la reine. Mais elles ne pondent pas d'ufs, si elles ont chacune trois larves ou plus à nourrir (Mamsch, 1965). Des groupes d'ouvrières, d'une part avec larves et d'autre part sans, ont été séparés de la reine. Les groupes d'ouvrières pondeuses n'attachaient pas d'attention à la reine replacée dans le nid ou encore l'attaquaient. Dans les groupes où les ouvrières étaient restées infertiles à cause du nourrissement du couvain, la reine était léchée d'une façon intensive et portée à l'intérieur du nid. A l'opposé des ouvrières stériles, les groupes d'ouvrières pondeuses isolées ne montraient aucune tendance à joindre le groupe de la reine. Le changement du comportement des ouvrières ne dépend donc pas de la durée de l'état orphelin; il n'est observé que chez les ouvrières pondeuses.


Herrn Prof. Dr.K. Gösswald, zum 60. Geburtstag gewidmet.  相似文献   
6.
Chromosomal mosaicism in chorionic villus samples (CVS) may arise from different sources, such as clonal diversity within the chorionic tissue or contamination with maternal cells. To determine the origin of karyotyped cells, we compared the immunocytochemical features of mitotic cells in CVS long-term cultures with histological sections of their tissue of origin, i.e. chorionic villi. Immunolabelling of intermediate filaments specific for epithelial cells (cytokeratin) and mesenchymal cells (vimentin) established that mitoses yielded from CVS long-term cultures indeed stem from independently growing clones derived from both the epithelial and mesenchymal parts of the chorionic villi. Thus, mosaicism in CVS cultures may reflect true genetic heterogeneity within the biopsy. However, epithelial chorionic cells undergo in vitro metaplasia leading to co-expression of cytokeratins and vimentin. Fetal-specific immune markers (-HCG and SP1-glycoprotein) are not reliably expressed in CVS cell culture.  相似文献   
7.
A mechanistic understanding of factors that structure spatiotemporal community composition is a major challenge in microbial ecology. Our study of microbial communities in the headwaters of three freshwater stream networks showed significant community changes at the small spatial scale of benthic habitats when compared to changes at mid- and large-spatial scales associated with stream order and catchment. Catchment (which included temperate and tropical catchments) had the strongest influence on community composition followed by habitat type (epipsammon or epilithon) and stream orders. Alpha diversity of benthic microbiomes resulted from interactions between catchment, habitat, and canopy. Epilithon contained relatively more Cyanobacteria and algae while Acidobacteria and Actinobacteria proportions were higher in epipsammic habitats. Turnover from replacement created ~60%–95% of beta diversity differences among habitats, stream orders, and catchments. Turnover within a habitat type generally decreased downstream indicating longitudinal linkages in stream networks while between habitat turnover also shaped benthic microbial community assembly. Our study suggests that factors influencing microbial community composition shift in dominance across spatial scales, with habitat dominating locally and catchment dominating globally.  相似文献   
8.
Spatial and size distribution of micro-organisms and their ETSactivity has been investigated in Ligurian Sea surface watersalong the Nice-Calvi transect across frontal areas from 18 to37 km offshore (TOMOFRONT 1 and 2 cruises, April 1988 and April-May1989 respectively). Aplastidic and plastidic nanoflagellatesand aplastidic picoflagellates were present in numbers closeto 0.25 x 104 cells ml–1, whereas plastidic picoflagellatesaccounted for about half this number. Correlations have beenevidenced between plastidic and aplastidic micro-organisms withinthe same size group, suggesting that they belong to a well-definedecosystem. The highest correlation between total ETS activityand abundance of the considered size groups was observed fornanoflagellates (r = 0.94, n = 22, and r = 0.90, n = 22 foraplastidic and plastidic cells respectively). The importanceof the role of nanoflagellates in surface waters, with respectto the overall ETS activity, was supported by results from sizefractionation which assigned to the 3–10 µm sizerange a 73.3% contribution to overall ETS activity. Resultsemphasize analysing global ETS activity of natural samples inorder to derive relationships between the different populationspresent in the sampled water. It is suggested that couplingflow cytometry to the ETS approach should be very helpful inthat respect.  相似文献   
9.
34 persons with G-6-PD deficiency were diagnosed, and the pathological enzyme-variants of red blood cells were characterized according to the recommendations of WHO. We conclude from the differing residual G-6-PD-activities in red blood cells of the propositi and the differing reactivity of the enzyme in kinetic and physicochemical characterizations that a multiple variety of rare pathological G-6-PD variants exists in the GDR. Using the estimated enzymeparameters it was not possible in all cases to compare directly the newly demonstrated G-6-PD variants with cases already described in the literature. In addition, the differing combinations of parameters render a classification more difficult.  相似文献   
10.
A simple, sensitive method for measuring Nτ-methylhistidine in biological samples using a deuterated internal standard and methane chemical ionization gas chromatography-mass spectrometry is described. After sample preparation, a single analysis can be completed in 3 min; analysis in duplicate, including sample preparation for 40 samples, can be completed at a rate of 15 min per sample. Nanomole amounts of Nτ-mmethylhistidine in urine or plasma samples are determined with a precision of 0.5%. Picomole amounts, released during in vitro rat epitrochlaris muscle incubations, are measured with a precision of 10%.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号