全文获取类型
收费全文 | 4145篇 |
免费 | 349篇 |
国内免费 | 1篇 |
出版年
2021年 | 41篇 |
2020年 | 24篇 |
2019年 | 32篇 |
2018年 | 38篇 |
2017年 | 46篇 |
2016年 | 79篇 |
2015年 | 122篇 |
2014年 | 163篇 |
2013年 | 205篇 |
2012年 | 222篇 |
2011年 | 210篇 |
2010年 | 159篇 |
2009年 | 154篇 |
2008年 | 221篇 |
2007年 | 237篇 |
2006年 | 215篇 |
2005年 | 219篇 |
2004年 | 241篇 |
2003年 | 230篇 |
2002年 | 246篇 |
2001年 | 68篇 |
2000年 | 50篇 |
1999年 | 53篇 |
1998年 | 85篇 |
1997年 | 60篇 |
1996年 | 49篇 |
1995年 | 69篇 |
1994年 | 51篇 |
1993年 | 53篇 |
1992年 | 52篇 |
1991年 | 49篇 |
1990年 | 33篇 |
1989年 | 49篇 |
1988年 | 41篇 |
1987年 | 35篇 |
1986年 | 25篇 |
1985年 | 45篇 |
1984年 | 48篇 |
1983年 | 27篇 |
1982年 | 42篇 |
1981年 | 38篇 |
1980年 | 23篇 |
1979年 | 20篇 |
1978年 | 23篇 |
1977年 | 22篇 |
1976年 | 34篇 |
1975年 | 29篇 |
1974年 | 24篇 |
1973年 | 20篇 |
1971年 | 21篇 |
排序方式: 共有4495条查询结果,搜索用时 15 毫秒
1.
2.
Karl-D. Entian Kai-U. Fröhlich Dieter Mecke 《Biochimica et Biophysica Acta (BBA)/General Subjects》1984,799(2):181-186
An electrophoretic method has been devised to investigate the changes in the enzymes and isoenzymes of carbohydrate metabolism, upon adding glucose to derepressed yeast cell. (i) Of the glycolytic enzymes tested, enolase II, pyruvate kinase and pyruvate decarboxylase were markedly increased. This increase was accompanied by an overall increase in glycolytic activity and was prevented by cycloheximide, an inhibitor of protein synthesis. (ii) In contrast, respiratory activity decreased after adding glucose. This decrease was clearly shown to be the result of repression of respiratory enzymes. A rapid decrease within a few minutes of adding glucose, by analogy with the so-called ‘Crabtree effect’, was not observed in yeast. (iii) The gluconeogenic enzymes, fructose-1,6-bisphosphatase and malate dehydrogenase, which are inactivated after adding glucose, showed no significant changes in electrophoretic mobilities. Hence, there was no evidence of enzyme modifications, which were postulated as initiating degradation. However, it was possible to investigate cytoplasmic and mitochondrial malate dehydrogenase isoenzymes separately. Synthesis of the mitochondrial isoenzyme was repressed, whereas only cytoplasmic malate hydrogenase was subject to glucose inactivation. 相似文献
3.
Siegfried Huneck Klaus Schreiber Hans Dieter Grimmecke 《Journal of Plant Growth Regulation》1984,3(1-3):75-84
Seventy-two Schiffs bases, 44 corresponding secondary amines, and 12 N-acetylated compounds were tested on their growth activity. Eighty-one compounds were active as growth inhibitors in at least one of three bioassays. 相似文献
4.
Michael Jae-Yoon Chung Abram L. Friesen Dieter Fox Andrew N. Meltzoff Rajesh P. N. Rao 《PloS one》2015,10(11)
A fundamental challenge in robotics today is building robots that can learn new skills by observing humans and imitating human actions. We propose a new Bayesian approach to robotic learning by imitation inspired by the developmental hypothesis that children use self-experience to bootstrap the process of intention recognition and goal-based imitation. Our approach allows an autonomous agent to: (i) learn probabilistic models of actions through self-discovery and experience, (ii) utilize these learned models for inferring the goals of human actions, and (iii) perform goal-based imitation for robotic learning and human-robot collaboration. Such an approach allows a robot to leverage its increasing repertoire of learned behaviors to interpret increasingly complex human actions and use the inferred goals for imitation, even when the robot has very different actuators from humans. We demonstrate our approach using two different scenarios: (i) a simulated robot that learns human-like gaze following behavior, and (ii) a robot that learns to imitate human actions in a tabletop organization task. In both cases, the agent learns a probabilistic model of its own actions, and uses this model for goal inference and goal-based imitation. We also show that the robotic agent can use its probabilistic model to seek human assistance when it recognizes that its inferred actions are too uncertain, risky, or impossible to perform, thereby opening the door to human-robot collaboration. 相似文献
5.
Laid Douidah Lieven De Zutter Filip Van Nieuwerburgh Dieter Deforce Hanne Ingmer Olivier Vandenberg Anne-Marie Van den Abeele Kurt Houf 《PloS one》2014,9(1)
In this study, we report the screening of four Arcobacter species for the presence of small and large plasmids. Plasmids were present in 9.9% of the 273 examined strains. One Arcobacter cryaerophilus and four Arcobacter butzleri plasmids were selected for further sequencing. The size of three small plasmids isolated from A. butzleri and the one from A. cryaerophilus strains ranged between 4.8 and 5.1 kb, and the size of the large plasmid, isolated from A. butzleri, was 27.4 kbp. The G+C content of all plasmids ranged between 25.4% and 26.2%. A total of 95% of the large plasmid sequence represents coding information, which contrasts to the 20 to 30% for the small plasmids. Some of the open reading frames showed a high homology to putative conserved domains found in other related organisms, such as replication, mobilization and genes involved in type IV secretion system. The large plasmid carried 35 coding sequences, including seven genes in a contiguous region of 11.6 kbp that encodes an orthologous type IV secretion system found in the Wolinella succinogenes genome, Helicobacter pylori and Campylobacter jejuni plasmids, which makes this plasmid interesting for further exploration. 相似文献
6.
7.
8.
Dieter Ammermann 《Chromosoma》1987,95(1):37-43
The variation in DNA content of the micronucleus (germinal nucleus) of Stylonychia lemnae and its relation to the number of chromosomes was examined. Different populations possess similar amounts of micronuclear DNA but there are differences of ±30% between clones of the same population. However, the DNA content varies by about 100% in the micronuclei during the lifetime of a clone. The haploid micronucleus contains 35 or 36 chromosomes which persist in the developing macronucleus anlagen and grow to giant chromosomes. Besides this remaining subset, the micronucleus contains a variable number of germ line restricted chromosomes (mean about 140; range between 100 and 180). The somatic macronucleus eliminates these elements early in its development. The varying number of the germ line restricted chromosomes is responsible for the variation in the micronuclear DNA content. 相似文献
9.
Jürgen Voigt Dieter Mergenhagen Petra Münzner Hans-Peter Vogeler Klaus Nagel 《Planta》1989,178(4):456-462
In light-dark-synchronized cultures of the unicellular green algaChlamydomonas reinhardtii, release of zoospores from the wall of the mother cell normally takes place during the second half of the dark period. The recently isolated mutant ls, however, needs light for the liberation of zoospores when grown photoautotrophically under a 12 h light-12 h dark regime. The light-induced release of zoospores was found to be prevented by addition of the photosystem-II inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea. Furthermore, light dependence of this process was shown to be abolished when the mutant ls was grown either photoautotrophically under a 14 h light-10 h dark regime or in the presence of acetate. Our findings indicate that the light-dependency of zoospore liberation observed in cultures of this particular mutant during photoautotrophic growth under a 12 h light-12 h dark regime might be attributed to an altered energy metabolism. The light-induced release of zoospores was found to be prevented by addition of cycloheximide or chloramphenicol, antibiotics which inhibit protein biosynthesis by cytoplasmic and organellar ribosomes, respectively. Actinomycin D, an inhibitor of RNA synthesis, however, did not affect the light-induced liberation of zoospores.Sporangia accumulate in stationary cultures of the mutant ls. Release of zoospores was observed when these sporangia were collected by centrifugation and incubated in the light after resuspension in fresh culture medium. Since liberation of zoospores was not observed after dilution of the stationary cultures with fresh culture medium, we suppose that components which interfere with the action of the sporangial autolysin are accumulated in the culture medium of the mutant ls.Abbreviation DCMU
3-(3,4-dichlorophenyl)-1,1-dimethylurea 相似文献
10.
Dieter Ehlers Ina Sakowski Werher Mohrig 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1989,159(4):481-489
Summary The high affinity of granulocytes of guinea pig and man to glass surfaces is modified by serum. Native serum contains both an adherence-promoting activity, which is related to complement, and components which reduce the adhesiveness of granulocytes. These components are stable at 56°C for 30 min and are tightly bound to the glass surface. -Lipoproteins are candidates for this adherence reducing ability of serum. Adherence promotion by native serum is mediated by coating the glass surface with C3b/C3bi. Human granulocytes from the peripheral blood adhered to glass surfaces coated by native human or guinea pig serum with C3b/C3bi to almost the same extent as in the presence of native serum, but on guinea pig granulocytes elicited in the peritoneal cavity, a cell surface metalloproteinase degraded the C3b/C3bi, thus reducing the adhesiveness of these cells. This proteinase was inhibited by MgEDTA, DTT, and 1,10-phenanthroline, whereby the high adhesiveness of granulocytes was restored to C3b/C3bi-coated glass.Abbreviations
BA
benzamidine hydrochloride
-
BTS
Bacillus thuringiensis subtoxicus
-
DTT
dithiothreitol
-
EAC
-amino-caproic acid
-
gp
guinea pig
-
LDL
low density lipoproteins
-
SEM
scanning electron microscopy 相似文献