全文获取类型
收费全文 | 3030篇 |
免费 | 193篇 |
专业分类
3223篇 |
出版年
2020年 | 19篇 |
2019年 | 18篇 |
2018年 | 32篇 |
2017年 | 29篇 |
2016年 | 45篇 |
2015年 | 83篇 |
2014年 | 109篇 |
2013年 | 154篇 |
2012年 | 149篇 |
2011年 | 158篇 |
2010年 | 93篇 |
2009年 | 81篇 |
2008年 | 140篇 |
2007年 | 186篇 |
2006年 | 173篇 |
2005年 | 156篇 |
2004年 | 154篇 |
2003年 | 138篇 |
2002年 | 131篇 |
2001年 | 28篇 |
2000年 | 20篇 |
1999年 | 35篇 |
1998年 | 33篇 |
1997年 | 34篇 |
1996年 | 31篇 |
1995年 | 37篇 |
1994年 | 27篇 |
1993年 | 41篇 |
1992年 | 19篇 |
1991年 | 21篇 |
1990年 | 27篇 |
1989年 | 29篇 |
1988年 | 36篇 |
1987年 | 30篇 |
1985年 | 31篇 |
1984年 | 27篇 |
1983年 | 40篇 |
1982年 | 37篇 |
1981年 | 36篇 |
1980年 | 40篇 |
1979年 | 30篇 |
1978年 | 33篇 |
1977年 | 28篇 |
1976年 | 23篇 |
1975年 | 24篇 |
1973年 | 25篇 |
1972年 | 18篇 |
1971年 | 18篇 |
1970年 | 21篇 |
1967年 | 18篇 |
排序方式: 共有3223条查询结果,搜索用时 15 毫秒
1.
Helmut Grimm 《Behavioural processes》1981,6(1):63-84
The endemic Anatolian cyprinodonts Aphanius chantrei, A. (Kosswigichtys) asquamatus, and A. anatoliae show definite interspecific differences in their territorial and sexual behaviour under laboratory conditions. Intraspecific differences were found in the nine populations of A. anatoliae investigated.A. chantrei and Kosswigichthys show almost the same territorial behaviour. In A. anatoliae territoriality is found in three populations; the remaining six populations show no territoriality.The sexual behaviour consists of visual display elements and of elements which enable the fish to keep close contact without actually touching each other. The sequence of elements can be variable. Only two populations of A. anatoliae have retained display elements; the remaining seven populations have lost all of them.A correlation is discussed between biotope conditions and sexual behaviour. Display and territorial behaviour may have become superfluous in extreme, sulphate-containing habitats, where a lack of flora has led to a lack of spawning sites. Under changing breeding conditions the newly evolved element with fish staying close together (male underneath the female) may have replaced the former display elements. 相似文献
2.
Claus König und Helmut Kaiser 《Journal of Ornithology》1985,126(4):443
Summary After a decrease and extinction due to deforestation the population has been reestablished by releasing captive-bred owls. Now about 40 territories are occupied with an average density of 0,8–1,0 territories/10 km2. Highest density: 17 territories/80 km2. 相似文献
3.
Analysis of the energy metabolism after incubation of Saccharomyces cerevisiae with sulfite or nitrite 总被引:1,自引:0,他引:1
After addition of 5 mM sulfite or nitrite to glucose-metabolizing cells of Saccharomyces cerevisiae a rapid decrease of the ATP content and an inversely proportional increase in the level of inorganic phosphate was observed. The concentration of ADP shows only small and transient changes. Cells of the yeast mutant pet 936, lacking mitochondrial F1ATPase, after addition of 5 mM sulfite or nitrite exhibit changes in ATP, ADP and inorganic phosphate very similar to those observed in wild type cells. They key enzyme of glucose degradation, glyceraldehyde-3-phosphate dehydrogenase was previously shown to be the most sulfiteor nitrite-sensitive enzyme of the glycolytic pathway. This enzyme shows the same sensitivity to sulfite or nitrite in cells of the mutant pet 936 as in wild type cells. It is concluded that the effects of sulfite or nitrite on ATP, ADP and inorganic phosphate are the result of inhibition of glyceraldehyde-3-phosphate dehydrogenase and not of inhibition of phosphorylation processes in the mitochondria. Levels of GTP, UTP and CTP show parallel changes to ATP. This is explained by the presence of very active nucleoside monophosphate kinases which cause a rapid exchange between the nucleoside phosphates. The effects of the sudden inhibition of glucose degradation by sulfite or nitrite on levels of ATP, ADP and inorganic phosphate are discussed in terms of the theory of Lynen (1942) on compensating phosphorylation and dephosphorylation in steady state glucose metabolizing yeast.Abbreviations ATP
adenosine triphosphate
- ADP
adenosine diphosphate
- AMP
adenosine monophosphate
- Pi
inorganic orthophosphate
Dedicated to Prof. Dr. Hans Grisebach on the occasion of his sixtieth birthday 相似文献
4.
5.
Helmut Leonhardt 《Cell and tissue research》1967,79(2):172-184
Zusammenfassung In der vorderen Wand des IV. Ventrikels und des Canalis centralis gegenüber der Area postrema liegen beim Kaninchen Nervenzellen, deren Fortsätze intraventrikulär mit 6 großen Protoplasmakugeln endigen, die mit Mitochondrien angefüllt sind. Das Perikaryon ist reich an Ergastoplasma, alle Teile der Zelle enthalten leere, 600 bis 1500 Å messende, und ein dichtes Granulum enthaltende, 650–1000 Å große Bläschen. Vermutlich werden Stoffe in den Liquor cerebrospinalis abgegeben. Dem Plasmalemm der Nervenzellen liegen Synapsen an.
Die Untersuchung wurde mit dankenswerter Unterstützung durch die Deutsche Forschungsgemeinschaft durchgeführt. 相似文献
Summary In the anterior wall of the IVth ventricle, opposite to the area postrema, nerve cells are found. Their processes end with spheroid swellings extending into the ventricle. These bulbs contain a large number of mitochondria, while ergastoplasm is seen in the perikaryon. The cytoplasm of the whole cell shows vesicles (600–1500 Å) and dense-core vesicles (650–1000 Å) which might be extruded into the liquor cerebrospinalis. The plasmalemma of the perikaryon is in contact with synapses.
Die Untersuchung wurde mit dankenswerter Unterstützung durch die Deutsche Forschungsgemeinschaft durchgeführt. 相似文献
6.
Summary The leaf shape of the mutantfiliformis (fil) ofHyoscyamus niger L. is strongly modified by external factors (like nutrition and light) as well as by the height of insertion. The name filiformis refers to thread-like leaves which always occur in the inflorencence; they may also be formed in the vegetative region, especially under short day conditions. Other leaves may have a small rhombic blade or a larger blade with irregular edges and deep incisions. Even pinnate leaves have been found. In contrast to the leaves of normalHyoscyamus, all mutant leaves (hypsophylls included) have a stalk-like basal portion that seems to be homologous to the basal part of the normal blade. This mutant is caused by one recessive factor which is linked neither toann nor topall.the submarginal initials of the normalHyoscyamus blade were always found dividing according to the periclinal-anticlinal type, while in the mutant the activity of the submarginal initials frequently resulted in a primarily biseriate mesophyll (so-called double-edged segmentation).This is apparently the first time that gene control of the mode of submarginal blade growth has been observed. Further differences between mutant and normalHyoscyamus concern the venation, the lengths of palisade cells and of stomata guard cells, the frequency of stomata per mm2, and the thickness of the blade.
Mit 7 Textabbildungen 相似文献
Mit 7 Textabbildungen 相似文献
7.
We have purified for the first time from green leaves a multifunctional protein (MFP) involved in fatty acid -oxidation. The protein, designated MFP IV, was extracted from green leaves of three-week-old cucumber (Cucumis sativus L.) plants. Chromatography on cation exchanger, separation on hydroxylapatite, and fast-protein liquid chromatography on Phenylsuperose led to a more than 7000-fold purification and to the isolation of an apparently homogeneous 80-kDa monomeric protein. This protein is immunologically related to the glyoxysomal MFP II, as evidenced by immunodecoration with antiserum raised against MFP II. Comparison of molecular masses of all MFPs presently known revealed that the MFP prepared from green leaves (MFP IV) is distinct from MFP II (76.5 kDa) and MFP I (74 kDa) from dark-grown cotyledons. By including other properties in this comparison, we demonstrated that MFP IV can also be distinguished from the glyoxysomal MFP III (81 kDa) and the bacterially expressed MFP-a (80 kDa). Moreover, MFP IV is a constituent of leaf peroxisomes and contains the activities of 2-enoyl-CoA hydratase (EC 4.2.1.17),l-3-hydroxyacyl-CoA dehydrogenase (EC 1.1.1.35) and 3-hydroxyacyl-CoA epimerase.Abbreviation MFP
multifunctional protein
This work was supported by grants from the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie. 相似文献
8.
Small intensely fluorescent (SIF) cells are paraganglionic cells derived from sympathicoblasts which may serve as interneurons,
endo-/paracrine cells or arterial chemoreceptors within sympathetic ganglia. Like paraganglionic cells of other locations,
e.g., carotid body glomus cells, they are responsive to hypoxia. Recent studies on glomus cells and other hypoxia-sensing
cells suggested the involvement of a b
558
-type cytochrome and intracellular generation of H2O2 in the process of oxygen sensing. In the present study, we demonstrate the occurrence of the small subunit of cytochrome b
558
, p22phox, in SIF cells of guinea-pig sympathetic ganglia by immunohistochemistry using two different antisera. H2O2 production was monitored in explanted intact superior cervical ganglia of 2-day-old rats by confocal laser scanning analysis
of rhodamine 123 fluorescence generated due to oxidation of dihydrorhodamine 123 by H2O2. Using this technique, SIF cell clusters appeared as sites of highest H2O2 production within the ganglia. Thus, SIF cells exhibit two key features of an oxidase system generating reactive oxygen species.
This may be involved in the proposed chain of events in oxygen sensing, but alternative cellular functions of this system
have also to be considered.
Accepted: 19 September 1996 相似文献
9.
Frieder Schauer Kirsten Henning Helmut Pscheidl Rolf M. Wittich Peter Fortnagel Heinz Wilkes Volker Sinnwell Wittko Francke 《Biodegradation》1995,6(2):173-180
Trichosporon beigelii SBUG 752 was able to transform diphenyl ether. By TLC, HPLC, GC, GC-MS, NMR- and UV-spectroscopy, several oxidation products were identified. The primary attack was initiated by a monooxygenation step, resulting in the formation of 4-hydroxydiphenyl ether, 2-hydroxydiphenyl ether and 3-hydroxydiphenyl ether (48:47:5). Further oxidation led to 3,4-dihydroxydiphenyl ether. As a characteristic product resulting from the cleavage of an aromatic ring, the lactone of 2-hydroxy-4-phenoxymuconic acid was identified. The possible mechanism of ring cleavage to yield this metabolite is discussed. 相似文献
10.
Helmut Kroll 《Vegetation History and Archaeobotany》1995,4(1):51-66
Publications on archaeological remains of cultivated plants have been collected, mainly from 1992 and 1993, with some earlier and later ones. A list is given of the finds according to taxon, country, site and age. 相似文献