全文获取类型
收费全文 | 16125篇 |
免费 | 1226篇 |
国内免费 | 10篇 |
专业分类
17361篇 |
出版年
2022年 | 85篇 |
2021年 | 175篇 |
2020年 | 127篇 |
2019年 | 163篇 |
2018年 | 230篇 |
2017年 | 209篇 |
2016年 | 310篇 |
2015年 | 537篇 |
2014年 | 572篇 |
2013年 | 753篇 |
2012年 | 978篇 |
2011年 | 857篇 |
2010年 | 632篇 |
2009年 | 525篇 |
2008年 | 769篇 |
2007年 | 781篇 |
2006年 | 752篇 |
2005年 | 768篇 |
2004年 | 715篇 |
2003年 | 757篇 |
2002年 | 709篇 |
2001年 | 174篇 |
2000年 | 129篇 |
1999年 | 170篇 |
1998年 | 217篇 |
1997年 | 189篇 |
1996年 | 179篇 |
1995年 | 184篇 |
1994年 | 152篇 |
1993年 | 187篇 |
1992年 | 130篇 |
1991年 | 168篇 |
1990年 | 158篇 |
1989年 | 125篇 |
1988年 | 148篇 |
1987年 | 131篇 |
1986年 | 105篇 |
1985年 | 131篇 |
1984年 | 188篇 |
1983年 | 158篇 |
1982年 | 161篇 |
1981年 | 173篇 |
1980年 | 143篇 |
1979年 | 119篇 |
1978年 | 144篇 |
1977年 | 116篇 |
1976年 | 98篇 |
1975年 | 106篇 |
1974年 | 93篇 |
1973年 | 75篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Hans C. Bjerring 《Acta zoologica》1991,72(4):223-232
Abstract The term vomer was coined over four centuries ago to denote one of the 23 bones normally comprising an adult human skull. As time went on more and more craniates were designated vomerate. To date, however, the issue as to whether brachiopterygian fish are or are not vomerate has remained unresolved. Those who consider these fish to be vomerate have suggested at least three different palatal bones as the homologue of the human vomer. Examination of embryological material of Polypterus senegalus shows that this brachiopterygian actually develops a vomer which eventually becomes united indistinguishably with the anterior part of the parasphenoid. The vomer is suggested to have arisen through the fusion of dental plates belonging to a supplementary set of buccopharyngeal denticulate bones. The other subethmoidal bones of the brachiopterygian palate seem likely to be derivatives of the tooth plates which originally were applied to the first two pairs of infrapharyngeals. When these endoskeletal elements were put to use for encapsulation of the organs of smell early in craniate phylogeny, some of the tooth plates that covered their inner surfaces fused to provide anterior palatal bones. Identified at one time or another as vomers, these bones are here termed glochinals and dacnils. 相似文献
32.
33.
Yongru Sun Berthold M. Heil Günter Kahl Hans Willy Kohlenbach 《Plant Cell, Tissue and Organ Culture》1987,8(1):91-100
Calli were initiated from flower buds, gynoecia and inflorescence segments of Haworthia magnifica v. Poelln. and subcultured on solid medium. Two liquid culture steps were necessary to prepare the calli for the isolation of protoplasts capable of sustained cell divisions. Plants were regenerated from protoplast-derived calli. The influence of both the osmolality of the culture media and exudates on the viability of protoplasts and protoplast-derived cell colonies is briefly discussed. 相似文献
34.
Peter Sackl und Georg Rauer 《Journal of Ornithology》1987,128(4):491-494
Zuammenfassung Im niederösterreichischen Waldviertel (200–700 m üNN) stieg der relative Anteil einjähriger von 17,9 auf 50% aller revierverteidigenden Hausrotschwanz- mit zunehmender Meereshöhe. Die Zunahme betrifft vor allem einjährige dercairei-Morphe, während dieparadoxus-Morphe in geringerer Anzahl und gleichförmiger als in allen Höhenbereichen auftrat.
The portion of first-year males in breeding populations of Black Redstarts (Phoenicurus ochruros) and their altitudinal distribution in the Waldviertel, Lower Austria
Summary In 1986, between April 13 and July 5, breeding territories of male Black Redstarts were mapped in Lower Austria (200–700 m NN), with regard to their age (first-year or older) and the plumage types of first-year (femalelike or adult malelike). Due to a greater percentage of femalelike subadult (cairei-type) in higher altitudes, the proportion of first-year was found to increase from 17,9 per cent at 200–300 m to 50 per cent above 600 m. On the contrary adultlike first-year (paradoxus-type) are evenly distributed in smaller numbers over the whole altitudinal range.相似文献
35.
N-Terminal Sequence of Pig Brain Choline Acetyltransferase Purified by a Rapid Procedure 总被引:6,自引:5,他引:1
Axel Braun Yves-Alain Barde Friedrich Lottspeich Werner Mewes Hans Thoenen 《Journal of neurochemistry》1987,48(1):16-21
A procedure is reported that allows the purification and amino terminal sequencing of pig brain choline acetyltransferase. The enzyme (present in extremely low amounts in this tissue) is eluted together with its antibody from an affinity column by a mild pH shift and the resulting enzyme-antibody complex separated by gel electrophoresis. The band corresponding to the enzyme is electroeluted from the gel using volatile solutions allowing the direct determination of the amino acid composition and partial sequence. The first 11 residues are: Pro-Ile-Leu-Glu-Lys-Thr-Pro-Pro-Lys-Met-Ala. 相似文献
36.
Voltage-dependent depolarization of bacterial membranes and artificial lipid bilayers by the peptide antibiotic nisin 总被引:24,自引:0,他引:24
The peptide antibiotic nisin is shown to disrupt valinomycin-induced potassium diffusion potentials imposed on intact cells of Staphylococcus cohnii 22. Membrane depolarization occurred rapidly at high diffusion potentials while at low potentials nisin-induced depolarization was slower suggesting that nisin requires a membrane potential for activity. This assumption was proven in experiments with planar lipid bilayers (black lipid membranes). Macroscopic conductivity measurements indicated a voltage-dependent action of nisin. The potential must have a trans-negative orientation with respect to the addition of nisin (added to the cis-side) and a sufficient magnitude (ca. -100 mV). With intact cells the threshold potential was lower (-50 to -80 mV at pH 7.5 and below -50 mV at pH 5.5). Single channel recordings resolved transient multistate pores, strongly resembling those introduced by melittin into artificial bilayers. The pores had diameters in the range of 0.2–1 nm, and lifetimes of few to several hundred milliseconds. The results indicate that nisin has to be regarded as a membrane-depolarizing agent which acts in a voltage-dependent fashion.Abbreviations BLM
Black lipid membranes
- CCCP
carbonyl cyanide m-chlorophenylhydrazone
- DOPC
dioleoyl phosphatidylcholine
- PS
phosphatidylserine
- TPP+
tetraphenylphosphonium cation 相似文献
37.
38.
39.
Marina Lotti Michael Noah Marina Stöffler-Meilicke Georg Stöffler 《Molecular & general genetics : MGG》1989,216(2-3):245-253
Summary Ribosomal proteins L4, L5, L20 and L25 have been localized on the surface of the 50S ribosomal subunit of Escherichia coli by immuno-electron microscopy. The two 5S RNA binding proteins L5 and L25 were both located at the central protuberance extending towards its base, at the interface side of the 50S particle. L5 was localized on the side of the central protuberance that faces the L1 protuberance, whereas L25 was localized on the side that faces the L7/L12 stalk. Proteins L4 and L20 were both located at the back of the 50S subunit; L4 was located in the vicinity of proteins L23 and L29, and protein L20 was localized between proteins L17 and L10 and is thus located below the origin of the L7/L12 stalk. 相似文献
40.
Extracts of denitrifying bacteria grown anaerobically with phenol and nitrate catalyzed an isotope exchange between 14CO2 and the carboxyl group of 4-hydroxybenzoate. This exchange reaction is ascribed to a novel enzyme, phenol carboxylase, initiating the anaerobic degradation of phenol by para-carboxylation to 4-hydroxybenzoate. Some properties of this enzyme were determined by studying the isotope exchange reaction. Phenol carboxylase was rapidly inactivated by oxygen; strictly anoxic conditions were essential for preserving enzyme activity. The exchange reaction specifically was catalyzed with 4-hydroxybenzoate but not with other aromatic acids. Only the carboxyl group was exchanged; [U-14C]phenol was not exchanged with the aromatic ring of 4-hydroxybenzoate. Exchange activity depended on Mn2+ and inorganic phosphate and was not inhibited by avidin. Ortho-phosphate could not be substituted by organic phosphates nor by inorganic anions; arsenate had no effect. The pH optimum was between pH 6.5–7.0. The specific activity was 100 nmol 14CO2 exchange · min-1 · mg-1 protein. Phenol grown cells contained 4-hydroxybenzoyl CoA synthetase activity (40 nmol · min-1 · mg-1 protein). The possible role of phenol carboxylase and 4-hydroxybenzoyl CoA synthetase in anaerobic phenol metabolism is discussed. 相似文献