全文获取类型
收费全文 | 11009篇 |
免费 | 885篇 |
国内免费 | 3篇 |
出版年
2022年 | 50篇 |
2021年 | 113篇 |
2020年 | 74篇 |
2019年 | 103篇 |
2018年 | 118篇 |
2017年 | 106篇 |
2016年 | 218篇 |
2015年 | 349篇 |
2014年 | 408篇 |
2013年 | 566篇 |
2012年 | 619篇 |
2011年 | 646篇 |
2010年 | 451篇 |
2009年 | 384篇 |
2008年 | 542篇 |
2007年 | 605篇 |
2006年 | 554篇 |
2005年 | 607篇 |
2004年 | 541篇 |
2003年 | 527篇 |
2002年 | 549篇 |
2001年 | 183篇 |
2000年 | 153篇 |
1999年 | 169篇 |
1998年 | 186篇 |
1997年 | 118篇 |
1996年 | 129篇 |
1995年 | 147篇 |
1994年 | 135篇 |
1993年 | 134篇 |
1992年 | 136篇 |
1991年 | 118篇 |
1990年 | 147篇 |
1989年 | 128篇 |
1988年 | 113篇 |
1987年 | 107篇 |
1986年 | 110篇 |
1985年 | 107篇 |
1984年 | 108篇 |
1983年 | 97篇 |
1982年 | 82篇 |
1981年 | 88篇 |
1980年 | 76篇 |
1979年 | 75篇 |
1978年 | 70篇 |
1977年 | 58篇 |
1976年 | 62篇 |
1975年 | 56篇 |
1974年 | 57篇 |
1968年 | 46篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
The conformation of reduced bovine pancreatic trypsin inhibitor (R-BPTI) under reducing conditions was monitored by measurements of nonradiative excitation energy-transfer efficiencies (E) between a donor probe attached to the N-terminal Arg1 residue and an acceptor attached to one of the lysine residues (15, 26, 41, or 46) [Amir, D., & Haas, E. (1987) Biochemistry 26, 2162-2175]. High-excitation energy-transfer efficiencies that approach those found in the native state were obtained for the reduced labeled BPTI derivatives in 0.5 M guanidine hydrochloride (Gdn.HCl) and 4 mM DTT. Unlike the dependence expected for a random coil chain, E does not decrease as a function of the number of residues between the labeled sites. The efficiency of energy transfer between probes attached to residues 1 and 15 in the reduced state is higher than that found for the same pair of sites in the native state or reduced unfolded (in 6 M Gdn.HCl) state. This segment also shows high dynamic flexibility. These results indicate that the overall structure of reduced BPTI under folding (but still reducing) conditions shows a high population of conformers with interprobe distances similar to those of the native state. Reduced BPTI seems to be in a molten globule state characterized by a flexible, compact structure, which probably reorganizes into the native structure when the folding is allowed to proceed under oxidizing conditions. 相似文献
82.
The Evolution of Restricted Recombination and the Accumulation of Repeated DNA Sequences 总被引:19,自引:6,他引:13
下载免费PDF全文
![点击此处可从《Genetics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We suggest hypotheses to account for two major features of chromosomal organization in higher eukaryotes. The first of these is the general restriction of crossing over in the neighborhood of centromeres and telomeres. We propose that this is a consequence of selection for reduced rates of unequal exchange between repeated DNA sequences for which the copy number is subject to stabilizing selection: microtubule binding sites, in the case of centromeres, and the short repeated sequences needed for terminal replication of a linear DNA molecule, in the case of telomeres. An association between proximal crossing over and nondisjunction would also favor the restriction of crossing over near the centromere. The second feature is the association between highly repeated DNA sequences of no obvious functional significance and regions of restricted crossing over. We show that highly repeated sequences are likely to persist longest (over evolutionary time) when crossing over is infrequent. This is because unequal exchange among repeated sequences generates single copy sequences, and a population that becomes fixed for a single copy sequence by drift remains in this state indefinitely (in the absence of gene amplification processes). Increased rates of exchange thus speed up the process of stochastic loss of repeated sequences. 相似文献
83.
Wolfgang Hofmann 《Hydrobiologia》1986,143(1):119-121
A succession of morphs from Bosmina coregoni f. coregoni to B. c. f. thersites, which vary in shell and antennule characters, occurred in an undated 176 cm long sediment core from the Neversdorfer See (N. Germany). 相似文献
84.
Role of Pili (Fimbriae) in Attachment of Bradyrhizobium japonicum to Soybean Roots 总被引:11,自引:2,他引:9
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Pili (fimbriae) were observed on cells of each of the five strains of Bradyrhizobium japonicum and the one strain of Rhizobium trifolii examined. Pili on B. japonicum were about 4 nm in diameter and polarly expressed. Piliated cells were estimated by transmission electron microscopy and hydrophobic attachment to polystyrene to constitute only a small percentage of the total population. The proportion of piliated cells in these populations was dependent on culture age in some strains. Piliated B. japonicum cells were selectively and quantitatively removed from suspension when cultures were incubated with either soybean roots or hydrophobic plastic surfaces, indicating that pili were involved in the attachment of the bacteria to these surfaces. Pili from B. japonicum 110 ARS were purified and found to have a subunit molecular weight of approximately 21,000. Treatment of B. japonicum suspensions with antiserum against the isolated pili reduced attachment to soybean roots by about 90% and nodulation by about 80%. Pili appear to be important mediators of attachment of B. japonicum to soybean roots under the conditions examined. 相似文献
85.
86.
87.
Summary With the aim of comparing the primary structures of gene products coded for by T-even bacteriophages we constructed clone libraries of the DNAs of bacteriophages T2 and T6. Using hybrid M13 phages carrying the gene for the T4-coded -glucosyl transferase (gt) we isolated corresponding T2 and T6 clones. The nucleotide sequences of the three gt genes and the amino acid sequences derived were compared. The differences between the genes and their products are discussed in terms of structure, function and evolutionary aspects.Abbreviations bp
base pair
- gt
glucosyl transferase
- HMC
5-hydroxymethyl cytosine
- orf
open reading frame
- Xgal
5-bromo-4-chloro-3-indolyl--d-galactoside 相似文献
88.
Zusammenfassung Im Bereich des Meßtischblattes Bad Wildungen (MTB 4820; grundlegende DatenMann 1983,Lübcke &Mann 1984) bevorzugt der Neuntöter Viehweiden (Abb. 3). Reviere an Viehweiden zeigen eine längere kontinuierliche Besetzungszeit (Abb. 4) im Vergleich zu anderen Nutzungsformen. Die Anzahl flügger Jungvögel ist in Viehweiderevieren größer im Gegensatz zu Revieren an Mähwiesen oder Brachflächen (Abb. 5). Dieser Unterschied des Reproduktionserfolges liegt nicht an unterschiedlichen Nahrungsdichten (Abb. 6), sondern an der besseren Zugänglichkeit.
Reihenfolge alphabetisch und umgekehrt proportional zur geleisteten Arbeit: R. B. Auswertung, W. L. & W. M. Kartierung, W. M. Brut- und Nahrungsbiologie. Sonderdruckanforderungen an R. B. 相似文献
Habitat selection in the Red-backed ShrikeLanius collurio
Summary In the area of Bad Wildungen (FRG; Hessia; MTB 4820; basic data inMann 1983,Lübcke &Mann 1984) the Red-backed Shrike selects for pastures (Abb. 3). Territories at pastures show a longer continual occupation in comparison to other land use systems (Abb. 4). The number of fledgelings is higher at pastures in comparison to meadows or fallow land (Abb. 5). This difference is not caused by higher insect densities (Abb. 6) but by better accessible prey due to permanent low vegetation at pastures.
Reihenfolge alphabetisch und umgekehrt proportional zur geleisteten Arbeit: R. B. Auswertung, W. L. & W. M. Kartierung, W. M. Brut- und Nahrungsbiologie. Sonderdruckanforderungen an R. B. 相似文献
89.
A library of Erwinia stewartii DNA was constructed in cosmid pVK100 and used to complement spontaneous and Mu pf7701-induced (designated by the prefix MU) avirulent mutants. Plasmid pES4507 restored water-soaking ability and extracellular polysaccharide (EPS) synthesis to mutants MU14110 and MU2B70 (group I); pES1044 restored water-soaking ability to MU43, MU51, MU136, MU141, and RDF6011 (group II); and pES2144 complemented four spontaneous EPS- mutants (group III). Hybridization of labeled plasmid DNA to Southern blots of genomic DNA from the mutants revealed that a Mu pf7701 insertion was associated with the respective cloned region in all mutants except MU2B70 and MU223. In these strains, the plasmid may be suppressing the avirulent phenotype rather than complementing the mutation. 相似文献
90.
Wolfgang Hagmann Claudio Denzlinger Stephan Rapp Gisbert Weckbecker Dietrich Keppler 《Prostaglandins & other lipid mediators》1986,31(2)
Mercapturic acid formation, an established pathway in the detoxication of xenobiotics, is demonstrated for cysteinyl leukotrienes generated in rats
after endotoxin treatment. The mercapturate N-acetyl-leukotriene E4 (N-acetyl-LTE4) represented a major metabolite eliminated into bile after injection of [3H]LTC4 as shown by cochromatography with synthetic N-acetyl-LTE4 in four different HPLC solvent systems. The identity of endogenoud N-acetyl-LTE4 elicited by endotoxin
was additionally verified by enzymatic deacetylation followed by chemical N-acetylation. The deacetylation was catalyzed by penicillin amidase. Endogenous cysteinyl leukotrienes were quantified by radioimmunoassay after HPLC separation. A N-acetyl-LTE4 concentration of 80 nmol/l was determined in bile collected between 30 and 60 min after endotoxin injection. Under this condition, other cysteinyl leukotrienes detected in bile by radioimmunoassay amounted to less than 5% of N-acetyl-LTE4. The mercapturic acid pathway, leading from the glutathione conjugate LTC4 to N-acetyl-LTE4, thus plays an important role in the deactivation and elimination of these potent endogenous mediators. 相似文献