全文获取类型
收费全文 | 3851篇 |
免费 | 480篇 |
国内免费 | 4篇 |
出版年
2021年 | 57篇 |
2020年 | 45篇 |
2019年 | 56篇 |
2018年 | 61篇 |
2017年 | 53篇 |
2016年 | 95篇 |
2015年 | 144篇 |
2014年 | 165篇 |
2013年 | 197篇 |
2012年 | 205篇 |
2011年 | 239篇 |
2010年 | 146篇 |
2009年 | 135篇 |
2008年 | 161篇 |
2007年 | 163篇 |
2006年 | 145篇 |
2005年 | 131篇 |
2004年 | 154篇 |
2003年 | 135篇 |
2002年 | 152篇 |
2001年 | 59篇 |
2000年 | 65篇 |
1999年 | 58篇 |
1998年 | 42篇 |
1997年 | 37篇 |
1996年 | 31篇 |
1995年 | 33篇 |
1994年 | 26篇 |
1993年 | 32篇 |
1992年 | 54篇 |
1991年 | 57篇 |
1990年 | 47篇 |
1989年 | 51篇 |
1988年 | 34篇 |
1987年 | 46篇 |
1986年 | 39篇 |
1985年 | 30篇 |
1984年 | 44篇 |
1983年 | 38篇 |
1982年 | 49篇 |
1981年 | 34篇 |
1980年 | 43篇 |
1977年 | 24篇 |
1976年 | 25篇 |
1975年 | 35篇 |
1974年 | 29篇 |
1973年 | 40篇 |
1972年 | 25篇 |
1970年 | 24篇 |
1969年 | 26篇 |
排序方式: 共有4335条查询结果,搜索用时 31 毫秒
1.
The use of day-old chickens trained on a single-trial passive avoidance task provides a useful paradigm for investigations into cellular mechanisms underlying memory formation. Pharmacological intervention studies indicate that there are three temporally identifiable stages of memory processing leading to the consolidation of information for this task. These stages, designated as short-term (STM; up to 15 min), intermediate-term (ITM; 15-55 min), and long-term (LTM; more than 55 min) memory, have been found to be sequentially dependent (Ng and Gibbs, 1989). In addition, ITM appears to consist of two physiologically distinguishable phases, A and B. Evidence in this laboratory suggests that the crossover between these ITM phases (at 30 min after training) represents a critical time-point for the triggering of LTM. 相似文献
2.
3.
George C. Prendergast Jackson B. Gibbs 《BioEssays : news and reviews in molecular, cellular and developmental biology》1994,16(3):187-191
Advances in the understanding of Ras oncoprotein function suggest novel points for anti-tumor intervention. First, upstream-acting guanine nucleotide exchange factors and SH2/SH3 domain-containing adaptor proteins that link Ras with growth factor receptor tyrosine kinases have recently been characterized. Second, work on downstream-acting Ras effector functions including the Ras GTPase-activating protein (p120GAP) and the Raf kinase has revealed direct biochemical interactions that are functionally required for oncogenic Ras signalling. We summarize progress in these areas and discuss the potential for novel applications to anti-cancer chemotherapy. 相似文献
4.
5.
Understanding the structure and function of protein complexes and multi‐domain proteins is highly important in biology, although the in vitro characterization of these systems is often complicated by their size or the transient nature of protein/protein interactions. To assist in the characterization of such protein complexes, we have developed a modular approach to fusion protein generation that relies upon S ortase‐mediated and Na tive chemical ligation using synthetic Pe ptide linkers (SNaPe) to link two separately expressed proteins. In this approach, we utilize two separate linking steps – sortase‐mediated and native chemical ligation – together with a library of peptide linkers to generate libraries of fusion proteins. We have demonstrated the viability of SNaPe to generate libraries from fusion protein constructs taken from the biosynthetic enzymes responsible for late stage aglycone assembly during glycopeptide antibiotic biosynthesis. Crucially, SNaPe was able to generate fusion proteins that are inaccessible via direct expression of the fusion construct itself. This highlights the advantages of SNaPe to not only access fusion proteins that have been previously unavailable for biochemical and structural characterization but also to do so in a manner that enables the linker itself to be controlled as an experimental parameter of fusion protein generation. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd. 相似文献
6.
Isolation of soil Streptomyces strains capable of degrading humic acids and analysis of their peroxidase activity 总被引:8,自引:0,他引:8
Abstract Fifteen Streptomyces strains capable of decolorizing humic acids in presence of glucose were isolated from soil samples using the dilute suspension technique and spread on agar plates. Six strains, displaying a significant and stable activity, were selected for further characterization. Some features of these isolates (carbon source utilization, enzyme production, antibiotic resistance) were compared with those of the reference strain Streptomyces viridosporus ATCC 39115. Degradation properties studied in batch cultures at pH 7.0 showed that the catabolic activity on humic acids was generally stimulated by incubation with 100% oxygen and was cell surface-associated. Peroxidase activity from cell-free extracts was analysed by using the oxidation of N,N,N′,N′-tetramethyl-phenylene-diamine. PAGE analysis revealed the existence of two major types of peroxidases (molecular mass: about 39.2 and 61.6 kDa), dividing the strains into two groups. The role of cell surface-associated peroxidase activity in the breakdown of humic acids is discussed. 相似文献
7.
Joran Martijn Anders E. Lind Max E. Schön Ian Spiertz Lina Juzokaite Ignas Bunikis Olga V. Pettersson Thijs J. G. Ettema 《Environmental microbiology》2019,21(7):2485-2498
Amplicon sequencing of the 16S rRNA gene is the predominant method to quantify microbial compositions and to discover novel lineages. However, traditional short amplicons often do not contain enough information to confidently resolve their phylogeny. Here we present a cost-effective protocol that amplifies a large part of the rRNA operon and sequences the amplicons with PacBio technology. We tested our method on a mock community and developed a read-curation pipeline that reduces the overall read error rate to 0.18%. Applying our method on four environmental samples, we captured near full-length rRNA operon amplicons from a large diversity of prokaryotes. The method operated at moderately high-throughput (22286–37,850 raw ccs reads) and generated a large amount of putative novel archaeal 23S rRNA gene sequences compared to the archaeal SILVA database. These long amplicons allowed for higher resolution during taxonomic classification by means of long (∼1000 bp) 16S rRNA gene fragments and for substantially more confident phylogenies by means of combined near full-length 16S and 23S rRNA gene sequences, compared to shorter traditional amplicons (250 bp of the 16S rRNA gene). We recommend our method to those who wish to cost-effectively and confidently estimate the phylogenetic diversity of prokaryotes in environmental samples at high throughput. 相似文献
8.
William J. Joiner Eliot B. Friedman Hsiao-Tung Hung Kyunghee Koh Mallory Sowcik Amita Sehgal Max B. Kelz 《PLoS genetics》2013,9(9)
A robust, bistable switch regulates the fluctuations between wakefulness and natural sleep as well as those between wakefulness and anesthetic-induced unresponsiveness. We previously provided experimental evidence for the existence of a behavioral barrier to transitions between these states of arousal, which we call neural inertia. Here we show that neural inertia is controlled by processes that contribute to sleep homeostasis and requires four genes involved in electrical excitability: Sh, sss, na and unc79. Although loss of function mutations in these genes can increase or decrease sensitivity to anesthesia induction, surprisingly, they all collapse neural inertia. These effects are genetically selective: neural inertia is not perturbed by loss-of-function mutations in all genes required for the sleep/wake cycle. These effects are also anatomically selective: sss acts in different neurons to influence arousal-promoting and arousal-suppressing processes underlying neural inertia. Supporting the idea that anesthesia and sleep share some, but not all, genetic and anatomical arousal-regulating pathways, we demonstrate that increasing homeostatic sleep drive widens the neural inertial barrier. We propose that processes selectively contributing to sleep homeostasis and neural inertia may be impaired in pathophysiological conditions such as coma and persistent vegetative states. 相似文献
9.
In the recent discussion how biotic systems may react to ocean acidification caused by the rapid rise in carbon dioxide partial pressure (pCO2) in the marine realm, substantial research is devoted to calcifiers such as stony corals. The antagonistic process – biologically induced carbonate dissolution via bioerosion – has largely been neglected. Unlike skeletal growth, we expect bioerosion by chemical means to be facilitated in a high-CO2 world. This study focuses on one of the most detrimental bioeroders, the sponge Cliona orientalis, which attacks and kills live corals on Australia’s Great Barrier Reef. Experimental exposure to lowered and elevated levels of pCO2 confirms a significant enforcement of the sponges’ bioerosion capacity with increasing pCO2 under more acidic conditions. Considering the substantial contribution of sponges to carbonate bioerosion, this finding implies that tropical reef ecosystems are facing the combined effects of weakened coral calcification and accelerated bioerosion, resulting in critical pressure on the dynamic balance between biogenic carbonate build-up and degradation. 相似文献
10.