全文获取类型
收费全文 | 6205篇 |
免费 | 520篇 |
国内免费 | 6篇 |
出版年
2024年 | 6篇 |
2023年 | 42篇 |
2022年 | 91篇 |
2021年 | 188篇 |
2020年 | 90篇 |
2019年 | 133篇 |
2018年 | 166篇 |
2017年 | 133篇 |
2016年 | 205篇 |
2015年 | 325篇 |
2014年 | 365篇 |
2013年 | 438篇 |
2012年 | 537篇 |
2011年 | 530篇 |
2010年 | 316篇 |
2009年 | 273篇 |
2008年 | 336篇 |
2007年 | 334篇 |
2006年 | 295篇 |
2005年 | 309篇 |
2004年 | 298篇 |
2003年 | 256篇 |
2002年 | 229篇 |
2001年 | 101篇 |
2000年 | 74篇 |
1999年 | 84篇 |
1998年 | 75篇 |
1997年 | 49篇 |
1996年 | 28篇 |
1995年 | 33篇 |
1994年 | 26篇 |
1993年 | 31篇 |
1992年 | 30篇 |
1991年 | 24篇 |
1990年 | 24篇 |
1989年 | 31篇 |
1988年 | 21篇 |
1987年 | 21篇 |
1986年 | 17篇 |
1985年 | 19篇 |
1984年 | 16篇 |
1983年 | 17篇 |
1982年 | 8篇 |
1981年 | 10篇 |
1980年 | 16篇 |
1979年 | 12篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1974年 | 6篇 |
1973年 | 7篇 |
排序方式: 共有6731条查询结果,搜索用时 15 毫秒
71.
Synopsis Masked metachromasia is demonstrated by staining with a metachromatic basic dye, after acid hydrolysis of suitably fixed tissue. We report that the addition of 20% Carbowax 20M (an inert polymer, mol. wt. about 20000) to the hydrolysis mixture improved the reaction. The improved method gives increased metachromasia, greater tolerance to variations in hydrolysis conditions, and demonstrates a greater proportion of cells — presumably due to a lower threshold of sensitivity. Lower molecular weight polymers (Carbowax 1000, Carbowax 6000) are less effective. 相似文献
72.
Natalie J. Beveridge Paul A. Tooney Adam P. Carroll Nham Tran Murray J. Cairns 《Cellular signalling》2009,21(12):1837-1845
Whole-genome microRNA and gene expression analyses were used to monitor changes during retinoic acid induced differentiation of neuroblasts in vitro. Interestingly, the entire miR-17 family was over-represented among the down-regulated miRNA. The implications of these changes are considerable, as target gene prediction suggests that the miR-17 family is involved in the regulation of the mitogen-activated protein kinase (MAPK) signaling pathway, synaptic plasticity and other markers of neuronal differentiation. Significantly, many of the target responses predicted by changes in miRNA expression were supported by the observed changes in gene expression. As expected, markers of neuronal differentiation such as anti-apoptotic protein B-cell lymphoma 2 (BCL2), myocyte enhancer factor-2D (MEF2D) and zipper protein kinase (MAP3K12; aka ZPK/MUK/DLK) were each up-regulated in response to differentiation. The expression of these genes was also reduced in response to miR-17 and miR-20a transfection, and more specifically they were also shown to contain functional miRNA recognition elements for members of the miR-17 family by reporter gene assay. This suggests that the miR-17 family have an integral role in fine-tuning the pathways involved in the regulation of neuronal differentiation. 相似文献
73.
74.
ATP is an important modulator of gating in type 1 ryanodine receptor (RyR1), also known as a Ca2+ release channel in skeletal muscle cells. The activating effect of ATP on this channel is achieved by directly binding to one or more sites on the RyR1 protein. However, the number and location of these sites have yet to be determined. To identify the ATP-binding regions within RyR1 we used 2N3ATP-2′,3′-Biotin-LC-Hydrazone (BioATP-HDZ), a photo-reactive ATP analog to covalently label the channel. We found that BioATP-HDZ binds RyR1 specifically with an IC50 = 0.6±0.2 mM, comparable with the reported EC50 for activation of RyR1 with ATP. Controlled proteolysis of labeled RyR1 followed by sequence analysis revealed three fragments with apparent molecular masses of 95, 45 and 70 kDa that were crosslinked by BioATP-HDZ and identified as RyR1 sequences. Our analysis identified four glycine-rich consensus motifs that can potentially constitute ATP-binding sites and are located within the N-terminal 95-kDa fragment. These putative nucleotide-binding sequences include amino acids 699–704, 701–706, 1081–1084 and 1195–1200, which are conserved among the three RyR isoforms. Located next to the N-terminal disease hotspot region in RyR1, these sequences may communicate the effects of ATP-binding to channel function by tuning conformational motions within the neighboring cytoplasmic regulatory domains. Two other labeled fragments lack ATP-binding consensus motifs and may form non-canonical ATP-binding sites. Based on domain topology in the 3D structure of RyR1 it is also conceivable that the identified ATP-binding regions, despite their wide separation in the primary sequence, may actually constitute the same non-contiguous ATP-binding pocket within the channel tetramer. 相似文献
75.
Plant Ecology - The distribution pattern of perennial native grasses in the dune systems of the Monte desert might be determined by the ability of plant roots to acquire water under drought... 相似文献
76.
Thinh T. Vu Nguyen Q. Hoa Anh Benjamin M. Rawson Dung V. Tran Hoa T. Nguyen Thinh N. Van 《American journal of primatology》2020,82(9):e23171
All gibbon species (Family: Hylobatidae) are considered threatened with extinction and recognized on the International Union for Conservation of Nature Red List of Threatened Species. Because gibbons are one of the most threatened families of primates, monitoring their status is now critically important. Long-term monitoring programs applying occupancy approaches, in addition to assessing occurrence probability, improves understanding of other population parameters such as site extinction or colonization probabilities, which elucidate temporal and spatial changes and are therefore important for guiding conservation efforts. In this study, we used multiple season occupancy models to monitor occurrence, extinction, and colonization probabilities for northern yellow-cheeked crested gibbon Nomascus annamensis in three adjacent protected areas in the Central Annamites mountain range, Vietnam. We collected data at 30 listening posts in 2012, 2014, and 2016 using the auditory point count method. Occurrence probabilities were highest in 2012 (0.74, confidence interval [CI]: 0.56–0.87) but slightly lower in 2014 (0.66, CI: 0.51–0.79) and 2016 (0.67, CI: 0.49–0.81). Extinction probabilities during the 2012–2014 and 2014–2016 intervals were 0.26 (0.14–0.44) and 0.25 (0.12–0.44), respectively. Colonization probabilities during 2012–2014 were 0.44 (0.19–0.73) and between 2014 and 2016 was 0.51 (0.26–0.75). Although local site extinctions have occurred, high recolonization probability helped to replenish the unoccupied sites and kept the occurrence probability stable. Long-term monitoring programs which use occurrence probability alone might not fully reveal the true dynamics of gibbon populations. We strongly recommend including multiple season occupancy models to monitor occurrence, extinction, and colonization probabilities in long-term gibbon monitoring programs. 相似文献
77.
Dinh Chuong Nguyen Duy Thanh Tran Thi Luu Luyen Doan Do Hwan Kim Nam Hoon Kim Joong Hee Lee 《Liver Transplantation》2020,10(8)
A novel hybrid of small core@shell structured CoSx@Cu2MoS4 uniformly hybridizing with a molybdenum dichalcogenide/N,S‐codoped graphene hetero‐network (CoSx@Cu2MoS4‐MoS2/NSG) is prepared by a facile route. It shows excellent performance toward the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) in alkaline medium. The hybrid exhibits rapid kinetics for ORR with high electron transfer number of ≈3.97 and exciting durability superior to commercial Pt/C. It also demonstrates great potential with remarkable stability for HER and OER, requiring low overpotential of 118.1 and 351.4 mV, respectively, to reach a current density of 10 mA cm?2. An electrolyzer based on CoSx@Cu2MoS4‐MoS2/NSG produces low cell voltage of 1.60 V and long‐term stability, surpassing a device of Pt/C + RuO2/C. In addition, a Zn‐air battery using cathodic CoSx@Cu2MoS4‐MoS2/NSG catalyst delivers a high cell voltage of ≈1.44 V and a power density of 40 mW cm?2 at 58 mA cm?2, better than the state‐of‐the‐art Pt/C catalyst. These achievements are due to the rational combination of highly active core@shell CoSx@Cu2MoS4 with large‐area and high‐porosity MoS2/NSG to produce unique physicochemical properties with multi‐integrated active centers and synergistic effects. The outperformances of such catalyst suggest an advanced candidate for multielectrocatalysis applications in metal‐air batteries and hydrogen production. 相似文献
78.
79.
Andrs García María Cecilia Scarf Alejandro Loydi Roberto Alejandro Distel 《Austral ecology》2020,45(1):70-78
In this study, we made an attempt to reveal how competition intensity from established plants impacts on palatable and unpalatable grass seedlings recruitment, in a natural mesic grassland of central Argentina. Our objective was to assess the seedling recruitment of a palatable species (Chascolytrum subaristatum) and an unpalatable species (Nassella trichotoma) in microsites differing in competition intensity from established plants. Identity (C. subaristatum and N. trichotoma) and defoliation severity were used as surrogate for competition intensity. In March 2017, we permanently marked established individuals of N. trichotoma and C. subaristatum and placed two circular plots adjacent to each individual. In one plot we added seeds of N. trichotoma and in the other seeds of C. subaristatum. After seeding, established plants were randomly assigned to one of three level of defoliation: without defoliation, low defoliation severity and high defoliation severity. From April to November 2017 (i.e. over a complete annual growing cycle), we measured seedling density, recruitment and growth. Our results supported the hypothesis that seedlings of palatable grasses are more competitive than seedlings of unpalatable grasses. Seedling of the palatable grass C. subaristatum recruited successfully regardless the intensity of competition from established plants, whereas seedlings of the unpalatable grass N. trichotoma recruited better under low competitive pressure from established plants. Our results suggest that the availability of microsites with low competitive pressure from the established vegetation, created by selective grazing of palatable grasses, promotes the recruitment of unpalatable grass seedlings. This mechanism may contribute to the species replacement process commonly observed in heavy grazed grasslands. 相似文献
80.
Adhesion to host cells is the first step in the virulence cycle of any pathogen. In Gram‐negative bacteria, adhesion is mediated, among other virulence factors such as the lipopolysaccharides, by specific outer‐membrane proteins generally termed adhesins that belong to a wide variety of families and have different evolutionary origins. In Brucella, a widespread zoonotic pathogen of animal and human health concern, adhesion is central as it may determine the intracellular fate of the bacterium, an essential stage in its pathogenesis. In the present paper, we further characterised a genomic locus that we have previously reported encodes an adhesin (BigA) with a bacterial immunoglobulin‐like domain (BIg‐like). We found that this region encodes a second adhesin, which we have named BigB; and PalA, a periplasmic protein necessary for the proper display in the outer membrane of BigA and BigB. Deletion of bigB or palA diminishes the adhesion of the bacterium and overexpression of BigB dramatically increases it. Incubation of cells with the recombinant BIg‐like domain of BigB induced important cytoskeletal rearrangements and affected the focal adhesion sites indicating that the adhesin targets cell–cell or cell–matrix proteins. We additionally show that PalA has a periplasmic localisation and is completely necessary for the proper display of BigA and BigB, probably avoiding their aggregation and facilitating their transport to the outer membrane. Our results indicate that this genomic island is entirely devoted to the adhesion of Brucella to host cells. 相似文献